JP2008205140A - Memory device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a memory device which is manufactured by forming a vanadium dioxide thin film, and to provide a memory device such as a resistance change type nonvolatile memory manufactured by it. <P>SOLUTION: The method of manufacturing the memory device includes a step S1 of installing a substrate and a target material consisting of vanadium or vanadium oxide in a vacuum container, a negative pressure step S2 in the vacuum container, a gas introduction step S3 of introducing a rare gas and oxygen gas into the vacuum container, a heating step S4 of heating the substrate by a heating means in the vacuum container, a step S5 of applying a high frequency voltage to the target material, and a step S6 of forming electrodes consisting of an electrically conductive metal contiguous to the vanadium dioxide thin film formed on the substrate. Further, the memory device comprises the substrate on which the vanadium dioxide thin film undergoing metal-insulator phase transition is manufactured, and the electrodes consisting of the electrically conductive metal contiguous to the vanadium dioxide thin film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a memory element manufacturing method for manufacturing a memory element such as a variable resistance nonvolatile memory, and a memory element manufactured thereby.

Vanadium oxide includes vanadium monoxide (VO), vanadium dioxide (VO ₂ ), divanadium trioxide (V ₂ O ₃ ), divanadium pentoxide (V ₂ O ₅ ), and trivanadium trioxide (V ₃ O ₇ ). It has various oxidation states. Among them, vanadium dioxide is suitably used for a bolometer-type infrared temperature sensor because of its large temperature coefficient of resistance (TCR).

  Among vanadium dioxide, a crystal having a monoclinic crystal form at room temperature exhibits a so-called metal-insulator phase transition around 68 ° C., and has a property that the electric resistance value changes greatly. For such vanadium dioxide crystals, changes in electrical resistance values of three to four digits under a temperature condition of 60 to 70 ° C. have been reported (see Non-Patent Document 1).

This non-patent document 1 describes that a vanadium dioxide thin film is formed by a thin film lamination method called a laser deposition method. The laser deposition method is a method in which a vacuum vessel for laminating thin films is irradiated with laser light from the outside to evaporate the target material, and the evaporated target material is deposited on the substrate in the form of a thin film.
Non-Patent Document 1 describes that electric field induced phase transition is performed by applying a voltage to a vanadium dioxide thin film formed by such a method.

  On the other hand, Non-Patent Document 2 is promising as a next-generation memory of a semiconductor integrated circuit, a resistance random access memory (ReRAM) having a structure in which a transition metal oxide is sandwiched between metal electrodes. It is stated that it is. In this type of memory element, a resistance change is caused by a voltage, and a resistance switching effect can be obtained by the level of the resistance state.

H-T. Kim, et al., Applied Physics Letters, 86, 242101 (2005) Akihito Sawa, “Resistance-change-type non-volatile memory (ReRAM) using transition metal oxide”, Applied Physics, Applied Physics Society, September 2006, Vol. 75, No. 9, p. 1109-1114

  However, the laser deposition method described in Non-Patent Document 1 requires a high-power laser device installed outside the vacuum vessel for performing thin film deposition, so that the substrate on which the vanadium dioxide thin film is formed is required. Not suitable for mass production.

  In addition, although intensive research has been conducted to obtain a vanadium dioxide thin film using a magnetron sputtering apparatus conventionally used for mass production, it is difficult to set conditions such as the oxygen flow rate, the pressure in the vacuum vessel, and the heating temperature of the substrate. Only a thin film containing a large amount of vanadium oxide other than vanadium dioxide could be obtained. For this reason, it is difficult to obtain a vanadium dioxide thin film that undergoes a metal-insulator phase transition. In order to obtain such a vanadium dioxide thin film, it has been necessary to spend a great deal of effort in finding the film forming conditions. Furthermore, when a conventionally used magnetron sputtering apparatus is used, the crystal structure of the obtained vanadium dioxide does not show a metal-insulator phase transition because it is a high-temperature phase (Tetragonal).

  As described in Non-Patent Document 2, although ReRAM is currently promising as a next-generation memory, the principle of the switching operation that is the basis of the memory element function is unknown, and the element characteristics Not designed or optimized.

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a method for manufacturing a memory element manufactured by forming a vanadium dioxide thin film and a memory element manufactured thereby.

  In order to solve the above problems, a method for manufacturing a memory device according to the present invention includes an installation process, a negative pressure process, a gas introduction process, a heating process, a high frequency voltage application process, and an electrode formation process. .

As described above, the memory element manufacturing method according to the present invention has a substrate installed on the heating means provided in the vacuum vessel in the installation step, and a holder portion having a magnet provided at a position facing the heating means. After installing the target material made of vanadium or vanadium oxide, the air in the vacuum vessel is exhausted in the negative pressure step to make the inside of the vacuum vessel a negative pressure of 5.7 to 9.3 × 10 ⁻⁴ Pa. And a rare gas and oxygen gas are introduce | transduced in a vacuum vessel at a gas introduction process, maintaining a negative pressure state. And after heating a board | substrate to 300-450 degreeC with a heating means at a heating process, it is a high frequency to each of the target material and the electroconductive metal member to which the power supply for applying a high frequency voltage was connected by the high frequency voltage application process. A voltage is applied to form a vanadium dioxide thin film that undergoes a metal-insulator phase transition on the substrate. In the electrode forming step, a memory element can be obtained by forming an electrode made of a conductive metal in contact with the vanadium dioxide thin film formed on the substrate.

In the memory element manufacturing method of the present invention, it is preferable that the gas introduction step introduces a rare gas at 40 to 100 sccm and an oxygen gas at 1 to 10 sccm.
In the memory element manufacturing method of the present invention, it is preferable that the pressure in the vacuum vessel after the gas introduction step is maintained at 0.5 to 5.0 Pa.
In the memory element manufacturing method of the present invention, it is preferable that the heating step heats the substrate to 300 to 400 ° C.

  By limiting the manufacturing conditions of the memory element to such a specific range, it is possible to form a monoclinic type (low temperature phase (Monoclinic)) of vanadium dioxide having a good crystalline state on the substrate. Become.

  In the memory device manufacturing method of the present invention, the high-frequency voltage applying step applies high-frequency current to the target material under conditions of high-frequency current: 10 to 100 MHz and high-frequency power: 100 to 1000 W, and high-frequency voltage is applied to the conductive metal member. It is preferable to apply under conditions of current: 10 to 100 MHz and high frequency power: 100 to 1000 W.

  When the high-frequency voltage application step is performed under such conditions, monoclinic low-temperature phase (Monoclinic) vanadium dioxide can be reliably formed on the substrate.

  In order to solve the above problems, a memory device according to the present invention includes a substrate on which a vanadium dioxide thin film that undergoes a metal-insulator phase transition is manufactured, and an electrode made of a conductive metal in contact with the vanadium dioxide thin film. The configuration.

  Since the memory element having such a configuration includes a thin film of vanadium dioxide that undergoes a metal-insulator phase transition and an electrode made of a conductive metal in contact with the thin film, an ohmic contact can be obtained. This makes it possible to provide a voltage-current characteristic with a resistance switching effect (that is, a memory function).

In the memory element of the present invention, the vanadium dioxide thin film preferably has a monoclinic crystal structure.
A memory element having such a vanadium dioxide thin film can have a good metal-insulator phase transition ability because the crystal structure of the vanadium dioxide thin film is a monoclinic crystal type. Therefore, it is possible to obtain an excellent memory element in which a resistance switching effect, that is, a memory function is easily generated in the voltage-current characteristics.

According to the memory device manufacturing method of the present invention, since the memory device is manufactured using the vanadium dioxide thin film that undergoes a metal-insulator phase transition, the memory device having a resistance switching effect (memory function) in voltage-current characteristics. Can be obtained.
Since the memory element according to the present invention uses a vanadium dioxide thin film that undergoes a metal-insulator phase transition, it has a resistance switching effect (memory function) in voltage-current characteristics. Further, the memory device according to the present invention has a clear principle of switching operation, and has an effect that the device characteristics as ReRAM can be designed and optimized.

Next, a memory device manufacturing method and a memory device according to the present invention will be described in detail with reference to the drawings as appropriate.
In the drawings to be referred to, FIG. 1 is an explanatory view showing a configuration example of a vanadium dioxide thin film forming apparatus used for manufacturing a memory element according to the present invention. FIG. 2 is a flowchart showing the process contents of the method for manufacturing a memory device according to the present invention.

The memory element manufacturing method according to the present invention is a suitable memory because the vanadium dioxide thin film becomes a good crystalline state when manufactured using a substrate provided with the vanadium dioxide thin film formed by the vanadium dioxide thin film forming apparatus 1 described later. An element can be manufactured.
Therefore, first, the vanadium dioxide thin film forming apparatus 1 used for manufacturing the memory element will be described with reference to FIG.

The vanadium dioxide thin film forming apparatus 1 is an apparatus that forms a vanadium dioxide thin film that undergoes a metal-insulator phase transition on a substrate 2 by sputtering using an ICP-assisted sputtering method.
Here, the ICP-assisted sputtering method refers to a sputtering method using high-density plasma generated by an inductive coupling method. When the ICP-assisted sputtering method is applied, each of electron density, electron temperature, and sheath voltage can be increased, and recoil particles can be reduced by lowering the self-bias. Can be sufficiently dissociated into oxygen atoms.

  The vanadium dioxide thin film forming apparatus 1 includes a vacuum vessel 3, a heating unit 4, a holder unit 5, a gas introduction pipe 6, and a power source 7, and between the heating unit 4 and the holder unit 5, The conductive metal member 8 is provided.

  The vacuum vessel 3 can be used without particular limitation as long as the inside of the vessel can be brought into a negative pressure state during sputtering, and a vacuum vessel used in a conventionally known sputtering apparatus can be suitably used. .

The heating means 4 is provided in the vacuum vessel 3, the substrate 2 is installed on a fixture provided in the heating means 4, and the substrate 2 is heated to 300 to 450 ° C., more preferably 300 to 400 ° C. To do.
When the heating temperature of the substrate 2 is in the above range, not only can the crystal exhibiting metal-insulator phase transition (monoclinic crystal) be grown well, but also the heat resistance of the substrate 2 and the durability of the heater. From the viewpoint of sex. In addition, since this temperature range is lower than the heating temperature by the conventional magnetron sputtering method, there is an advantage that the burden on other constituent materials to be integrated is reduced.
The heating time is not particularly limited as long as it can be heated to the above temperature.

  Such heating means 4 can be formed using, for example, a high melting point quartz plate and a Kanthal wire which is a heater wire for high temperature heating, but is not limited to this, and the temperature described above As long as the substrate 2 can be heated up to this point, a commonly used heating device can be used.

The substrate 2 is preferably made of Si or α-Al ₂ O ₃ (sapphire). Specifically, a single crystal silicon semiconductor wafer, a single crystal sapphire semiconductor wafer, or the like can be preferably used.
Since the vanadium dioxide thin film produced on the substrate 2 grows epitaxially, it is affected by the crystal structure of the substrate 2. Therefore, in order to obtain a thin film of vanadium dioxide having a good crystal state (monoclinic type), it is preferable to use the substrate 2 produced using these.

The holder unit 5 is provided at a position facing the heating unit 4 in the vacuum vessel 3, and vanadium (V), which is a target material 51 for forming the vanadium dioxide thin film 11 on the substrate 2, is installed. Yes. Further, the holder unit 5 includes a magnet 52 for generating a magnetic force on the target material 51 by a high frequency voltage applied from a power source 7 described later.
Here, vanadium to be installed in the holder portion 5 is preferably pure vanadium having a purity of 99.9% or more, but a vanadium oxide can also be installed.

  The gas introduction pipe 6 introduces a rare gas and an oxygen gas into the vacuum vessel 3. The rare gas is converted into plasma by the holder 5 to which a high frequency voltage is applied, and vanadium as the target material 51 is sputtered and deposited on the substrate 2. As described above, vanadium oxide can be installed as the target material 51. In such a case, in order to obtain a thin film of vanadium dioxide using the vanadium dioxide thin film forming apparatus, supply of oxygen gas and The point that the flow rate and the like need to be optimized is the same as when pure vanadium is used.

  The rare gas is preferably argon gas (Ar gas), but is not limited thereto. For example, helium gas (He gas), neon gas (Ne gas), krypton gas (Kr gas), xenon gas ( Xe gas) can also be used.

On the other hand, the oxygen gas introduced into the vacuum vessel 3 is also dissociated by the plasma to become active oxygen atoms (radicals), and vanadium atoms deposited on the substrate 2 are oxidized to generate vanadium dioxide. Note that when sputtering is performed with an ICP-assisted sputtering method at an appropriate oxygen gas concentration, a stoichiometric reaction with vanadium can proceed, so that vanadium monoxide (VO), divanadium trioxide (V ₂ O ₃ ), vanadium pentoxide (V ₂ O ₅ ), and vanadium oxide such as trivanadium trioxide (V ₃ O ₇ ) are hardly generated. As a result, a thin film (vanadium dioxide thin film 11) in which vanadium dioxide is selectively formed can be manufactured on the substrate 2.

And in this invention, it is set as the structure which provided the electroconductive metal member 8 to which the power supply 81 for applying a high frequency voltage was connected between the above-mentioned heating means 4 and the target material 51. FIG.
The conductive metal member 8 is preferably wound to form a coiled coil member in order to apply a high frequency voltage from a connected power source 81 to cause electromagnetic induction. In the case of a coil member, it is preferable to wind at least twice. In this way, an electromagnetic induction phenomenon can be suitably caused by applying a current to the conductive metal member 8. By generating the electromagnetic induction phenomenon, the plasma to be generated can be densified. As a result, a vanadium dioxide thin film that undergoes a metal-insulator phase transition that has not been conventionally obtained can be suitably manufactured on the substrate 2.

  Such a conductive metal member 8 is preferably made of stainless steel from the viewpoint that it is difficult to be sputtered even in plasma, has good electrical conductivity, and can be obtained at low cost. For example, titanium, copper, or the like can be used.

  As described above, the vanadium dioxide thin film forming apparatus 1 applies a high frequency voltage to the magnet 52 to turn a rare gas such as argon gas into plasma, and also applies a high frequency voltage to the conductive metal member 8. The plasma is densified, and the target material 51 is sputtered by the densified plasma to form a thin film on the substrate 2. At this time, the vanadium atoms moving toward the substrate 2 are introduced into the vacuum vessel 3 by the gas introduction tube 6 and are oxidized by the oxygen atoms dissociated by the plasma to become vanadium dioxide. That is, the vanadium dioxide thin film forming apparatus 1 can form a vanadium dioxide thin film that undergoes a metal-insulator phase transition by forming vanadium dioxide selectively on the substrate 2.

Next, a method for manufacturing a memory device according to the present invention will be described with reference to FIG.
As shown in FIG. 2, the memory device manufacturing method of the present invention includes an installation step S1, a negative pressure step S2, a gas introduction step S3, a heating step S4, a high frequency voltage application step S5, and an electrode formation step S6. , Comprising.
As described above, the method for manufacturing a memory element according to the present invention can form a suitable vanadium dioxide thin film 11 using the vanadium dioxide thin film forming apparatus 1 having the above-described configuration. Therefore, the aspect which performs from the installation process S1 to the high frequency voltage application process S5 by the said vanadium dioxide thin film formation apparatus 1 and performing electrode formation process S6 by a suitable means, for example, an etching apparatus etc. can be mentioned as an example.
Hereinafter, each step will be described in detail.

  First, in the installation step S1, the substrate 2 is installed on the heating means 4 provided in the vacuum vessel 3. Further, a target material 51 made of vanadium or vanadium oxide is placed on a holder portion 5 having a magnet 52 provided at a position facing the heating means 4.

Next, in the negative pressure step S2, the air in the vacuum vessel 3 is exhausted to make the inside of the vacuum vessel 3 have a negative pressure of 5.7 to 9.3 × 10 ⁻⁴ Pa. This is because, as will be described later, the atmospheric pressure condition in the vacuum vessel 3 after the gas introduction step S3 is adjusted to a range of 0.5 to 5.0 Pa.

Next, in the gas introduction step S3, a rare gas and an oxygen gas are introduced into the vacuum vessel 3.
At this time, the rare gas is introduced under the condition of 40 to 100 sccm, preferably 45 to 98 sccm, and the oxygen gas is introduced under the condition of 1 to 10 sccm, preferably 2 to 10 sccm. When the flow rate of the rare gas is in the range of 40 to 100 sccm, the generated plasma is in a preferable state. When the amount of oxygen gas introduced is in the range of 1 to 10 sccm, it becomes difficult to generate vanadium oxide other than vanadium dioxide. As a result, a thin film in which vanadium dioxide is selectively formed can be obtained.
And the atmospheric pressure in the vacuum vessel 3 after the gas introduction step S3 is maintained at 0.5 to 5.0 Pa, preferably 0.87 to 3.5 Pa. When the atmospheric pressure in the vacuum vessel 3 is in the range of 0.5 to 5.0 Pa, sputter film formation can be stably maintained, and discharge can be favorably performed.

  Next, in the heating step S4, the substrate 2 is heated by the heating means 4. The temperature at which the substrate 2 is heated is 300 to 450 ° C., preferably 300 to 400 ° C. The reason why the heating temperature of the substrate 2 is within this range has already been described, and will be omitted.

Next, in the high frequency voltage application step S <b> 5, after the heating step S <b> 4, a high frequency voltage is applied to each of the magnet 52 and the conductive metal member 8 of the holder unit 5 to form a vanadium dioxide thin film on the substrate 2.
In this high frequency voltage application step S5, the magnet 52 is applied under the conditions of high frequency current: 10 to 500 MHz, preferably 13.56 MHz, and high frequency power: 100 to 1000 W, preferably 100 to 500 W, more preferably 150 to 300 W. Apply under conditions. Similarly, the conductive metal member 8 is applied under the condition of high frequency current: 10 to 500 MHz, preferably 13.56 MHz, and high frequency power: 100 to 1000 W, preferably 100 to 500 W, more preferably 150 to 300 W. Apply under conditions. In addition, application time can be suitably changed with the thickness of the vanadium dioxide thin film to manufacture, For example, it is good to apply on the conditions for 30 to 60 minutes.

When the high-frequency voltage and high-frequency power applied to the magnet 52 are in these ranges, the plasma is generated in a good state and the oxygen molecules are dissociated into oxygen atoms, so a good vanadium dioxide thin film that undergoes a metal-insulator phase transition. Can be obtained.
Further, if the high-frequency current and high-frequency power applied to the conductive metal member 8 are within these ranges, sufficient support for plasma generation is sufficient to dissociate oxygen molecules, so that the metal-insulator phase transition occurs. A good vanadium dioxide thin film can be obtained. In addition, the possibility of generating other crystals such as V ₂ O ₅ can be reduced.
In addition, when the high frequency voltage application by high frequency voltage application process S5 is performed for about 30 minutes under the above-mentioned conditions, the vanadium dioxide thin film of about 200 nm thickness can be formed.

Next, in the electrode formation step S6, as described above, the electrode 12 made of a conductive metal that is in contact with the vanadium dioxide thin film 11 undergoing the metal-insulator phase transition is formed.
The conductive metal forming the electrode 12 may be any metal as long as it can form an ohmic contact with the vanadium dioxide thin film 11, but aluminum, gold, or the like is preferably used.
The shape of the electrode 12 is not particularly limited as long as an ohmic contact can be made with respect to the vanadium dioxide thin film 11. For example, by forming a pair of electrodes spaced apart from each other by an appropriate distance d on the vanadium dioxide thin film 11, a planar memory element 10 is formed, or a deep hole reaching the substrate 2 is formed to form an electrode. The stack type memory element 10 can be formed, or the trench type memory element 10 can be formed by stacking electrodes three-dimensionally high.
Such an electrode can be formed by a conventionally known technique such as photolithography or a shadow mask. For example, in the case of the above-described planar type electrode, as shown in FIG. 3, a lamination process S61 and a lithography process S62. It can be suitably formed by photolithography by the etching step S63 and the photoresist removing step S64. FIG. 3 is a flowchart showing an example of the electrode forming step S6.

  In the laminating step S61, the conductive metal is used to form a layer by PVD (physical vapor deposition), CVD (chemical vapor deposition), vacuum deposition, electroplating, sputtering or the like. A metal layer (not shown) is formed. Needless to say, the thickness and shape of the conductive metal layer can be set as appropriate.

Next, in the lithography step S62, a photoresist is applied on the formed conductive metal layer, and a predetermined pattern (for example, when the planar type memory element 10 is manufactured) is applied to the photoresist. A photomask that is exposed through a pattern mask having a pattern of electrodes 12 made of a conductive metal and that has a pattern that forms other wiring), and is cured so as to exhibit the predetermined pattern. The resist is removed to expose the conductive metal layer.
In this lithography step S62, a positive resist that changes a chemical structure soluble in a predetermined solution (for example, an alkaline solution) and leaves a predetermined pattern by a photochemical reaction of a portion irradiated with light, and a photo resist It is preferable to use any of the negative resists that change the chemical structure insoluble in a predetermined solution (for example, an alkaline solution) and leave the photoresist in a predetermined pattern by the photochemical reaction of the irradiated portion. it can.

Next, in the etching step S63, the exposed conductive metal layer is etched until the vanadium dioxide thin film 11 is exposed to form the electrode 12 made of a conductive metal conforming to a predetermined shape.
Although this etching step S63 can be suitably performed by either dry etching or wet etching, it is preferable to use dry etching in that high-precision fine processing can be performed according to the resist pattern. Moreover, it is preferable to use parallel plate type reactive ion etching as dry etching.

In the photoresist removal step S64, the memory device 10 is manufactured by removing the cured photoresist remaining on the conductive metal layer.
The photoresist is removed using a predetermined solution (for example, an alkaline solution) prepared according to the used photoresist.
Needless to say, in order to obtain the desired memory element 10, the above-described stacking step S61, lithography step S62, etching step S63, and photoresist removal step S64 may be repeated an appropriate number of times. Needless to say, operations other than those described above in manufacturing a memory element can be applied to operations in a general memory element manufacturing method.

  According to the memory element manufacturing method of the present invention described above, in order to obtain the vanadium dioxide thin film 11, it is not necessary to control the manufacturing conditions such as the oxygen flow rate and the heating temperature excessively precisely, and the metal-insulator can be easily obtained. A phase-changing vanadium dioxide thin film 11 can be obtained, and the vanadium dioxide thin film 11 is used, so that a good memory element 10 can be manufactured.

And the memory element 10 manufactured by the above-described memory element manufacturing method includes, for example, as shown in FIG. 4, a substrate 2 on which a vanadium dioxide thin film 11 that undergoes a metal-insulator phase transition is manufactured, a vanadium dioxide thin film 11, And an electrode 12 made of a conductive metal in contact therewith. FIG. 4 is a cross-sectional view showing an example of the configuration of the memory element according to the present invention.
In this memory element 10, since the vanadium dioxide thin film 11 manufactured on the substrate 2 has a good metal-insulator phase transition ability when the crystal structure is a monoclinic type, it has resistance to voltage-current characteristics. As described above, the switching effect, that is, the memory function is easily generated, which is preferable.

  Next, the memory element manufacturing method and the memory element of the present invention will be described with reference to examples.

First, a monoclinic low temperature phase (Monoclinic) vanadium dioxide (VO ₂ ) thin film is produced on a substrate by an internal coil type ICP assisted sputtering apparatus (vanadium dioxide thin film forming apparatus), and the vanadium dioxide thin film is used. We examined the memory device.

[experimental method]
First, a thin film of vanadium oxide was formed on a substrate using an internal coil type ICP assisted sputtering apparatus (high frequency magnetron sputtering apparatus) shown in FIG.
The interval between the upper electrode (target surface) and the lower electrode of the internal coil type ICP assisted sputtering apparatus was 55 mm, and a coil member (SUS 304) wound twice was inserted around 30 mm from the target surface.
Note that vanadium (V) (100 mmφ, purity 99.9%) was used as a target material, and a substrate made of single crystal c-plane sapphire was used. The vanadium dioxide thin film is formed with the following conditions: 200 W for the power applied to the ICP (ICP [W]), 200 W for the high frequency power (RF power [W]) applied to the magnet, and the flow rate of the rare gas (Ar gas). 40 sccm, the flow rate of oxygen gas (O ₂ ) was 0.5 sccm, the substrate heating temperature (T _s [° C.]) was 300 ° C., and the total pressure (Total Pressure [Pa]) in the vacuum vessel was 0.4 Pa.

  The crystallinity of the vanadium dioxide thin film formed on the substrate was evaluated by X-ray diffraction, and the resistivity (temperature-resistance characteristics) was evaluated by a four-terminal method. The measurement conditions of X-ray diffraction and the measurement conditions of the 4-terminal method are as follows.

The X-ray diffraction was measured using an X'pert MRD manufactured by Philips, and the X-ray output was measured at 40 kV and 40 mA. X-ray species in this case, was used Cu K _alpha line.
The measurement conditions of the four-terminal method were measured using K-89PS150 μR manufactured by Kyowa Riken Co., Ltd. under the conditions of a terminal interval of 1 mm and a current value range of 0.5 to 1.0 mA.

[Experimental result]
FIG. 5 is a diagram showing the results of X-ray diffraction of a vanadium oxide thin film formed on a substrate of a memory element. FIG. 5A is a vanadium oxide thin film manufactured without applying power to an ICP for comparison. FIG. 6B is a diagram showing the results of X-ray diffraction of a thin film of vanadium oxide formed by the memory element manufacturing method of the present invention. In the figure, the horizontal axis indicates 2θ (degrees), and the vertical axis indicates intensity (cps).

As shown in FIG. 5A, when a thin film of vanadium oxide is manufactured without ICP support, various crystalline V ₃ O ₇ ((220), (330), (440), (550), Although the peak of (660)) could be obtained, the peak of VO ₂ could not be obtained.
On the other hand, as shown in FIG. 5 (b), when a thin film of vanadium oxide was produced with ICP support, a peak of VO ₂ (020) could be obtained.

The temperature-resistance characteristics were evaluated using the vanadium oxide thin film shown in FIGS. 5A and 5B, and the graph is shown in FIG.
FIG. 6A is a graph showing a change characteristic of the electric resistance value with respect to the temperature of the vanadium oxide thin film in FIG. 5A, and FIG. 6B is an electric diagram with respect to the temperature of the vanadium dioxide thin film in FIG. It is a graph which shows the change characteristic of resistance value. In FIG. 6, the horizontal axis represents temperature (° C.), and the vertical axis represents resistance (Ω).

As shown in FIG. 6, when the temperature was raised, the resistance value of the thin film (b) was greatly reduced at about 60 ° C., and the phase transition from semiconductor characteristics to metallic characteristics was observed. Recognize. The change in electrical resistance value was more than three orders of magnitude. In addition, the vanadium oxide thin film (vanadium dioxide (VO ₂ ) thin film) shown in FIG. 5B showed a resistance value on the order of 10 ⁵ Ω at room temperature. The resistance value at 80 ° C. was 120Ω (ρ = 3.0 × 10 ⁻⁴ Ωcm). The hysteresis width at 10 ⁴ Ω was 7 ° C.
In contrast, as shown in FIG. 6A, it can be seen that a vanadium oxide thin film that is not VO ₂ does not undergo a metal-insulator phase transition.

  Next, a 1 kΩ resistor was connected to the vanadium oxide thin film in FIG. 5B, and two aluminum electrodes (Al electrodes) formed at intervals of 0.5 mm were provided to form an element. And the voltage-current characteristic when a voltage was applied between the said Al electrodes was evaluated. FIG. 7 shows a circuit diagram along with voltage-current characteristics. In FIG. 7, the horizontal axis represents voltage (V), and the vertical axis represents current (mA).

  As shown in FIG. 7, it can be seen that the current value of the thin film of vanadium oxide in FIG. 5B suddenly changes when the voltage reaches 55V. As described above, since a resistance of 1 kΩ is inserted in the circuit, when the voltage-current characteristics are analyzed, the resistance value of the thin film changes at the same voltage as that of FIG. 6 at the voltage of 55 V, that is, the metal-insulator phase transition occurs. I understand that. This result shows that the vanadium dioxide thin film manufactured by the vanadium dioxide thin film manufacturing apparatus shown in FIG. 1 causes a phase transition (electric field induced phase transition) by voltage application. The resistance value due to this electric field induced phase transition is 7 kΩ up to 55 V, but decreased to 150 Ω after the phase transition. The resistance change ratio was 45. In addition, after the phase transition, the resistance value remained low even when the voltage was lowered to 55 V or less, and a new characteristic was exhibited without returning to the original voltage-current characteristic curve.

  In other words, it was confirmed that there was a function of maintaining a low resistance value once the phase transition occurred. For example, if the first high resistance state is turned off and the low resistance state realized by applying a voltage of 55 V is turned on, the memory element function has a bi-stable on and off state. Thus, a variable resistance nonvolatile memory (ReRAM) is maintained in which the changed state is maintained under a certain voltage. As shown in FIG. 7, the element having the thin film of vanadium oxide in FIG. 5B is turned on when a voltage of 55 V or more (for example, a pulse voltage with a short application time) is applied, and thereafter 30 V or less. It can be seen that it is possible to return to the off state by applying a voltage of.

  Next, in the element having the structure shown in FIG. 7, the interval between the Al electrodes was narrowed to 0.1 mm, and a repeated sine wave (repetitive voltage of + and −) was applied to the element. FIG. 8 shows a trace waveform of the voltage-current characteristic. In FIG. 8, the horizontal axis indicates voltage (V), and the vertical axis indicates current (mA). Here, since the sine wave was 50 Hz, this waveform was acquired at a time of 0.02 s. From FIG. 8, it was found that the phase transition from the off state to the on state occurred at 9V. In FIG. 9 described later, this corresponds well with the metal-insulator phase transition at 10 V when the distance d between the two separated electrodes 12 is 0.1 mm (100 μm). I can say that. The electrical resistance value before the metal-insulator phase transition (that is, when the current is small) is 1400Ω, and the electrical resistance value after the metal-insulator phase transition (that is, when the current is large) is 20Ω, The ratio (ON-OFF ratio) was 70. It can be said that the value of this ratio is a sufficient value as a difference for discriminating between the two states of ON and OFF. Moreover, it can be said that by controlling the interval between the Al electrodes, it is possible to reduce the working voltage for controlling on and off.

  Further, FIG. 9 shows a voltage obtained by providing two conductive metal electrodes separated from each other by a predetermined distance d on a vanadium dioxide thin film formed on a single crystal c-plane sapphire substrate by the memory device manufacturing method of the present invention. It is a graph which shows the change characteristic of the electric current value when applying. The distance d between the two separated electrodes 12 is 0.1 mm, 0.5 mm, and 1.0 mm. In FIG. 9, the horizontal axis represents voltage (V) and the vertical axis represents current (mA).

As shown in FIG. 9, the vanadium dioxide thin film formed on the substrate of the single crystal c-plane sapphire has a metal-insulator phase transition according to the distance d between the pair of electrodes provided, and the distance d = 0. The current value abruptly changed around 10 V when 1 mm, around 50 V when the distance d = 0.5 mm, and around 90 V when the distance d = 1.0 mm. In this way, the current does not increase in proportion to the voltage, but increases rapidly as if jumping discontinuously, which means that the electric resistance value of the vanadium dioxide thin film rapidly increases from a large value to a small value. It means that it has transitioned to. In general, the memory operation condition is that the ratio of the electrical resistance values before and after this transition can be secured stably in one to two digits. However, as described above, in the memory element formed with the vanadium dioxide thin film of the present invention. The ratio was 70, and the operation was stable for several hours or more in time, and it was confirmed that the operation was stable at 1 × 10 ⁶ times or more. It is thought that it was able to work stably). Further, the memory element formed with the vanadium dioxide thin film of the present invention has a high frequency of 100 kHz or more with respect to rectangular wave pulse application (pulse voltage: 18 V, pulse duty: 10%) by a pulse generator (81101A Pulse generator manufactured by Agilent). However, it was confirmed that it works stably. In addition, the resistance value measurement at the time of measuring the switching time response of the memory element was calculated from the terminal voltage using a pure resistance of 50Ω.

  Further, from the results of the above experiments, it was found that in the heating step of the method for manufacturing a memory element of the present invention, a memory element capable of excellent metal-insulator phase transition can be manufactured even when the temperature for heating the substrate is 300 ° C. For example, assuming that the vanadium dioxide thin film is formed by the pulse laser method, it is also understood that the heating condition of the substrate can be greatly lowered in view of the necessity of heating the substrate to 500 ° C. It was. Therefore, it is suggested that the substrate and the vanadium dioxide thin film are not easily damaged by heating, and a better memory element (ReRAM) can be manufactured.

  The memory element manufacturing method and the memory element according to the present invention have been described in detail with specific examples. However, the scope of the present invention should not be construed as being limited to the contents of the above detailed description of the invention. Therefore, it should be interpreted widely based on the claims. In addition, a range that can be easily corresponded by a person having ordinary knowledge in the technical field based on the claims and the detailed description of the invention should be construed as being included in the scope of the right of the present invention. It is.

It is explanatory drawing which shows one structural example of the vanadium dioxide thin film formation apparatus used in order to manufacture the memory element based on this invention. It is a flowchart which shows the process content of the memory element manufacturing method which concerns on this invention. It is a flowchart which shows an example of electrode formation process S6. It is sectional drawing which shows an example of a structure of the memory element which concerns on this invention. FIG. 4 is a diagram showing the results of X-ray diffraction of a vanadium oxide thin film formed on a substrate of a memory element, where (a) is an X-ray diffraction of a vanadium oxide thin film manufactured without applying power to an ICP for comparison. (B) is a figure which shows the result of the X-ray diffraction of the thin film of vanadium oxide formed with the memory element manufacturing method of this invention. In the figure, the horizontal axis indicates 2θ (degrees), and the vertical axis indicates intensity (cps). FIG. 6 shows temperature-resistance characteristics of the vanadium oxide thin film shown in FIGS. In the figure, the horizontal axis represents temperature (° C.), and the vertical axis represents resistance (Ω). A thin film of vanadium oxide in FIG. 5B is connected to a resistance of 1 kΩ and provided with two aluminum electrodes (Al electrodes) formed at intervals of 0.5 mm to form an element. It is a figure which shows the voltage-current characteristic when a voltage is applied between them. In the figure, the horizontal axis represents voltage (V), and the vertical axis represents current (mA). FIG. 8 is a diagram showing a trace waveform of voltage-current characteristics in the element having the structure shown in FIG. 7 in which the interval between Al electrodes is narrowed to 0.1 mm and a repetitive sine wave (repetitive voltage of +, −) is applied to the element. . In the figure, the horizontal axis represents voltage (V), and the vertical axis represents current (mA). Current when a voltage is applied by providing two conductive metal electrodes separated by a predetermined distance d on a vanadium dioxide thin film formed on a single crystal c-plane sapphire substrate by the memory device manufacturing method of the present invention. It is a graph which shows the change characteristic of a value. The distance d is 0.1 mm, 0.5 mm, and 1.0 mm, the horizontal axis in the figure indicates voltage (V), and the vertical axis indicates current (mA).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vanadium dioxide thin film formation apparatus 2 Board | substrate 3 Vacuum container 4 Heating means 5 Holder part 51 Target material 52 Magnet 6 Gas introduction pipe 7 Power supply 8 Conductive metal member 81 Power supply 10 Memory element 11 Vanadium dioxide thin film 12 Conductive electrode S1 Installation process S2 Negative pressure process S3 Gas introduction process S4 Heating process S5 High frequency voltage application process S6 Electrode formation process S61 Lamination process S62 Lithography process S63 Etching process S64 Photoresist removal process

Claims (7)

An installation step of installing a target material made of vanadium or vanadium oxide on a holder portion having a magnet provided at a position facing the heating unit, while installing a substrate on a heating unit provided in a vacuum vessel;
A negative pressure step of evacuating the air in the vacuum vessel to bring the inside of the vacuum vessel to a negative pressure of 5.7 to 9.3 × 10 ⁻⁴ Pa;
A gas introduction step of introducing a rare gas and an oxygen gas into the vacuum vessel while maintaining a negative pressure state;
A heating step of heating the substrate to 300 to 450 ° C. by the heating means;
After the heating step, a vanadium dioxide thin film that undergoes a metal-insulator phase transition on the substrate by applying a high-frequency voltage to each of the target material and a conductive metal member connected to a power source that applies a high-frequency voltage. A high-frequency voltage application step for forming
An electrode forming step of forming an electrode made of a conductive metal in contact with the vanadium dioxide thin film formed on the substrate;
A method for manufacturing a memory device, comprising:   2. The method of manufacturing a memory element according to claim 1, wherein in the gas introducing step, the rare gas is introduced under the conditions of 40 to 100 sccm and the oxygen gas is introduced under the conditions of 1 to 10 sccm.   The memory element manufacturing method according to claim 1, wherein the pressure in the vacuum vessel after the gas introduction step is maintained at 0.5 to 5.0 Pa.   4. The method of manufacturing a memory element according to claim 1, wherein the heating step heats the substrate to 300 to 400 ° C. 5. The high frequency voltage application step includes:
Applied to the target material under the conditions of high frequency current: 10 to 100 MHz, high frequency power: 100 to 1000 W, and
5. The memory element manufacturing method according to claim 1, wherein the conductive metal member is applied under conditions of a high-frequency current of 10 to 100 MHz and a high-frequency power of 100 to 1000 W. 6. . A substrate on which a vanadium dioxide thin film that undergoes a metal-insulator transition is manufactured;
An electrode made of a conductive metal in contact with the vanadium dioxide thin film;
A memory device comprising:   The memory device according to claim 6, wherein the vanadium dioxide thin film has a monoclinic crystal structure.