Semiconductor memory device

According to one embodiment, a semiconductor memory device includes a plurality of first interconnects extending in a first direction, a plurality of second interconnects extending in a second direction crossing the first direction, and a memory element provided between the first interconnect and the second interconnect at a portion where the first interconnect crosses the second interconnect. The memory element includes a variable resistance film and a stress generating film stacked with the variable resistance film to apply stress to the variable resistance film in a surface direction.

FIELD

BACKGROUND

A resistance change element has been proposed as a memory cell of a new nonvolatile semiconductor memory device. A variable resistance film can be switched to at least two resistance states having relatively different resistances by controlling the magnitude, polarity, and application time of the voltage applied to the variable resistance film, etc.

For example, an ion-movement type resistance change element has been proposed in which the resistance is changed by causing metal ions and/or oxygen ions inside the variable resistance film to move by an applied voltage.

DETAILED DESCRIPTION

According to one embodiment, a semiconductor memory device includes a plurality of first interconnects extending in a first direction, a plurality of second interconnects extending in a second direction crossing the first direction, and a memory element provided between the first interconnect and the second interconnect at a portion where the first interconnect crosses the second interconnect. The memory element includes a variable resistance film and a stress generating film stacked with the variable resistance film to apply stress to the variable resistance film in a surface direction.

Various embodiments will be described hereinafter with reference to the accompanying drawings. Similar components in the drawings are marked with like reference numerals.

First Embodiment

FIG. 1is a schematic perspective view of an example of a memory cell array1in a semiconductor memory device of a first embodiment.

The memory cell array1includes multiple first interconnects11and multiple second interconnects12. Further, the memory cell array1includes stacked films10having columnar configurations provided between the first interconnects11and the second interconnects12.

The first interconnects11and the second interconnects12cross each other three-dimensionally to be non-parallel. For example, the first interconnects11extend in a first direction (a Y direction); the second interconnects12extend in a second direction (an X direction) orthogonal to the first direction; and the first interconnects11and the second interconnects12are orthogonal to each other. Each of the multiple stacked films10is provided at a cross point where the first interconnect11and the second interconnect12cross each other.

The multiple stacked films10are disposed in two-dimensional directions (XY directions) in, for example, a matrix configuration; and an array having the matrix configuration is multiply stacked in a third direction (a Z direction) orthogonal to the XY plane.

FIG. 1shows, for example, a portion in which4layers of an array of 3 rows by 3 columns are stacked.

The first interconnect11is shared by the stacked films10on and under the first interconnect11. Similarly, the second interconnect12is shared by the stacked films10on and under the second interconnect12.

The stacked film10includes a memory element (a memory cell).

FIG. 2Ais a schematic cross-sectional view showing an example of the memory element.

The memory element includes a lower layer electrode21, an upper layer electrode22, and a variable resistance film20that is provided between the lower layer electrode21and the upper layer electrode22.

The variable resistance film20is stacked on the lower layer electrode21; and the lower layer electrode21contacts the lower surface of the variable resistance film20.

The upper layer electrode22is stacked on the variable resistance film20to contact the upper surface of the variable resistance film20.

The variable resistance film20is electrically switchable between a state (a set state) in which the resistance is relatively low and a state (a reset state) in which the resistance is relatively high to nonvolatilely store data.

The variable resistance film20includes a metal oxide. For example, the variable resistance film20includes an oxide of at least one element selected from lithium (Li), manganese (Mn), tantalum (Ta), niobium (Nb), chromium (Cr), nickel (Ni), tungsten (W), cobalt (Co), iron (Fe), hafnium (Hf), titanium (Ti), silicon (Si), and zirconium (Zr).

The variable resistance film20in the low resistance state (the set state) which has a relatively low resistance can be switched to the high resistance state (the reset state) which has a relatively high resistance when a reset voltage is applied to the variable resistance film20via the interconnects11and12on and under the memory element subjected to the operation. The variable resistance film20can be switched to the low resistance state (the set state) when a set voltage that is higher than the reset voltage is applied to the variable resistance film20in the high resistance state (the reset state).

According to the embodiment, the resistance value is changed by electrically causing metal ions and/or oxygen ions inside the variable resistance film20to move. Such an ion-movement type resistance change element is largely considered to have two improvement points due to the material of the variable resistance film20.

One point is that, because the ions move easily, even in the case where programming using the ion movement is performed, there is a high probability of the ions returning to the original positions; and the data retention characteristics degrade.

One other point is that the ions do not move easily; and the number of possible reads and programs decreases due to the ions undesirably moving while damaging the crystal of the main material.

It is considered that the former occurs because the paths of the ions inside the crystal of the main material are sufficiently large for the size of the ions; and the ions unfortunately can move easily.

It is considered that the latter occurs because the paths of the ions are so small that the crystal of the main material is undesirably damaged.

In either case, it is difficult to realize both a sufficient number of programs and a sufficient retention time of data.

For example, the variable resistance film20of the embodiment includes mainly LiCoO2, LiMn2O4, LiNiO2, LiFePO4, etc., as the metal oxide.

The resistance of the variable resistance film20is changed by causing the Li ions to move to the lower layer electrode21vicinity and/or the upper layer electrode22vicinity by applying a voltage between the upper and lower electrodes22and21.

However, because it is possible for the Li ions inside the Li oxide film to move easily, the Li ions easily return to the original positions when the voltage application is stopped.

Therefore, according to the embodiment, the lattice constant of the main material crystal of the variable resistance film20is adjusted by applying stress to the variable resistance film20.

For example, in the example shown inFIG. 2A, compressive stress is applied to the variable resistance film20by stacking the upper layer electrode22that has compressive stress on the variable resistance film20.

In the first embodiment, the direction of the stress of each of the films is the surface direction of the film.

The lattice constant in the surface direction of the variable resistance film20to which the compressive stress is applied by the upper layer electrode22becomes smaller than prior to the compressive stress being applied, that is, prior to forming the upper layer electrode22. When the upper layer electrode22is peeled after forming the upper layer electrode22, the compressive stress that had been applied to the variable resistance film20from the upper layer electrode22is relaxed; and the lattice constant in the surface direction of the variable resistance film20becomes larger than that of the state in which the upper layer electrode22was stacked on the variable resistance film20.

The variable resistance film20itself may not have compressive stress. Even in the case where the variable resistance film20has tensile stress, the tensile stress of the variable resistance film20becomes smaller than prior to forming the upper layer electrode22by the formation of the upper layer electrode22that has compressive stress; and it is possible to reduce the lattice constant.

The change of the lattice constant (the lattice strain) can be analyzed by, for example, Nano Beam Electron Diffraction to obtain an electron diffraction pattern by irradiating a nanobeam having a diameter of several tens of nm.

By the lattice constant of the variable resistance film20becoming small, the paths of the Li ions become narrow; and the Li ions move less easily.

Thereby, it is possible to stably store the data memory state because the Li ions that move due to the voltage application are stored at substantially the same positions even after stopping the voltage application.

For example, a titanium nitride film formed by sputtering using a titanium target in a nitrogen atmosphere can be used as the upper layer electrode22which is the stress generating film. It is possible to generate the compressive stress and it is possible to adjust the magnitude of the stress by adjusting the film formation temperature and nitrogen content of the sputtering film formation of the titanium nitride film, etc. The upper layer electrode22is formed to have compressive stress that is, for example, not less than 1 GPa.

Also, a film other than the electrodes can be used as the stress generating film.

FIG. 2Bshows the structure of a memory element in which a stress generating film32is stacked on the upper layer electrode22.

The stress generating film32has compressive stress. The compressive stress of the stress generating film32is applied to the upper layer electrode22, which is stacked under the stress generating film32and is in contact with the stress generating film32, and is further applied to the variable resistance film20under the upper layer electrode22.

The lattice constant in the surface direction of the variable resistance film20to which the compressive stress is applied by the stress generating film32becomes smaller than prior to the compressive stress being applied, that is, prior to forming the stress generating film32. When the stress generating film32is peeled after forming the stress generating film32, the compressive stress that had been applied to the variable resistance film20from the stress generating film32is relaxed; and the lattice constant in the surface direction of the variable resistance film20becomes larger than that of the state in which the stress generating film32was stacked on the variable resistance film20.

In such a case as well, the variable resistance film20itself may not have compressive stress. Even in the case where the variable resistance film20has tensile stress, the tensile stress of the variable resistance film20becomes smaller than prior to forming the stress generating film32by the formation of the stress generating film32that has compressive stress; and it is possible to reduce the lattice constant.

By the lattice constant of the variable resistance film20becoming small, the paths of the Li ions become narrow; the Li ions move less easily; and it is possible to stably store the data memory state because the Li ions that move due to the voltage application are stored at the same positions even after stopping the voltage application.

The stress generating film32is an insulating film or a conductor film.

The stress generating film32is, for example, a silicon nitride film. Compressive stress can be applied to the silicon nitride film and the magnitude of the compressive stress can be adjusted by adjusting the nitrogen content (the nitrogen concentration) and/or film formation temperature of the silicon nitride film. The stress generating film32is formed to have, for example, compressive stress that is not less than 1 GPa.

Also, as shown inFIG. 2C, compressive stress may be applied to both the upper layer electrode22and the lower layer electrode21; and the compressive stress can be applied to the variable resistance film20from both the upper layer electrode22and the lower layer electrode21. The upper layer electrode22and the lower layer electrode21have compressive stress that is in the surface direction of the film and in the same direction.

The lower layer electrode21may include the same film as the upper layer electrode22, e.g., a titanium nitride film. By performing annealing after forming the variable resistance film20on the lower layer electrode21, the compressive stress can be generated in the lower layer electrode21; and the compressive stress can be applied to the variable resistance film20from the lower layer electrode21.

Also, as shown inFIG. 3A, a structure may be used in which only the lower layer electrode21is used as the stress generating film. By performing annealing after forming the variable resistance film20on the lower layer electrode21, the compressive stress can be generated in the lower layer electrode21; and the compressive stress can be applied to the variable resistance film20from the lower layer electrode21.

Further, as shown inFIG. 3B, a structure may be used in which a stacked body having the variable resistance film20interposed between the electrodes21and22is interposed between the stress generating film32and a stress generating film31.

The lower layer electrode21is stacked on the stress generating film31; and the stress generating film32is stacked on the upper layer electrode22.

The stress generating film31on the lower side and the stress generating film32on the upper side have compressive stress that is in the surface direction of the film and in the same direction.

The stress generating film31and the stress generating film32are the same film, e.g., a silicon nitride film.

Also, as shown inFIG. 3C, the compressive stress may be applied to the variable resistance film20by only the stress generating film31stacked under the lower layer electrode21.

By performing annealing after forming the variable resistance film20on the stress generating film31with the lower layer electrode21interposed, the compressive stress can be generated in the stress generating film31; and the compressive stress can be applied from the stress generating film31to the variable resistance film20via the lower layer electrode21.

The variable resistance film20is not limited to Li oxide and may have a structure including, for example, Mn3O4. There is a possibility that the crystal of the Mn3O4which is used as the main material may be damaged when the Mn ions move inside the Mn3O4due to the voltage application; and there are cases where the number of possible programs and erases becomes low.

Therefore, when the variable resistance film20includes Mn3O4, it is favorable to use a stress generating film that has tensile stress rather than compressive stress.

Thereby, it is possible to increase the lattice constant of the variable resistance film20, widen the paths of the Mn ions, and drastically increase the number of possible programs and erases.

Further, the resistance can be changed by causing the oxygen ions to move inside the film by a voltage application for the variable resistance film20including a metal oxide such as TaOx, NbOx, CrOx, NiOx, WOx, CoOx, FeOx, HfOx, TiOx, SiOx, ZrOx, etc. In these films as well, the crystal is damaged easily because the paths of the oxygen ions are small.

Accordingly, it is possible to widen the paths of the oxygen ions and drastically increase the number of programs and erases by stacking a stress generating film that has tensile stress for the variable resistance film20in which the movement of the oxygen ions contributes to the resistance change.

In the example shown inFIG. 4A, tensile stress is applied to the variable resistance film20by stacking the upper layer electrode22that has tensile stress on the variable resistance film20.

The lattice constant in the surface direction of the variable resistance film20to which the tensile stress is applied by the upper layer electrode22becomes larger than prior to the tensile stress being applied, that is, prior to forming the upper layer electrode22. When the upper layer electrode22is peeled after forming the upper layer electrode22, the tensile stress that had been applied to the variable resistance film20from the upper layer electrode22is relaxed; and the lattice constant in the surface direction of the variable resistance film20becomes smaller than that of the state in which the upper layer electrode22was stacked on the variable resistance film20.

The variable resistance film20itself may not have tensile stress. Even in the case where the variable resistance film20has compressive stress, the compressive stress of the variable resistance film20becomes smaller than prior to forming the upper layer electrode22by the formation of the upper layer electrode22that has tensile stress; and it is possible to increase the lattice constant.

By the lattice constant of the variable resistance film20becoming large, the paths of the ions widen; and the ions move more easily.

Thereby, the crystal damage due to the movement of the ions can be suppressed; and it is possible to drastically increase the number of possible programs and erases.

For example, a titanium nitride film formed by sputtering using a titanium target in a nitrogen atmosphere can be used as the upper layer electrode22which is the tensile stress generating film. By adjusting the nitrogen content and/or film formation temperature of the titanium nitride film, it is possible to generate tensile stress in the titanium nitride film; and it is possible to adjust the magnitude of the tensile stress.

For example, it is possible to change a compressive stress of about 1 GPa to a tensile stress of several hundred MPa by reducing the DC power and by reducing the TiN density in DC (direct current) sputtering.

A film other than the electrodes can be used as the tensile stress generating film.

FIG. 4Bshows the structure of a memory element in which the stress generating film32is stacked on the upper layer electrode22.

The stress generating film32has tensile stress. The tensile stress of the stress generating film32is applied to the upper layer electrode22, which is stacked under the stress generating film32and is in contact with the stress generating film32, and is further applied to the variable resistance film20under the upper layer electrode22.

The lattice constant in the surface direction of the variable resistance film20to which the tensile stress is applied by the stress generating film32becomes larger than prior to the tensile stress being applied, that is, prior to forming the stress generating film32. When the stress generating film32is peeled after forming the stress generating film32, the tensile stress that had been applied to the variable resistance film20from the stress generating film32is relaxed; and the lattice constant in the surface direction of the variable resistance film20becomes smaller than that of the state in which the stress generating film32was stacked on the variable resistance film20.

In such a case as well, the variable resistance film20itself may not have tensile stress. Even in the case where the variable resistance film20has compressive stress, the compressive stress of the variable resistance film20becomes smaller than prior to forming the stress generating film32by the formation of the stress generating film32that has tensile stress; and it is possible to increase the lattice constant.

By the lattice constant of the variable resistance film20becoming large, the paths of the ions widen; the ions move more easily; the crystal damage due to the movement of the ions can be suppressed; and it is possible to drastically increase the number of possible programs and erases.

The stress generating film32is an insulating film or a conductor film.

The stress generating film32is, for example, a silicon nitride film. By adjusting the nitrogen content (the nitrogen concentration) and/or film formation temperature of the silicon nitride film, tensile stress can be applied to the silicon nitride film; and the magnitude of the tensile stress can be adjusted. The stress generating film32is formed to have tensile stress that is, for example, not less than 1 GPa.

Also, as shown inFIG. 4C, the tensile stress can be applied to both the upper layer electrode22and the lower layer electrode21; and the tensile stress can be applied to the variable resistance film20from both the upper layer electrode22and the lower layer electrode21. The upper layer electrode22and the lower layer electrode21have tensile stress that is in the surface direction of the film and in the same direction.

The lower layer electrode21may include the same film as the upper layer electrode22, e.g., a titanium nitride film. By performing annealing after forming the variable resistance film20on the lower layer electrode21, the tensile stress can be generated in the lower layer electrode21; and the tensile stress can be applied to the variable resistance film20from the lower layer electrode21.

Further, as shown inFIG. 5A, a structure may be used in which only the lower layer electrode21is used as the stress generating film. By performing annealing after forming the variable resistance film20on the lower layer electrode21, the tensile stress can be generated in the lower layer electrode21; and the tensile stress can be applied to the variable resistance film20from the lower layer electrode21.

Also, as shown inFIG. 5B, a structure may be used in which a stacked body having the variable resistance film20interposed between the electrodes21and22is interposed between the stress generating film32and the stress generating film31.

The lower layer electrode21is stacked on the stress generating film31; and the stress generating film32is stacked on the upper layer electrode22.

The stress generating film31on the lower side and the stress generating film32on the upper side have tensile stress that is in the surface direction of the film and in the same direction.

The stress generating film31and the stress generating film32are the same film, e.g., a silicon nitride film.

Also, as shown inFIG. 5C, the tensile stress may be applied to the variable resistance film20by only the stress generating film31stacked under the lower layer electrode21.

By performing annealing after forming the variable resistance film20on the stress generating film31with the lower layer electrode21interposed, the tensile stress can be generated in the stress generating film31; and the tensile stress can be applied from the stress generating film31to the variable resistance film20via the lower layer electrode21.

Second Embodiment

FIG. 6is a schematic perspective view showing an example of a memory cell array of a semiconductor memory device of a second embodiment.

The memory cell array of the second embodiment is provided on a not-shown substrate and includes multiple variable resistance films50having tubular configurations extending in the Z direction (first direction) perpendicular to a major surface of the substrate.

Here, two directions that are orthogonal to each other in a plane parallel to the major surface of the substrate and orthogonal to the Z direction are taken as the X direction (second direction) and the Y direction (third direction).

Center electrodes52having columnar configurations extending in the Z direction are provided inside the variable resistance films50. The variable resistance films50are provided at the outer circumferences of the center electrodes52having the columnar configurations.

The multiple center electrodes52and the multiple variable resistance films50are disposed in a matrix configuration when the major surface of the substrate is viewed in plan.

Multiple outer electrodes51are multiply arranged in the X direction to be disposed between the center electrodes52. Here, the outer electrodes51are provided between the variable resistance films50that are adjacent to each other in the X direction; and the outer electrodes51are shared by the variable resistance films50that are adjacent to each other in the X direction.

The outer electrodes51extend in the Y direction. Here, the outer electrodes51are shared by the variable resistance films50of the center electrodes52that are adjacent to each other in the Y direction. Also, the outer electrodes51are stacked in the Z direction with a not-shown inter-layer insulating film interposed.

The variable resistance film50includes a metal oxide. The variable resistance film50includes, for example, an oxide of at least one element selected from lithium (Li), manganese (Mn), tantalum (Ta), niobium (Nb), chromium (Cr), nickel (Ni), tungsten (W), cobalt (Co), iron (Fe), hafnium (Hf), titanium (Ti), silicon (Si), and zirconium (Zr).

When a voltage is applied to the center electrode52and the outer electrode51, the ions of the region of the variable resistance film50interposed between the center electrode52and the outer electrode51move; the resistance of the region changes; and the programming and erasing of data are performed.

Two data can be stored by two outer electrodes51of the same layer being disposed at one center electrode52with the variable resistance film interposed in the X direction.

In the second embodiment as well, stress is applied to the variable resistance film50.

FIG. 7Ais a schematic cross-sectional view of one variable resistance film50and a pair of outer electrodes51having the variable resistance film50interposed in the X direction and corresponds to a cross section parallel to the XY plane ofFIG. 6.

In the example shown inFIG. 7A, stress is applied to the variable resistance film50by generating stress in the center electrode52that is provided in the columnar configuration inside the variable resistance film50.

In the second embodiment, the direction of the stress of the stress generating film having the columnar configuration is the central direction; and the direction of the stress of the variable resistance film50having the tubular configuration is the circumferential direction.

Compressive stress that is in the circumferential direction or the Y direction is generated in the center electrode52that is used as the stress generating film at the portion opposing the outer electrode51with the variable resistance film50interposed. The compressive stress is applied to the portion of the variable resistance film50that is interposed between the outer electrode51and the center electrode52.

Thereby, the lattice constant in the circumferential direction or the Y direction of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becomes smaller than prior to the compressive stress being applied, that is, prior to forming the center electrode52. When the center electrode52is removed, the compressive stress that had been applied to the variable resistance film50from the center electrode52is relaxed; and the lattice constant in the circumferential direction or the Y direction of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becomes larger than that of the state in which the center electrode52had been formed.

By the lattice constant of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becoming small, the paths of the Li ions become narrow; and the Li ions move less easily.

Thereby, it is possible to stably store the data memory state because the Li ions that move due to the voltage application are stored at the same positions even after stopping the voltage application.

After making multiple holes in a stacked body on the substrate to extend in the Z direction, the variable resistance film50is formed in tubular configurations at the inner circumferential walls of the holes.

Continuing, the center electrode52is formed as a film inside the variable resistance film50. For example, a titanium nitride film formed by sputtering using a titanium target in a nitrogen atmosphere can be used as the center electrode52which is the stress generating film.

Then, in the example shown inFIG. 7B, a center electrode62is provided in a tubular configuration inside the variable resistance film50; and a stress generating film53having a columnar configuration extending in the Z direction is provided inside the center electrode62.

The direction of the stress of the stress generating film53having the columnar configuration is the central direction. The stress is applied to the center electrode62, and is further applied as compressive stress to the portion of the variable resistance film50interposed between the outer electrode51and the center electrode52.

Thereby, the lattice constant in the circumferential direction or the Y direction of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becomes smaller than prior to the compressive stress being applied, that is, prior to forming the stress generating film53. When the stress generating film53is removed, the stress that had been applied to the variable resistance film50from the stress generating film53is relaxed; and the lattice constant in the circumferential direction or the Y direction of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becomes larger than that of the state in which the stress generating film53had been formed.

By the lattice constant of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becoming small, the paths of the Li ions become narrow; and the Li ions move less easily.

Thereby, it is possible to stably store the data memory state because the Li ions that move due to the voltage application are stored at the same positions even after stopping the voltage application.

After making multiple holes in a stacked body on the substrate to extend in the Z direction, the variable resistance film50is formed in tubular configurations at the inner circumferential walls of the holes.

Continuing, the center electrode62is formed in tubular configurations at the inner circumferential walls of the variable resistance film50.

Continuing, the stress generating film53is formed inside the center electrode62.

The stress generating film53is an insulating film or a conductor film. The stress generating film53is, for example, a silicon nitride film.

Also, similarly to the first embodiment, it is possible to widen the paths of the ions and drastically increase the number of programs and erases by applying tensile stress in the circumferential direction or the Y direction to the portion of the variable resistance film50that includes an oxide of at least one element selected from manganese, tantalum, niobium, chromium, nickel, tungsten, cobalt, iron, hafnium, titanium, silicon, and zirconium and is between the outer electrode51and the center electrode52.

In the example shown inFIG. 8A, stress is applied to the variable resistance film50by generating stress in the center electrode52that is provided in a columnar configuration inside the variable resistance film50to cause the center electrode52to expand in the outer circumferential direction.

Tensile stress is generated in the circumferential direction or the Y direction in the center electrode52that is used as the stress generating film at the portion opposing the outer electrode51with the variable resistance film50interposed. The tensile stress is applied to the portion of the variable resistance film50interposed between the outer electrode51and the center electrode52.

Thereby, the lattice constant in the circumferential direction or the Y direction of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becomes larger than prior to the tensile stress being applied, that is, prior to forming the center electrode52. When the center electrode52is removed, the tensile stress that had been applied to the variable resistance film50from the center electrode52is relaxed; and the lattice constant in the circumferential direction or the Y direction of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becomes smaller than that of the state in which the center electrode52had been formed.

By the lattice constant of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becoming large, the paths of the ions widen; and the ions move more easily.

Thereby, the crystal damage due to the movement of the ions can be suppressed; and it is possible to drastically increase the number of possible programs and erases.

Then, in the example shown inFIG. 8B, the center electrode62is provided in a tubular configuration inside the variable resistance film50; and the stress generating film53having a columnar configuration extending in the Z direction is provided inside the center electrode62.

Stress is generated in the stress generating film53having the columnar configuration to cause the stress generating film53to expand in the outer circumferential direction. The stress is applied to the center electrode62and is further applied as tensile stress to the portion of the variable resistance film50interposed between the outer electrode51and the center electrode52.

Thereby, the lattice constant in the circumferential direction or the Y direction of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becomes larger than prior to the tensile stress being applied, that is, prior to forming the stress generating film53. When the stress generating film53is removed, the tensile stress that had been applied to the variable resistance film50from the stress generating film53is relaxed; and the lattice constant in the circumferential direction or the Y direction of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becomes smaller than that of the state in which the stress generating film53had been formed.

By the lattice constant of the variable resistance film50at the portion interposed between the outer electrode51and the center electrode52becoming large, the paths of the ions widen; and the ions move more easily.

Thereby, the crystal damage due to the movement of the ions can be suppressed; and it is possible to drastically increase the number of possible programs and erases.

According to the embodiments described above, stress is applied to the variable resistance film; and the lattice constant of the variable resistance film is adjusted appropriately according to the main material crystal and/or type of the mobile ions of the variable resistance film. Thereby, the decrease of the number of possible programs and erases due to the damage of the main material crystal due to the ion movement inside the variable resistance film or the degradation of the data retention characteristics due to the ease of the ion movement inside the variable resistance film can be suppressed.