JP2015185605A - Resistance change element and nonvolatile storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistance change element capable of stabilized operation, and a nonvolatile storage device.SOLUTION: A resistance change element including first and second electrodes, first and second layers, and a metal part is provided. The first layer is provided between the first and second electrodes, contains an oxide of a first element, and is an insulating layer. The metal part is provided between the first layer and the first electrode, and contains a first metal. The second layer is provided between the first layer and the first electrode, and contains at least a part of the metal part and a second metal, in a second direction crossing a first direction from the first electrode toward the second electrode. The length in the first direction of a region containing the first metal in the first layer, in the low resistance state, is longer than the length of the region in the high resistance state. The free energy generated per unit substance amount of the oxide of a second metal is larger than the free energy generated per unit substance amount of the oxide of a first element.

Description

  Embodiments described herein relate generally to a variable resistance element and a nonvolatile memory device.

  For example, resistance variable elements have been developed. Development of high-speed and large-capacity nonvolatile memory devices using resistance change elements has been attracting attention. In such a resistance change element, stable operation is desired. It is desired to improve characteristics such as reliability.

JP 2012-253192 A

  Embodiments of the present invention provide a variable resistance element and a nonvolatile memory device capable of stable operation.

  According to the embodiment of the present invention, a variable resistance element including a first electrode, a second electrode, a first layer, a metal part, and a second layer is provided. The first layer is provided between the first electrode and the second electrode, includes an oxide of the first element, and is insulative. The metal part is provided between the first layer and the first electrode and includes a first metal. The second layer is provided between the first layer and the first electrode, and in the second direction intersecting the first direction from the first electrode toward the second electrode, at least one of the metal parts. Part and a second metal. The length in the first direction of the region including the first metal in the first layer in the first state is longer than the length of the region in the second state, or the first layer in the first state. There is a region containing the first metal therein, and in the second state, the first layer does not contain the first metal. The electrical resistance between the first electrode and the second electrode in the first state is lower than the electrical resistance between the first electrode and the second electrode in the second state. The generation free energy per unit substance amount of the second metal oxide is larger than the generation free energy per unit substance amount of the oxide of the first element.

It is a typical sectional view showing the resistance change element concerning a 1st embodiment. 2A and 2B are schematic cross-sectional views illustrating the operation of the variable resistance element according to the first embodiment. FIG. 3A and FIG. 3B are graphs showing the characteristics of the variable resistance element. It is a typical sectional view showing the resistance change element concerning a 1st embodiment. FIG. 5A and FIG. 5B are schematic perspective views showing the nonvolatile memory device according to the second embodiment.

Each embodiment will be described below with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratios may be represented differently depending on the drawings.
Note that, in the present specification and each drawing, the same elements as those described above with reference to the previous drawings are denoted by the same reference numerals, and detailed description thereof is omitted as appropriate.

(First embodiment)
FIG. 1 is a schematic cross-sectional view illustrating the variable resistance element according to the first embodiment.

  As illustrated in FIG. 1, the variable resistance element 101 according to the embodiment includes a first electrode 10, a second electrode 20, a first layer 31, a second layer 32, and a metal part 40.

  The first electrode 10 includes, for example, at least one of tungsten (W), aluminum (Al), and copper (Cu). Here, for example, tungsten (W) is used for the first electrode 10.

  For example, polycrystalline silicon is used for the second electrode 20. For example, phosphorus (P) is introduced into the polycrystalline silicon. Thereby, for example, the resistivity of the second electrode 20 is adjusted. A metal such as tungsten (W) may be used for the second electrode 20.

  A first direction from the second electrode 20 toward the first electrode 10 is taken as a Z-axis direction. One direction perpendicular to the Z-axis direction is taken as an X-axis direction. A direction perpendicular to the X-axis direction and perpendicular to the Z-axis direction is taken as a Y-axis direction.

The first layer 31 is provided between the first electrode 10 and the second electrode 20. The first layer 31 includes an oxide of the first element. Examples of the first element include silicon (Si), hafnium (Hf), nickel (Ni), vanadium (V), zirconium (Zr), molybdenum (Mo), aluminum (Al), chromium (Cr), and niobium (Nb). ). For example, Si is used as the first element, and the first layer 31 includes silicon oxide (SiO ₂ ). The first layer 31 may include silicon oxynitride. The first layer 31 is, for example, insulative. The thickness (the length along the Z-axis direction) of the first layer 31 can be set to 2 nm or more and 20 nm or less, for example.

  The metal part 40 is provided between the first layer 31 and the first electrode 10. For example, a part of the metal part 40 is in contact with the first layer 31. The metal part 40 includes a first metal. The first metal includes, for example, at least one of silver (Ag), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), and aluminum (Al). For example, Ag is used for the first metal.

  The second layer 32 is provided between the first layer 31 and the first electrode 10. The second layer 32 is aligned with at least a part of the metal part 40 in the second direction intersecting with the Z-axis direction (first direction). In the example illustrated in FIG. 1, the second layer 32 is provided between the plurality of portions 40 a of the metal part 40 and between the plurality of portions 40 a and the first electrode 10. The second layer 32 includes a second metal. As the second metal, at least one of tungsten (W), hafnium (Hf), molybdenum (Mo), zirconium (Zr), and chromium (Cr) is used.

  For example, a set voltage is applied between the first electrode 10 and the second electrode 20. Thereby, for example, the first metal contained in the metal part 40 is ionized and diffused into the first layer 31 to form a conductive path called a filament. By forming the filament in the first layer 31, the resistance change element 101 changes from the high resistance state to the low resistance state.

  A reset voltage is applied between the first electrode 10 and the second electrode 20. The polarity of the reset voltage is opposite to the polarity of the set voltage, for example. Thereby, for example, the first metal contained in the filament in the first layer 31 is ionized. As the filament is decomposed in this manner, the resistance change element 101 changes from the low resistance state to the high resistance state.

  By applying a voltage between the first electrode 10 and the second electrode 20, for example, a state in which the filament is extended and a state in which the filament is disassembled can be switched. For example, ions of the first metal enter and exit the first layer 31. The electrical resistance between the first electrode 10 and the second electrode 20 changes reversibly.

2A and 2B are schematic cross-sectional views illustrating the operation of the variable resistance element according to the first embodiment.
FIG. 2A illustrates the low resistance state (first state ST1) of the variable resistance element 101.
FIG. 2B illustrates the high resistance state (second state ST2) of the variable resistance element 101.

  As shown in FIG. 2A, the filament 35 is formed in the first layer 31 in the low resistance state. For example, the filament 35 is in a state of extending in the direction from the metal part 40 toward the second electrode 20 in the first layer 31.

  In the growth process of the filament 35, a set voltage is applied between the first electrode 10 and the second electrode 20. In the state where the set voltage is applied, the potential of the first electrode 10 is higher than the potential of the second electrode 20. Thereby, for example, the first metal of the metal part 40 is ionized and enters the first layer 31. Further, for example, electrons are supplied to the first layer 31 via the second electrode 20. In the first layer 31, the ionized first metal and electrons are bonded. Thereby, for example, the filament 35 grows in the first layer 31.

  As shown in FIG. 2B, in the high resistance state, the filament 35 in the first layer 31 is in a state of being decomposed compared to the low resistance state.

  In the process of disassembling the filament 35, a reset voltage is applied between the first electrode 10 and the second electrode. In the state where the reset voltage is applied, the potential of the first electrode 10 is lower than the potential of the second electrode 20. For example, holes are supplied to the first layer 31 via the second electrode 20. Thereby, for example, the first metal of the filament 35 in the first layer 31 is ionized. For example, the ionized first metal is collected in the metal part 40.

  The length along the Z-axis direction of the region 35r including the first metal in the first layer 31 in the low resistance state is the first length L1. The length along the Z-axis direction of the region 35r including the first metal in the first layer 31 in the high resistance state is the second length L2. The first length L1 is longer than the second length L2.

  For example, in the high resistance state, the first layer 31 may not include the region 35r containing the first metal. In this case, there is a region 35r including the first metal in the first layer 31 in the low resistance state, and the first layer 31 does not include the first metal in the high resistance state. In this way, the high resistance state and the low resistance state may be switched.

  In the resistance change element 101 according to the embodiment, the second layer 32 is, for example, a barrier metal. The metal part 40 is formed as a thin film, and a barrier metal is provided thereon. Thereby, for example, the adhesion between the first metal and the first layer 31 is improved, and deterioration of characteristics can be suppressed.

The thickness of the metal part 40 is, for example, 5 nm or less. The metal part 40 may include a plurality of portions 40a. Each of the plurality of portions 40a is separated from each other in a direction intersecting with the Z-axis direction, for example. That is, the metal part 40 may have an island shape.
Some of the plurality of portions 40a of the metal part 40 may be in contact with each other in the direction in the XY plane. That is, the metal part 40 may have a net shape.

  In the embodiment, the second layer 32 is made of a metal that hardly reacts with the first layer 31. For example, when the second layer 32 and the first layer 31 react, an oxide of the second metal contained in the second layer 32 is generated between the second layer 32 and the first layer 31. When a voltage is applied between the first electrode 10 and the second electrode 20, a current may flow through the oxide of the second metal. This current deteriorates the characteristics of the variable resistance element as a leakage current.

  In the embodiment, the generation free energy per unit substance amount of the second metal oxide is larger than the generation free energy per unit substance amount of the oxide of the first element. That is, the second metal contained in the second layer hardly reacts with the first layer 31, and the oxide of the second metal is not easily generated. Thus, a metal having low reactivity with the first layer 31 is used as the barrier metal. For example, the reliability of the variable resistance element is improved. For example, leakage current is suppressed and the characteristics of the element are improved.

FIG. 3A and FIG. 3B are graphs illustrating characteristics of the resistance change element.
The horizontal axes of FIG. 3A and FIG. 3B represent the voltage V1 (volt: V) applied between the first electrode 10 and the second electrode 20. 3A and 3B, the vertical axis represents the current I1 (ampere: A) that flows between the first electrode 10 and the second electrode 20.

  FIG. 3A illustrates the characteristics of the variable resistance element 102 according to the first embodiment. The variable resistance element 102 has the same configuration as that described for the variable resistance element 101.

In this example, Si is used as the first element. That is, the first layer 31 includes SiO ₂ . Ag is used for the first metal. The thickness of the metal part 40 is about 1 nm. W is used for the second metal. The second layer 32 includes WN. The thickness of the second layer 32 is about 190 nm.

In this case, the free energy of formation of the oxide of the first element (ie, SiO ₂ ) is −856 kJ / mol. The free energy of formation of the second metal oxide (ie, WO ₃ ) is −764 kJ / mol. Thus, the free energy of formation of the oxide of the first element is smaller than the formation energy of the oxide of the second metal. For example, the reaction between the second metal (W) and the first layer (SiO ₂ ) is represented by the formula W + SiO ₂ + (1/2) O ₂ → WO ₃ . The change ΔG in free energy at this time is +92 kJ / mol. For this reason, an oxide of the second metal is hardly generated. For example, leakage current can be suppressed.

  As shown in FIG. 3A, in the variable resistance element 102, for example, hysteresis is observed in the relationship between the voltage V1 and the current I1. For example, it can be seen that the electrical resistance changes corresponding to two states, a low resistance state (first state ST1) and a high resistance state (second state ST2).

  FIG. 3B illustrates characteristics of the resistance change element 190 of the reference example. In the resistance change element 190 of the reference example, titanium (Ti) is used as the second metal. The second layer 32 includes TiN. Other than this, the resistance change element 190 has the same configuration as that described for the resistance change element 102.

In the case of this reference example, the free energy of formation of the oxide of the second metal (that is, TiO ₂ ) is −885 kJ / mol. This is smaller than the free energy of formation (-856 kJ / mol) of the oxide (SiO ₂ ) of the first element. For example, the reaction between the second metal (Ti) and the first layer (SiO ₂ ) is represented by the formula Ti + SiO ₂ → TiO ₂ . The change in free energy at this time is −29 kJ / mol. For this reason, in the resistance change element 190 of the reference example, the second metal easily reacts with the first layer 31. TiO ₂ is easily generated between the second layer 32 and the first layer 31. For example, a leakage current flows between the first electrode 10 and the second electrode 20 through the TiO ₂ . For this reason, switching between the high resistance state and the low resistance state is not sufficiently performed, and the characteristics of the element deteriorate.

  As shown in FIG. 3B, in the resistance change element 190 of the reference example, no hysteresis is observed in the relationship between the voltage and the current.

  Thus, the leakage current can be suppressed by using a metal having a relatively low reactivity with the first layer 31 as the metal used for the second layer 32. Thereby, switching between the high resistance state and the low resistance state can be performed stably. A variable resistance element capable of stable operation can be obtained.

As described above, Mo may be used for the second metal. For example, the generation free energy of MoO ₃ is −668 kJ / mol, which is smaller than the generation free energy of SiO ₂ .

For example, the generation free energy per unit substance amount of the first metal oxide is larger than the generation free energy per unit substance amount of the second metal oxide. In this example, the generation free energy of the oxide (Ag ₂ O) of the first metal (Ag) is, for example, −11 kJ / mol. The reactivity with the first layer 31 of the first metal is low. Thereby, for example, the oxide of the first metal is hardly formed, and the leakage current can be suppressed. A variable resistance element capable of stable operation can be obtained.

FIG. 4 is a schematic cross-sectional view illustrating the resistance change element according to the first embodiment.
FIG. 4 illustrates the variable resistance element 103. Also in the resistance change element 103, the first electrode 10, the second electrode 20, the first layer 31, the second layer 32, the metal part 40, and the like are provided. For these, the same configuration as that described for the variable resistance element 102 can be applied.

  As illustrated in FIG. 4, the variable resistance element 103 further includes a third layer 33. The third layer 33 is provided between the first layer 31 and the second electrode 20.

  The third layer 33 includes, for example, an oxide of the first element. For example, at least one of silicon oxide and silicon oxynitride can be used. For example, at least one of the substances included in the third layer 33 is different from the substance included in the first layer 31.

  Thus, a laminated body is provided between the second electrode 20 and the metal part 40. Thereby, for example, in each of the high resistance state and the low resistance state, the length along the Z-axis direction of the filament (region including the first metal) formed in the first layer 31 or the third layer 33 This makes it easier to control.

  In the laminated body provided between the second electrode 20 and the metal part 40, the number of laminated layers may be two or more.

(Second Embodiment)
The present embodiment relates to a nonvolatile memory device. The nonvolatile memory device according to the embodiment includes any of the resistance change elements described in the first embodiment and modifications thereof. For example, the nonvolatile memory device according to the present embodiment includes, for example, any one of the resistance change elements described above and the control unit 50 that applies a voltage between the first electrode 10 and the second electrode 20. According to the present embodiment, a nonvolatile memory device capable of stable operation can be provided.

FIG. 5A and FIG. 5B are schematic perspective views illustrating the nonvolatile memory device according to the second embodiment.
As shown in FIG. 5A, the nonvolatile memory device 250 according to the present embodiment includes a plurality of first wirings WR1, a plurality of second wirings WR2, and a plurality of memory cells MC. The plurality of memory cells MC include the resistance change element according to the embodiment and modifications thereof.

  The plurality of first wirings WR1 intersects the plurality of second wirings WR2 three-dimensionally. For example, the first wiring WR1 extends along the X-axis direction. The second wiring WR2 extends along the Y-axis direction. In this example, the Y-axis direction is orthogonal to the X-axis direction. A direction orthogonal to the X-axis direction and the Y-axis direction is taken as a Z-axis direction. In this example, the second wiring WR2 is separated from the first wiring WR1 in the Z-axis direction.

  Each of the plurality of memory cells MC (resistance change elements) is disposed at a position between the plurality of first wirings WR1 and the plurality of second wirings WR2.

  Each of the first wiring WR1 and the second wiring WR2 is electrically connected to the control unit 50. A voltage is applied to the memory cell MC through the first wiring WR1 and the second wiring WR2, and the above operation is performed.

  The first wiring WR1 includes, for example, first to third bit lines BL1 to BL3. The second wiring WR2 includes first to third word lines WL1 to WL3. The state of the memory cell MC is written, read, or erased by these bit lines and word lines.

  In the embodiment, a rectifying element (for example, a diode) may be provided at least at a position between the first wiring WR1 and the resistance change element and between the second wiring WR2 and the resistance change element.

  As shown in FIG. 5B, the nonvolatile memory device 251 according to the present embodiment includes a plurality of element memory layers MA stacked on each other. The plurality of element memory layers MA are stacked, for example, along the Z-axis direction. In this example, four element memory layers MA, that is, first to fourth element memory layers MA1 to MA4 are provided. The number of element memory layers MA is arbitrary.

  Each of the element memory layers MA includes a first wiring WR1, a second wiring WR2, and a memory cell MC.

  The first element memory layer MA1 includes a first layer bit line BLL1 (including bit lines BL11, BL12, and BL13), a first layer word line WLL1 (including word lines WL11, WL12, and WL13), and a first layer memory. Cell MC1.

  The second element memory layer MA2 includes a second layer bit line BLL2 (including bit lines BL21, BL22, and BL23), a first layer word line WLL1 (including word lines WL11, WL12, and WL13), and a second layer memory. Cell MC2.

  The third element memory layer MA2 includes a second layer bit line BLL2 (including bit lines BL21, BL22, and BL23), a second layer word line WLL2 (including word lines WL21, WL22, and WL23), and a third layer memory. Cell MC3.

  The fourth element memory layer MA4 includes a third layer bit line BLL3 (including bit lines BL31, BL32, and BL33), a second layer word line WLL2 (including word lines WL21, WL22, and WL23), and a fourth layer memory. Cell MC4.

  In this example, the bit line BL or the word line WL is shared in the element memory layers MA adjacent along the Z-axis direction. The embodiment is not limited to this. For example, an interlayer insulating film may be provided between element memory layers MA adjacent along the Z-axis direction, and a bit line BL and a word line WL may be provided in each of the element memory layers MA. In this case, the extending direction of the bit line BL and the extending direction of the word line WL in each of the element memory layers MA are arbitrary.

  According to the present embodiment, a metal having a relatively low reactivity with the first layer 31 is used for the second metal contained in the second layer 32. Thereby, switching between the high resistance state and the low resistance state can be realized with high reliability. According to the embodiment, a highly reliable element can be obtained.

  According to the embodiment, it is possible to provide a variable resistance element and a non-volatile memory device capable of stable operation.

  In the present specification, “vertical” is not strictly vertical, but includes, for example, variations in the manufacturing process, and may be substantially vertical.

The embodiments of the present invention have been described above with reference to specific examples. However, embodiments of the present invention are not limited to these specific examples. For example, regarding the specific configuration of each element such as the first electrode, the second electrode, the first layer, the second layer, and the metal portion, the present invention is similarly implemented by appropriately selecting from a known range by those skilled in the art. As long as the same effect can be obtained, it is included in the scope of the present invention.
Moreover, what combined any two or more elements of each specific example in the technically possible range is also included in the scope of the present invention as long as the gist of the present invention is included.

  In addition, all variable resistance elements and nonvolatile memory devices that can be implemented by those skilled in the art based on the variable resistance elements and nonvolatile memory devices described above as embodiments of the present invention are also included in the present invention. As long as the gist is included, it belongs to the scope of the present invention.

  In addition, in the category of the idea of the present invention, those skilled in the art can conceive of various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the present invention. .

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 10 ... 1st electrode, 20 ... 2nd electrode, 31 ... 1st layer, 32 ... 2nd layer, 33 ... 3rd layer, 35 ... Filament, 35r ... area | region, 40 ... Metal part, 40a ... part, 50 ... Control 101, 103, 190 ... variable resistance element, 250 ... non-volatile memory device, 251 ... non-volatile memory device, BL, BL11-BL13, BL21-BL23, BL31-BL33 ... bit lines, BL1-BL3 ... first 3rd bit line, BLL1 to BLL3 ... 1st to 3rd layer bit line, I1 ... Current, L1 ... 1st length, L2 ... 2nd length, MA ... Element memory layer, MA1 to MA4 ... 1st to 1st 4 element memory layer, MC ... memory cell, MC1 ... 1st to 4th layer memory cell, ST1 ... 1st state, ST2 ... 2nd state, V1 ... voltage, WL ... word line, WL11-WL13 WL21～WL23 ... word lines, WL1 to WL3 ... first to third word lines, WLL1~WLL2 ... first to the second layer word line, WR1 ... first wiring, WR2 ... second wiring

Claims (11)

A first electrode;
A second electrode;
An insulating first layer provided between the first electrode and the second electrode and including an oxide of a first element;
A metal part provided between the first layer and the first electrode and including a first metal;
In a second direction that is provided between the first layer and the first electrode and intersects the first direction from the first electrode toward the second electrode, at least a part of the metal portion and the second metal A second layer including,
With
In the first state, the length in the first direction of the region containing the first metal in the first layer is longer than the length of the region in the second state, or in the first state, the first There is a region containing the first metal in one layer, and in the second state, the first layer does not contain the first metal,
The electrical resistance between the first electrode and the second electrode in the first state is lower than the electrical resistance between the first electrode and the second electrode in the second state,
A variable resistance element in which a free energy of formation per unit substance amount of the oxide of the second metal is larger than a free energy of formation per unit quantity of oxide of the first element.   2. The variable resistance element according to claim 1, wherein the first element includes at least one of silicon, hafnium, nickel, vanadium, zirconium, molybdenum, aluminum, chromium, and niobium.   The variable resistance element according to claim 1, wherein the first layer includes at least one of silicon oxide and silicon oxynitride.   The resistance change element according to claim 1, wherein the first metal includes at least one of silver, cobalt, nickel, copper, zinc, and aluminum.   The resistance change element according to claim 1, wherein the second metal includes at least one of tungsten, molybdenum, zirconium, chromium, and hafnium.   The variable resistance element according to claim 1, wherein a length of the metal part along the first direction is 5 nm or less.   The resistance change element according to claim 1, further comprising a third layer provided between the first layer and the second electrode and including an oxide of the first element.   The generation free energy per unit substance amount of the oxide of one metal is larger than the generation free energy per unit substance amount of the second metal oxide. Variable resistance element. The metal part includes a plurality of parts,
9. The variable resistance element according to claim 1, wherein each of the plurality of portions is spaced from each other in a direction intersecting the first direction. The variable resistance element according to any one of claims 1 to 9,
A controller that applies a voltage between the first electrode and the second electrode;
A non-volatile storage device. A plurality of first wires;
A plurality of second wires;
Further comprising
The plurality of first wirings intersect with the plurality of second wirings,
A plurality of the variable resistance elements are provided,
The nonvolatile memory device according to claim 10, wherein each of the plurality of resistance change elements is disposed at a position between the plurality of first wirings and the plurality of second wirings.

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