JP2014022660A - Variable resistance element, and nonvolatile semiconductor memory device provided with variable resistance element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a variable resistance element which can be driven at a low voltage and a low current, and is suitable for a highly integrated nonvolatile memory.SOLUTION: A variable resistance element 2 is formed of a metal oxide film 13 sandwiched between a first electrode 15 and a second electrode 12, and is formed by arranging oxygen pulling out substances 14 in the first electrode 15, which can pull out oxygen from the metal oxide film 13. The oxygen pulling out substances are in contact with the metal oxide film 13 in a part of a boundary face of the metal oxide film 13 and the first electrode 15. Oxide generation free energy of the oxygen pulling out substance 14 is lower than that of the first electrode 15, and accordingly, regions 16 having high oxygen deficient concentration are locally formed in the metal oxide film 13. Thereby, leak current at the forming can be maintained to be low while a forming voltage is reduced. As a result, the variable resistance element can be driven at a low voltage and a low current.

Description

  The present invention relates to a non-volatile variable resistance element configured by sandwiching a first electrode, a second electrode, and a layer made of a metal oxide as a variable resistor between both electrodes, and the variable resistance element. The present invention relates to a non-volatile semiconductor memory device used for storing data.

  In recent years, various devices such as FeRAM (Ferroelectric RAM), MRAM (Magnetic RAM), PRAM (Phase Change RAM), etc. as next-generation non-volatile random access memory (NVRAM) capable of high-speed operation instead of flash memory. A structure has been proposed, and intense development competition has been conducted from the viewpoint of high performance, high reliability, low cost, and process consistency.

  For these existing technologies, a resistive non-volatile memory RRAM (Resistive Random Access Memory) (registered trademark) using a variable resistive element whose electric resistance reversibly changes by applying a voltage pulse has been proposed. This configuration is shown in FIG.

  As shown in FIG. 7, the variable resistance element of the conventional configuration has a structure in which a lower electrode 103, a variable resistor 102, and an upper electrode 101 are sequentially stacked, and a voltage is applied between the upper electrode 101 and the lower electrode 103. By applying a pulse, the resistance value can be reversibly changed. A novel nonvolatile semiconductor memory device can be realized by reading a resistance value that changes by this reversible resistance change operation (hereinafter referred to as “switching operation”).

  In this nonvolatile semiconductor memory device, a plurality of memory cells including variable resistance elements are arranged in a matrix in the row direction and the column direction to form a memory cell array, and data is written to each memory cell in the memory cell array. Peripheral circuits for controlling erase and read operations are arranged. As this memory cell, one memory cell is composed of one select transistor T and one variable resistance element R (referred to as “1T1R type”) because of the difference in the components. There is a memory cell or the like composed of only one variable resistance element R (referred to as “1R type”). Among these, FIG. 8 shows a configuration example of a 1T1R type memory cell.

  FIG. 8 is an equivalent circuit diagram showing a configuration example of a memory cell array including 1T1R type memory cells. The gate of the selection transistor T of each memory cell is connected to the word lines (WL1 to WLn), and the source of the selection transistor T of each memory cell is connected to the source lines (SL1 to SLn) (n is a natural number). . One electrode of the variable resistance element R for each memory cell is connected to the drain of the selection transistor T, and the other electrode of the variable resistance element R is connected to the bit lines (BL1 to BLm) (m Is a natural number). The word lines WL1 to WLn are connected to the word line decoder 106, the source lines SL1 to SLn are connected to the source line decoder 107, and the bit lines BL1 to BLm are connected to the bit line decoder 105, respectively. Yes. A specific bit line, word line, and source line for write, erase, and read operations to a specific memory cell in the memory cell array 104 are selected according to an address input (not shown).

  As described above, the selection transistor T and the variable resistance element R are arranged in series, so that the transistor of the memory cell selected by the change in the potential of the word line is turned on, and the memory selected by the change in the potential of the bit line. The cell can be selectively written or erased only to the variable resistance element R of the cell.

  FIG. 9 is an equivalent circuit diagram illustrating a configuration example of a 1R type memory cell. Each memory cell includes only the variable resistance element R, and one electrode of the variable resistance element R is connected to the word lines (WL1 to WLn) and the other electrode is connected to the bit lines (BL1 to BLm). The word lines WL1 to WLn are connected to the word line decoder 106, and the bit lines BL1 to BLm are connected to the bit line decoder 105, respectively. A specific bit line and word line for writing, erasing and reading operations to a specific memory cell in the memory cell array 108 are selected according to an address input (not shown).

In the above variable resistance element R, as a variable resistance material used as a variable resistor, by applying a voltage pulse to a perovskite material known for a super-giant magnetoresistance effect by, for example, Shangquing Liu of the University of Houston of USA or Alex Ignatiev Methods for reversibly changing the electrical resistance are disclosed in Patent Document 1 and Non-Patent Document 1 below. Although this method uses a perovskite material known for its giant magnetoresistance effect, a resistance change of several orders of magnitude appears even at room temperature without applying a magnetic field. In the element structure exemplified in Patent Document 1, a praseodymium / calcium / manganese oxide Pr _1-x Ca _x MnO ₃ (PCMO) film, which is a perovskite oxide, is used as a variable resistor material.

Other variable resistor materials include oxides of transition metal elements such as titanium oxide (TiO ₂ ) films, nickel oxide (NiO) films, zinc oxide (ZnO) films, and niobium oxide (Nb ₂ O ₅ ) films. It is known from Non-Patent Document 2 and Non-Patent Document 3 that it exhibits reversible resistance change.

US Pat. No. 6,204,139

Liu, S .; Q. In addition, “Electrical-pulse-induced reversible resistance change effect in magnetosensitive films”, Applied Physics Letter, Vol. 76, pp. 2749-2751, 2000 H. Pagna, et al., “Bistable Switching in Electroformed Metal-Insulator-Metal Devices”, Phys. Stat. Sol. (A), vol. 108, pp. 11-65, 1988 Baek, I. et al. G. In addition, “Highly Scalable Non-volatile Resistive Memory Using Simple Binary Oxide Driven Asymmetric Universal Voltage Pulses”, IEDM 04, p. 587-590, 2004

  In such a variable resistance element using a transition metal oxide as a variable resistor, it is necessary to perform a soft breakdown process called so-called forming in order to make resistance switching possible. As a result of such soft breakdown, a conductive path (hereinafter referred to as “filament” as appropriate) is generated due to oxygen defects formed in a filament shape in the metal oxide, and it is said that a resistance change occurs due to opening and closing of the filament. ing. The voltage (forming voltage) required for this soft breakdown is higher than the write voltage for information recording.

  On the other hand, in order to realize a highly integrated nonvolatile memory, it is necessary to drive the variable resistance element using a fine transistor, so it is necessary to reduce the forming voltage.

  Here, it is known that the forming voltage is substantially proportional to the film thickness of the metal oxide used as the variable resistor. The simplest method for reducing the forming voltage is as shown in Non-Patent Document 3. It is to reduce the thickness of the metal oxide.

  However, as the metal oxide film becomes thinner, the leakage current during forming (current during dielectric breakdown) increases. As a result, the current required for forming becomes large.

  Incidentally, it is known that the current required for rewriting the variable resistance element has a positive correlation with the amount of current during forming. That is, if the amount of current during forming is large, the current required for rewriting the variable resistance element also increases. This is because the larger the current during forming, the thicker the filament path generated and the greater the variation. On the contrary, the current required for opening / closing the filament path that causes resistance switching, that is, the current required for rewriting can be reduced as the current flowing during forming is limited and the thickness of the filament path is reduced. .

  Therefore, simply reducing the film thickness of the metal oxide film to reduce the forming voltage increases the amount of current during forming and increases the current required for rewriting the variable resistance element. It becomes difficult to drive the variable resistance element using the transistor.

  SUMMARY OF THE INVENTION In view of the above-described problems in the prior art, the present invention provides a variable resistance element having a configuration capable of forming at low voltage and low current by reducing leakage current during forming while reducing forming voltage. Is the purpose.

  It is another object of the present invention to provide a highly integrated nonvolatile semiconductor memory device that includes such a variable resistance element and is easy to manufacture.

In order to achieve the above object, a variable resistance element according to the present invention has an n-type metal oxide film sandwiched between a first electrode and a second electrode, and responds to application of electrical stress between the electrodes. A variable resistance element in which the electrical resistance between the electrodes changes reversibly,
The variable resistance element is:
By performing the forming process, the resistance state between the electrodes changes from the initial high resistance state before the forming process to the variable resistance state, and the electrical stress is applied between the electrodes in the variable resistance state. Thus, the resistance state defined by the electrical resistance between the two electrodes transitions between two or more different states, and one resistance state after the transition is used for storing information,
In the variable resistance state, when a positive voltage is applied to the first electrode with reference to the second electrode, a transition is made to a lower resistance state,
An oxygen extracting material capable of extracting oxygen from the metal oxide film is dispersed and arranged in islands or particles at least at the interface with the metal oxide film in the first electrode,
The oxide formation free energy of at least one element excluding oxygen constituting the oxygen abstraction material is lower than the oxide formation free energy of the element constituting the first electrode excluding the oxygen abstraction material,
The oxygen-extracting substance is in contact with the metal oxide film at a part of the interface between the metal oxide film and the first electrode.

  In the variable resistance element according to the present invention having the above characteristics, the oxygen-extracting substance is further dispersed in the first electrode in the form of particles, and the average particle diameter of the oxygen-extracting substance is 50 nm or less. preferable.

  In the variable resistance element according to the present invention having the above characteristics, the metal oxide film is further composed of an oxide of any element of Hf, Zr, Ti, Ta, V, Nb, and W, or strontium titanate. It is preferable.

  In the variable resistance element according to the present invention having the above characteristics, it is preferable that the oxygen extracting material further includes any element of Ti, V, Al, Hf, and Zr.

  In the variable resistance element according to the present invention having the above characteristics, the work function of the second electrode is preferably 4.5 eV or more.

  In order to achieve the above object, a non-volatile semiconductor memory device according to the present invention comprises a memory cell array in which a plurality of variable resistance elements according to the present invention having the above characteristics are arranged in at least the column direction in the row or column direction. And

  According to the present invention, in a variable resistance element in which a metal oxide film (variable resistor) is sandwiched between a first electrode and a second electrode, an oxygen extracting material having a low free energy for oxide formation is disposed in the first electrode. The oxygen-extracting substance is in contact with the metal oxide film at a part of the interface between the metal oxide film and the first electrode. As a result, oxygen is extracted from the metal oxide film into the oxygen-extracting substance, and a region having a high oxygen deficiency concentration is locally formed in the metal oxide film, thereby reducing leakage current during forming while reducing the forming voltage. Can be kept low.

  As a result, forming can be performed without increasing the current required for forming while lowering the forming voltage, and a variable resistance element that can be driven with low voltage and low current can be realized. As a result, the variable resistance element can be easily driven using a fine transistor with a low breakdown voltage, and a highly integrated nonvolatile semiconductor memory device including such a variable resistance element can be easily realized.

Sectional schematic diagram showing an example of the structure of the variable resistance element of the present invention Table showing metal oxide free energy and work function values The figure which shows the change of the electric current amount which flows into a variable resistance element with respect to the voltage applied to the variable resistance element at the time of forming voltage measurement The figure which shows oxygen concentration distribution of the boundary vicinity of the 1st electrode and metal oxide film (resistance change layer) after heat processing in the conventional variable resistance element which uses Ta or Ti as the 1st electrode. 1 is a circuit block diagram showing a schematic configuration of a nonvolatile semiconductor memory device according to the present invention. Sectional drawing which shows the schematic structure of a memory cell array provided with the variable resistance element of this invention Schematic diagram showing the element structure of a conventional variable resistance element Equivalent circuit diagram showing one configuration example of 1T1R type memory cell Equivalent circuit diagram showing one configuration example of 1R type memory cell Diagram showing the size of particulate or island-like oxygen scavenging substances The figure which shows the calculation method of the average particle diameter of the particulate or island-like oxygen drawing substance

<First Embodiment>
FIG. 1 is a cross-sectional view schematically showing an element structure of a variable resistance element 2 used in a nonvolatile semiconductor memory device according to an embodiment of the present invention (hereinafter, referred to as “present apparatus 1” as appropriate). In the drawings shown below, for the convenience of explanation, the main part is shown with emphasis, and the dimensional ratio of each part of the element may not always match the actual dimensional ratio.

In the present embodiment, hafnium oxide (HfO _X ), which is an insulating layer having a large band gap, is selected and used as the variable resistance layer (variable resistor). However, the present invention is not limited to this configuration. Zirconium oxide (ZrO _X ), titanium oxide (TiO _X ), tantalum oxide (TaO _X ), vanadium oxide (VO _X ), niobium oxide (NbO _X ), tungsten oxide (WO _X ), or titanic acid as the resistance change layer Strontium (SrTiO _x ) or the like may be used. These are all n-type metal oxides.

  When these transition metal oxides are used as the resistance change layer, the initial resistance immediately after the manufacture of the variable resistance element is very high, so that a high resistance state and a low resistance state can be switched by an electrical stress. Before use, a voltage pulse having a voltage amplitude larger than that of a voltage pulse used for a normal rewrite operation and a longer pulse width is applied to a variable resistance element in an initial state immediately after manufacturing to form a current path in which resistance switching occurs. It is necessary to perform so-called forming processing. It is known that the current path (called a filament) formed by this forming process determines the electrical characteristics of the subsequent device.

  In the variable resistance element 2, a second electrode 12, a metal oxide film 13 that is a resistance change layer, and a first electrode 15 are deposited and patterned in this order on an insulating film 11 formed on a substrate 10. Is formed. Here, in the variable resistance element 2, a Schottky interface is formed on the interface side between the second electrode 12 and the metal oxide film 13, and the electronic state in the vicinity of the interface changes reversibly by application of electrical stress. As a result, the resistance is changed.

  Further, an oxygen extracting material 14 is disposed in the first electrode 15. The oxygen extracting material 14 is in contact with the metal oxide film 13 at a part of the interface between the metal oxide film 13 and the first electrode 15.

  The oxygen extracting material 14 has the ability to extract oxygen from the metal oxide film 13 and has a work function smaller than that of the second electrode 12 so that resistance switching occurs stably on the interface side of the second electrode 12. Composed of materials. More specifically, the work function of the second electrode 12 is 4.5 eV or more, and the work function of the oxygen extracting material 14 is less than the work function of the second electrode 12, preferably 4.5 eV or less. The materials of the second electrode 12 and the oxygen extracting substance 14 are selected. Since the oxygen extracting material 14 is in contact with the metal oxide film 13, the oxygen in the metal oxide film 13 moves to the oxygen extracting material 14 side during the heat treatment process and the forming voltage application, so that the filament Facilitates the formation of

  On the other hand, the first electrode 15 is made of a material that is less likely to extract oxygen than the oxygen extracting material 14. In other words, the first electrode 15 is selected from materials whose oxide generation free energy is higher than the oxide generation free energy of at least one element excluding oxygen constituting the oxygen extracting material 14. Furthermore, the oxide formation free energy of the first electrode 15 is more preferably 100 kJ or more per mole of oxygen molecule than the oxide formation free energy of at least one element excluding oxygen constituting the oxygen extracting material 14. Thereby, since the oxygen extracting substance 14 is in contact with the metal oxide film 13 at a part of the interface between the metal oxide film 13 and the first electrode 15, the oxygen extracting substance 14 and the metal oxide film 13 A portion having a high oxygen vacancy concentration (region 16 in FIG. 1) in the contact portion on the metal oxide film 13 side is locally formed in the metal oxide film 13.

  The first electrode 15 is also preferably made of a material having a work function smaller than that of the second electrode 12 so that resistance switching occurs stably on the interface side of the second electrode 12, similarly to the oxygen extracting material 14. More preferably, the material of the first electrode 15 may be selected so that the work function of the first electrode 15 is 4.5 eV or less.

  Here, as an example of a conductive material that can be used as the oxygen extracting substance 14 and easily extract oxygen, Ti (4.3 eV), V (4.3 eV), Al (4.2 eV), Hf (3.9 eV). ) And Zr (4.1 eV). The work function value of each metal is shown in parentheses. Such a conductive material is formed in the form of nanoparticles and dispersed in the first electrode, or formed on the metal oxide film 13 in the form of nano-sized islands. The variable resistance element 2 in which the oxygen extracting material 14 is in contact with the metal oxide film 13 at a part of the interface with the first electrode 15 can be formed. The average particle diameter of the nanoparticulate oxygen extracting material 14 or the average size of the nanosized island oxygen extracting material is preferably about the same as the filament diameter. The filament diameter is considered to be about 50 nm or less, although it depends on the forming conditions and the material of the metal oxide film 13. Accordingly, the average particle diameter or average size is preferably 50 nm or less, and more preferably 5 to 10 nm.

  Examples of materials that can be used as the second electrode 12 include titanium nitride (TiN: 4.7 eV) or titanium oxynitride, a material having a relatively large work function and often used in an LSI manufacturing process. Tantalum (TaNx: 4.05 to 5.4 eV depending on the stoichiometric composition x of nitrogen), tantalum oxynitride, aluminum aluminum nitride, W (4.5 eV), Ni (5.2 eV), etc. Is available. The work function value of each metal is shown in parentheses.

As a material that can be used as the first electrode 15, oxygen at 427 ° C. (700 K in consideration of the thermal history of the manufacturing process) of oxides of metals such as Ta, Ti, V, Al, W, Nb, Hf, and Zr. The value of oxide formation free energy [kJ / mol] per mole of molecule and the work function value of each metal are shown in FIG. As shown in FIG. 2, the oxide formation free energy is low in the order of Hf, Al, Zr, Ti, Ta, Nb, V, and W. For example, when TiO _X is used as the oxygen extracting substance 14, Ta, Nb, V, and W can be used as the first electrode material, respectively.

  The variable resistance element 2 thus configured transitions to a lower resistance state when a positive voltage is applied to the first electrode 15 with respect to the second electrode 12 in the variable resistance state after the forming process. When a positive voltage is applied to the second electrode 12 with the first electrode 15 as a reference, a transition is made to a higher resistance state. That is, the variable resistance element 2 exhibits a bipolar switching characteristic in which the polarity of the voltage pulse necessary for rewriting is reversed between an increase in resistance and a decrease in resistance.

  A method for manufacturing the variable resistance element 2 will be described below. First, a 200 nm thick silicon oxide film is formed as the insulating film 11 on the single crystal silicon substrate 10 by a thermal oxidation method. Thereafter, a titanium nitride film having a thickness of, for example, 100 nm is formed on the silicon oxide film 11 as a material of the second electrode 12 by a sputtering method.

  Thereafter, a hafnium oxide film having a thickness of 3 to 5 nm (here, 5 nm) is formed on the titanium nitride film 12 by sputtering or ALD (Atomic Layer Deposition) as a material of the metal oxide film 13, for example. Further, titanium is deposited as the oxygen extracting substance 14 in a particle shape or an island shape. Here, in order to deposit the oxygen extracting substance in the form of particles or islands, generally known methods such as sputtering, nanoparticle deposition using thermal plasma, and immersion in a nanoparticle solution can be used.

  For example, in the deposition by sputtering, ion irradiation from the plasma to the substrate surface is sufficiently performed so that an element from the target migrates on the substrate and easily grows in an island shape. The irradiation energy of ions to the substrate surface is about 10 to 50 eV, and the ratio of the number of ions per unit time unit area to the substrate surface to the number of irradiation per unit time unit area of atoms flying from the target to the substrate surface is 10 The above is preferable. Moreover, you may use together the board | substrate heating of about 300 degreeC or more. The nanoparticle diameter can be controlled by plasma excitation power, ion irradiation energy to the substrate, substrate heating temperature, target-substrate distance, and the like.

  Nanoparticle deposition by thermal plasma is a deposition method in which raw material (metal powder or a solution in which metal powder is dispersed) is injected into thermal plasma generated by applying high-frequency power to a plasma source gas close to atmospheric pressure. is there. The metal injected into the thermal plasma evaporates and is cooled while flying to the substrate to become nanoparticles. The nanoparticle diameter can be controlled by the high-frequency power and the distance between the evaporated metal source and the substrate.

  In addition, a Langmuir-Blodgett (LB) film is used for deposition by immersion in a nanoparticle solution. When a substrate having a single layer of LB film formed on the metal oxide film 13 is immersed in a solution in which nanoparticles subjected to surface treatment are dispersed, the nanoparticles are deposited on the substrate surface. As described above, the average particle size of the particulate or island-like oxygen extracting material 14 is preferably 50 nm or less, and more preferably 5 to 10 nm. The solution in which the nanoparticles are dispersed is available in various particle size ranges, and is preferably 50 nm or less, more preferably 5 to 10 nm as described above.

The size of the oxygen scavenging substance 14 in the form of particles or islands can be measured by cross-sectional observation. As shown in FIG. 10, various cross-sectional shapes of the oxygen extracting material 14 are assumed. As shown by the arrows in FIG. 10, the size of each particle is φi, and the average particle diameter φm is φm = Σ _i fiφi / it may be calculated by the sigma _i fi (Figure 11). The average particle diameter φm is preferably 50 nm or less, more preferably 5 to 10 nm.

  Thereafter, a tantalum thin film having a thickness of, for example, 150 nm is formed on the oxygen extracting substance 14 as a material of the first electrode 15 by a sputtering method. Finally, a pattern by a photoresist process is formed, and an element region of, for example, 0.4 μm × 0.4 μm is formed by dry etching as shown in FIG. Thereby, the variable resistance element 2 is produced. Thereafter, heat treatment is performed, and interlayer insulation film formation, wiring, and the like are performed as necessary.

  Thereafter, a forming voltage is applied between the first electrode and the second electrode to form the variable resistance element 2 in a variable resistance state in which the resistance can be changed.

  Hereinafter, it will be described that the above configuration is effective for solving the problem. FIG. 3 is a diagram showing IV characteristics of a variable resistance element 3 (3a, 3b) having a conventional configuration manufactured by a process excluding the deposition of the oxygen extracting material 14 in the manufacture of the variable resistance element 2 described above. A change in the amount of current flowing through the variable resistance element with respect to the voltage applied to the variable resistance element during forming voltage measurement is shown. In the figure, the voltage at which the current sharply increases is the measured value of the forming voltage. Further, in FIG. 3, the IV characteristics of the element 3a using Ta as the first electrode 15 and the element 3b including only the Ti used for the first electrode 15 as an oxygen extracting material in this embodiment are compared. Yes. In the experiment, a semiconductor parameter analyzer (Agilent Technology 4156C) was used to measure the voltage at which the amount of current exceeded a predetermined value while increasing the applied voltage from 0 V to 5 V in 10 mV steps.

The element 3a using 5 nm thick HfO _X as the metal oxide film 13 and 100 nm Ta as the first electrode 15 and the same 5 nm thick HfO _X as the metal oxide film 13 are used as the first electrode 15. As compared with the element 3b using 100 nm Ti instead of Ta, the forming voltage can be lowered by using the Ti electrode rather than using the Ta electrode. This is because Ti has a lower free energy for oxide formation than Ta and oxygen can be easily extracted from the metal oxide film 13.

  FIG. 4 shows the SIMS (Secondary-Ion Mass Spectroscopy: Secondary Ion Mass Spectroscopy) analysis of the oxygen concentration distribution in the vicinity of the boundary between the first electrode 15 and the metal oxide film 13 layer of the element 3a and element 3b after heat treatment at 350 ° C. ). As can be seen from FIG. 4, the element 3b using the Ti electrode (FIG. 4 right) has a larger oxygen diffusion to the electrode side than the element 3a using the Ta electrode (FIG. 4 left).

  Therefore, after using a Ta electrode as the first electrode 15, Ti and a metal oxide film are disposed in the first electrode 15 as the oxygen extracting substance 14 with Ti having a lower free energy of oxide generation than Ta. A region 16 having a high oxygen vacancy concentration is formed on the side of the metal oxide film 13 at the interface with which 13 is in contact, and the withstand voltage decreases, so that the forming voltage can be reduced.

  However, when the oxygen extracting material 14 is in contact with the entire surface of the metal oxide film 13, oxygen vacancies are introduced over the entire surface of the metal oxide film 13, so that the leakage current at the time of forming becomes too large (initial stage). There is a concern that the resistance value of the state becomes too low). As a result, there arises another problem that the current required for forming becomes large and that the resistance value in the high resistance state cannot be increased.

  In principle, the resistance value in the high resistance state cannot be higher than the resistance value in the initial state. For this reason, if an attempt is made to achieve a certain resistance change ratio when the resistance value in the initial state is not sufficiently high, the resistance value in the low resistance state has to be lowered. However, as a result, the write current for making a transition from the low resistance state to the high resistance state becomes large.

  However, in the present invention, the oxygen extracting substance 14 is not in contact with the entire surface of the interface with the metal oxide film 13 but in contact with part of the interface between the first electrode 15 and the metal oxide film 13. . With such a configuration, the effect of extracting oxygen toward the first electrode 15 is small at the interface between the first electrode 15 and the metal oxide film 13 that is not in contact with the oxygen extracting material 14, so that the leakage current increases. The forming voltage can be reduced while suppressing the above. Preferably, if the oxygen extracting material 14 is in contact with the metal oxide film 13 and the area of the interface where the region 16 having a high oxygen vacancy concentration is formed is sufficiently smaller than the first electrode area (preferably 1 / 10 or less), the voltage required for forming can be reduced and the leakage current can be kept low.

  As described above, since the variable resistance element 2 can form a region having a low withstand voltage locally by the oxygen extracting material 14 extracting oxygen from the metal oxide film 13, the leakage current can be reduced while reducing the forming voltage. Can be kept low. As a result, it is possible to realize a variable resistance element that can be driven with a low voltage and a low current and is suitable for a highly integrated nonvolatile memory.

Second Embodiment
An example of the device 1 of the present invention including the above-described variable resistance element 2 is shown in FIG. FIG. 5 is a circuit block diagram showing a schematic configuration of the device 1 of the present invention. The device 1 of the present invention includes a memory cell array 21, a control circuit 22, a voltage generation circuit 23, a word line decoder 24, and a bit line decoder 25, respectively. It is equipped with.

  The memory cell array 21 includes a plurality of memory cells including the variable resistance elements 2 arranged in a matrix in the row and column directions, and memory cells belonging to the same column are connected by bit lines extending in the column direction, and extend in the row direction. For example, the memory cell array shown in the equivalent circuit diagram of FIG. 8 or FIG. 9 in which memory cells belonging to the same row are connected to each other by a word line, a selected word line voltage and an unselected word line voltage via the word line Any one of the selected bit line voltage and the non-selected bit line voltage is applied to each via the bit line, so that the external operation is performed in each of the write, erase, read, and forming processes. It is possible to select one or a plurality of memory cells to be operated designated by address input from.

  The memory cell array 21 may be a 1R structure memory cell array (see FIG. 9) in which the unit memory cell does not include a current limiting element, or a 1D1R structure memory cell array in which the unit memory cell includes a diode as a current limiting element, or a unit memory cell. 1T1R memory cell array (see FIG. 8) including a transistor as a current limiting element. In a memory cell array having a 1D1R structure, one end of a diode and one electrode of a variable resistance element are connected in series to form a memory cell, and either one of the other end of the diode and the other electrode of the variable resistance element is Are connected to either the bit line or the word line. In a memory cell array having a 1T1R structure, either one of a source or drain of a transistor and one electrode of a variable resistance element are connected in series to form a memory cell, and the other of the source or drain of a transistor not connected to the variable resistance element One of the other electrodes of the non-volatile variable resistance element not connected to the transistor is connected to a bit line extending in the column direction, and the other is connected to a common source line for supplying a ground voltage. The gate terminals of the transistors are connected to a word line extending in the row direction.

  The control circuit 22 controls each memory operation of writing (setting), erasing (resetting) and reading of the memory cell array 21, and controls forming processing. Specifically, the control circuit 22 uses the word line decoder 24 and the bit line decoder 25 based on the address signal input from the address line, the data input input from the data line, and the control input signal input from the control signal line. To control each memory operation and forming process of the memory cell. In the example shown in FIG. 5, the control circuit 22 has functions as a general address buffer circuit, data input / output buffer circuit, and control input buffer circuit (not shown).

  The voltage generation circuit 23 is configured to select a selected word line voltage and non-voltage necessary for selecting a memory cell to be operated in each memory operation of writing (set), erasing (reset), and reading, and a memory cell forming process. A selected word line voltage is generated and supplied to the word line decoder 24, and a selected bit line voltage and a non-selected bit line voltage are generated and supplied to the bit line decoder 25.

  When a memory cell to be operated is input to an address line and specified in each of memory operations for writing (set), erasing (reset), and reading, and a memory cell forming process, the word line decoder 24 receives the address A word line corresponding to an address signal input to the line is selected, and a selected word line voltage and a non-selected word line voltage are respectively applied to the selected word line and the non-selected word line.

  When the memory cell to be operated is input to the address line and specified in each of the write (set), erase (reset), and read memory operations and the memory cell forming process, the bit line decoder 25 receives the address. A bit line corresponding to the address signal input to the line is selected, and a selected bit line voltage and a non-selected bit line voltage are respectively applied to the selected bit line and the non-selected bit line.

  The detailed circuit configuration, device structure, and manufacturing method of the control circuit 22, the voltage generation circuit 23, the word line decoder 24, and the bit line decoder 25 can be realized using a known circuit configuration. Since it can be manufactured using a semiconductor manufacturing technique, the description is omitted.

  FIG. 6 shows a structural cross-sectional view of an example of the memory cell array 21 including the variable resistance element 2 of the present invention. The memory cell array 21a shown in FIG. 6 is a memory cell array having a 1T1R structure, and the first electrode 15 formed in an island shape has a bit line BL extending on the interlayer insulating film 33 in the column direction (lateral direction in FIG. 6). It is connected to the. A contact plug that connects the transistor T formed in the lower layer through the island-shaped metal wiring 31 and the contact plug 32 serves as the second electrode 12 in contact with the metal oxide film 13. And in the contact part (element formation area) of the 2nd electrode 12 with the metal oxide film 13, the variable resistance element which consists of the 2nd electrode 12, the metal oxide film 13, the oxygen extraction substance 14, and the 1st electrode 15 2 is formed.

  In the above embodiment, in the memory cell array having the 1T1R structure, the source line is common to all the memory cells and the ground voltage is supplied. However, the source line extends in the column direction and belongs to the same column. The memory cells may be connected to each other, or the memory cells that extend in the row direction and belong to the same row may be connected to each other. Furthermore, by providing a source line decoder 26 (not shown) for individually applying the selected source line voltage and the unselected source line voltage supplied by the voltage generation circuit 23 to each source line, writing (set) and erasing ( It is possible to select a memory cell to be operated by designating a memory cell for each row or column at the time of each memory operation for resetting and reading and at the time of memory cell forming processing. When the memory cell to be operated is input to the address line and designated, the source line decoder 26 selects the source line corresponding to the address signal input to the address line, and selects the selected source line and the non-selected source line. A selected source line voltage and an unselected source line voltage are respectively applied to the source lines.

  In the above embodiment, the memory cell array 21 is a 1D1R cross-point memory cell array including a diode in the memory cell, or a 1T1R cross-point memory cell array including a transistor in the memory cell. The present invention is not limited to this configuration, and the variable resistance element of the present invention, which includes the metal oxide film 13 as a resistance change layer and further includes the oxygen extracting material 14 in the first electrode 15, is employed in the memory cell. As long as the memory cells are arranged in a matrix, the present invention can be applied to any memory cell array.

  Furthermore, although the case where the metal oxide film 13 is in direct contact with the second electrode 12 is illustrated as a configuration of the variable resistance element 2 in the above embodiment, the present invention is not limited to this. In order to reduce the element variation of the filament formed by forming the tunnel insulating film between the second electrode 12 and the metal oxide film 13 so as to have a function as a non-linear current limiting element, and the forming process. In addition, a configuration in which a buffer layer for suppressing a sudden increase in current flowing between both electrodes of the variable resistance element upon completion of the forming process is conceivable.

  Moreover, in the said embodiment, although the thing of the element structure shown by FIG. 1 was illustrated as a structure of the variable resistance element 2, this invention is not limited to the element of this structure.

  INDUSTRIAL APPLICABILITY The present invention can be used for a nonvolatile semiconductor memory device, and particularly includes a nonvolatile variable resistance element in which a resistance state transitions due to voltage application and the resistance state after the transition is held in a nonvolatile manner. It can be used for a semiconductor memory device.

1: Nonvolatile semiconductor memory device according to the present invention 2: Variable resistance element according to the present invention 3, 3a, 3b: Conventional variable resistance element 10: Substrate 11: Insulating film (silicon oxide film)
12: Second electrode 13: Metal oxide film 14: Oxygen extracting material 15: First electrode 16: Region where oxygen concentration is locally increased by oxygen moving from the metal oxide film to the oxygen extracting material 21 21a, 104, 108: memory cell array 22: control circuit 23: voltage generation circuit 24, 106: word line decoder 25, 105: bit line decoder 26, 107: source line decoder 31: metal wiring 32: contact plug 33: interlayer Insulating film 101: Upper electrode 102: Variable resistor 103: Lower electrode BL, BL1 to BLm: Bit line R: Variable resistance element SL, SL1 to SLn: Source line T: Select transistor WL, WL1 to WLn: Word line

Claims (6)

An n-type metal oxide film is sandwiched between the first electrode and the second electrode, and the electrical resistance between the two electrodes changes reversibly according to the application of electrical stress between the two electrodes. A resistance element,
The variable resistance element is:
By performing the forming process, the resistance state between the two electrodes changes from the initial high resistance state before the forming process to a variable resistance state,
In the variable resistance state, by applying the electrical stress between the electrodes, the resistance state defined by the electrical resistance between the electrodes transitions between two or more different states, and one after the transition. Is used for storing information,
In the variable resistance state, when a positive voltage is applied to the first electrode with reference to the second electrode, a transition is made to a lower resistance state,
An oxygen extracting material capable of extracting oxygen from the metal oxide film is dispersed and arranged in islands or particles at least at the interface with the metal oxide film in the first electrode,
The oxide formation free energy of at least one element excluding oxygen constituting the oxygen abstraction material is lower than the oxide formation free energy of the element constituting the first electrode excluding the oxygen abstraction material,
The variable resistance element, wherein the oxygen extracting material is in contact with the metal oxide film at a part of an interface between the metal oxide film and the first electrode. The oxygen-extracting substance is dispersed in the form of particles in the first electrode;
The variable resistance element according to claim 1, wherein an average particle diameter of the oxygen extracting material is 50 nm or less.   The metal oxide film is made of an oxide of any element of Hf, Zr, Ti, Ta, V, Nb, and W, or strontium titanate. Variable resistance element.   The variable resistance element according to any one of claims 1 to 3, wherein the oxygen extracting material is configured to include any element of Ti, V, Al, Hf, and Zr.   The variable resistance element according to claim 1, wherein a work function of the second electrode is 4.5 eV or more. 6. A non-volatile semiconductor memory device comprising a memory cell array in which a plurality of variable resistance elements according to claim 1 are arranged in at least a column direction in a row or column direction.

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