JP2010003827A - Nonvolatile storage element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonvolatile storage element which uses an oxygen-deficient transition metal oxide as a resistance varying material and has reversibly stable rewriting characteristics. <P>SOLUTION: The nonvolatile storage element has a first electrode 203, a second electrode 205, and a resistance varying layer 204 interposed between the first electrode 203 and second electrode 205 and containing the oxygen-deficient transition metal oxide (AOx when transition metal is denoted by A) which reversibly varies in resistance value with an electric signal applied between both the electrodes, and satisfies E<SB>E</SB>-E<SB>T</SB>≥0.34 eV, where E<SB>E</SB>is the standard electrode potential of at least one of the first electrode 203 and second electrode 205 (providing that the material constituting the electrode is none of Ag, Au, Ir, Pt, Ru, Ti and W) and E<SB>T</SB>is the standard electrode potential of the transition metal A. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a nonvolatile memory element, and more particularly to a variable resistance nonvolatile memory element whose resistance value changes in accordance with an applied electrical signal.

  In recent years, with the advancement of digital technology, electronic devices such as portable information devices and information home appliances have become more sophisticated. Therefore, there are increasing demands for increasing the capacity of nonvolatile memory elements, reducing the write power, increasing the write / read time, and extending the life.

  In response to such demands, it is said that there is a limit to miniaturization of existing flash memories using floating gates. On the other hand, a non-volatile memory element (resistance variable memory) that uses a resistance change material as a material for the memory portion can be configured with a memory element having a simple structure composed of a resistance change element. In addition, low power consumption is expected.

  When the resistance change material is used as the material of the memory portion, for example, the resistance value is changed from a high resistance to a low resistance and from a low resistance to a high resistance by an input such as an electric pulse. In this case, it is necessary to clearly distinguish between the two values of low resistance and high resistance, and to stably change between the low resistance and the high resistance at high speed, and to hold these two values in a nonvolatile manner. . Conventionally, various proposals have been made for the purpose of stabilizing the memory characteristics and miniaturizing the memory element.

As one of such proposals, a memory cell includes a resistance change element that includes two electrodes and a recording layer sandwiched between the electrodes and is configured to reversibly change the resistance value of the recording layer. Japanese Patent Application Laid-Open No. H10-228707 discloses a memory element configured with the above. A binary transition metal oxide is used for the variable resistance element. For example, NiO, TiO ₂ , HfO, NbO ₂ , ZnO, WO ₃ and CoO are disclosed as resistance change materials. Patent Document 2 discloses oxides of transition metals such as Ni, Nb, Ti, Zr, Hf, Co, Fe, Cu, and Cr, and in particular, oxides in which oxygen is insufficient from the stoichiometric composition (hereinafter referred to as “oxide”). (Referred to as oxygen-deficient transition metal oxide) as a variable resistance material. Here, the oxygen-deficient transition metal oxide will be explained a little more. Taking hafnium as an example, in the case of hafnium, HfO ₂ is an oxide having a stoichiometric composition. This HfO ₂ contains oxygen twice as much as hafnium, which is 66.7% in terms of oxygen content. An oxide having an oxygen content lower than 66.7% is called an oxygen-deficient transition metal oxide. In this example, since it is an oxide of hafnium (Hf), it can be expressed as an oxygen-deficient hafnium oxide.

As for the upper and lower electrode materials sandwiching the variable resistance layer, for example, Patent Document 2 discloses oxides of iridium (Ir), platinum (Pt), ruthenium (Ru), tungsten (W), Ir and Ru. Titanium (Ti) nitride, polysilicon, and the like are disclosed. Furthermore, Patent Document 3 discloses a nonvolatile memory element using Pt, Ir, osmium (Os), Ru, rhodium (Rh), palladium (Pd), Ti, cobalt (Co), W, or the like as an electrode material. Has been.
JP 2005-317976 A JP 2006-140464 A JP 2006-344875 A

  However, a memory element using an oxygen-deficient transition metal oxide as a resistance change element has a problem that its operation (specifically, rewriting characteristics) is unstable.

  An object of the present invention is to provide a nonvolatile memory element that uses an oxygen-deficient transition metal oxide as a resistance change material and has reversibly stable rewriting characteristics.

  The present inventors have intensively studied to solve the above problems. As a result, the phenomenon of resistance change in oxygen-deficient transition metal oxides depends on the relationship between the standard electrode potential of the transition metal that constitutes the oxygen-deficient transition metal oxide and the standard electrode potential of the material that constitutes the electrode. I got the knowledge to do. Note that the above-mentioned prior art documents do not show any knowledge, data, or the like regarding the dependence of the resistance change phenomenon on the electrode material in the oxygen-deficient transition metal oxide, the stability of the resistance change, etc.

The present invention has been made on the basis of the above-described knowledge, and is interposed between the first electrode, the second electrode, the first electrode and the second electrode, and according to an electrical signal applied between the two electrodes. An oxygen-deficient transition metal oxide whose resistance value reversibly changes (AOx when the transition metal is A), and at least one of the first electrode and the second electrode. The standard electrode potential of one electrode (however, the materials constituting this electrode excluding Ag, Au, Ir, Pt, Ru, Ti, and W) are E _E , and the standard electrode potential of the transition metal A is E _T Then, E _E and E _T satisfy E _E −E _T ≧ 0.34 eV.

More preferably, E _E and E _T satisfy E _E −E _T ≧ 1.12 eV.

The transition metal A is preferably hafnium, and E _E and E _T preferably satisfy E _E −E _T ≧ 0.95 eV.

More preferably, the transition metal A is hafnium, and E _E and E _T satisfy E _E −E _T ≧ 1.65 eV.

Preferably, the transition metal A is tantalum, and E _E and E _T satisfy E _E −E _T ≧ 0.34 eV.

  At least one of the first electrode and the second electrode may be made of Cu.

  At least one of the first electrode and the second electrode may be made of Ni.

  The resistance change layer preferably increases and decreases its resistance value by applying electrical pulses having different polarities as the electrical signal between the first electrode and the second electrode.

  The present invention is configured as described above, and has an effect of providing a nonvolatile memory element having reversibly stable rewriting characteristics.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the element which is the same or it corresponds through all the figures, and the description may be abbreviate | omitted.

(Examination of resistance change site)
Before describing the embodiment, the examination of the resistance change part important for understanding the present invention will be described.

  The present inventors first decided to examine the resistance change site in order to grasp the correlation between the electrode and the oxide of the oxygen-deficient transition metal. And the non-volatile memory element for the examination was produced, and the electrical property was investigated.

  FIG. 1 is a schematic diagram showing a cross section of a nonvolatile memory element for examining resistance change sites. In the nonvolatile memory element 100, as shown in FIG. 1, two electrodes 101 to 104 made of a total of four Pt were formed, two above and below an oxygen-deficient tantalum oxide layer 105 having a thickness of 100 nm. Then, an electric pulse with a voltage of +2.0 V with a pulse width of 100 nsec and an electric pulse with a voltage of −1.5 V with a pulse width of 100 nsec were applied to the electrode 101 with reference to the electrode 102. Then, the nonvolatile memory element 100 was increased in resistance when an electric pulse having a voltage of +2.0 V was applied, and decreased in resistance when an electric pulse having a voltage of −1.5 V was applied. Thus, the resistance value between four electrodes was measured in each of the high resistance state and the low resistance state. Specifically, between the electrode 101 and the electrode 103, between the electrode 101 and the electrode 104, between the electrode 102 and the electrode 103, between the electrode 102 and the electrode 104, between the electrode 103 and the electrode 104, Each resistance value was measured. Then, the above measurement was repeated 10 times. These measured resistance values are summarized in Table 1.

  As shown in Table 1, a change in the resistance value was observed only in the portion related to the electrode 101, and the result that the resistance value hardly changed in the place where the electrode 101 was not involved was obtained. From this, it can be seen that the resistance change occurred only in the vicinity of the electrode 101 when a voltage was applied between the electrode 101 and the electrode 102.

  From the above, it can be said that the resistance change in the resistance change element using the oxygen-deficient tantalum oxide for the resistance change layer is only in the portion near the electrode in the oxygen-deficient tantalum oxide layer 105. Further, when the resistance is increased, it is considered that the vicinity of the electrode on the side having a high potential causes a resistance change (in this case, when the resistance is increased, the electrode 101 has a higher resistance than the electrode 102). Voltage is applied).

(First embodiment)
The first embodiment of the present invention exemplifies a nonvolatile memory element using an oxygen-deficient tantalum oxide as an oxygen-deficient transition metal oxide constituting the resistance change layer.

[Constitution]
FIG. 2 is a cross-sectional view showing the configuration of the nonvolatile memory element according to the first embodiment of the present invention.

  As shown in FIG. 2, the nonvolatile memory element 200 of the present embodiment is formed on a substrate 201, an insulating layer 202 made of an oxide layer formed on the substrate 201, and the insulating layer 202. A lower electrode layer (first electrode) 203; an upper electrode layer (second electrode) 205; and an oxygen-deficient tantalum oxide layer 204 as a resistance change layer sandwiched between the lower electrode layer 203 and the upper electrode layer 205. ing.

  The standard electrode potential of at least one of the upper electrode layer 205 and the lower electrode layer 203 satisfies a specific relationship with the standard electrode potential of tantalum Ta constituting the oxygen-deficient tantalum oxide. This will be described in detail later. The other electrode layers 203 and 205 are not particularly limited with respect to this specific relationship.

When the nonvolatile memory element 200 is driven, a voltage satisfying a predetermined condition is applied between the lower electrode layer 203 and the upper electrode layer 205 by an external power source.
[Production method]
Next, a method for manufacturing the nonvolatile memory element 200 of the present embodiment will be described.
First, an insulating layer 202 including an oxide layer having a thickness of 200 nm is formed over a substrate 201 that is single crystal silicon by a thermal oxidation method. Then, a metal thin film with a thickness of 100 nm as the lower electrode layer 203 is formed on the insulating layer 202 by a sputtering method.

Next, an oxygen-deficient tantalum oxide layer 204 was deposited on the lower electrode layer 203 to a thickness of 30 nm. Here, the oxygen-deficient tantalum oxide was formed by sputtering a Ta target in Ar and O ₂ gas. In this embodiment mode, since a sputtering apparatus different from the metal thin film used as the lower electrode layer 203 and the oxygen-deficient tantalum oxide layer is used, the substrate 201 is temporarily placed in the atmosphere after the lower electrode layer 203 is formed. And introduced into a sputtering apparatus for depositing oxygen-deficient tantalum oxide. Specific sputtering conditions for depositing the oxygen-deficient tantalum oxide are such that the degree of vacuum (back pressure) in the sputtering apparatus before starting sputtering is about 7 × 10 ⁻⁴ Pa, and the power during sputtering is The total gas pressure of 250 W, argon gas and oxygen gas was 3.3 Pa, the partial pressure ratio of oxygen gas was 3.8%, the set temperature of the substrate was 30 ° C., and the film formation time was 7 minutes. As a result, an oxygen-deficient tantalum oxide layer 204 having an oxygen content of about 58% was deposited to 30 nm.

  Thereafter, the substrate 201 was once taken out again into the atmosphere, and then introduced into another sputtering apparatus for forming the upper electrode 205. Then, a metal thin film having a thickness of 150 nm was formed as the upper electrode layer 205 on the oxygen-deficient tantalum oxide layer 204 by a sputtering method.

  Through the above process, a nonvolatile memory element 200 in which the upper and lower sides of an oxygen-deficient tantalum oxide were sandwiched between metal thin films was produced.

(Second Embodiment)
The second embodiment of the present invention exemplifies a nonvolatile memory element using oxygen-deficient hafnium oxide as the oxygen-deficient transition metal oxide constituting the resistance change layer.
[Constitution]
FIG. 3 is a cross-sectional view showing a configuration of a nonvolatile memory element according to the second embodiment of the present invention.

  As shown in FIG. 3, the nonvolatile memory element 400 of this embodiment is formed on a substrate 401, an insulating layer 402 made of an oxide layer formed on the substrate 401, and the insulating layer 402. A lower electrode layer (first electrode) 403; an upper electrode layer (second electrode) 405; and an oxygen-deficient hafnium oxide layer 404 as a resistance change layer sandwiched between the lower electrode layer 403 and the upper electrode layer 405. ing.

  The standard electrode potential of at least one of the upper electrode layer 405 and the lower electrode layer 403 satisfies a specific relationship with the standard electrode potential of hafnium Hf constituting the oxygen-deficient hafnium oxide. This will be described in detail later. The other electrode layers 403 and 405 are not particularly limited with respect to this specific relationship.

When driving the nonvolatile memory element 400, a voltage satisfying a predetermined condition is applied between the lower electrode layer 403 and the upper electrode layer 405 by an external power source.
[Production method]
First, an insulating layer 402 including an oxide layer having a thickness of 200 nm is formed over a substrate 401 that is single crystal silicon by a thermal oxidation method. Then, a metal thin film with a thickness of 100 nm as the lower electrode layer 403 is formed on the insulating layer 402 by a sputtering method.

Next, an oxygen-deficient hafnium oxide layer 404 was deposited on the lower electrode layer 403 by 30 nm. Here, the oxygen-deficient hafnium oxide was formed by sputtering an Hf target in Ar and O ₂ gases. In this embodiment mode, since a sputtering apparatus different from the metal thin film used as the lower electrode layer 403 and the oxygen-deficient hafnium oxide layer is used, the substrate 401 is once placed in the atmosphere after the lower electrode layer 403 is formed. And introduced into a sputtering apparatus for depositing oxygen-deficient hafnium oxide. The specific sputtering conditions for depositing the oxygen-deficient hafnium oxide are that the degree of vacuum (back pressure) in the sputtering apparatus before starting sputtering is about 1 × 10 ⁻⁵ Pa, and the power during sputtering is The total gas pressure of 300 W, argon gas and oxygen gas combined was 0.7 Pa, the partial pressure ratio of oxygen gas was 2.5%, the set temperature of the substrate was 30 ° C., and the film formation time was 3.5 minutes. As a result, an oxygen-deficient hafnium oxide layer 404 having an oxygen content of about 57% was deposited to 30 nm.

  Thereafter, the substrate 401 was once again taken out into the atmosphere and then introduced into another sputtering apparatus for forming the upper electrode 405. Then, a 150 nm thick metal thin film was formed as the upper electrode layer 405 on the oxygen-deficient hafnium oxide layer 404 by a sputtering method.

Through the above process, a nonvolatile memory element 400 in which the upper and lower sides of an oxygen-deficient hafnium oxide were sandwiched between metal thin films was manufactured.
(Study on suitable electrode materials)
With respect to the nonvolatile memory elements according to the first and second embodiments fabricated as described above, the ease of resistance change when the electrode material was changed in various ways was evaluated. In this study, two types of oxygen-deficient transition metal oxides, oxygen-deficient tantalum oxide and oxygen-deficient hafnium oxide, are used as the oxygen-deficient transition metal oxide, and the lower electrodes 203 and 403 are made of tungsten. (W), the materials of the upper electrodes 205 and 405 were changed to a plurality of types of materials shown in Tables 2 and 3. Table 2 shows the case where tantalum oxide is used as the transition metal oxide, and Table 3 shows the case where hafnium oxide is used as the transition metal oxide. Here, the oxygen-deficient transition metal oxide means that when the transition metal is A and the oxide is AOx, x is represented by a non-stoichiometric ratio, and oxygen is insufficient from the stoichiometric composition. Oxide. About the above, the state of resistance change was investigated. In the measurement of the resistance change of the nonvolatile memory element in Table 2 (first embodiment), the voltage of the electric pulse when the resistance is changed varies slightly depending on the sample, but the lower electrode 203 is used as a reference. The voltage when the resistance of the upper electrode 205 is increased is +1.8 to +2.5 V, 100 nsec, and the voltage when the resistance is decreased is -1.3 to -1.6 V, an electric voltage of 100 nsec. Pulses were applied alternately. In the measurement of the resistance change of the nonvolatile memory element in Table 3 (second embodiment), the voltage of the electric pulse when the resistance is changed varies slightly depending on the sample, but the lower electrode 403 is used as a reference. When the resistance of the upper electrode 405 is increased, the voltage is +1.6 to +1.9 V and 100 nsec, and when the resistance is decreased, the voltage is −1.1 to −1.3 V and an electric voltage of 100 nsec. Pulses were applied alternately. Here, the reason why the material of the lower electrodes 203 and 403 is fixed to W is that W is relatively hardly oxidized, is a stable material, and is relatively easy to process.

  These individual measurement results are shown in FIGS. These measurement results are collectively shown in FIG.

  FIG. 4 is a graph showing the correlation between the difference in the standard electrode potential of the electrode material with respect to the standard electrode potential of the transition metal constituting the oxygen-deficient transition metal oxide and the resistance change of the oxygen-deficient transition metal oxide. FIGS. 5 to 13 are diagrams showing a change in resistance with respect to the number of electric pulses applied in a nonvolatile memory element using an oxygen-deficient tantalum oxide. 14 to 20 are diagrams showing a change in resistance with respect to the number of electric pulses applied in a nonvolatile memory element using oxygen-deficient hafnium oxide.

  5 to 13 show non-volatile memory elements Ta-A (platinum), Ta-B (iridium), Ta-C (silver), Ta-D (copper), and Ta-E (nickel) shown in Table 2, respectively. ), Ta-F (tungsten), Ta-G (tantalum), Ta-H (titanium), and Ta-I (aluminum). 14 to 20 show the nonvolatile memory elements Hf-A (platinum), Hf-B (copper), Hf-C (tungsten), Hf-D (tantalum), and Hf-E shown in Table 3, respectively. The measurement results for (hafnium), Hf-F (titanium), and Hf-G (aluminum) are shown.

As shown in FIG. 4, when the standard electrode potential of the electrode material is E _E and the standard electrode potential of the transition metal of the oxygen-deficient transition metal oxide is E _T , an electrode material satisfying E _E −E _T ≦ 0 is obtained. The element used did not show a resistance change phenomenon.

  That is, as shown in FIGS. 4, 11, 12, and 13, among elements using oxygen-deficient tantalum oxide, element Ta-G using Ta for the upper electrode and Ti for the upper electrode were used. In the element Ta-H and the element Ta-I using Al as the upper electrode, no resistance change phenomenon was observed.

  Similarly, as shown in FIGS. 4, 18, 19, and 20, among elements using oxygen-deficient hafnium oxide, element Hf-E using Hf for the upper electrode and Ti for the upper electrode are used. In the device Hf-F and the device Hf-G using Al as the upper electrode, no resistance change phenomenon was observed.

Conversely, for a nonvolatile memory element using an electrode material that satisfies E _E -E _T > 0, when a positive and negative voltage is applied alternately, the resistance value changes to repeat at low resistance and high resistance, It was confirmed that it has a function of a nonvolatile memory element.

  Next, the stability of the resistance change of the nonvolatile memory element that exhibits these resistance changes will be considered.

As shown in FIGS. 4 and 10, among the elements using oxygen-deficient tantalum oxide, the element Ta-F using W (E _E −E _T = 0.7 eV) for the upper electrode has a slight resistance. There was a change, but the change was small. On the other hand, as shown in FIG. 4 and FIG. 8, for the element Ta-D (E _E -E _T = 1.12 eV) using Cu for the upper electrode, when positive and negative voltages are alternately applied, There is a change of the resistance value of one digit or more and the number of times of 20 times or more, and the resistance changes stably. Also, as shown in FIGS. 4, 5, 6, and 7, an element Ta—C using Ag for the upper electrode (E _E− E _T = 1.40 eV) and an element using Pt for the upper electrode For Ta-A (E _E -E _T = 1.78 eV) and the element Ta-B using Ir as the upper electrode (E _E -E _T = 1.77 eV), when positive and negative voltages are alternately applied, There is a change in the resistance value of one digit or more in the change width and 20 or more times in the number of times, and the resistance changes stably.

Also, as shown in FIGS. 4 and 17, among the elements using oxygen-deficient hafnium oxide, the element Hf-D (E _E -E _T = 0.95 eV) using Ta for the upper electrode is slightly The resistance change was observed, but the change width was small. On the other hand, as shown in FIGS. 4 and 16, for the element Hf-C (E _E −E _T = 1.65 eV) using W as the upper electrode, when the positive and negative voltages are alternately applied, There is a change of the resistance value of one digit or more and the number of times of 20 times or more, and the resistance changes stably. Also, as shown in FIGS. 4, 14, and 15, a device Hf-B (E _E −E _T = 2.07 eV) using Cu for the upper electrode and a device Hf− using Pt for the upper electrode. For A (E _E -E _T = 2.73 eV), when positive and negative voltages are alternately applied, there is a change in the resistance value of one digit or more in the change width and 20 or more times in the number of changes, and the resistance change stably. is doing.

Here, referring to FIG. 4 and FIG. 11, among the elements using oxygen-deficient tantalum oxide, the element Ta-G (E _E -E _T = 0 eV) using Ta as the upper electrode has no resistance change. While no phenomenon was observed, referring to FIGS. 4 and 9, a slight resistance change was observed in the element Ta-E (E _E −E _T = 0.34 eV) using Ni as the upper electrode. From this, it is considered that it is necessary for the element using the oxygen-deficient tantalum oxide to satisfy the condition of E _E −E _T ≧ 0.34 eV in order to perform the resistance changing operation.

4 and 10, in the element Ta-F (E _E -E _T = 0.7 eV) using W for the upper electrode, a slight resistance change was observed, but the change width was small. On the other hand, referring to FIG. 4 and FIG. 8, for the element Ta-D (E _E -E _T = 1.12 eV) using Cu as the upper electrode, when positive and negative voltages are alternately applied as described above. Since the resistance value changes by one digit or more in the change width and 20 times or more in the number of times, in order for the element using the oxygen-deficient tantalum oxide to stably perform the resistance changing operation, E _E -E It is considered necessary to satisfy the condition of _T ≧ 1.12 eV.

4 and 18, among the elements using oxygen-deficient hafnium oxide, in the element Hf-E (E _E -E _T = 0 eV) using Hf for the upper electrode, there is no resistance change phenomenon. 4 and FIG. 17, in the element Hf-D (E _E -E _T = 0.95 eV) using Ta as the upper electrode, a slight resistance change is caused as described above. Therefore, it is considered that it is necessary for the element using the oxygen-deficient hafnium oxide to satisfy the condition of E _E −E _T ≧ 0.95 eV in order to perform the resistance change operation.

Further, referring to FIG. 4 and FIG. 17, in the element Hf-D (E _E -E _T = 0.95 eV) using Ta for the upper electrode, a slight resistance change was observed as described above, but the change was observed. 4 and 16, when the element Hf-C (E _E -E _T = 1.65 eV) using W as the upper electrode is used, the positive and negative voltages are alternately switched as described above. In order for the element using the oxygen-deficient hafnium oxide to perform a resistance change operation stably, the resistance value changes by one digit or more in the change width and 20 times or more in the number of changes. It is considered necessary to satisfy the condition of E _E −E _T ≧ 1.65 eV.

  Next, the transition resistance standard for oxygen-deficient transition metal oxides is summarized by combining the resistance change of elements using oxygen-deficient tantalum oxide and the resistance change of elements using oxygen-deficient hafnium oxide. The correlation between the difference in the standard electrode potential of the electrode material with respect to the electrode potential and the resistance change of the oxygen-deficient transition metal oxide is considered.

  As shown in FIG. 4, when the resistance change of the oxygen-deficient transition metal oxide is plotted against the difference in the standard electrode potential of the electrode material with respect to the standard electrode potential of the transition metal constituting the oxygen-deficient transition metal oxide, There is a good correlation between the two. That is, the resistance change occurs when the electrode is made of a material having a higher standard electrode potential than Ta and Hf which are transition metals constituting the resistance change film, and the resistance change is less likely to occur with a lower material. I understand. It can be seen that the resistance change is more likely to occur as the difference in the standard electrode potential of the electrode material with respect to the standard electrode potential of the transition metal is larger, and the resistance change is less likely to occur as the difference becomes smaller. In general, the standard electrode potential is one index of the ease of oxidation. If this value is large, it means that it is difficult to oxidize, and if it is small, it means that it is easily oxidized. From this, it is presumed that the ease of oxidation plays a major role in the mechanism of the resistance change phenomenon.

  According to the mechanism of this resistance change phenomenon, this examination result is universalized and applied to oxygen-deficient transition metal oxides and electrode materials other than the oxygen-deficient transition metal oxides and electrode materials examined here. be able to.

Then, in order for the element using the oxygen-deficient transition metal oxide to perform the resistance changing operation, it is considered necessary to satisfy the condition of E _E −E _T ≧ 0.34 eV.

In addition, in order for a device using an oxygen-deficient transition metal oxide to stably perform a resistance change operation, it is considered necessary to satisfy the condition of E _E −E _T ≧ 1.12 eV.

[Example 1]
According to the mechanism of the resistance change phenomenon described above, when a voltage is applied to the nonvolatile memory element, the oxidation reaction occurs on the anode side, that is, on the higher potential side. Therefore, in order to more easily cause a resistance change, an electrode using a standard electrode potential higher than the electrode potential of the transition metal of the oxygen-deficient transition metal oxide needs to be disposed on the anode. Therefore, in this example, in the first embodiment, the upper electrode layer 205 is made of Pt (E _E −E _T = 1.73 eV). The resistance change layer 204 is made of an oxygen-deficient tantalum oxide.

  The resistance change with respect to the number of electric pulses applied in the nonvolatile memory element of Example 1 configured as described above is shown in FIG. The resistance change in FIG. 5 is based on the lower electrode 403, and an electric pulse of +2.5 V with a pulse width of 100 nsec and an electric pulse of −1.5 V with a pulse width of 100 nsec are alternately applied to the upper electrode 405. And applied to the measurement. In this case, the resistance value is about 600Ω when an electric pulse of + 2.5V is applied, and is stably changed to 60Ω when an electric pulse of −1.5V is applied.

[Example 2]
In this example, the upper electrode layer 405 is made of Cu in the second embodiment. That is, oxygen-deficient hafnium oxide was used as the material of the resistance change layer 404, and Cu (E _E -E _T = 2.07 eV) was used as the material of the upper electrode layer 405. Such a nonvolatile memory element (Hf-B) stably changes its resistance as described above. In addition, since Cu has a good affinity with a semiconductor process, the oxygen-deficient hafnium oxide memory element using Cu as the upper electrode is a promising candidate for a nonvolatile memory element.

  The state of the resistance change is shown in FIG. The resistance change in FIG. 15 is based on the lower electrode 403. The electric pulse of + 1.9V with a pulse width of 100 nsec and the electric pulse of −1.3V with a pulse width of 100 nsec are alternately applied to the upper electrode 405. And applied to the measurement. In this case, the resistance value is about 1000Ω when an electric pulse of + 1.9V is applied, and 200Ω when an electric pulse of −1.3V is applied.

[Example 3]
In Example 1, an electrode using a standard electrode potential higher than the electrode potential of the transition metal of the oxygen-deficient transition metal oxide was disposed on the anode. However, considering the manufacturing process of the nonvolatile memory element, it is easier to manufacture the lower electrode layers 203 and 403 and the upper electrode layers 205 and 405 made of the same material. Therefore, in this example, in the first and second embodiments, both the anode and the cathode, that is, the lower electrode layers 203 and 403 and the upper electrode layers 205 and 405 are combined with an oxygen-deficient transition metal oxide. Made of the same material used having a standard electrode potential higher than that of the transition metal. However, as it is, the electrode that behaves as an anode is not specified, and the resistance change may become unstable. Therefore, in the oxygen-deficient transition metal oxide layers 204 and 404 that are resistance change layers, the oxygen concentration is distributed so that the oxygen concentration is higher toward the side closer to the electrode that should act as the anode (for example, the upper electrode layers 205 and 405). Was held. Since the oxygen-deficient transition metal oxide layers 204 and 404 can have an oxygen concentration distribution by a known method, the description thereof is omitted.

  With such a configuration, it is possible to obtain a non-volatile memory element that exhibits stable resistance change with the upper electrode layers 205 and 405 as anodes and is easy to manufacture.

  The nonvolatile memory element of the present invention is capable of high-speed operation and has stable rewriting characteristics, and is nonvolatile for use in various electronic devices such as digital home appliances, memory cards, portable telephones, and personal computers. It is useful as a memory element.

It is a schematic diagram which shows the cross section of the non-volatile memory element for resistance change site | part examination. It is sectional drawing which showed the structure of the non-volatile memory element which concerns on the 1st Embodiment of this invention. It is sectional drawing which showed the structure of the non-volatile memory element which concerns on the 2nd Embodiment of this invention. It is a graph which shows the correlation with the difference of the standard electrode potential of the electrode material with respect to the standard electrode potential of the transition metal which comprises oxygen-deficient transition metal oxide, and the resistance change of oxygen-deficient transition metal oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when Pt is used for the upper electrode in the non-volatile memory element using oxygen-deficient tantalum oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when Ir is used for the upper electrode in the non-volatile memory element using oxygen-deficient tantalum oxide. It is a figure which shows resistance change with respect to the frequency | count of an electric pulse applied when Ag is used for an upper electrode in the non-volatile memory element using an oxygen deficient tantalum oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when using Cu for an upper electrode in the non-volatile memory element using an oxygen deficient tantalum oxide. It is a figure which shows the resistance change with respect to the frequency | count of the application of an electric pulse when using Ni for an upper electrode in the non-volatile memory element using an oxygen deficient tantalum oxide. It is a figure which shows the resistance change with respect to the frequency | count of the application of an electric pulse when W is used for the upper electrode in the non-volatile memory element using an oxygen deficient tantalum oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when Ta is used for the upper electrode in the non-volatile memory element using oxygen-deficient tantalum oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when Ti is used for the upper electrode in the non-volatile memory element using oxygen-deficient tantalum oxide. FIG. 5 is a diagram showing a change in resistance with respect to the number of electric pulses applied when Al is used for an upper electrode in a nonvolatile memory element using an oxygen-deficient tantalum oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when Pt is used for the upper electrode in the non-volatile memory element using oxygen-deficient hafnium oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when Cu is used for an upper electrode in the non-volatile memory element using oxygen-deficient hafnium oxide. It is a figure which shows the resistance change with respect to the frequency | count of the application of an electrical pulse when W is used for the upper electrode in the non-volatile memory element using oxygen-deficient hafnium oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when Ta is used for the upper electrode in the non-volatile memory element using oxygen-deficient hafnium oxide. It is a figure which shows resistance change with respect to the frequency | count of application of an electric pulse when Hf is used for an upper electrode in a nonvolatile memory element using oxygen-deficient hafnium oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when Ti is used for the upper electrode in the non-volatile memory element using oxygen-deficient hafnium oxide. It is a figure which shows resistance change with respect to the frequency | count of the application of an electric pulse when Al is used for the upper electrode in the non-volatile memory element using oxygen-deficient hafnium oxide.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Nonvolatile memory element for resistance change examination 101 1st electrode 102 2nd electrode 103 3rd electrode 104 4th electrode 105 Oxygen deficient tantalum oxide layer 200, 400 Nonvolatile memory element 201, 401 Substrate 202, 402 Insulation Layers 203 and 403 Lower electrode layer 204 Resistance change layer (oxygen-deficient tantalum oxide layer)
205, 405 Upper electrode layer 404 Resistance change layer (oxygen-deficient hafnium oxide layer)

Claims (8)

An oxygen-deficient transition that intervenes between the first electrode, the second electrode, the first electrode, and the second electrode, and whose resistance value reversibly changes according to an electrical signal applied between the two electrodes. A variable resistance layer containing a metal oxide (AOx when the transition metal is A),
At least one of the first electrode and the second electrode (hereinafter referred to as a specific electrode (however, the material constituting the specific electrode excludes Ag, Au, Ir, Pt, Ru, Ti, and W)) When the standard electrode potential is E _E and the standard electrode potential of the transition metal A is E _T , E _E and E _T are
A non-volatile memory element that satisfies E _E −E _T ≧ 0.34 eV. E _E and E _T are
The nonvolatile memory element according to claim 1, wherein E _E −E _T ≧ 1.12 eV is satisfied. The transition metal A is hafnium;
E _E and E _T are
The nonvolatile memory element according to claim 1, wherein E _E −E _T ≧ 0.95 eV is satisfied. E _E and E _T are
The nonvolatile memory element according to claim 3, wherein E _E −E _T ≧ 1.65 eV is satisfied. The transition metal A is tantalum;
E _E and E _T are
The nonvolatile memory element according to claim 1, wherein E _E −E _T ≧ 0.34 eV is satisfied.   The nonvolatile memory element according to claim 1, wherein the specific electrode is made of Cu.   The nonvolatile memory element according to claim 1, wherein the specific electrode is made of Ni.   2. The nonvolatile layer according to claim 1, wherein a resistance value of the variable resistance layer increases or decreases by applying an electric pulse having different polarities as the electric signal between the first electrode and the second electrode. Memory element.

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