Element of the memory device with the structure of metal-insulator - metal
(57) Abstract:The invention relates to memory devices implemented using the methods of micro - and nanotechnology. The inventive element of the memory device includes two metal electrodes separated vinyl slit, and conductive carbon phase in the slit, placed in a medium containing organic matter, so that access of the molecules of this substance to the crack, consistently conductive carbon phase in the insulating slits on the anode side is a dielectric layer, excluding the possibility of approximation carbon conductive phase to the surface of the anode at a distance less than the thickness of the dielectric layer, which is in the range of 1 - 100 nm. The anode should consist of aluminum. 1 C.p. f-crystals, 4 Il. The invention relates to micro - and nanoelectronics, and in particular to memory devices implemented using the methods of micro - and nanotechnology.Well known element of a memory device having a sandwich structure (layered structure) metal-insulator-metal (MIM), in which the insulator used thin dielectric films of different oxides with a thickness from 10 nm to several microns, which is located Alla upper electrode. After fabrication of such a structure, it is placed in a vacuum and the operation is performed, called electrothermally and consisting in Palace to the electrodes voltage amplitude of about 15 C. as a result, the device becomes volt-ampere characteristics (VAC), similar to those shown in Fig. 4,b, and can therefore perform the function of the memory element. It is established that the possibility of electroforming depends on the composition and pressure of the residual atmosphere in the vacuum chamber, and the result is the formation in the structure of the molded channels similar to channels breakdown (see Gaponenko, C. M., " Izv. higher education institutions. Physics. 1992. N 5. S. 115-120) between the lower and upper electrodes, which are responsible for the occurrence of the unusual electrical properties. I.e. significant to obtain the necessary WAH is the penetration of the molecules of the residual atmosphere in the generated structure.The disadvantage of this device is the low reproducibility of the characteristics that are associated with poor controllability of the consequences of the operation electroforming.Elements described memory device in the form of a planar MIM structure, which is a two film metal electrode deposited on the dielectric pontania thin film of the metal wire, besieged between its thicker sections. The characteristic width occurs, resulting in this technology - in the order of micrometer. The surface of the dielectric substrate in this place is modified and contains metal particles remaining after evaporation of the material of tire, which is fundamental for further development WAH necessary forms. Speaking of metal as the material of the electrodes, mean only a high concentration of free carriers and low resistivity. In particular, can be used and the electrodes are made of graphite, which in the strict sense of the metal is not.The resulting structure is placed in vacuum, the residual atmosphere which contains organic molecules (typically molecules of oil from vacuum pumps). The planar design of the MIM structure, provides free access of organic molecules by an insulating gap. Next, the operation electroforming involving the adsorption of organic molecules on the surface of the slit, consisting in applying to the electrodes, as a rule, cyclically varying from 0 to 15 V voltage. Electroforming leads to the creation of an insulating gap between the electrodes wire the spine structure and the formation of ISLANDS, similar to the one shown in Fig. 4,b, including the effects of switching and memory. Steady-state I-V characteristics is N-shaped for both directions of change of voltage at low values which it corresponds to the enabled state (ON).The switching patterns in the OFF state is carried out by a sharp relief when it is located on the descending branch of the CVC. Reverse switching occurs when the voltage is increased to a certain threshold Uthlocated near 2, in which the structure abruptly enters the ON state. In the absence of stress, both conditions can be maintained indefinitely. All this allows such a structure, called MIM-diode with conductive carbon paths to perform the function of the memory element. He was selected as a prototype, coinciding with the invention of the most essential features. Obviously, the mechanism funkzionirovanija such a MIM diode (mardzvincau C. M., Levin, C. L.//journal of technical physics. 1994. So 64. Vol. 12. C. 88-011) is education in the insulating slit conductive carbon phase (PFM), and in the last - insulating gap of nanometer width, which varies in accordance with the magnitude of the voltage on the structure due to the process of the particles, activated by the heating of the substance in the gap due to dzhoulevo heat. A significant role is played by the modulation transparency of the potential barrier, which determines the current through the insulating gap. A specific voltage value corresponds to the equilibrium width of the insulating gap. If the structure is in a state that is described by a point on the descending branch of the CVC, and the voltage is abruptly turned off, due to the relative slowness of the process of formation of the AFPS equilibrium insulating gap with a large width is "frozen". This corresponds to the OFF state. Subsequent increase in voltage is absent until the threshold voltage Uthin which because of the increased transparency of the potential barrier with increasing voltage appears a small current and is "unfreezing" carbon structure. Rapidly restore the equilibrium gap of less width that corresponds to a lower voltage, and dramatically increases the current, which means the switching device from the OFF state to ON.The disadvantages of the described element of the memory device are narrow voltage range corresponding to the sustainability of an off state is supplied to the device capacity. This is due, in particular, with small values of the insulating gap in the UPF, which, according to the results of measurement using a scanning tunneling microscope, is less than 1 nm (H. Pagnia, N. Sotnik, Wirth W. // Int. J. Electron. 1990. Vol. 69. N 1. P. 25-32).The aim of the invention is to increase the voltage range of the stable existence of a power-off state of the MIM diode with active carbon environment. Another goal that can be achieved by the same means, is a decrease in the current through the device is in an enabled state.This objective is achieved in that in a well-known element of the memory device with the structure of metal-insulator-metal, comprising two metal electrodes separated vinyl slit, and conductive carbon phase in the slit, placed in a medium containing organic matter, so that access of the molecules of this substance to the crack, consistently conductive carbon phase in the insulating slits on the anode side is a dielectric layer, excluding the possibility of approximation carbon conductive phase to the surface of the anode at a distance less than the thickness of the dielectric layer, which is in the range of 1 - 100 nm.Malinow the width of the insulating gap (when PFM fills the insulating gap, until the dielectric layer, which corresponds to the enabled state of the device), which by its size, more usually rolling forming an insulating gap in PFM in the prototype (less than 1 nm), leads to the decrease of the currents in the device in the on state, because now their value is limited by the conductivity of the dielectric layer. The shape and dimensions of the dielectric layer, in particular its dimensions in the plane perpendicular to the direction of the anode - cathode should exclude the possibility of approximation of the AFPS to the surface of the anode at a distance less than the thickness of the dielectric layer, which occurs due to the growth of the AFPS in the direction of flow of the flow of electrons. If the lateral dimensions of the dielectric layer will be too low, PFM can simply "wrap" a dielectric layer which is closer to the anode. The transition to the off state occurs in the case that the voltage of the electrical breakdown of the dielectric layer (without irreversible changes in its structure). Thus the conductivity of the dielectric increases sharply, and all the voltage is applied to the AFPS, which leads to its partial "burnout" on the anode side and the establishment of equilibrium values of the insulating gap corresponding to this voltage. Increase Serenada it in the insulator state, that automatically adds to the equilibrium width of the gap equal to the thickness of the dielectric. This increased in comparison with the equilibrium width of the insulating gap and causes the increase of the threshold voltage Uthwhen switching patterns.In addition, to simplify the manufacturing technology of the memory element, the anode is made of aluminum.This is due to the fact that on the surface of aluminium in normal conditions spontaneously to form a continuous layer of natural oxide thickness of about 2 nm, which is a high quality dielectric. This eliminates the need to use special techniques for its formation.In the sources of information not found information similar to the proposed item of the memory device, which allows to make a conclusion about its novelty.In addition, the set of features of the proposed device is not obvious to a person skilled from the achieved level techniques for solving tasks, that confirms the device according to the criterion of "inventive step".In Fig. 1 schematically depicts an open sandwich-MIM-structure with an insulating gap nanomaterala slit; 3 is a top metal electrode; 4 - bottom metal electrode.In Fig. 2 schematically shows a memory element with a structure of metal-insulator-metal in the form of an open "sandwich"structure with a dielectric layer between the UPF and the anode (MIM diode with a layer of dielectric), where a is a view of the open end; b - profile structure; 1 - dielectric film anodic aluminum oxide; 2 - insulating gap; 3 - upper metal electrode (cathode); 4 - bottom metal electrode (anode); 5 - layer dielectric, excluding the approximation of the AFPS to the surface of the anode; 6 - carbon conductive phase (PFM).In Fig. 3 shows current-voltage characteristics of open-sandwich-MIM-structure, which reflects the process of its electroforming (the film thickness of oxide H = 24 nm; the perimeter of the open end 40 μm; the ballast resistance Rb= 5 Mω; non consecutive passes: 1 - 1st, 2 - 3, 3 - 5, 4 - after 10-th, 5 - VAC ballast resistance without patterns.In Fig. 4 shows current-voltage characteristics; (a) of the memory element with the structure of metal-insulator-metal in the form of an open "sandwich"structure with a dielectric layer between the UPF and the anode (MIM diode with a dielectric layer); the structure formed with the ballast >= 0; (b) traditional planar MIM diode with carbon conductive paths obtained by the burning of gold film thickness of 15 nm; tire width 20 μm; 1 - slow (quasi-static) scan voltage; 2 - quick disconnect voltage, 3 - slow increase of the voltage after a quick disconnect.The memory element with the structure of metal-insulator-metal dielectric layer between the UPF and the anode with the most controlled geometric and electric characteristics can be manufactured in the form of an open "sandwich"structure (Fig. 1, a) with nanometer thickness of the dielectric film 1. In this case, the insulating slit 2, an open access organic molecules, created by local etching the upper metal electrode 3 and the dielectric film 1 a conventional three-layer MIM structure. Slit width H by setting the thickness of the dielectric film, and its nanometer size determines the high field strength at normal stresses on the metal electrodes, which ensures the occurrence of the initial conductivity in the structure.As the substrate used was a silicon wafer covered with silicon oxide. Metal film polymerase one of the best insulators in thin film state, formed liquid anodizing lower aluminum electrode 4. This produces a high quality dielectric, which in itself defies electroforming in sandwich structures. In this case, it is a useful property, excluding moulding outside of the open end of the dielectric film, which was created by precision etching of the anodic oxide of aluminum. The thickness H ranged from 15 to 40 nm. In plan (Fig. 1,b) the fabricated structure was an overlapping of the metal wire (electrodes) 3 and 4, separated by a dielectric film 1 anodic oxide. The upper electrode was etched square window through which further etched oxide and which is several micrometers defended from edges of the bottom electrode in order to avoid possible edge effects. Window sizes ranged from 3 to 16 μm. After etching of the anodic oxide, even if it is removed completely, on the surface of the lower aluminum electrode exists, at least, the natural oxide of aluminum, the thickness of which is about 2 nm. In Fig. 2 b schematically shows, in particular, the structure of the formed insulating gap with regard to close to the real profile of the etching. Layer dialectometrical anode 4, thereby eliminating the possibility of approaching formed in the future when electroforming UPF 6 to the anode at a distance less than the thickness of the dielectric layer.Made so open sandwich-MIM-structures were placed in a vacuum chamber which was pumped sequentially mechanical and steam-pumps, thereby ensuring normal for electroforming gaseous atmosphere containing vapors of organic molecules. The electrodes were applied voltage of a triangular shape with an amplitude of 10-20 and In a period of about 10 s, and the current after pre-amplification was recorded by a recorder. Consistently MIM-structures included ballast resistor, preventing the development in it of catastrophic breakdown. In Fig. 3 shows typical curves describing the process electroforming (education UPF and transformation, thus, the MIM structure in MIM diodes) and characterizing the development of the current through the structure with an insulating gap width H of the order of 20 nm for several cycles of change (passes) of the voltage U on the metal electrodes when the ballast resistance Rb= 5 Mω.On the first pass, the current missing until U=9 V, at which it appears leap ("point of separation"), the Oia. After about 10 passes WAH goes on curve 4 and further changes near her weakly, if U does not exceed a certain value. In the event of a breach of the terms of a possible sharp (leap) decrease in current and subsequent gradual recovery to baseline values. This limit WACH depends on the value of the ballast resistance, the role of which is to automatically limit the growth of the voltage on the structure during the growth of current in the circuit. For comparison in Fig. 3 shows a straight line, corresponding to the inclusion of only one ballast resistance.It is seen that at high voltages the slope of the marginal curve 4 is almost the same as the slope of the straight. This means that in this area, despite the increase in U, the voltage on the structure changes slightly. If Rb= 0 or value is too small, gradual increase in the current ends catastrophic breakdown.In Fig. 4,and shows a typical I-V characteristics of the obtained element of the memory device (MIM diode with a dielectric layer) that when Rb= 5 MW injected into the marginal curve 4 (Fig. 3) and then the ballast resistor is disabled. The period of the sweep voltage is kept the same. For comparison in Fig. 4,b and bring their ways, received by the burning of the conductive bus width, having the same order as the perimeter of the open end of the "sandwich"-MIM-structure (40 μm). The similar shape of the curves indicating the proximity of the processes occurring in both cases. At the same time, there are notable differences I-V characteristics in Fig. 4,a and 4,b. First, the magnitude of the current in case of a MIM diode with a layer of dielectric by 3 - 4 orders of magnitude less than at almost the same perimeter. Secondly, being "off" when U increase to values corresponding to the complete shut-off (minimum VAH), open the "sandwich"structure is usually not "included" in this voltage range at any number of passages, remaining on the branches OFF as in the case of direct and reverse changes U.To go to the branch ON need, by connecting a ballast resistor to a voltage several volts higher amplitude sweep at shutdown. In this case, developing an accelerated process of forming unlike the original slower (Fig. 3). Traditional MIME-diode (Fig. 4,b) transition to an on state during reverse U, showing, however, a significant hysteresis. In addition, being disabled by a voltage pulse with a short back-to-back, when the placenta. the case of a MIM diode with a layer of dielectric such effect, as noted above, is not observed, i.e., the threshold voltage Uthmuch more and greater than the amplitude of the sweep when the disable structure.Less current in the MIM-diode with a layer of dielectric is partially related to the fact that formed a relatively small part of its perimeter. However, if these molded parts have been completely similar to traditional MIME-diode, the N-shaped I-V characteristics, though with smaller currents, would be observed and reverse the course of the voltage. The lack of growth with reduction of U means that the AFPS in the insulating gap does not have time to recover, because not just small currents, and current density on moulded parts, which are limited to some additional factor which is missing in the traditional MIME-diode.All observed features of the MIM diode with a dielectric layer associated with the presence dielectric layer 5 in the form of residual oxide included consistently with the scope of the AFPS 6 (Fig. 2). Then the current really should be limited by the conductivity of the residual oxide, because of its thickness (not less than 2 nm) is considerably greater than the width of the insulating gap traditional MIM diode included in the dielectric operates as follows. When reaching the "separation point" (Fig. 3), taking into account the imperfection of the surfaces of the partition starts autoemission with some random nanostray on the cathode surface 3 (Fig. 2,a). The electrodes are injected to the organic dielectric, causing the dissociation of molecules and the formation of particles UPF 6. Because refocusing action of the electric field near nanostray and scattering of electrons, the current density as the distance from the cathode decreases, and because it is limited by the conductivity of the residual oxide, temperature, caused dzhoulevo heating, do not reach the values required for the disappearance of the particles of the AFPS ("burning"). Therefore, the formation of a coherent conductive carbon cluster particles (i.e., a solid plot conductive carbon phase) begins, in contrast to conventional MIM diode from cathode (due to the higher current density in this area).Thus, UPF born near the cathode and as moulding extends toward the anode, increasing the conductivity of the insulating slits, resulting in a gradual increase in the current. If the electric circuit is appropriately selected ballast resistor, automatically limiting appraisal 5. This state corresponds to the limiting curve 4 in Fig.3.Provided that the resistance of the AFPS is small (and this is true, because it is similar to the composition of the graphite), the initial branch of the curve ON Fig. 4,and is just WACH residual oxide on which falls the applied voltage. Taking into account the actual thickness and high quality, it can be expected that most of the conductivity mechanism is tunneling, which qualitatively explains the nature of the nonlinearity of the curve in this area. Further, with increasing U in the residual oxide is achieved field strength causing impact ionization and generation of the avalanche (electrical breakdown). The resistance of the dielectric layer decreases sharply, and the current through the structure increases, "without burning through" certain parts of the AFPS, as observed on the descending branch of the CVC. Dielectric breakdown does not cause it irreversible changes, because before "fade" UPF primarily due to the worst thermal contact her with the substrate. This dramatically reduces the field strength in the residual oxide due to the redistribution of the potential, and the tide goes out.The recorder does not have time to respond to these short current pulses, reflecting only what its steady-state I-V characteristics. With the presence of the dielectric layer is connected and the lack of inclusion patterns in the whole range of U, the smaller, which was cut off. In the event of an avalanche in the residual oxide almost all the voltage is applied to the UPF, due to partial "burning out" the last set of equilibrium width of the insulating gap (the gap between the UPF and the dielectric layer in a state with a high conductivity) corresponding to this value of u After the completion of the process of restoration of the initial resistance of the residual oxide) total width of the insulating gap is larger than the magnitude of the thickness of the residual oxide. Therefore for the emergence of current needed to "on" structure (re-forming), requiring a certain field strength in the gap, it is necessary to apply a voltage Uthsignificantly large when outages occurred.Of the described mechanism element of the memory device (MIM diode with a dielectric layer) can be obtained and the maximum thickness of the dielectric layer included in series with UPF: the main condition is that the electric breakdown has taken place at not too high naprjazhennejshie U = 10 Century For typical values of field strength E of the electric breakdown in which the dielectric is still good enough, about 106V/cm, we obtain the estimate of the maximum thickness of the dielectric layer h=U/E=100 nm. This value is included in the claims as the upper boundary of the range. This implies that the dielectric layer exists conductivity, allowing electroforming patterns.Thus, information in sufficient detail to explain constructive and technological features of the proposed element of the memory device, describe the principles of its action and confirm the possibility of its implementation. 1. Element of the memory device with the structure of metal-insulator-metal, comprising two metal electrodes separated vinyl slit, and conductive carbon phase in the slit, placed in a medium containing organic matter, so that access of the molecules of this substance to the slit, characterized in that in series with conductive carbon phase in the insulating slits on the anode side is a dielectric layer, excluding the possibility of approximation of conductive carbon phase LASS="ptx2">2. Item under item 1, characterized in that the anode is made of aluminum.
FIELD: computer science.
SUBSTANCE: memory cell, containing three-layer structure, including two electrodes, between which a functional zone is located, as electrodes metal and/or semiconductor and/or conducting polymer and/or conducting and optically transparent oxide or sulfide are used, and functional zone is made of organic, metal-organic and non-organic materials with different types of active elements built in molecular and/or crystalline structure, and also their combinations with each other and/or clusters on their basis, which change their condition or position under effect from outside electrical field and/or light radiation.
EFFECT: higher efficiency, broader functional capabilities, higher manufacturability.
25 cl, 24 dwg