Piezoelectric elements and MEMS devices using the same piezoelectric elements

Abstract

[Problem] The purpose of the present invention is to provide: a piezoelectric element which does not have a buffer layer, has sufficient piezoelectric characteristics and stability, and can be further reduced in size as compared with conventional piezoelectric elements; and a MEMS device which uses the piezoelectric element. [Solution] The present invention comprises: a piezoelectric layer 10 that is formed of a nitride material which has a wurtzite crystal structure; a first electrode 20 that is provided on one surface of the piezoelectric layer; and a second electrode 30 that is provided on the other surface of the piezoelectric layer. The first electrode is formed of a first nitride material that has a wurtzite crystal structure and an electrical resistivity of 1.0 × 10-3 Ω∙cm or less. The second electrode is formed of a second nitride material that has a wurtzite crystal structure and an electrical resistivity of 1.0 × 10-3 Ω∙cm or less.

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric element composed of an electrode and a piezoelectric material made of a wurtzite-type crystal structure material, and a MEMS device using the piezoelectric element. [Background technology]

[0002] Devices that utilize the piezoelectric effect are used in a wide range of fields, and their use is expanding in portable devices such as mobile phones, where miniaturization and power saving are strongly demanded. One example of this is the FBAR filter, which uses a film bulk acoustic resonator (FBAR).

[0003] FBAR filters are resonator filters that utilize the thickness-longitudinal vibration mode of a thin film exhibiting piezoelectric response, and possess the characteristic of being capable of resonance in the gigahertz band. Because FBAR filters have such characteristics, they are low-loss and can operate over a wide bandwidth, and are expected to contribute to further high-frequency compatibility, miniaturization, and power saving in portable devices.

[0004] As shown in Figures 17 and 18, conventional piezoelectric elements used in such FBARs, particularly piezoelectric elements 200A and 200B in which the piezoelectric layer is made of wurtzite-type crystal material, were constructed by stacking the lower electrode 230, the piezoelectric layer 210, and the upper electrode 220 in order from bottom to top on a buffer layer 250 provided on a substrate 300 (see Non-Patent Literature 1), or by stacking the lower electrode 230, the buffer layer 250, the piezoelectric layer 210, and the upper electrode 220 in order from bottom to top on the substrate 300. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Moreira et al, Vacuum, 86 (2011) 23 [Overview of the project] [Problems that the invention aims to solve]

[0006] The reason why the conventional piezoelectric elements described above were provided with a buffer layer is that by providing a buffer layer, the crystallinity of the piezoelectric layer provided on the buffer layer can be improved, thereby enabling the formation of a stable piezoelectric layer.

[0007] However, adding a buffer layer increases the thickness of the piezoelectric element, which presents a problem in that it prevents further miniaturization of the piezoelectric element.

[0008] Furthermore, the need to form a buffer layer complicates the manufacturing process of piezoelectric elements, leading to decreased productivity and increased production costs.

[0009] In view of the circumstances described above, the present invention aims to provide a piezoelectric element that does not have a buffer layer, has sufficient piezoelectric properties and stability, and can be miniaturized compared to conventional piezoelectric elements, by improving the crystallinity (crystallinity of the wurtzite crystal structure) of the piezoelectric layer provided (formed) on the upper or lower electrode by fabricating an upper or lower electrode using an electrode material that is conductive and has a wurtzite crystal structure, thereby providing a piezoelectric element that does not have a buffer layer, has sufficient piezoelectric properties and stability, and can be miniaturized compared to conventional piezoelectric elements, as well as a MEMS device using the piezoelectric element. [Means for solving the problem]

[0010] As a result of diligent research into the aforementioned problems, the inventors of this invention have discovered the following groundbreaking piezoelectric element and MEMS device using that piezoelectric element.

[0011] A first aspect of the present invention for solving the above problems is a piezoelectric element including at least one piezoelectric material layer having a wurtzite crystal structure, a first electrode provided on one surface of the piezoelectric material layer, and a second electrode provided on the other surface of the piezoelectric material layer, wherein at least one of the first electrode and the second electrode has a wurtzite crystal structure and is made of a nitride material having an electrical resistivity of 1.0×10 -3 Ω·cm or less, and is characterized by a piezoelectric element.

[0012] According to such a first aspect, by fabricating the first electrode or the second electrode using a nitride material having conductivity and a wurtzite crystal structure, the crystallinity (crystallinity of the wurtzite crystal structure) of the piezoelectric material layer provided (formed) on the first electrode or the second electrode can be improved. As a result, a piezoelectric element can be provided that has no buffer layer, has sufficient piezoelectric characteristics and stability, and can be made smaller than conventional piezoelectric elements.

[0013] A second aspect of the present invention is that the first electrode material and the second electrode material have a wurtzite crystal structure and are made of a nitride material having an electrical resistivity of 1.0×10 -3 Ω·cm or less, and is characterized by the piezoelectric element according to the first aspect.

[0014] According to such a second aspect, further, since the piezoelectric material layer is a wurtzite crystal, the crystallinity (crystallinity of the wurtzite crystal structure) of the second electrode or the first electrode provided (formed) on the piezoelectric material layer can also be improved. As a result, a piezoelectric element having higher piezoelectric characteristics and stability can be provided.

[0015] A third aspect of the present invention is that the nitride material is represented by the chemical formula A1 α1 B1 β1 Al 1-α1-β1 N or the chemical formula A1 α1 B1 β1 Ga 1-α1-β1 N, where α1 and β1 satisfy the following formula (1), or the chemical formula B2 β2 Al 1-β2 N or the chemical formula B2β2 Ga 1-β2 The piezoelectric element according to the first embodiment is characterized in that it is represented by N, β2 satisfies the following equation (2), and B1 and B2 include monovalent elements. 0 < α1 / β1 < 6·····(1) 0 < β2 < 0.52 ·····(2) (0 < α1 < 1, 0 < β1 < 1, A1 is at least one of Mg, Zn, and Ni, and B1 and B2 are at least one of Au, Ag, and Cu.)

[0016] According to this third embodiment, by fabricating the first or second electrode using a nitride material having higher conductivity and a wurtzite crystal structure, the crystallinity (crystallinity of the wurtzite crystal structure) of the piezoelectric layer provided (formed) on the first or second electrode can be improved. In addition, because the piezoelectric layer has high crystallinity (crystallinity of the wurtzite crystal structure), the crystallinity (crystallinity of the wurtzite crystal structure) of the second or first electrode provided (formed) on the piezoelectric layer can also be improved. As a result, it is possible to provide a piezoelectric element that does not have a buffer layer, has sufficient piezoelectric properties and stability, and can be further miniaturized compared to conventional piezoelectric elements.

[0017] A fourth aspect of the present invention is a piezoelectric element according to the third aspect, characterized in that monovalent B1 is present in the largest amount compared to B1 with other valencies, or monovalent B2 is present in the largest amount compared to B2 with other valencies.

[0018] According to this fourth embodiment, the crystallinity (crystallinity of the wurtzite crystal structure) of the piezoelectric layer provided (formed) on the first or second electrode can be improved by using a nitride material that has even higher conductivity and a wurtzite crystal structure to fabricate the first or second electrode. In addition, because the piezoelectric layer has high crystallinity (crystallinity of the wurtzite crystal structure), the crystallinity (crystallinity of the wurtzite crystal structure) of the second or first electrode provided (formed) on the piezoelectric layer can also be improved. As a result, it is possible to provide a piezoelectric element that does not have a buffer layer, has sufficient piezoelectric properties and stability, and can be further miniaturized compared to conventional piezoelectric elements.

[0019] A fifth aspect of the present invention is that α1 and β1 satisfy the following equations (3) and (4), The piezoelectric element is as described in feature 3. 1 ≤ α1 / β1 ≤ 5·····(3) 0 < α1 + β1 ≤ 0.3 ···(4)

[0020] According to this fifth embodiment, by fabricating the first or second electrode using a nitride material having higher conductivity and a wurtzite crystal structure, the crystallinity (crystallinity of the wurtzite crystal structure) of the piezoelectric layer provided (formed) on the first or second electrode can be improved. In addition, because the piezoelectric layer has high crystallinity (crystallinity of the wurtzite crystal structure), the crystallinity (crystallinity of the wurtzite crystal structure) of the second or first electrode provided (formed) on the piezoelectric layer can also be improved. As a result, it is possible to provide a piezoelectric element that does not have a buffer layer, has sufficient piezoelectric properties and stability, and can be further miniaturized compared to conventional piezoelectric elements.

[0021] A sixth aspect of the present invention is a piezoelectric element according to the first aspect, characterized in that the Young's moduli of the first electrode and the second electrode are equal to or greater than the Young's moduli of the piezoelectric layer.

[0022] According to this sixth embodiment, a high electromechanical coupling coefficient K eff 2 A piezoelectric element having an effective electromechanical coupling coefficient can be provided.

[0023] A seventh aspect of the present invention is a piezoelectric element according to the first aspect, characterized in that the thickness t1 of the first electrode, the thickness d of the piezoelectric element, and the thickness t2 of the second electrode satisfy the following equation (5). 0.025≦(t1+t2) / d≦0.2 (5)

[0024] According to this seventh aspect, a higher K eff 2 A piezoelectric element can be provided.

[0025] An eighth aspect of the present invention is a piezoelectric element according to any one of the first to seventh aspects, characterized in that a first electrode or a second electrode is provided on the surface of a substrate.

[0026] According to this eighth embodiment, a piezoelectric element can be easily manufactured that does not have a buffer layer, has sufficient piezoelectric properties and stability, and is even smaller than conventional piezoelectric elements.

[0027] A ninth aspect of the present invention is a MEMS device using the piezoelectric element described in the first aspect.

[0028] Here, "MEMS device" is not particularly limited to any micro-electromechanical system, and examples include physical sensors and actuators such as high-frequency filters, pressure sensors, acceleration sensors, and gyroscopes, as well as microphones, fingerprint sensors, vibration generators, transistors, inverters, transducers, SAW devices, ferroelectric memory, diodes, or batteries.

[0029] According to this ninth embodiment, a smaller MEMS device can be provided.

[0030] The specification of Japanese Patent Application No. 2024-31861 is incorporated herein by reference as part of this specification. [Brief explanation of the drawing]

[0031] [Figure 1] Figure 1 is a schematic cross-sectional view of a piezoelectric element according to Embodiment 1. [Figure 2] Figure 2 is a table showing the composition of the examples. [Figure 3] Figure 3 is a graph showing the measurement results of the X-ray diffraction (XRD) apparatus for Examples 5, 7, and 8. [Figure 4] Figure 4 is a graph showing the results of measuring the valences of Mg and Au in Examples 1-5 and 1-8. [Figure 5] Figure 5 is a graph showing the results of measuring the valence of Mg in Mg0.050Au0.037Al0.913N (top row), Mg0.073Au0.036Al0.891N (second from the top), Mg0.101Au0.033Al0.866N (third from the top), and Mg0.388Au0.081Al0.531N. [Figure 6] Figure 6 shows the results of measuring the valence of Au in Mg0.050Au0.037Al0.913N. [Figure 7] Figure 7 is a table showing the electrical resistivity of the thin films of Examples 1-5, 1-7, 1-8, and 1-13 to 1-27. [Figure 8] Figure 8 is a schematic cross-sectional view of electrode-equivalent thin films and piezoelectric-equivalent thin films fabricated to investigate the crystallinity of semiconductor devices. [Figure 9] Figure 9 is a table showing the measurement results of the full width at half maximum of the rocking curve. [Figure 10] Figure 10 is a graph showing the measurement results of the maximum diffraction intensity at the crystal plane (002) when the molar ratio of Mg to Au is changed. [Figure 11] Figure 11 is a graph showing the measurement results of the maximum diffraction intensity at the crystal plane (002) when the Mg+Au combination is varied. [Figure 12]Figure 12 is a table showing the compositions of Examples 2-1 to 2-11. [Figure 13] Figure 13 is a graph showing the measurement results of the X-ray diffractometer (XRD) for Examples 2-1 to 2-3. [Figure 14] Figure 14 is a graph showing the results of measuring the valence of Au in Au0.02Al0.98N. [Figure 15] Figure 15 is a table showing the composition and electrical resistivity of Examples 2-5 to 2-11. [Figure 16] Figure 16 is a graph showing the measurement results of the maximum diffraction intensity at the crystal plane (002) when the Au concentration is varied. [Figure 17] Figure 17 is a schematic cross-sectional view of a conventional piezoelectric element. [Figure 18] Figure 18 is a schematic cross-sectional view of a conventional piezoelectric element. [Modes for carrying out the invention]

[0032] Embodiments of the piezoelectric element and the MEMS device using the piezoelectric element according to the present invention will be described below with reference to the attached drawings. However, the present invention is not limited to the embodiments described below.

[0033] (Embodiment 1) Figure 1 is a schematic cross-sectional view of the piezoelectric element according to this embodiment. As shown in this figure, the piezoelectric element 1 according to this embodiment is directly provided on the surface of the substrate 100 and consists of a second electrode 30 (lower electrode), a piezoelectric layer 10 directly provided on the upper surface of the second electrode 30, and a first electrode 20 (upper electrode) directly provided on the piezoelectric layer 10. In other words, unlike the conventional piezoelectric element described above, the piezoelectric element 1 does not have a buffer layer. Note that the terms "first" and "second" used for the electrodes are for ease of explanation and may be used interchangeably, and do not particularly limit the positional relationship.

[0034] The piezoelectric layer 10 is not particularly limited as long as it contains at least one piezoelectric material layer having piezoelectric properties and a wurtzite crystal structure. That is, the piezoelectric layer 10 may consist of one or more piezoelectric material layers having a wurtzite crystal structure, or it may consist of one or more piezoelectric material layers having a wurtzite crystal structure and one or more other piezoelectric material layers.

[0035] Furthermore, the material constituting the piezoelectric material layer used in this piezoelectric layer 10 is not particularly limited as long as it has piezoelectric properties and a wurtzite crystal structure. Examples of materials constituting the piezoelectric material layer used in the piezoelectric layer 10 include AlN, GaN, InN, AlGaN, ScAlN, ScGaN, ScAlGaN, YAlN, YbAlN, YbGaN, YbAlGaN, BAlN, BGaN, BAlGaN, ZnO, LiZnO and CeMnZnO, as well as nitride materials described in the specification of Japanese Patent Application No. 2020-212574, nitride materials described in the specification of Japanese Patent Application No. 2021-027147, and Japanese Patent Application No. 2021-501 Examples include the nitride material described in the specification of Patent No. 655, the nitride material described in the specification of Japanese Patent Application No. 2023-188952, the nitride material described in the specification of Japanese Patent Application No. 2020-168462, the nitride material described in the specification of Japanese Patent Application No. 2020-168463, the nitride material described in the specification of Japanese Patent Application No. 2018-231681, and the nitride material described in the specification of Japanese Patent Application No. 2019-020273. The thickness of the piezoelectric layer 10 is not particularly limited.

[0036] Next, the first electrode 20 and the second electrode 30 will be described. The first electrode 20 has a wurtzite-type crystal structure and an electrical resistivity of 1.0 × 10⁻⁶. -3 The resistivity of the first nitride material is not particularly limited, as long as it is a nitride material with a resistivity of Ω·cm or less (first nitride material, first electrode material). -6 Ω cm or more, 1.0×10 -3Preferably less than Ω·cm, and 1.47 × 10 -6 Ω cm or more, 1.47×10 -4 A value of Ω·cm or less is preferable.

[0037] For example, the first nitride material is chemical formula A1 α1 B1 β1 Al 1-α1-β1 N or chemical formula A1 α1 B1 β1 Ga 1-α1-β1 Represented by N, α1 and β1 satisfy the following equation (1), and B1 may include monovalent forms. 0 < α1 / β1 < 6·····(1) Furthermore, it is more preferable that monovalent B1 is present in the largest amount compared to B1 with other valencies. In addition, α1 and β1 that satisfy the following equations (3) and (4) are more preferable because they result in less structural mismatch with the piezoelectric layer 10. 1 ≤ α1 / β1 ≤ 5·····(3) 0 < α1 + β1 ≤ 0.3 ···(4) Furthermore, A1 is at least one of magnesium (Mg), zinc (Zn), and nickel (Ni), and may be any one of Mg, Zn, or Ni, or multiple elements of Mg, Zn, and Ni. Similarly, B1 is at least one of gold (Au), silver (Ag), and copper (Cu), and may be any one of Au, Ag, or Cu, or multiple elements of Au, Ag, and Cu. Moreover, if A1 and B1 consist of multiple elements, the ratio of those elements is not particularly limited.

[0038] Here, one method generally known for improving the conductivity of a material is to add (dope) an element with a lower valence than a predetermined element that makes up the material. The valences of aluminum and gallium in the first nitride material are 3 (Al 3+ , Ga 3+ Since it is a divalent element (Mg 2+ Ca 2+ ,Sr 2+ Ba 2+ Zn 2+ ,Ni 2+,Pt 2+ ,Cd 2+ ,Mn 2+ ,Ru 2+ ,Ir 2+ ) and monovalent elements (Li + Na + ,K + ,Au + Ag + ,Cu + According to band theory, when these elements are added (doped), they act as acceptors, forming an acceptor level just above the valence band. As a result, carriers can move, improving conductivity (decreasing electrical resistivity).

[0039] Therefore, as will be explained later, Mg α1 Au β1 Al 1-α1-β1 N, Zn α1 Ag β1 Al 1-α1-β1 N, Mg α1 Au β1 Ga 1-α1-β1 N, Mg α1 Cu β1 Ga 1-α1-β1 N, Mg α1 Ag β1 Al 1-α1-β1 N, Mg α1 Cu β1 Al 1-α1-β1 N and Ni α1 Cu β1 Al 1-α1-β1 The electrical resistivity of the first nitride material composed of N is 1.0 × 10 -3 If it is less than Ω·cm, then the above chemical formula A1 α1 B1 β1 Al 1-α1-β1 N or chemical formula A1 α1 B1 β1 Ga 1-α1-β1 In N, the electrical resistivity of the first nitride material composed of a combination of other elements is 1.0 × 10⁻⁶. -3 It can be estimated that the value will be less than Ω·cm.

[0040] Furthermore, if the Young's modulus of the first electrode 20 is equal to or greater than that of the piezoelectric layer 10, the electromechanical coupling coefficient K of the piezoelectric element 1 is determined. eff 2 This is preferable because it increases the performance. Furthermore, when the piezoelectric layer 10 is composed of aluminum scandium nitride, it is more preferable that the Young's modulus of the first electrode 20 is equal to or greater than the Young's modulus of the piezoelectric layer 10, and in the range of 50 GPa or more and 500 GPa or less, and particularly preferable that it is equal to or greater than the Young's modulus of the piezoelectric layer 10, and in the range of 200 GPa or more and 450 GPa or less. The thickness t1 of the first electrode 20 is not particularly limited.

[0041] The second electrode 30 has a wurtzite-type crystal structure and an electrical resistivity of 10 -3 The resistivity of the nitride material (second nitride material, second electrode material) is not particularly limited as long as it is Ω·cm or less. -6 Ω cm or more, 1.0×10 -3 Preferably less than Ω·cm, and 1.47 × 10 -6 Ω cm or more, 1.47×10 -4 A value of Ω·cm or less is preferable.

[0042] As for the second nitride material, similar to the first nitride material, for example, chemical formula A1' α1’ B1' β1’ Al 1-α1’-β1’ N or chemical formula A1' α1’ B1' β1’ Ga 1-α1’-β1’ Represented by N, α1' and β1' satisfy the following equation (6), and B1' includes monovalent forms. 0 < α1' / β1' < 6 ·····(6)

[0043] Furthermore, it is more preferable that monovalent B1' is present in the largest amount compared to B1' with other valencies. Also, α1' and β1' that satisfy the following equations (7) and (8) are more preferable because they result in less structural mismatch with the piezoelectric layer 10. 1 ≤ α1’ / β1’ ≤ 5 ····· (7) 0 < α1’ + β1’ ≤ 0.3 ··· (8)

[0044] Here, A1’ is at least one of magnesium (Mg), zinc (Zn), and nickel (Ni), and it may be any one of Mg, Zn, and Ni, or a plurality of elements among Mg, Zn, and Ni. Also, B1’ is at least one of gold (Au), silver (Ag), and copper (Cu), and it may be any one of Au, Ag, and Cu, or a plurality of elements among Au, Ag, and Cu. When A1’ and B1’ are a plurality of elements, the ratio of these elements is not particularly limited.

[0045] Here, similar to the first electrode 20, Mg α1’ Au β1’ Al 1-α1’-β1’ N, Zn α1’ Ag β1’ Al 1-α1’-β1’ N, Mg α1’ Au β1’ Ga 1-α1’-β1’ N, Mg α1’ Cu β1’ Ga 1-α1’-β1’ N, Mg α1’ Ag β1’ Al 1-α1’-β1’ N, Mg α1’ Cu β1’ Al 1-α1’-β1’ N and Ni α1’ Cu β1’ Al 1-α1’-β1’ If the resistivity of the second nitride material composed of N is 1.0 × 10 -3 Ω·cm or less, for the above-mentioned chemical formula A1’ α1’ B1’ β1’ Al 1-α1’-β1’ N or the chemical formula A1’ α1’ B1’ β1’ Ga 1-α1’-β1’ N, it can be estimated that the resistivity of the second nitride material composed of other element combinations will be 1.0 × 10 -3 Ω·cm or less.

[0046] Furthermore, similar to the first electrode 20, if the Young's modulus of the second electrode 30 is equal to or greater than that of the piezoelectric layer 10, the electromechanical coupling coefficient K eff 2 This is preferable because it increases the value. The thickness t2 of the second electrode 30 is not particularly limited.

[0047] Here, the first nitride material and the second nitride material may be composed of the same nitride material or of different nitride materials. Furthermore, the first nitride material and the second nitride material may be composed of the same nitride material and have the same thickness (t1=t2).

[0048] Furthermore, in the piezoelectric element 1 that satisfies equations (1), (3), (4), and (6) to (8) above, the second electrode 30 has even higher crystallinity (crystallinity of a wurtzite crystal structure), which further improves the crystallinity (crystallinity of a wurtzite crystal structure) of the piezoelectric layer 10 provided (formed) on the second electrode 30. In addition, because the piezoelectric layer 10 has even higher crystallinity (crystallinity of a wurtzite crystal structure), the crystallinity (crystallinity of a wurtzite crystal structure) of the first electrode 20 provided (formed) on the piezoelectric layer 10 can also be further improved. As a result, a piezoelectric element with such a structure does not have a buffer layer, has sufficient piezoelectric properties and high stability, and can be made smaller compared to conventional piezoelectric elements.

[0049] Furthermore, the piezoelectric element according to the present invention, including this embodiment, can be manufactured by known manufacturing methods.

[0050] As described above, by constructing the piezoelectric element 1, the crystallinity (crystallinity of the wurtzite crystal) of the piezoelectric layer 10 provided (formed) on the electrode can be improved by fabricating the electrode (first electrode 20 or second electrode 30) using a nitride material having a wurtzite crystal structure. Furthermore, since the piezoelectric layer 10 is a wurtzite crystal, the crystallinity (crystallinity of the wurtzite crystal structure) of the second electrode 30 or first electrode 20 provided (formed) on the piezoelectric layer 10 can also be improved. As a result, it is possible to provide a piezoelectric element that does not have a buffer layer, has sufficient piezoelectric properties and stability, and can be made smaller compared to conventional piezoelectric elements.

[0051] <Examples of electrodes> Using the following apparatus and sputtering target, a 0.05 μm to 2 μm thick nitride material thin film (Mg) containing magnesium, zinc, or nickel (A1=Mg, Zn, or Ni) and gold, silver, or copper (B1=Au, Ag, or Cu) is sputtered onto an n-type silicon substrate with a resistivity (electrical resistivity) of 0.02 Ωcm. α1 Au β1 Al 1-α1-β1 N, Zn α1 Ag β1 Al 1-α1-β1 N, Mg α1 Au β1 Ga 1-α1-β1 N, Mg α1 Cu β1 Ga 1-α1-β1 N, Mg α1 Ag β1 Al 1-α1-β1 N, Mg α1 Cu β1 Al 1-α1-β1 N and Ni α1 Cu β1 Al 1-α1-β1 N) was created. Multi-channel simultaneous sputtering deposition system (manufactured by Kenix Corporation) Magnesium sputtering target material (purity: 99.99%) Zinc sputtering target material (purity: 99.9%) Nickel sputtering target material (purity: 99.9%) Gold sputtering target material (purity: 99.9%) Silver sputtering target material (purity: 99.9%) Copper sputtering target material (purity: 99.9%) Aluminum sputtering target material (purity: 99.999%) Gallium nitride sputtering target material (purity: 99.99%) Gas: A mixed gas of nitrogen (purity: 99.99995% or higher) and argon gas (purity: 99.9999% or higher) (mixing ratio (nitrogen:argon) 30:70) Substrate heating temperature: 500℃

[0052] The film deposition experiment involved setting the air pressure inside the sputtering chamber to 10 -5 The procedure was performed after evacuating the area with a vacuum pump to achieve a high vacuum of less than Pa. In addition, to avoid contamination with impurities such as oxygen, the target surface was cleaned immediately after mounting the target and immediately before each film deposition experiment.

[0053] The composition of each obtained nitride material thin film is shown in Figure 2, and the X-ray diffraction (XRD) measurement results for Examples 1-5, 1-7, and 1-8 are shown in Figure 3. As can be seen from this figure, each obtained aluminum nitride thin film was found to have a wurtzite-type crystal structure.

[0054] Next, Figure 4 shows the results of measuring the valencies of Mg and Au in Examples 1-5 and 1-8 using an X-ray photoelectron spectroscopy (XPS) apparatus. 0.050 Au 0.037 Al 0.913 N (top row), Mg 0.073 Au 0.036 Al 0.891 N (second from the top), Mg 0.101 Au 0.033 Al 0.866 N (third from the top) and Mg 0.388 Au 0.081 Al 0.531 Figure 5 shows the results of measuring the valence of Mg for N (bottom row) using an X-ray diffraction (XRD) device.0.050 Au 0.037 Al 0.913 Figure 6 shows the results of measuring the valence of Au in N. The peaks shown in these figures represent the binding energy of each element. From Figures 4 and 5, it was found that the binding energy of Mg2p is the same as that of Mg with a valence of 2 (+2). Similarly, from Figures 4 and 6, it was found that the binding energy of Au4f is the same as that of Au with a valence of 1 (+1). Therefore, the thin films of Examples 1-5 and 1-8, as well as Mg 0.050 Au 0.037 Al 0.913 N and Mg 0.101 Au 0.033 Al 0.866 The valence of Mg contained in N is 2 (+2), and the thin films of Examples 1-5 and 1-8, as well as Mg 0.050 Au 0.037 Al 0.913 Au with a valence (valence) of N is 1 (+1) and Au is 0 (Au 0 It was found that it contains more than ).

[0055] Furthermore, the electrical resistivity of the thin films of Examples 1-5, 1-7, 1-8, and 1-13 to 1-27 was measured using a resistivity / Hall measurement system (Resist Test 8300: manufactured by Toyo Technica Co., Ltd.). The results are shown in Figure 7. As can be seen from this figure, the electrical resistivity of the obtained nitride thin films was 7.8 × 10⁻⁶. -4 The resistivity is less than or equal to Ω·cm, and with the exception of Examples 1-25 and 1-26, the electrical resistivity of the obtained nitride thin films is 1.47 × 10⁻⁶. -4 It was found to be less than Ω·cm.

[0056] <Crystallization of semiconductor devices> As shown in Figure 8, the silicon substrate contains Zn, which corresponds to the second electrode. 0.03 Ag 0.02 Al 0.95 A N thin film was fabricated, and an AlN thin film corresponding to the piezoelectric layer was formed on it. Then, using an X-ray diffractometer (manufactured by Rigaku Corporation), Zn 0.03 Ag 0.02Al 0.95 The full width at half maximum (FWHM) of the rocking curves of the (002) crystal plane of N thin films and AlN thin films was measured. The results are shown in Figure 9.

[0057] As can be seen from this figure, the full width at half maximum of the rocking curve of the AlN thin film corresponding to the piezoelectric layer was found to be sufficiently small. In other words, it was found that a piezoelectric layer with high wurtzite crystallinity can be formed even without a buffer layer.

[0058] Next, aluminum nitride thin film (Mg α1 Au β1 Al 1-α1-β1 Figure 10 shows the maximum measurement results of the diffraction intensity of the crystal plane (002) measured by an X-ray diffractometer (XRD) when the molar ratio (α1 / β1) of Mg and Au in N) is varied. As can be seen from this figure, it was found that in the range of 0 < α1 / β1 < 6, the aluminum nitride thin film has a wurtzite crystal structure, and in the range of 1 ≤ α / β ≤ 5, it has a wurtzite crystal structure with higher crystallinity.

[0059] Furthermore, in the range of 1 ≤ α1 / β1 ≤ 5, the aluminum nitride thin film (Mg 2+ α1 Au 1+ β1 Al 1-α1-β1 N) was fabricated. Figure 11 shows the measurement results of the maximum diffraction intensity of the crystal plane (002) of each aluminum nitride thin film, as measured by an X-ray diffractometer (XRD).

[0060] This figure shows that aluminum nitride thin films in the range 0 < α1 + β1 < 0.3 have a highly crystalline wurtzite-type crystal structure. Although difficult to see in this figure, the maximum diffraction intensity of the crystal plane (002) of the aluminum nitride thin film at α1 + β1 = 0.3 is greater than that of the film at α1 + β1 = 0.4.

[0061] (Embodiment 2) In Embodiment 1, aluminum nitride (AlN) and gallium nitride (GaN) doped with both elements were used as the first and second electrode materials, but the present invention is not limited thereto. For example, aluminum nitride doped with only one element or gallium nitride doped with only one element may be used as the first and second electrode materials.

[0062] Specifically, as the first electrode material, for example, chemical formula B2 β2 Al 1-β2 N or chemical formula B2 β2 Ga 1-β2 Represented by N, β2 satisfies equation (2) below, and B2 includes monovalent forms. 0 < β2 < 0.52 ·····(2) Furthermore, a range of 0 < β2 < 0.2 for β2 is more preferable.

[0063] Furthermore, a compound in which monovalent B2 is present in the largest quantity compared to B2 with other valencies is more preferable.

[0064] Note that B2 is at least one of gold (Au), silver (Ag), and copper (Cu), and may be any one of Au, Ag, or Cu, or multiple elements of Au, Ag, and Cu. Furthermore, if B2 consists of multiple elements, the ratio of those elements is not particularly limited.

[0065] Furthermore, as the second electrode material, for example, similar to the first electrode material, a material with chemical formula B2' β2’ Al 1-β2’ N or chemical formula B2' β2’ Ga 1-β2’ Represented by N, β2' satisfies equation (9) below, and B2' includes monovalent forms. 0 < β2' < 0.52 ·····(9) Furthermore, a range of 0 < β2' < 0.2 is more preferable for β2'.

[0066] Furthermore, it is more preferable that the monovalent B2' is present in the largest quantity compared to B2' with other valencies.

[0067] Note that B2' is at least one of gold (Au), silver (Ag), and copper (Cu), and may be any one of Au, Ag, or Cu, or multiple elements of Au, Ag, and Cu. Furthermore, if B2' is multiple elements, the ratio of those elements is not particularly limited. The same effects as in Embodiment 1 can be obtained by constructing a piezoelectric element using such electrode materials.

[0068] <Examples of electrodes> Using the following apparatus and sputtering targets, nitride thin films with a thickness of 0.05 μm to 2 μm, containing gold or copper (B2=Au, Cu), were fabricated on an n-type silicon substrate with a resistivity (electrical resistivity) of 0.02 Ωcm. Multi-channel simultaneous sputtering deposition system (manufactured by Kenix Corporation) Gold sputtering target material (purity: 99.9%) Copper sputtering target material (purity: 99.9%) Aluminum sputtering target material (purity: 99.999%) Gallium nitride sputtering target material (purity: 99.99%) Gas: A mixed gas of nitrogen (purity: 99.99995% or higher) and argon gas (purity: 99.9999% or higher) (mixing ratio (nitrogen:argon) 30:70) Substrate heating temperature: 500℃

[0069] The film deposition experiment involved setting the air pressure inside the sputtering chamber to 10 -5 The procedure was performed after evacuating the area with a vacuum pump to achieve a high vacuum of less than Pa. In addition, to avoid contamination with impurities such as oxygen, the target surface was cleaned immediately after mounting the target and immediately before each film deposition experiment.

[0070] The composition of each obtained nitride material thin film is shown in Figure 12, and the X-ray diffraction (XRD) measurement results for Examples 2-1 to 2-3 are shown in Figure 13. As can be seen from this figure, it was found that each of the obtained aluminum nitride thin films in Examples 2-1 to 2-3 has a wurtzite-type crystal structure.

[0071] Next, Au 0.02 Al 0.98 Figure 14 shows the results of measuring the valence of Au for N using an X-ray photoelectron spectroscopy (XPS) instrument. The peaks shown in this figure represent the binding energy of each element. It was found that the binding energy of Au4f is the same as that of Au with a valence of 1 (+1). Therefore, Au 0.02 Al 0.98 In the N thin film, Au with a valence of 1 (+1) is 0 valence Au(Au 0 It was found that it contains more than ).

[0072] Furthermore, using a resistivity / Hall measurement system (manufactured by Toyo Technica Co., Ltd.), Example 2-4 (Au 0.10 Al 0.90 The electrical resistivity of N) was measured and found to be 5.48 × 10⁻⁶. -4 It was Ω·cm.

[0073] Furthermore, the electrical resistivity of Examples 2-5 to 2-11 was measured using a resistivity measuring device (Resist Test 8300: manufactured by Toyo Technica Co., Ltd.). The results are shown in Figure 15. From this figure, the electrical resistivity of Examples 2-5 to 2-11 is 1.0 × 10⁻⁶. -3 It was found to be smaller than Ω·cm.

[0074] Next, aluminum nitride thin film (Au β2 Al 1-β2 Figure 16 shows the maximum diffraction intensity of the crystal plane (002) measured by an X-ray diffractometer (XRD) when the Au concentration in N) was varied. As can be seen from this figure, it was found that the aluminum nitride thin film has a wurtzite-type crystal structure when 0 < β2 < 0.2.

[0075] (Embodiment 3) In Embodiments 1 and 2, the first electrode and the second electrode were constructed using the nitride material described above, but the present invention is not limited thereto. For example, either the first electrode or the second electrode may be constructed from a known electrode material. The electrode material is not particularly limited and examples include Pt.

[0076] (Other embodiments) In Embodiment 1, the thickness of the piezoelectric element was not limited, but the thickness of the piezoelectric element may be limited. Specifically, the piezoelectric element may be configured such that the thickness t1 of the first electrode, the thickness t2 of the second electrode, and the thickness d of the piezoelectric element satisfy the following equation (5). 0.025≦(t1+t2) / d≦0.2 (5) The piezoelectric element configured in this way has a high electromechanical coupling coefficient K eff 2 It will possess.

[0077] Needless to say, piezoelectric elements can be fabricated using the first and second electrodes described above. Furthermore, it goes without saying that MEMS devices can be fabricated using these piezoelectric elements. [Explanation of Symbols]

[0078] 1, 200A, 200B piezoelectric element 10,210 piezoelectric layer 20, 220 1st electrode 30, 230 2nd electrode 100, 300 circuit boards 250 buffer layers

Claims

1. A piezoelectric layer comprising at least one piezoelectric material layer having a wurtzite-type crystal structure, A first electrode provided on one side of the piezoelectric layer, A piezoelectric element comprising: a second electrode provided on the other side of the piezoelectric layer, At least one of the first electrode and the second electrode has a wurtzite-type crystal structure and an electrical resistivity of 1.0 × 10⁻⁶ －３ Made of nitride material with an Ω·cm or less, A piezoelectric element characterized by the following features.

2. The first electrode material and the second electrode material have a wurtzite-type crystal structure and an electrical resistivity of 1.0 × 10⁻⁶ －３ The piezoelectric element according to claim 1, characterized in that it is made of the nitride material with an Ω·cm or less.

3. The nitride material is Chemical formula A1 α１ B1 β１ Al １－α１－β１ N or chemical formula A1 α１ B1 β１ Ga １－α１－β１ Represented by N, α1 and β1 satisfy the following equation (1): or Chemical formula B2 β２ Al １－β２ N or chemical formula B2 β２ Ga １－β２ represented by N, and β2 satisfies the following formula (2): The piezoelectric element according to claim 1 or 2, characterized in that B1 and B2 include monovalent elements. ０＜α１／β１＜６・・・・・（１） ０＜β２＜０．５２・・・・・（２） (0 < α1 < 1, 0 < β1 < 1, A1 is at least one of Mg, Zn, and Ni, and B1 and B2 are at least one of Au, Ag, and Cu.)

4. Monovalent B1 is present in the largest quantity compared to B1 with other valencies, or monovalent B2 is present in the largest quantity compared to B2 with other valencies. The piezoelectric element according to feature 3.

5. α1 and β1 satisfy equations (3) and (4) below, The piezoelectric element according to feature 3. １≦α１／β１≦５・・・・・（３） ０＜α１＋β１≦０．３・・・（４）

6. The piezoelectric element according to claim 1, characterized in that the Young's moduli of the first electrode and the second electrode are equal to or greater than the Young's moduli of the piezoelectric layer.

7. The thickness t1 of the first electrode, the thickness d of the piezoelectric element, and the thickness t2 of the second electrode satisfy the following equation (5): The piezoelectric element according to feature 1. 0.025≦(t1+t2) / d≦0.2 (5)

8. The piezoelectric element according to claim 1, characterized in that the first electrode or the second electrode is provided on the surface of a substrate.

9. A MEMS device using the piezoelectric element described in claim 1.

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