Nitride material, piezoelectric body composed of same, MEMS device using piezoelectric body thereof, nitride material thereof, ferroelectric body composed of same, and electronic element using ferroelectric body thereof

Abstract

[Problem] The present invention provides: a gallium nitride to which scandium having a piezoelectric constant d33 that exceeds 14 pC / N is added, a gallium nitride to which scandium having a piezoelectric constant d33 that exceeds 16.9 pC / N is added, especially a gallium nitride material to which scandium having a piezoelectric constant d33 that is higher than the value (27.6 pC / N) of the maximum piezoelectric constant d33 of aluminum nitride to which scandium is added is added; a piezoelectric body which is composed of the same; an MEMS device which uses the piezoelectric body; the gallium nitride material; a ferroelectric body which is composed of the same; an electronic element which uses the ferroelectric body; and a method for producing the gallium nitride material to which the scandium is added. [Solution] The present invention provides a nitride material which is represented by chemical formula ScxGa1-xN, wherein x is within the range of 0.39 to 0.54 inclusive, and the length of a c-axis in a crystal structure is within the range of not less than 4.94 × 10-10 m but less than 5.2 × 10-10 m.

Description

Nitride material, piezoelectric body made of the same, MEMS device using the piezoelectric body, nitride material, ferroelectric body made of the same, and electronic element using the ferroelectric body

[0001] The present invention relates to a scandium-doped gallium nitride material, a piezoelectric body made of the same, a MEMS device using the piezoelectric body, the gallium nitride material, a ferroelectric material made of the same, and an electronic element using the ferroelectric material.

[0002] Devices utilizing the piezoelectric phenomenon are used in a wide range of fields, and their use is expanding in portable devices such as mobile phones, where there is a strong demand for miniaturization and power saving. One example is an FBAR filter using a film bulk acoustic wave resonator (FBAR).

[0003] FBAR filters are filters that use resonators that utilize the thickness-extensional vibration mode of a thin film that exhibits piezoelectric response, and have the characteristic of being able to resonate in the gigahertz band. FBAR filters with these characteristics have low loss and can operate over a wide frequency range, and are therefore expected to contribute to the further improvement of portable devices' high-frequency compatibility, miniaturization, and power savings.

[0004] Examples of piezoelectric materials for the piezoelectric thin film used in such FBARs include scandium-doped aluminum nitride (see Patent Document 1) and scandium-doped gallium nitride (see Patent Document 2). In particular, scandium-doped aluminum nitride has a high piezoelectric constant (d ３３ ) and is used as a high-frequency filter for the fifth-generation mobile communication system (5G). Furthermore, scandium-doped aluminum nitride is expected to be used in a variety of MEMS (microelectromechanical system) devices, including physical sensors such as pressure sensors, acceleration sensors, and gyro sensors, as well as actuators, microphones, speakers, ultrasonic oscillators, ultrasonic sensors, fingerprint authentication sensors, and vibration power generators.

[0005] JP 2009-10926 A Japanese Patent No. 6698159 A

[0006] Uehara et al. , Applied Physics letters 114, 012902, 2019. Tholander al. , Physical Review B 87, 094107 2013. Akiyama et al. , Applied Physics letters 95, 162107, 2009.

[0007] However, scandium-doped gallium nitride (Sc ｘ Ga １－ｘ N) maximum piezoelectric constant d ３３ is 14 pC / N (see Non-Patent Document 1), and the piezoelectric constant d ３３ Sc having ｘ Ga １－ｘ The problem was that N did not exist. ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ is 16.9 pC / N (see Non-Patent Document 2).

[0008] Therefore, the above-mentioned scandium-doped aluminum nitride (Sc ｘ Al １－ｘ N) maximum piezoelectric constant d ３３ Sc exceeding (27.6 pC / N) (see Non-Patent Document 3) ｘ Ga １－ｘ The problem was that N naturally did not exist.

[0009] In view of the above circumstances, the present invention provides a piezoelectric material having a piezoelectric constant d exceeding 14 pC / N. ３３ Scandium-doped gallium nitride with a piezoelectric constant d exceeding 16.9 pC / N ３３ The maximum piezoelectric constant d of scandium-doped gallium nitride, particularly scandium-doped aluminum nitride, ３３ The piezoelectric constant d is higher than the value of ３３The present invention aims to provide a scandium-doped gallium nitride material having the above formula, a piezoelectric body made thereof, a MEMS device using the piezoelectric body, the gallium nitride material, a ferroelectric body made thereof, and an electronic element using the ferroelectric body, as well as a method for producing the scandium-doped gallium nitride.

[0010] The inventors of the present invention have conducted extensive research into the above-mentioned problems, and as a result have discovered that gallium nitride (Sc) doped with scandium (Sc) within a predetermined concentration range can be obtained. ｘ Ga １－ｘ N) having a c-axis (c-axis in the crystal structure) length within a predetermined range is the same as the conventional Sc ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ (14 pC / N), and the Sc calculated by the first-principles calculation described above. ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ (16.9 pC / N), and the maximum piezoelectric constant d ３３ Piezoelectric constant d higher than (27.6 pC / N) ３３ The inventors have discovered that the nitride material has high ferroelectricity and has invented the following revolutionary nitride material. The contents of Japanese Patent Application No. 2023-188952 are incorporated herein by reference as part of this specification.

[0011] The first aspect of the present invention for solving the above problem is a compound represented by the chemical formula Sc ｘ Ga １－ｘ N, where x is in the range of 0.39 to 0.54, and the length of the c-axis in the crystal structure is 4.94 × 10 －１０ m or more, 5.2×10 －１０ The nitride material is characterized in that the SiO 2 content is in the range of 0.1 m or less.

[0012] Here, the "c-axis" refers to the axis that forms an angle of 90 degrees with the other two axes among the three axes of a hexagonal crystal such as a wurtzite crystal.

[0013] According to the first aspect, the piezoelectric constant d exceeds 16.9 pC / N.３３ It is possible to provide scandium-doped gallium nitride having the following formula:

[0014] A second aspect of the present invention is the nitride material according to the first aspect, characterized in that x is in the range of 0.45 or more and 0.54 or less.

[0015] According to the second aspect, a higher maximum piezoelectric constant d ３３ It is possible to provide scandium-doped gallium nitride having the following formula:

[0016] A third aspect of the present invention is the nitride material according to the first aspect, characterized in that x is in the range of 0.5 to 0.54.

[0017] According to the third aspect, a high maximum piezoelectric constant d ３３ It is possible to provide scandium-doped gallium nitride having the following formula:

[0018] In the fourth aspect of the present invention, the length of the c-axis is 4.94 × 10 －１０ m or more, 5.05×10 －１０ The nitride material according to the first aspect is characterized in that the n-type n-type n is in the range of m or less.

[0019] According to the fourth aspect, a higher maximum piezoelectric constant d ３３ It is possible to provide scandium-doped gallium nitride having the following formula:

[0020] In the fifth aspect of the present invention, the length of the a-axis in the crystal structure is 3.4 × 10 －１０ m or more, 3.5×10 －１０ The nitride material according to the first aspect is characterized in that the n-type n-type n is in the range of m or less.

[0021] Here, the "a-axes" refer to two axes that form an angle of 90 degrees with the c-axis, and these axes have the same lattice constant.

[0022] According to the fifth aspect, a higher piezoelectric constant d ３３ It is possible to provide scandium-doped gallium nitride having the following formula:

[0023] In the sixth aspect of the present invention, the length of the a-axis is 3.44 × 10 －１０m or more, 3.48×10 －１０ The nitride material according to the first aspect is characterized in that the n-type n-type n is in the range of m or less.

[0024] According to the sixth aspect, the maximum piezoelectric constant d ３３ It is possible to provide scandium-doped gallium nitride having the following formula:

[0025] A seventh aspect of the present invention is the nitride material according to the first aspect, characterized in that the thickness is in the range of 1 nm to 3000 nm.

[0026] According to the seventh aspect, a high piezoelectric constant d ３３ It is possible to provide scandium-doped gallium nitride having the following formula:

[0027] An eighth aspect of the present invention is a piezoelectric body made of the nitride material according to any one of the first to seventh aspects.

[0028] According to the eighth aspect, a high piezoelectric constant d ３３ It is possible to provide a piezoelectric body having the following.

[0029] A ninth aspect of the present invention is a piezoelectric body comprising the nitride material according to any one of the first to seventh aspects provided on a substrate, and at least one intermediate layer provided between the nitride material and the substrate.

[0030] According to the ninth aspect, the crystallinity (degree of crystallization) of the piezoelectric body is improved, so that a piezoelectric body having higher piezoelectricity can be provided.

[0031] A tenth aspect of the present invention is the piezoelectric body according to the ninth aspect, characterized in that a diffusion layer containing a substance constituting the intermediate layer and a substance constituting the piezoelectric body is further provided between the intermediate layer and the piezoelectric body.

[0032] According to the tenth aspect, similarly to the ninth aspect, it is possible to provide a piezoelectric body having high piezoelectricity.

[0033] An eleventh aspect of the present invention resides in a MEMS device using the piezoelectric body according to the eighth aspect.

[0034] Here, the term "MEMS device" is not particularly limited as long as it is a microelectromechanical system, and examples thereof include high-frequency filters such as FBAR filters and SMRs (Solidly Mounted Resonators), physical sensors and actuators such as vibrators, pressure sensors, acceleration sensors, and gyro sensors, microphones, speakers, ultrasonic oscillators, ultrasonic sensors, fingerprint authentication sensors, vibration power generators, and energy harvesters.

[0035] According to the eleventh aspect, it is possible to provide a MEMS device that is compatible with high frequencies, is miniaturized, and has low power consumption. In particular, when the MEMS device is a high-frequency filter, it is possible to provide a device that has lower loss and is operable over a wide band compared to conventional high-frequency filters.

[0036] A twelfth aspect of the present invention resides in a ferroelectric material made of the nitride material according to any one of the first to seventh aspects.

[0037] According to the twelfth aspect, a ferroelectric material having high ferroelectricity can be provided.

[0038] A thirteenth aspect of the present invention resides in an electronic device using the ferroelectric material according to the twelfth aspect.

[0039] Here, "electronic elements" include elements such as ferroelectric nonvolatile memories (including field-effect ferroelectric nonvolatile memories), variable resistance nonvolatile memories, piezo-resistive transistors, energy storage elements, piezo elements (piezoelectric elements), pyroelectric elements, piezoelectric sensors, and electro-caloric effect elements.

[0040] According to the thirteenth aspect, since the material has high ferroelectricity, it is possible to provide a small-sized, high-performance electronic device.

[0041] A fourteenth aspect of the present invention is a method for producing a nitride material using a sputtering method to produce the nitride material according to any one of the first to seventh aspects, characterized in that the sputtering gas contains nitrogen, and the sputtering targets used are a target composed of scandium and a target composed of gallium nitride, a target composed of scandium and an alloy containing scandium and gallium, a target composed of gallium nitride and an alloy containing scandium and gallium, or a target composed of an alloy containing scandium and gallium.

[0042] According to the fourteenth aspect, a high piezoelectric constant d ３３ It is possible to manufacture a piezoelectric body having the following characteristics.

[0043] A fifteenth aspect of the present invention resides in the method for producing a nitride material according to the fourteenth aspect, characterized in that the heating temperature during film formation of the substrate on which the nitride material is formed is in the range of 25°C or higher and lower than 400°C.

[0044] According to the fifteenth aspect, a higher piezoelectric constant d ３３ It is possible to manufacture a piezoelectric body having the following characteristics.

[0045] Fig. 1 is a schematic cross-sectional view of a piezoelectric thin film according to embodiment 1. Fig. 2 is a table showing the conditions for depositing each piezoelectric thin film in Example 1 and data for each piezoelectric film. Fig. 3 is a table showing the substrate heating temperature and piezoelectric constant d ３３ 4 is a table showing data for each piezoelectric thin film in Example 2. FIG. 5 is a table showing data for each piezoelectric thin film in Example 3. FIG. 6 is a table showing conditions for depositing each piezoelectric thin film in Example 4 and data for each piezoelectric film. FIG. 7 is a table showing conditions for depositing each piezoelectric thin film in Example 5 and data for each piezoelectric film. FIG. 8 is a table showing conditions for depositing each piezoelectric thin film in Example 6 and data for each piezoelectric film. FIG. 9 is a graph showing the relationship between the Sc concentration and the piezoelectric constant d ３３ 10 is a graph showing the relationship between the length of the c-axis and the piezoelectric constant d３３ 11 is a graph showing the relationship between the length of the a-axis and the piezoelectric constant d ３３ Fig. 12 is a schematic cross-sectional view of a piezoelectric thin film according to embodiment 2. Fig. 13 is a table showing data on each ferroelectric thin film in Example 7. Fig. 14 is a graph showing the hysteresis loop of the ferroelectric thin film No. 3 in Example 7.

[0046] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the nitride material according to the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments.

[0047] 1 is a schematic side view of a piezoelectric thin film made of a nitride material according to this embodiment. As shown in this figure, a piezoelectric thin film 1 is formed on a substrate 10.

[0048] There are no particular limitations on the thickness or material of the substrate 10, as long as the piezoelectric thin film 1 can be formed on the surface thereof. Examples of the substrate 10 include heat-resistant alloys such as silicon and Inconel, and resin films such as polyimide.

[0049] The piezoelectric thin film 1 is represented by the chemical formula Sc ｘ Ga １－ｘ N, x is in the range of 0.39 to 0.54, and the length of the c-axis in the crystal structure is 4.94 × 10 －１０ m or more, 5.2×10 －１０ The nitride material is characterized in that the thickness of the nitride film is in the range of 0.1 m or less.

[0050] Such a piezoelectric thin film 1 is at least as good as conventional Sc ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ The value of Sc calculated by first-principles calculation is higher than the value of 14 pC / N. ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ Maximum piezoelectric constant d higher than (16.9 pC / N) ３３ It has.

[0051] Here, the piezoelectric thin film 1 in which x is in the range of 0.45 or more and 0.54 or less in the above chemical formula has a higher maximum piezoelectric constant d３３ The piezoelectric material having x in the range of 0.5 to 0.54 also has a high maximum piezoelectric constant d ３３ It is preferable because

[0052] In addition, the length of the c-axis in these crystal structures is 4.94 × 10 －１０ m or more, 5.05×10 －１０ The piezoelectric thin film 1 in the range of Sc ｘ Al １－ｘ Maximum piezoelectric constant d of N ３３ Piezoelectric constant d higher than (27.6 pC / N) ３３ Furthermore, the length of the a-axis in these crystal structures is particularly preferred because it has a value of 3.40 × 10 －１０ m or more, 3.5×10 －１０ The piezoelectric thin film 1 in the range of 0.05 to 0.25 has a higher piezoelectric constant d ３３ is more preferable because it has a value of 3.44×10 －１０ m or more, 3.48×10 －１０ The piezoelectric thin film 1 in the range of 0.1 m or less has a higher piezoelectric constant d ３３ It is particularly preferred because it has a value of

[0053] The thickness (film thickness) of the piezoelectric thin film 1 is not particularly limited, but is preferably 1 nm to 3000 nm, more preferably 10 nm to 1000 nm, and particularly preferably 100 nm to 1000 nm.

[0054] Furthermore, the piezoelectric thin film 1 may contain a rare gas such as argon (Ar) or neon (Ne), and it is particularly preferable that the piezoelectric thin film 1 contains Ar. For example, the piezoelectric thin film 1 containing Ar has the chemical formula (Sc ｘ Ga １－ｘ ) １－ｙ Ar ｙExamples of nitride materials represented by Ar include those in which x is in the range of 0.39 to 0.54 and y is in the range of 0.0016 to 0.006, those in which x is in the range of 0.45 to 0.54 and y is in the range of 0.0016 to 0.006, and those in which x is in the range of 0.5 to 0.54 and y is in the range of 0.0016 to 0.006. Piezoelectric thin films made of such nitride materials containing Ar have a high piezoelectric constant d ３３ It has.

[0055] The high frequency filter using these piezoelectric thin films 1 is ｘ Al １－ｘ Compared to high-frequency filters configured with N, this has low loss and can operate over a wide band. As a result, portable devices can be made to support higher frequencies, be more compact, and consume less power. The configuration of the high-frequency filter is not particularly limited, and it can be manufactured with a known configuration.

[0056] Next, a method for manufacturing the piezoelectric thin film 1 according to this embodiment will be described. The piezoelectric thin film 1 can be manufactured using a manufacturing method such as a sputtering method or a vapor deposition method, similar to a general piezoelectric thin film. Specifically, for example, a method for manufacturing the piezoelectric thin film 1 using a nitrogen gas (N ２ ) atmosphere or nitrogen gas (N ２ The film can be manufactured by simultaneously sputtering two targets onto a substrate 10 (e.g., a silicon (Si) substrate) in a mixed atmosphere of scandium (Sb) and argon gas (Ar). Combinations of the two targets include a target made of scandium and a target made of gallium nitride (GaN), a target made of scandium and a target made of an alloy containing scandium and gallium, or a target made of gallium nitride and a target made of an alloy containing scandium and gallium.

[0057] As the sputtering target, only a target made of an alloy containing scandium and gallium (a target made of an alloy containing scandium and gallium alone) may be used. The alloy containing scandium and gallium is not particularly limited as long as the ratio of Sc to the total amount of Sc and Ga in the sputtering target is 25 atomic % or more and less than 100 atomic %. Specific examples of the alloy containing scandium and gallium include Ga ３ Sc, Ga ２ Sc, Ga ３ Sc ２ , GaSc, Ga ４ Sc ５ and Ga ３ Sc ５ and the like.

[0058] The sputtering gas may contain a rare gas other than Ar. By using a sputtering gas containing a rare gas such as Ar, a high piezoelectric constant d ３３ Sc having ｘ Ga １－ｘ N can be easily produced. The rare gas may be a single gas such as Ar, or a mixed gas consisting of multiple types of rare gases, such as a mixed gas of Ar and Kr. Of these rare gases, Ar alone is particularly preferable. By including Ar in the sputtering gas, the piezoelectric thin film made of the nitride material according to the present invention can be more easily produced.

[0059] The concentration of the rare gas contained in the sputtering gas is not particularly limited, but is preferably in the range of 5 mol % to 95 mol %, more preferably 20 mol % to 95 mol %, and particularly preferably 50 mol % to 90 mol %.

[0060] Furthermore, the temperature (substrate heating temperature) during film formation of the substrate on which the piezoelectric thin film 1 is formed is preferably in the range of room temperature (25°C) or higher and less than 400°C, as this makes it easier to produce the piezoelectric thin film 1; more preferably in the range of 100°C to 350°C, as this makes it easier to produce the piezoelectric thin film 1; and particularly preferably in the range of 150°C to 300°C, as this makes it even easier to produce the piezoelectric thin film 1.

[0061] Furthermore, the pressure of the sputtering gas is not particularly limited, but is preferably 1 Pa or less, more preferably in the range of 0.1 Pa to 0.7 Pa, and particularly preferably in the range of 0.2 Pa to 0.5 Pa. Example 1

[0062] Using the following equipment and sputtering target, a scandium-doped gallium nitride piezoelectric thin film (Sc) shown in FIG. 2 was deposited on a conductive silicon substrate (0.02 Ω cm or less) on which a Hf intermediate layer (thickness: 100 nm to 130 nm) had been previously formed. ｘ Ga １－ｘ N) was prepared.

[0063] Sputtering deposition equipment (ULVAC) Sc sputtering target material (purity: 99.99%) GaN powder sintered sputtering target material (purity: 99.99%) Gas: mixed gas of nitrogen (purity: 99.99995% or more) and argon gas (purity: 99.9999% or more) (mixing ratio (nitrogen:argon) 30:70) Sputtering gas pressure: 0.25 Pa Substrate heating temperature: 35 to 200°C

[0064] The substrate heating temperature and piezoelectric constant d during the deposition of each of the obtained piezoelectric thin films ３３ 3 shows a graph showing the relationship between Sc and Sc. As can be seen from this graph, each piezoelectric film according to Example 1 (film formed at a substrate heating temperature of 35 to 200° C.) has a value of Sc calculated by first-principles calculation. ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ Piezoelectric constant d higher than (16.9 pC / N) ３３ It was found that the piezoelectric constant d ３３ After depositing an Al film having a diameter of 2.5 mm as an upper electrode by vapor deposition, the evaluation was carried out using a piezometer (PM300 (manufactured by Alpha Corporation)).

[0065] Using the following equipment and sputtering target, a scandium-doped gallium nitride piezoelectric thin film (ScN) shown in FIG. ｘ Ga １－ｘ N) was deposited directly on a conductive silicon substrate (0.02 Ω·cm or less).

[0066] Sputtering deposition apparatus (manufactured by ULVAC) Sc sputtering target material (purity: 99.99%) GaN powder sintered sputtering target material (purity: 99.99%) Gas: mixed gas of nitrogen (purity: 99.99995% or more) and argon gas (purity: 99.9999% or more) (mixing ratio (nitrogen:argon) 30:70) Sputtering gas pressure: 0.25 Pa Substrate heating temperature: 150°C Example 3

[0067] Using the following equipment and sputtering target, a scandium-doped gallium nitride piezoelectric thin film (ScN) shown in FIG. ｘ Ga １－ｘ A film of ScGa alloy sputtering target material (Sc:Ga=50:50, purity: 99.99%), Sc metal sputtering target material (purity: 99.99%), gas: mixed gas of nitrogen (purity: 99.99995% or more) and argon gas (purity: 99.9999% or more) (mixing ratio (nitrogen:argon) 30:70), sputtering gas pressure: 0.25 Pa, substrate heating temperature: 200° C. Example 4

[0068] Using the following equipment and sputtering target, a scandium-doped gallium nitride piezoelectric thin film (ScN) shown in FIG. ｘ Ga １－ｘ N) was deposited directly on a conductive silicon substrate (0.02 Ω·cm or less).

[0069] Sputtering deposition apparatus (manufactured by ULVAC) Sc sputtering target material (purity: 99.99%) GaN powder sintered sputtering target material (purity: 99.99%) Gas: mixed gas of nitrogen (purity: 99.99995% or more) and argon gas (purity: 99.9999% or more) (mixing ratio (nitrogen:argon) 10:90 to 30:70) Sputtering gas pressure: 0.45 Pa Substrate heating temperature: 200°C Example 5

[0070] Using the following equipment and sputtering target, a scandium-doped gallium nitride piezoelectric thin film (ScN) shown in FIG. ｘ Ga １－ｘ N) was deposited directly on a conductive silicon substrate (0.02 Ω·cm or less).

[0071] Sputtering deposition apparatus (manufactured by ULVAC, Inc.) ScGa alloy sputtering target material (Sc:Ga=50:50, purity: 99.9%) Sc metal sputtering target material (purity: 99.99%) Gas: mixed gas of nitrogen (purity: 99.99995% or more) and argon gas (purity: 99.9999% or more) (mixing ratio (nitrogen:argon) 10:90 to 50:50) Sputtering gas pressure: 0.45 Pa Substrate heating temperature: 200°C Example 6

[0072] Using the following equipment and sputtering target, a scandium-doped gallium nitride piezoelectric thin film (ScN) shown in FIG. ｘ Ga １－ｘ N) was deposited directly on a conductive silicon substrate (0.02 Ω·cm or less).

[0073] Sputtering deposition equipment (ULVAC) Sc sputtering target material (purity: 99.99%) GaN powder sintered sputtering target material (purity: 99.99%) Gas: mixed gas of nitrogen (purity: 99.99995% or more) and argon gas (purity: 99.9999% or more) (mixing ratio (nitrogen:argon) 12:88) Sputtering gas pressure: 0.45 Pa Substrate heating temperature: 150 to 300°C

[0074] Next, for each of the piezoelectric thin films in Examples 1 to 6, the Sc concentration and the piezoelectric constant d ３３The graph showing the relationship between the length of the c-axis and the piezoelectric constant d ３３ A graph showing the relationship between the above and the above is shown in Figure 10. Note that the data from Non-Patent Document 1 in these figures refers to that described in the above-mentioned Non-Patent Document. The same applies hereinafter.

[0075] As can be seen from these figures, the piezoelectric constant d ３３ is a conventional Sc ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ That is, when x is in the range of 0.39 to 0.54 and the length of the c-axis is 4.94 × 10 －１０ m or more, 5.2×10 －１０ The piezoelectric thin film in the range smaller than m is at least the conventional Sc ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ (14 pC / N), which is higher than the Sc calculated by first-principles calculation. ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ (16.9 pC / N).

[0076] Further, x is in the range of 0.45 to 0.54, and the length of the c-axis is 4.94 × 10 －１０ m or more, 5.05×10 －１０ The piezoelectric thin film having a thickness smaller than m is made of scandium-doped aluminum nitride (ScN) as described in Non-Patent Document 3. ｘ Al １－ｘ N) maximum piezoelectric constant d ３３ Piezoelectric constant d higher than (27.6 pC / N) ３３ It was found that it has.

[0077] Furthermore, for each of the piezoelectric thin films in Examples 1 to 6, the length of the a-axis and the piezoelectric constant d ３３ As can be seen from this graph, when the length of the a-axis is 3.4 × 10 －１０ m or more, 3.5×10 －１０ The piezoelectric thin film in the range of 0.1 m or less is ｘ Ga １－ｘMaximum piezoelectric constant d of N ３３ (14 pC / N), which is higher than the Sc calculated by first-principles calculation. ｘ Ga １－ｘ Maximum piezoelectric constant d of N ３３ (16.9 pC / N). The length of the a-axis was 3.44 × 10 －１０ m or more, 3.48×10 －１０ The piezoelectric thin film having a thickness smaller than m is made of scandium-doped aluminum nitride (ScN) as described in Non-Patent Document 3. ｘ Al １－ｘ N) maximum piezoelectric constant d ３３ Piezoelectric constant d higher than (27.6 pC / N) ３３ It was found that it has.

[0078] In the first embodiment, the piezoelectric thin film is formed directly on the substrate, but the present invention is not limited to this. For example, as shown in FIG. 12, an intermediate layer 20 may be provided between the substrate 10 and the piezoelectric thin film 1A.

[0079] Here, the material and thickness of the intermediate layer 20 are not particularly limited as long as the piezoelectric thin film 1A can be formed on the intermediate layer 20. Examples of the intermediate layer include aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), titanium nitride (TiN), scandium nitride (ScN), ytterbium nitride (YbN), molybdenum (Mo), tungsten (W), hafnium (Hf), titanium (Ti), ruthenium (Ru), and ruthenium oxide (RuO). ２ ), chromium (Cr), chromium nitride (CrN), platinum (Pt), gold (Au), silver (Ag), copper (Cu), aluminum (Al), tantalum (Ta), iridium (Ir), palladium (Pd), and nickel (Ni), and those having a thickness of 1 to 200 nm and made of these materials are listed.

[0080] By providing such an intermediate layer 20 on the substrate 10, the crystallinity (degree of crystallization) of the piezoelectric thin film 1A is improved, and the piezoelectric constant d ３３ Sc with ｘ Ga１－ｘ N can be formed.

[0081] (Embodiment 3) In the above-described embodiment 2, the piezoelectric thin film is formed directly on the intermediate layer, but the present invention is not limited to this. For example, a diffusion layer containing the material constituting the intermediate layer and the material constituting the piezoelectric thin film may be further provided between the intermediate layer and the piezoelectric thin film. Note that the diffusion layer can be formed, for example, by forming the piezoelectric thin film on the intermediate layer and then applying heat thereto. Even when a diffusion layer is provided in this manner, the same effects as those of embodiment 2 can be obtained.

[0082] (Embodiment 4) In the above-described embodiment, the nitride material according to the present invention is used as a piezoelectric body, but the present invention is not limited to this. The nitride material according to the present invention has ferroelectricity and can also be used as a ferroelectric body. <Example 7>

[0083] Using the following equipment and sputtering target, a ferroelectric thin film of scandium-doped gallium nitride (ScN) was prepared. ｘ Ga １－ｘ N) was deposited directly on a conductive silicon substrate (0.02 Ω·cm or less).

[0084] Sputtering deposition equipment (ULVAC) Sc sputtering target material (purity: 99.99%) GaN powder sintered sputtering target material (purity: 99.99%) Gas: mixed gas of nitrogen (purity: 99.99995% or more) and argon gas (purity: 99.9999% or more) (mixing ratio (nitrogen:argon) 12:88) Sputtering gas pressure: 0.45 Pa Substrate heating temperature: 250°C

[0085] The obtained ferroelectric thin films are shown in Figure 13, and for the ferroelectric thin film No. 0.3, a 100 μm diameter Pt was attached as an upper electrode by vapor deposition, and then the ferroelectricity (electric field-polarization characteristics) was measured using FCE10-S / 400-A (manufactured by Toyo Corporation), and the results are shown in Figure 14. From this figure, it was found that the ferroelectric thin film No. 0.3 has ferroelectricity, as it shows a clear hysteresis loop.

[0086] Other Embodiments In the first embodiment, a piezoelectric thin film using the nitride material according to the present invention has been described as an example, but the present invention is not limited thereto. For example, the nitride material according to the present invention can also be applied to electronic elements such as MEMS devices and ferroelectric memories. Known structures can be adopted for the MEMS devices and electronic elements.

[0087] A ferroelectric memory using the nitride material according to the present invention has higher spontaneous polarization and higher memory performance than conventional ferroelectric memories.

[0088] 1, 1A Piezoelectric thin film 10 Substrate 20 Intermediate layer

Claims

1. Chemical formula Sc ｘ G １－ｘ N, where x is in the range of 0.39 to 0.54, and the length of the c-axis in the crystal structure is 4.94×10 －１０ m or more, 5.2×10 －１０ m or less.

2. The nitride material according to claim 1, wherein x is in the range of 0.45 to 0.

54.

3. The nitride material according to claim 1, wherein x is in the range of 0.5 to 0.

54.

4. The length of the c-axis is 4.94 × 10 －１０ m or more, 5.05×10 －１０ 2. The nitride material according to claim 1, wherein the n-type nitride material is in the range of m or less.

5. The length of the a-axis in the crystal structure is 3.4 × 10 －１０ m or more, 3.5×10 －１０ 2. The nitride material according to claim 1, wherein the n-type nitride material is in the range of m or less.

6. The length of the a-axis is 3.44 x 10 －１０ m or more, 3.48×10 －１０ 6. The nitride material according to claim 5, wherein the n-type nitride material is in the range of m or less.

7. The nitride material according to claim 1, characterized in that the thickness is in the range of 1 nm to 3000 nm.

8. A piezoelectric body made of the nitride material according to any one of claims 1 to 7.

9. A piezoelectric body comprising a nitride material according to any one of claims 1 to 7 provided on a substrate, and at least one intermediate layer provided between the nitride material and the substrate.

10. The piezoelectric element according to claim 9, further comprising a diffusion layer between the intermediate layer and the piezoelectric element, the diffusion layer containing the material constituting the intermediate layer and the material constituting the piezoelectric element.

11. A MEMS device using the piezoelectric material according to claim 8.

12. A ferroelectric material comprising the nitride material according to any one of claims 1 to 7.

13. An electronic device using the ferroelectric material according to claim 12.

14. A method for producing a nitride material according to any one of claims 1 to 7 using a sputtering method, characterized in that a sputtering gas containing nitrogen is used, and the sputtering targets used are a target composed of scandium and a target composed of gallium nitride, a target composed of scandium and a target composed of an alloy containing scandium and gallium, a target composed of gallium nitride and a target composed of an alloy containing scandium and gallium, or a target composed of an alloy containing scandium and gallium.

15. The method for producing a nitride material according to claim 14, characterized in that the heating temperature during film formation of the substrate on which the nitride material is formed is in the range of 25°C or higher and lower than 400°C.

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