WO2009145308A1

WO2009145308A1 - Semiconductor device, element recovery circuit, and element recovery method

Info

Publication number: WO2009145308A1
Application number: PCT/JP2009/059882
Authority: WO
Inventors: 潤砂村; 仁彦伊藤
Original assignee: 日本電気株式会社
Priority date: 2008-05-30
Filing date: 2009-05-29
Publication date: 2009-12-03
Also published as: JPWO2009145308A1

Abstract

Provided is a semiconductor device (1) including a variable resistance element (10). The variable resistance element (10) has a characteristic of changing from a first resistance state to a second resistance state in which the resistance value is lower than that in the first resistance state when a first voltage pulse is inputted and changing from the second resistance state to the first resistance state when a second voltage pulse is inputted. When the variable resistance element (10) does not change the resistance state even if the first or second voltage pulse is inputted, a recovery process of inputting a third voltage pulse having a polarity opposite to that of the first and second voltage pulses and a voltage amplitude set to a predetermined value is performed, and the variable resistance element (10) recovers the property.

Description

Semiconductor device, element regeneration circuit, and element regeneration method

The present invention relates to a semiconductor device having a variable resistance element, an element regeneration circuit, and an element regeneration method that can switch an electric resistance in a film between a low resistance state and a high resistance state by applying a voltage to an electrode.

In recent years, the demand for nonvolatile memories as rewritable semiconductor memory devices has increased. In flash memory, which is a typical example of nonvolatile memory, the one using a floating gate is the mainstream, but it is said that it is difficult to thin the tunnel gate oxide film, and it is approaching the limit of miniaturization. Has been. On the other hand, a memory using a resistance variable element has been proposed as a nonvolatile memory that breaks down the miniaturization limit of a flash memory. These are expected as general-purpose memories that operate at high speed as well as conventional nonvolatile memories.

Memory using resistance change elements includes magnetic RAM (MRAM), phase change RAM (PRAM), resistive RAM (ReRAM), and programmable metallization cell (PMC). Each of these has a unique rewrite condition, resistance change rate, and number of rewrites, but those having a high resistance change rate defined by the resistance ratio between the low resistance state and the high resistance state are ReRAM and PMC. A higher read margin can be expected.

In a resistance change element such as PRAM, ReRAM, or PMC, the switching operation from the high resistance state to the low resistance state is often referred to as a set operation, and the switching operation from the low resistance state to the high resistance state is often referred to as a reset operation. Also in this specification, the switching operation from the high resistance state to the low resistance state is defined as a set operation, and the switching operation from the low resistance state to the high resistance state is defined as a reset operation.

PMC uses ionic conduction and electrochemical reaction during the set / reset operation, so that voltages having different polarities are applied to the resistance change element in the set operation and the reset operation. On the other hand, in the ReRAM set / reset operation, there are reported examples of using different polar voltages for the set / reset operation as in the PMC and performing the same polarity (or unipolar) voltage application. .

An example of ReRAM using a perovskite material is disclosed in US Pat. No. 6,204,139 (hereinafter referred to as Patent Document 1). In the ReRAM disclosed in this document, it is possible to repeat the set / reset operation by applying voltage pulses having different polarities to the resistance change element for each operation of setting and resetting.

On the other hand, examples of ReRAM using a transition metal oxide are disclosed in Japanese Patent Application Laid-Open No. 2004-363604 (hereinafter referred to as Patent Document 2) and Japanese Patent Application Laid-Open No. 2006-279042 (hereinafter referred to as Patent Document 3). It is disclosed. In the ReRAM disclosed in these documents, a unipolar voltage is used for both set and reset operations. Since the set / reset operation can be performed by unipolar voltage sweep or voltage pulse application, a negative voltage generation circuit is unnecessary, and the peripheral circuit in the memory circuit can be made smaller and the cell occupation area can be increased. .

A configuration example of a semiconductor memory device having a resistance change element ReRAM using a transition metal oxide described in Patent Document 2 and Patent Document 3 will be briefly described with reference to FIG.

A semiconductor memory device 100 shown in FIG. 1 includes a MOS (Metal Oxide Semiconductor) transistor 101 and a resistance change element 102. The MOS transistor 101 has a source electrode 111, a drain electrode 112, and a gate electrode 114. Impurity diffusion layers to be the source electrode 111 and the drain electrode 112 are formed on the surface of the semiconductor silicon substrate 110, and a gate insulating film 113 typified by a silicon oxide film is formed on the silicon substrate 110, typified by polysilicon. A gate electrode 114 is formed on the gate insulating film 113.

The resistance change element 102 includes two

electrodes

115 and 116 and a variable resistor 117 sandwiched between these two electrodes. The electrode 115 is connected to the drain electrode 112 of the MOS transistor 101, and the electrode 116 is connected to a wiring 118 provided in the upper layer.

In the semiconductor memory device 100 shown in FIG. 1, the switching operation of the variable resistance element 102 using a unipolar voltage will be described with reference to FIG. Here, the voltage applied between the two

electrodes

115 and 116 of the resistance change element 102 is denoted as V _SW .

In the semiconductor memory device 100, in order to apply a desired voltage V _SW to the resistance change element 102, a voltage higher than V _SW is applied between the source electrode 111 and the wiring 118, and the MOS transistor 101 is turned on from the off state. A voltage that is equal to or higher than a threshold voltage to be in a state may be applied to the gate electrode 114. The relationship between the voltage V _SW applied to the resistance change element 102 and the current flowing through the resistance change element 102 is the relationship shown in the graph of FIG.

When the variable resistance element 102 is in the low resistance state, that is, in the set state, the variable resistance element 102 behaves according to the voltage-current characteristic 121 shown in FIG. 2 with respect to the applied voltage _VSW . Since the V _SW is low region of the low-resistance state, flows much current, it exceeds voltages V ₁ there is a V _SW, the current value is rapidly reduced. This is a result of switching of the variable resistance element 102 to the high resistance state, that is, the reset state. When V _SW further increases and V _SW exceeds a certain voltage V ₂ , the current value increases rapidly. This is a result of the resistance change element 102 switching to the set state again.

On the other hand, when the resistance change element 102 is in the high resistance state, that is, the reset state, the resistance change element 102 exhibits a behavior according to the voltage-current characteristic 122 shown in FIG. 2 with respect to the applied voltage _VSW . In a region where V _SW is low, a high resistance state is present, so that current does not flow easily, but the high resistance state does not change even when the voltage V ₁ is exceeded. When V _SW further increases and V _SW exceeds voltage V ₂ , the current value increases rapidly.

From the graph shown in FIG. _2, but in the region of V SW _{<V 1} which is stable both in the high resistance state and low resistance _state, a high resistance state is stabilized in the region of _{_{V 1 <V SW <V 2}} , V low resistance state in the region of the _SW> V ₂ is found to be stable. In Patent Document 2, it is recommended to perform the reset operation for the variable resistance element under the condition of V ₁ <V _SW <V ₂ and the set operation under the condition of V _SW > V ₂ by using this behavior. On the other hand, in Patent Document 3, the set operation is performed by applying a voltage pulse for 1 nanosecond to 100 nanoseconds under the condition of V _SW > V ₂ , and the reset operation is performed under the condition of V ₁ <V _SW <V ₂ . The voltage pulse is preferably applied by applying 1 microsecond to 100 microseconds.

The present inventors are engaged in research and development of semiconductor memory devices, and are conducting various studies on improving the performance of semiconductor memory devices. In particular, investigations have been made on ReRAM, which is considered to be advantageous for miniaturization, in a resistance change element in which the resistance value at the time of setting is low regardless of the area. Among ReRAMs, unipolar operation is considered important for circuit configuration, and resistance variable materials centering on transition metal oxides are being studied. As we continued to study the performance improvement of semiconductor memory devices, we faced several difficulties. Here, the points considered to be important are described below.

When the above-described structure disclosed in Patent Document 2 is prototyped and the improvement of the performance of the semiconductor memory device is examined, when data is rewritten repeatedly, the resistance value changes as shown in FIG. I understood it. That is, as the number of rewrites increases, the transition from the low resistance state to the high resistance state, that is, the reset operation becomes difficult at a certain point, and the switching operation does not occur. On the other hand, as shown in FIG. 4, it has been found that the transition from the high resistance state to the low resistance state, that is, the set operation may be difficult. 3 and 4 both limit the number of times of rewriting with respect to the variable resistance element, and limit the lifetime of the variable resistance element.

Moreover, as a symptom that the switching operation does not occur, it is difficult to make a transition from the high resistance state to the low resistance state, that is, the set operation before repeating the switching operation many times, that is, even at a relatively early stage after using the variable resistance element. It has also been found that there are cases where

The semiconductor memory device clarified in the present invention solves the problem that has been clarified after manufacturing the semiconductor device having the variable resistance element ReRAM in the above-described example.

One of the objects of the present invention is to provide a semiconductor device and an element in which a switching operation can be performed again when the variable resistance element is fixed in a high resistance state or a low resistance state and a desired characteristic cannot be obtained in the variable resistance element. A reproduction circuit and an element reproduction method are provided.

In the semiconductor device according to one aspect of the present invention, when the first voltage pulse is input, the semiconductor device transits from the first resistance state to the second resistance state having a lower resistance value, and the second voltage pulse is input. Then, the variable resistance element includes a variable resistance element having a characteristic of transition from the second resistance state to the first resistance state, and the resistance change element does not transition even when the first or second voltage pulse is input. When a restoration process is performed in which a third voltage pulse having a positive or negative sign opposite to that of the first or second voltage pulse and a voltage amplitude set to a predetermined value is input, the above characteristics are obtained. It is something to restore.

In the semiconductor device according to one aspect of the present invention, when the first voltage pulse is input, the semiconductor device transits from the first resistance state to the second resistance state having a lower resistance value, and the second voltage pulse is input. Then, the variable resistance element includes a variable resistance element having a characteristic of transition from the second resistance state to the first resistance state, and the resistance change element does not transition even when the first or second voltage pulse is input. When a restoration process is performed in which a third voltage pulse having an amplitude larger than that of the input voltage pulse is input, the above characteristics are restored.

In the element regeneration circuit according to one aspect of the present invention, when the first voltage pulse is input, the element resistance circuit transits from the first resistance state to the second resistance state having a lower resistance value, and the second voltage pulse is input. Then, a voltage pulse generator for inputting a voltage pulse to the variable resistance element having a characteristic of transitioning from the second resistance state to the first resistance state, and the first or second voltage pulse to the variable resistance element When the resistance state of the resistance change element does not transition even if is input, the third or second voltage pulse having the opposite sign and the voltage amplitude set to a predetermined value with respect to the first or second voltage pulse And a control unit that causes the voltage pulse generation unit to perform a restoration process for inputting the voltage pulse to the resistance change element.

In the element regeneration circuit according to one aspect of the present invention, when the first voltage pulse is input, the element resistance circuit transits from the first resistance state to the second resistance state having a lower resistance value, and the second voltage pulse is input. Then, a voltage pulse generator for inputting a voltage pulse to the variable resistance element having a characteristic of transitioning from the second resistance state to the first resistance state, and the first or second voltage pulse to the variable resistance element When the resistance state does not transition even if is input, a control unit that causes the voltage pulse generation unit to perform a restoration process of inputting a third voltage pulse having a larger amplitude than the input voltage pulse to the resistance change element, It is the composition which has.

In the element regeneration method according to one aspect of the present invention, when a first voltage pulse is input, a transition is made from the first resistance state to a second resistance state having a lower resistance value, and the second voltage pulse is input. If so, a method for reproducing a resistance change element having a characteristic of transitioning from a second resistance state to a first resistance state, wherein the first or second voltage pulse is input to the resistance change element, and the resistance change element is input. When the resistance state of the resistance change element does not transition even when the first or second voltage pulse is input, the sign of the positive or negative sign is opposite to that of the first or second voltage pulse, and the voltage amplitude is predetermined. A third voltage pulse set to a value is input to the resistance change element.

In the element regeneration method according to one aspect of the present invention, when a first voltage pulse is input, a transition is made from the first resistance state to a second resistance state having a lower resistance value, and the second voltage pulse is input. If so, a method for reproducing a resistance change element having a characteristic of transitioning from a second resistance state to a first resistance state, wherein the first or second voltage pulse is input to the resistance change element, and the resistance change element is input. When the resistance state does not change even if the first or second voltage pulse is input, a third voltage pulse having an amplitude larger than that of the input voltage pulse is input to the resistance change element.

FIG. 1 is a diagram showing a configuration of a related semiconductor device. FIG. 2 is a diagram illustrating the operation of the related semiconductor device. FIG. 3 is a diagram showing a change in resistance value of a related semiconductor device. FIG. 4 is a diagram showing a change in resistance value of a related semiconductor device. FIG. 5 is a diagram showing an example of the configuration of the semiconductor device according to the embodiment of the present invention. FIG. 6 is a block diagram showing a configuration example of the rewrite power supply circuit shown in FIG. FIG. 7 is a diagram illustrating an example of the operation of the semiconductor device according to the first embodiment. FIG. 8 is a diagram illustrating an example of voltage pulses used in the semiconductor device according to the first embodiment. FIG. 9 is a diagram illustrating an example of changes in the resistance value of the semiconductor device according to the first embodiment. FIG. 10 is a diagram illustrating an example of voltage pulses used in the characteristic restoration process in the first embodiment. FIG. 11 is a diagram illustrating an example of the characteristic restoration process in the first embodiment. FIG. 12 is a diagram illustrating an example of voltage pulses used in the semiconductor device according to the second embodiment. FIG. 13 is a diagram illustrating an example of changes in the resistance value of the semiconductor device according to the second embodiment. FIG. 14 is a diagram illustrating an example of voltage pulses used in the semiconductor device according to the third embodiment. FIG. 15 is a diagram illustrating an example of changes in the resistance value of the semiconductor device according to the third embodiment.

In order to solve the above problems, the present inventors have repeatedly studied a method for regenerating the variable resistance element. Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 5 is a schematic diagram showing a configuration example of a semiconductor device that performs a reproducing operation of the resistance change element in the present embodiment. As shown in FIG. 5, the semiconductor device 1 has a configuration including a resistance change element 10 to which a rewrite power supply circuit 14 is connected. The resistance change element 10 includes a first electrode 11 and a second electrode 12, and a variable resistor 13 sandwiched between the two electrodes. The first electrode 11 is connected to the rewrite power supply circuit 14, and the second electrode 12 is connected to a ground line (ground line).

As a material constituting the resistance change element 10, various combinations of variable resistors and electrode materials have been reported, and any combination of materials used for the resistance change element 10 can be used. Examples of the material of the variable resistor 13 include compounds composed of any one of oxygen, nitrogen, sulfur, selenium, tellurium, or a combination thereof, as synthesized with the base metal. Among these, a compound composed of a metal and oxygen is given as a representative example of the material of the variable resistor 13.

As the metal constituting the variable resistor 13, Cr, Ti, V, Ni, Cu, Zr, Nb, Mo, Hf, Ta, and W are effective, and among them, Ti, Ni, and Cu are given as typical examples. . For the film formation of the variable resistor 13, a sputtering method, a laser ablation method, a vapor phase chemical growth method or the like may be used. The film thickness of the variable resistor 13 is preferably in the range of approximately 5 nanometers to 300 nanometers.

On the other hand, as the first electrode 11 and the second electrode 12, various metals can be used. Among them, TaN, TiN, Ru, Pt, W, Mo, Ta, and the like are given as typical examples.

The rewrite power supply circuit 14 will be described. FIG. 6 is a block diagram showing a configuration example of the rewrite power supply circuit shown in FIG. As shown in FIG. 6, the rewrite power supply circuit 14 includes a voltage pulse generation unit 141 that generates a voltage pulse, a measurement unit 143 that measures the resistance value of the resistance change element 10, and a voltage based on the measurement result of the measurement unit 143. And a control unit 142 that controls the pulse generation unit 141. The control unit 142 may have a configuration including a CPU (Central Processing Unit) that executes processing according to a program and a memory that stores the program, or may be a dedicated circuit for executing predetermined processing.

The voltage pulse generator 141 is supplied with a power supply voltage from the outside, and outputs a voltage pulse to the resistance change element 10 in accordance with an instruction from the controller 142. The measurement unit 143 measures the resistance value of the variable resistance element 10 and transmits the result to the control unit 142. The measured resistance value is an example of an evaluation value indicating an index of the characteristic of the resistance change element 10. The normal characteristic of the resistance change element 10 means a state in which the set operation and the reset operation can be normally performed.

When a rewrite instruction for instructing the resistance change element 10 to perform a set operation or a reset operation is input from the outside, the control unit 142 sends the instruction to the voltage pulse generation unit 141 and corresponds to the input instruction. The voltage pulse is output to the voltage pulse generator 141. In addition, the control unit 142 is registered in advance with a value that is a criterion for determining whether or not the characteristic of the resistance change element 10 is abnormal. Then, when the control unit 142 receives the evaluation value from the measurement unit 143, the control unit 142 compares the value with a value serving as a determination criterion, and if the comparison result determines that the resistance change element 10 is abnormal, The voltage pulse generation unit 141 is instructed to perform the restoration process. By performing the restoration process, the characteristic restoration process is performed in the variable resistance element 10. The condition of the voltage pulse for performing the restoration process is registered in the control unit 142 in advance.

Note that, here, a value that is a criterion for determining whether or not the characteristic of the resistance change element 10 is abnormal is registered in the control unit 142, but may be registered in the measurement unit 143. In addition, although the voltage pulse condition for performing the restoration process is registered in the control unit 142, it may be registered in the voltage pulse generation unit 141.

Further, the second electrode 12 side is not limited to the ground line 15 shown in this form, and another circuit or transistor may be connected. What is important is that the rewrite power supply circuit 14 has the capability to apply a sufficient voltage for rewriting the resistance change element 10 between the first electrode 11 and the second electrode 12 of the resistance change element 10. .

In FIG. 5, the resistance change element 10 and the rewrite power supply circuit 14 are directly connected, but one or a plurality of transistors are provided between the resistance change element 10 and the rewrite power supply circuit 14 as in a memory circuit. May be provided.

The semiconductor device of this embodiment transitions from a high resistance state to a low resistance state when a first voltage pulse is input, and transitions from a low resistance state to a high resistance state when a second voltage pulse is input. When the characteristic of the variable resistance element does not exhibit the intended change, the voltage value of the variable resistance element is a predetermined value opposite to that of the first or second voltage pulse. When a voltage pulse set to any value within the range is applied, a process of restoring the characteristics of the variable resistance element is performed.

In addition, the semiconductor device of this embodiment includes means for measuring an evaluation value that serves as an index of the characteristic of the resistance change element when the first or second voltage pulse is input, and the evaluation value measured by the measuring means. However, when a predetermined value is reached, a process of restoring the characteristics by applying a voltage pulse having a predetermined polarity and voltage value to the variable resistance element may be performed.

In addition, the semiconductor device of this embodiment includes means for measuring an evaluation value that serves as an index of the characteristic of the resistance change element when the first or second voltage pulse is input, and the evaluation value measured by the measuring means. Is a process of restoring the characteristics by applying a voltage pulse having a predetermined polarity and voltage value to the resistance change element when the intended characteristics are not obtained as a result of comparison with a preset reference value. It may be done.

The voltage pulse in which the polarity and the voltage value are determined in advance may be a voltage pulse having an opposite sign to that of the first or second voltage pulse and the voltage value being set to any value within a predetermined range. .

If the operation that changes the resistance change element from the low resistance state to the high resistance state is defined as the reset operation, the resistance value after the reset operation is measured as an evaluation value, and the resistance change element changes from the high resistance state to the low resistance state. If the operation to be performed is defined as a set operation, a resistance value after the set operation may be measured as an evaluation value.

In the process performed to restore the above characteristics, the amplitude of the applied voltage pulse is not less than 0.5 times and not more than 3 times the absolute value of the voltage pulse applied when recording information. Is preferable, and it is more preferable that it is 0.75 times or more and 1.5 times or less.

The semiconductor device according to another embodiment of the present invention transitions from the high resistance state to the low resistance state when the first voltage pulse is input, and from the low resistance state when the second voltage pulse is input. In a semiconductor device having a resistance change element that transitions to a resistance state, when the characteristic of the resistance change element does not exhibit the intended change, a voltage having a larger amplitude than the first or second voltage pulse is applied to the resistance change element. A process of restoring the characteristics by applying a pulse is performed.

In the process performed to restore the above characteristics, it is preferable that the amplitude of the applied voltage pulse is 1.01 to 3 times the voltage of the voltage pulse applied when recording information. Moreover, it is preferable that a pulse for restoring the above characteristics is continuously applied twice or more.

Immediately after the process performed to restore the above characteristics, the amplitude of the voltage pulse applied when recording information is 3/4 or less of the voltage pulse amplitude applied when recording normal information. It is preferable that

Further, by applying a voltage having the same sign between the first electrode and the second electrode with respect to the variable resistance element, the low resistance state and the high resistance state may be reversibly changed.

The semiconductor device having a variable resistance element according to the present invention described above can be sufficiently realized by using a current integrated circuit formation technique, and any semiconductor device having an integrated circuit formation technology for a related semiconductor device can be used. The apparatus can be reproduced without any problem. By using the semiconductor device regeneration method disclosed by the present invention for a resistance change element in which a desired set / reset operation has ceased to occur, the resistance change element is regenerated into a switchable state, The lifetime of not only the resistance change element but also the semiconductor device having the resistance change element can be extended.

According to the semiconductor device of the present invention, the number of switching of the resistance change element can be greatly improved from about several hundred times, and the life of the semiconductor device having the resistance change element and the resistance change element can be greatly extended. Become. In addition, even in a relatively early stage after using the variable resistance element, when a switching operation that transitions from a high resistance state to a low resistance state, that is, when a setting operation becomes difficult, the switching operation can be performed again. It becomes possible to return to. As a result, the yield of the variable resistance element and the semiconductor device having the variable resistance element can be greatly improved.

In order to describe the above-described embodiment of the present invention in more detail, examples will be described in detail below with reference to the drawings.

The inventors of the present invention have studied the unipolar operation centered on the variable resistance element in the semiconductor device 1 having the above configuration. A variable resistance element 10 having a variable resistor 13 having a thickness of 100 nanometers and made of NiO, and a first electrode 11 and a second electrode 12 made of Ru was produced.

In the following, it is assumed that the voltage pulse input to the resistance change element 10 is performed by the rewrite power supply circuit 14 by external instruction input or control processing of the control unit 142, and detailed description thereof is omitted.

FIG. 7 is a graph showing a specific example of the unipolar operation of the variable resistance element in the semiconductor device of this example.

In the setting operation from the high resistance state to the low resistance state, for example, a pulse having a voltage amplitude of 8 volts and a 300 nanosecond pulse may be applied. Further, in the reset operation from the low resistance state to the high resistance state, for example, a pulse having a voltage amplitude of 3 volts and 50 microseconds may be applied. Such switching between the high resistance state and the low resistance state can be realized under the conditions of the set operation and the reset operation.

By the way, in this resistance change element 10, when the rewrite operation is repeatedly performed, the high resistance state and the low resistance state are satisfactorily switched up to several hundred times. Thereafter, the low resistance state is changed to the high resistance state. In many cases, the transition, i.e., the reset operation becomes difficult, and the switching operation does not occur. The situation is as shown in FIG.

Such a behavior of the resistance value is not preferable from the viewpoint of the lifetime of the resistance change element 10 and the semiconductor device 1. However, the behavior of the resistance change element 10 is recovered by the following method, and switching is performed. It was found that the characteristics can be restored.

As a characteristic restoration process, a switching operation does not occur by applying a voltage pulse having a sign opposite to that of a voltage pulse that is normally applied when recording information to the variable resistance element 10 in which the switching operation does not occur. The variable resistance element 10 can be brought into a switchable state again. Thus, by performing the characteristic restoration process, it is possible to significantly extend the lifetimes of the variable resistance element 10 and the semiconductor device 1.

FIG. 8 schematically shows voltage pulses used in the set / reset operation and the characteristic restoration process during normal unipolar operation. FIG. 9 schematically shows a normal set / reset operation, a state in which switching does not occur, a characteristic restoration process, and a change in resistance value after characteristic restoration.

In the case of the variable resistor 13 having the above film thickness, the voltage amplitude necessary for the characteristic restoration process when the reset operation becomes difficult is about −4 volts to −24 volts, more preferably −6 volts. To about -12 volts. In this case, the voltage amplitude necessary for the normal set operation is about 8 volts. Further, when the film thickness of NiO serving as the variable resistor 13 is 50 nanometers, in the setting operation from the high resistance state to the low resistance state, for example, a pulse having a voltage amplitude of 4 volts may be applied. The voltage amplitude required for the characteristic restoration process is about -2 volts to -12 volts. Therefore, in the characteristic restoration process when the reset operation becomes difficult, the sign is reversed, and the absolute value of the voltage amplitude is about 0.5 to 3 times, more preferably 0.75 to 1.5 times that of the set operation. It will be enough if it is about.

It was also found that the pulse width applied in the characteristic restoration process is effective from a short one nanosecond to a long one second. It has also been found that more reliable characteristic restoration is possible when the same pulse is input many times. When executing the characteristic restoration process, it is preferable to input the voltage pulse to the resistance change element 10 continuously two or more times within a predetermined time.

Further, it was found that, in the element subjected to the characteristic restoration process, when information is recorded immediately after, it is preferable that the amplitude of the applied voltage pulse is set lower than the voltage used in normal information recording. For example, in the case of the variable resistor 13 having a film thickness of 100 nanometers described above, a voltage amplitude of 8 volts is used for normal information recording, and -4 volts to -12 volts are used in the characteristic restoration process. At the time of recording information immediately after the process, it was found that a sufficient setting operation could be performed with a voltage of 3/4 or less of 8 volts, that is, 6 volts or less.

In the above, the characteristic restoration process in the case of the unipolar operation in which the voltage having the same sign is applied in the set operation and the reset operation has been described. However, the above method has different codes in the set operation and the reset operation. It can be extended to a characteristic restoration process in the case of bipolar operation in which a voltage is applied.

FIG. 10 schematically shows voltage pulses used for the set / reset operation and the characteristic restoration process during normal bipolar operation.

For example, the set operation from the high resistance state to the low resistance state has a voltage amplitude of 8 volts, a pulse of 300 nanoseconds is applied, and the reset operation from the low resistance state to the high resistance state is the set operation. A case where a pulse of 10 microseconds having a voltage amplitude of -4 volts as an opposite sign is applied will be described. In this case, when the transition from the low resistance state to the high resistance state, that is, the reset operation becomes difficult and the switching operation does not occur, the variable resistor 13 having a film thickness of 100 nanometers undergoes the characteristic restoration process. The required voltage amplitude was about -4 volts to -24 volts, more preferably about -6 volts to -12 volts. Further, when the film thickness of NiO serving as the variable resistor 13 is 50 nanometers, in the setting operation from the high resistance state to the low resistance state, for example, a pulse having a voltage amplitude of 4 volts may be applied. The voltage amplitude required for the characteristic restoration process was about -2 volts to -12 volts. Therefore, in the characteristic restoration process when the reset operation becomes difficult, the sign is reversed, and the absolute value of the voltage amplitude is about 0.5 to 3 times, more preferably 0.75 to 1.5 times that of the set operation. It will be enough if it is about.

Subsequently, another reproduction method will be described in this embodiment. It monitors the characteristic variation and performs the characteristic restoration process.

In this reproduction method, the resistance value of the resistance change element 10 is evaluated after the reset operation. As a result, it is possible to manage whether or not the reset operation of the resistance change element 10 has been reliably performed, and it is possible to determine whether or not to perform the characteristic restoration process. The procedure of this reproduction method will be described with reference to the flowchart shown in FIG. Here, a description will be given of a case where the control unit 142 of the rewrite power supply circuit 14 executes processing according to the procedure shown in FIG.

When a reset operation instruction is input from the outside, the control unit 142 causes the voltage pulse generation unit 141 to generate a voltage pulse for the reset operation, and the voltage pulse generation unit 141 sends the generated voltage pulse to the resistance change element 10. Apply (step 1). Thereby, the resistance change element 10 is changed from the low resistance state to the high resistance state. Subsequently, the measurement unit 143 measures the resistance value and transmits the measurement value to the control unit 142. When receiving the measurement value from the measurement unit 143, the control unit 142 compares the measurement value with the set value (step 2). The set value is a lower limit value of the resistance value when the variable resistance element 10 is normally reset, and is recorded in the control unit 142.

And the control part 142 determines whether a measured value is larger than a setting value, in order to investigate whether the variable resistance element 10 will be in the desired high resistance state by reset operation (step 3). In step 3, when the measured value of the resistance change element 10 is about the resistance value after the setting operation, the measured value becomes smaller than the set value. If the measured value is smaller than the set value, it indicates that the reset operation is difficult, and the intended characteristic change is not obtained. Therefore, the control unit 142 determines that it is necessary to cause the variable resistance element 10 to undergo a characteristic restoration process, and executes a characteristic restoration process (step 4).

On the other hand, when the measured value of the resistance change element 10 is sufficiently higher than the resistance value after the set operation in Step 3, the measured value becomes larger than the set value. That the measured value is larger than the set value indicates that the reset operation is normally performed, and the intended characteristic change is obtained. For this reason, the control unit 142 determines that the variable resistance element 10 exhibits normal characteristics, and waits until the next set operation based on the rewrite instruction input is performed (step 5).

By performing such a regeneration method on the variable resistance element 10 in which the reset operation becomes difficult and switching has not occurred, it becomes possible to make the variable resistance element 10 switchable again. It has been shown. This includes the resistance change element 10 and the resistance change element 10 regardless of whether the resistance change element 10 is applied to a memory circuit or used in a rewritable logic circuit typified by a field programmable gate array. This means that the life of the semiconductor device 1 can be extended.

In Example 1, NiO was used as the variable resistor 13, but it was found that the behavior shown differs when the material of the variable resistor 13 is different. This example relates to a method for regenerating a variable resistance element when a material different from that of the first embodiment is used as the variable resistor material.

In this example, the variable resistance element 10 having the variable resistor 13 having a film thickness of 100 nanometers and the material being TiO (N) and the first electrode 11 and the second electrode 12 having the material Ru was used.

In the unipolar operation of the variable resistance element 10 of the present embodiment, in the set operation from the high resistance state to the low resistance state, for example, a pulse having a voltage amplitude of 8 volts and a pulse of 300 nanoseconds may be applied. Further, in the reset operation from the low resistance state to the high resistance state, for example, a pulse having a voltage amplitude of 3 volts and 50 microseconds may be applied. Such switching between the high resistance state and the low resistance state can be realized under the conditions of the set operation and the reset operation.

By the way, in this resistance change element 10, when rewriting operation is repeated, the high resistance state and the low resistance state are satisfactorily switched up to several hundred times. Thereafter, the high resistance state is changed to the low resistance state. Transition, that is, the set operation becomes difficult, and there are many cases where the switching operation does not occur. The phenomenon that the reset operation becomes difficult with NiO occurs, but the set operation becomes difficult with TiO (N), which is a major difference from the first embodiment.

FIG. 12 schematically shows voltage pulses used for a set / reset operation and a characteristic restoration process during normal unipolar operation. FIG. 13 schematically shows a normal set / reset operation, a state in which switching does not occur, a characteristic restoration process, and a change in resistance value after characteristic restoration.

In the case of the variable resistor 13 having the above film thickness, the voltage amplitude necessary for the characteristic restoration process when the set operation becomes difficult is about −1.5 volts to −9 volts, more preferably − 2.25 volts to -4.5 volts. In this case, the voltage amplitude required for the normal reset operation is about 3 volts. In addition, when the film thickness of TiON that is the variable resistor 13 is 50 nanometers, in the reset operation from the low resistance state to the high resistance state, for example, a pulse having a voltage amplitude of 1.5 volts may be applied. In this case, the voltage amplitude required for the characteristic restoration process is about -0.75 to -4.5 volts. Therefore, in the characteristic restoration process when the set operation becomes difficult, the sign is reversed and the absolute value of the voltage amplitude is about 0.5 to 3 times, more preferably 0.75 to 1.5 times that of the reset operation. It will be enough if it is about.

Furthermore, it was found that, in the element that has undergone the characteristic restoration process, when erasing information immediately after, it is preferable to set the amplitude of the applied voltage pulse lower than the voltage used during normal information erasure. For example, in the case of the variable resistor 13 having a film thickness of 100 nanometers described above, a voltage amplitude of 3 volts is used for normal information erasing, and −1.5 to −4.5 volts is used in the characteristic restoration process. However, when erasing information immediately after the characteristic restoration process, it was found that a sufficient setting operation can be performed at a voltage of 3/4 or less of 3 volts, that is, 2.25 volts or less.

For example, in the set operation from the high resistance state to the low resistance state, a pulse of 300 nanoseconds having a voltage amplitude of 8 volts is applied, and in the reset operation from the low resistance state to the high resistance state, it is opposite to the set operation. A case will be described in which a pulse having a voltage amplitude of -4 volts as a sign and a pulse of 10 microseconds is applied. In this case, when the transition from the high resistance state to the low resistance state, that is, the set operation becomes difficult and the switching operation does not occur, the voltage amplitude necessary for the characteristic restoration process has a film thickness of 100 nanometers. In the case of the variable resistor 13, it was about 8 to 12 volts. Further, when the film thickness of TiON which is the variable resistor 13 is 50 nanometers, in the reset operation from the low resistance state to the high resistance state, for example, a pulse having a voltage amplitude of −2 volts may be applied. In this case, the voltage amplitude required for the characteristic restoration process was about 4 to 6 volts. Therefore, in the characteristic restoration process when the set operation becomes difficult, the sign is reversed and the absolute value of the voltage amplitude may be about 2 to 3 times that of the set operation.

In this reproduction method, the resistance value of the variable resistance element 10 is evaluated after the set operation. Thereby, it is possible to manage whether or not the setting operation of the resistance change element 10 has been performed reliably, and it is possible to determine whether or not to perform the characteristic restoration process.

The procedure of the reproduction method described below is the same as that in the flowchart shown in FIG. 11 except that the setting operation in step 1 and the resetting operation in step 5 are interchanged and the setting value in step 3 and the direction of the inequality sign are changed. Same as 1. The set value is an upper limit value of the resistance value when the variable resistance element 10 is normally set. Hereinafter, the outline of the procedure will be described with reference to FIG. Note that when the control unit 142 executes this reproduction method, the description is omitted because it is the same as the description of the first embodiment.

First, in step 1, a set operation is performed on the resistance change element 10. That is, a voltage pulse necessary for the set operation is applied to the resistance change element 10 to change the resistance change element 10 from the high resistance state to the low resistance state. Subsequently, the resistance value of the variable resistance element 10 is measured. At this time, the measured value of the variable resistance element 10 and the set value are compared (step 2), and it is determined whether the desired low resistance state is achieved by the set operation (step 3). In step 3, when the measured value of the resistance change element 10 is about the resistance value after the reset operation, it indicates that the set operation is difficult, and the intended characteristic change is not obtained. Therefore, a characteristic restoration process is necessary. Therefore, if it is determined in step 3 that the characteristic restoration process is necessary, the process proceeds to step 4 to perform the characteristic restoration process. On the other hand, when the measured value of the resistance change element 10 is sufficiently lower than the resistance value after the reset operation, the next switching is possible (step 5).

By using such a regeneration method for a resistance change element in which the set operation is difficult and switching has not occurred, the resistance change element 10 can be switched again. This includes the resistance change element 10 and the resistance change element 10 regardless of whether the resistance change element 10 is applied to a memory circuit or used in a rewritable logic circuit typified by a field programmable gate array. This means that the life of the semiconductor device 1 can be extended.

In the first and second embodiments, when the number of rewrites of the resistance change element increases, there is a switching operation for transition from the low resistance state to the high resistance state, or a switching operation for transition from the high resistance state to the low resistance state. The method of regenerating the resistance change element for the symptom that it does not occur in the above is shown.

It was found that the symptom that the switching operation does not occur is not limited to the stage after repeating the switching operation many times, but can occur even at a relatively early stage after starting to use the variable resistance element before repeating the switching operation many times. . It has also been found that even in a relatively early stage after using the variable resistance element, the set operation, which is a switching operation for transitioning from the high resistance state to the low resistance state, may be difficult. The present embodiment relates to a method for regenerating a variable resistance element that has become unable to perform a switching operation at an initial stage.

In the present embodiment, description will be made using a variable resistance element 13 having a film thickness of 100 nanometers and a material NiO, and a variable resistance element 10 having a first electrode 11 and a second electrode 12 made of Ru. In the following, it is assumed that the voltage pulse input to the resistance change element 10 is performed by the rewrite power supply circuit 14 by an external instruction input or a control process of the control unit 142, and detailed description thereof is omitted.

In the unipolar operation in the variable resistance element 10 of this embodiment, as shown in FIG. 7, in the set operation from the high resistance state to the low resistance state, for example, a pulse of 300 nanoseconds having a voltage amplitude of 8 volts is used. May be applied. In the reset operation from the low resistance state to the high resistance state, for example, a pulse of 50 microseconds having a voltage amplitude of 3 volts may be applied. Such switching between the high resistance state and the low resistance state can be realized under the conditions of the set operation and the reset operation.

By the way, in the variable resistance element 10, in a relatively early stage after the use of the variable resistance element 10, a transition from a high resistance state to a low resistance state, that is, a set operation becomes difficult, and there are many cases where a switching operation does not occur. occured. Such a case is not preferable from the viewpoint of the yield of the resistance change element 10 and the semiconductor device 1, but the behavior is restored to the resistance change element 10 by the following method to restore the switching characteristics. I found out that I could do it.

As a characteristic restoration process, a switching operation is caused by applying a voltage pulse having a voltage amplitude larger than that of a voltage pulse normally applied when recording information to the variable resistance element 10 in which the switching operation has not occurred. The resistance change element 10 which has disappeared can be brought into a switchable state again. Thus, by performing the characteristic restoration process, the yield of the variable resistance element 10 and the semiconductor device 1 can be significantly increased.

FIG. 14 schematically shows voltage pulses used for the set / reset operation and the characteristic restoration process during normal unipolar operation. FIG. 15 schematically shows a normal set / reset operation, a state where switching does not occur, a characteristic restoration process, and a transition of the resistance value after the characteristic restoration.

In the case of the variable resistor 13 having the above film thickness, the voltage amplitude required for the characteristic restoration process when the set operation becomes difficult is about 8.1 to 24 volts, more preferably 8.8. It was about 18 volts from the bolt. In this case, the voltage amplitude necessary for the normal set operation is about 8 volts. Further, when the film thickness of NiO serving as the variable resistor 13 is 50 nanometers, in the setting operation from the high resistance state to the low resistance state, for example, a pulse having a voltage amplitude of 4 volts may be applied. The voltage amplitude required for the characteristic restoration process is about 4.05 to 12 volts. Therefore, in the characteristic restoration process when the set operation becomes difficult, the sign is reversed and the absolute value of the voltage amplitude may be about 1.01 to 3 times that of the set operation.

It was also found that the pulse width applied in the characteristic restoration process is effective from a short one nanosecond to a long one second. It was also found that more reliable characteristic restoration is possible by inputting the same pulse many times. When executing the characteristic restoration process, it is preferable to input the voltage pulse to the resistance change element 10 continuously two or more times within a predetermined time.

Further, it was found that, in the element subjected to the characteristic restoration process, when information is recorded immediately after, it is preferable that the amplitude of the applied voltage pulse is set lower than the voltage used in normal information recording. The amplitude of the voltage pulse to be applied immediately after it may be about 3/4 of the amplitude of the voltage pulse applied at the time of information rewriting, as in the first or second embodiment.

For example, in the set operation from the high resistance state to the low resistance state, a pulse of 300 nanoseconds having a voltage amplitude of 8 volts is applied, and in the reset operation from the low resistance state to the high resistance state, it is opposite to the set operation. A case will be described in which a pulse having a voltage amplitude of -4 volts as a sign and a pulse of 10 microseconds is applied. In this case, when the transition from the high resistance state to the low resistance state, that is, the set operation becomes difficult and the switching operation does not occur, the voltage amplitude necessary for the characteristic restoration process has a film thickness of 100 nanometers. In the case of the variable resistor 13, it was about 8.1 to 24 volts. Further, when the film thickness of NiO which is the variable resistor 13 is 50 nanometers, in the setting operation from the high resistance state to the low resistance state, for example, a pulse having a voltage amplitude of 4 volts may be applied. The voltage amplitude required for the characteristic restoration process was about 4.05 to 12 volts. Therefore, in the characteristic restoration process when the set operation becomes difficult, the sign is reversed and the absolute value of the voltage amplitude may be about 1.01 to 3 times that of the set operation.

First, in step 1, a set operation is performed on the resistance change element 10. That is, a voltage pulse necessary for the set operation is applied to change the resistance change element 10 from the high resistance state to the low resistance state. Subsequently, the resistance value of the variable resistance element 10 is measured. At this time, the measured value of the variable resistance element 10 and the set value are compared (step 2), and it is determined whether the desired low resistance state is achieved by the set operation (step 3). In step 3, when the measured value of the resistance change element 10 is about the resistance value after the reset operation, it indicates that the set operation is difficult, and the intended characteristic change is not obtained. Therefore, a characteristic restoration process is necessary. Therefore, if it is determined in step 3 that the characteristic restoration process is necessary, the process proceeds to step 4 to perform the characteristic restoration process. On the other hand, when the measured value of the resistance change element 10 is sufficiently lower than the resistance value after the reset operation, the next switching is possible (step 5).

By using such a reproducing method for the resistance change element 10 in which the setting operation of the resistance change element 10 becomes difficult at a relatively early stage after starting to be used and switching has not occurred, the resistance change element 10 is used. It has been shown that it becomes possible to switch to a state in which switching can be performed again. This method can be applied even when the set operation becomes difficult after the repeated operation is performed many times. This includes the resistance change element 10 and the resistance change element 10 regardless of whether the resistance change element 10 is applied to a memory circuit or used in a rewritable logic circuit typified by a field programmable gate array. This means that the yield of the semiconductor device 1 can be improved and the life can be extended.

In the present embodiment, the characteristic restoring process of the resistance change element 10 when the setting operation of the resistance change element 10 becomes difficult at a relatively early stage after being used has been described. However, the reset operation becomes difficult. In this case, the reproduction method of this embodiment may be applied.

As described above, data rewriting was repeatedly performed on a semiconductor device having a resistance change element capable of switching the electrical resistance in the film between a low resistance state and a high resistance state by applying a voltage to the electrode. However, when the set operation / reset operation becomes difficult and is fixed in either the high resistance state or the low resistance state, and the desired operation cannot be obtained, the semiconductor described in the first to third embodiments according to the present invention. By the method of regenerating the device, the variable resistance element could be brought into a state where the switching operation can be performed again.

According to the present invention, it is possible to extend the lifetime of the variable resistance element and the semiconductor device having the variable resistance element. It is also possible to improve the yield of the variable resistance element and the semiconductor device having the variable resistance element. The application range of the variable resistance element extends over a wide range from a semiconductor memory device configured by arranging variable resistance elements on a matrix and a semiconductor device using the variable resistance element as a switch connecting the first circuit and the second circuit. I can expect.

In addition to the above-described ReRAM, there are various configurations of variable resistance elements. Even if the resistance change element has other configurations, the number of rewritable times is limited, and the resistance change element can recover its characteristics by a pulse having a sign opposite to that of the voltage used when recording data. The present invention can be applied. Also, the present invention can be applied to any resistance change element that has a finite number of rewritable times and whose characteristics can be recovered by a pulse having a voltage amplitude larger than the voltage used when recording data. Is possible.

Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Note that this application incorporates all the contents of Japanese Patent Application No. 2008-142453 filed on May 30, 2008, and claims priority based on this Japanese application.

DESCRIPTION OF SYMBOLS 1 Semiconductor device 10 Resistance change element 11 1st electrode 12 2nd electrode 13 Variable resistor 14 Rewriting power supply circuit 15 Ground line 141 Voltage pulse generation part 142 Control part 143 Measurement part

Claims

When a first voltage pulse is input, a transition is made from the first resistance state to a second resistance state having a lower resistance value than the first resistance state, and when the second voltage pulse is input, the second resistance state is changed. A variable resistance element having a characteristic of transitioning from the resistance state to the first resistance state,
When the resistance change element does not transition even if the first or second voltage pulse is input, the resistance change element has a positive / negative sign opposite to that of the first or second voltage pulse, and a voltage A semiconductor device that restores to the above characteristics when a restoration process is performed in which a third voltage pulse having an amplitude set to a predetermined value is input.
A measurement unit that measures an evaluation value serving as an index of characteristics of the resistance change element when the first or second voltage pulse is input;
When the evaluation value measured by the measurement unit reaches a preset value, a voltage pulse having a predetermined polarity and voltage value is applied to the resistance change element, so that the restoration process is performed. The semiconductor device according to claim 1.
A measurement unit that measures an evaluation value serving as an index of characteristics of the resistance change element when the first or second voltage pulse is input;
The evaluation value measured by the measurement unit is compared with a predetermined reference value. If the resistance change element does not exhibit the characteristics as a result of comparison, a voltage pulse having a predetermined polarity and voltage value is obtained. The semiconductor device according to claim 1, wherein the restoration process is performed by being applied to the variable resistance element.
4. The semiconductor device according to claim 2, wherein a voltage pulse having a predetermined polarity and voltage value is equivalent to the third voltage pulse.
The said measurement part measures the resistance value of this resistance change element as said evaluation value, if said 1st voltage pulse is input into said resistance change element, The range of Claim 2 or 3 of Claim Semiconductor device.
The said measurement part measures the resistance value of this resistance change element as said evaluation value, when said 2nd voltage pulse is input into said resistance change element, The range of Claim 2 or 3 of Claim Semiconductor device.
The control unit according to any one of claims 2 to 6, further comprising a control unit that determines whether or not to perform the restoration process on the variable resistance element based on the evaluation value measured by the measurement unit. The semiconductor device according to 1.
8. The device according to claim 1, wherein the amplitude of the third voltage pulse is not less than 0.5 times and not more than 3 times the absolute value of the amplitude of the first or second voltage pulse. The semiconductor device according to item.
The semiconductor device according to claim 8, wherein an amplitude of the third voltage pulse is 0.75 times or more and 1.5 times or less of an absolute value of the amplitude of the first or second voltage pulse.
When a first voltage pulse is input, a transition is made from the first resistance state to a second resistance state having a lower resistance value than the first resistance state, and when the second voltage pulse is input, the second resistance state is changed. A variable resistance element having a characteristic of transitioning from the resistance state to the first resistance state,
The resistance change element performs a restoration process in which a third voltage pulse having an amplitude larger than the input voltage pulse is input when the resistance state does not change even when the first or second voltage pulse is input. A semiconductor device that restores the characteristics when performed.
11. The semiconductor device according to claim 10, wherein the amplitude of the third voltage pulse is 1.01 to 3 times the amplitude of the first or second voltage pulse.
The semiconductor device according to any one of claims 1 to 11, wherein the third voltage pulse is input to the variable resistance element continuously two or more times.
When the first or second voltage pulse is input for the first time after the restoration process is performed on the variable resistance element, the amplitude of the voltage pulse input to the variable resistance element is the first or second voltage pulse. The semiconductor device according to any one of claims 1 to 11, wherein the semiconductor device has 3/4 of an amplitude of a voltage pulse.
The semiconductor device according to any one of claims 1 to 13, wherein the first and second voltages have the same sign.
When a first voltage pulse is input, a transition is made from the first resistance state to a second resistance state having a lower resistance value than the first resistance state, and when the second voltage pulse is input, the second resistance state is changed. A voltage pulse generator for inputting a voltage pulse to the variable resistance element having a characteristic of transition from the resistance state to the first resistance state;
Even if the first or second voltage pulse is input to the resistance change element, when the resistance state of the resistance change element does not change, the sign of the first or second voltage pulse is reversed. And a controller that causes the voltage pulse generator to perform a restoration process of inputting a third voltage pulse having a voltage amplitude set to a predetermined value to the resistance change element;
An element regeneration circuit having
When a first voltage pulse is input, a transition is made from the first resistance state to a second resistance state having a lower resistance value than the first resistance state, and when the second voltage pulse is input, the second resistance state is changed. A voltage pulse generator for inputting a voltage pulse to the variable resistance element having a characteristic of transition from the resistance state to the first resistance state;
Even if the first or second voltage pulse is input to the variable resistance element, if the resistance state does not transition, a third voltage pulse having an amplitude larger than the input voltage pulse is input to the variable resistance element. A controller that causes the voltage pulse generator to perform a restoration process;
An element regeneration circuit having
When a first voltage pulse is input, a transition is made from the first resistance state to a second resistance state having a lower resistance value than the first resistance state, and when the second voltage pulse is input, the second resistance state is changed. A method for regenerating a variable resistance element having a characteristic of transitioning from the resistance state to the first resistance state,
Inputting the first or second voltage pulse to the variable resistance element;
If the resistance state of the resistance change element does not change even if the first or second voltage pulse is input to the resistance change element, the sign of the first or second voltage pulse is reversed. And the element regeneration method which inputs the 3rd voltage pulse by which the voltage amplitude was set to the predetermined value to the said resistance change element.
When a first voltage pulse is input, a transition is made from the first resistance state to a second resistance state having a lower resistance value than the first resistance state, and when the second voltage pulse is input, the second resistance state is changed. A method for regenerating a variable resistance element having a characteristic of transitioning from the resistance state to the first resistance state,
Inputting the first or second voltage pulse to the variable resistance element;
Even if the first or second voltage pulse is input to the variable resistance element, when the resistance state does not transition, a third voltage pulse having a larger amplitude than the input voltage pulse is input to the variable resistance element. Element regeneration method.