Amorphous oxide and field transistor using it

FIELD: electricity.

SUBSTANCE: amorphous oxide the composition of which changes in direction of the thickness of layer contains the compound the composition of crystal state of which is presented with formula In2-XM3XO3(Zn1-YM2YO)m , where M2 - element of group II with atomic number which is less than that of Zn (for example Mg or Ca), M3 - element of group III with atomic number which is less than that of In (for example B, Al, Ga or Y), x is within the range of 0 to 2, y is within the range of 0 to 1 and m is 0 or natural number which his less than 6, and at that, amorphous oxide has concentration of electron carriers of not less than 1012/cm3 and less than 1018/cm3 and has electron mobility which increases with increase of concentration of electron carriers.

EFFECT: amorphous oxide operates as semi-conductor to be used in active layer of transistor.

7 cl, 10 dwg

 

The technical FIELD TO WHICH the INVENTION RELATES.

The present invention relates to an amorphous oxide. The present invention also relates to a field effect transistor made using the specified amorphous oxide.

The LEVEL of TECHNOLOGY

In recent years, flat panel display (TTD) is widespread as a result of technological progress in the field of liquid crystals and electroluminescence (EL). TTD is driven by active matrix circuit, consisting of thin-film field-effect transistor (TFT)using as an active layer of a thin amorphous silicon film or a thin film of polycrystalline silicon, located on the glass substrate.

On the other hand, an attempt was made instead of the glass substrate to use is easy and flexible polymer substrate to further reduce the thickness of the DPP, to make it more thin and resistant to destruction. However, as for the production of the transistor using the above-described thin silicon film requires a thermal process with a relatively high temperature, it is difficult to form a thin silicon film directly on a polymer substrate with low heat resistance.

In this regard, has been actively developed (paved patent application of Japan No. 2003-298062) T Is T, using a thin oxide semiconductor film containing in the main, for example, ZnO, which can be formed into a film at low temperature.

However, a TFT using a conventional thin film of oxide semiconductor does not provide performance at a level which is characteristic of TFT using silicon.

The present invention relates to amorphous oxide, and to a field effect transistor using amorphous oxide.

DISCLOSURE of INVENTIONS

The aim of the present invention is the provision of an amorphous oxide, which functions as a suitable semiconductor for use in the active layer of the semiconductor device, such as a thin-film transistor, and providing a field-effect transistor.

According to the aspect of the present invention is an amorphous oxide containing microcrystals having a concentration of electronic carriers less than 1018/cm3. Amorphous oxide preferably contains at least one element selected from the group consisting of In, Zn and Sn.

Alternatively, the amorphous oxide preferably represents any one oxide selected from the group consisting of an oxide containing In, Zn and Sn; an oxide containing In and Zn; an oxide containing In and Sn; and an oxide containing In.

As lternative amorphous oxide is preferably an oxide, containing In, Zn and Sn.

According to another aspect of the present invention is an amorphous oxide in which the electron mobility increases with increasing concentration of electronic carriers.

According to another variant implementation of the present invention is a field-effect transistor containing an active layer formed of an amorphous oxide containing microcrystals and the gate electrode, is formed in such a way that he was converted to the active layer through the gate insulator.

The transistor is preferably a transistor normally off type.

According to another variant implementation of the present invention is an amorphous oxide whose composition varies with the thickness of the layer and which has a concentration of electronic carriers less than 1018/cm3.

Amorphous oxide preferably contains at least one element selected from the group consisting of In, Zn and Sn.

Alternatively, the amorphous oxide is preferably selected from the group consisting of an oxide containing In, Zn and Sn; an oxide containing In and Zn; an oxide containing In and Sn; and an oxide containing In.

Alternatively, the amorphous oxide is preferably an oxide containing In, Zn and Sn.

According to another aspect of the present invention p is dostavlyaetsya field-effect transistor, contains

the active layer of an amorphous oxide whose composition varies with layer thickness and

a gate electrode formed in such a way that he was converted to the active layer through the gate insulator,

moreover, the active layer contains a first region and a second region which is located closer to the gate insulator than the first region, and the oxygen concentration in the first region is higher than the oxygen concentration in the second region.

According to another aspect of the present invention is a field-effect transistor containing

the active layer of an amorphous oxide having at least one element selected from the group consisting of In, Zn and Sn, and

a gate electrode formed in such a way that he was converted to the active layer through the gate insulator,

moreover, the active layer contains a first region and a second region, which is located to the insulator of the shutter closer to the first area, and the concentration In the second region is higher than the oxygen concentration in the first region or the concentration of Zn in the second region is higher than the oxygen concentration in the first region.

According to another variant implementation of the present invention is an amorphous oxide whose composition varies in the thickness direction of the layer,

moreover, the electron mobility increases with increasing conc is Tracii electronic media.

According to another aspect of the present invention is a field-effect transistor containing

the active layer of an amorphous oxide having at least one element selected from the group consisting of In and Zn, and

a gate electrode formed in such a way that he was converted to the active layer through the gate insulator,

moreover, the active layer contains a first region and a second region which is located closer to the gate insulator than the first region, and the concentration In the second region is higher than the concentration In the first region, or the concentration of Zn in the second region is higher than the concentration of Zn in the first area.

According to another variant implementation of the present invention is an amorphous oxide containing a single element type or many types of elements selected from the group consisting of Li, Na, Mn, Ni, Pd, Cu, Cd, C, N, P, Ti, Zr, V, Ru, Ge, Sn and F, and having the concentration of electronic carriers less than 1018/cm3.

Amorphous oxide preferably contains at least one element selected from the group consisting of In, Zn and Sn.

Alternatively, the amorphous oxide is preferably selected from the group consisting of an oxide containing In, Zn and Sn; an oxide containing In and Zn; an oxide containing In and Sn; an oxide containing In.

Alternatively, the amorphous oxide is preferably sod is RIT In, Zn and Ga.

According to another aspect of the present invention is an amorphous oxide containing at least one element selected from the group consisting of Li, Na, Mn, Ni, Pd, Cu, Cd, C, N, P, Ti, Zr, V, Ru, Ge, Sn and F, and the electron mobility increases with increasing concentration of electronic carriers.

According to another aspect of the present invention is a field-effect transistor containing

the active layer of an amorphous oxide containing at least one element selected from the group consisting of Li, Na, Mn, Ni, Pd, Cu, Cd, C, N, P, Ti, Zr, V, Ru, Ge, Sn and F, and

a gate electrode formed in such a way that he was converted to the active layer through the gate insulator.

Moreover, in the present invention, the amorphous oxide is preferably selected from the group consisting of an oxide containing In, Zn and Sn; an oxide containing In and Zn; an oxide containing In and Sn; an oxide containing In.

Studies of the oxide semiconductor by the authors of the present invention found that the above-mentioned ZnO is formed as a polycrystalline phase, causing carrier scattering at the interface between polycrystalline pellets with a lower electron mobility. Moreover, it was found that ZnO is formed a large number of oxygen defects, resulting in a large quantity the of electrons and complicates the reduction of electrical conductivity. Thus, even if the transistor is not applied, the voltage of the gate, between the source terminal and the drain terminal there is a strong electric current, which allows you to get a normally off state of the TFT and increases the ratio of the transistor on/off.

The authors of the present invention studied film of an amorphous oxide of ZnxMyInzO(x+3y/2+3z/2)(where M represents at least one of Al or Ga), described in application laid on the Japan patent No. 2000-044236. The material has a concentration of electronic carriers is not less than 1×1018/cm3suitable for use as a transparent electrode. However, the oxide with a concentration of electronic carriers is not less than 1×1018/cm3used in the channel layer of the TFT may not provide a sufficient ratio of on/off and is not suitable for TFT normally off type. Thus, the conventional film of the amorphous oxide does not provide the concentration of electronic carriers, less than 1×1018/cm3.

The authors of the present invention manufactured TFT, using as the active layer of the field effect transistor of amorphous oxide with a concentration of electronic carriers is less than 1×1018/cm3. It was found that the TFT has the desired characteristics and can be used in Plescop the compulsory display, such as a light-emitting device.

Moreover, the authors of the present invention investigated the material InGaO3(ZnO)mand conditions of formation of a film of this material and found that by controlling the parameters of the oxygen-containing atmosphere during the formation of a film can increase the carrier concentration in the material to less than 1×1018/cm3.

The above explanations are given from the point of view of using amorphous oxide as the active layer, which functions, for example, as a channel layer of the TFT. However, the present invention is not limited to the case in which the active layer.

The above description is mainly given for the case in which the amorphous oxide is used as the active layer functioning as a channel layer of the TFT. However, the present invention is not limited to such a case.

According to the present invention is an amorphous oxide, which is suitable for use in the channel layer of the transistor, such as TFT. The present invention also provides a field-effect transistor, having a good performance.

BRIEF DESCRIPTION of DRAWINGS

Figure 1 is a graph showing the relationship between the concentration of electronic carriers in the amorphous film on the basis of n-Ga-Zn-O, formed by the method of pulsed laser deposition, and the partial pressure of oxygen during film formation;

Figure 2 is a graph showing the relationship between the conductivity of an amorphous film on the basis of an In-Ga-Zn-O, is formed by a sputtering method in an argon atmosphere, and the partial pressure of oxygen during film formation;

Figure 3 is a graph showing the relationship between the number of electronic media and the electron mobility in amorphous film on the basis of an In-Ga-Zn-O, formed by the method of pulsed laser deposition;

Figa, 4B and 4C are diagrams showing the change in conductivity, carrier concentration and mobility of electrons depending on the values of x in the film InGaO3(Zn1-xMgxO)formed by the method of pulsed laser deposition in the atmosphere at a partial pressure of oxygen equal to 0.8 PA;

Figure 5 is a block diagram showing the structure of a MOS-transistor with a top gate;

6 is a graph showing the current-voltage characteristic of the MOS transistor with a top gate;

7 is a block diagram showing a device for pulsed laser deposition;

Fig is a block diagram showing a device for fo is the formation of a film by sputtering.

BEST MODES for IMPLEMENTING the PRESENT INVENTION

The following describes 1-3 embodiments of the invention. Then described the material of the amorphous oxide used in the present invention. In the following embodiments, the implementation of the oxide-based In-Ga-Zn-O, as a rule, is described in the variants of implementation; however, the present invention is not limited to such material.

The first variant of implementation: amorphous oxide having microcrystals

The first variant embodiment of the invention relates to amorphous oxide, characterized in that it contains microcrystal (microcrystals). Contains or no microcrystal (microcrystals) in the amorphous oxide, determine, using THE (transmission electron microscopy) photograph of a section formed by a film of the amorphous oxide. The film of the amorphous oxide according to the present invention contains an In-Ga-Zn-O, and the composition of the film of the amorphous oxide in the crystalline state represented InGaO3(ZnO)m(m is a natural number less than 6).

The oxides indicated in the description, the term “amorphous oxide, have the concentration of electronic carriers less than 1018/cm3or tend in which to increase the electron mobility increases the concentration of electronic carriers. According ottima use of TFT, it is preferable to manufacture TFT normally off type.

Alternatively, the film of the amorphous oxide according to the present invention contains an In-Ga-Zn-Mg-O, and the composition of the film of the amorphous oxide in the crystalline state represented InGaO3(Zn1-xMgxO)m(m is a natural number less than 6, 0<x≤1). It is preferable that the film of the amorphous oxide have an electron mobility greater than 1 cm2/·Sec.

The authors of the present invention found that the use of such above-mentioned film as a channel layer creates the opportunity for flexible TFT with the following performance characteristics: current shutter less than 0.1 microamps in the TFT is turned off (normally off), the ratio of the on/off exceeds 1×103and is permeable to visible light.

This transparent film is characterized by the fact that the electron mobility increases with the increase in the number of conducting electrons. As a substrate for formation of a transparent film can be used a glass substrate, a plastic substrate or plastic film.

When used as a channel layer of the transistor transparent oxide film is preferable to use as the gate insulator of one type of compounds selected from the group consisting of Al2O3Y 2O3and HfO2or a mixed crystal compound containing at least two kinds of compounds selected from the group consisting of Al2O3, Y2O3and HfO2.

With the aim of increasing the electric resistance is preferable formation of the film (transparent oxide film) in oxygen-containing atmosphere under irradiation of light without the addition of extraneous ions.

The composition of the film

In transparent thin film of the amorphous oxide, which has a composition in a crystalline state represented as InGaO3(ZnO)m(m is a natural number less than 6), the amorphous state is maintained up to a temperature of 800°C or above, if m is less than 6. However, as m increases, in other words, the ratio of ZnO to InGaO3increases (i.e. the composition of the film is approaching ZnO)film crystallized easier.

For this reason, it is preferable that the value of m was less than 6 when using an amorphous film as a channel layer of an amorphous TFT. However, it was found that the formation of the film when exposed to light micro-crystals can be formed even at small values of m.

The film can be formed by a method of forming a film from the vapor phase with a polycrystalline sintered body having a composition InGO 3(ZnO)mused as a target. For a method of forming a film from the vapor phase are suitable sputtering method, and the method of pulsed laser deposition. Moreover, the sputtering method is preferable from the viewpoint of mass production.

However, when the formation of such amorphous films under normal conditions are mainly generated oxygen defects. Therefore, the concentration of electronic carriers may not be reduced below 1×1018/cm3in other words, 10 s/Cm or less in terms of electrical conductivity. When using such a conventional thin film cannot be formed transistor normally off type. However, if the transparent film of the amorphous oxide having a composition of In-Ga-Zn-O, and the composition in a crystalline state represented InGaO3(ZnO)m(m is a natural number less than 6)is formed by the method of pulsed laser deposition, using the device shown in Fig.7, in an atmosphere having a partial pressure of oxygen above the 3.2 PA, the concentration of electronic carriers can be reduced lower than 1×1018/cm3. In this case, the substrate is not specially heated and thus supports approximately room temperature. If the substrate used is a plastic film,the temperature of the plastic film preferably is maintained below 100°C.

According to a variant embodiment of the invention, the amorphous oxide contains In-Ga-Zn-O and is formed using the method of pulsed laser deposition when exposed to light. More specifically, the invention relates to a transparent thin film of an amorphous oxide containing microcrystal (microcrystals), represented by the structure in the crystalline state in the form of InGaO3(ZnO)m(m is a natural number less than 6). By using such a film can be formed transistor normally off type.

In such a thin film can be obtained electron mobility in excess of 1 cm2/·Sec, and high on/off in excess of 1×103.

Moreover, the present invention relates to amorphous oxide containing In-Ga-Zn-O and is formed by a sputtering method using gaseous argon when exposed to light. More specifically, the present invention relates to a transparent thin film of an amorphous oxide containing microcrystal (microcrystals), represented by the structure in the crystalline state in the form of InGaO3(ZnO)m(m is a natural number less than 6). Such film can be obtained by a sputtering method using the device shown in Fig, in an atmosphere with a partial pressure of oxygen above 1×10-2PA. In that case, the temperature of the substrate is not specifically increase and, thus, support approximately room temperature. If the substrate used is a plastic film, the temperature of the substrate preferably is maintained below 100°C. the Number of electronic media can be reduced by increasing the partial pressure of oxygen.

More specifically, the present invention relates to amorphous oxide containing In-Ga-Zn-O and formed by the sputtering method, the irradiation of light. According to the present invention, the transistor is normally off type with respect to on/off in excess of 1×103may be formed using a transparent thin film of an amorphous oxide containing microcrystal (microcrystals), represented by the structure in the crystalline state in the form of InGaO3(ZnO)m(m is a natural number less than 6).

In a thin film manufactured using the method of pulsed laser deposition and sputtering method, the irradiation of light, the electron mobility increases with the increase in the number of conducting electrons.

In this case, if the target uses a polycrystal InGaO3(Zn1-xMgxO)m(m is a natural number less than 6, 0<x≤1)can be obtained amorphous film with a high resistance having a composition InGaO3 (Zn1-xMgxO)meven at a partial pressure of oxygen is less than 1 PA.

As described above, it is possible to avoid the formation of oxygen defects by adjusting the partial pressure of oxygen. In the result, the concentration of electronic carriers can be reduced without adding the set of extraneous ions. The amorphous oxide according to the present invention can be obtained by forming a thin film according to any one of 1 to 5 when exposed to light. If you are using the device according to 7 or 8, the film can be formed at a partial pressure of oxygen, for example, in a given area, as described below. In the amorphous state containing microcrystal (microcrystals) the boundary grains microcrystal covered (surrounded) amorphous structure. Consequently, there is virtually no boundary grains, capable of capturing moving electrons and holes in contrast to the polycrystalline state, like zinc oxide. The result can be obtained amorphous thin film having a high electron mobility. Moreover, the number of conductive electrons can be reduced without adding the set of extraneous ions. Because the electrons are not scattered by ions of an impurity, can be kept high electron mobility. The microcrystals according to the present invented the Yu is not limited microcrystals, having a composition represented as InGaO3(ZnO)m(m is a natural number less than 6).

In a transistor with a thin film using the above-mentioned transparent film, the gate insulator is preferably formed of a mixed crystal compound containing at least two compounds selected from the group consisting of Al2O3, Y2O3and HfO2. If the defect (deficit) on the boundary between the gate insulating thin film and a thin film channel layer, the electron mobility decreases and there is a hysteresis as a characteristic of the transistor. Moreover, if the type of the gate insulator is different, the leakage current changes greatly. For this reason, it is necessary to choose a suitable gate insulator for the channel layer. If you use Al2O3film (gate insulator), the leakage current can be reduced. If you use Y2O3film (gate insulator), can be reduced hysteresis. If you are using HfO2film having a high dielectric constant may be increased electron mobility. Moreover, if you are using a mixed crystal of these compounds (as insulator gate), it is possible to form a TFT having a small leakage current and hysteresis and large moveable is here electrons. Since the process of forming the gate insulator and the process of forming the channel layer can be performed at room temperature, can be formed not only TFT with a checkerboard structure, as well as TFT with reverse checkerboard structure.

TFT is a device having three terminals, namely terminal gate, the source terminal and the drain terminal. A semiconductor thin film formed on an insulating substrate such as ceramic, glass, or plastic substrate used in TFT as a channel layer for the migration of electrons and holes through the layer. The current through the channel layer is controlled by applying a voltage to the terminal of the shutter, thereby switching the current between the source terminal and the drain terminal. Since the TFT has such a switching function, he is an active device. It should be noted that the microcrystals contained in the amorphous oxide can be formed by irradiation with light (namely, irradiation with light using a halogen lamp or UV irradiation), as mentioned above, and can be formed in other ways in addition to exposure to light.

Second option: the compositional distribution of the amorphous oxide

According to this variant implementation of the amorphous oxide is characterized by the composition, change the I in the direction of thickness.

The phrase “composition varying in the thickness direction” means the quantity of oxygen contained in the oxide, is changed in the direction of film thickness, and the elements constituting the oxide, are changed in the middle (i.e. changes), and changes the contents of the elements constituting the oxide.

Therefore, if the amorphous oxide is used as the active layer (also referred to as channel layer of the field-effect transistor, for example, the following is the preferred structure. In the transistor having an active layer containing an amorphous oxide and the gate insulator, which are in contact with each other at the interface, the layer of amorphous oxide is arranged in such a way that the oxygen concentration near the interface is higher than in the region remote from the boundary. In this case, since the electrical resistance of the layer of amorphous oxide, which is located closer to the boundary of the section, above, the so-called channel transistor is formed within a layer of amorphous oxide, remote from the boundary. This structure is preferred when the boundary is a rough surface, because it can be reduced leakage current.

That is, in the case of using the above-mentioned amorphous oxide as the active layer of the transistor is preferred developed the AMB active layer so to include the first area and the second area, located to the insulator of the shutter closer to the first area, and the oxygen concentration in the second region exceeded the oxygen concentration in the first region. In this regard, it is not necessary that the two areas differed in their borders, but their corresponding formulations may change gradually or stepwise.

In particular, the concentration of electronic carriers amorphous oxide is preferably less than 1018/cm3.

The direction of the film formed on the substrate, means any area that is not a direction to the substrate plane, i.e. the direction perpendicular to the substrate plane. Moreover, in the transistor having an active layer formed of an amorphous oxide having at least one element selected from the group consisting of In and Zn, and the gate insulator in contact with the active layer at the interface, the concentration of In and Zn contained in the region of the layer of amorphous oxide (the active layer), located close to the boundary, higher than their concentration in areas located further from the boundary. In this case, can be increased drift mobility of electrons.

That is, in the case of using the above-mentioned amorphous oxide as the active layer of the transistor p is edocfile is the development of the active layer so to include the first area and the second area, which is located to the insulator of the shutter closer to the first area, and the concentration of In and Zn in the second region higher than their concentration in the first region.

According to the second variant of the invention, the oxide film contains an In-Ga-Zn-O, and its composition varies in the thickness direction of the film, and is characterized by the fact that the composition of the part having the crystalline state, presented in the form of InGaO3(ZnO)m(m is a natural number less than 6), and the concentration of electronic carriers below 1×1018/cm3.

Alternatively, an oxide film according to the second variant embodiment of the invention is a transparent film of an amorphous oxide containing In-Ga-Zn-Mg-O and characterized in that the composition is changed in the direction of film thickness, and composition of the parts being in the crystalline state, presented in the form of InGaO3(Zn1-xMgxO)m(m is a natural number less than 6, 0<x≤1), and the concentration of electronic carriers below 1×1018/cm3. It should be noted that it is also preferable that these films had an electron mobility greater than 1 cm2/·Sec.

If the above film is used as the channel layer, it is preferable to obtain a flexible TFT, Meuse what about the following characteristics of the transistor: the current shutter less than 0.1 increasing volume of computer when TFT is turned off (normally off), the ratio of the on/off above 1×104the permeability to visible light.

It should be noted that this transparent film is different in that the electron mobility increases with the increase in the number of conducting electrons. As a substrate for formation of a transparent film can be used a glass substrate, a plastic substrate or plastic film.

If the transparent oxide film is used as the channel layer of the transistor, it is preferable to use as the gate insulator of one type of compounds selected from the group consisting of Al2O3, Y2O3and HfO2or a mixed crystal compound containing at least two kinds of compounds selected from the group consisting of Al2O3, Y2O3and HfO2.

It is preferable that the film (transparent oxide film was formed in an atmosphere containing oxygen, without adding extraneous ions with the aim of increasing electrical resistance.

The authors of the present invention has found a specific feature politology thin film of the amorphous oxide. That is, the electron mobility increases with the increase in the number of conducting electrons. Was formed TFT using such p the evaluation, and it was found that further improved the operating characteristics of the transistor, such as the ratio of on/off, the saturation current is in the cutoff state and the switching speed.

In film transistor formed using a transparent politology thin film of the amorphous oxide as a channel layer, if the electron mobility is greater than 1 cm2/·Sec, preferably greater than 5 cm2/·Sec, and the concentration of electronic carriers below 1×1018/cm3, preferably below 1×1016/cm3the current between the drain terminal and the source during shutdown (no applied voltage at the gate) can be reduced below 10 microamps, preferably below 0.1 microamps. Moreover, in this case (when using the above-mentioned thin film), if the electron mobility greater than 1 cm2/·Sec, preferably greater than 5 cm2/·Sec, the saturation current after the cut-off may be increased above 10 microamps. In other words, the ratio of on/OFF can be increased up to 1×104.

In TFT high voltage is applied to the terminal of the shutter in a state of cutoff that leads to a large density of electrons in the channel. Therefore, according to the present invention, the saturation current can be increased during a corresponding increase in the odvisnosti electrons. As a result of nearly all operating characteristics of the transistor, such as on/off, saturation current and the switching speed increase and improve. It should be noted that in normal connection, when the number of electrons between them clash with each other, resulting in reduced electron mobility.

The amorphous oxide according to the present invention can be used in a TFT having a checkerboard structure (top gate), in which the gate insulator and the terminal gate formed sequentially in this order on the semiconductor channel layer, and a TFT having a reverse checkerboard structure (bottom gate), in which the gate insulator and semiconductor channel layer formed sequentially in this order on the terminal bolt.

The composition of the film

In transparent thin film of the amorphous oxide, crystalline part of which has a composition represented as InGaO3(ZnO)m(m is a natural number less than 6), if the value of m is less than 6, the amorphous state can stably be maintained to a temperature of 800°C or more. However, with increasing values of m, in other words, the ratio of ZnO to InGaO3increases (i.e. the composition of the film is approaching ZnO)film crystallized easier.

For this reason, it is preferable, to m was less than 6, if the amorphous film is used as a channel layer of an amorphous TFT.

In the thin-film transistor using the above-mentioned transparent film, preferably used a gate insulator formed of a mixed crystal compound containing one type of compound selected from the group consisting of Al2O3, Y2O3and HfO2or a mixed crystal compound containing at least two kinds of compounds selected from the group consisting of Al2O3, Y2O3and HfO2. If the defect (deficit) on the boundary between the gate insulating thin film and a thin film channel layer, the electron mobility decreases and there is a hysteresis as a characteristic of the transistor. Moreover, if the type of the gate insulator is different, the leakage current changes greatly. For this reason, it is necessary to choose a suitable gate insulator for the channel layer. If you use Al2O3film (gate insulator), the leakage current can be reduced. If you use Y2O3film (gate insulator), can be reduced hysteresis. If you are using HfO2film having a high dielectric constant may be increased electron mobility. Moreover, if you are using mixed is rystall of these compounds (as insulator shutter), it is possible to form a TFT having a small leakage current and hysteresis and a large electron mobility. Since the process of forming the gate insulator and the process of forming the channel layer can be performed at room temperature, can be formed not only TFT with a checkerboard structure, as well as TFT with reverse checkerboard structure.

TFT is a device having three terminals, namely terminal gate, the source terminal and the drain terminal. A semiconductor thin film formed on an insulating substrate such as ceramic, glass, or plastic substrate, are used in TFT as a channel layer for the migration of electrons and holes through the layer. The current through the channel layer is controlled by applying a voltage to the terminal of the shutter, thereby switching the current between the source terminal and the drain terminal. Since the TFT has such a switching function, he is an active device.

As described above, the second embodiment of the invention relates to improvements in composition in the thickness direction of the transparent film, which functions as an active layer of a field-effect transistor (TFT), if the TFT is formed by using a transparent film.

For a more detailed explanation, when using the method of pulsed laser OS the input voltage to the composition varies in the direction of film thickness by changing the partial pressure of oxygen in the direction of film thickness, changing the energy of oscillation of the pulse laser or a frequency oscillations, or changing the distance between the target and the substrate in the direction of film thickness. On the other hand, if you do a checkerboard distribution, composition changes in the direction of film thickness in addition to the chess order of the target, such as In2O3or ZnO. For example, if the film is formed in an atmosphere of oxygen, the amount of oxygen contained in the film increases with increasing distance between target and substrate. Moreover, if a ZnO target is added during formation of a film, the film formed after addition of Zn target, the amount of Zn is increased.

Third option: an amorphous oxide containing additive (additive)

The amorphous oxide according to the present invention is characterized by the fact that the amorphous oxide contains as an additive at least one or more types of elements selected from the group consisting of Li, Na, Mn, Ni, Pd, Cu, Cd, C, N, P, Ti, Zr, V, Ru, Ge, Sn and F. the Introduction of additives in the amorphous oxide is achieved by introducing additives in the gas used in the device formation film, or in the target material used in the device. Typically, after forming a film of the amorphous oxide without additives in the film can be introduced additive, as described below in Arah.

The concentration of electronic carriers amorphous film preferably less than 1018/cm3.

The amorphous oxide according to the present invention may include a transparent amorphous oxide containing In-Ga-Zn-O, the composition of which is in the crystalline state represented InGaO3(ZnO)m(m is a natural number less than 6), and includes an oxide containing In-Ga-Zn-Mg-O, the composition of which is in the crystalline state represented InGaO3(Zn1-xMgxO)m(m is a natural number less than 6, 0<x≤1). Moreover, in such oxides, at least as an additive make one type or many types of elements selected from the group consisting of Li, Na, Mn, Ni, Pd, Cu, Cd, C, N and P.

Thus can be reduced concentration of electronic carriers. Even though the concentration of electronic carriers is significantly reduced, it is possible to prevent a decrease in the mobility of electronic media, easily adjusting the concentration of electronic carriers. As a result, if the transparent film of the amorphous oxide is used as the channel layer of the TFT, the resulting plate TFT has the same characteristics, even if the TFT plate has a large area.

If as an impurity (additives) are Li, Na, Mn, Ni, Pd, Cu, Cd, C, N and P, such impurities can be replaced by any one of In, Ga and Zn, O, which serve as acceptor, and can reduce the density of electronic media, although details of the mechanism are unknown. In the conventional semiconductor oxide as the oxygen concentration cannot be adjusted properly, there is a large deficit of oxygen. Moreover, in most cases, if the deficit is formed at the grain boundary as a result of polycrystalline state, the density of electronic media may well not be adjusted even with the introduction of impurities. In this regard, the transparent film of the amorphous oxide according to the present invention has a small oxygen deficiency and has no grain boundaries due to the amorphous state. In this case, it is assumed that the impurities are effectively function as acceptors. If a thin film is formed by increasing the partial pressure of oxygen to reduce the density of electronic media, changes the skeleton atomic bonds, increasing the tail of the distribution in the conduction band. If the electrons are captured in the tail of the distribution, the mobility of the electronic media may be significantly lower. However, additives Li, Na, Mn, Ni, Pd, Cu, Cd, C, N and P provide the opportunity to adjust the density of the medium, while maintaining the partial pressure of oxygen in a suitable range. Therefore, probably, is moveable is any electronic media is less influenced. Thus, if the present invention compared with the case in which the concentration of electronic carriers and the mobility of the electronic media are regulated by only the partial pressure of oxygen, the uniformity of operating characteristics of the oxide film in the plate can be easily increased, even if a large substrate.

The additive may be selected from the group consisting of Ti, Zr, V, Ru, Ge, Sn, and F, as mentioned above.

It should be noted that the impurity concentration necessary to obtain the desired effect (amorphous film) is about 0.1 to 3 atom.%, higher than the concentration in crystalline form, is formed of Si, etc. Such assumption exists because the probability that the atoms will occupy the position, effective to influence the valence electrons is lower in the amorphous state than in the crystalline state. More generally, a desired impurity is introduced into the target using the method of introducing impurities. In the case of such impurities like C, N and P, they can be introduced into the film by introducing an atmosphere gas such as CH4, NO, and PH3together with oxygen. If the impurity metal is introduced after formation of the transparent film of the amorphous oxide film is introduced into contact with a solution or paste containing metal ions. Moreover, if you use t the Kai substrate, as glass, having a high heat resistance, such metals are preferably contained in the substrate, then the substrate is heated during and after the formation of the film, thus, there is a diffusion of metals in the transparent film of the amorphous oxide. As a source of Na, for example, there may be used sodium glass, because it contains 10-20 atom.% Na.

Figure 5 shows the typical structure of a TFT device. In the TFT device part, which can effectively reduce the density of electronic media is a part of the channel layer 2 located between the drain electrode 5 and the electrode 6 of the source. On the contrary, the advantage lies in the fact that part of the channel layer 2 in contact with the drain electrode 5 and the electrode 6 of the source, has a high density of electronic media. This is because it can maintain good contact with the electrodes. In other words, the impurity concentration in this part preferably below. This design can be obtained by casting the channel layer 2 in contact with the solution containing impurities after formation of the drain electrode 5 and the electrode 6 of the source and before the formation of the insulating film 3 shutter. Thus, impurities can diffuse through the drain electrode 5 and the electrode 6 of the source used as the mask.

Figure 5 is the actu channel layer 2, especially in contact with the substrate, slightly affected by the regulatory impact of the gate electrode 4 in relation to the density of electronic media. Therefore, to increase the ratio on/off is useful to the density of electronic media specified part was strongly suppressed in advance. In addition, it is effective to increase the concentration of impurities, in particular, at the interface facing the substrate. Such structure can be obtained by adjusting the concentration of the gas, such as CH4, NO, and PH3intended for introduction into the atmosphere so that the first gas was supplied with excessive concentration, then the concentration gradually decreased. Alternatively, in the case of impurities, such as Na, which were previously in the substrate, this structure can be obtained by using the Na diffusion by heating the substrate at a suitable temperature.

As an additive, at least in the amorphous oxide can be entered one type or many types of elements selected from the group consisting of Ti, Zr, V, Ru, Ge, Sn, and F. In this case, it is assumed that the electron mobility can be increased up to 1 cm2/V·sec or more, and even up to 5 cm2/V·sec or more at the same time maintaining the concentration of electronic carriers below 1×1018/cm3 . Even if the increase in drift mobility of electrons with it rarely increases the concentration of electronic carriers. In this case, if the transparent film of the amorphous oxide is used as the channel layer, it is possible to obtain a TFT having a high ratio of on/off and high saturation current during the cutoff, and high switching speed. Moreover, it is easy to increase the uniformity of operating characteristics in the plate, even if a large substrate, compared with the case in which the concentration of electronic carriers and the mobility of the electronic media are controlled only by adjusting the partial pressure of oxygen.

Although the details of this mechanism are unknown, if the oxide is formed by increasing the partial pressure of oxygen increases the density of States in the tail of the distribution, under the conduction band. However, it is possible that impurities such as Ti, Zr, V, Ru, Ge, Sn, and F, have an impact on the skeleton atomic bonds, thus reducing the tail of the distribution, resulting in the mobility of carriers can be increased, while maintaining the density of electronic media.

Such impurities mentioned above are preferably used in the concentration range of about 0.1 to 3 atom.% or 0.01-1 atom.% The term “atom.%” represents the proportion of atoms of the element forming oxide. It should be noted that if the amount of oxygen is difficult to measure, the above relationship can be defined through the relations of the numbers of atoms of elements other than oxygen. In a more General sense, the desired impurity can be introduced into the target using the method of introducing impurities. In the case of impurity F it can be introduced into the film by introducing into the atmosphere together with oxygen gas such as SF6, SiF4or ClF3. If as an impurity is injected metal after forming the transparent film of the amorphous oxide, the film is introduced into contact with a solution or paste containing metal ions.

Figure 5 shows the typical structure of a TFT device. In the TFT device part, which requires a particularly high electron mobility, is a part of the channel layer 2 in contact with the insulator 3 of the shutter. Effective is the increase in the concentration of impurities of the present invention, in particular, at the interface, which is in contact with the insulating film 3 shutter. Such structure can be obtained by introducing an atmosphere gas such as SF6, SiF4and ClF3during the formation of the channel layer, at the same time increasing the concentration of the gas (starting from a lower level).

The present invention in sushnost is important, however, the structure of atomic bonds can be formed in a suitable way by regulating the amount of oxygen the amount of oxygen defects).

In the above description, the amount of oxygen in the transparent oxide film is controlled by forming a film in an atmosphere containing a given amount of oxygen. Also, it is preferable that after forming the oxide film, it was treated in the atmosphere containing oxygen, thus controlling (reducing or increasing) the number of oxygen defects.

For effective management of the number of oxygen defects in the film is treated in an atmosphere containing oxygen at a temperature of from 0 to 300°C (including both boundaries), preferably from 25 to 250°C (including both boundaries), more preferably from 100 to 200°C (including both boundaries).

As a rule, not only the formation of the film, as well as treatment after film formation can be performed in the atmosphere containing oxygen. Moreover, under condition of reception of the given concentration of electronic carriers (less than 1×1018/cm3) can be formed film without adjusting the partial pressure of oxygen and, therefore, the film can be processed in an atmosphere containing oxygen.

In the present invention, the lowest level electronic wear the oil is changed depending on the use of the resulting oxide film, more specifically, device type, circuits and devices; however, preferred, for example, 1×1014/cm3or more.

Below will be described in detail amorphous oxides used in the implementation options 1-3. In amorphous oxides or methods for their preparation are the following additional conditions. According to the first variant embodiment of the invention in terms of getting added exposure to light. According to the second variant embodiment of the invention the tool changes the composition of the film used, as described in the examples. According to the third variant embodiment of the invention in addition to the conditions for forming the film are the gas and the target is to add impurities, or after the formation of a film can be used the specified method of adding impurities in the amorphous oxide is shown below.

AMORPHOUS OXIDE

Described in more detail below the active layer, used above in options 1-3 implementation.

The concentration of electronic carriers in the amorphous oxide in the present invention is the value measured at room temperature. Room temperature is a temperature in the range from 0°C to about 40°C., for example, 25°C. the Concentration of electronic carriers in the amorphous oxide in the present invention need not necessarily be less than 1018/cm3 within the entire region from 0°C to 40°C. for Example, the acceptable concentration of electronic carriers less than 1018/cm3at a temperature of 25°C. At lower concentrations of electronic media, not more than 1017/cm3or not more than 1016/cm3can be obtained with a high yield of TFT normally off type.

In this specification the definition of “less than 1018/cm3” means “is preferably less than 1×1018/cm3and more preferably less than 1.0×1018/cm3”. The concentration of electronic carriers can be measured by measuring the Hall effect.

Amorphous oxide of the present invention is an oxide, which detects the halo pattern and that has no characteristic diffraction lines in the x-ray diffraction spectrometry.

In amorphous oxide of the present invention, the lower limit of the concentration of electronic carriers is, for example, 1×1012/cm3, but is not limited to this limit, since it can be used as a channel layer of the TFT.

Accordingly, in the present invention the concentration of electronic carriers govern by the selection of material, composition, conditions of manufacture, etc. of amorphous oxide, for example, as in the following examples, the button she was within, for example, from 1×1012/cm3up to 1×1018/cm3preferably from 1×1013/cm3up to 1×1017/cm3, more preferably from 1×1015/cm3up to 1×1016/cm3.

Amorphous oxide other than InZnGa oxides may be selected appropriately from In oxides, InxZn1-xoxides (0,2≤x≤1), InxSn1-xoxides (0,8≤x≤1), Inx(Zn,Sn)1-xoxides (0,15≤x≤1). Inx(Zn,Sn)1-xthe oxide may also be an Inx(ZnySn1-y)1-x(0≤y≤1).

If In the oxide contains no Zn or Sn, then In may be partially substituted Ga: InxGa1-xoxide (0≤x≤1).

Amorphous oxide with a concentration of electronic carriers 1×1018/cm3that obtained by the authors of the present invention, described in more detail below.

One group of the above-mentioned oxides typically has a composition of In-Ga-Zn-O, presented in the form of InGaO3(ZnO)m(m: natural number less than 6) in a crystalline state, and contains the electronic media with a concentration less than 1×1018/cm3.

Another group of the above-mentioned oxides typically has a composition of In-Ga-Zn-Mg-O, presented in the form of InGaO3(Zn1-xMgxO)m(m: natural number less than 6, 0<x≤1) in the crystalline state, and contains the electronic media with a concentration less than 1×1018/cm3.

the Lenka, consisting of such oxide, preferably designed for the mobility of electrons is greater than 1 cm2/·Sec.

Using the above film as a channel layer, can be obtained TFT normally off type with the current shutter less than 0.1 microamps and the ratio of on/off is higher than 1×103that is also transparent to visible light and flexible.

In the above film, the electron mobility increases with the conduction electrons. The substrate for forming a transparent film includes a glass plate, a plastic plate and a plastic film.

When using the above film of the amorphous oxide as a channel layer, at least one of the layers consisting of Al2O3, Y2O3and HfO2or crystal mixtures may be used as the gate insulator.

In a preferred embodiment, the film formed in an atmosphere containing gaseous oxygen, without adding in the amorphous oxide impurities to increase electrical resistance.

The authors of the present invention have found that a thin amorphous film politology oxides have characteristics, which consists in the fact that the electron mobility increases with increasing Koli is estva of conduction electrons, and in addition, it was found that the TFT obtained by the use of such a film has superior characteristics of the transistor, such as the ratio of on/off, the saturation current is in the cutoff state and the switching speed. Thus, the TFT normally off type can be obtained by using an amorphous oxide.

By using a ton of film of the amorphous oxide as a channel layer of the thin film transistor can be obtained electron mobility greater than 1 cm2/·Sec, preferably greater than 5 cm2/·Sec. The current between the drain terminal and the source terminal in the off state (no applied voltage gate) can be controlled so that it was less than 10 microamps, preferably less than 0.1 increasing volume of computer when carrier concentration lower than 1×1018/cm3, preferably lower than 1×1016/cm3. In addition, by using such a thin film saturation current after the cut-off may be increased to 10 microamps or more, and the ratio of on/off can be higher than 1×103when the electron mobility is higher than 1 cm2/·Sec, preferably higher than 5 cm2/·Sec.

In a state of cutoff TFT to the terminal of the gate high voltage is applied, and the channel electrons have a high density. Therefore, according to the but the present invention is the saturation current can be increased in accordance with increase of electron mobility. Thus, it can be improved characteristics of the transistor, such as the increase of the ratio on/off, increase of the saturation current and increase the speed of switching. In contrast, using conventional compounds increase the number of electrons reduces the mobility of the electrons due to collisions between electrons.

The structure of the above-described TFT may be a structure in staggered (top gate), in which the gate insulator and the terminal gate sequentially formed on the semiconductor channel layer, or structure in a reverse staggered (bottom gate), in which the gate insulator and the semiconductor channel layer sequentially formed on the terminal bolt.

The first process is the formation of a film: PLD process

A thin film of an amorphous oxide comprising InGaO3(ZnO)m(m: natural number less than 6) in a crystalline state is stable at high temperatures up to 800°C or above, if m is less than 6, whereas the increase in m, that is, with increase of the ratio of ZnO to InGaO3closer to the composition of ZnO, the oxide has a tendency to crystallize. Therefore, for use as a channel layer of an amorphous TFT is preferable that the value of m oxide was less than 6.

<> The formation of the film preferably is in the process of forming film in a gas phase by using a target of polycrystalline sintered compact having a composition InGaO3(ZnO)m. Suitable processes are the formation of a film in a gas phase, sputtering and pulsed laser deposition. For mass production is particularly suitable spraying.

However, when forming an amorphous film in normal conditions can occur oxygen defects, so it is impossible to obtain the concentration of electronic carriers is less than 1×1018/cm3and conductivity of less than 10 Cm/see this film cannot be created, the transistor is normally off type.

The authors of the present invention was created In-Ga-Zn-O film using pulsed laser deposition using the apparatus shown in Fig.7.

The film formation was carried out by using such a PLD device for forming a film, as shown in Fig.7.

7 reference position indicate the following: 701 - PH (rotary pump); 702 - TDS (turbomolecular pump); 703 - preparatory chamber; 704 - e-gun for RHEED; 705 - tool mounting substrate for rotation and vertical movement of the substrate; 706 - box input laser beam; 707 - substrate; 708 - target; 709 - source radicals; 710 from Artie for gas supply; 711 - a means of fixing targets for rotation and vertical movement of the target; 712 - line bypass; 713 - main line; 714 - TDS (turbomolecular pump); 715 - PH (rotary pump); 716 - titanium gas absorbing capacity pump; 717 - blind; 718 - IM (ion gauge); 719 - MP (Pirani gauge); 720 - BCH (pressure transducer Baratron) and 721 camera growth.

The semiconductor thin film of the In-Ga-Zn-O amorphous oxide layer on SiO2a glass substrate (Corning Co.: 1737) pulsed laser deposition using a KrF excimer laser. As a pre-treatment prior to deposition the substrate was washed for degreasing using ultrasound acetone, ethanol, and ultrapure water for five minutes each and dried at 100°C.

Polycrystalline target was a InGaO3(ZnO)4sintered compact (about the size of 20 mm in diameter, 5 mm in thickness), which was obtained by wet mixing In2O3, Ga2O3and ZnO (4-normal solution of each reagent) as the source material (solvent: ethanol), firing the mixture (1000°C, 2 hours), dry grinding and sintering (1550°C, 2 hours). Target had a conductivity of 90 Cm/see

The film formation was carried out by maintaining the final pressure in the cell growth of 2×10-6PA and the partial pressure of oxygen during growth to 6.5 PA. Partial d is the pressure of oxygen in the chamber 721 growth was 6.5 PA, and the temperature of the substrate was 25°C. the distance between the target 708 and substrate 707, holding the film was 30 mm, power input via the window 706 input was in the range of 1.5-3 MJ/cm2/pulse. The pulse duration was 20 NS, repetition frequency was set to 10 Hz, and the point of exposure was represented by a square 1×1 mm In the above-described conditions, the formed film with a speed of 7 nm/min

The obtained thin film investigated by the method of small-angle x-ray (SAXS) (method of thin films, the incidence angle: 0,5°): a clear diffraction peak was not observed. Thus obtained thin film type In-Ga-Zn-O was considered to be amorphous. The coefficient of reflection of x-rays and analysis of its pattern was found root-mean-square surface roughness (Rrms), is equal to approximately 0.5 nm, and a film thickness of approximately 120 nm. From x-ray fluorescence analysis (XRF) it was found that the metal content in the film corresponds to the ratio of In:Ga:Zn = 0,98:1,02:4. The conductivity was lower than about 1×10-2Cm/see was estimated concentration of electronic carriers, which was less than 1×1016/cm3. The electron mobility was about 5 cm2/·Sec. By analyzing the absorption of light was measured width of the forbidden zone in the optical range in the resulting amorphous thin film, the which was approximately 3 eV.

The above results show that the obtained thin film type In-Ga-Zn-O is a transparent thin film having the amorphous phase composition close to that of crystalline InGaO3(ZnO)4that has less oxygen defects and lower electrical conductivity.

The formation of the above-described film is explained in particular with reference to Figure 1. Figure 1 shows the dependence of the concentration of electronic carriers in the formed transparent thin film made of amorphous oxide from the partial pressure of oxygen for film composition InGaO3(ZnO)m(m: an integer number less than 6) in a prospective crystalline state in the same conditions of formation of a film, as described in the example above.

By forming the film in an atmosphere having a partial pressure of oxygen higher than 4.5 PA in the same conditions as described above, the concentration of electronic carriers can be reduced to less than 1×1018/cm3as shown in figure 1. In this film formation, the substrate can be at a temperature close to room temperature without special heating. To use a flexible plastic film as the substrate temperature of the substrate is preferably kept lower than 100°C.

The higher the partial pressure of oxygen can lead to a decrease what, s the concentration of electronic carriers. For example, as shown in figure 1, thin InGaO3(ZnO)4film formed at a temperature of the substrate 25°C and a partial pressure of oxygen equal to 5 PA, had a lower concentration of electronic carriers, component 1×1016/cm3.

In the resulting thin film, the electron mobility was higher than 1 cm2/·Sec, as shown in figure 2. However, the film, layered by means of pulsed laser deposition at a partial pressure of oxygen higher than 6.5 PA, as in this example, had an uneven surface that is unsuitable for the channel layer of the TFT.

Accordingly, in the above example, the transistor is normally off type can be created by using a thin transparent oxide represented by the formula InGaO3(ZnO)m(m: an integer number less than 6) in a crystalline state, is formed at a partial pressure of oxygen higher than 4.5 PA, preferably higher than 5 PA, but below 6.5 PA method of pulsed laser deposition.

The obtained thin film had an electron mobility greater than 1 cm2/·Sec, and the ratio of on/off could exceed 1×103.

As described above, when forming InGaZn oxide films by PLD method under the conditions shown in this example, the partial pressure of oxygen was maintained in the range from 4.5 to 6.5 PA.

To achieve conc is the electronic media 1×10 18/cm3it is necessary to control the oxygen partial pressure, the structure of the device formation film, the type and composition of the material for the formation of a film.

Then, MOS transistor with a top gate, as shown in Figure 5, produced by forming an amorphous oxide using the above device at a partial pressure of oxygen, 6.5 PA. In particular, on the glass substrate 1 formed politology amorphous InGaO3(ZnO)4the film thickness of 120 nm for use as a channel layer 2 of the above-described method of forming a thin amorphous Ga-Ga-Zn-O film. In addition, it was layered InGaO3(ZnO)4film having a higher conductivity, and a gold film with a thickness of 30 nm pulsed laser deposition at a partial pressure of oxygen in the chamber is below 1 PA. Then the drain terminal 5 and terminal 6 of the source formed by the photolithography method and the method of inverse lithography. Finally, Y2O3the film was formed to the insulator 3 of the shutter by deposition using electron beam evaporation (thickness: 90 nm, relative dielectric constant: about 15, the density of leakage current: 1×10-3A/cm3at a voltage of 0.5 MV/cm). It was formed of a gold film, and the terminal 4 gate was formed with the specific photolithography and a method of inverse lithography.

Performance evaluation element MOS transistor

Figure 6 shows the volt-ampere characteristic element of a MOS-transistor, measured at room temperature. Given that the drain current IDSincreases with increasing voltage drain VDSit is obvious that the channel is an n-type semiconductor. This is consistent with the fact that the amorphous-type semiconductor In-Ga-Zn-O refers to n-type. IDSis saturated (clipped) at VDS=6 V, which is typical for a semiconductor transistor. Evaluation of the characteristics of the shutter, it was found that a threshold value of gate voltage VGSwhen the voltage VDS=4 is approximately -0,5 Century When VG=10 occurred In the current IDS=1,0×10-5A. This corresponds to the impact of the bias on the gate on the carriers in the semiconductor thin amorphous In-Ga-Zn-O film.

The ratio of on/off of the transistor exceeded 1×103. From the output characteristics to calculate the field-effect mobility, which was approximately 7 cm2/·Sec. According to similar measurements of the emission of visible light does not change the characteristics of the element.

According to the present invention can be manufactured thin-film transistor that has a channel layer containing the electronic media with a lower concentration is a situation to achieve a higher specific resistance and achieve higher mobility of electrons.

The above amorphous oxide has good features, namely that the electron mobility increases with increasing concentration of electronic carriers, and has a degenerate case. In this example, a thin film was formed on the glass substrate. However, a plastic plate or film can also be used as a substrate, since the film formation can be carried out at room temperature. Moreover, the amorphous oxide obtained in this example, absorbs visible light only in a small amount, allowing you to create flexible transparent TFT.

A second process of forming the film: the process of sputtering (SP)

Below is described the formation of thin films of high-frequency SP process in the atmosphere of gaseous argon.

SP process is performed using the device shown in Fig. On Fig reference position indicate the following: 807 - substrate for the formation of a film; 808 - target; 805 - tool mounting substrate equipped with a cooling mechanism; 814 - turbomolecular pump; 815 - rotary pump; 817 - blind; 818 - ion gauge; 819 - gauge Pirani; 821 camera growth and 830 - valve shutter.

The substrate 807 for the formation of a film was a SiO2a glass substrate (Corning Co.: 1737), which was washed for degreasing using ult is Azbuka acetone, ethanol and ultrapure water for five minutes each and dried at 100°C.

The target consisted of a polycrystalline sintered compact having a composition InGaO3(ZnO)4(20 mm in diameter, 5 mm in thickness), which was obtained by wet mixing In2O3, Ga2O3and ZnO (4-normal solution of each reagent) as the source material (solvent: ethanol), firing the mixture (1000°C, 2 hours), dry grinding and sintering (1550°C, 2 hours). Target 808 had a conductivity of 90 Cm/cm and was politology.

The final value of the vacuum in the cell growth 821 was 1×10-4Torr. During the growth of the total pressure of oxygen and argon was maintained in the range from 4 to 0.1×10-1PA. The ratio of the partial pressure of argon and oxygen was changed in the range of oxygen partial pressure from 1×10-3up to 2×10-1PA.

The temperature of the substrate was room temperature. The distance between the target 808 and substrate 807 for the formation of a film was 30 mm

Supplied electric power was 180 watts of RF, and the rate of formation of the film was 10 nm/min

The obtained thin film investigated by the method of small-angle x-ray (SAXS) (method of thin films, the incidence angle: 0,5°): a clear diffraction peak was not observed. Thus obtained thin film type In-Ga-Zn-O was considered the isomorphous. The coefficient of reflection of x-rays and analysis of its pattern was found root-mean-square surface roughness (Rrms), is equal to approximately 0.5 nm, and a film thickness of approximately 120 nm. From x-ray fluorescence analysis (XRF) it was found that the metal content in the film corresponds to the ratio of In:Ga:Zn=0,98:1,02:4.

The film was formed under different partial pressures of oxygen environment, and measured the electrical conductivity of the amorphous oxide film. The result is shown in Figure 3.

As shown in Figure 3, the conductivity can be reduced to values less than 10 s/Cm by the process of film formation in an atmosphere with a partial pressure of oxygen greater than 3×10-2PA. The number of electronic media can be reduced by increasing the partial pressure of oxygen.

As shown in Figure 3, for example, thin InGaO3(ZnO)4film formed at a temperature of the substrate is 25°C and a partial pressure of oxygen of 1×10-1PA had lower conductivity of approximately 1×10-10Cm/see moreover, thin InGaO3(ZnO)4the film is formed at a partial pressure of oxygen of 1×10-1PA had a too high resistance, while having no measurable conductivity. This film, while n is the fact that the electron mobility is not measurable, the electron mobility was estimated as equal to about 1 cm2/·Sec by extrapolation from the values of films with a higher concentration of electronic carriers.

Thus, the transistor is normally off type with respect to on/off higher than 1×103can be obtained by using a transparent thin film of an amorphous oxide containing In-Ga-Zn-O presented in the crystalline state as InGaO3(ZnO)m(m: natural number less than 6), obtained by the method of vacuum deposition in an argon atmosphere containing oxygen with a partial pressure above 3×10-2PA, preferably higher than 5×10-1PA.

When using the device and the material used in this example, the film formation by sputtering is carried out at a partial pressure of oxygen in the range from 3×10-2PA to 5×10-1PA. In this regard, in a thin film, obtained by pulsed laser deposition, or sputtering, electron mobility increases with the increase in the number of conducting electrons.

As described above, by controlling the partial pressure of oxygen you can reduce the number of oxygen defects, and thus can be reduced concentration of electronic carriers. In amorphous thin film, the electron mobility can be high because of amorn the m state, no boundaries between grains in contrast to the polycrystalline state.

In this regard, the replacement of the glass substrate 200 μm polyethylene terephthalate (PET) film does not change the properties formed the film of the amorphous oxide InGaO3(ZnO)4.

Amorphous film InGaO3(Zn1-xMgxO)m(m: natural number less than 6, 0<x≤1) with high resistivity can be obtained by using as a target of polycrystalline InGaO3(Zn1-xMgxO)meven at a partial pressure of oxygen below 1 PA. For example, using a target in which 80% of the Zn atoms is substituted by an Mg, you can get the concentration of electronic carriers below 1×1016/cm3(resistivity of about 1×10-2Cm/cm) using pulsed laser deposition in an atmosphere containing oxygen with a partial pressure of 0.8 PA. In this film, the electron mobility is lower than the electron mobility in the film, not containing Mg, but the reduction is insignificant: the electron mobility is about 5 cm2/V·s at room temperature, which is higher than the electron mobility in amorphous silicon by about one order of magnitude. When the film formation under the same conditions, the increase in the Mg content decreases as conductivity and electron mobility. Therefore, the Mg content is about 20%-85% (of 0.2<x<0,85).

In thin-film Tran is iStore, using the above amorphous oxide film, the gate insulator preferably contains a complex crystalline compound composed of 2 or more Al2O3, Y2O3, HfO2and mixtures thereof.

The presence of a defect at the interface between the thin film insulating layer shutter and a thin film channel layer reduces the mobility of electrons is the cause of the hysteresis performance of the transistor. Moreover, the leakage current strongly depends on the type of insulator bolt. Therefore, the gate insulator should be chosen in such a way that it was appropriate for the channel layer. The leakage current can be reduced by using Al2O3film, the hysteresis can be reduced by using Y2O3film, and the electron mobility can be increased using HfO2film having a high dielectric constant. TFT can be formed by using crystalline complex compounds of the above oxides, which can lead to less leakage current, a smaller hysteresis and higher mobility of the electrons. Since the process of forming the gate insulator and the process of forming the channel layer may be conducted at room temperature, the TFT can be staggered or placed in reverse chess poradek is.

Thus formed TFT is threateningly element with the terminal gate, the source terminal and the drain terminal. Such a TFT is formed by forming a thin semiconductor film on an insulating substrate of ceramic, glass or plastic material as a channel layer for the transfer of electrons or holes and serves as an active element having a function to control the current flowing through the channel layer by applying a voltage to the terminal gate and switching current between the source terminal and the drain terminal.

In the present invention it is also important that the planned concentration of electronic carriers was achieved by controlling the amount of oxygen defects.

In the above description, the amount of oxygen in the film of the amorphous oxide is controlled by the concentration of oxygen in the atmosphere, the formation of a film. Otherwise, the number of oxygen defects can be controlled (increased or decreased), followed by treatment of the oxide film in an atmosphere containing oxygen, as in the preferred embodiment.

For effective management of the number of oxygen defects, the temperature of the atmosphere containing oxygen is maintained in the range from 0°C to 300°C, preferably from 25°C to 250°C, bol is e preferably from 100°C. to 200°C.

Naturally, the film can be formed in the atmosphere containing oxygen, and further followed by treatment in an atmosphere containing oxygen. Otherwise, the film is formed without control the partial pressure of oxygen, and the subsequent processing takes place in the atmosphere containing oxygen is provided that can be achieved planned concentration of electronic carriers (less than 1×1018/cm3).

The lower limit of the concentration of electronic carriers in the present invention is, for example, 1×1014/cm3that depends on the type of the element or device used for the manufacture of the film.

A wider range of materials

After studying the materials for the system it was found that the amorphous oxide composition, of at least one oxide of the elements Zn, In and Sn can be used for the film of the amorphous oxide with a low carrier concentration and high electron mobility. Found that such a film of the amorphous oxide has a specific property, namely, that the increase in its number of conduction electrons increases the electron mobility. Using this film, can be manufactured TFT normally off type, which has good properties such as the ratio of on/off, the saturation current is able use the key and switching speed.

In the present invention can be used oxide, having any one of the operating characteristics (a)to(h)below:

(a) an amorphous oxide having a concentration of electronic carriers is less than 1×1018/cm3;

(b) an amorphous oxide in which the electron mobility increases with increasing concentration of electronic carriers;

(C) an amorphous oxide mentioned above in paragraphs (a) and (b), in which the electron mobility at room temperature is higher than 0.1 cm2/·Sec (at room temperature refers to a temperature ranging from about 0°to about 40°C. the Term “amorphous compound” means a compound that has only a halo pattern no characteristic diffraction pattern in the diffraction spectrum of x-rays. The electron mobility means mobility, measured using Hall effect);

(d) amorphous oxide mentioned above in paragraphs (b), (C)with the degenerate nature of the conductivity (the term “degenerate nature conductivity” means a condition in which thermal activation energy in the temperature dependence of the resistivity does not exceed 30 MeV);

(e) an amorphous oxide mentioned in any of paragraphs (a)to(d), which as a constituent element contains at least one element of Zn, In and Sn;

(f) film from the isomorphous oxide, made of amorphous oxide described above in paragraph (e), and optionally at least one element from:

elements of group 2 M2 with atomic number less than that of Zn (Mg and CA),

elements of group 3 M3 with atomic number less than that In (B, Al, Ga and Y),

elements of group 4 M4 with atomic number less than that of Sn (Si, Ge and Zr),

elements of group 5 M5 (V, Nb and Ta) and

Lu and W to reduce the concentration of electronic carriers;

(g) film of the amorphous oxide, as described in any of paragraphs (a)to(f), consisting of one compound having a composition of In1-xM3xO3(Zn1-yM2yO)m(0≤x≤1; 0≤y≤1; m is 0 or a natural number less than 6) in a crystalline state, or a mixture of compounds with different m, for example from M3, representing Ga, and, for example, M2 represents Mg;

(h) film of the amorphous oxide, as described in any of paragraphs (a)to(g), formed on a plastic substrate or plastic film.

The present invention also provides a field-effect transistor, is used as the channel layer of the above amorphous oxide or a film of the amorphous oxide.

Field-effect transistor is produced using as a channel layer of a film of the amorphous oxide, which has a concentration of electronic carriers is less than 1×1018/cm3but more than 1×1015 3that has a source terminal, a drain terminal and a terminal of the shutter located between the gate insulator. If between the terminals of the source and drain applied voltage of about 5 V without the application of gate voltage, electric current between the terminals of the source and drain is about 1×10-7ampere.

The electron mobility in the crystalline oxide increases with overlapping s-orbitals of the metal ions. In the crystal of the oxide of Zn, In, or Sn with large atomic numbers of e-mobility is in the range from 0.1 to 200 cm2/·Sec.

In the oxide oxygen ions and metal bound ionic bonds that do not have orientation and having a random structure. Therefore, in the oxide in an amorphous state, the electron mobility can be comparable with the electron mobility in the crystalline state.

On the other hand, the substitution of Zn, In, or Sn elements with lower atomic numbers reduces the electron mobility. Thus, the electron mobility in amorphous oxide of the present invention is in the range from 0.01 to 20 cm2/·Sec.

In the transistor having a channel layer composed of the above-described oxide, the gate insulator is preferably formed of Al2O3, Y2O3, HfO2or a mixed crystal compound containing the th two or more of these oxides.

The presence of a defect at the interface between the thin film insulating the gate, and a thin film channel layer reduces the mobility of the electrons and causes the hysteresis performance of the transistor. Moreover, the leakage current strongly depends on the type of insulator bolt. Therefore, the gate insulator should be chosen so that it was suitable for the channel layer. The leakage current can be reduced by using a film of Al2O3the hysteresis can be reduced by using a film of Y2O3and the electron mobility can be increased by using a film of HfO2having a high dielectric constant. When using a complex crystalline compound of the above oxides can be manufactured TFT, which has a smaller leakage current, a smaller hysteresis and has a large electron mobility. Since the process of forming the gate insulator and the process of forming the channel layer can take place at room temperature, can be formed TFT having a checkerboard structure or inverse checkerboard structure.

The film of oxide In2O3can be formed by deposition from the gas phase, and the addition of water vapor with a partial pressure of approximately 0.1 PA, the atmosphere of the formation of a film does form an amorphous film.

ZnO and SnO2matched with the public can not easily be formed as an amorphous film. For the formation of a film of ZnO in amorphous form, add In2O3in the amount equal to about 20 atom.%. For the formation of a film of SnO2in amorphous form, add In2O3in the amount equal to 90 atom.%. When forming an amorphous film type Sn-In-O in the atmosphere the formation of a film introducing nitrogen gas with a partial pressure of approximately 0.1 PA.

In the above film can be added to an element capable of forming a complex oxide selected from the elements of the M2 group 2 with atomic number smaller than that of Zn (Mg and Ca), elements of M3 group 3 with atomic number smaller than that In (B, Al, Ga and Y), elements M4 group 4 with atomic number smaller than that of Sn (Si, Ge and Zr), elements M5 group 5 (V, Nb and Ta), Lu and W. Adding these elements stabilizes the amorphous film at room temperature and expands the set of compositions for forming an amorphous film.

In particular, Appendix B, Si or Ge leads to the formation of covalent bonds, which is effective to stabilize the amorphous phase. Adding a complex oxide consisting of ions with very different radii of ions is effective to stabilize the amorphous phase. For example, in-Zn-O film formation, stable at room temperature, must be contained In a quantity of more than 20 atom.%. However, the addition of Mg in Koli is este, equal In, gives the opportunity to form a stable amorphous film in composition with the content In less than 15 atom.%.

When forming a film by deposition from a gas phase film of the amorphous oxide with a concentration of electronic carriers in the range of 1×1015/cm3up to 1×1018/cm3can be obtained by controlling the atmosphere, the formation of a film.

The film of the amorphous oxide can be suitably formed using a deposition process, for example by the process of pulsed laser deposition process (PLD), spraying (process SP) and a deposition process using electron beam evaporation. For processes of deposition from the gas phase process PLD is suitable from the viewpoint of easy control of the composition of the material, while the process SP is suitable from the viewpoint of mass production. However, the process of forming a thin film, it is not limited.

The formation of a film of the amorphous oxide, In-Zn-Ga-O using the PLD process

Amorphous oxide, In-Zn-Ga-O besieged on a glass substrate (Corning Co.: 1737) process PLD using a KrF excimer laser with a polycrystalline sintered compact as a target having a composition InGaO3(ZnO) or InGaO3(ZnO)4.

Used the device shown in Fig.7, which by mentioning the fact above, and conditions of film formation were the same as described above for the device.

The temperature of the substrate was 25°C.

Two of the obtained thin films are investigated by the method of small angle x-ray (SAXS) (method of thin films, the incidence angle: 0,5°): a clear diffraction peak was not observed, which showed that the obtained thin film type In-Ga-Zn-O, manufactured using two different targets were amorphous.

The coefficient of reflection of x-rays and analysis of its pattern was found root-mean-square surface roughness (Rrms), is equal to approximately 0.5 nm, and a film thickness of approximately 120 nm. From x-ray fluorescence analysis (XRF) it was found that the film obtained with a target of polycrystalline sintered compact InGaO3(ZnO), had a metal content with the ratio of In:Ga:Zn=1,1:1,1:0,9, whereas the film obtained with a target of polycrystalline sintered compact InGaO3(ZnO)4had the metal content with the ratio of In:Ga:Zn=0,98:1,02:4.

Film of the amorphous oxide formed at different partial pressures of the atmosphere for the formation of a film with a target having a composition InGaO3(ZnO)4. The formed film of the amorphous oxide was measured by the concentration of electronic carriers. The results are presented in figure 1. When forming the film in the atmosphere, is within the oxygen partial pressure is higher than 4.2V PA, the concentration of electronic carriers could be reduced to values not exceeding 1×1018/cm3as shown in figure 1. In this film formation, the substrate can be placed almost at room temperature without heating. At a partial pressure of oxygen lower than 6.5 PA surface of the obtained film of the amorphous oxide were flat.

At a partial pressure of oxygen equal to 5 PA, an amorphous film formed with the target InGaO3(ZnO)4the concentration of electronic carriers was 1×1016/cm3the conductivity was equal to 1×10-2Cm/cm, and the electron mobility was assessed approximately 5 cm2/·Sec. From the analysis of the spectrum of light absorption was measured width of the forbidden zone in the optical range in the resulting thin amorphous oxide film which was approximately 3 eV.

A higher partial pressure further reduces the concentration of electronic carriers. As shown in figure 1, in the film of the amorphous oxide, In-Zn-Ga-O, formed at the temperature of substrate 25°C. and at a partial pressure of oxygen equal to 6 PA, the concentration of electronic carriers was below 8×1015/cm3(conductivity approximately 8×10-3Cm/cm). The electron mobility in the film was estimated as equal to 1 cm2/·The EC or more. However, when using PLD at a partial pressure of oxygen, 6.5 PA or higher deposited film had a rough surface and was not suitable for use as a channel layer of the TFT.

Film of the amorphous oxide, In-Zn-Ga-O formed under different partial pressures of oxygen in the atmosphere the formation of a film with a target consisting of a polycrystalline sintered compact having a composition InGaO3(ZnO)4. In the resulting films investigated the relationship between the concentration of electronic carriers and electron mobility. The results are shown in figure 2. By increasing the concentration of electronic carriers from 1×1016/cm3up to 1×1020/cm3the electron mobility was increased from about 3 cm2/·Seconds to about 11 cm2/·Sec. The same trend was observed in amorphous oxide films obtained using a polycrystalline sintered InGaO3(ZnO) target.

The film of the amorphous oxide, In-Zn-Ga-O, which was formed on a 200 μm polyethylene terephthalate (PET) film instead of the glass substrate had similar characteristics.

The formation of a film of the amorphous oxide, In-Zn-Ga-Mg-O using the PLD process

Film of InGaO3(Zn1-xMgxO)4(0<x≤1) formed on the glass substrate using PLD process, and the uses target InGaO 3(Zn1-xMgxO)4(0<x≤1). The device used is shown in Fig.7.

As the substrate used a glass substrate (Corning Co.: 1737). As a pre-treatment prior to deposition the substrate was washed for degreasing using ultrasound acetone, ethanol, and ultrapure water for five minutes each and dried at 100°C. the Target was a sintered compact InGaO3(Zn1-xMgxO)4(x=1-0) (size: 20 mm in diameter, 5 mm in thickness). Target got wet mixing starting materials In2O3, Ga2O3and ZnO (4-normal solution of each reagent) (solvent: ethanol), firing the mixture (1000°C, 2 hours), dry grinding and sintering (1550°C, 2 hours). The final pressure in the cell growth was 2×10-6PA. The oxygen partial pressure during growth was maintained equal to 0.8 PA. The temperature of the substrate was room temperature (25°C). The distance between the target and the substrate for the formation of a film was 30 mm KrF excimer laser is radiated with a capacity of 1.5 MJ/cm2/pulse with a pulse duration of 20 NS, repetition rate 10 Hz, and the point of exposure was represented by a square 1×1 mm, the Rate of formation of the film was 7 nm/min oxygen Partial pressure in the atmosphere the formation of a film was 0.8 PA. Temperature podlog and was equal to 25°C.

The obtained thin film investigated by the method of small-angle x-ray (SAXS) (method of thin films, the incidence angle: 0,5°): a clear diffraction peak was not observed. Thus, the obtained thin film type In-Ga-Zn-Mg-O was amorphous. The obtained film had a flat surface.

Using targets with different values of x (with different Mg content), the film of the amorphous oxide type In-Ga-Zn-Mg-O formed at a partial pressure of oxygen equal to 0.8 PA, the atmosphere for the formation of a film with the purpose of studying the dependence of the conductivity, the concentration of electronic carriers and the mobility of electrons on the value of X.

The results are shown in figa, 4B and 4C. If the value x of the film of the amorphous oxide formed by a process PLD at a partial pressure of oxygen in the atmosphere, equal to 0.8 PA, more of 0.4, the concentration of electronic carriers decreased to a value less than 1×1018/cm3. In the amorphous film with a value of x greater of 0.4, the electron mobility was greater than 1 cm2/·Sec.

As shown in figa, 4B and 4C, the concentration of electronic carriers is lower than 1×1016/cm3can be obtained in the film produced by the method of pulsed laser deposition using a target in which 80 atom.% Zn replaced by Mg, and at a partial pressure of oxygen equal to 0.8 PA (delineation about 1×10 -2Cm/cm). In this film, the electron mobility is lower in comparison with the film not containing Mg, but not much. The electron mobility in the films is about 5 cm2/·Sec, which is higher than the electron mobility in amorphous silicon by about one order of magnitude. In the same conditions of formation of the film as the electrical conductivity and electron mobility in the film decreases with increasing Mg content. Therefore, it is preferable that the Mg content in the film was more than 20 AMTA.% and less than 85 atom.% (of 0.2<x<0,85), more preferably of 0.5<x<0,85.

An amorphous film of InGaO3(Zn1-xMgxO)4(0<x≤1)formed on a 200 μm polyethylene terephthalate (PET) film instead of the glass substrate, with similar characteristics.

The formation of a film of the amorphous oxide In2O3using the PLD process

In2O3the film was formed to 200 µm PET film using a target consisting of In2O3polycrystalline sintered compact using the PLD process using KrF excimer laser.

Used the device shown in Fig.7. The substrate for the formation of a film was a SiO2a glass substrate (Corning Co.: 1737).

As a pre-treatment prior to deposition the substrate was washed for degreasing IP is by the use of ultrasound acetone, ethanol and ultrapure water for five minutes each and dried at 100°C.

The target consisted of In2O3sintered compact (size: 20 mm in diameter and 5 mm in thickness), it was obtained by firing the source reagent In2O3(4-normal reagent solution) (1000°C, 2 hours), dry grinding and sintering (1550°C, 2 hours).

The final pressure in the cell growth was 2×10-6PA, the oxygen partial pressure during growth was equal to 5 PA, and the temperature of the substrate is 25°C.

The partial pressure of water vapor was 0.1 PA, and the oxygen radicals were generated by the device for generating oxygen radicals when applied power of 200 watts.

The distance between the target and the substrate for the formation of a film was 40 mm, power KrF excimer laser was 0.5 MJ/cm2/pulse with a pulse duration of 20 NS, repetition rate 10 Hz, and the point of exposure was a square of size 1×1 mm

The rate of formation of the film was 3 nm/min

The obtained thin film investigated by the method of small-angle x-ray (SAXS) (method of thin films, the incidence angle: 0,5°): a clear diffraction peak was not observed, which showed that the obtained film type In-O was amorphous. The film thickness was 80 nm.

In the obtained film of the amorphous oxide type In-O, the concentration of electronic nose the residents was 5×10 17/cm3and the electron mobility was approximately 7 cm2/·Sec.

The formation of a film of the amorphous oxide, In-Sn-O using the PLD process

Oxide film type In-Sn-O was formed on a 200 µm PET film using a target consisting of a polycrystalline sintered compact (Infor 0.9Sna 0.1)O3,1using process PLD using a KrF excimer laser. Used the device shown in Fig.7.

The substrate for the formation of a film was a SiO2a glass substrate (Corning Co.: 1737).

As a pre-treatment prior to deposition the substrate was washed for degreasing using ultrasound acetone, ethanol, and ultrapure water for five minutes each and dried at 100°C.

The target consisted of In2O3-SnO2sintered compact (size: 20 mm in diameter and 5 mm in thickness), it got wet mixing starting materials In2O3-SnO2(4-normal reagent solution) (solvent: ethanol), firing the mixture (1000°C, 2 hours), dry grinding and sintering (1550°C, 2 hours).

The substrate was at room temperature. The oxygen partial pressure was 5 PA. The partial nitrogen pressure was 0.1 PA. Oxygen radicals were generated by the device for generating oxygen radicals when applied power of 200 watts.

2/pulse with a pulse duration of 20 NS, repetition rate 10 Hz, and the point of exposure was represented by a square with a size of 1×1 mm

The rate of formation of the film was 6 nm/min

The obtained thin film investigated by the method of small-angle x-ray (SAXS) (method of thin films, the incidence angle: 0,5°): a clear diffraction peak was not observed, which showed that the obtained film type In-Sn-O was amorphous.

In the obtained film of the amorphous oxide, In-Sn-O, the concentration of electronic carriers was 8×1017/cm3and the electron mobility was approximately 5 cm2/·Sec. The film thickness was 100 nm.

The formation of a film of the amorphous oxide type In-Ga-O using the PLD process

The substrate for the formation of a film was a SiO2a glass substrate (Corning Co.: 1737).

As a pre-treatment prior to deposition the substrate was washed for degreasing using ultrasound acetone, ethanol, and ultrapure water for five minutes each and dried at 100°C.

The target was a sintered compact (In2O3)1-x-(Ga2O3)x(x=0-1) (size: 20 mm in diameter and 5 mm in thickness). For example, when x=0.1 target is a polycrystalline sintered compact (In,9 Gaa 0.1)2O3.

Target got wet mixing starting materials In2O3-Ga2O3(4-normal solution of reagents) (solvent: ethanol), firing the mixture (1000°C, 2 hours), dry grinding and sintering (1550°C, 2 hours).

The final pressure in the cell growth was 2×10-6PA. The oxygen partial pressure during growth was set to 1 PA.

The substrate was at room temperature. The distance between the target and the substrate for the formation of a film was 30 mm Power KrF excimer laser was 1.5 MJ/cm2/pulse with a pulse duration of 20 NS, repetition rate of 10 Hz. Point of exposure was represented by a square with a size of 1×1 mm, the Rate of formation of the film was 6 nm/min

The temperature of the substrate was 25°C. the oxygen Partial pressure was 1 PA. The obtained thin film investigated by the method of small-angle x-ray (SAXS) (method of thin films, the incidence angle: 0,5°): a clear diffraction peak was not observed, which showed that the obtained film type In-Ga-O was amorphous. The film thickness was 120 nm.

In the obtained film of the amorphous oxide type In-Ga-O, the concentration of electronic carriers was 8×1016/cm3and the electron mobility was approximately 1 cm2/·Sec.

Fabrication of TFT element by splinky of the amorphous oxide type In-Ga-Zn-O (a glass substrate).

Manufactured TFT with a top shutter, shown in figure 5.

First film of the amorphous oxide type In-Ga-Zn-O manufactured on the glass substrate 1 by using the above device PLS, using a target consisting of a polycrystalline sintered compact having a composition InGaO3(ZnO)4at a partial pressure of oxygen equal to 5 PA. Formed In-Ga-Zn-O film had a thickness of 120 nm was used as the channel layer 2.

Next, the PLD method at a partial pressure of oxygen in the chamber is below 1 PA were layered one film of the amorphous oxide type In-Ga-Zn-O with a higher electron mobility and a gold film, each of which had a thickness of 30 nm. Then of them were formed by the drain terminal 5 and terminal 6 of the source by way of photolithography and inverse lithography.

Finally, a deposition method using electron beam evaporation was formed Y2O3film as the gate insulator (thickness: 90 nm, relative dielectric constant: about 15, the density of leakage current: 1×10-3A/cm2when a voltage of 0.5 MV/cm). Then was formed the gold film, from which then the photolithography method and the method of inverse lithography was formed terminal 4 gate. The channel length was 50 μm and a width of 200 microns.

Assessment of working features is istics of the TFT element

Figure 6 shows the current-voltage characteristic of the TFT element at room temperature. The drain current IDSincreases with increasing voltage drain VDSthat shows that the channel has a conductance of n-type.

This is consistent with the fact that the amorphous-type semiconductor In-Ga-Zn-O is a n-type semiconductor. IDSsaturated (clipped) at VDS=6 V, which is typical for a semiconductor transistor. Evaluation of the performance of the shutter found that the threshold value of gate voltage VGSwhen a voltage VDS=4 is approximately -0,5 Century, the Current IDS=1,0×10-5And occurs when VG=10th Century, This corresponds to the impact of the bias on the gate on the carriers in the semiconductor thin amorphous In-Ga-Zn-O film is used as the insulator.

The ratio of on/off of the transistor is higher than 1×103. Output performance calculated the field-effect mobility, which is in the region of saturation was approximately 7 cm2/·Sec. The irradiation of visible light do not change the operating characteristics of the obtained element according to the same measurement.

Amorphous oxide with a concentration of electronic carriers is lower than 1×1018/cm3can be used as a channel layer of the TFT. A more preferred concentration e novtel the th lower than 1×10 17/cm3even more preferred is lower than 1×1016/cm3.

Fabrication of TFT element with a film of the amorphous oxide, In-Zn-Ga-O (amorphous substrate).

Made a TFT element with the upper shutter, shown in figure 5.

First film of the amorphous oxide type In-Ga-Zn-O made on a polyethylene terephthalate (PET) substrate 1 by using the above device PLS, using a target consisting of a polycrystalline sintered compact having a composition InGaO3(ZnO) at a partial pressure of oxygen in the atmosphere, equal to 5 PA. The formed film had a thickness of 120 nm was used as the channel layer 2.

Next, the PLD method at a partial pressure of oxygen in the chamber is below 1 PA were layered one film of the amorphous oxide type In-Ga-Zn-O with a higher electron mobility and a gold film, each of which had a thickness of 30 nm. Then of them were formed by the drain terminal 5 and terminal 6 of the source by way of photolithography and inverse lithography.

Finally, a deposition method using electron beam evaporation was formed insulator 3 shutter. Next it was formed of a gold film, from which then the photolithography method and the method of inverse lithography was formed terminal 4 gate. The channel length was 50 μm and a width of 200 μm. Three TFT in Sopianae patterns produced, using one of the three types of insulators shutter: Y2O3(thickness 140 nm), Al2O3(thickness 130 μm) and HfO2(thickness 140 μm).

Performance evaluation of the TFT element

The TFT elements formed on the PET film at room temperature had a volt-ampere characteristics similar to those shown in Fig.6. The drain current IDSincreases with increasing voltage drain VDSthat shows that the channel is n-type conductance. This is consistent with the fact that type semiconductor In-Ga-Zn-O is a n-type semiconductor. IDSsaturated (clipped) at VDS=6 V, which is typical for a semiconductor transistor. Current IDS=1,0×10-8And occurs when VG=0 V, and current IDS=2,0×10-5And occurs when VG=10th Century, This corresponds to the impact of the bias on the gate on the media in the insulator in the semiconductor thin amorphous In-Ga-Zn-O film.

The ratio of on/off of the transistor is higher than 1×103. Output performance calculated the field-effect mobility, which is in the region of saturation was approximately 7 cm2/·Sec.

The elements formed on the PET film were bent to the radius of curvature of 30 mm, and in this state were measured performance characteristics of the transistor. However, in the working characteristics of the changes was not observed. The irradiation of visible light do not change the operating characteristics of the transistor.

TFT, using as an insulator shutter Al2O3the film also had operational characteristics of the transistor, shown in figure 6. Current IDS=1,0×10-8And occurs when VG=0 V, and current IDS=5,0×10-6And occurs when VG=10th Century, the Ratio of on/off of the transistor is higher than 1×102. From the output characteristics was computed field-effect mobility, which in saturation is 2 cm2/·Sec.

TFT, using as an insulator shutter HfO2the film also had operational characteristics of the transistor, shown in figure 6. Current IDS=1,0×10-8And occurs when VG=0 V, and current IDS=1,0×10-6And occurs when VG=10th Century, the Ratio of on/off of the transistor is higher than 1×102. From the output characteristics was computed field-effect mobility, which in saturation is 10 cm2/·Sec.

Fabrication of TFT element with a film of the amorphous oxide In2O3type using the method PLD

Manufactured TFT with a top shutter, shown in figure 5.

First, on a polyethylene terephthalate (PET) substrate 1 by the PLD method has produced a film of the amorphous oxide type In2O3as the channel layer 2 is the thickness of 80 nm.

Next, the PLD method at a partial pressure of oxygen in the chamber is below 1 PA and an applied voltage of 0 V, to a device for the generation of oxygen radicals on her were layered one film of the amorphous oxide type In2O3with the greater mobility of electrons and a gold layer, each of which had a thickness of 30 nm. Then of them were formed by the drain terminal 5 and terminal 6 of the source by way of photolithography and inverse lithography.

Finally, a deposition method using electron beam evaporation was formed Y2O3the film quality of the insulator 3 of the shutter. Next it was formed of a gold film, from which then the photolithography method and the method of inverse lithography was formed terminal 4 gate.

Performance evaluation of the TFT element

Studied the current-voltage characteristics of elements formed on the PET film at room temperature. The drain current IDSincreased with increasing voltage drain VDSthat showed that the channel is n-type conductance. This is consistent with the fact that the amorphous oxide film of the type In-O is a n-type semiconductor. IDSsaturated (clipped) at VDS=6 V, which is typical for a semiconductor transistor. Current IDS=2,0×10-8And occurs when VG=0 V, and current IDS=2,0×10-6 And occurs when V G=10th Century, This corresponds to the impact of the bias on the gate on the carriers in the semiconductor thin amorphous In-O film.

The ratio of on/off of the transistor is higher than 1×102. Output performance calculated the field-effect mobility, which is in the saturation region is about 1×10 cm2/·Sec. TFT element formed on the glass substrate had similar characteristics.

The elements formed on the PET film were bent to the radius of curvature of 30 mm, and in this state were measured performance characteristics of the transistor. In performance changes were observed.

The fabrication of the TFT film of the amorphous oxide, In-Sn-O using the PLD process

Manufactured TFT with a top shutter, shown in figure 5.

First, on a polyethylene terephthalate (PET) film 1 by the PLD method has shaped film 2 of amorphous oxide, In-Sn-O thickness of 100 nm as a channel layer.

Next on her way PLD at a partial pressure of oxygen in the chamber is below 1 PA and an applied voltage of 0 V to the device generating oxygen radicals were layered one film of the amorphous oxide, In-Sn-O with a higher electron mobility and a gold layer, each of which had a thickness of 30 nm. Then of them were formed by the drain terminal 5 and terminal 6 of the source by way totalitar the AI and inverse lithography.

Finally, a deposition method using electron-beam evaporation was formed Y2O3the film quality of the insulator 3 of the shutter. Next it was formed of a gold film, from which then the photolithography method and the method of inverse lithography was formed terminal 4 gate.

Performance evaluation of the TFT element

Investigated the current-voltage characteristics of the TFT elements formed on the PET film at room temperature. The drain current IDSincreased with increasing voltage drain VDSthat shows that the channel is n-type conductance. This is consistent with the fact that the film of the amorphous oxide, In-Sn-O is a n-type semiconductor. IDSsaturated (clipped) at VDS=6 V, which is characteristic of the transistor. Current IDS=5×10-8And occurs when VG=0 V, and current IDS=5,0×10-5And occurs when VG=10th Century, This corresponds to the impact of the bias on the gate on the media in the insulator film of the amorphous oxide, In-Sn-O.

The ratio of on/off of the transistor was approximately 1×103. Output performance calculated the field-effect mobility, which is in the region of saturation was approximately 5 cm2/·Sec. TFT element formed on the glass substrate, had a similar feature is I.

The elements formed on the PET film were bent to the radius of curvature of 30 mm, and in this state were measured performance characteristics of the transistor. In performance changes were observed.

Fabrication of TFT element with a film of the amorphous oxide type In-Ga-O using the PLD process

Manufactured TFT with a top shutter, shown in figure 5.

First, on a polyethylene terephthalate (PET) film 1 by the PLD method shown in example 6, was shaped film 2 of amorphous oxide type In-Ga-O thickness of 120 nm as a channel layer.

Next on her way PLD at a partial pressure of oxygen in the chamber is below 1 PA and attached to the device generating oxygen radicals voltage of 0 V was layered another film of the amorphous oxide type In-Ga-O with a higher electron mobility and a gold film, each of which had a thickness of 30 nm. Then of them were formed by the drain terminal 5 and terminal 6 of the source by way of photolithography and inverse lithography.

Finally, a deposition method using electron beam evaporation was formed Y2O3the film quality of the insulator 3 of the shutter. Next it was formed of a gold film, from which then the photolithography method and the method of inverse lithography was formed terminal 4 gate.

Performance evaluation ELEH the enta TFT

Investigated the current-voltage characteristics of the TFT elements formed on the PET film at room temperature. The drain current IDSincreased with increasing voltage drain VDSthat showed that the channel is n-type conductance. This is consistent with the fact that the film of the amorphous oxide type In-Ga-O is a n-type semiconductor. IDSsaturated (clipped) at VDS=6 V, which is characteristic of the transistor. Current IDS=1×10-8And appeared at VG=0 V, and current IDS=1,0×10-6And appeared at VG=10th Century, This corresponds to the impact of the bias on the gate on the media in the insulator film of the amorphous oxide type In-Ga-O.

The ratio of on/off of the transistor was approximately 1×102. Output performance calculated the field-effect mobility, which is in the region of saturation was approximately 0.8 cm2/·Sec. TFT element formed on the glass substrate had similar characteristics.

The elements formed on the PET film were curved with a curvature radius of 30 mm, and in this state were measured performance characteristics of the transistor. In performance changes were observed.

Amorphous oxide with a concentration of electronic carriers is lower than 1×1018/cm3can be used as a channel layer of the TFT. More p is impactfully the concentration of electronic carriers is lower than 1×10 17/cm3even more preferred is lower than 1×1016/cm3.

Below are examples of the implementation of the present invention.

Example 1: obtaining an In-Ga-Zn-O amorphous thin film containing microcrystals

The film is produced by the device shown in Fig.7. The method of pulsed laser deposition using a KrF excimer laser is performed, using as a target a sintered polycrystalline body having a composition InGaO3(ZnO)4. On a glass substrate (1737 production Corning Incorporated) precipitated semiconductor thin film on the basis of an In-Ga-Zn-O amorphous oxide. At the stage of formation of a film surface of the substrate is irradiated by a halogen lamp (20 mW/cm2). The presence or absence of microcrystals is confirmed by the inspection region of the film using THE (transmission electron microscope).

Obtaining MOS transistor (field effect transistor metal-insulator-semiconductor)

Make the device MOS transistor with a top gate, shown in figure 5. First semiconducting amorphous InGaO3(ZnO)4a film thickness of 30 nm, containing microcrystals and serves as the channel layer (2), is formed on the glass substrate (1) according to the above method of obtaining In-Ga-Zn-O amorphous thin film containing microcryst is lly. Moreover, the resulting structure layer InGaO3(ZnO)4film and a gold film with a higher conductivity, each with a thickness of 30 nm using the method of pulsed laser deposition, while setting the partial pressure of oxygen in the chamber is below 1 PA. Then the terminal (5) of the drain terminal (6) the source is formed by the photolithography method and the method of inverse lithography. Finally, Y2O3the film serves as the insulator (3) shutter formed by the method of electron-beam deposition (obtained film has a thickness of 90-110 nm, the specific dielectric constant of about 15, the density of the leakage current of 1×10-3A/cm2when the application voltage of 0.5 MV/cm). Therefore, a gold film is formed on the resulting structure and then create the terminal (4) of the shutter by the photolithography method and the method of inverse lithography. Thus form a field-effect transistor.

The ratio of on/off of the transistor exceeds 1×104. If the drift mobility is calculated on the basis of the characteristics of power, the drift mobility of electrons of about 7.5 cm2/·S get in a saturated field. Made so the device is irradiated with visible light and subjected to the same measurement. Thus any change in the characteristics of the transistor does not occur.

Bo is her, in the above examples to obtain an In-Ga-Zn-O thin film containing microcrystals, effective results are obtained if the substrate is irradiated with light having an energy density of 0.3 mW/cm2- 100 mW/cm2. As a result the transistor on/off can be increased, and may be obtained at most of the drift mobility of electrons. For this reason, preferably, the irradiation of light. Although it varies depending on the number of microcrystals in the film of the amorphous oxide, the presence of microcrystals is generally confirmed, if the detected peak with the help of diffraction.

Example 2: obtaining an In-Ga-Zn-O amorphous thin film having a composition distribution in the direction of film thickness

Semi-conducting thin film on the basis of an In-Ga-Zn-O amorphous oxide having a composition distribution in the thickness direction of the film precipitated on the glass substrate (1737 production Corning Incorporated) by the method of pulsed laser deposition using a KrF excimer laser, using as a target a sintered polycrystalline body having a composition InGaO3(ZnO)4. The film is precipitated in the chamber, having an internal partial pressure of oxygen within the specified range, increasing the distance between the target and the substrate to 5 mm As the distance increases, if estvo oxygen, put the formed film is increased. It should be noted that the temperature of the substrate is set to 25°C.

Example 2 (to form a thin film having a composition distribution in the thickness direction of the film) of the composition can be varied by changing the partial pressure of oxygen in the direction of film thickness, or alternatively by changing the energy of the oscillation frequency or oscillation of the pulse laser. Thus, it is possible to reduce the leakage current, or you can increase the ratio of the transistor on/off, and can also be increased drift mobility of electrons.

Example 3: obtaining an In-Ga-Zn-O amorphous thin film having a composition distribution in the direction of film thickness

Film formed by a sputtering method using gaseous argon. As targets are made (1) polycrystalline sintered body having a composition InGaO3(ZnO)4and (2) the sintered body of zinc oxide. Then onto a glass substrate (1737 production Corning Incorporated) layer In-Ga-Zn-O amorphous thin film having a composition distribution in the thickness direction. The film formed by the sputtering method in the atmosphere with a given partial pressure of oxygen, first using target (1), then using the target (1) target (2) at the same time. So what Braz, you can get an In-Ga-Zn-O amorphous thin film having a composition distribution in the thickness direction. It should be noted that the temperature of the substrate support at 25°C.

In-Ga-Zn-O amorphous thin film having a composition distribution in the thickness direction can be obtained as follows. The composition is distributed in the direction of film thickness by sputtering In2O3target simultaneously or separately, or by changing the partial pressure of oxygen in the direction of film thickness, or alternatively by changing the power supplied in the direction of film thickness for each of the target during sputtering. In particular, it is expected that in the amorphous thin film near the gate insulator increases the drift mobility of electrons with increasing number of In2O3or ZnO.

Example 4: obtaining an In-Ga-Zn-O(N) amorphous thin films

The following describes a method of obtaining an amorphous oxide containing nitrogen (N) as an additive.

Semi-conducting amorphous film on the basis of an In-Ga-Zn-O amorphous oxide containing nitrogen as an impurity (denoted simply as “In-Ga-Zn-O(N)”), layer on the glass substrate of the same type as described above, the method of pulsed laser deposition using a KrF excimer laser, using as target InGaO3(ZnO)4 polycrystalline sintered body. It should be noted that the oxygen partial pressure inside the chamber is set to, for example, 4 PA, the partial pressure of nitrogen is set to 1 PA, and the temperature of the substrate is equal to 25°C. the Compositional ratio of oxygen to nitrogen in the thin film is preferably about 50:1, as analyzed using the second ion mass spectrum (SIMS).

Example 5: receiving an In-Ga-Zn-O(Ti) amorphous thin films

Semiconductor thin film on the basis of an In-Ga-Zn-O amorphous oxide layer on a glass substrate (1737 production Corning Incorporated) by the method of pulsed laser deposition using a KrF excimer laser, using as a target a sintered polycrystalline body having a composition InGaO3(ZnO)4. The obtained thin film on the basis of an In-Ga-Zn-O-impregnated with an aqueous solution of trichloride titanium at 80°C. Then the film annealed at 300°C in air. Thus, Ti can be entered in the amorphous oxide in the form of impurities. When analyzing the concentration of Ti in a thin film on its surface in the direction of the substrate by SIMS, the concentration of Ti on the surface is about 0.5% and gradually increases in the direction of the substrate.

The amorphous oxide according to the present invention layer on the channel layer of the transistor. Such a transistor can be used on lesofat as a switching device for LCD and display devices and organic EL. Alternatively, the amorphous oxide can be deposited on flexible material such as plastic film, for forming a semiconductor thin film. This semiconductor thin film can be widely used as a panel for flexible display devices, IC cards and ID cards.

This application claims the priority of Japanese patent application No. 2004-326687, filed November 10, 2004 and is included in the present description in its entirety by reference.

1. Amorphous oxide whose composition varies in the thickness direction of the layer containing the compound having in the crystalline state the composition represented by a formula In2-XM3XO3(Zn1-YM2YO)mwhere M2 is an element of group II with atomic number less than that of Zn (e.g. Mg or CA), M3 is an element of group III of atomic number less than that In (for example, Al, Ga, or Y), x is in the interval from 0 to 2, y is in the interval from 0 to 1 and m is 0 or natural number smaller than 6 and the amorphous oxide has a concentration of electronic carriers is not less than 1012/cm3and less than 1018/cm3and has the mobility of electrons, which increases with increasing concentration of electronic carriers.

2. The amorphous oxide according to claim 1, and an amorphous oxide contains at least one e is ement, selected from the group consisting of In, Zn and Sn.

3. The amorphous oxide according to claim 1, in which the amorphous oxide is any selected from the group consisting of an oxide containing In, Zn and Sn, an oxide containing In and Zn, an oxide containing In and Sn; and an oxide containing In.

4. The amorphous oxide according to claim 1, and an amorphous oxide contains In, Ga and Zn.

5. Field-effect transistor containing
the active layer of an amorphous oxide whose composition varies in the thickness direction of the layer, and
a gate electrode formed in such a way that he was converted to the active layer through the gate insulator, the active layer contains a compound having in the crystalline state the composition represented by a formula In2-xM3xO3(Zn1-YM2YO)mwhere M2 is an element of group II with atomic number less than that of Zn (e.g. Mg or CA), M3 is an element of group III of atomic number less than that In (for example, Al, Ga, or Y), x is in the interval from 0 to 2, y is in the interval from 0 to 1 and m is 0 or natural number smaller than 6, and thus the active layer has a concentration of electronic carriers is not less than 1012/cm3and less than 1018/cm3and has the mobility of electrons, which increases with increasing concentration of electronic media, and the active layer contains a first region and a second region, which is located b is cognate to the gate insulator, than the first region, and the oxygen concentration in the second region is higher than the oxygen concentration in the first region.

6. Field-effect transistor containing an active layer of an amorphous oxide containing at least one element selected from the group consisting of In and Zn, and a gate electrode formed in such a way that he was converted to the active layer through the gate insulator, and an active layer contains a first region and a second region, which is located to the insulator of the shutter closer to the first area, and the concentration In the second region is higher than the concentration In the first region, or the concentration of Zn in the second region is higher than the concentration of Zn in the first area.

7. Field-effect transistor according to claim 6, in which an active layer of amorphous oxide contains a compound having in the crystalline state the composition represented by the formula
In2-xM3xO3(Zn1-YM2YO)mwhere M2 is an element of group II with atomic number less than that of Zn (e.g. Mg or CA), M3 is an element of group III of atomic number less than that In (for example, Al, Ga, or Y),
x is in the interval from 0 to 2, y is in the interval from 0 to 1 and m is 0 or natural number smaller than 6, and thus the active layer has a concentration of electronic carriers is not less than 1012/cm3and less than 1018/cm3and has the mobility of electron is Ronov, which increases with increasing concentration of electronic carriers.



 

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