Piezoelectric element and MEMS device using same

Abstract

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 compared to conventional piezoelectric elements; and a MEMS device which uses the piezoelectric element. This piezoelectric element is provided with: a piezoelectric layer (10) comprising a nitride material having a wurtzite crystal structure; a first electrode (20) provided on one surface of the piezoelectric layer; a second electrode (30) provided on the other surface of the piezoelectric layer; the first electrode has a wurtzite-type crystal structure and is made of a first nitride material having a resistivity of 1.0 * 10 <-3 > [Omega] cm or less. The second electrode has a wurtzite-type crystal structure and is made of a second nitride material having a resistivity of 1.0 * 10 <-3 > [Omega] cm or less.

Description

Technical Field

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

[0002] Devices utilizing piezoelectricity 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 in high demand. One example is the FBAR filter, which uses a film bulk acoustic resonator (FBAR).

[0003] FBAR filters are filters composed of resonators that utilize the thickness-longitudinal vibration modes of a thin film exhibiting piezoelectric response. These FBAR filters are capable of resonating in the gigahertz frequency band. FBAR filters with this characteristic have low loss and can operate over a wide bandwidth, thus promising to contribute to further advancements in portable devices in terms of higher frequency, miniaturization, and power saving.

[0004] like Figure 17 as well as Figure 18 As shown, conventional piezoelectric elements used in FBARs, particularly piezoelectric elements 200A and 200B whose piezoelectric layer is made of a wurtzite-type crystal material, are constructed by sequentially stacking a lower electrode 230, a piezoelectric layer 210, and an upper electrode 220 from bottom to top on a buffer layer 250 disposed on a substrate 300 (see Non-Patent Document 1), or by sequentially stacking a lower electrode 230, a buffer layer 250, a piezoelectric layer 210, and an upper electrode 220 from bottom to top on a substrate 300.

[0005] Existing technical documents Non-patent literature Non-patent literature 1: Moreira et al, Vacuum, 86(2011)23 Summary of the Invention The problem that the invention aims to solve The reason for setting a buffer layer in the existing piezoelectric element is that by setting a buffer layer, the crystallinity of the piezoelectric layer set on the buffer layer can be improved, thus forming a stable piezoelectric layer.

[0006] However, by adding a buffer layer, the thickness of the piezoelectric element increases, which makes it impossible to miniaturize the piezoelectric element.

[0007] Furthermore, the need to form a buffer layer complicates the manufacturing process of piezoelectric elements, reduces productivity, and increases production costs.

[0008] In view of the above, the present invention aims to improve the crystallinity (crystallization of wurtzite crystal structure) of the piezoelectric layer disposed (formed) on the upper or lower electrode by using an electrode material with conductivity and a wurtzite crystal structure to fabricate the upper or lower electrode, thereby providing a piezoelectric element that does not have a buffer layer and has sufficient piezoelectric characteristics and stability, and further, a piezoelectric element that can be miniaturized compared with existing piezoelectric elements, as well as a MEMS device using the piezoelectric element.

[0009] Methods for solving problems The inventors of this invention continued to conduct in-depth research on the above-mentioned problems, and as a result, discovered the following epoch-making piezoelectric element and MEMS devices using the piezoelectric element.

[0010] A first aspect of the present invention for solving the above-mentioned problems comprises a piezoelectric element, including: a piezoelectric body layer comprising at least one layer of piezoelectric material having a wurtzite crystal structure; a first electrode disposed on one surface of the piezoelectric body layer; and a second electrode disposed on the other surface of the piezoelectric body layer; characterized in that at least one of the first electrode and the second electrode has a wurtzite crystal structure and is composed of a material with a resistivity of 1.0 × 10⁻⁶. -3 It consists of nitride materials with a Ω·cm or lower.

[0011] According to this first method, by using a conductive nitride material with a wurtzite-type crystal structure to fabricate the first or second electrode, the crystallinity (crystallization of the wurtzite-type crystal structure) of the piezoelectric layer disposed (formed) on the first or second electrode can be improved. As a result, a piezoelectric element without a buffer layer can be provided, exhibiting sufficient piezoelectric properties and stability, and further, it can be miniaturized compared to existing piezoelectric elements.

[0012] The second aspect of the present invention is that, according to the piezoelectric element of the first aspect, the first electrode material and the second electrode material have a wurtzite crystal structure and are composed of a resistivity of 1.0 × 10⁻⁶. -3 It consists of nitride materials with a Ω·cm or lower.

[0013] According to this second method, since the piezoelectric layer is a wurtzite-type crystal, the crystallinity (crystallization of the wurtzite-type crystal structure) of the second electrode or the first electrode disposed (formed) on the piezoelectric layer can also be improved. As a result, a piezoelectric element with higher piezoelectric characteristics and stability can be provided.

[0014] The third aspect of the present invention is that, according to the piezoelectric element of the first aspect, the nitride material is in the form of chemical formula A1. α1 B1 β1 Al1-α1-β1 N or chemical formula Al α1 B1 β1 Ga 1-α1-β1 N represents, and α1 and β1 satisfy the following equation (1); or, the nitride material is represented by the chemical formula B2. β2 Al 1-β2 N or chemical formula B2 β2 Ga 1-β2 N represents , and β2 satisfies the following equation (2); B1 and B2 contain substances with a monovalent valence; 0 < α1 / β1 < 6……(1); 0 < β² < 0.5²……(2); Wherein, 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.

[0015] According to this third method, by using a nitride material with higher conductivity and a wurtzite-type crystal structure to fabricate the first or second electrode, the crystallinity (crystallinity of the wurtzite-type crystal structure) of the piezoelectric layer disposed (formed) on the first or second electrode can be improved. Furthermore, since the piezoelectric layer has higher crystallinity (crystallinity of the wurtzite-type crystal structure), the crystallinity (crystallinity of the wurtzite-type crystal structure) of the second or first electrode disposed (formed) on the piezoelectric layer can also be further improved. As a result, a piezoelectric element that does not require a buffer layer, possesses sufficient piezoelectric characteristics and stability, and can be further miniaturized compared to existing piezoelectric elements can be provided.

[0016] The fourth aspect of the present invention is that, according to the third aspect, the piezoelectric element is characterized in that, compared with B1 in valence states other than valence 1, the content of B1 in valence 1 is the highest; or, compared with B2 in valence states other than valence 1, the content of B2 in valence 1 is the highest.

[0017] According to this fourth method, by using a nitride material with further high conductivity and a wurtzite-type crystal structure to fabricate the first or second electrode, the crystallinity (crystallinity of the wurtzite-type crystal structure) of the piezoelectric layer disposed (formed) on the first or second electrode can be improved. Furthermore, since the piezoelectric layer has higher crystallinity (crystallinity of the wurtzite-type crystal structure), the crystallinity (crystallinity of the wurtzite-type crystal structure) of the second or first electrode disposed (formed) on the piezoelectric layer can also be further improved. As a result, a piezoelectric element that does not require a buffer layer, possesses sufficient piezoelectric characteristics and stability, and can be further miniaturized compared to existing piezoelectric elements can be provided.

[0018] The fifth aspect of the present invention is that, according to claim 3, the piezoelectric element is characterized in that α1 and β1 satisfy the following equations (3) and (4); 1≤α1 / β1≤5……(3); 0<α1+β1≤0.3……(4).

[0019] According to this fifth method, by using a nitride material with higher conductivity and a wurtzite-type crystal structure to fabricate the first or second electrode, the crystallinity (crystallinity of the wurtzite-type crystal structure) of the piezoelectric layer disposed (formed) on the first or second electrode can be improved. Furthermore, since the piezoelectric layer has higher crystallinity (crystallinity of the wurtzite-type crystal structure), the crystallinity (crystallinity of the wurtzite-type crystal structure) of the second or first electrode disposed (formed) on the piezoelectric layer can also be further improved. As a result, a piezoelectric element that does not require a buffer layer, possesses sufficient piezoelectric characteristics and stability, and can be further miniaturized compared to existing piezoelectric elements can be provided.

[0020] The sixth aspect of the present invention is that, according to the piezoelectric element of the first aspect, the Young's modulus of the first electrode and the second electrode is equal to or greater than the Young's modulus of the piezoelectric layer.

[0021] According to this sixth method, it is possible to provide a high electromechanical coupling coefficient K. eff 2 Piezoelectric elements with an effective electromechanical coupling coefficient.

[0022] The seventh aspect of the present invention is that, according to the piezoelectric element of the first aspect, 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).

[0023] According to this seventh method, it is possible to provide a higher K eff 2 Piezoelectric elements.

[0024] The eighth aspect of the present invention is that, according to any one of the first to seventh aspects, the piezoelectric element is characterized in that a first electrode or a second electrode is disposed on the surface of a substrate.

[0025] According to this eighth method, it is possible to easily manufacture a piezoelectric element that does not have a buffer layer and has sufficient piezoelectric properties and stability. Furthermore, compared with existing piezoelectric elements, it is possible to further miniaturize the piezoelectric element.

[0026] The ninth aspect of the present invention is a MEMS device that uses the piezoelectric element described in the first aspect.

[0027] Here, the term "MEMS device" can refer to any microelectromechanical system without any particular limitation. Examples include: high-frequency filters, pressure sensors, accelerometers, gyroscopes and other physical sensors or actuators, microphones, fingerprint authentication sensors, vibration generators, transistors, inverters, transducers, SAW devices, ferroelectric memories, diodes or batteries, etc.

[0028] According to this ninth approach, smaller MEMS devices can be provided.

[0029] It should be noted that the description of Japanese invention patent application 2024-31861 is incorporated herein by reference. Attached Figure Description

[0030] Figure 1 This is a schematic cross-sectional view of the piezoelectric element according to Embodiment 1.

[0031] Figure 2 This is a table showing the components of the embodiments.

[0032] Figure 3 These are graphs showing the X-ray diffraction (XRD) measurement results of Examples 5, 7, and 8.

[0033] Figure 4 This is a graph showing the results of determining the atomic valence of Mg and Au in Examples 1-5 and Examples 1-8.

[0034] Figure 5 This indicates the determination of Mg 0.050 Au 0.037 Al 0.913 N (top section), Mg 0.073 Au 0.036 Al 0.891 N (second paragraph from the top), Mg 0.101 Au 0.033 Al 0.866 N (3rd paragraph from the top) and Mg 0.388 Au 0.081 Al 0.531 A graph showing the atomic valence of N in Mg.

[0035] Figure 6 This indicates the determination of Mg 0.050 Au 0.037 Al 0.913 A graph showing the atomic valence of Au in N.

[0036] Figure 7This is a table showing the resistivity of the thin films of Examples 1-5, 1-7, 1-8, 1-13 to 1-27.

[0037] Figure 8 This is a schematic cross-sectional view of the electrode equivalent thin film and the piezoelectric equivalent thin film, which were fabricated to investigate the crystallinity of semiconductor devices.

[0038] Figure 9 It is a table showing the measurement results of the half-peak width of the rocking curve.

[0039] Figure 10 This is a graph showing the measurement results of the maximum diffraction intensity of the crystal plane (002) under varying molar ratios of Mg and Au.

[0040] Figure 11 This is a graph showing the measurement results of the maximum diffraction intensity of the (002) crystal plane under the condition of changing Mg+Au.

[0041] Figure 12 This is a table showing the components of Examples 2-1 to 2-11.

[0042] Figure 13 These are graphs showing the X-ray diffraction (XRD) measurement results of Examples 2-1 to 2-3.

[0043] Figure 14 This indicates the measurement of Au. 0.02 Al 0.98 A graph showing the atomic valence of Au in N.

[0044] Figure 15 This is a table showing the components and resistivity of Examples 2-5 to 2-11.

[0045] Figure 16 This is a graph showing the measured maximum diffraction intensity of the (002) crystal plane under varying Au concentrations.

[0046] Figure 17 This is a schematic cross-sectional view of an existing piezoelectric element.

[0047] Figure 18 This is a schematic cross-sectional view of an existing piezoelectric element. Detailed Implementation

[0048] Hereinafter, embodiments of the piezoelectric element of the present invention and MEMS devices using the piezoelectric element will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited to the following embodiments.

[0049] (Implementation Method 1) Figure 1This is a schematic cross-sectional view of the piezoelectric element of Embodiment 1. As shown in the figure, the piezoelectric element 1 of this embodiment is directly disposed on the surface of the substrate 100, and is composed of a second electrode 30 (lower electrode), a piezoelectric layer 10 directly disposed on the upper surface of the second electrode 30, and a first electrode 20 (upper electrode) directly disposed on the piezoelectric layer 10. That is, unlike the conventional piezoelectric elements described above, the piezoelectric element 1 does not have a buffer layer. It should be noted that the terms "first" and "second" used in the electrodes are for ease of explanation, and "first" can also be used as "second" and "second" as "first," rather than being terms that specifically limit positional relationships.

[0050] The piezoelectric layer 10 only needs to include at least one layer of piezoelectric material with piezoelectricity and a wurtzite crystal structure, and there is no particular limitation. That is, the piezoelectric layer 10 can be composed of one or more layers of piezoelectric material with a wurtzite crystal structure, or it can be composed of one or more layers of piezoelectric material with a wurtzite crystal structure and one or more other piezoelectric material layers.

[0051] Furthermore, the material constituting the piezoelectric material layer used in the piezoelectric layer 10 is not particularly limited as long as it is a material with piezoelectricity and a wurtzite-type 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; nitride materials described in Japanese Patent Application No. 2020-212574; nitride materials described in Japanese Patent Application No. 2021-027147; and other materials described in Japanese Patent Application No. 2021-027147. The nitride materials described in Japanese Patent Application No. 2021-501655, Japanese Patent Application No. 2023-188952, Japanese Patent Application No. 2020-168462, Japanese Patent Application No. 2020-168463, Japanese Patent Application No. 2018-231681, and Japanese Patent Application No. 2019-020273, etc. It should be noted that the thickness of the piezoelectric layer 10 is not particularly limited.

[0052] Next, the first electrode 20 and the second electrode 30 will be described. The first electrode 20 simply needs to have a wurtzite-type crystal structure and a resistivity of 1.0 × 10⁻⁶. -3There are no particular limitations on nitride materials (first nitride material, first electrode material) with resistivity below Ω·cm. It should be noted that the resistivity of the first nitride material is preferably 1.47 × 10⁻⁶. -6 Ω·cm or more, 1.0×10 -3 Below Ω·cm, more preferably 1.47×10 -6 Ω·cm or higher, 1.47×10 -4 Below Ω·cm.

[0053] As a first nitride material, examples include: those with the chemical formula Al α1 B1 β1 Al 1-α1-β1 N or chemical formula Al α1 B1 β 1Ga 1-α1-β1 N represents that α1 and β1 satisfy the following equation (1), and B1 is a material containing a monovalent substance.

[0054] 0 < α1 / β1 < 6……(1) Furthermore, materials with the highest content of B1 in the monovalent state compared to B1 in valence states other than monovalent are preferred. In addition, materials whose α1 and β1 satisfy the following equations (3) and (4) have less structural mismatch with the piezoelectric layer 10, and are therefore preferred.

[0055] 1≤α1 / β1≤5……(3) 0 < α1 + β1 ≤ 0.3 ……(4) It should be noted that A1 is at least one of magnesium (Mg), zinc (Zn), and nickel (Ni), and can be any one of Mg, Zn, and Ni, or multiple elements of Mg, Zn, and Ni. Furthermore, B1 is at least one of gold (Au), silver (Ag), and copper (Cu), and can be any one of Au, Ag, and Cu, or multiple elements of Au, Ag, and Cu. Further, when A1 and B1 are multiple elements, the ratio of these elements is not particularly limited.

[0056] Here, as a common method to improve the conductivity of a material, it is known to add (dopant) elements with valences smaller than those of the specified elements constituting the material. Since the valences of aluminum and gallium in the first nitride material are 3 (Al... 3+ Ga 3+ Therefore, adding (doping) divalent elements (Mg) 2+ Ca 2+ 、Sr 2+ Ba 2+ Zn 2+ Ni 2+ Pt 2+ Cd2+ Mn 2+ Ru 2+ Ir 2+ ) or monovalent element (Li + Na + K + Au + Ag + Cu + When these elements are in the valence band, according to band theory, they act as acceptors, forming an acceptor level directly above the valence band. As a result, the carrier can move, increasing conductivity (decreasing resistivity).

[0057] Therefore, as will be discussed later, if 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 α 1Cu 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 resistivity of the first nitride material composed of N is 1.0 × 10⁻⁶. -3 Below Ω·cm, then in the above chemical formula A1 α1 B1 β1 Al 1-α1-β1 N or chemical formula Al α1 B1 β 1Ga 1-α1-β1 In N, it can be estimated that the resistivity of the first nitride material composed of combinations of other elements is 1.0 × 10⁻⁶. -3 Below Ω·cm.

[0058] Furthermore, if the Young's modulus of the first electrode 20 is equal to or greater than the Young's modulus of the piezoelectric layer 10, then the electromechanical coupling coefficient K of the piezoelectric element 1 is... eff 2The higher the value, the better. Further, when the piezoelectric layer 10 is composed of aluminum scandium nitride, more preferably, 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 falls within the range of 50 GPa or more and 500 GPa or less; particularly preferably, it is equal to or greater than the Young's modulus of the piezoelectric layer 10, and falls within the range of 200 GPa or more and 450 GPa or less. It should be noted that the thickness t1 of the first electrode 20 is not particularly limited.

[0059] The second electrode 30 must have a wurtzite crystal structure and a resistivity of 10 Ω·cm. -3 Nitride materials with resistivity below Ω·cm (second nitride material, second electrode material) are not particularly limited. It should be noted that, like the first nitride material, the resistivity of the second nitride material is preferably 1.47 × 10⁻⁶. -6 Ω·cm or more, 1.0×10 -3 Below Ω·cm, more preferably 1.47×10 -6 Ω·cm or higher, 1.47×10 -4 Below Ω·cm.

[0060] As a second nitride material, similar to the first nitride material, examples include: those with the chemical formula Al' α1' B1' β1' Al 1-α1'-β1' N or chemical formula Al' α1' B1' β1' Ga 1-α1'-β1' N represents that α1' and β1' satisfy the following equation (6), and B1' is a material containing a monovalent substance.

[0061] 0<α1' / β1'<6……(6) Furthermore, materials with the highest content of B1' in the monovalent state compared to B1' in valence states other than monovalent are preferred. In addition, materials whose α1' and β1' satisfy the following equations (7) and (8) have less structural mismatch with the piezoelectric layer 10, and are therefore preferred.

[0062] 1≤α1' / β1'≤5……(7) 0 < α1' + β1' ≤ 0.3……(8) It should be noted that A1' is at least one of magnesium (Mg), zinc (Zn), and nickel (Ni), and can be any one of Mg, Zn, and Ni, or multiple elements of Mg, Zn, and Ni. Furthermore, B1' is at least one of gold (Au), silver (Ag), and copper (Cu), and can be any one of Au, Ag, and Cu, or multiple elements of Au, Ag, and Cu. It should also be noted that when A1' and B1' are multiple elements, the ratio of these elements is not particularly limited.

[0063] Here, similarly to the first electrode 20, if it is made of 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 resistivity of the second nitride material composed of N is 1.0 × 10⁻⁶. -3 Below Ω·cm, then in the above chemical formula A1' α1' B1' β1' Al 1-α1'-β1' N or chemical formula Al' α1' B1' β1' Ga 1-α1'-β1' In N, it can be estimated that the resistivity of the second nitride material composed of combinations of other elements is 1.0 × 10⁻⁶. -3 Below Ω·cm.

[0064] Furthermore, similar to the first electrode 20, if the Young's modulus of the second electrode 30 is equal to or greater than the Young's modulus of the piezoelectric layer 10, then the electromechanical coupling coefficient K... eff 2 The thickness increases, therefore it is preferred. It should be noted that the thickness t2 of the second electrode 30 is not particularly limited.

[0065] Here, the first nitride material and the second nitride material can be composed of the same nitride material or different nitride materials. Furthermore, the first nitride material and the second nitride material can be composed of the same nitride material, and their respective thicknesses can be the same (t1=t2).

[0066] It should be noted that the piezoelectric element 1 satisfying equations (1), (3), (4), and (6) to (8) above can further improve the crystallinity (crystallization of wurtzite crystal structure) of the piezoelectric layer 10 disposed (formed) on the second electrode 30 because the second electrode 30 has higher crystallinity (crystallization of wurtzite crystal structure). Furthermore, because the piezoelectric layer 10 has higher crystallinity (crystallization of wurtzite crystal structure), it can also further improve the crystallinity (crystallization of wurtzite crystal structure) of the first electrode 20 disposed (formed) on the piezoelectric layer 10. As a result, this piezoelectric element has no buffer layer, possesses sufficient piezoelectric characteristics and high stability, and furthermore, can be miniaturized compared to existing piezoelectric elements.

[0067] It should be noted that the piezoelectric elements of the present invention, including those in this embodiment, can be manufactured using known manufacturing methods.

[0068] By constructing the piezoelectric element 1 as described above and using a nitride material with a wurtzite crystal structure to fabricate the electrodes (first electrode 20 or second electrode 30), the crystallinity (crystallinity of the wurtzite crystal) of the piezoelectric layer 10 disposed (formed) on the electrodes can be improved. Furthermore, since the piezoelectric layer 10 is a wurtzite crystal, the crystallinity (crystallinity of the wurtzite crystal structure) of the second electrode 30 or the first electrode 20 disposed (formed) on the piezoelectric layer 10 can also be improved. As a result, a piezoelectric element without a buffer layer, possessing sufficient piezoelectric characteristics and stability, can be provided, and furthermore, it can be miniaturized compared to existing piezoelectric elements.

[0069] <Electrode Examples> Using the following apparatus and sputtering target, a thin film of nitride material (Mg) with a thickness of 0.05 μm-2 μm, containing magnesium, zinc, or nickel (Al=Mg, Zn, or Ni) and gold, silver, or copper (B1=Au, Ag, or Cu), is fabricated on an n-type silicon substrate with a specific 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-β1N, 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).

[0070] Multi-element simultaneous sputtering coating system (manufactured by Kenix Corporation) Magnesium sputtering target (purity: 99.99%) Zinc sputtering target (purity: 99.9%) Nickel sputtering target (purity: 99.9%) Gold sputtering target (purity: 99.9%) Silver sputtering target (purity: 99.9%) Copper sputtering target (purity: 99.9%) Aluminum sputtering target (purity: 99.999%) Gallium nitride sputtering target (purity: 99.99%) Gas: A mixture of nitrogen (purity: ≥99.99995%) and argon (purity: ≥99.9999%) (mixing ratio: nitrogen: argon 30:70). Substrate heating temperature: 500℃ In the film formation experiment, a vacuum pump was used to exhaust gas, bringing the pressure inside the sputtering chamber to 10. -5 The experiment was conducted under a high vacuum below Pa. Furthermore, to avoid the introduction of impurities such as oxygen, the target surface was cleaned immediately after target mounting and before each film deposition experiment.

[0071] The composition of the obtained nitride material films is as follows: Figure 2 As shown, the X-ray diffraction (XRD) measurements for Examples 1-5, 1-7, and 1-8 are as follows: Figure 3 As shown in the figure, each aluminum nitride film obtained has a wurtzite-type crystal structure.

[0072] Next, regarding Examples 1-5 and Examples 1-8, the results of determining the atomic valences of Mg and Au using X-ray photoelectron spectroscopy (XPS) are as follows: Figure 4 As shown. Furthermore, X-ray diffraction (XRD) was used to analyze Mg. 0.050 Au 0.037 Al 0.913 N (top section), Mg 0.073 Au 0.036 Al0.891 N (second paragraph from the top), Mg 0.101 Au 0.033 Al 0.866 N (3rd paragraph from the top) and Mg 0.388 Au 0.081 Al 0.531 N (bottom section), the results of determining the valence of Mg are as follows Figure 5 As shown, the determination of Mg 0.050 Au 0.037 Al 0.913 The results of the atomic valence of N and Au are as follows: Figure 6 As shown in the figures, the peaks in these figures represent the binding energies of the elements. Furthermore, from... Figure 4 and Figure 5 It can be seen that the binding energy of Mg2p is consistent with that of Mg when the atomic valence is 2 (+2). Similarly, from Figure 4 and Figure 6 It can be seen that the binding energy of Au4f is consistent with that of Au with an atomic valence of 1 (+1). Therefore, it can be seen that the films of Examples 1-5 and Examples 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 in N is 2 (+2); the thin films of Examples 1-5 and 1-8, and Mg 0.050 Au 0.037 Al 0.913 The proportion of Au with a valence of 1 (+1) is equal to the proportion of Au with a valence of 0. 0 It contains a lot of ).

[0073] Furthermore, the resistivity of the thin films in Examples 1-5, 1-7, 1-8, and 1-13 to 1-27 was measured using a specific resistivity / Hall effect measurement system (Resist Test 8300: manufactured by Dongyang Technology Co., Ltd.). The results are as follows: Figure 7 As shown in the figure, the resistivity of the obtained nitride film is 7.8 × 10⁻⁶. -4 Below Ω·cm, except for Examples 1-25 and 1-26, the resistivity of the obtained nitride film is 1.47 × 10⁻⁶. -4 Below Ω·cm.

[0074] <Crystallization of Semiconductor Devices> like Figure 8 As shown, Zn, which acts as a second electrode, is fabricated on a silicon substrate. 0.03 Ag 0.02 Al 0.95A nitrogen-containing thin film was formed, on which an AlN thin film, equivalent to a piezoelectric layer, was formed. Then, the Zn content was determined using an X-ray diffractometer (Rigaku Corporation). 0.03 Ag 0.02 Al 0.95 The full width at half maximum (FWHM) of the rocking curves for the (002) crystal plane of N thin films and AlN thin films. The results are as follows: Figure 9 As shown.

[0075] As shown in the figure, the half-width at half-maximum (WHM) of the rocking curve of the AlN film, which corresponds to the piezoelectric layer, is sufficiently small. That is, it can be seen that a piezoelectric layer with high wurtzite crystallinity can be formed even without a buffer layer.

[0076] Next, aluminum nitride thin films (Mg) will be made. α1 Au β1 Al 1-α1-β1 The measurement results of the maximum diffraction intensity of the crystal plane (002) by X-ray diffraction (XRD) under the condition of varying the molar ratio (α1 / β1) of Mg to Au in N) are as follows. Figure 10 As shown in the figure, aluminum nitride films exhibit a wurtzite-type crystal structure in the range of 0 < α1 / β1 < 6, and a more crystalline wurtzite-type crystal structure in the range of 1 ≤ α / β ≤ 5.

[0077] Furthermore, aluminum nitride (Mg) thin films were fabricated in the range of 1 ≤ α1 / β1 ≤ 5, where the value of α1 + β1 varied. 2+ α 1Au 1+ β1 Al 1-α1-β1 N). Furthermore, the results of measuring the maximum diffraction intensity of each aluminum nitride thin film on the (002) crystal plane using X-ray diffraction (XRD) are as follows: Figure 11 As shown.

[0078] As shown in the figure, aluminum nitride films in the range of 0 < α1 + β1 < 0.3 exhibit a highly crystalline wurtzite-type crystal structure. Furthermore, although it is difficult to discern in the figure, the maximum diffraction intensity of the (002) crystal plane of the aluminum nitride film at α1 + β1 = 0.3 is greater than that at α1 + β1 = 0.4.

[0079] (Implementation Method 2) In Embodiment 1, aluminum nitride (AlN) and gallium nitride (GaN), both of which are doped with two elements, were used as the first and second electrode materials, but the present invention is not limited thereto. For example, aluminum nitride or gallium nitride, which are doped with only one element, can be used as the first and second electrode materials.

[0080] Specifically, as a first electrode material, examples include: chemical formula B2 β2 Al 1-β2 N or chemical formula B2 β 2Ga 1-β2 N represents that β2 satisfies the following equation (2), and B2 is a material containing a monovalent substance.

[0081] 0 < β² < 0.5² … (2) It should be noted that β2 is more preferably in the range of 0 < β2 < 0.2.

[0082] Furthermore, it is preferable to use a material with the highest content of B2 in the monovalent state compared to B2 in valence states other than monovalent.

[0083] It should be noted that B2 is at least one of gold (Au), silver (Ag), and copper (Cu), and can be any one of Au, Ag, and Cu, or multiple elements of Au, Ag, and Cu. Furthermore, when B2 is composed of multiple elements, the ratio of these elements is not particularly limited.

[0084] Furthermore, as with the first electrode material, examples of second electrode materials include, for instance, those with the chemical formula B2'. β2' Al 1-β2' N or chemical formula B2' β2' Ga 1-β2' N represents that β2' satisfies the following equation (9), and B2' is a material containing a monovalent substance.

[0085] 0<β2'<0.52……(9) It should be noted that β2' is more preferably in the range of 0 < β2' < 0.2.

[0086] Furthermore, it is preferable to use a material with the highest content of B2' with a valence other than valence 1.

[0087] It should be noted that B2' is at least one of gold (Au), silver (Ag), and copper (Cu), and can be any one of Au, Ag, and Cu, or multiple elements of Au, Ag, and Cu. Furthermore, when B2' is composed of multiple elements, the ratio of these elements is not particularly limited. Even when using this electrode material to construct a piezoelectric element, the same effect as in Embodiment 1 can be obtained.

[0088] <Electrode Examples> Using the following apparatus and sputtering target, a nitride material film with a thickness of 0.05μm-2μm containing gold or copper (B2=Au, Cu) is fabricated on an n-type silicon substrate with a specific resistance (resistivity) of 0.02Ωcm.

[0089] Multi-element simultaneous sputtering coating system (manufactured by Kenix Corporation) Gold sputtering target (purity: 99.9%) Copper sputtering target (purity: 99.9%) Aluminum sputtering target (purity: 99.999%) Gallium nitride sputtering target (purity: 99.99%) Gas: A mixture of nitrogen (purity: ≥99.99995%) and argon (purity: ≥99.9999%) (mixing ratio: nitrogen: argon 30:70). Substrate heating temperature: 500℃ In the film formation experiment, a vacuum pump was used to exhaust gas to bring the pressure inside the sputtering chamber to 10. -5 The experiment was conducted under a high vacuum below Pa. Furthermore, to avoid the introduction of impurities such as oxygen, the target surface was cleaned immediately after target mounting and before each film deposition experiment.

[0090] The composition of the obtained nitride material films is as follows: Figure 12 As shown, the X-ray diffraction (XRD) measurement results of Examples 2-1 to 2-3 are as follows: Figure 13 As shown in the figure, the aluminum nitride films obtained in Examples 2-1 to 2-3 all have a wurtzite-type crystal structure.

[0091] Next, regarding Au 0.02 Al 0.98 The results of determining the valence of Au using X-ray photoelectron spectroscopy (XPS) are as follows: Figure 14 As shown in the figure, the peaks represent the binding energies of each element. Furthermore, the binding energy of Au₄f coincides with that of Au with a valence of 1 (+1). Therefore, it can be concluded that Au… 0.02 Al 0.98 In N thin films, the content of Au with a valence of 1 (+1) is equal to that of Au with a valence of 0 (Au(Au+1)) 0 It contains a lot of ).

[0092] Furthermore, the specific resistance / Hall effect measurement system (manufactured by Dongyang Technology Co., Ltd.) was used to measure the specific resistance of Examples 2-4 (Au). 0.10 Al 0.90 The resistivity of N) is 5.48 × 10⁻⁶. -4 Ω·cm.

[0093] In addition, the resistivity of Examples 2-5 to 2-11 was measured using a resistivity meter (Resist Test 8300: manufactured by Dongyang Technology Co., Ltd.). The results are as follows: Figure 15 As shown in the figure, the resistivity of Examples 2-5 to 2-11 is less than 1.0 × 10⁻⁶.-3 Ω·cm.

[0094] Next, aluminum nitride thin films (Au) will be made... β2 Al 1-β2 The measurement results of the maximum value of the diffraction intensity of the crystal plane (002) by X-ray diffraction (XRD) under the condition of varying Au concentration in N) are as follows. Figure 16 The figure indicates that, within the range of 0 < β2 < 0.2, the aluminum nitride film exhibits a wurtzite-type crystal structure.

[0095] (Implementation Method 3) In embodiments 1 and 2, the first and second electrodes are constructed using the aforementioned nitride materials, but the present invention is not limited thereto. For example, either the first or second electrode can be constructed using known electrode materials. The electrode materials are not particularly limited; for example, Pt can be cited.

[0096] (Other implementation methods) In embodiment 1, the thickness of the piezoelectric element is not limited, but the thickness of the piezoelectric element may be limited. Specifically, the piezoelectric element may be constructed 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).

[0097] 0.025≤(t1+t2) / d≤0.2……(5) Piezoelectric elements constructed in this way have a high electromechanical coupling coefficient K. eff 2 .

[0098] It should be noted that the first and second electrodes described above can certainly be used to fabricate piezoelectric elements. Furthermore, these piezoelectric elements can certainly be used to fabricate MEMS devices.

[0099] Symbol Explanation 1. 200A, 200B: Piezoelectric elements; 10, 210: Piezoelectric layer; 20, 220: First electrode; 30, 230: Second electrode; 100, 300: substrate; 250: Buffer layer.

Claims

1. Piezoelectric element, possessing: The piezoelectric layer comprises at least one layer of piezoelectric material having a wurtzite-type crystal structure; The first electrode is disposed on one surface of the piezoelectric layer; The second electrode is disposed on the other side of the piezoelectric layer; Its features are, At least one of the first electrode and the second electrode has a wurtzite-type crystal structure and is composed of a resistivity of 1.0 × 10⁻⁶. -3 It consists of nitride materials with a Ω·cm or lower.

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

3. The piezoelectric element according to claim 1 or 2, characterized in that, The nitride material is in the form of chemical formula A1 α1 B1 β 1Al 1-α1-β1 N or chemical formula Al α1 B1 β1 Ga 1-α1-β1 N represents, and α1 and β1 satisfy the following equation (1); or, The nitride material has the chemical formula B2. β2 Al 1-β2 N or chemical formula B2 β2 Ga 1-β2 N represents , and β2 satisfies the following equation (2); B1 and B2 contain substances with a monovalent valence; 0<α1 / β1<6……(1)； 0<β2<0.52……(2)； Wherein, 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. The piezoelectric element according to claim 3, characterized in that, Compared to B1 in valence states other than monovalent, monovalent B1 has the highest content; or, Compared to B2 in valence states other than monovalent, monovalent B2 has the highest content.

5. The piezoelectric element according to claim 3, characterized in that, α1 and β1 satisfy the following equations (3) and (4); 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 modulus of the first electrode and the second electrode is equal to or greater than that of the piezoelectric layer.

7. The piezoelectric element according to claim 1, 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).

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

9. A MEMS device using the piezoelectric element of claim 1.

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