WO2013136731A1 - 抵抗変化型不揮発性記憶装置 - Google Patents
抵抗変化型不揮発性記憶装置 Download PDFInfo
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- WO2013136731A1 WO2013136731A1 PCT/JP2013/001438 JP2013001438W WO2013136731A1 WO 2013136731 A1 WO2013136731 A1 WO 2013136731A1 JP 2013001438 W JP2013001438 W JP 2013001438W WO 2013136731 A1 WO2013136731 A1 WO 2013136731A1
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0021—Auxiliary circuits
- G11C13/0069—Writing or programming circuits or methods
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
- G11C13/0002—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements
- G11C13/0007—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using resistive RAM [RRAM] elements comprising metal oxide memory material, e.g. perovskites
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
- H10B63/20—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices comprising selection components having two electrodes, e.g. diodes
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10B—ELECTRONIC MEMORY DEVICES
- H10B63/00—Resistance change memory devices, e.g. resistive RAM [ReRAM] devices
- H10B63/80—Arrangements comprising multiple bistable or multi-stable switching components of the same type on a plane parallel to the substrate, e.g. cross-point arrays
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C2213/00—Indexing scheme relating to G11C13/00 for features not covered by this group
- G11C2213/70—Resistive array aspects
- G11C2213/72—Array wherein the access device being a diode
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/021—Formation of the switching material, e.g. layer deposition
- H10N70/026—Formation of the switching material, e.g. layer deposition by physical vapor deposition, e.g. sputtering
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/011—Manufacture or treatment of multistable switching devices
- H10N70/061—Patterning of the switching material
- H10N70/063—Patterning of the switching material by etching of pre-deposited switching material layers, e.g. lithography
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/20—Multistable switching devices, e.g. memristors
- H10N70/24—Multistable switching devices, e.g. memristors based on migration or redistribution of ionic species, e.g. anions, vacancies
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/821—Device geometry
- H10N70/826—Device geometry adapted for essentially vertical current flow, e.g. sandwich or pillar type devices
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N70/00—Solid-state devices without a potential-jump barrier or surface barrier, and specially adapted for rectifying, amplifying, oscillating or switching
- H10N70/801—Constructional details of multistable switching devices
- H10N70/881—Switching materials
- H10N70/883—Oxides or nitrides
- H10N70/8833—Binary metal oxides, e.g. TaOx
Definitions
- the present invention relates to a variable resistance nonvolatile memory device including a memory cell having a resistance change element whose resistance value reversibly changes based on an electrical signal and a current control element.
- the resistance change element refers to an element having a property that a resistance value (resistance state) is reversibly changed by applying an electric signal (voltage pulse) and the state is maintained.
- the variable resistance element has a simple configuration including a variable resistance layer formed using a variable resistance material between the first electrode layer and the second electrode layer.
- a resistance change element is different from a phase change element (PCRAM) in which a resistance value changes due to a change in a crystal state due to heat generated by an electrical stimulus, and an electrical stimulus is directly, that is, through exchange of electrons.
- PCRAM phase change element
- the resistance value of the element is changed by changing the redox state of the variable resistance material.
- nonvolatile memory device using a resistance change element for example, a 1T1R type memory cell in which a transistor and a resistance change element are connected in series at the intersection of a bit line and a word line arranged orthogonally
- a nonvolatile memory device in which are arranged in a matrix is known. Further, with the aim of further higher integration, the resistance value is changed from the high resistance state to the low resistance state in the normal operation at the position of the intersection of the bit line and the word line arranged orthogonally (LR conversion).
- a 1D1R type memory cell in which a diode element that functions as a current control element (current-steering element) that controls a current amount and a resistance change element are connected in series is arranged in an array.
- a cross-point type nonvolatile memory device and a cross-point type nonvolatile memory device in which the 1D1R type memory cells are stacked in multiple layers are also known.
- the resistance change element in order to allow the resistance change layer to reversibly transition between a high resistance state and a low resistance state, the resistance change element is formed after the resistance change element is formed.
- a forming operation for applying an initial break voltage is performed.
- the resistance value of the resistance change element in the initial state after the formation of the resistance change element is much higher than the high resistance value when the resistance changes normally.
- the voltage value of the initial break voltage is generally a voltage value having a larger absolute value than the voltage value of the electrical signal applied to change the resistance state of the resistance change element during the normal operation of the nonvolatile memory device. It has become.
- variable resistance element By performing the forming operation, the variable resistance element has a high resistance state having a resistance value lower than the initial resistance value immediately after manufacture and a low resistance value lower than the high resistance state according to the voltage applied between the upper and lower electrodes. The resistance changes between the resistance states.
- an object of the present invention is to provide a non-volatile memory device capable of satisfactorily limiting a current during a forming operation in a cross-point type non-volatile memory device using a resistance change element.
- variable resistance nonvolatile memory device transitions to a low-resistance state when a first voltage having a first polarity is applied
- a resistance change element that transitions to a high resistance state having a resistance value higher than that of the low resistance state when a second voltage having a second polarity opposite to the polarity of the second resistance is applied
- a first value that is an arbitrary value smaller than a voltage value, and a current that flows when a voltage having a polarity of the first polarity is applied is defined as a first current, and an absolute value is the first value.
- a current control element in which the first current is larger than the second current when the current flowing when the voltage having the polarity of the second polarity is applied is the second current;
- a plurality of memory cells connected to each other, a plurality of first signal lines intersecting with each other, and a plurality of memory cells The second signal line and the plurality of memory cells are arranged at intersections of the plurality of first signal lines and the plurality of second signal lines, and one end of the memory cell arranged at each intersection is the first
- a memory cell array connected to a signal line and having the other end connected to the second signal line, and applied to the plurality of memory cells via the plurality of first signal lines and the plurality of second signal lines.
- a writing circuit for generating a bipolar voltage.
- variable resistance nonvolatile memory device According to the variable resistance nonvolatile memory device according to the present disclosure, it is possible to satisfactorily limit the current during the forming operation.
- FIG. 1 is a cross-sectional view showing an example of a configuration of a nonvolatile memory element and a memory cell array according to the embodiment.
- FIG. 2 is a top view showing an example of the configuration of the nonvolatile memory element and the memory cell array according to the embodiment.
- FIG. 3A is a graph illustrating a current-voltage characteristic in the forming operation in the HR direction in the variable resistance element alone constituting the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 3B is a graph showing the relationship between the resistance value and the voltage in the forming operation in the HR direction in the variable resistance element alone constituting the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 3A is a graph illustrating a current-voltage characteristic in the forming operation in the HR direction in the variable resistance element alone constituting the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 3B is a graph showing the relationship between the resistance value and the voltage in the forming operation in the HR direction in the
- FIG. 4A is a graph showing a current-voltage characteristic in a normal write operation with the variable resistance element alone constituting the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 4B is a graph illustrating a relationship between a resistance value and a voltage in a normal write operation of the variable resistance element alone constituting the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 5A is an energy band diagram in the thickness direction of a current control element having asymmetric current-voltage characteristics that constitutes the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 5B is a graph schematically showing current-voltage characteristics of a current control element having asymmetric current-voltage characteristics, which constitutes the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 6 is a block diagram showing the configuration of the memory cell array and its peripheral circuits of the variable resistance nonvolatile memory device according to the first embodiment.
- FIG. 7A is a step view illustrating the method of manufacturing the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 7B is a step view illustrating the method of manufacturing the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 7C is a step view illustrating the method of manufacturing the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 7D is a step view illustrating the method of manufacturing the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 7E is a step view illustrating the method of manufacturing the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 7A is a step view illustrating the method of manufacturing the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 7B is a step view illustrating the method of manufacturing the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 7F is a step diagram illustrating the method of manufacturing the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 7G is a step view illustrating the method of manufacturing the variable resistance nonvolatile memory device according to the embodiment.
- FIG. 8 is a schematic block diagram showing the configuration of the memory cell array and its peripheral circuits of the variable resistance nonvolatile memory device according to the second embodiment.
- FIG. 9 is a circuit diagram showing a configuration of a conventional memory cell array and its peripheral circuits.
- FIG. 10 is a graph showing current-voltage characteristics of current control elements in a conventional memory cell array.
- FIG. 11 is a circuit diagram showing a configuration of a conventional memory cell array and its peripheral circuits.
- FIG. 12 is a circuit diagram showing a configuration of a conventional peripheral circuit.
- variable resistance nonvolatile memory device transitions to a low-resistance state when a first voltage having a first polarity is applied, and the second polarity is opposite to the first polarity.
- a variable resistance element that transitions to a high resistance state having a resistance value higher than that of the low resistance state, and an arbitrary value that is greater than 0 and less than a predetermined voltage value
- a current that flows when a voltage having a first value and a polarity is the first polarity is defined as a first current, an absolute value is the first value, and a polarity is the second value.
- a plurality of memories formed by connecting in series a current control element in which the first current is larger than the second current when the current flowing when a voltage having a polarity of is applied is the second current A cell, a plurality of first signal lines and a plurality of second signal lines intersecting with each other;
- Each of the memory cells is arranged at each intersection of the plurality of first signal lines and the plurality of second signal lines, one end of the memory cell arranged at each intersection is connected to the first signal line, and the other
- a memory cell array having an end connected to the second signal line and a bipolar voltage applied to the plurality of memory cells via the plurality of first signal lines and the plurality of second signal lines are generated.
- a writing circuit is
- a first current limiting circuit is provided which is inserted into a path of current flowing from the write circuit to the plurality of memory cells and limits a current in a direction to change the plurality of memory cells to the low resistance state. You may do it.
- a first current limiting circuit which is inserted into a path of current flowing from the write circuit to the plurality of memory cells and limits a current in a direction to change the plurality of memory cells to the low resistance state; And a second current limiting circuit that is inserted into a path of a current flowing from the memory cell to the plurality of memory cells and limits a current in a direction to change the plurality of memory cells to the high resistance state.
- the current limit value of the second current limit circuit may be less than the withstand current of the current control element.
- the current limit value of the second current limiting circuit may be a current value required when the variable resistance element changes to the high resistance state.
- the current limit value of the first current limit circuit may be configured to be equal to the current limit value of the second current limit circuit.
- the write circuit After the formation of the plurality of memory cells and before execution of a normal write operation, the write circuit has a voltage having the second polarity greater than the second voltage with respect to the plurality of memory cells. You may comprise so that the forming operation which applies may be performed.
- the “oxygen content” is the ratio of oxygen atoms to the total number of atoms constituting the metal oxide.
- the oxygen content of Ta 2 O 5 is the ratio of oxygen atoms to the total number of atoms (O / (Ta + O)), which is 71.4 atm%. Therefore, the oxygen-deficient tantalum oxide has an oxygen content greater than 0 and less than 71.4 atm%.
- the oxygen content has a corresponding relationship with the degree of oxygen deficiency. That is, when the oxygen content of the second metal oxide is greater than the oxygen content of the first metal oxide, the oxygen deficiency of the second metal oxide is greater than the oxygen deficiency of the first metal oxide. small.
- Oxygen deficiency refers to an oxide having a stoichiometric composition (the stoichiometric composition having the highest resistance value in the case where there are a plurality of stoichiometric compositions) in a metal oxide. Is the ratio of oxygen deficiency to the amount of oxygen constituting. A metal oxide having a stoichiometric composition is more stable and has a higher resistance value than a metal oxide having another composition.
- the oxide having the stoichiometric composition according to the above definition is Ta 2 O 5 , and can be expressed as TaO 2.5 .
- the oxygen excess metal oxide has a negative oxygen deficiency.
- the oxygen deficiency is described as including a positive value, 0, and a negative value.
- An oxide with a low degree of oxygen deficiency has a high resistance value because it is closer to a stoichiometric oxide, and an oxide with a high degree of oxygen deficiency has a low resistance value because it is closer to the metal constituting the oxide.
- Oxygen-deficient metal oxide is a metal with a low oxygen content (atomic ratio: the ratio of the number of oxygen atoms to the total number of atoms) compared to a metal oxide having a stoichiometric composition. Means oxide.
- a metal oxide having a stoichiometric composition refers to a metal oxide having an oxygen deficiency of 0%.
- Standard electrode potential is generally an index of the ease of oxidation. If this value is large, it is difficult to oxidize, and if it is small, it means that it is easily oxidized.
- “Current control element” refers to an element having a characteristic that resistance is low and current flows well in a predetermined voltage range, and resistance is high and current does not easily flow in other voltage ranges.
- the “current control element” is roughly classified into a unidirectional diode and a bidirectional diode.
- Unidirectional diodes are general diodes that have a low resistance and a good current flow when a voltage of a predetermined polarity or higher is applied. In other voltage ranges, the unidirectional diode has a high resistance and a low current flow characteristic.
- Have Typical unidirectional diodes are pn junction diodes and Schottky diodes.
- the bidirectional diode is applied regardless of the electrical signal of any polarity of the first polarity (for example, negative polarity) and the second polarity (for example, positive polarity) opposite to the first polarity.
- the current-voltage characteristic (monotonic increase characteristic) that the absolute value of the flowing current increases as the absolute value of the applied voltage increases, and the rate of change of the current with respect to the voltage (slope: current) as the absolute value of the applied voltage increases. (Amount of change in absolute value / amount of change in absolute value of voltage) increases).
- Typical bidirectional diodes are MIM diodes, MSM diodes, varistors and the like.
- the low resistance state indicates a state belonging to the first range in which the resistance value of the resistance change element is set to a lower range than the high resistance state.
- the high resistance state indicates a state belonging to the second range in which the resistance value of the variable resistance element is set to a higher range than that in the low resistance state.
- the first range in the low resistance state and the second range in the high resistance state are different by one digit or more.
- the resistance value decreases by about an order of magnitude, so that the current change becomes steep.
- Patent Document 1 in a normal operation, writing is performed so that the resistance state of the resistance change element is changed from a high resistance state to a low resistance state in a 1D1R type memory cell (normal low resistance writing) ), A method for limiting the write current has been proposed.
- FIG. 9 is a circuit diagram showing a configuration of a memory cell array and a peripheral circuit portion of a cross-point type nonvolatile memory device using 1D1R type memory cells described in Patent Document 1.
- FIG. 10 shows current-voltage characteristics of the current control element constituting the 1D1R type memory cell described in Patent Document 1.
- a unidirectional diode is used as a current control element of a memory cell, and the reverse bias direction of the unidirectional diode is the same as the polarity at which the resistance change element has a low resistance.
- the memory cell is configured. It has been shown that this configuration can suppress a change in current when the resistance change element changes to a low resistance state when performing resistance-reduction writing in the normal operation for the resistance change element. Furthermore, it is shown that a current limiting circuit (lower part of FIG. 9) provided in the peripheral circuit section suppresses a current change when the variable resistance element changes to a low resistance state.
- Patent Document 2 when a memory cell using a unipolar variable resistance element is written so that the variable resistance element changes from a low resistance state to a high resistance state (high resistance writing), the memory cell array is externally connected. There has been proposed a method of limiting a write current using a provided current limiting circuit.
- FIG. 11 is a circuit diagram showing a configuration of a memory cell array and a peripheral circuit portion of a cross-point type nonvolatile memory device using 1D1R type memory cells described in Patent Document 2.
- FIG. 12 is a circuit diagram showing a configuration of a current limiting circuit provided in the peripheral circuit portion of the nonvolatile memory device described in Patent Document 2.
- Patent Document 2 a current limiting circuit provided outside the memory cell array shown in FIG. 12 is used when performing high resistance writing in the variable resistance element in normal operation.
- a high voltage is applied and the resistance is prevented from being lowered again.
- Patent Document 1 and Patent Document 2 show a nonvolatile memory device that performs current limitation in low-resistance writing or high-resistance writing during normal operation.
- the resistance change element including the resistance change layer formed using the resistance change material between the first electrode layer and the second electrode layer
- the resistance change In order to enable the layer to reversibly transition between a high resistance state and a low resistance state, a forming operation may be performed once in the initial stage after manufacturing.
- the inventors of the present application are examining a method of forming a resistance change element in a cross-point type memory cell array composed of 1D1R type memory cells each including a bidirectional diode element and a bipolar resistance change element.
- a 1D1R type cross-point type memory cell array in general, the resistance state of a resistance change element is changed from a first resistance state having a higher resistance value than a high resistance state in normal operation to a resistance value lower than that of the first resistance state.
- a forming operation in the LR direction is performed in which a voltage is applied in the same direction as the low resistance writing in the normal operation.
- the low resistance state in the normal operation is set as the second resistance state, and the voltage in the LR direction is applied.
- the resistance value of the first resistance state is two orders of magnitude or more compared to the high resistance state, and three or more orders of magnitude compared to the low resistance state. That is, in the forming operation in the LR direction, the resistance value rapidly decreases by 3 digits or more when the resistance change element is formed. For this reason, it is difficult to stably control the resistance value after forming, and there is a problem that the resistance value may be excessively lowered depending on the characteristics of the variable resistance element and the configuration of the peripheral circuit. In this case, when a normal write operation is performed after forming, there is a problem that a voltage cannot be applied to the resistance change element and the resistance change operation cannot be performed.
- the resistance value rapidly decreases by three orders of magnitude or more. Therefore, when the resistance change element is formed, the current flowing through the memory cell increases rapidly. For this reason, when a current larger than the withstand capability of the diode constituting the memory cell flows through the memory cell, the diode may be destroyed.
- the present inventors are examining a forming operation in the HR direction in which a voltage is applied in the same direction as the high resistance writing in the normal operation.
- the normal high resistance state is set as the second resistance state, and the voltage in the HR direction is applied. Therefore, the amount of change in the resistance value of the resistance change element is smaller than in the forming operation in the LR direction.
- the resistance value of the resistance change element is small, and it is possible to better prevent the resistance value from excessively decreasing.
- the resistance change element whose resistance value is too low and lower than the low resistance state cannot be returned to the transitionable resistance value and becomes defective. is there.
- the target resistance state is the high resistance state. Therefore, the current flowing at the time of transition to the high resistance state is the LR direction in which the target resistance state is the low resistance state. Therefore, the number of variable resistance elements that become defective can be reduced.
- variable resistance element when the variable resistance element is formed, the resistance value of the variable resistance element decreases by two digits or more, and the current flowing through the memory cell increases rapidly. Therefore, it is required to suppress a sudden increase in the current flowing through the memory cell even in the forming operation in the HR direction.
- the absolute value of the voltage used in the forming operation in the HR direction is larger than the absolute value of the voltage used in the forming operation in the LR direction. For this reason, in the forming operation in the HR direction, the current flowing through the memory cell may increase rapidly even when compared with the forming operation in the LR direction.
- the resistance value may decrease too much, resulting in a resistance value lower than the high resistance state (low resistance state).
- the current flowing in the memory cell may increase rapidly.
- Patent Document 1 when a voltage is applied in the LR direction by a diode provided in the memory cell, the current change can be suppressed. However, when a voltage is applied in the HR direction, the current change is suppressed. It is difficult. That is, even if the configuration of Patent Document 1 is applied, there is a problem that the current during the forming operation in the HR direction cannot be limited and stable forming cannot be performed.
- the current limiting circuit used at the time of high resistance writing in the normal operation described in Patent Document 2 can suppress a change in current when a voltage is applied in the HR direction to some extent.
- the current limiting circuit is provided outside the memory cell array, the followability of the current change is limited as compared with the case where the current changing element is provided inside the memory cell as in Patent Document 1. Since the current change at the time of forming is abrupt, the current limiting circuit described in Patent Document 2 has a problem that the followability to the current change in the forming operation in the HR direction is not sufficient and stable forming cannot be performed.
- Embodiment 1 The nonvolatile memory device (resistance variable nonvolatile memory device) according to Embodiment 1 will be described with reference to the drawings.
- the nonvolatile memory device includes a memory cell in which a resistance change element and a current control element capable of limiting current when a voltage is applied in the HR direction are connected in series.
- FIG. 1 is a cross-sectional view showing a configuration example of a memory cell array among the components of the nonvolatile memory device according to the present embodiment.
- FIG. 2 is a top view illustrating an example of a schematic configuration of the nonvolatile memory element and the nonvolatile memory device according to the first embodiment of the present invention.
- a cross-sectional view of a cross-section taken along the alternate long and short dash line indicated by 1A-1A 'in FIG. 2 in the direction of the arrow corresponds to FIG.
- the memory cell array 10 of the present embodiment is roughly composed of the substrate 100 and the main surface of the substrate 100 in parallel with each other and in the X direction (the left-right direction in FIGS. 1 and 2).
- a plurality of first wirings 101 formed so as to extend in parallel to each other in a plane parallel to the main surface of the substrate 100 above the plurality of first wirings 101 and in the Y direction (in FIG.
- a plurality of second wirings 119 formed so as to extend in a vertical direction (vertical direction in FIG.
- the memory cell 11 is provided so as to connect (electrically connect, the same applies hereinafter) the first wiring 101 and the second wiring 119 corresponding to each of the positions (three-dimensional intersections) where the wiring 119 intersects three-dimensionally. And be prepared To have.
- the memory cell 11 includes a resistance change element 105, a current control element 112, and a third contact plug 110 that connects the resistance change element 105 and the current control element 112.
- the resistance change element 105 includes a lower electrode 106 (first electrode), an upper electrode 108 (second electrode), and a resistance change layer 107 interposed between the lower electrode 106 and the upper electrode 108. .
- the lower electrode 106 and the resistance change layer 107 are in physical contact, and the upper electrode 108 and the resistance change layer 107 are in physical contact.
- the current control element 112 is a current control element with a current limiting function when the resistance is increased, and a semiconductor layer interposed between the first electrode 113, the second electrode 115, and the first electrode 113 and the second electrode 115. 114.
- the first electrode 113 and the semiconductor layer 114 are in physical contact, and the second electrode 115 and the semiconductor layer 114 are in physical contact.
- variable resistance element 105 and the current control element 112 constituting the memory cell 11 are connected via the third contact plug 110. It is not limited.
- the upper electrode 108 constituting the resistance change element 105 and the first electrode 113 constituting the current control element 112 may be in direct contact with each other or may be configured to share the electrode.
- the current control element 112 is formed on the resistance change element 105.
- the resistance change element 105 may be formed on the current control element 112.
- a plurality of first wirings 101 extending in the X direction are formed on the substrate 100, and a first interlayer insulating layer 102 is formed so as to cover the first wirings 101. ing.
- a plurality of resistors are arranged on the first interlayer insulating layer 102 so as to be arranged at equal intervals on the first wiring 101 as viewed from the Z direction (the stacking direction of the first wiring 101, the upper direction in FIG. 1).
- a change element 105 is formed.
- the first wiring 101 and the lower electrode 106 of the variable resistance element 105 located thereabove are connected by a first contact plug 103 formed so as to penetrate the first interlayer insulating layer 102.
- a second interlayer insulating layer 109 is formed on the first interlayer insulating layer 102 so as to cover the variable resistance element 105.
- a plurality of current control elements 112 are formed on the second interlayer insulating layer 109 so as to overlap the resistance change element 105 when viewed from the Z direction.
- the third contact plug 110 connects (shorts) the upper electrode 108 of the variable resistance element 105 and the first electrode 113 of the current control element 112 without passing through either the variable resistance layer 107 or the semiconductor layer 114. .
- a third interlayer insulating layer 116 is formed on the second interlayer insulating layer 109 so as to cover the current control element 112.
- a second wiring 119 is formed on the third interlayer insulating layer 116 so as to be orthogonal to the first wiring 101 when viewed from the X direction and to overlap the resistance change element 105 and the current control element 112. Yes.
- the second wiring 119 and the second electrode 115 of the current control element 112 below the second wiring 119 are connected by a fifth contact plug 117 formed so as to penetrate the third interlayer insulating layer 116.
- a lead-out wiring 120 is formed outside the region where the memory cells 11 are arranged as viewed from the Z direction so as to extend in parallel with the second wiring 119, that is, in the Y direction.
- the first wiring 101 and the lead wiring 120 are formed so as to penetrate the second contact plug 104 formed so as to penetrate the first interlayer insulating layer 102 and the second interlayer insulating layer 109.
- the fourth contact plug 111 is connected to the sixth contact plug 118 formed so as to penetrate the third interlayer insulating layer 116. That is, the second contact plug 104, the fourth contact plug 111, and the sixth contact plug 118 are stacked in this order and connected to each other to form a stack contact, and the first wiring 101 and the lead wiring 120 is connected.
- the first wiring 101, the second wiring 119, and the lead-out wiring 120 are made of, for example, aluminum.
- the first interlayer insulating layer 102, the second interlayer insulating layer 109, and the third interlayer insulating layer 116 are made of, for example, silicon oxide.
- the first contact plug 103, the second contact plug 104, the third contact plug 110, the fourth contact plug 111, the fifth contact plug 117, and the sixth contact plug 118 are made of, for example, tungsten. .
- the resistance change element 105 includes the lower electrode 106, the upper electrode 108, and the resistance change layer 107 interposed between the lower electrode 106 and the upper electrode 108.
- the resistance change layer 107 is a layer that is interposed between the lower electrode 106 and the upper electrode 108, and whose resistance value reversibly changes based on an electrical signal applied between the lower electrode 106 and the upper electrode 108. .
- it is a layer that reversibly transitions between a high resistance state and a low resistance state in accordance with the polarity of the voltage applied between the lower electrode 106 and the upper electrode 108.
- the resistance change layer 107 is configured by depositing a resistance change material including an oxygen-deficient metal oxide to a thickness of, for example, 30 nm.
- the resistance change layer 107 may be made of a resistance change material including an oxygen-deficient tantalum oxide (TaO x : 0 ⁇ x ⁇ 2.5). Note that although tantalum oxide is described as an example in this embodiment, other metal oxides such as oxygen-deficient hafnium oxide (HfO x : 0 ⁇ x ⁇ 2) may be used.
- a transition metal or aluminum (Al) can be used as a metal constituting the resistance change layer 107.
- a transition metal or aluminum (Al) can be used as the transition metal.
- tantalum (Ta), titanium (Ti), hafnium (Hf), zirconium (Zr), niobium (Nb), tungsten (W), nickel (Ni), or the like can be used. Since transition metals can take a plurality of oxidation states, different resistance states can be realized by oxidation-reduction reactions.
- the resistance change layer 107 includes a first resistance change layer 107a having a large oxygen deficiency and a second resistance change layer 107b having a low oxygen deficiency stacked in the film thickness direction.
- the first resistance change layer 107 a is in contact with the lower electrode 106
- the second resistance change layer 107 b is in contact with the upper electrode 108.
- the oxygen deficiency of the second resistance change layer 107b is considered to be close to 0.
- the oxygen resistance may be higher than the stoichiometric composition.
- variable resistance element 105 including the variable resistance layer 107 configured as described above
- a conductive path filament having a larger oxygen deficiency than the second variable resistance layer 107b is formed in the second variable resistance layer 107b. It is considered that an oxidation reaction or a reduction reaction occurs in the conductive path depending on the polarity of the applied voltage, and the resistance value of the resistance change element 105 changes.
- a different metal may be used for the first metal constituting the first resistance change layer 107a and the second metal constituting the second resistance change layer 107b.
- the second resistance change layer may have a lower degree of oxygen deficiency than the first metal oxide, that is, may have a higher resistance.
- the standard electrode potential of the second metal may be lower than the standard electrode potential of the first metal.
- the standard electrode potential represents a characteristic that the higher the value is, the more difficult it is to oxidize. Thereby, an oxidation-reduction reaction easily occurs in the second metal oxide having a relatively low standard electrode potential. Note that the resistance change phenomenon is caused by a change in the filament (conducting path) caused by an oxidation-reduction reaction in a minute local region formed in the second metal oxide having a high resistance. Degree) is considered to change.
- metal oxide Al 2 O 3
- Al 2 O 3 aluminum oxide
- oxygen-deficient tantalum oxide (TaO x ) may be used for the first metal oxide
- aluminum oxide (Al 2 O 3 ) may be used for the second metal oxide.
- the standard electrode potential of the lower electrode material constituting the lower electrode 106 is V 1
- the standard electrode potential of the upper electrode material constituting the upper electrode 108 is V 2
- oxygen deficiency contained in the resistance change layer 107 In the type of metal oxide, when the standard electrode potential of the metal constituting the metal oxide is Vt, the metal oxide is made of a material that satisfies the relationship of Vt ⁇ V2 and V1 ⁇ V2.
- the upper electrode material is less likely to be oxidized than the resistance change material.
- the upper electrode material constituting the upper electrode 108 is not oxidized and reduced, and the resistance change material constituting the resistance change layer 107 is oxidized. Reduced.
- the oxidation state of the resistance change layer 107 changes and a resistance change phenomenon appears.
- V1 ⁇ V2 the oxidation / reduction reaction at the electrode interface is preferentially developed on the upper electrode 108 side. That is, the interface where the resistance change phenomenon appears can be fixed to the upper electrode 108 side.
- Examples of the material of the lower electrode 106 include tantalum nitride (TaN), tungsten (W), nickel (Ni), tantalum (Ta), titanium (Ti), aluminum (Al), and titanium nitride (TiN).
- a material having a lower standard electrode potential than the metal constituting the first metal oxide to be the first resistance change layer 107a can be used.
- As the material of the upper electrode 108 for example, platinum (Pt), iridium (Ir), palladium (Pd), or the like, which constitutes the second metal oxide to be the second resistance change layer 107b, and the lower electrode 106 are used.
- a material having a higher standard electrode potential than the constituent material can be used.
- the standard electrode potential V1 of tantalum nitride is 0.48V
- the standard electrode potential V2 of platinum or iridium as the upper electrode material is about 1.1V, which is a variable resistance material.
- the standard electrode potential Vt of tantalum oxide is ⁇ 0.6V. Therefore, the relationship of Vt ⁇ V2 and V1 ⁇ V2 is satisfied.
- the standard electrode potential Vt of hafnium is ⁇ 1.55 V. Therefore, even when hafnium oxide is used, the above upper electrode material and lower electrode material are used. If so, the relationship of Vt ⁇ V2 and V1 ⁇ V2 is satisfied.
- a positive voltage positive electrical signal, voltage pulse in the HR direction
- current flows from the upper electrode 108 to the lower electrode 106.
- electrons are taken from the conductive path in the second variable resistance layer 107b to the upper electrode 108, whereby the variable resistance material constituting the conductive path is oxidized and the resistance value increases.
- a negative voltage negative electrical signal, voltage pulse in the LR direction
- current flows from the lower electrode 106 to the upper electrode 108.
- electrons are applied from the upper electrode 108 to the conductive path on the upper electrode 108 side, whereby the variable resistance material constituting the conductive path is reduced and the resistance value decreases.
- variable resistance element 105 the characteristics at the time of forming operation in the HR direction of the variable resistance element 105 when tantalum oxide (TaO x : 0 ⁇ x ⁇ 2.5) is used as the variable resistance material constituting the variable resistance layer 107. This will be described with reference to FIGS. 3A and 3B.
- FIG. 3A is a graph showing an example of a current-voltage characteristic during the forming operation of the variable resistance element.
- FIG. 3B is a graph showing the relationship between the resistance value and the voltage during the forming operation in the HR direction of the variable resistance element 105.
- FIG. 3A shows the resistance value of the resistance change element 105 when 0.4 V is applied again after applying a voltage to the resistance change element 105 at each point in FIG. 3A.
- variable resistance element 105 when the variable resistance element 105 is formed, the resistance value rapidly decreases by two digits or more. For this reason, even in the forming operation in the HR direction, it is difficult for the variable resistance element 105 alone to stably control the resistance value after forming.
- FIG. 1 the characteristics at the time of normal write operation of the resistance change element 105 when tantalum oxide (TaO x : 0 ⁇ x ⁇ 2.5) is used as a resistance change material constituting the resistance change layer 107 are shown in FIG. A description will be given based on FIGS. 4A, 4B, and 4C.
- FIG. 4A is a graph showing an example of current-voltage characteristics of the variable resistance element 105 alone during a normal write operation.
- FIG. 4B is a graph showing the relationship between the resistance value and voltage (write voltage) of the variable resistance element alone during normal write operation.
- a negative voltage (write voltage in the LR direction) is applied to the upper electrode 108 with respect to the lower electrode 106, and the absolute value of the voltage gradually increases.
- the resistance state changes in the direction from point A to point B, and changes from the high resistance state to the low resistance state (state of point C) at point B.
- Yes low resistance
- the write voltage at point B is about -1.2 V, and the current is about -5 ⁇ A.
- a positive voltage (write voltage in the HR direction) is applied to the upper electrode 108 with respect to the lower electrode 106. Is applied in such a manner that the absolute value of the voltage gradually increases, the resistance value changes in the direction from the point D to the point E, and the resistance state changes at the point E. Change to a high resistance state (state of F point) (high resistance).
- the write voltage at point E is about +1.1 V
- the current is about +60 ⁇ A
- the absolute value of the write voltage is substantially the same as when the resistance is increased (point B).
- variable resistance element 105 In order to increase the resistance of the variable resistance element 105 during a normal write operation, it is necessary to pass a current of about 60 ⁇ A so as to reach the point E, but the current fluctuation at the time of increasing the resistance is moderate (E In the direction from the point to the point F) and the current decreases.
- a current of about 5 ⁇ A may be passed so as to reach point B.
- the current fluctuation at the time of resistance reduction is steep, and as can be seen from FIG. To point C, the resistance value decreases rapidly by one digit or more.
- the current control element 112 of the present embodiment is a current control element with a current limiting function when the resistance is increased, and includes the first electrode 113, the second electrode 115, the first electrode 113, and the second electrode.
- a semiconductor layer 114 interposed between the electrodes 115 is provided.
- the first electrode 113, the second electrode 115, and the semiconductor layer 114 have a work function of the first electrode 113 of ⁇ 1, an electron affinity of the semiconductor layer of ⁇ s, and a work function of the second electrode 115 of ⁇ 2, ⁇ s ⁇ 2 ⁇ It is made of a material that satisfies ⁇ 1.
- the first electrode 113 is made of a material containing tantalum nitride.
- the semiconductor layer 114 is formed by depositing nitrogen-deficient silicon nitride at 3 to 20 nm.
- the second electrode 115 is made of a material made of a metal different from the metal constituting the first electrode 113, and is made of a material containing tungsten.
- the work function ⁇ 2 of tungsten is 4.6 eV
- the electron affinity ⁇ s of silicon is 3.78 eV
- the work function ⁇ 1 of tantalum nitride is 4.76 eV
- the electron affinity of the nitrogen-deficient silicon nitride is that of silicon. Since it is considered close to the electron affinity, ⁇ s ⁇ 2 ⁇ 1 is satisfied.
- the current control element 112 is an MSM diode using a Schottky barrier formed at the metal-semiconductor interface.
- the MSM diode when the absolute value of the voltage is below a certain level, the MSM diode exhibits a high resistance value due to the influence of the Schottky barrier generated at the reverse bias interface, but when the absolute value of the voltage exceeds the certain level, The resistance value has a feature of rapidly decreasing.
- the current control element 112 used in this embodiment has current-voltage characteristics that are asymmetric with respect to the polarity of the voltage.
- FIG. 5A is an energy band diagram in the thickness direction of the current control element 112 having asymmetric current-voltage characteristics.
- FIG. 5B is a graph schematically showing current-voltage characteristics of the current control element 112 of FIG. 5A.
- the broken line (I) indicates the current-voltage characteristic of the current control element that is symmetrical with respect to the polarity
- the solid line (II) indicates the current-voltage characteristic of the current control element 112 of the present invention. .
- the first electrode 113 is used as a reference, and the second electrode 115 has a first value a having an absolute value greater than 0 and smaller than a predetermined voltage value, and having a polarity.
- the negative current flows when the voltage of the (first polarity) and is -aV applied first current i - and then, the polarity absolute value a first value a positive polarity (first polarity a different second current flowing when a voltage is applied to the a is + aV polarity) when the second current i +, the first current i - a second current i + more larger such current - Has voltage characteristics.
- the current control element 112 of the present embodiment has asymmetric current-voltage characteristics, and at least the absolute value of the first value a described above is greater than the threshold value of the current control element (voltage at which current starts to flow).
- the threshold value of the current control element voltage at which current starts to flow.
- any voltage greater than the threshold value is applied when the negative polarity (first polarity) voltage is applied than when the positive polarity (second polarity) voltage is applied.
- the current driving capability is high (
- the forming operation in the HR direction is performed in which a positive polarity (second polarity) voltage is applied to the upper electrode 108 with the lower electrode 106 of the resistance change element 105 as a reference. .
- variable resistance element 105 when the variable resistance element 105 is formed, in this embodiment, a current flows from the upper electrode 108 to the lower electrode 106 of the variable resistance element 105.
- a current flowing in such a direction means that a voltage having a polarity (second polarity) is applied to the corresponding current control element 112 so that the second electrode 115 has a positive potential with respect to the first electrode 113.
- second polarity a voltage having a polarity
- the current control element 112 as shown in FIG. 5B, + aV current i + when voltage is applied, the current i when the voltage of -aV is applied - to be smaller than Has been.
- the polarity at which the second electrode 115 becomes positive with respect to the first electrode 113 is a polarity at which the current drive capability of the current control element 112 is reduced.
- the direction of the voltage for forming the resistance change layer 107 of the resistance change element 105 is the same as the direction in which the current control capability of the current control element 112 is small. Further, the direction of the voltage for changing the resistance change layer 107 of the resistance change element 105 from the high resistance state to the low resistance state is the same as the direction in which the current driving capability of the current control element is large.
- the current control element 112 can suppress rapid current fluctuation during forming. Therefore, it is possible to realize a variable resistance nonvolatile memory element and a nonvolatile memory device that can stably perform the forming operation of the variable resistance element 105.
- FIG. 6 is a block diagram showing the configuration of the nonvolatile memory device according to this embodiment.
- the non-volatile storage device 200 receives the memory body 201, an address signal input from the outside, an address input circuit 208 for selecting and instructing a predetermined address, and a control signal input from the outside. And a control circuit 209 for controlling the operation of the memory body 201.
- the memory body 201 detects the amount of current flowing through the memory cell array 10, the row selection circuit 203, the column selection circuit 204, the write circuit 205, and the selected bit line, and whether the stored data is “1” or “
- a read circuit 206 that determines whether the data is “0” and a data input / output circuit 207 that performs input / output processing of input / output data via the terminal DQ are provided.
- the memory cell array 10 has m ⁇ n (m and n are natural numbers; only 4 bits in 2 rows and 2 columns are shown in FIG. 6) memory cells Mij (natural numbers where i ⁇ m, j ⁇ n. Are arranged in a matrix in the row direction (X direction in FIG. 6) and the column direction (Y direction in FIG. 6).
- one end of the resistance change element Rij is one end of the current control element Dij
- the other end of the resistance change element Rij is the bit line BLj
- the other end of the current control element Dij is the word line WLi. , Each connected.
- bit lines BL1 to BLn correspond to the first wiring 101 shown in FIG. 1
- word lines WL1 to WLm correspond to the second wiring 119 shown in FIG. 1
- the resistance change element Rij corresponds to the resistance change element 105 shown in FIG. 1
- the current control element Dij corresponds to the current control element 112 shown in FIG.
- the row selection circuit 203 selectively selects the word lines WL1 to WLm in a read operation or a normal write operation based on an instruction from the control circuit 209.
- the column selection circuit 204 selectively selects the bit lines BL1 to BLn in a read operation or a normal write operation based on an instruction from the control circuit 209.
- the data input / output circuit 207 receives the data input signal Din and outputs it to the write circuit 205 during the write operation. In a read operation, an output signal from the read circuit 206 is output as an output signal Dout to the outside of the nonvolatile memory device 200.
- the write circuit 205 is provided in a path between the first LR circuit 205a1 and the second HR circuit 205a2 for driving the bit lines BL1 to BLn, and between the first LR circuit 205a1 and the column selection circuit 204, and in the LR direction.
- the write circuit 205 when the data input signal Din indicates data “0”, the write circuit 205 performs low resistance write to the resistance change element Rij of the selected memory cell Mij. More specifically, the write circuit 205 drives the bit line BLj to a high level by the first LR circuit 205a1 and drives the word line WLi to a low level by the second LR circuit 205c2 when performing low resistance writing. .
- the write circuit 205 performs high resistance write to the resistance change element Rij of the selected memory cell Mij. More specifically, the write circuit 205 drives the word line WLi to the high level by the first HR circuit 205c1 and drives the bit line BLj to the low level by the second HR circuit 205a2 when performing high resistance writing. .
- the current limiting circuit 205b1 is connected to peripheral circuits such as the column selection circuit 204 and wirings such as the bit lines BL1 to BLn, and has a large capacitive load. And lower than the current control element Dij. For this reason, it is desirable to arrange the current limiting circuit 205b1 as close to the memory cell array 10 as possible.
- the current limiting circuit 205b1 can suppress a current change caused by low resistance writing.
- the resistance value at the time of low resistance can be controlled by controlling the current limiting value of the current limiting circuit 205b1, as described in detail in International Publication No. 2010/119671 (patent document).
- the current limiting circuit 205b1 is arranged in the immediate vicinity of the LR circuit 1 (205a1).
- the LR circuit 2 (205c2) is provided. ) Or inside the row selection circuit 203 and the column selection circuit 204.
- a first wiring 101 is formed on a substrate 100 on which transistors, other wirings, and the like are formed using a desired mask.
- a first interlayer insulating layer 102 is formed on the entire surface of the substrate 100 so as to cover the first wiring 101. Further, a contact hole (opening) that penetrates through the first interlayer insulating layer 102 and reaches the first wiring 101 is formed, and a filler containing tungsten as a main component is embedded in the contact hole, whereby the first Contact plug 103 and second contact plug 104 are formed.
- a lower electrode material layer made of tantalum nitride, a first oxygen-deficient tantalum oxide having a high degree of oxygen deficiency is formed on the first interlayer insulating layer 102.
- a variable resistance material layer, a second variable resistance material layer made of oxygen-deficient tantalum oxide having a lower oxygen deficiency than the first variable resistance material layer, and an upper electrode material layer made of iridium Films are formed in this order.
- the first variable resistance material layer and the second variable resistance material layer can be formed by so-called reactive sputtering in which a tantalum target is sputtered in an argon and oxygen gas atmosphere.
- the second variable resistance material layer, the surface of the first variable resistance material layer may be formed by plasma oxidation, Ta 2 O 5 sputter using the Ta 2 O 5 targets, CVD method or ALD method, or the like
- the film may be formed by other methods.
- patterning is performed using a desired mask so that the upper end surface of the first contact plug 103 is covered and the upper end surface of the second contact plug 104 is exposed, and the lower electrode 106 of the variable resistance element 105, the first electrode Of the variable resistance layer 107a and the second variable resistance layer 107b, and the upper electrode 108 are formed (corresponding to the first step).
- a second interlayer insulating layer 109 is formed on the entire surface of the first interlayer insulating layer 102 so as to cover the variable resistance element 105. Further, a contact hole (opening) reaching the upper electrode 108 of the resistance change element 105 through the second interlayer insulating layer 109 and a contact hole reaching the second contact plug 104 through the second interlayer insulating layer 109. (Opening) is formed.
- a third contact plug 110 is formed by embedding a filler containing tungsten as a main component in the former contact hole.
- a fourth contact plug 111 is formed by embedding a filler containing tungsten as a main component in the latter contact hole.
- a first electrode material layer made of tantalum nitride (TaN) on the second interlayer insulating layer 109, a semiconductor material layer made of silicon or nitrogen-deficient silicon nitride, A second electrode material layer made of tungsten is formed in this order.
- the work function of the first electrode material is ⁇ 1
- the work function of the second electrode material is ⁇ 2
- the electron affinity of the semiconductor layer is ⁇ s, ⁇ s ⁇ 2 ⁇ 1.
- patterning is performed with a desired mask so that the upper end surface of the third contact plug 110 is covered and the upper end surface of the fourth contact plug 111 is exposed, and the first electrode 113 and the semiconductor layer 114 of the current control element 112 are patterned.
- the second electrode 115 is formed (corresponding to the second step).
- a third interlayer insulating layer 116 is formed on the entire surface of the second interlayer insulating layer so as to cover the current control element 112. Further, a contact hole (opening) that reaches the second electrode 115 of the current control element 112 through the third interlayer insulating layer 116 and a contact that reaches the fourth contact plug 111 through the third interlayer insulating layer 116. A hole (opening) is formed.
- a fifth contact plug 117 is formed by embedding a filler containing tungsten as a main component in the former contact hole.
- a sixth contact plug 118 is formed by embedding a filler containing tungsten as a main component in the latter contact hole.
- a wiring material is deposited on the third interlayer insulating layer 116 and patterned using a desired mask so as to cover the upper end surface of the fifth contact plug 117.
- the lead-out wiring 120 is formed so that the second wiring 119 covers the upper end surface of the sixth contact plug 118.
- the memory cell array 10 and peripheral circuits shown in FIG. 6 (row selection circuit 203, column selection circuit 204, write circuit 205, read circuit 206, data input / output circuit 207, address input circuit 208, and control circuit 209).
- a forming step of applying a voltage of the second polarity to the memory cell Mij is performed.
- the resistance value of the resistance change element Rij (the resistance change element 105 in FIG. 1) constituting the memory cell Mij transitions from the first resistance state having a higher resistance value than the high resistance state to the high resistance state, Normal write operation becomes possible.
- nonvolatile memory device resistance variable nonvolatile memory device
- the current control element is provided in the memory cell, it is possible to satisfactorily follow a sudden change in current.
- the resistance change element 105 is first formed, and the current control element 112 is formed thereon. First, the current control element 112 is formed, and the resistance change is formed thereon.
- the element 105 may be formed.
- the resistance change element 105 has a higher resistance when a write current flows from the upper electrode 108 toward the lower electrode 106 and a lower resistance when the write current flows from the lower electrode 106 toward the upper electrode 108.
- the standard electrode potential is configured to be larger than both the metal constituting the resistance change layer and the standard electrode potential of the lower electrode 106, but may be configured upside down in a direction perpendicular to the substrate surface. In that case, the current control element 112 is also configured upside down in a direction perpendicular to the substrate surface.
- the nonvolatile memory device of this embodiment is different from the nonvolatile memory device of Embodiment 1 in that a voltage in the HR direction (second polarity voltage, high resistance writing at the time of high resistance writing)
- a current limiting circuit 205b2 is provided for limiting the current flowing through the memory cell when the applied voltage is applied.
- FIG. 8 is a block diagram showing the configuration of the nonvolatile memory device according to this embodiment.
- the nonvolatile memory device 200 includes a memory main body 201, an address input circuit 208 that receives an externally input address signal and selects and designates a predetermined address, and is externally input. And a control circuit 209 that controls the operation of the memory body 201.
- the configurations of the address input circuit 208 and the control circuit 209 are the same as those in the first embodiment.
- the memory main unit 201 includes a memory cell array 10, a row selection circuit 203, a column selection circuit 204, a write circuit 205, a read circuit 206, and a data input / output circuit 207.
- the configurations other than the write circuit 205, that is, the configurations of the memory cell array 10, the row selection circuit 203, the column selection circuit 204, the read circuit 206, and the data input / output circuit 207 are the same as those in the first embodiment.
- the write circuit 205 of this embodiment is provided in a path between the first LR circuit 205a1 and the second HR circuit 205a2 for driving the bit lines BL1 to BLn, and between the first LR circuit 205a1 and the column selection circuit 204.
- the second LR circuit 205c2 and the first HR circuit 205c1 for driving the word lines WL1 to WLm
- the current limiting circuit 205b2 is provided in a path between the second HR circuit 205a2 and the column selection circuit 204, and limits the current flowing through the memory cell Mij when a voltage is applied in the HR direction. Note that the configurations of the first LR circuit 205a1, the second HR circuit 205a2, the current limiting circuit 205b1, the second LR circuit 205c2, and the first HR circuit 205c1 are the same as those in the first embodiment.
- the current flowing through the resistance change element Rij can be limited by the current limiting circuit 205b1, and the forming operation in the HR direction or high resistance writing can be performed. Is performed, the current flowing through the resistance change element Rij can be limited by the current limiting circuit 205b2.
- the current limiting circuit 205b1 and the current limiting circuit 205b2 have the same current limiting value.
- the current limit value is a value less than the withstand current of the current control element Dij, and is set to a current value necessary when the resistance change element Rij changes to the high resistance state.
- the current limit value of the current limiting circuit 205b2 is set to be less than the breakdown limit current of the current control element Dij, and the current flowing through the memory cell Mij is the current control element Dij (FIG. It is possible to prevent the breakdown limit current of one current control element 112) from being exceeded. Thereby, it is possible to prevent the current control element Dij from being destroyed during the forming operation in the HR direction, and further to prevent the reliability from being lowered.
- the current limit value of the current limiting circuit 205b2 is set to a current required for increasing the resistance of the variable resistance element 105 ( ⁇ breakdown limit current), the resistance value of the variable resistance element during the forming operation Is in the vicinity of the resistance value in the high resistance state, so that the resistance value can be prevented from excessively decreasing.
- the current limiting circuit 205b2 may be configured to operate even when the resistance is increased during normal operation, or may be configured to function only during forming.
- the current limit value of the current limiting circuit 205b1 that limits the current when a voltage in the LR direction is applied ( ⁇ current required when the resistance of the variable resistance element 105 is increased) and HR conversion. If the current limit value of the current limit circuit 205b2 that limits the current when a voltage in the direction is applied is set to the same value, the resistance value of the resistance change element is higher than the resistance value in the high resistance state during the forming operation. Since it becomes a resistance value, it can prevent that a resistance value falls excessively.
- the bidirectional resistance change element used in the present invention as shown in FIG. 4A, the same current is generally required when the resistance is increased and when the resistance is decreased. When the resistance is increased during the operation, a current larger than the current when the resistance is decreased is required. Therefore, the current limiting circuit 205b2 is configured to work only during the forming operation.
- the oxygen-deficient tantalum oxide is used as the variable resistance material constituting the variable resistance layer 107.
- the present invention is not limited to this.
- the variable resistance material other metal oxides lacking oxygen may be used.
- hafnium oxide or zirconium oxide may be used.
- the resistance change element 105 may have a laminated structure of the resistance change layer 107. That is, even if the resistance change layer 107 has a stacked structure of a first resistance change layer made of the first metal oxide and a second resistance change layer made of the second metal oxide. good.
- the second resistance change layer may have a lower degree of oxygen deficiency and a smaller film thickness than the first resistance change layer.
- a first tantalum oxide layer composition: TaO x
- the second tantalum oxide layer composition: TaO y
- the first tantalum oxide layer can be formed by, for example, a reactive sputtering method in which a tantalum target is sputtered in an oxygen gas atmosphere.
- the second tantalum oxide layer can be formed by, for example, a reactive sputtering method in which a tantalum target is sputtered in an oxygen gas atmosphere.
- the variable resistance layer includes a multilayer structure of a first hafnium oxide layer (composition: HfO x ) and a second hafnium oxide layer (composition: HfO y ).
- HfO x first hafnium oxide layer
- HfO y second hafnium oxide layer
- the second hafnium oxide layer (HfO y ) is in contact with the upper electrode, the film thickness is 3 nm or more and 4 nm or less, and 0.9 ⁇ x ⁇ 1.6 and 1.8 ⁇ y are satisfied. May be.
- the first hafnium oxide layer can be generated, for example, by a reactive sputtering method using an Hf target and performing sputtering in argon gas and oxygen gas.
- the second hafnium oxide layer can be formed by exposing the surface of the first hafnium oxide layer with, for example, plasma of argon gas and oxygen gas.
- the variable resistance layer has a multilayer structure of a first zirconium oxide layer (composition: ZrO x ) and a second zirconium oxide layer (composition: ZrO y ).
- first zirconium oxide layer composition: ZrO x
- second zirconium oxide layer composition: ZrO y
- the film thickness is 1 nm or more and 5 nm or less
- 0.9 ⁇ x ⁇ 1.4 and 1.9 ⁇ y are satisfied. May be.
- the first zirconium oxide layer can be formed, for example, by a reactive sputtering method using a Zr target and performing sputtering in argon gas and oxygen gas.
- the second zirconium oxide layer can be formed, for example, by exposing the surface of the first zirconium oxide layer to plasma of argon gas and oxygen gas.
- the first metal constituting the first metal oxide that becomes the first variable resistance layer and the second metal oxide that becomes the second variable resistance layer are configured.
- a different metal may be used as the second metal.
- the second metal oxide may have a lower degree of oxygen deficiency than the first metal oxide, that is, the resistance may be higher.
- the resistance change layer 107 only needs to include an oxide layer such as tantalum, hafnium, zirconium, etc. as a main resistance change layer that exhibits resistance change, and for example, contains a trace amount of other elements. It doesn't matter. It is also possible to intentionally include a small amount of other elements by fine adjustment of the resistance value, and such a case is also included in the scope of the present invention. For example, if nitrogen is added to the resistance change layer, the resistance value of the resistance change layer increases and the reactivity of resistance change can be improved.
- an oxide layer such as tantalum, hafnium, zirconium, etc.
- an unintended trace element may be mixed into the resistive film due to residual gas or outgassing from the vacuum vessel wall. Naturally, it is also included in the scope of the present invention when mixed into the film.
- variable resistance nonvolatile element realized by making various modifications conceived by those skilled in the art without departing from the gist of the present invention, or by arbitrarily combining the components in the embodiment, and a method for manufacturing the variable resistance nonvolatile element are also included in the present invention. include.
- variable resistance nonvolatile memory device of the present invention has high reliability and stable rewriting characteristics, and is used in various electronic devices such as digital home appliances, memory cards, portable telephones, and personal computers. This is useful as a memory device.
Abstract
Description
本発明の一態様に係る抵抗変化型不揮発性記憶装置は、第1の極性の第1の電圧が印加された場合に、低抵抗状態に遷移し、前記第1の極性とは逆の第2の極性の第2の電圧が印加された場合に、前記低抵抗状態より抵抗値の高い高抵抗状態に遷移する抵抗変化素子と、絶対値が0より大きく所定の電圧値より小さい任意の値である第1の値であって、極性が前記第1の極性である電圧を印加したときに流れる電流を第1の電流とし、絶対値が前記第1の値であって、極性が前記第2の極性である電圧を印加したときに流れる電流を第2の電流とするとき、前記第1の電流が前記第2の電流より大きくなる電流制御素子と、を直列に接続してなる複数のメモリセルと、互いに交差する複数の第1信号線および複数の第2信号線と、前記複数のメモリセルの各々を前記複数の第1信号線と前記複数の第2信号線との各交差部に配置し、各交差部に配置されたメモリセルの一端を前記第1信号線に接続し、他端を前記第2信号線に接続してなるメモリセルアレイと、前記複数のメモリセルに前記複数の第1信号線および前記複数の第2信号線を介して印加される両極性の電圧を発生する書き込み回路と、を備える。
実施形態において、「酸素含有率」は、金属酸化物を構成する総原子数に占める酸素原子の比率である。例えば、Ta2O5の酸素含有率は、総原子数に占める酸素原子の比率(O/(Ta+O))であり、71.4atm%となる。したがって、酸素不足型のタンタル酸化物は、酸素含有率は0より大きく、71.4atm%より小さいことになる。例えば、第1の金属酸化物層を構成する金属と、第2の金属酸化物層を構成する金属とが同種である場合、酸素含有率は酸素不足度と対応関係にある。すなわち、第2の金属酸化物の酸素含有率が第1の金属酸化物の酸素含有率よりも大きいとき、第2の金属酸化物の酸素不足度は第1の金属酸化物の酸素不足度より小さい。
上述した1D1R型のメモリセルで用いられる抵抗変化素子では、通常動作において、抵抗変化素子の抵抗状態を高抵抗状態から低抵抗状態に変化させる低抵抗化書き込みと、抵抗変化素子の抵抗状態を低抵抗状態から高抵抗状態に変化させる書き込む高抵抗化書き込みとを行っている。
ところで、上述したように、第1電極層と第2電極層との間に、抵抗変化材料を用いて形成された抵抗変化層を備えた抵抗変化素子を用いた不揮発性記憶装置では、抵抗変化層を高抵抗状態と低抵抗状態との間で可逆的に遷移可能にするために、製造後、初期に一度、フォーミング動作を行う場合がある。
実施の形態1に係る不揮発性記憶装置(抵抗変化型不揮発性記憶装置)について、図面を基に説明する。
先ず、不揮発性記憶装置を構成するメモリセルアレイと、当該メモリセルアレイを構成するメモリセルの構成について、図1および図2を基に説明する。
上述したように、本実施の形態の抵抗変化素子105は、下部電極106と、上部電極108と、下部電極106と上部電極108との間に介在する抵抗変化層107とを備えている。
以下、抵抗変化素子105単体での、即ち、電流制御素子112を接続しない場合のHR化方向のフォーミング動作時の特性について、図3Aおよび図3Bを基に説明する。
次に、抵抗変化素子105単体での、即ち、電流制御素子112を接続しないと仮定した場合の通常の書き込み動作時の特性について、図4A~図4Cを基に説明する。
上述したように、本実施の形態の電流制御素子112は、高抵抗化時の電流制限機能付き電流制御素子であり、第1電極113と、第2電極115と、第1電極113と第2電極115との間に介在する半導体層114とを備えている。
次に、本実施の形態における電流制御素子112の特性について説明する。
本実施の形態のメモリセルアレイ10では、フォーミング動作において、抵抗変化素子105の下部電極106を基準として上部電極108に正極性(第2の極性)の電圧を印加するHR化方向のフォーミング動作を行う。
図6は、本実施の形態に係る不揮発性記憶装置の構成を示すブロック図である。
図7A~図7Gは、本実施の形態の不揮発性記憶装置の製造方法における各工程を示す断面図である。
実施の形態2に係る不揮発性記憶装置(抵抗変化型不揮発性記憶装置)について、図8を基に説明する。
なお、上記実施の形態1および実施の形態2では、抵抗変化層107を構成する抵抗変化材料として、酸素不足型のタンタル酸化物を用いたが、これに限るものではない。抵抗変化材料としては、酸素不足型の他の金属酸化物を用いてもよい。酸素不足型の他の金属酸化物としては、例えば、ハフニウム酸化物やジルコニウム酸化物を用いても構わない。ハフニウム酸化物を用いる場合には、ハフニウム酸化物の組成をHfOxとすると、少なくとも0<x<2.0としてもよい。さらに、0.9≦x≦1.6程度としてもよい。また、ジルコニウム酸化物を用いる場合には、ジルコニウム酸化物の組成をZrOxとすると、少なくとも0<x<2.0としてもよい。さらに、0.9≦x≦1.4程度としてもよい。このような組成範囲とすることにより、安定した抵抗変化動作を実現することができる。
11 メモリセル
100 基板
101 第1の配線
102 第1の層間絶縁層
103 第1のコンタクトプラグ
104 第2のコンタクトプラグ
105 抵抗変化素子
106 下部電極
107 抵抗変化層
108 上部電極
109 第2の層間絶縁層
110 第3のコンタクトプラグ
111 第4のコンタクトプラグ
112 電流制御素子
113 第1電極
114 半導体層
115 第2電極
116 第3の層間絶縁層
117 第5のコンタクトプラグ
118 第6のコンタクトプラグ
119 第2の配線
120 引き出し配線
200 不揮発性記憶装置
201 メモリ本体部
203 行選択回路
204 列選択回路
205 書き込み回路
205a1 第1LR化回路
205a2 第2HR化回路
205b1 電流制限回路
205b2 電流制限回路
205c1 第1HR化回路
205c2 第2LR化回路
206 読み出し回路
207 データ入出力回路
208 アドレス入力回路
209 制御回路
Rij 抵抗変化素子
Dij 電流制御素子
Mij メモリセル
Claims (7)
- 第1の極性の第1の電圧が印加された場合に、低抵抗状態に遷移し、前記第1の極性とは逆の第2の極性の第2の電圧が印加された場合に、前記低抵抗状態より抵抗値の高い高抵抗状態に遷移する抵抗変化素子と、
絶対値が0より大きく所定の電圧値より小さい任意の値である第1の値であって、極性が前記第1の極性である電圧を印加したときに流れる電流を第1の電流とし、絶対値が前記第1の値であって、極性が前記第2の極性である電圧を印加したときに流れる電流を第2の電流とするとき、前記第1の電流が前記第2の電流より大きくなる電流制御素子と、を直列に接続してなる複数のメモリセルと、
互いに交差する複数の第1信号線および複数の第2信号線と、
前記複数のメモリセルの各々を前記複数の第1信号線と前記複数の第2信号線との各交差部に配置し、各交差部に配置されたメモリセルの一端を前記第1信号線に接続し、他端を前記第2信号線に接続してなるメモリセルアレイと、
前記複数のメモリセルに前記複数の第1信号線および前記複数の第2信号線を介して印加される両極性の電圧を発生する書き込み回路と、を備える
抵抗変化型不揮発性記憶装置。 - 前記書き込み回路から前記複数のメモリセルへ流れる電流の経路に挿入され、前記複数のメモリセルを前記低抵抗状態に変化させる方向の電流を制限する第1の電流制限回路を備える
請求項1に記載の抵抗変化型不揮発性記憶装置。 - 前記書き込み回路から前記複数のメモリセルへ流れる電流の経路に挿入され、前記複数のメモリセルを前記低抵抗状態に変化させる方向の電流を制限する第1の電流制限回路と、
前記書き込み回路から前記複数のメモリセルへ流れる電流の経路に挿入され、前記複数のメモリセルを前記高抵抗状態に変化させる方向の電流を制限する第2の電流制限回路とを備える
請求項1に記載の抵抗変化型不揮発性記憶装置。 - 前記第2の電流制限回路の電流制限値は、前記電流制御素子の耐電流未満である
請求項3に記載の抵抗変化型不揮発性記憶装置。 - 前記第2の電流制限回路の電流制限値は、前記抵抗変化素子が前記高抵抗状態に変化する時に必要な電流値である
請求項3に記載の抵抗変化型不揮発性記憶装置。 - 前記第1の電流制限回路の電流制限値は、前記第2の電流制限回路の電流制限値と等しい
請求項3に記載の抵抗変化型不揮発性記憶装置。 - 前記書き込み回路は、前記複数のメモリセルの形成後、通常の書き込み動作の実行前に、前記複数のメモリセルに対し、絶対値が前記第2の電圧より大きい前記第2の極性の電圧を印加するフォーミング動作を行う
請求項1に記載の抵抗変化型不揮発性記憶装置。
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