Nitride piezoelectric body and MEMS device using the same

Abstract

The present invention aims to provide an aluminum nitride having a higher performance index (d 33 , g 33 and K 2 A nitride piezoelectric body having a value of at least one of the above) and a MEMS device using the nitride piezoelectric body. The solution of the present invention is a piezoelectric body having a chemical formula of Al 1‑X‑Y Mg X Ta Y N represents that X+Y is less than 1, X is in the range of greater than 0 and less than 1, Y is in the range of greater than 0 and less than 1, and Ta includes tetravalent Ta.

Description

Technical Field

[0001] The present invention relates to a piezoelectric body of aluminum nitride to which magnesium and tantalum are added, and a MEMS device using the piezoelectric body. Background Art

[0002] Devices utilizing the piezoelectric phenomenon are used in a wide range of fields, and their use is increasing in portable devices such as mobile phones, which are strongly required to be smaller and more power-efficient. One example of such devices is a film bulk acoustic resonator (FBAR) filter using a film bulk acoustic resonator (FBAR).

[0003] The FBAR filter is a filter based on a resonator using a thickness longitudinal vibration mode of a thin film showing piezoelectric responsiveness, and has the characteristic of being able to resonate in the gigahertz band. The FBAR filter having such characteristics has low loss and can operate in a wide frequency band, and is therefore expected to contribute to further high-frequency response, miniaturization, and power saving of portable devices.

[0004] As piezoelectric materials for piezoelectric thin films of such FBARs, for example, aluminum nitride with scandium added (see Patent Document 1), aluminum nitride with magnesium and tantalum added (Patent Document 2), etc. can be cited. In particular, aluminum nitride with scandium added has a high piezoelectric constant and is expected to be used in the next generation of high-frequency filters. In addition, it is expected to be used in various MEMS (micro electro mechanical system) devices such as pressure sensors, acceleration sensors, gyroscope sensors, etc., actuators, microphones, fingerprint authentication sensors, and vibration generators.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2009-10926

[0008] Patent Document 2: Japanese Patent No. 5904591 Summary of the invention

[0009] Problems to be solved by the invention

[0010] However, scandium (Sc) is an expensive rare earth element, and a piezoelectric body composed of aluminum nitride (AlN) to which scandium is added has a problem in that the manufacturing cost becomes higher than that of a piezoelectric body composed of other substances.

[0011] In addition, although Patent Document 2 discloses a piezoelectric body composed of aluminum nitride (AlN) to which magnesium (Mg) and tantalum (Ta) are added, it is a material based on numerical calculations. Specifically, it discloses the results of numerical calculations when magnesium (12.5 atomic %) with a valence of 2 and tantalum (6.25 atomic %) with a valence of 5 are doped into aluminum nitride.

[0012] However, the piezoelectric body disclosed in Patent Document 2 is a piezoelectric body based on numerical calculations, and there is a question of whether the atomic valence (valence number) of tantalum used in the calculation is correct. The details will be described later. 1-X-Y Mg X Ta Y The tantalum contained in the N) includes not only tantalum with a valence of five but also tantalum with other valences, which is completely different from what is disclosed in Patent Document 2.

[0013] In view of the above situation, the object of the present invention is to provide an aluminum nitride having a higher performance index (d 33 , g 33 and K 2 A nitride piezoelectric having a value of at least any one of the above) and a MEMS device using the nitride piezoelectric.

[0014] Methods for solving problems

[0015] The inventors of the present invention have continued to conduct intensive studies on the above-mentioned problems, and as a result, have discovered a revolutionary piezoelectric body of aluminum nitride (AlN) to which magnesium (Mg) and tantalum (Ta) are added as described below.

[0016] A first aspect of the present invention for solving the above-mentioned problems is a piezoelectric body characterized by having a chemical formula of Al 1-X-Y Mg X Ta Y N represents that X+Y is less than 1, X is in the range of greater than 0 and less than 1, Y is in the range of greater than 0 and less than 1, and Ta includes tetravalent Ta.

[0017] Here, "tetravalent Ta" means Ta having an atomic valence of 4. The valence of Ta can be detected by, for example, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XANES), TEM-EELS, or the like.

[0018] In the first mode, it is possible to provide an aluminum nitride having a higher performance index (d 33 , g 33 and K 2 A nitride piezoelectric having a value of at least any one of the values ​​​​(in ).

[0019] A second aspect of the present invention is the piezoelectric body according to the first aspect, characterized in that tetravalent Ta is contained in the largest amount compared to Ta other than tetravalent Ta.

[0020] In this second mode, a higher performance index (d 33 , g 33 and K 2 A nitride piezoelectric having a value of at least any one of the values ​​​​(in ).

[0021] A third aspect of the present invention is the piezoelectric body according to the first or second aspect, characterized in that X / Y is greater than 2 and is 5 or less.

[0022] In the third embodiment, a higher performance index (d 33 , g 33 and K 2 A nitride piezoelectric having a value of at least any one of the values ​​​​(in ).

[0023] A fourth aspect of the present invention is the piezoelectric body according to the first or second aspect, characterized in that X / Y is greater than 2.5 and is 4 or less.

[0024] In the fourth aspect, a device having a particularly high performance index (d 33 , g 33 and K 2 A nitride piezoelectric having a value of at least any one of the values ​​​​(in ).

[0025] A fifth aspect of the present invention is the piezoelectric body according to any one of the first to fourth aspects, wherein X+Y is larger than 0.0 and equal to or smaller than 0.4.

[0026] In the fifth aspect, a device having a higher performance index (d 33 , g 33 and K 2 A nitride piezoelectric having a value of at least any one of the values ​​​​(in ).

[0027] A sixth aspect of the present invention is the piezoelectric body according to any one of the first to fourth aspects, wherein X+Y is greater than or equal to 0.15 and less than or equal to 0.35.

[0028] In the sixth aspect, a device having a higher performance index (d 33 , g 33 and K 2 A nitride piezoelectric having a value of at least any one of the values ​​​​(in ).

[0029] A seventh aspect of the present invention is a piezoelectric body characterized in that the piezoelectric body described in any one of the first to sixth aspects is provided on a substrate, and at least one intermediate layer is provided between the piezoelectric body and the substrate.

[0030] In the seventh aspect, the crystallinity (degree of crystallinity) of the piezoelectric body is improved, so that a device having a higher performance index (d 33 and g 33 A nitride piezoelectric having a value of at least any one of the values ​​​​(in ).

[0031] The eighth embodiment of the present invention is a piezoelectric body described in the seventh embodiment, characterized in that the intermediate layer contains at least one of aluminum nitride, gallium nitride, indium nitride, titanium nitride, scandium nitride, ytterbium nitride, molybdenum, tungsten, hafnium, titanium, ruthenium, ruthenium oxide, chromium, chromium nitride, platinum, gold, silver, copper, aluminum, tantalum, iridium, palladium and nickel.

[0032] In the eighth aspect, the crystallinity (degree of crystallinity) of the piezoelectric body is further improved, so that a device having a higher performance index (d 33 , g 33 and K 2 A nitride piezoelectric having a value of at least any one of the values ​​​​(in ).

[0033] A ninth aspect of the present invention is the piezoelectric body described in the seventh or eighth aspect, characterized in that a diffusion layer is further provided between the intermediate layer and the piezoelectric body, and the diffusion layer contains a substance constituting the intermediate layer and a substance constituting the piezoelectric body.

[0034] In the ninth aspect, similarly to the seventh and eighth aspects, a high performance index (d 33 , g 33 and K 2 A nitride piezoelectric having a value of at least any one of the values ​​​​(in ).

[0035] A tenth aspect of the present invention is a MEMS device using the piezoelectric body according to any one of the first to ninth aspects.

[0036] Here, the so-called "MEMS device" is not particularly limited as long as it is a micro electromechanical system. For example, it includes physical sensors such as FBAR filters, pressure sensors, acceleration sensors, gyroscope sensors, actuators, microphones, fingerprint authentication sensors, vibration generators, energy harvesters, etc.

[0037] The tenth aspect can provide a MEMS device that can cope with high frequencies, is compact, and saves power. In particular, when the MEMS device is a high-frequency filter, it can provide a device that has low loss and can operate in a wide frequency band compared to conventional high-frequency filters. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] [ Figure 1 ] Figure 1 This is a schematic cross-sectional view of the piezoelectric thin film according to the first embodiment.

[0039] [ Figure 2 ] Figure 2 It is a graph showing the relationship between the binding energy (Binding energy) and the strength (Intensity) in each piezoelectric thin film.

[0040] [ Figure 3 ] Figure 3 It is a graph showing the relationship between the molar ratio of tantalum and magnesium and the ratio of the peak region of the 4f orbital of tantalum.

[0041] [ Figure 4 ] Figure 4 is the piezoelectric constant d 33 A graph showing the relationship between the atomic percentage ratio of Mg / Ta.

[0042] [ Figure 5 ] Figure 5 is the relationship between the concentration of dopants (Mg+Ta) and the piezoelectric constant d 33 A curve graph of the relationship.

[0043] [ Figure 6 ] Figure 6 It represents the concentration of dopant (Mg+Ta) and relative dielectric constant ε r A curve graph of the relationship.

[0044] [ Figure 7 ] Figure 7 is the relationship between the concentration of dopant (Mg+Ta) and the piezoelectric output constant g 33 A curve graph of the relationship.

[0045] [ Figure 8 ] Figure 8 is the relationship between the concentration of dopants (Mg+Ta, Sc) and the piezoelectric output constant g 33 A curve graph of the relationship.

[0046] [ Fig. 9 ] Fig. 9 It shows the relationship between the concentration of dopants (Mg+Ta, Sc) and the electromechanical coupling coefficient K 2 A curve graph of the relationship.

[0047] [ Fig.10 ] Fig.10 This is a schematic cross-sectional view of the piezoelectric thin film according to the second embodiment. DETAILED DESCRIPTION

[0048] Hereinafter, embodiments of the piezoelectric thin film of the present invention will be described with reference to the drawings. It should be noted that the present invention is not limited to the following embodiments, and the shape is not limited, and it is of course not necessary to be a thin film.

[0049] (Implementation Method 1)

[0050] Figure 1 As shown in this figure, a piezoelectric thin film 1 is formed on a substrate 10. The thickness of the piezoelectric thin film 1 is not particularly limited, but is preferably in the range of 0.1 to 30 μm, and 0.1 to 2 μm is particularly preferred because of excellent adhesion.

[0051] The substrate 10 may be any substrate 10 on a surface thereof, and its thickness, material, etc. are not particularly limited as long as the piezoelectric thin film 1 can be formed thereon. Examples of the substrate 10 include heat-resistant alloys such as silicon and Inconel, and resin films such as polyimide.

[0052] The piezoelectric film 1 is composed of a chemical formula of Al 1-X-Y Mg X Ta Y N represents that X+Y is less than 1, X is in the range of greater than 0 and less than 1, and Y is in the range of greater than 0 and less than 1, and the piezoelectric thin film 1 is composed of aluminum nitride (AlN) added (doped) with magnesium (Mg) and tantalum (Ta). Moreover, the piezoelectric thin film 1 contains Ta with a valence of 4. It should be noted that the valence of Ta can be detected by X-ray photoelectron spectroscopy (XPS) or the like.

[0053] The piezoelectric thin film 1 thus constructed has a higher performance index (d 33 , g 33 and K 2 At least any 1 of the values ​​in .

[0054] Here, Ta may contain Ta with a valence other than tetravalent (for example, trivalent or pentavalent), but it is preferred that the piezoelectric thin film 1 contain the largest amount of tetravalent Ta compared to the amount of Ta other than tetravalent Ta. The piezoelectric thin film 1 thus constructed has a higher performance index (d 33 , g 33 and K 2 At least any 1 of the values ​​in .

[0055] In addition, if the content ratio of tetravalent Ta in Ta contained in the piezoelectric thin film 1 is 30% or more, a higher performance index (d 33 , g 33 and K 2 If the content ratio of tetravalent Ta is 45% or more, the piezoelectric thin film 1 having a value of at least any one of the above) has a further improved performance index (d 33 , g 33 and K 2 If the content ratio of tetravalent Ta is 50% or more, the piezoelectric thin film 1 having a particularly high performance index (d 33, g 33 and K 2 A piezoelectric film 1 having a value of at least any one of the values.

[0056] Furthermore, it is preferable that the piezoelectric thin film 1 has a ratio X / Y greater than 2 and not more than 5 in the above chemical formula. The piezoelectric thin film 1 thus constituted has a further improved performance index (d 33 , g 33 and K 2 At least any 1 of the values ​​in .

[0057] Furthermore, it is more preferable that the piezoelectric thin film 1 has a ratio X / Y greater than 2.5 and not more than 4 in the above chemical formula. The piezoelectric thin film 1 thus constituted has a particularly high performance index (d 33 , g 33 and K 2 At least any 1 of the values ​​in .

[0058] Next, it is more preferable that the piezoelectric thin film 1 has X+Y greater than 0.0 and less than 0.4 in the above chemical formula. The piezoelectric thin film 1 thus constituted has a higher performance index (d 33 , g 33 and K 2 At least any 1 of the values ​​in .

[0059] Furthermore, it is more preferable that the piezoelectric thin film 1 has a value of 0.15 or more and 0.35 or less in the above chemical formula. The piezoelectric thin film 1 thus constituted has a further improved performance index (d 33 , g 33 and K 2 At least any 1 of the values ​​in .

[0060] Furthermore, it is particularly preferable that the piezoelectric thin film 1 has a value of 0.2 or more and 0.3 or less in the above chemical formula. The piezoelectric thin film 1 thus constituted has a particularly high performance index (d 33 , g 33 and K 2 At least any 1 of the values ​​in .

[0061] Moreover, the high-frequency filter using these piezoelectric thin films 1 has low loss compared to conventional high-frequency filters and can operate in a wide frequency band. As a result, portable devices can be made more high-frequency responsive, miniaturized, and power-saving. In addition, the structure of the high-frequency filter is not particularly limited and can be manufactured with a known structure.

[0062] Next, the manufacturing method of the piezoelectric thin film 1 of the present embodiment is described. The piezoelectric thin film 1 can be manufactured by a manufacturing method such as a sputtering method and a vapor deposition method, similarly to a general piezoelectric thin film. Specifically, for example, a target composed of tantalum, a target composed of magnesium, and a target composed of aluminum (Al) can be simultaneously sputtered on a substrate 10 (for example, a silicon (Si) substrate) in a nitrogen (N2) atmosphere or in a mixed atmosphere of nitrogen (N2) and argon (Ar) (the gas pressure is less than 1 Pa). It should be noted that as a target, an alloy containing tantalum, magnesium, and aluminum in a specified ratio can be used.

[0063] It should be noted that a layer including a substance constituting the substrate and a substance constituting the piezoelectric thin film may be formed between the substrate and the piezoelectric thin film. Such a layer may be formed, for example, by forming the piezoelectric thin film on the substrate and then heating them.

[0064] (Example)

[0065] Using the following apparatus and sputtering target, a piezoelectric thin film of aluminum nitride (AlN) with a thickness of 0.4 to 1.5 μm and doped with tantalum and magnesium was prepared on an n-type silicon substrate with a resistivity of 0.02 Ωcm. 1-X-Y Mg X Ta Y N).

[0066] Multi-element simultaneous sputtering film forming equipment (manufactured by Eiko Engineering Co., Ltd.)

[0067] Tantalum sputtering target (concentration: 99.999%)

[0068] Magnesium sputtering target (concentration: 99.999%)

[0069] Aluminum sputtering target (concentration: 99.999%)

[0070] Gas: A mixture of nitrogen (purity: 99.99995% or more) and argon (purity: 99.9999% or more) (mixing ratio 50:50)

[0071] Substrate heating temperature: 500°C

[0072] In the film forming experiment, the pressure in the sputtering chamber was reduced to 10 by using a vacuum pump. -6 In order to avoid the incorporation of impurities such as oxygen, the target surface was cleaned immediately after the target was installed or before each film forming experiment.

[0073] The relationship between the binding energy and the intensity of each piezoelectric thin film measured by XPS (manufactured by Shimadzu / KRATOS Manufacturing Co., Ltd., AXIS-165) is shown in FIG. Figure 2 The relationship between the molar ratio of tantalum to magnesium and the ratio of the peak area of ​​the 4f orbital of tantalum is shown in Figure 3 As can be seen from these figures, as the ratio of magnesium to tantalum atomic percentage (Mg / Ta) increases, Ta 5+ and Ta 3+ The proportion becomes smaller, but Ta 4+ In addition, it can be seen that in the range of 1≤Mg / Ta≤3, 5+ and Ta 3+ In comparison, 4+ The ratio of the number of atoms is the highest.

[0074] then, Figure 4 The piezoelectric constant d is shown when the concentration of the dopant (Mg+Ta) is 15 to 26 at.%. 33 The relationship between the piezoelectric constant d 33 The value of increases as Mg / Ta becomes larger than 1 and becomes the highest at 3.1. As Mg / Ta becomes larger than 3.1, the piezoelectric constant d 33 It should be noted that the piezoelectric constant d 33 , and the measurement was performed using a piezoelectric meter (Piezotest PM300 manufactured by Alpha Corporation).

[0075] and then, Figure 5 The dopant concentration (Mg+Ta) and the piezoelectric constant d are shown. 33 Here, the atomic percentage ratio of Mg / Ta is fixed at 3.1. As can be seen from the figure, as the concentration of dopant (Mg+Ta) increases, the piezoelectric constant d 33 The value of becomes higher and reaches the highest value at 24.3 at.%. In addition, the piezoelectric constant d of aluminum nitride without any element added is 0 when the concentration of dopant (Mg+Ta) is 0. 33 The value of .

[0076] in addition, Figure 6 The dopant concentration (Mg+Ta) and the relative dielectric constant ε are shown. r Here, the atomic percentage ratio of Mg / Ta is fixed at 3.1. As can be seen from the figure, the concentration of the dopant (Mg+Ta) is approximately constant up to 24.3 at.% (ε r = 10), but as the concentration of dopants (Mg + Ta) is higher than 24.3 at.%, the relative dielectric constant ε r The value of becomes higher.

[0077] Furthermore, based on the above data, the piezoelectric output constant g is calculated using the following formula: 33Here we use ε0=8.8542e -12 .

[0078] [Number 1]

[0079]

[0080] and, Figure 7 The obtained piezoelectric output constant g is shown 33 Here, the atomic percentage ratio of Mg / Ta is fixed at 3.1. According to this figure, the piezoelectric output constant g 33 The value of increases as the concentration of the dopant (Mg+Ta) increases, reaching the highest value at 24.3at.%. Moreover, it can be seen that as the concentration of the dopant (Mg+Ta) increases above 24.3at.%, the piezoelectric output constant g 33 The value of gradually decreases. It should be noted that the concentration of the dopant (Mg+Ta) is 0, which is the piezoelectric output constant g of aluminum nitride without any element added. 33 The value of .

[0081] in addition, Figure 8 The concentration of each dopant (Mg+Ta, Sc) and the piezoelectric output constant g are shown. 33 As can be seen from the figure, before the concentration of each dopant reaches 24.3 at.%, the aluminum nitride piezoelectric film (Al 1-X- Y Mg X Ta Y N) has a better performance than aluminum nitride piezoelectric film (Al1-XSc X N) High piezoelectric output constant g 33 .

[0082] As can be seen from the above, the piezoelectric film of this embodiment has a higher performance index (d) than aluminum nitride without any element added, when the atomic percentage ratio of Mg / Ta is greater than 1 and less than 4, and the concentration of the dopant (Mg+Ta) is greater than 0.0 and less than 0.4. 33 and g 33 ) value.

[0083] and then, Fig. 9 The concentration of each dopant (Mg+Ta) and the electromechanical coupling coefficient K are shown. 2 According to this figure, the electromechanical coupling coefficient K 2 The value of increases as the concentration of the dopant (Mg+Ta) increases, reaching the highest value at 24.3at.%. Moreover, it can be seen that as the concentration of the dopant (Mg+Ta) increases above 24.3at.%, the piezoelectric output constant g 33The value of gradually decreases. It should be noted that the electromechanical coupling coefficient K 2 It can be calculated using the following formula.

[0084] [Number 2]

[0085] k 2 =e 33 ×g 33

[0086] It should be noted that e 33 The piezoelectric stress constant is calculated using software such as VASP (Vienna Ab initio Simulation Package) which uses a calculation method called first-principle calculation.

[0087] (Implementation Method 2)

[0088] In the above-mentioned first embodiment, the piezoelectric thin film is directly produced on the substrate, but the present invention is not limited to this. Fig.10 As shown in FIG. 1 , an intermediate layer 20 may be provided between the substrate 10 and the piezoelectric thin film 1A.

[0089] Here, as the intermediate layer 20, the material, thickness, etc. are not particularly limited as long as the piezoelectric thin film 1A can be formed on the intermediate layer 20. As the intermediate layer, for example, a layer with a thickness of 50 to 200 nm composed of 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), ruthenium oxide (RuO2), chromium (Cr), chromium nitride (CrN), platinum (Pt), gold (Au), silver (Ag), copper (Cu), aluminum (Al), tantalum (Ta), iridium (Ir), palladium (Pd) and nickel (Ni) can be cited.

[0090] By providing such an intermediate layer 20 on the substrate 10, the crystallinity (degree of crystallinity) of the piezoelectric thin film 1A is improved, so that a piezoelectric thin film having a higher performance index (d) than the piezoelectric thin film of the first embodiment can be formed. 33 , g 33 and K 2 Aluminum nitride piezoelectric thin film (Al 1-X-Y Mg X Ta Y N).

[0091] (Implementation method 3)

[0092] In the above-mentioned embodiment 2, the piezoelectric thin film is directly formed on the intermediate layer, but the present invention is not limited to this. For example, a diffusion layer containing a substance constituting the intermediate layer and a substance constituting the piezoelectric thin film may be further provided between the intermediate layer and the piezoelectric thin film. It should be noted that the diffusion layer may be formed, for example, by applying heat to the piezoelectric thin film after forming the piezoelectric thin film on the intermediate layer. Even if the diffusion layer is provided in this way, the same effect as in embodiment 2 can be obtained.

[0093] Explanation of symbols

[0094] 1.1A: Piezoelectric film,

[0095] 10: Substrate,

[0096] 20: Middle layer.

Claims

1. A piezoelectric body, characterized in that: By chemical formula Al 1-X-Y Mg X Ta Y N means, X+Y is less than 1, and X is in the range of greater than 0 and less than 1, and Y is in the range of greater than 0 and less than 1, Ta includes tetravalent Ta, Compared with other than tetravalent Ta, tetravalent Ta is contained in the largest amount.

2. A piezoelectric body, characterized in that: By chemical formula Al 1-X-Y Mg X Ta Y N means, X+Y is less than 1, and X is in the range of greater than 0 and less than 1, and Y is in the range of greater than 0 and less than 1, Ta includes tetravalent Ta, X / Y is greater than 2 and 5 or less.

3. The piezoelectric body according to claim 1, wherein: X / Y is greater than 2.5 and less than or equal to 4.

4. The piezoelectric body according to any one of claims 1 to 3, characterized in that X+Y is greater than 0.0 and less than or equal to 0.

4.

5. The piezoelectric body according to any one of claims 1 to 3, characterized in that X+Y is greater than or equal to 0.15 and less than or equal to 0.

35.

6. A piezoelectric body, characterized in that: The piezoelectric body according to claim 1 is provided on a substrate, and at least one intermediate layer is provided between the piezoelectric body and the substrate.

7. The piezoelectric body according to claim 6, characterized in that: The intermediate layer includes at least one of aluminum nitride, gallium nitride, indium nitride, titanium nitride, scandium nitride, ytterbium nitride, molybdenum, tungsten, hafnium, titanium, ruthenium, ruthenium oxide, chromium, chromium nitride, platinum, gold, silver, copper, aluminum, tantalum, iridium, palladium and nickel.

8. The piezoelectric body according to claim 6 or 7, characterized in that: A diffusion layer is further provided between the intermediate layer and the piezoelectric body. The diffusion layer contains a substance constituting the intermediate layer and a substance constituting the piezoelectric body.

9. A MEMS device using the piezoelectric body according to any one of claims 6 to 8.

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