Manufacturing method of gas sensor with nanostructure, and gas sensor on its basis

FIELD: measurement equipment.

SUBSTANCE: invention relates to manufacture of gas sensors intended for detection of different gases. The invention proposes a gas sensor manufacturing method, in which a heterostructure is formed of different materials; a gas-sensitive layer is made in it; after that, it is fixed in the sensor housing, and contact pads are connected to terminals of the housing by means of contact conductors. The gas-sensitive layer is made in the form of a thin tread-like nanostructure (SiO2)20%(SnO2)80%, where 20% - mass fraction of SiO2, and 80% - mass fraction of component SnO2, by application of sol of orthosilicic acid, which contains stannum hydroxide, onto a silicone surface by means of a centrifuge with further annealing. An area with width of 1 mcm and depth of 200 nm is formed on the surface of the substrate surface by a method of local anodic oxidation. Sol is prepared at two stages: at the first stage, Tetraethoxysilane (TEOS) and ethyl alcohol (95%) is mixed in the ratio of 1:1.046 at room temperature, and the mixture is exposed during about 30 minutes, and at the second stage, to the obtained solution there introduced is distilled water in the ratio of 1:0.323; hydrochloric acid (HCl) in the ratio of 1:0.05; stannum chloride dihydrate (SnCl2·2H2O) in the ratio of 1:0.399, where TEOS volume is accepted as one, and stirred at least during 60 minutes. The invention also proposes a gas sensor with a nanostructure, which is made as per the proposed method.

EFFECT: increasing gas sensor sensitivity.

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The present invention relates to measuring technique and can be used in the manufacture of gas sensors of new generation, designed for detection of various gases.

Currently, gas sensors are used extensively in virtually all sectors of industry, transport and agriculture, and medicine. Gas sensors are the basis for creating systems, fire and environmental safety. The most common gas sensors based on semiconducting metal oxides such as tin oxide (SnO2). The mechanism of action of these devices is based on the change of electrical conductivity of semiconductors n-type conductivity in the course of what is happening on their surface chemical reactions, for example the interaction detected gas with hammarbyhamnen oxygen. Sensors based on SnO2low cost, good response time and a number of other advantages. Their typical disadvantages are long time reset (due to the finite time of the desorption gases) and insufficient selectivity to detektivami gases.

There is a method of analyzing a semiconductor sensors gas mixtures containing flammable gases, such as CO and H2. As the gas sensitive layer is used dioxide ol the VA, doped with antimony. Obtained by the invention of the gas sensitive film SnO2found high sensitivity to H2and CO in the atmospheres of O2/N2and O2/N2/vapor-H2O. Temperature range of sensitivity of the sensors obtained by this method is 200-550°C [1].

Known sensor device for the detection of CO, comprising an insulating substrate with the measuring electrodes, the layer of semiconductor oxide and a catalytic layer containing one of the following metals Pt, Rh, Pd on the oxide carrier and the heating element. The specified device provides relatively high sensitivity to CO at a moderate temperature of the heating element (120°C and below). The disadvantages of the proposed device are the low stability of the sensor caused by the degradation of a sensitive layer of a semiconductor oxide.

Known sensor device for display CO., in which as the material of the sensing element used tin oxide with finely dispersed platinum, to create the optimum porous structure of the active layer are used additives silicates such as feldspars and bentonite [3]. An advantage of the device is a separate determination of carbon monoxide and hydrogen. A disadvantage of the device is as is the high electrical resistance of the sensitive layer, what complicates the measurement of the touch signal and significantly complicates the design.

The known method of sensory analysis of gas mixtures containing gaseous reductants (CO and H2) and O2. As catalysts to increase the sensitivity of gas sensitive layer based on tin dioxide to CO and H2used RuCl3and PtCl2. In the way it is shown that the optimal concentration of RuCl3and PtCl2in SnO2for detection of CO and H2are 1-5 mol.%. Ru and Pt, which was introduced into the matrix by impregnation dioxide tin chlorides of these elements. The films obtained on the basis of these substances can be used in the temperature range of 200-350°C [4].

The closest to the technical nature of the proposed solution is a method of manufacturing a sensing element of a gas sensor in thin-film technology [5]. It is that form a heterostructure made of different materials (dielectric substrate, pads of platinum on one side of the substrate, the heater on the other hand), which form the gas sensitive layer (film of tin dioxide with a thickness of 50 and 100 nm with the contents of antimony 1.5 ATA. %). As the substrate used plate polikor thickness of 150 μm. Contacts to the layers of tin dioxide and the heater on the back side forms the shape sputtering platinum with subsequent photolithographic-etching prior to the deposition of films of tin dioxide (SnO 2). Ultrathin layers of catalytic get platinum cathode sputtering. Prepared samples are subjected to a stabilizing annealing in air at 400°C for 24 hours. The disadvantage of this method is not high enough sensitivity to different restorative gases (for example, pairs of ethyl alcohol).

The technical result of the invention is to increase the sensitivity of the gas sensor.

This is achieved by the known method of manufacturing the gas sensor with a nanostructure, namely, that form a heterostructure made of different materials, which form the gas sensitive layer, after which it is fixed in the sensor housing and contact pads connected to the housing using the contact conductors, in accordance with the invention the gas sensitive layer is formed in the form of a thin filiform nanostructures (SiO2)20%(SnO2)80%where a 20% mass fraction of SiO2and 80% - mass fraction of component SnO2by applying Zola orthosilicic acid containing tin hydroxide, on a substrate made of silicon, on which surface using local anodic oxidation region formed with a width of 1 μm, a depth of 200 nm, using a centrifuge and subsequent annealing, the Sol prepared in two stages, the first stage mix is a tetraethoxysilane (TEOS) and ethanol (95%) in the ratio 1:at 1,046 at room temperature and the mixture is kept for 30 minutes, then in the second stage the resulting solution is injected distilled water in the ratio 1:0,323, hydrochloric acid (HCl) in the ratio 1:0,05, the two-water tin chloride (SnCl2·2H2O) in the ratio 1:0,399, where the unit received the amount of TEOS, and stirred for at least 60 minutes, and Sol orthosilicic acid is applied on a substrate made of silicon (Si) using a centrifuge using the dispenser when the speed of rotation of the centrifuge 3000 rpm for 2 minutes, and annealing is carried out at a temperature of 600°C for 30 minutes in air.

In the gas sensor with a nanostructure fabricated by the proposed method, comprising a housing mounted therein heterogeneous structure of the thin film material formed on a substrate of semiconductor gas sensitive layer and the pad to him, formed in a heterogeneous structure, the conclusions of the housing and the contact wires connecting the pads with the conclusions of the corps, in accordance with the invention the gas sensitive layer is made as thin filiform nanostructures based on Zola orthosilicic acid containing tin hydroxide, on a substrate of silicon, on which surface using local anodic oxidation region formed with a width of 1 μm, a depth of 200 nm, using a centrifuge and subsequent annealing, Sol is zgotovlen in two stages, in the first phase, mixing tetraethoxysilane and ethanol, and in the second stage the resulting solution was administered distilled water, hydrochloric acid (HCl) and the two-water tin chloride (SnCl2·H2O), and tetraethoxysilane and ethyl alcohol in the ratio of 1:at 1,046, distilled water in the ratio 1:0,323, hydrochloric acid (HCl) in the ratio 1:0,05, the two-water tin chloride (SnCl2·2H2O) in the ratio 1:1,597.

In Fig.1 shows the design of the gas sensor, which is manufactured by the proposed methods. The gas sensor includes a housing 1 (Fig.1), heterogeneous structure 2 (thin film material), in which the generated gas sensitive layer 3 (thin filiform nanostructure), pads 4, the contact wires 5, the conclusions of the case 6, the fitting 7, the insulator 8, the substrate 9 (made of silicon, on which surface using local anodic oxidation region formed with a width of 1 μm, a depth of 200 nm).

According to the proposed method the Sol orthosilicic acid containing tin hydroxide, prepared in two stages for applying on a substrate 9 made of silicon (Fig.1). At the first stage mixing tetraethoxysilane and ethyl alcohol, the mixture is kept for 30 minutes before proceeding to the second stage. The exposure time is set based on the time of reaction is the exchange interaction between atrato what sisalana and ethyl alcohol, in the result of which is formed ethyl ester articlenews acid. At the second stage after the introduction of distilled water, hydrochloric acid (HCl) and two-water of tin chloride (SnCl2·2H2O) the mixture is stirred for at least 60 minutes. The process set based on the time of reaction is hydrolysis of the ester, which is formed orthographia acid. And based on the fact that during this same time, at this stage, the formation of tin hydroxide (Sn(OH)2and flows through the polycondensation reaction articlenews acid.

Sol articlenews acid containing tin oxide, is applied to the substrate 9 (Fig.1) made of silicon (Si), which on the surface using local anodic oxidation region formed with a width of 1 μm, a depth of 200 nm using a centrifuge using the dispenser when the speed of rotation of the centrifuge 3000 rpm for 2 minutes. The use of such modes centrifuge allows you to achieve a uniform distribution of Zola, and partially remove the solvent from the film.

As a substrate of silicon (Si) can be used silicon wafer EFC (111) with a thickness of 200-300 μm, oxidized industrially oxygen, having an oxide layer of SiO2thickness of about 800 nm. On the surface of the substrate using local anodic oxidation of the formed area of the width of 1 μm, the depth of 200 nm, in which the formation of gas sensitive layer in the form of a thin filiform nanostructures (SiO2)20%(SnO2)80%where a 20% mass fraction of SiO2and 80% - mass fraction of component SnO2. In Fig.2 shows the surface morphology of the gas sensitive layer 3, obtained using scanning electron microscopy (SEM), with mass fraction of tin dioxide (SnO2) to 80% (Fig.2A - increase in 5000 time Fig.2B is an increase of 300,000 times).

Annealing is carried out at a temperature of 600°C for 30 minutes in air. The use of such process parameters allows you to completely remove the solvent from the pores on the surface and in the bulk of the film, as well as to carry out reaction for the decomposition articlenews acid (Si(OH)4) to silicon dioxide (SiO2and tin hydroxide (Sn(OH)4) to tin dioxide (SnO2). Pads 4 to the gas sensitive layer of Ag was formed by viginia at a temperature of 600°C.

Gas sensor operates as follows. Gas sensitive layer 3 using the package pin 6 include in-pavement measuring circuit (bridge) as one of her shoulders, using the trimmer resistor (not shown), a bridge balance (the meter set to zero in the absence of gas). The interaction of the gas with getcust the nutrient layer leads to a change in its conductivity in the course of what is happening on the surface chemical reactions, for example, the interaction detected gas with hammarbyhamnen oxygen. As gas sensitive layer 3 include in-pavement measuring circuit, the variation of gas concentration is balanced, which is a function of concentration.

In Fig.3 presents the dependence of the signal of the sensor (5) gas sensitive layer 3 on the concentration of detected gas - ethanol vapor (s): curve 1 - gas sensitive layer in the form of a solid film SnO2curve 2 - gas sensitive layer in the form of a thin filiform nanostructures (SiO2)20%(SnO2)80%where a 20% mass fraction of SiO2and 80% - mass fraction of component SnO2. You can see that the presence of a thin filiform nanostructures (SiO2)20%(SnO2)80%(curve 2) touch signal when the same concentration of gas is significantly greater than in its absence (curve 1). Thin thread-like nanostructure (SiO2)20%(SnO2)80%obtained through Sol-gel technology is percolation structure. This structure has the highest sensitivity due to the following circumstances. When finding patterns in the air hemicorporectomy oxygen creates a depletion layer near the jumpers grains, therefore, this structure has a high resistance (R). When exposed to gases reductants ethanol vapor) on a thin thread-like nanostructure (SiO 2)20%(SnO2)80%within a certain time (t) there are various chemical reactions, including the binding of chemisorbed oxygen. When this depletion disappears and the resistance (R) decreases significantly (Fig.4). Gas sensitive layer in the form of a solid film SnO2has a structure corresponding spinodal decomposition. This structure is much less sensitive to gases than the percolation structure.

Due to the distinctive features of the invention increases the sensitivity of the gas sensor.

As a result of experimental tests of samples of the gas sensor made in accordance with the invention, it was found that significantly increases the sensitivity of gas sensors.

The proposed method of manufacturing the gas sensor with a nanostructure and a gas sensor based on it favorably known and can be widely used in the manufacture of gas sensors.

Sources of information

1. U. S. Pat. No. 4614669, 30.09.1986.

2. U.S. patent 4792433, MKI G01N 20/16, 1988.

3. Patent UK 2249179, MKI G01N 27/12, 1992.

4. U. S. Pat. No. 4397888, 09.08.1983.

5. Anisimov, O. C., Maximova N. K. Filonov N. G. Features of the response of thin films of Pt/SnO2:Sb on the impact of CO // Journal of physical chemistry, 2004, 78. No. 10. - S. 1907-1912.

1. A method of manufacturing a gas Senso is and with a nanostructure namely, that form a heterostructure made of different materials, which form the gas sensitive layer, after which it is fixed in the sensor housing and contact pads connected to the housing using the contact conductors, characterized in that the gas sensitive layer is formed in the form of a thin filiform nanostructures (SiO2)20%(SnO2)80%where a 20% mass fraction of SiO2and 80% - mass fraction of component SnO2by applying Zola orthosilicic acid containing tin hydroxide, on a substrate made of silicon, on which surface using local anodic oxidation region formed with a width of 1 μm, a depth of 200 nm, using a centrifuge and subsequent annealing, the Sol prepared in two stages, the first stage mixing tetraethoxysilane (TEOS) and ethanol (95%) in the ratio 1:at 1,046 at room temperature and the mixture is kept for 30 minutes, then at the second stage, the obtained solution is injected distilled water in the ratio 1:0,323, hydrochloric acid (HCl) in the ratio 1:of 0.05, the two-water tin chloride (SnCl2·2H2O) in the ratio 1:0,399, where the unit received the amount of TEOS, and stirred for at least 60 minutes.

2. Gas sensor with a nanostructure made under item 1, comprising a housing mounted therein heterogeneous structure of the thin film material formed on a substrate of semiconductor, gas sensitive layer and the pad to him, formed in a heterogeneous structure, the conclusions of the housing and the contact wires connecting the pads with the conclusions of the casing, the gas sensitive layer is made as thin filiform nanostructures based on Zola orthosilicic acid containing tin hydroxide, on a substrate of silicon, on which surface using local anodic oxidation region formed with a width of 1 μm, a depth of 200 nm, using a centrifuge and subsequent annealing, which is prepared in two stages, in first stage, mixing tetraethoxysilane and ethanol, and in the second stage the resulting solution was administered distilled water, salt acid (HCl) and the two-water tin chloride (SnCl2·2H2O), and tetraethoxysilane and ethyl alcohol in the ratio of 1:at 1,046, distilled water in the ratio 1:0,323, hydrochloric acid (HCl) in the ratio 1:0,05, the two-water tin chloride (SnCl2·2H2O) in the ratio 1:1,597.



 

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