Resistive change type nonvolatile memory element and resistive change type nonvolatile memory device using the same

Abstract

The present application relates to a resistance change type nonvolatile memory element and a resistance change type nonvolatile memory device using the same. A resistance change type nonvolatile memory element (20) includes a first electrode (2), a second electrode (4), and a resistance change layer (3) interposed between the first electrode (2) and the second electrode (4) and reversibly changes a resistance value based on an electric signal applied between the electrodes. The resistance change layer (3) includes a first resistance change layer (3c) composed of a first metal oxide of an oxygen deficiency type formed of a first metal element and oxygen and a second resistance change layer (3d) formed of the first metal element, a second metal element different from the first metal element, and oxygen and composed of a complex oxide different in oxygen deficiency degree from the first metal oxide. The complex oxide has a smaller oxygen deficiency degree than the first metal oxide, and has a smaller oxygen diffusion coefficient at room temperature than a second metal oxide formed of the first metal element and oxygen and having an oxygen deficiency degree equal to that of the complex oxide.

Description

TECHNICAL FIELD

[0001] The present application relates to a resistance change type nonvolatile memory element whose resistance value changes in correspondence with an applied electric signal, and a resistance change type nonvolatile memory device using the same. BACKGROUND

[0002] In recent years, with the progress of digital technology, electronic devices such as portable information devices and information home appliances have been further highly functionalized. With the high functionalization of these electronic devices, the miniaturization and high speed of semiconductor elements used therefor are rapidly progressing. Among them, the use of a large capacity nonvolatile memory typified by a flash memory is rapidly expanding.

[0003] Further, as a next-generation novel nonvolatile memory to replace the flash memory, research and development of a resistance change type nonvolatile memory device using a so-called resistance change element are being conducted. The resistance change element refers to an element having a property that a resistance value reversibly changes in correspondence with an electric signal, and further capable of nonvolatilely storing information corresponding to the resistance value (for example, see Patent Document 1).

[0004] As a prior art in which such a resistance change element operates, for example, a nonvolatile resistance change element using a perovskite material such as Pr (1-x) Ca x MnO3[PCMO], LaSrMnO3[LSMO], GdBaCo x O y [GBCO], a transition metal oxide such as NiO (nickel oxide), V2O (vanadium oxide), ZnO (zinc oxide), Nb2O5 (niobium oxide), TiO2 (titanium oxide), WO3 (tungsten oxide), or CoO (cobalt oxide) is proposed. This technology is a technology in which an oxide material is applied with a voltage pulse which is a wave-like voltage having a short duration, and the resistance value is increased or decreased, and data is stored in correspondence with the changed resistance value (for example, see Patent Document 2).

[0005] PRIOR ART DOCUMENTS

[0006] PATENT DOCUMENTS

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-363604

[0008] Patent Document 2: U.S. Patent No. 6204139 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] In view of the future increase in capacity of nonvolatile memory, there is a demand for reducing the operating power or operating current of nonvolatile memory elements. However, it is known that nonvolatile memory elements including a resistance change element generally have deteriorated data retention characteristics as the operating current is reduced. Here, the data retention characteristics refer to characteristics indicating to what extent information recorded in a nonvolatile memory element can be recorded stably for a long time in a state where the power is later turned off, and are characteristics indicating "non-volatility", and thus are one of the most important characteristics in nonvolatile memory.

[0011] The present application was completed in view of the above-described circumstances, and a main object thereof is to provide a resistance change type nonvolatile memory element capable of stably storing information for a long time and a resistance change type nonvolatile memory device using the same.

[0012] Means for solving the problem

[0013] To solve the above-described problem, the resistance change type nonvolatile memory element of the present application includes a first electrode, a second electrode, and a resistance change layer, the resistance change layer being interposed between the first electrode and the second electrode and reversibly changing a resistance value based on an electric signal applied between the two electrodes, wherein the resistance change layer includes a first resistance change layer composed of a first metal oxide of an oxygen deficiency type, the first metal oxide being formed of a first metal element and oxygen, and a second resistance change layer formed of the first metal element, a second metal element different from the first metal element, and oxygen, and composed of a composite oxide of an oxygen deficiency degree different from that of the first metal oxide, the composite oxide having a smaller oxygen diffusion coefficient at room temperature than a second metal oxide formed of the first metal element and oxygen and having an oxygen deficiency degree equal to that of the composite oxide.

[0014] In addition, the resistance change type nonvolatile memory device of the present application includes a memory cell array formed on a substrate and a voltage application circuit, wherein the memory cell array includes a plurality of the resistance change type nonvolatile memory elements arranged in a matrix, and the voltage application circuit performs data writing and erasing and data reading with respect to a prescribed resistance change type nonvolatile memory element.

[0015] Effects of the Invention

[0016] The resistance change type nonvolatile memory element and the resistance change type nonvolatile memory device using the same according to the present application can stably store information for a long time. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1A is a schematic view showing one example of the configuration of a resistance change element of the related art.

[0018] Figure 1B is a schematic view showing one example of the configuration of a resistance change element of Embodiment 1.

[0019] Figure 2 (a) to (e) are process sectional views showing one example of a manufacturing method of a resistance change element of Embodiment 1.

[0020] Figure 3 is a schematic view showing one example of the circuit configuration for operating a resistance change element of Embodiment 1.

[0021] Figure 4 is a schematic view showing a change in the resistance value of a resistance change layer of Embodiment 1.

[0022] Figure 5 is a schematic view showing one example of the circuit configuration for operating a resistance change element of Embodiment 1.

[0023] Figure 6A is a cross-sectional schematic view of a resistance change element of the related art in a low resistance state.

[0024] Figure 6B is a cross-sectional schematic view of a resistance change element of the related art in a high resistance state.

[0025] Figure 6C is a cross-sectional schematic view of a resistance change element of Embodiment 1 in a low resistance state.

[0026] Figure 6D is a cross-sectional schematic view of a resistance change element of Embodiment 1 in a high resistance state.

[0027] Figure 7A is a graph showing the results of resistance change voltage evaluation of Embodiment 1.

[0028] Figure 7B is a graph showing the results of data retention characteristic evaluation of Embodiment 1.

[0029] Figure 8 is a block diagram showing one example of the configuration of a nonvolatile memory device of Embodiment 2.

[0030] Figure 9 is a block diagram showing one example of the configuration of a nonvolatile memory device of Embodiment 3. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the present application will be described with reference to the accompanying drawings. In addition, each of the embodiments described hereinafter shows one specific example of implementation. Therefore, numerical values, shapes, materials, component elements, arrangement positions and connection modes of component elements, steps, orders of steps, and the like indicated in the following embodiments are one example, and do not limit the gist of the present application. The present application is only limited by the claims.

[0032] For the component elements among the component elements in the following embodiments which are not recited in the independent claims indicating the highest concept of the present application, it will be described as the component elements which are not essential to achieve the problem of the present application but constitute a mode which can be adopted.

[0033] The present inventors have made intensive studies in order to improve the data retention life of a resistance change type nonvolatile memory element, and as a result, have obtained a resistance change type nonvolatile memory element whose data retention characteristics are improved compared to the past. Hereinafter, the resistance change type nonvolatile memory element will be simply referred to as a resistance change element for the sake of brevity.

[0034] The resistance change element has a first electrode, a second electrode, and a resistance change layer formed of a metal oxide, the resistance change layer being sandwiched between the first electrode and the second electrode and reversibly changing a resistance value based on an electric signal applied between the two electrodes. The resistance change layer is composed of a laminated structure of a first resistance change layer and a second resistance change layer, the second resistance change layer being composed in such a manner that a second metal element is contained in addition to a first metal element and oxygen which constitute the first resistance change layer. By using a material which contributes to a reduction in the oxygen diffusion coefficient in the second resistance change layer as the second metal element, a resistance change element whose data retention characteristics are improved compared to the past is obtained.

[0035] Hereinafter, the details of the resistance change element will be described together with the embodiments as appropriate.

[0036] (Embodiment 1)

[0037] (Structure of resistance change element)

[0038] First, one example of the structure of the resistance change element of Embodiment 1 will be described while comparing with the structure of the resistance change element in the related art.

[0039] Figure 1A is a schematic view showing one example of the structure of the resistance change element in the related art.

[0040] Figure 1B is a schematic view showing one example of the structure of the resistance change element of Embodiment 1.

[0041] As Figure 1A、 Figure 1B As shown in FIG. 1, the resistance change element 10 of the related art and the resistance change element 20 of the present embodiment each include a substrate 1, a first electrode 2 formed on the substrate 1, a resistance change layer 3 formed on the first electrode 2, and a second electrode 4 formed on the resistance change layer 3. Here, the first electrode 2 and the second electrode 4 are electrically connected to the resistance change layer 3.

[0042] Further, the first electrode 2 can be different in size from the second electrode 4, or can be the same in size. In addition, the first electrode 2, the second electrode 4, and the resistance change layer 3 can be arranged in the reverse order, or can be arranged in the lateral direction.

[0043] The substrate 1 is composed of, for example, a silicon substrate on which a circuit element such as a transistor is formed. In addition, the first electrode 2 and the second electrode 4 are composed of, for example, one or more of Au (gold), Pt (platinum), Ir (iridium), Cu (copper), W (tungsten), TaN (tantalum nitride), and TiN (titanium nitride).

[0044] In the case of the resistance change element 10, the resistance change layer 3 is composed of a metal oxide. As one example, the resistance change layer 3 in the resistance change element 10 has a structure in which a first tantalum oxide layer 3a as a first resistance change layer and a second tantalum oxide layer 3b as a second resistance change layer are stacked. The oxygen content ratio of the second tantalum oxide layer 3b is higher than that of the first tantalum oxide layer 3a.

[0045] Here, the "oxygen content ratio" refers to the ratio of the number of oxygen atoms to the total number of atoms constituting the metal oxide. For example, the oxygen content ratio of Ta2O5 is the ratio of the number of oxygen atoms to the total number of atoms (O / (Ta+O)), which is 71.4 atomic%. Thus, the oxygen content ratio of the oxygen-deficient tantalum oxide is greater than 0 and less than 71.4 atomic%.

[0046] For example, in the case where the metal constituting the first metal oxide layer and the metal constituting the second metal oxide layer are the same, the oxygen content ratio and the oxygen deficiency degree are in a corresponding relationship. That is, when the oxygen content ratio of the second metal oxide is greater than that of the first metal oxide, the oxygen deficiency degree of the second metal oxide is smaller than that of the first metal oxide.

[0047] In addition, the "oxygen deficiency degree" refers to the proportion of the oxygen that is deficient in the metal oxide to the amount of oxygen constituting the stoichiometric oxide. Further, in the case where different multiple stoichiometric oxides exist in the metal oxide, the composition of the oxide having the highest resistance value is defined as the stoichiometric composition.

[0048] Thus, the metal oxide having the stoichiometric composition defined above is more stable than the metal oxide having other compositions, and has a higher resistance value.

[0049] For example, in the case where the metal is Ta (tantalum), since the stoichiometrically composed oxide is Ta2O5, it can be expressed as TaO 2.5 TaO 2.5 The degree of oxygen deficiency of TaO 1.5 The degree of oxygen deficiency becomes a degree of oxygen deficiency = (2.5 - 1.5) / 2.5 = 40%. On the other hand, the degree of oxygen deficiency of the oxygen-excess metal oxide becomes a negative value. Furthermore, in the present specification, unless otherwise specified, the degree of oxygen deficiency is described in a manner that includes a positive value, 0, and a negative value.

[0050] The oxide having a small degree of oxygen deficiency is closer to the stoichiometrically composed oxide, and thus has a high resistivity, and the oxide having a large degree of oxygen deficiency is closer to the metal constituting the oxide, and thus has a low resistivity.

[0051] The "oxygen-deficient metal oxide" refers to a metal oxide having a smaller content of oxygen (atomic ratio: proportion of the number of oxygen atoms in the total number of atoms) than a metal oxide having a stoichiometric composition.

[0052] The "metal oxide having a stoichiometric composition" refers to a metal oxide having a degree of oxygen deficiency of 0%. For example, in the case of a tantalum oxide, it refers to Ta2O5, which is an insulator.

[0053] In contrast, the oxygen-deficient metal oxide has conductivity.

[0054] On the other hand, in the case of the resistance change element 20, the resistance change layer 3 is configured by laminating a tantalum oxide layer 3c as a first resistance change layer and a composite oxide layer 3d as a second resistance change layer. The tantalum oxide layer 3c is composed of an oxygen-deficient tantalum oxide formed of Ta and O (oxygen), and the composite oxide layer 3d is composed of an oxygen-deficient oxide formed of Ta, an additional metal element different from Ta, and O. The degree of oxygen deficiency of the composite oxide layer 3d is smaller than that of the tantalum oxide layer 3c.

[0055] Here, Ta is one example of the first metal element, and the tantalum oxide constituting the tantalum oxide layer 3c is one example of the first metal oxide. In addition, the additional metal element is one example of the second metal element, and the oxide of Ta and the additional metal element constituting the composite oxide layer 3d is one example of the composite oxide.

[0056] Furthermore, in the case of the composite oxide, depending on the kind of the additional metal element, the stoichiometric composition of the oxide is different, and thus the degree of oxygen deficiency can more generally express the amount of oxygen defects in the oxide than the oxygen content. Therefore, in the present specification, when the amount of oxygen defects in the composite oxide is particularly studied, it is described in terms of the degree of oxygen deficiency.

[0057] As for the resistance change element 10, the composition of the tantalum oxide constituting the first tantalum oxide layer 3a is set to TaOx x In this case, 0 < x < 2.5, and the composition of the tantalum oxide constituting the second tantalum oxide layer 3b is set to TaOy y In this case, it is sufficient that x < y. Particularly in the case where it is set to 0.8 < x < 1.9 and 2.1 < y < 2.5, it is possible to stably and rapidly change the resistance value of the resistance change layer 3.

[0058] If this is explained in terms of the degree of oxygen deficiency, in the case where the degree of oxygen deficiency of the tantalum oxide constituting the first tantalum oxide layer 3a is p and the degree of oxygen deficiency of the tantalum oxide constituting the second tantalum oxide layer 3b is q, it is sufficient that 0% < p < 100% and p > q. Particularly in the case where it is set to 24% < p < 68% and it is set to 0 < q < 16%, it means that it is possible to stably and rapidly change the resistance value of the resistance change layer 3.

[0059] As for the resistance change element 20 as well, in the case where the degree of oxygen deficiency of the tantalum oxide constituting the tantalum oxide layer 3c is r and the degree of oxygen deficiency of the composite oxide constituting the composite oxide layer 3d is s, it is sufficient that 0% < r < 100% and r > s. Particularly it is possible to set in the range of 24% < r < 68% and 0 < s < 16%.

[0060] The degree of oxygen deficiency of the composite oxide corresponds to the composition as described below. For example, consider the case where the composite oxide layer 3d is a composite oxide formed of Ta, Al (aluminum) as an additional metal element, and O, and the element composition ratio of Ta to Al is 1 : 1. In this case, the composition of the tantalum oxide and the aluminum oxide having the stoichiometric composition is Ta2O5and Al2O3, respectively, and thus when the composition of the composite oxide is s = 0% as the stoichiometric composition, it becomes TaAlO4, and when s = 10%, it becomes TaAlO 3.6 .

[0061] As for the thickness of the resistance change layer 3, it is confirmed that the change in the resistance value is recognized as long as it is 1 μm or less, but it can be 40 nm or less. In the case of a film thickness of 40 nm or less, it is easy to process when photolithography and etching are used as a layout process, and it is possible to reduce the voltage value of the voltage pulse required to change the resistance value of the resistance change layer 3. On the other hand, from the viewpoint of more reliably avoiding breakdown, that is, insulation breakdown, when a voltage pulse is applied, it is possible to set the thickness of the resistance change layer 3 to be at least 5 nm or more.

[0062] In addition, regarding the thickness of the composite oxide layer 3d, from the viewpoint of being able to reduce the possibility of the initial resistance value becoming excessively high and obtaining a stable resistance change, it can be set to about 1 nm to 8 nm.

[0063] Referring again to Figure 1B In the case of operating the resistance change element 20, the first electrode 2 and the second electrode 4 are electrically connected to different terminals of the power supply 5 via the terminals 7 and 8, respectively. Here, the resistance change element 20 can also be electrically connected to the power supply 5 with the protective resistance 6 interposed therebetween.

[0064] As the power supply 5, an electric pulse application device for driving the resistance change element 20 is constituted in a manner in which a voltage pulse of an electric pulse of a prescribed polarity, voltage, and time width can be applied to the resistance change element 20. The voltage pulse is applied between the first terminal 7 and the second terminal 8.

[0065] Further, the protective resistance 6 is used to prevent destruction of the resistance change element due to overcurrent, and in the present embodiment, for example, the resistance value thereof can be set to 4.5 kΩ.

[0066] Further, in the following description, the voltage of the voltage pulse applied between the two electrodes of the resistance change element 20 is specified by the potential of the second terminal 8 with the first terminal 7 as a reference. In addition, the polarity of the current when a positive voltage is applied to the second terminal 8 is defined as positive.

[0067] (Method of manufacturing resistance change element)

[0068] Next, one example of a method of manufacturing the resistance change element 20 as shown in Figure 2 will be described. Here, a case in which the composite oxide layer 3d is a composite oxide formed of Ta, Al, and O will be described.

[0069] First, as shown in Figure 2 (a), for example, a first electrode 2 formed of tantalum nitride having a thickness of 20 nm is formed on the substrate 1 by a sputtering method.

[0070] Next, as shown in Figure 2 (b), for example, a tantalum oxide layer 3c is formed on the first electrode 2 by a so-called reactive sputtering method in which a metal tantalum target is sputtered in an argon gas and an oxygen gas. Here, regarding the oxygen deficiency degree in the tantalum oxide layer 3c, it can be easily adjusted by changing the flow ratio of the oxygen gas to the argon gas. In addition, the substrate temperature can be set to room temperature without being particularly heated.

[0071] Next, as shown in Figure 2As shown in (c), a tantalum oxide target (e.g., Ta2O5) with a high oxygen content and an aluminum oxide target (e.g., Al2O3) with a high oxygen content are used, and a composite oxide layer 3d with a lower oxygen deficiency is formed, for example, by sputtering. Thus, a composite oxide layer 3d with a lower oxygen deficiency than the previously formed tantalum oxide layer 3c is formed on the surface of the tantalum oxide layer 3c.

[0072] In this way, the resistance variation layer 3 is formed using a tantalum oxide target and an aluminum oxide target by sputtering under synchronous discharge, but is not limited to this example. The resistance variation layer 3 can also be formed using a tantalum oxide target and an aluminum oxide target by sputtering under alternating stacking based on alternating discharge. Alternatively, it can be formed using a metallic tantalum target and a metallic aluminum target by reactive sputtering under an oxygen atmosphere.

[0073] Here, the oxygen-deficient tantalum oxide layer 3c and the composite oxide layer 3d correspond to the first resistance variation layer and the second resistance variation layer, respectively, and the oxygen-deficient tantalum oxide layer 3c and the composite oxide layer 3d formed in this way constitute the resistance variation layer 3. Furthermore, in this embodiment, the oxygen-deficient tantalum oxide layer 3c and the composite oxide layer 3d are in an amorphous state, but either or both of the oxygen-deficient tantalum oxide layer 3c and the composite oxide layer 3d may be in a crystalline state.

[0074] Next, as Figure 2 As shown in (d), for example, by sputtering in Figure 2 (c) A second electrode 4 with a thickness of 5 nm formed of Ir is formed on the resistance-changing layer 3, thereby obtaining a stacked structure constituting the resistance-changing element 20. In this embodiment, Ir is used as the second electrode 4, but in addition, noble metals such as Pt, Pd (palladium), and Ru (ruthenium) or metal nitrides such as TiN and TaN can also be used as the second electrode.

[0075] Finally, as Figure 2 As shown in (e), in order to form the resistance changing element 20, a desired mask is used to pattern the first electrode 2, the oxygen-deficient tantalum oxide layer 3c, the composite oxide layer 3d, and the second electrode 4. Thus, the resistance changing element 20 is formed by sandwiching the first electrode 2 and the second electrode 4 with the resistance changing layer 3, which is a stacked structure formed by the oxygen-deficient tantalum oxide layer 3c and the composite oxide layer 3d.

[0076] Furthermore, when forming the resistance-changing element 20, the first electrode 2, the tantalum oxide layer 3c, the composite oxide layer 3d, and the second electrode 4 can be patterned uniformly using a single mask, or each layer can be patterned using an individual mask.

[0077] Further, the size and shape of the first electrode 2 and the second electrode 4 and the resistance change layer 3 can be adjusted by a photomask and photolithography.

[0078] In the present embodiment, the size of the second electrode 4 and the resistance change layer 3 is set to 0.1 μm x 0.1 μm (area: 0.01 μm 2 ) and the size of the portion where the first electrode 2 and the resistance change layer 3 are in contact is also set to 0.1 μm x 0.1 μm (area: 0.01 μm 2 ). However, such size and shape is one example and can be appropriately changed by layout design.

[0079] Further, in the present embodiment, as one example, the degree of oxygen deficiency r of the tantalum oxide layer 3c of the oxygen-deficient type is set to 38% and the degree of oxygen deficiency s of the composite oxide layer 3d is set to around 1%. Further, the thickness of the resistance change layer 3 is set to 24 nm, the thickness of the tantalum oxide layer 3c is set to about 20 nm, and the thickness of the composite oxide layer 3d is set to about 4 nm.

[0080] Further, although r = 38% and s = 1% are set in the present embodiment, the values of r and s are not limited to this example. As described above, for example, even if r is changed between 24% < r < 68% and s is changed between 0 < s < 16%, stable resistance change equivalent to the resistance change characteristics in the present embodiment can be achieved.

[0081] (Operation of resistance change element)

[0082] Next, the operation of the resistance change element 20 obtained by the above manufacturing method will be described with reference to Figure 1B

[0083] Hereinafter, a case where the resistance value of the resistance change layer 3 is at a prescribed high value (for example, 300 kΩ) is referred to as a high resistance state, and similarly, a case where it is at a prescribed low value (for example, 12 kΩ) is referred to as a low resistance state.

[0084] Further, a process in which the resistance value of the resistance change layer 3 is reduced and the resistance change layer 3 changes from the high resistance state to the low resistance state by applying a write voltage pulse which is a voltage pulse of negative polarity between the first terminal 7 and the second terminal 8 using the power supply 5 as shown in FIG. 2A is referred to as a write process. Figure 1B

[0085] Further, a process in which the resistance value of the resistance change layer 3 is increased and the resistance change layer 3 changes from the low resistance state to the high resistance state by applying an erase voltage pulse which is a voltage pulse of positive polarity between the first terminal 7 and the second terminal 8 is referred to as an erase process.

[0086] ​​Further, the voltage pulse of positive polarity means a voltage pulse in which the second terminal 8 becomes a positive voltage with the first terminal 7 as a reference, and the voltage pulse of negative polarity means a voltage pulse in which the first terminal 7 becomes a positive voltage with the second terminal 8 as a reference.

[0087] By repeating such a write process and an erase process, the resistance change element 20 operates as a nonvolatile memory element.

[0088] Here, an initial process is explained. In the present embodiment, the initial process is executed before the first write process described above. The initial process means a preparatory process for realizing stable resistance change operation in the subsequent write process and erase process.

[0089] Generally, the resistance change element 20 immediately after manufacturing has an initial resistance value higher than a high resistance state at the time of normal resistance change, and in this state, even if the write voltage pulse or the erase voltage pulse at the time of normal operation is applied, resistance change does not occur.

[0090] Therefore, in the initial process, the first initial voltage pulse (high resistance breakdown) of positive polarity and the second initial voltage pulse (low resistance breakdown) of negative polarity are sequentially applied between the first terminal 7 and the second terminal 8.

[0091] When the first initial voltage pulse is applied, the resistance value of the resistance change layer 3 decreases from the initial resistance value to a first resistance value, and then when the second initial voltage pulse is applied, the resistance value of the resistance change layer 3 further decreases from the first resistance value to a second resistance value.

[0092] After that, by applying the write voltage pulse or the erase voltage pulse at the time of normal operation, the resistance change element 20 repeatedly performs resistance change between the high resistance state and the low resistance state.

[0093] That is, the initial process is a process performed on the resistance change element 20 in an initial state in which no voltage has been applied after the resistance change element 20 is manufactured.

[0094] Further, in the initial process described above, the first initial voltage pulse of positive polarity and the second initial voltage pulse of negative polarity are used, but it is also possible to use only the polarity of either the first initial voltage pulse or the second initial voltage pulse to decrease the resistance value of the resistance change layer 3 from the initial resistance value to the resistance value at the time of normal operation.

[0095] By going through the initial process described above, a local region having a higher degree of oxygen deficiency than the surrounding degree of oxygen deficiency, which is called a filament, is formed in the resistance change layer 3. Further, in the calculation of the diffusion coefficient based on computer simulation described later, the degree of oxygen deficiency of the filament is set to 20% based on past analysis results.

[0096] When the usual resistance change operation after the initial process is performed, the resistance state is changed from the high resistance state to the low resistance state by applying a write voltage pulse which is a voltage pulse of negative polarity between the first terminal 7 and the second terminal 8. In addition, the resistance state is changed from the low resistance state to the high resistance state by applying an erase voltage pulse which is a voltage pulse of positive polarity between the first terminal 7 and the second terminal 8.

[0097] As a mechanism of the resistance change operation at this time, it is considered that the degree of oxygen deficiency in the filament is increased by the write voltage pulse and decreased by the erase voltage pulse. Here, when the degrees of oxygen deficiency in the filament in the high resistance state and the low resistance state at the time of the resistance change operation are NHVO and NLVO, respectively, the relation of NHVO < NLVO is satisfied.

[0098] Further, in the present embodiment, the filament is formed by the initial process, but it is not necessary to form the filament by the initial process. For example, by providing a composite oxide layer having a degree of oxygen deficiency sufficiently larger than 0% when the resistance change element is formed, the filament can be substituted.

[0099] Figure 3 is a view showing one example of a circuit configuration for operating the resistance change element 20 and an example of operation in a case where data is written to the resistance change element 20.

[0100] As shown in Figure 3 , the circuit is provided with the resistance change element 20, the first terminal 7, and the second terminal 8. As shown in Figure 1B , the second electrode 4 of the resistance change element 20 is electrically connected to the second terminal 8, and the first electrode 2 is electrically connected to the first terminal 7.

[0101] In addition, a transistor 13 is provided between the first electrode 2 of the resistance change element 20 and the first terminal 7. The transistor functions as a switching element for selecting the resistance change element 20 and a protection resistor. By applying a gate voltage Vg to the transistor 13, a prescribed voltage pulse is supplied to the resistance change element 20 via the transistor 13.

[0102] Figure 4 is a view showing changes in the resistance value of the resistance change layer 3 in the write process and the erase process for the resistance change element 20. The write process is a low resistance process for writing a theoretical value 0 to the resistance change element 20; the erase process is a high resistance process for writing a theoretical value 1 to the resistance change element 20. Further, as shown in Figure 3As shown, in terms of the low resistance process and the high resistance process, when a positive voltage pulse is applied, a predetermined positive voltage pulse is supplied to the second terminal 8 with the first terminal 7 as a reference, and when a negative voltage pulse is applied, a predetermined positive voltage pulse is supplied to the first terminal 7 with the second terminal 8 as a reference.

[0103] When the resistance changing layer 3 of the resistance changing element 20 is in a high resistance state at a certain moment, if a negative low-resistivity voltage pulse (second voltage pulse: voltage value VRL) is supplied to the second terminal 8, the resistance value of the resistance changing layer 3 changes from a high resistance value RH to a low resistance value RL. On the other hand, when the resistance value of the resistance changing layer 3 is low resistance value RL, if a positive high-resistivity voltage pulse (first voltage pulse: voltage value VRH) is supplied to the second terminal 8, the resistance value of the resistance changing layer 3 changes from a low resistance value RL to a high resistance value RH.

[0104] Figure 5 This diagram illustrates an example of the circuit configuration that enables the resistance changing element 20 to operate, and an example of its operation when the data written to the resistance changing element 20 is read out.

[0105] like Figure 5 As shown, when reading data, a readout voltage is supplied to the second terminal 8 with reference to the first terminal 7. This readout voltage is a value that will not cause the resistance of the resistance-changing element 20 to change even when supplied with it, and is specified with reference to the first electrode 2 and the ground point.

[0106] (Mechanism for improving data retention properties by introducing materials with low oxygen diffusion coefficient)

[0107] Here, we will explain the inferred mechanism by which replacing the second tantalum oxide layer 3b in the resistance changing element 10 with a composite oxide layer 3d in the resistance changing element 20, which has a small oxygen diffusion coefficient, improves the data retention characteristics. However, no definitive conclusion has been reached regarding the above-mentioned mechanism for improving data retention characteristics, so only possibilities are described.

[0108] First, the differences between the high resistance state and the low resistance state of a resistance-changing element will be explained. Figure 6A A cross-sectional schematic diagram of the resistance changing element 10 in a low-resistance state is shown. Figure 6B A cross-sectional schematic diagram of the resistance changing element 10 in a high-resistance state is shown.

[0109] Regarding the resistance changing element 10, both the low resistance state and the high resistance state have lower resistance values ​​than the initial state. Therefore, it is assumed that even in any resistance state, there is a filament 3e in the tantalum oxide layer 3b that connects the upper electrode 4 to the tantalum oxide layer 3a.

[0110] It is assumed that the resistance value of the resistance changing element 10 is determined by the amount of oxygen defects 9 present in the filament 3e, and the oxygen content NLO in the filament 3e of the resistance changing element 10 in the low resistance state is... x The oxygen content NHO in the filament 3e of the element with high resistance change is related to the resistance change. x Satisfy NLO x <NHO x This relationship also applies to the resistance-changing element 20.

[0111] The relationship between oxygen defects 9 within the filament 3e and the resistance values ​​of the resistance-changing elements 10 and 20 will be explained at a more microscopic level. It is assumed that tiny conductive paths formed by the connections of oxygen defects exist within the filament 3e. In a low-resistance state, there are a sufficient number of oxygen defects 9, thus these tiny conductive paths connect the upper electrode 2 to the tantalum oxide 3a. On the other hand, in a high-resistance state, the amount of oxygen defects 9 is small, therefore these tiny conductive paths are interrupted midway.

[0112] Based on the resistance change mechanism described above, it is believed that the change from low resistance to high resistance in the data holding state after the resistance change is equivalent to the following situation: the connection of the tiny conductive path in the filament 3e is fragile, so the surrounding oxygen diffuses into the tiny conductive path and combines with a certain oxygen defect 9, thereby the tiny conductive path is interrupted midway.

[0113] In contrast, such as Figure 6C As shown, for the resistance changing element 20, as the layer containing the filament 3e, a composite oxide layer 3d is used that further contains an additional metal element 11 different from Ta and has a smaller oxygen diffusion coefficient than the tantalum oxide layer 3b. Therefore, the amount of oxygen diffusion during data retention is reduced compared to the past, thus suppressing the diffusion of surrounding oxygen into the small conductive path and its combination with oxygen defects 9. It is presumed that, compared to the past, long-term data retention, especially the retention of a low-resistance state, can be achieved.

[0114] On the other hand, it is believed that the change from a high resistance state to a low resistance state in the data holding state after the resistance change is equivalent to the following situation: the tiny conductive path in the filament 3e is interrupted in the middle, but when there are many oxygen defects, new oxygen defects are generated through oxygen diffusion and combine with the existing oxygen defects, thereby connecting the interrupted tiny conductive path.

[0115] In contrast, regarding the resistance changing element 20, such as Figure 6DAs the layer in which the filament 3e exists, a composite oxide layer 3d further containing an additional metal element 11 different from Ta and having a smaller oxygen diffusion coefficient than the tantalum oxide layer 3b is used. Thus, the amount of oxygen diffusion at the time of data retention is reduced compared to the past, and therefore it is possible to suppress the connection in which a minute conductive path is generated due to oxygen diffusion within the filament 3e in the high resistance state. As a result, it is possible to achieve long-term data retention, particularly in the high resistance state, compared to the past.

[0116] The above describes an example of the resistance change element 20 in which a tantalum oxide is used for the first resistance change layer and a composite oxide in which an additional metal element different from Ta is added to the tantalum oxide is used for the second resistance change layer, but is not limited to this example. The same description applies as long as the resistance change element in which an oxide of a metal other than Ta is used for the first resistance change layer and a composite oxide in which an additional metal element is added to the oxide of the metal other than Ta is used for the second resistance change layer satisfies the size relationship of the oxygen diffusion coefficients.

[0117] (Embodiment of Composite Oxide)

[0118] Regarding the composite oxide used for the second resistance change layer of the present embodiment, appropriate additional metal elements were investigated, and therefore the following describes the investigation.

[0119] Regarding the composite oxide used for the second resistance change layer of the present embodiment, appropriate additional metal elements were investigated, and therefore the following describes the investigation.

[0120] Further, regarding the calculation of the diffusion coefficient based on the computer simulation described later, the local region in which the degree of oxygen deficiency is large, that is, the filament generated in the initial process of the operation of the resistance change element 20 in the composite oxide layer 3d was calculated based on the past analysis results with the degree of oxygen deficiency set to 20%.

[0121] First, the oxygen diffusion coefficient of the composite oxide was calculated as follows.

[0122] The metal oxides and composite oxides to be simulated were set with Ta as the first metal element and a metal element selected from among Al, Hf (hafnium), V (vanadium), and Si (silicon) as the second metal element. Specifically, five types of tantalum oxide not containing the second metal element, tantalum-aluminum composite oxide, tantalum-hafnium composite oxide, tantalum-silicon composite oxide, and tantalum-vanadium composite oxide were set. The tantalum oxide not containing the second metal element is a comparative example for comparison with the composite oxides, and corresponds to the constituting material of the second resistance variable layer of the related art. The tantalum oxide as the comparative example is referred to as the second metal oxide in order to distinguish it from the tantalum oxide as the first metal oxide constituting the first resistance variable layer.

[0123] The compositions of the five types of metal oxides and composite oxides that were simulated are shown in Table 1. The number of atoms for the simulation was set in such a manner that the number of atoms of tantalum element with respect to the tantalum oxide corresponding to the resistance variable element of the related art becomes 54. Further, the larger the number of atoms, the more precisely the simulation can be performed; however, on the other hand, the time for the simulation becomes large, and therefore the above value was set. However, it is not necessarily required that the simulation be performed with the above number of atoms, and the same results as the present results can be obtained even if the simulation is performed with other numbers of atoms.

[0124] Table 1

[0125]

[0126] With the resistance variable element in the present embodiment, the filament 3e is formed in the resistance variable layer 3 by the above initial process. Through past quantitative analysis, it is estimated that the oxygen deficiency of the tantalum oxide in the filament 3e is about 20% or so.

[0127] Therefore, in the simulation, the oxygen deficiency of each of the above five types of metal oxides and composite oxides was set to be 20% of the composition. The composition of the tantalum oxide having an oxygen deficiency of 20% is Ta 54 O 108 Further, with the composite oxides containing tantalum and the second metal element, about 22% of 54 tantalum atoms, i.e., 12 tantalum atoms, were replaced with the second metal element (corresponding to 24 oxygen atoms in the tantalum oxide having an oxygen deficiency of 20%). By setting the number of the second metal element after the replacement to the number of the metal oxide having an oxygen deficiency of 20% constituted by the second metal element and 24 oxygen atoms, the oxygen deficiency of the entire composite oxide was set to be 20%.

[0128] Thus, for example, with the tantalum-aluminum composite oxide, it was set to be (Ta 42 O 84 )-(Al 20 O 24). The same is true for other complex oxides. Furthermore, it is considered that although the simulation was performed with (Ta 42 O 84 ) was performed, but the same results as this time can be obtained even when performed with different compositions. In addition, it is considered that although the degree of oxygen deficiency was set to 20% in the calculation this time, it is not necessary to set the degree of oxygen deficiency to 20%, but the same results as this time can be obtained as long as the same degree of oxygen deficiency is set in each metal oxide.

[0129] In addition, it is effective to study in detail how much of the percentage of tantalum atoms is replaced with the second metal element later.

[0130] For the five kinds of metal oxides and complex oxides thus set, the structure that becomes the most stable state at 4000K was calculated by first principle calculation based on the Birch-Murnaghan equation of state. Specifically, as an index of the state becoming stable, the structure in which the internal energy becomes the smallest was calculated. Through this calculation, the bulk modulus under the structure that becomes the most stable state was calculated.

[0131] The bulk modulus is defined from the curvature of the Helmholtz free energy, which is the sum of the internal energy and entropy, but in this simulation, the value of the bulk modulus was calculated by fitting the Helmholtz free energy to be equal to the internal energy. However, it is considered that the same results as this time can be obtained in the magnitude relationship of the bulk modulus even when the simulation is performed without setting the Helmholtz free energy to be equal to the internal energy.

[0132] Next, with respect to the structure that becomes the most stable state, the movement of oxygen atoms between 50 picoseconds was simulated, the total distance of each oxygen atom movement was calculated and averaged, and thus the oxygen diffusion coefficient in each metal oxide at 4000K was calculated.

[0133] Further, the simulation related to the movement of oxygen atoms over a period of 130 picoseconds or more was also performed at 3000K, and the oxygen diffusion coefficient in each metal oxide at 3000K was calculated.

[0134] Finally, based on the values of the oxygen diffusion coefficient in each metal oxide at 4000K and 3000K, the value of the oxygen diffusion coefficient at 300K, which corresponds to room temperature, was calculated based on the Arrhenius equation.

[0135] The simulation results thus calculated are shown in Table 1. As is clear from Table 1, with respect to both the tantalum-aluminum complex oxide and the tantalum-hafnium complex oxide, the oxygen diffusion coefficient is smaller than that of the tantalum oxide. On the other hand, with respect to both the tantalum-aluminum complex oxide and the tantalum-hafnium complex oxide, the bulk modulus is larger than that of the tantalum oxide.

[0136] Here, the bulk modulus refers to the inverse of the proportion of volume change under a certain pressure, and it is generally considered that a material having a large bulk modulus is strong or hard.

[0137] Thus, the above simulation results can be explained as follows. That is, in the case of the tantalum-aluminum composite oxide and the tantalum-hafnium composite oxide having a large bulk modulus, the network of the composite oxide is firmly bound, and thus the phenomenon of oxygen atoms separating from the network and diffusing is less likely to occur than in the case of the tantalum oxide.

[0138] Further, in the four types of composite oxides for which calculations were performed this time, there is a positive correlation between the bulk modulus of the composite oxide and the melting point of the stoichiometric oxide formed from the second metal element and oxygen that constitute the composite oxide, except for the tantalum-silicon composite oxide.

[0139] The tantalum-silicon composite oxide is the only one in which silicon is a semiconductor and the organosilicon oxide is a covalently bound oxide in this study, and thus although the melting point is high, the bulk modulus is small, and the reduction in the diffusion coefficient is small. In view of this, it is presumed that by using a general metal element that forms an ionically bound oxide as the second metal element and mixing a metal oxide having a high melting point formed from the second metal element and oxygen with the tantalum oxide to produce a composite oxide, the bulk modulus of the composite oxide increases, and as a result, the oxygen diffusion coefficient decreases.

[0140] Based on this viewpoint, it is considered that the second metal element that constitutes the composite oxide in the present embodiment can be selected from among metals, i.e., Zn (zinc), Ti (titanium), Ga (gallium), Ni (nickel), Al, Y (yttrium), Zr (zirconium), Mg (magnesium), and Hf, whose oxides have a higher melting point than the tantalum oxide.

[0141] However, the above phenomenon of reduction in the oxygen diffusion coefficient can be more related to other reasons that were not studied this time, and thus among all the metal elements whose oxides have a higher melting point than the tantalum oxide, the bulk modulus does not necessarily automatically become large. In addition, in the case of a composite metal oxide having a bulk modulus larger than the tantalum oxide, the oxygen diffusion coefficient does not necessarily automatically become small.

[0142] Based on the simulation results of the first-principles calculation explained above, in the present embodiment, for the tantalum-aluminum composite oxide and the tantalum-hafnium composite oxide for which a reduction in the oxygen diffusion coefficient was confirmed, a resistance change element was produced using the manufacturing method and the operation method of the resistance change element in the present embodiment, and was actually operated.

[0143] Figure 7AElement composition dependency of a resistance change voltage of a resistance change element composed of a second resistance change layer of a tantalum-aluminum composite oxide or a tantalum-hafnium composite oxide. Here, the resistance change voltage refers to a voltage that causes a resistance change in the resistance change element by being applied thereto. The horizontal axis element composition ratio indicates a composition ratio of a second metal element included in the composite oxide constituting the second resistance change layer to the sum of a first metal element and the second metal element. Here, the first metal element is Ta, and the second metal element is Al or Hf. The composition ratio 0 indicates an oxide containing no Al or Hf and containing only Ta.

[0144] It was found that the resistance change voltage increased by adding Al or Hf to the tantalum oxide. Figure 7A

[0145] It is considered that the resistance change phenomenon in the resistance change element corresponds to a change in the amount of oxygen defects 9 in the filament 3e by moving oxygen ions by electric energy, and thus a larger voltage needs to be applied to the resistance change layer 3 having a small oxygen diffusion coefficient.

[0146] That is, it is considered that Figure 7A The result of the test experimentally shows that the oxygen diffusion coefficient decreases by adding Al or Hf to the tantalum oxide.

[0147] However, on the other hand, with the large capacity of the nonvolatile memory, a decrease in operating voltage is required, and thus an increase in the applied voltage of 0.2 V or less is desired for the tantalum oxide. From such a viewpoint, the tendency was predicted from the element composition dependency of the resistance change voltage, and as a result, the composition ratio of the second metal element included in the composite oxide to the sum of the first metal element and the second metal element can be, for example, 10% to 50%.

[0148] Further, in the present embodiment, evaluation of the data retention characteristics was performed on the resistance change element group in which the tantalum oxide, the tantalum-aluminum composite oxide, and the tantalum-hafnium composite oxide were used as the second resistance change layer of the resistance change element in the present embodiment.

[0149] Here, the resistance change operation conditions performed in the present embodiment are specifically shown. As a general resistance change operation, as for a write voltage pulse, the pulse voltage was set to be negative with the current flowing in the resistance change element being 150 μA at the time of applying the pulse, and the pulse application time was set to 100 ns. In addition, as for an erase voltage pulse, the pulse voltage was set to +1.8 V, and the pulse application time was set to 100 ns. In the present embodiment, after the initial process described above was performed, the general resistance change operation was repeated 1000 times under the above conditions.

[0150] ​As described above, the resistance retention characteristics of the prepared resistance-changing element group were evaluated. Furthermore, the resistance value of the resistance-changing element used in this embodiment exhibits the characteristic that almost no degradation is observed even after 10 years or more at around room temperature. Therefore, the non-volatile memory element was kept in a constant temperature bath at 210°C to accelerate degradation, and the retention characteristics were evaluated. In addition, the non-volatile memory element was removed from the constant temperature bath and its resistance value was measured at room temperature.

[0151] Figure 7B The diagram illustrates a comparative example of a resistance-changing element group with a second resistance-changing layer composed of tantalum oxide, and an embodiment of a resistance-changing element group composed of tantalum-aluminum composite oxide and tantalum-hafnium composite oxide, showing the relative degradation of retention characteristics. Figure 7B As an example of the relative degradation of the characteristics, the rate of decrease in read current caused by the increase in resistance value in the low resistance state is expressed as 1, and the rate of decrease in the resistance-changing element group of the comparative example is expressed as 1.

[0152] Depend on Figure 7B It can be seen that, for the resistance changing element group with the second resistance changing layer composed of tantalum-aluminum composite oxide and tantalum-hafnium composite oxide, the relative degradation (reduction rate of readout current) is smaller than that of the resistance changing element group with the second resistance changing layer composed of tantalum oxide. That is, it can be seen that the rate of increase of resistance value in the low resistance state is suppressed, thereby improving the retention characteristic.

[0153] As can be seen from the above, by using the resistance changing element of this embodiment, information can be stored more stably for a longer period of time compared to the past.

[0154] (Implementation Method 2)

[0155] Embodiment 2 is a non-volatile memory device of the 1 transistor / 1 non-volatile memory type (1T1R type) configured using the resistance changing element described in Embodiment 1. The configuration and operation of this non-volatile memory device will be described below.

[0156] Figure 8 This is a block diagram illustrating an example of the configuration of a non-volatile storage device according to Embodiment 2.

[0157] like Figure 8 As shown, the 1T1R type non-volatile memory device 100 of this embodiment has a memory main body 101 on a semiconductor substrate. The memory main body 101 includes a memory cell array 102 having a resistance-changing element and an access transistor, and a voltage application circuit. Here, the access transistor is an example of a current-controlled element.

[0158] The voltage application circuit includes, for example, a row selection circuit / driver 103, a column selection circuit 104, a write circuit 105, a sense amplifier 106, and a data input / output circuit 107.

[0159] The write circuit 105 controls the application of voltage to the memory cells in the initial process and the data write process and the read process. The sense amplifier 106 detects the amount of current flowing in the selected bit line, and determines which data of the stored 2-value data. The data input / output circuit 107 performs input / output processing of input / output data via the terminal DQ.

[0160] In addition, the nonvolatile memory device 100 further includes a VCP (cell plate) power supply 108, an address input circuit 109, and a control circuit 110. The address input circuit 109 accepts an address signal input from the outside. The control circuit 110 controls the operation of the memory main body 101 based on a control signal input from the outside.

[0161] The memory cell array 102 includes a plurality of word lines WL0, WL1, WL2,..., and a plurality of bit lines BL0, BL1, BL2,..., which are arranged in a cross pattern on a semiconductor substrate, a plurality of access transistors T11, T12, T13, T21, T22, T23, T31, T32, T33,..., which are provided corresponding to the intersections of the word lines WL0, WL1, WL2,..., and the bit lines BL0, BL1, BL2,..., and a plurality of memory cells M111, M112, M113, M121, M122, M123, M131, M132, M133 (hereinafter referred to as "memory cells M111, M112,...") which are provided one-to-one with the access transistors T11, T12,.... Here, the memory cells M111, M112,... correspond to the resistance change element 20 of Embodiment 1.

[0162] In addition, the memory cell array 102 includes a plurality of plate lines PL0, PL1, PL2,..., which are arranged in parallel with the word lines WL0, WL1, WL2,....

[0163] The drain electrodes of the access transistors T11, T12, T13,..., respectively, are connected to the bit line BL0, the drain electrodes of the access transistors T21, T22, T23,..., are connected to the bit line BL1, and the drain electrodes of the access transistors T31, T32, T33,..., are connected to the bit line BL2, respectively.

[0164] In addition, the gate electrodes of the access transistors T11, T21, T31,..., are connected to the word line WL0, the gate electrodes of the access transistors T12, T22, T32,..., are connected to the word line WL1, and the gate electrodes of the access transistors T13, T23, T33,... are connected to the word line WL2, respectively.

[0165] Further, the sources of the access transistors T11, T12,... are connected to the memory cells M111, M112,..., respectively.

[0166] In addition, the memory cells M111, M121, M131,... are connected to the plate line PL0, respectively, the memory cells M112, M122, M132,... are connected to the plate line PL1, and the memory cells M113, M123, M133,... are connected to the plate line PL2, respectively.

[0167] As for the nonvolatile memory device 100 configured as above, the address input circuit 109 receives an address signal from an external circuit (not shown), and outputs a row address signal to the row selection circuit / driver 103 and a column address signal to the column selection circuit 104 on the basis of the address signal.

[0168] Here, the address signal is a signal indicating a specific memory cell selected from among the plurality of memory cells M111, M112,.... In addition, the row address signal is a signal indicating an address of a row in the address indicated by the address signal, and the column address signal is a signal indicating an address of a column in the address indicated by the address signal.

[0169] In addition, as for the control circuit 110, in an initial process, a write signal is output to the write circuit 105, the write signal instructing application of a first initial voltage pulse and a second initial voltage pulse to each of the memory cells M111, M112,.... The write circuit 105 outputs a signal to the column selection circuit 104 in a case where the write signal is received, the signal instructing application of the first initial voltage pulse and the second initial voltage pulse to all the bit lines BL0, BL1, BL2,....

[0170] Further, the column selection circuit 104 applies the first initial voltage pulse and the second initial voltage pulse to all the bit lines BL0, BL1, BL2,... in a case where the signal is received. At this time, the row selection circuit / driver 103 applies a prescribed voltage to all the word lines WL0, WL1, WL2,....

[0171] Through the above operation, the initial process is completed.

[0172] Then, as for the control circuit 110, in a data write process, a write signal is output to the write circuit 105, the write signal instructing application of a write voltage pulse or an erase voltage pulse in correspondence with input data Din input to the input / output circuit 107. On the other hand, as for the control circuit 110, in a data read process, a read signal is output to the column selection circuit 104, the read signal instructing application of a read voltage pulse.

[0173] The row selection circuit / driver 103 accepts a row address signal output from the address input circuit 109, selects any of the plurality of word lines WL0, WL1, WL2,..., corresponding to the row address signal, and applies a prescribed voltage to the selected word line.

[0174] In addition, the column selection circuit 104 accepts a column address signal output from the address input circuit 109, selects any of the plurality of bit lines BL0, BL1, BL2,..., corresponding to the column address signal, and applies a write voltage pulse, an erase voltage pulse, or a voltage pulse for readout to the selected bit line.

[0175] The write circuit 105 outputs a signal that instructs the column selection circuit 104 to apply a write voltage pulse or an erase voltage pulse to the selected bit line, in a case where a write signal output from the control circuit 110 is accepted.

[0176] As for the readout amplifier 106, during readout of data, the amount of current flowing in the selected bit line that is the object of readout is detected, and the stored data is identified. In the case of the present embodiment, the resistance state of each memory cell M111, M112,... is set to two states of high and low, and these states are made to correspond to each data. Therefore, the readout amplifier 106 identifies in which state the resistance state of the resistance change layer of the selected memory cell is, and determines which data of the 2-value data is stored in correspondence thereto. As a result, the obtained output data DO is output to the outside circuit via the data input / output circuit 107.

[0177] According to the nonvolatile storage device 100, the memory cells M111, M112,... that are the resistance change elements 20 of Embodiment 1 are used, and therefore information can be stored stably for a long period of time.

[0178] (Embodiment 3)

[0179] Embodiment 3 is a cross-point type nonvolatile storage device configured using the resistance change element described in Embodiment 1. Hereinafter, the configuration and operation of the nonvolatile storage device will be described.

[0180] Figure 9 is a block diagram showing one example of the configuration of the nonvolatile storage device of Embodiment 3.

[0181] As shown in Figure 9 , the nonvolatile storage device 200 of the present embodiment has a memory main part 201 on a semiconductor substrate. The memory main part 201 has a memory cell array 202, a row selection circuit / driver 203, a column selection circuit / driver 204, a write circuit 205, a readout amplifier 206, and a data input / output circuit 207.

[0182] The write circuit 205 controls the application of voltages to the memory cells in the initial process and the data write process and the read process. The sense amplifier 206 detects the amount of current flowing in the selected bit line to identify which data of the stored 2-value data. The data input / output circuit 207 performs input / output processing of data input / output via the terminal DQ.

[0183] In addition, the nonvolatile memory device 200 further includes an address input circuit 208 and a control circuit 209. The address input circuit 208 accepts an address signal input from the outside. The control circuit 209 controls the operation of the memory main unit 201 based on a control signal input from the outside.

[0184] The memory array 202 includes a plurality of word lines WL0, WL1, WL2,... formed parallel to each other on a semiconductor substrate and a plurality of bit lines BL0, BL1, BL2,... formed parallel to each other in a plane parallel to the main surface of the semiconductor substrate above the word lines WL0, WL1, WL2,... and intersecting the plurality of word lines WL0, WL1, WL2,... in three dimensions.

[0185] In addition, a plurality of memory cells M211, M212, M213, M221, M222, M223, M231, M232, M233,... are provided in a matrix corresponding to the intersections of the word lines WL0, WL1, WL2,... and the bit lines BL0, BL1, BL2,.... Here, the memory cells M211, M212,... are configured by connecting elements corresponding to the resistance change element 20 of Embodiment 1 and a current control element composed of a MIM (Metal-Insulator-Metal) diode or a MSM (Metal-Semiconductor-Metal) diode, or the like.

[0186] With the nonvolatile memory device 200 configured as described above, the address input circuit 208 accepts an address signal from an external circuit (not shown), outputs a row address signal to the row selection circuit / driver 203 and a column address signal to the column selection circuit / driver 204 based on the address signal. Here, the address signal is a signal indicating the address of a specific memory cell selected from among the plurality of memory cells M211, M212,.... In addition, the row address signal is a signal indicating the address of the row in the address indicated by the address signal, and the column address signal is a signal indicating the address of the same column.

[0187] Further, with respect to the control circuit 209, in the initial process, a write signal is output to the write circuit 205, the write signal instructing application of the first initial voltage pulse and the second initial voltage pulse to the memory cells M211, M212,... in order. In a case where the write circuit 205 accepts the write signal, a signal is output to the row selection circuit / driver 203, the signal instructing application of a prescribed voltage to all the word lines WL0, WL1, WL2,..., and a signal is output to the column selection circuit / driver 204, the signal instructing application of the first initial voltage pulse and the second initial voltage pulse to all the bit lines BL0, BL1, BL2,....

[0188] Through the above, the initial process ends.

[0189] Then, with respect to the control circuit 209, in the data write process, a write signal is output to the write circuit 205 in correspondence with the input data Din input to the data input / output circuit 207, the write signal instructing application of a write voltage pulse or an erase voltage pulse. On the other hand, with respect to the control circuit 209, in the data read process, a read signal is output to the column selection circuit / driver 204, the read signal instructing application of a read voltage pulse.

[0190] The row selection circuit / driver 203 accepts a row address signal output from the address input circuit 208, selects any of the plurality of word lines WL0, WL1, WL2,... in correspondence with the row address signal, and applies a prescribed voltage to the selected word line.

[0191] Further, the column selection circuit / driver 204 accepts a column address signal output from the address input circuit 208, selects any of the plurality of bit lines BL0, BL1, BL2,... in correspondence with the column address signal, and applies a write voltage pulse, an erase voltage pulse, or a read voltage pulse to the selected bit line.

[0192] In a case where the write circuit 205 accepts the write signal output from the control circuit 209, a signal is output to the row selection circuit / driver 203, the signal instructing application of a voltage to the selected word line, and a signal is output to the column selection circuit / driver 204, the signal instructing application of a write voltage pulse or an erase voltage pulse to the selected bit line.

[0193] As for the readout amplifier 206, during the readout of data, the amount of current flowing in the selected bit line as the readout target is detected, and the stored data is identified. In the case of the present embodiment, the resistance state of each memory cell M211, M212,... is set to two states of high and low, and these states are made to correspond to each data. Therefore, the readout amplifier 206 identifies in which state the resistance state of the resistance change layer of the selected memory cell is, and determines which data of the 2-value data is stored in correspondence thereto. As a result, the obtained output data DO is output to an external circuit via the data input / output circuit 207.

[0194] According to the nonvolatile storage device 200, the memory cells M211, M212,... including the element corresponding to the resistance change element 20 of Embodiment 1 are used, and thus information can be stored stably for a long period of time.

[0195] Further, by stacking the memory array in the nonvolatile storage device of the present embodiment in a three-dimensional manner as shown in Figure 9 By providing the multi-layered memory array thus configured, a nonvolatile storage device of a super large capacity can be realized.

[0196] (SUMMARY)

[0197] As described above, the resistance change type nonvolatile storage element of the present application includes a first electrode, a second electrode, and a resistance change layer, the resistance change layer being sandwiched between the first electrode and the second electrode and reversibly changing in resistance value based on an electric signal applied between the two electrodes, wherein the resistance change layer includes a first resistance change layer composed of a first metal oxide of an oxygen deficiency type, the first metal oxide being formed of a first metal element and oxygen, and a second resistance change layer formed of the first metal element, a second metal element different from the first metal element, and oxygen, and composed of a composite oxide of an oxygen deficiency degree different from that of the first metal oxide, the composite oxide having a smaller oxygen diffusion coefficient at room temperature than a second metal oxide formed of the first metal element and oxygen and having an oxygen deficiency degree equal to that of the composite oxide.

[0198] Further, in the resistance change type nonvolatile storage element of the present application, the volume elastic modulus of the composite oxide can be larger than that of the second metal oxide.

[0199] In addition, in the resistance change type nonvolatile memory element of the present application, the melting point of the stoichiometric composition of the oxide of the second metal element can be higher than the melting point of the stoichiometric composition of the oxide of the first metal element.

[0200] In addition, in the resistance change type nonvolatile memory element of the present application, the second metal element forms an ionically bound oxide.

[0201] In addition, in the resistance change type nonvolatile memory element of the present application, the resistivity of the composite oxide is larger than the resistivity of the first metal oxide.

[0202] In addition, in the resistance change type nonvolatile memory element of the present application, the first metal element can be a transition metal or Al.

[0203] In addition, in the resistance change type nonvolatile memory element of the present application, the first metal element can be tantalum.

[0204] In addition, in the resistance change type nonvolatile memory element of the present application, the second metal element can be any of Zn, Ti, Ga, Ni, Al, Y, Zr, Mg, and Hf.

[0205] In addition, in the resistance change type nonvolatile memory element of the present application, the second metal element can be Al or Hf.

[0206] In addition, in the resistance change type nonvolatile memory element of the present application, the composition ratio of the second metal element to the sum of the first metal element and the second metal element in the composite oxide can be 10% to 50%.

[0207] In addition, in the resistance change type nonvolatile memory element of the present application, the first resistance change layer and the second resistance change layer can both be in an amorphous state.

[0208] In addition, in the resistance change type nonvolatile memory element of the present application, the second resistance change layer can be arranged in a manner sandwiched between the second electrode and the first resistance change layer, and the second electrode can be formed of a noble metal.

[0209] In addition, in the resistance change type nonvolatile memory element of the present application, the second resistance change layer can be arranged in a manner sandwiched between the second electrode and the first resistance change layer, and the second electrode can be formed of a transition metal nitride.

[0210] In addition, in the resistance change type nonvolatile memory element of the present application, the change in the reversible resistance value based on the electric signal applied between the first electrode and the second electrode is caused by the movement of oxygen ions.

[0211] Further, in the resistance change type nonvolatile memory element of the present application, the resistance change layer can have a local region with a high degree of oxygen deficiency in the second resistance change layer.

[0212] Further, in the resistance change type nonvolatile memory element of the present application, a current control element electrically connected to the first electrode or the second electrode can be further provided.

[0213] Further, in the resistance change type nonvolatile memory element of the present application, the current control element can be a transistor or a diode.

[0214] Further, the resistance change type nonvolatile memory device of the present application includes a memory cell array formed on a substrate and a voltage application circuit, wherein the resistance change type nonvolatile memory element of claim 1 is arranged in a matrix in the memory cell array, and the voltage application circuit performs data writing and erasing and data reading for a prescribed resistance change type nonvolatile memory element.

[0215] Further, in the resistance change type nonvolatile memory device of the present application, the resistance change type nonvolatile memory element further includes a current control element electrically connected to the first electrode or the second electrode, and the current control element can be a transistor.

[0216] Further, in the resistance change type nonvolatile memory device of the present application, the resistance change type nonvolatile memory element further includes a current control element electrically connected to the first electrode or the second electrode, and the current control element can be a diode.

[0217] Industrial Applicability

[0218] The resistance change type nonvolatile memory element of the present application and the resistance change type nonvolatile memory device using the memory cell are capable of storing information stably for a long period of time, and are particularly useful as a resistance change type nonvolatile memory element for various electronic devices such as data servers or personal information recording media, and a resistance change type nonvolatile memory device using the memory cell.

[0219] Explanation of Symbols

[0220] 1 substrate

[0221] 2 first electrode

[0222] 3 resistance change layer

[0223] 3a first tantalum oxide layer

[0224] 3b second tantalum oxide layer

[0225] 3c tantalum oxide layer

[0226] 3d composite oxide layer

[0227] 3e filament

[0228] 4 second electrode

[0229] 5 power supply

[0230] 6 protective resistor

[0231] 7 first terminal

[0232] 8 second terminal

[0233] 9 oxygen deficiency

[0234] 10, 20 resistance change element

[0235] 11 additional metal element

[0236] 13 transistor

[0237] 100 nonvolatile storage device

[0238] 101 memory main part

[0239] 102 memory array

[0240] 103 row selection circuit / driver

[0241] 104 column selection circuit

[0242] 105 write circuit

[0243] 106 sense amplifier

[0244] 107 data input / output circuit

[0245] 108 power supply

[0246] 109 address input circuit

[0247] 110 control circuit

[0248] 200 nonvolatile storage device

[0249] 201 memory main part

[0250] 202 memory array

[0251] 203 row selection circuit / driver

[0252] 204 column selection circuit / driver

[0253] 205 write circuit

[0254] 206 sense amplifier

[0255] 207 data input / output circuit

[0256] 208 address input circuit

[0257] 209 control circuit

Claims

1. A variable resistance nonvolatile storage element comprising a first electrode, a second electrode, and a variable resistance layer, the variable resistance layer being interposed between the first electrode and the second electrode and reversibly changing a resistance value based on an electric signal applied between the two electrodes, wherein the variable resistance layer having a first variable resistance layer composed of a first metal oxide of an oxygen deficiency type formed of a first metal element and oxygen, and a second variable resistance layer formed of the first metal element, a second metal element different from the first metal element, and oxygen, and composed of a composite oxide of an oxygen deficiency different from that of the first metal oxide, the oxygen deficiency of the composite oxide being smaller than the oxygen deficiency of the first metal oxide, the oxygen diffusion coefficient of the composite oxide at room temperature being smaller than the oxygen diffusion coefficient at room temperature of a second metal oxide formed of the first metal element and oxygen and having an oxygen deficiency equal to the oxygen deficiency of the composite oxide, the second metal element forming an ionic bonding oxide.

2. A variable resistance nonvolatile storage element comprising a first electrode, a second electrode, and a variable resistance layer, the variable resistance layer being interposed between the first electrode and the second electrode and reversibly changing a resistance value based on an electric signal applied between the two electrodes, wherein the variable resistance layer having a first variable resistance layer composed of a first metal oxide of an oxygen deficiency type formed of a first metal element and oxygen, and a second variable resistance layer formed of the first metal element, a second metal element different from the first metal element, and oxygen, and composed of a composite oxide of an oxygen deficiency different from that of the first metal oxide, the oxygen deficiency of the composite oxide being smaller than the oxygen deficiency of the first metal oxide, the oxygen diffusion coefficient of the composite oxide at room temperature being smaller than the oxygen diffusion coefficient at room temperature of a second metal oxide formed of the first metal element and oxygen and having an oxygen deficiency equal to the oxygen deficiency of the composite oxide, the bulk modulus of the composite oxide being larger than the bulk modulus of the second metal oxide.

3. A variable resistance nonvolatile storage element comprising a first electrode, a second electrode, and a variable resistance layer, the variable resistance layer being interposed between the first electrode and the second electrode and reversibly changing a resistance value based on an electric signal applied between the two electrodes, wherein, the variable resistance layer having a first variable resistance layer composed of a first metal oxide of an oxygen deficiency type formed of a first metal element and oxygen, and a second variable resistance layer formed of the first metal element, a second metal element different from the first metal element, and oxygen, and composed of a composite oxide of an oxygen deficiency different from that of the first metal oxide, the oxygen deficiency of the composite oxide being smaller than the oxygen deficiency of the first metal oxide, The composite oxide has an oxygen diffusion coefficient at room temperature that is smaller than an oxygen diffusion coefficient at room temperature of a second metal oxide formed of the first metal element and oxygen and having an oxygen deficiency degree equal to that of the composite oxide. The melting point of the oxide of the second metal element in stoichiometric composition is higher than the melting point of the oxide of the first metal element in stoichiometric composition.

4. The variable resistance nonvolatile storage element according to claim 1, wherein The composite oxide has a higher resistivity than the first metal oxide.

5. The variable resistance nonvolatile storage element according to claim 1, wherein The first metal element is a transition metal or Al (aluminum).

6. The variable resistance nonvolatile storage element according to claim 5, wherein The first metal element is Ta (tantalum).

7. The variable resistance nonvolatile storage element according to claim 5, wherein The second metal element is any of Zn (zinc), Ti (titanium), Ga (gallium), Ni (nickel), Al, Y (yttrium), Zr (zirconium), Mg (magnesium), and Hf (hafnium).

8. The variable resistance nonvolatile storage element according to claim 7, wherein The second metal element is Al or Hf.

9. The variable resistance nonvolatile storage element according to claim 5, wherein The composition ratio of the second metal element to the sum of the first metal element and the second metal element in the composite oxide is 10% to 50%.

10. The variable resistance nonvolatile storage element according to claim 1, wherein Both the first resistance change layer and the second resistance change layer are in an amorphous state.

11. The variable resistance nonvolatile storage element according to claim 1, wherein The second resistance change layer is arranged in a manner sandwiched between the second electrode and the first resistance change layer, and the second electrode is formed of a noble metal.

12. The variable resistance nonvolatile storage element according to claim 1, wherein The second resistance change layer is arranged in a manner sandwiched between the second electrode and the first resistance change layer, and the second electrode is formed of a transition metal nitride.

13. The variable resistance nonvolatile storage element according to claim 1, wherein Reversible changes in resistance value based on an electric signal applied between the first electrode and the second electrode are caused by movement of oxygen ions.

14. The variable resistance nonvolatile storage element according to claim 1, wherein The resistance change layer has a local region with a large oxygen deficiency degree within the second resistance change layer.

15. The resistance change type nonvolatile memory element according to any one of claims 1 to 14, further comprising a current control element electrically connected to the first electrode or the second electrode.

16. The variable resistance nonvolatile storage element according to claim 15, wherein The current control element is a transistor or a diode.

17. A resistance change type nonvolatile memory device comprising a memory cell array and a voltage application circuit formed on a substrate, wherein In the memory cell array, a plurality of the resistance change type nonvolatile memory elements according to claim 1 are arranged in a matrix, The voltage application circuit performs writing and erasing of data and reading of data to and from a prescribed resistance change type nonvolatile memory element.

18. The variable resistance nonvolatile storage device according to claim 17, wherein, The resistance change type nonvolatile memory elements each further comprise a current control element electrically connected to the first electrode or the second electrode, The current control element is a transistor.

19. The variable resistance nonvolatile storage device according to claim 17, wherein, The resistance change type nonvolatile memory elements each further comprise a current control element electrically connected to the first electrode or the second electrode, The current control element is a diode.

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