Surface acoustic wave device for suppressing stray wave excitation

Abstract

The invention discloses a surface acoustic wave device for suppressing stray wave excitation. The surface acoustic wave device includes: a support substrate; a piezoelectric layer formed on the support substrate; and an I DT electrode on the piezoelectric layer, in which a thickness of the piezoelectric layer is 2.4 lambda or less when a wavelength of a surface acoustic wave excited at the I DT electrode is lambda.

Description

Technical Field

[0001] The present invention relates to a surface acoustic wave device which combines a piezoelectric layer and a substrate to suppress the excitation of stray waves. Background Art

[0002] Surface acoustic wave (SAW) refers to a wave that propagates along the surface of an elastic solid. The surface acoustic wave propagates in the form of energy concentrated near the surface, which is equivalent to a mechanical wave. A surface acoustic wave device is an electromechanical device that uses the interaction between surface acoustic waves and conduction electrons and uses surface acoustic waves transmitted to the surface of a piezoelectric crystal. Surface acoustic wave devices can be used in a very wide range of industrial applications including sensors, oscillators, filters, etc., and can be miniaturized and lightweight, and have many advantages such as robustness, stability, sensitivity, low cost, and real-time performance.

[0003] Patent document 1 discloses a structure combining a sapphire substrate with a piezoelectric layer made of LiTaO3, and proposes a structure in which when the thickness of the piezoelectric layer is T and the thickness of the sapphire substrate is t, T / t<1 / 3, and when the wavelength of the surface wave is λ, T / λ>10. In this structure, when T / λ is not equal to or greater than 10, the stray amplitude is considered to be large.

[0004] Prior art literature

[0005] (Patent Document 1) US6933810B2 Summary of the invention

[0006] Therefore, the present invention has been made in view of the above-mentioned problems, and an object thereof is to provide a configuration for suppressing the excitation of stray waves in a surface acoustic wave device combining a piezoelectric layer and a substrate.

[0007] The technical problems of the present invention are not limited to the above-mentioned technical problems, and other unmentioned technical problems will be clearly understood by those skilled in the art from the following description.

[0008] To achieve the above objective, according to one aspect of the present invention, there is provided a surface acoustic wave device, comprising: a supporting substrate; and a piezoelectric layer formed on the supporting substrate, wherein the thickness of the piezoelectric layer is 2.4λ or less.

[0009] In some embodiments of the present invention, the support substrate may include a sapphire substrate, and the piezoelectric layer may include LiTaO3.

[0010] In some embodiments of the present invention, the sapphire substrate is a C-plane, and when the propagation direction of the surface acoustic wave is the Euler angle (0,0,Θ), Θ can be 0° or a multiple of 60°, and the thickness of the piezoelectric layer can be greater than or equal to 0.15λ and less than or equal to 0.30λ.

[0011] In some embodiments of the present invention, the thickness of the piezoelectric layer may be greater than or equal to 0.20λ and less than or equal to 0.30λ.

[0012] In some embodiments of the present invention, the cutting angle of the piezoelectric layer may be greater than or equal to 15°Y and less than or equal to 52°Y.

[0013] In some embodiments of the present invention, the cutting angle of the piezoelectric layer may be greater than or equal to 20°Y and less than or equal to 50°Y.

[0014] In some embodiments of the present invention, the sapphire substrate may be an A-plane (Ap l ane), and when the propagation direction of the surface acoustic wave is the Euler angle (0, 90°, Θ), Θ may be 0° or 180°, and the thickness of the piezoelectric layer may be 0.30λ or greater.

[0015] In some embodiments of the present invention, the thickness of the piezoelectric layer may be 0.35λ or greater.

[0016] In some embodiments of the present invention, the sapphire substrate may be an A-plane, and when the propagation direction of the surface acoustic wave is the Euler angle (0, 90°, Θ), Θ may be 90° or 270°.

[0017] In some embodiments of the present invention, the thickness of the piezoelectric layer may be 0.30λ or greater.

[0018] In some embodiments of the present invention, the thickness of the piezoelectric layer may be 0.35λ or greater.

[0019] In some embodiments of the present invention, the sapphire substrate may be an R-plane (Rp l ane). When the surface acoustic wave propagation direction of the sapphire substrate is the Euler angle (60°, 57.6°, Θ), Θ may be 0, 90°, 180° or 270°, and the thickness of the piezoelectric layer may be 0.30λ or greater.

[0020] In some embodiments of the present invention, the thickness of the piezoelectric layer may be 0.34λ or greater.

[0021] According to the surface acoustic wave device of the present invention, the intensity of stray wave excitation can be suppressed, and the number of excitations can also be kept at a low level.

[0022] The effects of the present invention are not limited to the above-mentioned effects, and other unmentioned effects will be clearly understood by those skilled in the art from the description of the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a diagram showing a SAW resonator.

[0024] Figure 2is a diagram showing simulation results of the admittance characteristics of a SAW resonator according to the prior art.

[0025] Figure 3 This shows that when the piezoelectric layer thickness is set to 20λ in the SAW resonator Figure 1 A diagram showing the simulation results of the admittance characteristics of the SAW resonator.

[0026] Figure 4 This shows that when the piezoelectric layer thickness is set to 1λ in the SAW resonator Figure 1 A diagram showing the simulation results of the admittance characteristics of the SAW resonator.

[0027] Figure 5 is a diagram showing simulation results of the admittance characteristic and the conductance characteristic of the SAW resonator when the thickness of the piezoelectric layer is set to 0.1λ.

[0028] Figure 6 This is a graph showing the relationship between the thickness of the piezoelectric layer and the minimum conductance value near the antiresonance frequency.

[0029] Figure 7a and 7b are graphs showing the admittance characteristic and the conductance characteristic of the SAW resonator when the piezoelectric layer thickness is 2λ and 1λ, respectively.

[0030] Figure 8 This is a graph showing the bulk wave sound velocity of a C-plane sapphire substrate.

[0031] Fig. 9 This is a comparison chart showing the SAW resonator admittance characteristics when the slow shear wave sound velocity of the C-plane sapphire substrate is the lowest (0,0,0) and when the slow shear wave sound velocity is the highest (0,0,30).

[0032] Fig.10 is a graph showing the admittance characteristics of the SAW resonator calculated as a function of changing the thickness of the piezoelectric layer when the Euler angles of the C-plane sapphire substrate are set to (0,0,0).

[0033] Fig.11 The figure is a graph showing the calculated acoustic velocity, electromechanical coupling coefficient and amplitude as a function of the thickness of the piezoelectric layer in the main mode, plate mode and Rayleigh wave mode of the surface acoustic wave device having the admittance characteristics of the present invention.

[0034] Fig.12 This is a graph showing the bulk wave acoustic velocity of the A-plane sapphire substrate.

[0035] Fig.13is a graph showing the admittance characteristics of the SAW resonator calculated as a function of changing the thickness of the piezoelectric layer when the Euler angle of the A-plane sapphire substrate is set to (0, 90°, 0).

[0036] Fig.14 It is a graph showing the acoustic velocity, electromechanical coupling coefficient and amplitude calculated in the main mode, plate mode and Rayleigh wave mode having the admittance characteristics of the surface acoustic wave device of the present invention as a function of the thickness of the piezoelectric layer.

[0037] Fig.15 This is a graph showing the admittance characteristics of the SAW resonator calculated when the thickness of the piezoelectric layer is changed while rotating the SAW propagation direction by 90° to 270° on the A-plane sapphire substrate.

[0038] Fig.16 It is a graph showing the acoustic velocity, electromechanical coupling coefficient and amplitude calculated in the main mode, plate mode and Rayleigh wave mode having the admittance characteristics of the surface acoustic wave device of the present invention as a function of the thickness of the piezoelectric layer.

[0039] Fig.17 This is a graph showing the bulk wave acoustic velocity of an R-plane sapphire substrate.

[0040] Fig.18 is a graph showing the admittance characteristics of the SAW resonator calculated as a function of changing the thickness of the piezoelectric layer when the Euler angle of the A-plane sapphire substrate is set to (60°, 57.4°, 0).

[0041] Fig.19 It is a graph showing the acoustic velocity, electromechanical coupling coefficient and amplitude calculated in the main mode, plate mode and Rayleigh wave mode having the admittance characteristics of the surface acoustic wave device of the present invention as a function of the thickness of the piezoelectric layer.

[0042] Fig. 20 : is a graph showing the admittance characteristics of the SAW resonator calculated when the orientation of the piezoelectric layer is changed when the C-plane sapphire substrate is set to (0,0,0).

[0043] Fig.21 It is a graph showing the acoustic velocity, electromechanical coupling coefficient and amplitude calculated in the main mode, plate mode and Rayleigh wave mode having the admittance characteristics of the surface acoustic wave device of the present invention as a function of the thickness of the piezoelectric layer.

[0044] Description of symbols

[0045] 100: Support substrate

[0046] 130: Piezoelectric layer

[0047] 150: IDT electrode DETAILED DESCRIPTION

[0048] The advantages and features of the present invention and the methods for achieving these advantages and features will be clearly demonstrated by the embodiments described in detail below and the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and will be implemented in various different forms. These embodiments are only used to make the disclosure of the present invention complete and fully inform those skilled in the art of the scope of the present invention, and the present invention is defined only by the scope of the claims. The same reference numerals refer to the same elements throughout the specification.

[0049] "And / or" includes each and every item mentioned and all combinations of one or more of the mentioned items.

[0050] The terms used in this specification are intended to describe embodiments rather than to limit the present invention. In this specification, singular forms also include plural forms unless otherwise specified in the article. The terms "include" and / or "comprising..." used in this specification mean that the components, steps, operations and / or elements mentioned do not exclude the existence or addition of one or more other components, steps, operations and / or elements.

[0051] Unless otherwise defined, all terms (including technical and scientific terms) used in this specification may be used as the meanings generally understood by those skilled in the art. In addition, unless clearly and specifically defined, terms defined in commonly used dictionaries will not be idealized or over-interpreted.

[0052] Figure 1 is a diagram showing a SAW resonator, Figure 2 is a diagram showing simulation results of the admittance characteristics of a SAW resonator according to the prior art.

[0053] Reference Figure 1 The piezoelectric layer 130 including LiTaO3 propagates at 42°YcutX and has a thickness of 10λ. The support substrate 100 including sapphire is C-plane and the propagation direction is A-plane direction. That is, the Euler angle is set to (0,0,0).

[0054] The IDT electrode 150 includes aluminum and has a thickness of 7% standardized by the wavelength of the surface acoustic wave. The spacing of the IDT electrode 150 is 1 μm, and the wavelength λ of the surface acoustic wave is 2 μm. The duty cycle of the IDT electrode 150 is 0.5. Figure 2 As shown, in addition to the main resonance around 2 GHz, spurious responses appear in the range of about 2.1 GHz to about 3 GHz.

[0055] Figure 3 The figure shows that when the thickness of the piezoelectric layer 130 is set to 20λ in the SAW resonator Figure 1 The figure shows the simulation results of the admittance characteristics of the SAW resonator. Figure 3 , it can be seen that Figure 2Compared with the case where the thickness of the piezoelectric layer 130 is 10λ, the amplitude of the stray wave is reduced and the frequency interval of the stray wave is also reduced.

[0056] Figure 4 The figure shows that when the thickness of the piezoelectric layer 130 is set to 1λ in the SAW resonator Figure 1 The figure shows the simulation results of the admittance characteristics of the SAW resonator. Figure 4 As shown, it can be seen that the thinner the piezoelectric layer 130 is, the greater the amplitude of the stray wave is, but the frequency interval of the stray wave is narrower.

[0057] When the thickness of the piezoelectric layer 130 is reduced to less than 1λ, since the acoustic velocity of the wafer supporting the substrate 100 is higher than the acoustic velocity of the surface acoustic wave of the piezoelectric layer 130 , the effect of SAW energy confinement in the piezoelectric layer 130 begins to occur.

[0058] Figure 5 1 is a diagram showing simulation results of the admittance characteristic (a) and the conductance characteristic (b) of the SAW resonator when the thickness of the piezoelectric layer 130 is set to 0.1λ. Figure 1 Like the SAW resonator, the stacked structure of the piezoelectric layer and the supporting substrate is shown in blue, while the result of the single structure of the piezoelectric layer is shown in red.

[0059] Reference Figure 5 , the loss performance of the SAW resonator is determined by the conductivity characteristics near the resonant frequency and anti-resonant frequency of the SAW resonator. Near the anti-resonant frequency, the smaller the conductance, the smaller the loss. In the case of a single piezoelectric layer structure, the minimum conductance value near the anti-resonant frequency is -72dB, while in the case of a stacked structure of a piezoelectric layer and a supporting substrate, the minimum conductance value is -85dB.

[0060] Furthermore, the SAW excited at the cut corner of the single piezoelectric layer structure is a so-called leaky SAW, and since the bulk wave is radiated in the depth direction of the substrate in the frequency region above the antiresonance frequency, the conductance value and loss appear to be large.

[0061] On the other hand, in the stacked structure of the piezoelectric layer and the supporting substrate, since the minimum shear wave velocity of the supporting substrate is 5,751 m / s and the sound velocity of the SAW is 4,900 m / s or higher at this time, the radiation of the body wave in the depth direction of the substrate is suppressed. It can be seen that the conductance value is small in the entire frequency range from the frequency near the antiresonance frequency to 6 GHz.

[0062] Figure 6 This is a graph showing the relationship between the thickness of the piezoelectric layer and the minimum conductance value near the antiresonance frequency. The horizontal axis represents the thickness of the piezoelectric layer in λ, and the vertical axis represents the conductance value.

[0063] Reference Figure 6, when the thickness of the piezoelectric layer is 2.4λ or more, the minimum conductance value (-72dB) of the single piezoelectric layer structure is the same as the minimum conductance value of the stacked structure of the piezoelectric layer and the supporting substrate. That is, when the LT thickness is 2.4λ or less, it can be seen that the effect of suppressing leaky SAW body wave radiation begins to appear.

[0064] Figure 7a and 7b The graphs show the admittance characteristics (a) and conductance characteristics (b) of the SAW resonator when the piezoelectric layer thickness is 2λ and 1λ, respectively. Figure 7a and 7b ,As mentioned above, the stacked structure of the piezoelectric layer and the supporting substrate is represented by the blue graph, while the result of the piezoelectric layer single structure is shown in the red graph.

[0065] As described above, it can be seen that when the thickness of the piezoelectric layer is 2.4λ or less, the conductance and loss are small near the antiresonance frequency, but a large amount of stray excitation is generated. The stray waves are mainly generated by the Rayleigh wave generated on the surface of the piezoelectric layer, the combination of the slow longitudinal body wave of the sapphire substrate and the electric field excited at the IDT electrode, the combination of the slow transverse body wave of the sapphire substrate and the electric field excited at the IDT electrode, or the combination of the fast transverse body wave of the sapphire substrate and the electric field excited at the IDT electrode. Other stray waves are higher-order modes of the stray waves generated above, or are generated by a combination of two or more of the above, but since their amplitudes are generally smaller than the fundamental mode, they do not pose a big problem.

[0066] When using a single crystal sapphire substrate, the acoustic velocity of the body wave changes depending on the cutting direction. Therefore, depending on the cutting direction, the frequency of the generated stray waves may change. Currently, there are three types of sapphire substrates distributed in the industry, including C-side, A-side, and R-side. When stacking wafers, the propagation direction of the surface acoustic wave on the wafer can be selected.

[0067] Figure 8 This is a graph showing the bulk wave acoustic velocity of a C-plane (Cp l ane) sapphire substrate.

[0068] Reference Figure 8 , the horizontal axis represents the propagation direction of the surface acoustic wave in the sapphire substrate, and the Euler angle is set to (0,0,Θ).

[0069] exist Figure 8 In the graph, Vl is the fastest longitudinal wave, Vfs is the fast shear wave, and Vss is the slow shear wave. It can be seen that due to the crystal symmetry of the sapphire substrate, the sound velocity of the shear wave is equal in a period of 60°, and the speed of the slow shear wave is 0°, which is the lowest at multiples of 60°.

[0070] Fig. 9This is a comparison chart showing the SAW resonator admittance characteristics when the slow shear wave sound velocity of the C-plane sapphire substrate is the lowest (0,0,0) and when the slow shear wave sound velocity is the highest (0,0,30).

[0071] The orientation of the piezoelectric layer is 42° YX propagation, and the thickness of the piezoelectric layer is 0.25λ. The λ of the IDT electrode is 2μm, the duty cycle is 0.5, the material of the IDT electrode is aluminum, and the thickness of the IDT electrode standardized by λ is 7%.

[0072] like Fig. 9 As shown, the spurious wave response when the orientation of the sapphire substrate is (0,0,0) Fig. 9 (a)) and the spurious wave response when the orientation of the sapphire substrate is (0, 0, 30°) Fig. 9 (b)) is significantly different. At the main mode resonant frequency, the spurious wave response of the Rayleigh wave mode exists at around 2.1 GHz, and the spurious wave response of the plate mode exists at around 3 GHz. It can be seen that when the orientation of the sapphire substrate is (0,0,30°), the response of the Rayleigh wave mode and the plate mode is large, but when the orientation is (0,0,0), the response can be suppressed to a small value.

[0073] Regarding the plate mode, the slow shear wave velocity of the sapphire substrate is 5751m / s at (0,0,0), but it is as high as 6052m / s at (0,0,30°). Therefore, in the case of (0,0,0), since the wavelength λ of the elastic wave generated by the IDT electrode is 2μm, when the frequency of the plate mode is 5751 / 2=2875.5MHz or lower, the SAW energy of the plate mode is confined in the piezoelectric layer, and the amplitude of the plate mode increases. On the other hand, in the case of (0,0,30°), when the frequency of the plate mode is lower than 3026MHz, the SAW energy of the plate mode is confined in the piezoelectric layer, and the amplitude of the plate mode increases.

[0074] Thus, the amplitude of the plate mode varies significantly depending on the occurrence frequency of the plate mode, which can be determined by the distance from the piezoelectric layer to the sapphire substrate, i.e., the thickness of the piezoelectric layer, and the slow shear wave velocity of the sapphire substrate.

[0075] Fig.10 is a graph showing the admittance characteristics of the SAW resonator calculated as a function of changing the thickness of the piezoelectric layer when the Euler angle of the C-plane sapphire substrate is set to (0,0,0). The orientation of the piezoelectric layer is 42°YX propagation, and the thickness of the piezoelectric layer is 0.25λ. The λ of the IDT electrode is 2μm, the duty cycle is 0.5, the material of the IDT electrode is aluminum, and the thickness of the IDT electrode normalized by λ is 7%. The results calculated using the piezoelectric layer thickness as a parameter in the range of 0 to 0.5λ are shown.

[0076] like Fig.10As shown, it can be seen that the responses of the plate mode and the Rayleigh wave mode vary greatly depending on the thickness of the piezoelectric layer.

[0077] Fig.11 It is a graph showing the calculated sound velocity Vsaw, electromechanical coupling coefficient k2 and amplitude Zrat io in the main mode, plate mode and Rayleigh wave mode having the admittance characteristics of the surface acoustic wave device of the present invention as a function of the thickness of the piezoelectric layer.

[0078] In the main mode, when the thickness of the piezoelectric layer is 0.05λ or more, a sufficiently large amplitude Zrat io can be obtained. In the plate mode, when the thickness of the piezoelectric layer is 0.30λ or less, the amplitude can be reduced; in the Rayleigh wave mode, when the thickness of the piezoelectric layer is 0.15λ or more, preferably 0.2λ or more, the amplitude can be reduced.

[0079] Thus, when the Euler angle of the C-plane sapphire substrate is (0,0,0), by setting the thickness of the piezoelectric layer to be greater than or equal to 0.15λ and less than or equal to 0.30λ, a surface acoustic wave resonator with small amplitudes of a plate mode and a Rayleigh wave mode can be realized.

[0080] Fig.12 This is a graph showing the bulk acoustic velocity of the A-side sapphire substrate. The horizontal axis represents the propagation direction of the surface acoustic wave in the sapphire substrate, and the Euler angle is set to (0, 90°, Θ).

[0081] Reference Fig.12 , in the case of the A-plane, there are two interesting directions of propagation. When θ is 0 or 180°, the slow S-wave has the lowest velocity; when θ is 90° or 270°, the velocities of the slow and fast S-waves are the same. When the slow and fast S-waves have the same velocity, the number of modes of the generated wave is less than when the velocities are different.

[0082] Fig.13 This is a graph showing the admittance characteristics of the SAW resonator calculated as a function of changing the thickness of the piezoelectric layer when the Euler angle of the A-side sapphire substrate is set to (0, 90°, 0). The orientation of the piezoelectric layer is 42° YX propagation, the λ of the IDT electrode is 2μm, the duty cycle is 0.5, the material of the IDT electrode is aluminum, and the thickness of the IDT electrode normalized by λ is 7%. This is the result calculated using the piezoelectric layer thickness as a parameter in the range of 0 to 0.5λ.

[0083] With C-plane sapphire substrate ( Fig.10 ) case, it can be seen that the thickness conditions of the piezoelectric layer that generate the plate mode and the Rayleigh wave mode are different.

[0084] Fig.14It is a graph showing the calculated sound velocity Vsaw, electromechanical coupling coefficient k2 and amplitude Zrat io in the main mode, plate mode and Rayleigh wave mode having the admittance characteristics of the surface acoustic wave device of the present invention as a function of the thickness of the piezoelectric layer.

[0085] In the main mode, as in the case of the C-plane, a sufficiently large amplitude Zrat io can be obtained when the thickness of the piezoelectric layer is 0.05λ or more. In the plate mode, the amplitude can be reduced when the thickness of the piezoelectric layer is 0.14λ or less; in the Rayleigh wave mode, the amplitude can be reduced when the thickness of the piezoelectric layer is 0.30λ or more, preferably 0.35λ or more.

[0086] In summary, when the sapphire substrate is A-plane and the Euler angle is (0,90°,0) or (0,90°,180°), there is no orientation of the sapphire substrate that can suppress both the plate mode and the Rayleigh wave mode. However, when configuring a filter or multiplexer using a surface acoustic wave resonator, the Rayleigh wave mode with a sound velocity close to the main mode may generate a peak in the passband of the filter or multiplexer, so when implementing the filter, the Rayleigh wave mode is more important than the plate mode with a reduced sound velocity.

[0087] Therefore, when the Euler angle of the A-side sapphire substrate is (0, 90°, 0) or (0, 90°, 180°), a surface acoustic wave resonator with a small amplitude of a Rayleigh wave mode can be realized by setting the thickness of the piezoelectric layer to 0.30λ or greater, preferably to 0.35λ or greater.

[0088] Fig.15 This is a graph showing the admittance characteristics of the SAW resonator calculated when the thickness of the piezoelectric layer is changed when the SAW propagation direction is rotated 90° to 270° on the A-side sapphire substrate, that is, when the Euler angle is set to (0, 90°, 90°) or (0, 90°, 270°). The orientation of the piezoelectric layer is 42° YX propagation, the λ of the IDT electrode is 2μm, the duty cycle is 0.5, the material of the IDT electrode is aluminum, and the thickness of the IDT electrode normalized by λ is 7%. This is the result of calculation using the piezoelectric layer thickness as a parameter in the range of 0 to 0.5λ.

[0089] Even in Fig.15 In the case of , it can also be seen that the frequencies and amplitudes of the plate mode and Rayleigh wave mode are different. In the first-order plate mode, when the thickness of the piezoelectric layer exceeds 0.22λ, it is strongly excited, and because the body wave sound speeds of slow shear waves and fast shear waves in this sapphire substrate are the same, it can be seen that the number of plate modes higher than the first-order plate mode is less compared to (0,90°,0) on the A surface.

[0090] When the first-order plate mode satisfies the required characteristics of the filter, the small number of high-order spurious wave modes is beneficial to the attenuation characteristics of the filter.

[0091] Fig.16 It is a graph showing the calculated sound velocity Vsaw, electromechanical coupling coefficient k2 and amplitude Zrat io in the main mode, plate mode and Rayleigh wave mode having the admittance characteristics of the surface acoustic wave device of the present invention as a function of the thickness of the piezoelectric layer.

[0092] In the main mode, as in the case of the C-plane, a sufficiently large amplitude Zrat io can be obtained when the thickness of the piezoelectric layer is 0.05λ or more. In the plate mode, the amplitude can be reduced when the thickness of the piezoelectric layer is 0.24λ or less; in the Rayleigh wave mode, the amplitude can be reduced when the thickness of the piezoelectric layer is 0.30λ or more, preferably 0.32λ or more.

[0093] In summary, when the sapphire substrate is A-plane and the Euler angle is (0, 90°, 90°) or (0, 90°, 270°), there is no orientation of the sapphire substrate that can suppress both the plate mode and the Rayleigh wave mode. However, when configuring a filter or multiplexer using a surface acoustic wave resonator, the Rayleigh wave mode with a sound velocity close to the main mode may generate a peak in the passband of the filter or multiplexer, so when implementing the filter, the Rayleigh wave mode is more important than the plate mode with a reduced sound velocity.

[0094] Therefore, when the Euler angle of the A-side sapphire substrate is (0, 90°, 90°) or (0, 90°, 270°), by setting the thickness of the piezoelectric layer to 0.30λ or more, preferably to 0.32λ or more, a surface acoustic wave resonator with a small amplitude of a Rayleigh wave mode can be realized. In addition, this surface acoustic wave resonator has the characteristic of a small number of high-order plate modes.

[0095] Fig.17 This is a graph showing the bulk acoustic velocity of an R-plane sapphire substrate. The horizontal axis represents the propagation direction of the surface acoustic wave in the sapphire substrate, and the propagation direction is expressed in Euler angles (60°, 57.6°, θ).

[0096] Reference Fig.17 , in the case of the R-plane, there are two interesting propagation directions. When Θ is 0 or 90°, the speed of the slow S-wave is the lowest, and when Θ is a multiple of 90°, the speeds of the slow S-wave become equal. In addition, when Θ is 45°, 135°, 225°, and 315°, the speeds of the slow and fast S-waves approach each other, and the number of occurrences of the plate mode does not decrease, but the frequency of occurrence becomes close.

[0097] Fig.18This is a graph showing the admittance characteristics of the SAW resonator calculated as a function of changing the thickness of the piezoelectric layer when the Euler angle of the A-side sapphire substrate is set to (60°, 57.4°, 0). The orientation of the piezoelectric layer is 42° YX propagation, the λ of the IDT electrode is 2μm, the duty cycle is 0.5, the material of the IDT electrode is aluminum, and the thickness of the IDT electrode normalized by λ is 7%. This is the result of calculation using the piezoelectric layer thickness as a parameter in the range of 0 to 0.5λ.

[0098] When the sapphire substrate is an R-plane, the excitation characteristics of each mode are similar to those of the C-plane.

[0099] Fig.19 It is a graph showing the acoustic velocity, electromechanical coupling coefficient and amplitude calculated in the main mode, plate mode and Rayleigh wave mode having the admittance characteristics of the surface acoustic wave device of the present invention as a function of the thickness of the piezoelectric layer.

[0100] In the main mode, as in the case of the C-plane, a sufficiently large amplitude Zrat io can be obtained when the thickness of the piezoelectric layer is 0.05λ or more. In the plate mode, the amplitude can be reduced when the thickness of the piezoelectric layer is 0.30λ or less; in the Rayleigh wave mode, the amplitude can be reduced when the thickness of the piezoelectric layer is 0.30λ or more, preferably 0.34λ or more.

[0101] In summary, when the sapphire substrate is an R-plane and the Euler angle is (60°, 57.6°, 0°), (60°, 57.6°, 90°), (60°, 57.6°, 180°) or (60°, 57.6°, 270°), there is no orientation of the sapphire substrate that can suppress both the plate mode and the Rayleigh wave mode. However, when configuring a filter or a multiplexer using a surface acoustic wave resonator, since the Rayleigh wave mode with a sound velocity close to the main mode may generate a peak within the passband of the filter or multiplexer, the Rayleigh wave mode is more important than the plate mode with a reduced sound velocity when implementing the filter.

[0102] Therefore, when the Euler angle of the R-plane sapphire substrate is (60°, 57.6°, 0°), (60°, 57.6°, 90°), (60°, 57.6°, 180°) or (60°, 57.6°, 270°), by setting the thickness of the piezoelectric layer to 0.30λ or greater, preferably to 0.34λ or greater, a surface acoustic wave resonator with a small amplitude of a Rayleigh wave mode can be realized.

[0103] Fig. 20This is a graph showing the admittance characteristics of the SAW resonator calculated when the orientation of the piezoelectric layer is changed with the C-plane sapphire substrate set to (0,0,0). The cutting angle of the piezoelectric layer is set to the rotated Y-plate, the propagation direction of the surface acoustic wave is the X-direction of the piezoelectric layer, the λ of the IDT electrode is 2μm, the duty cycle is 0.5, the material of the IDT electrode is aluminum, and the thickness of the IDT electrode normalized by λ is 7%. This is calculated using the cutting angle of the piezoelectric layer as a parameter in the range of 0 to 55°.

[0104] like Fig. 20 As shown in FIG. 1 , it can be seen that although the cutting angle of the piezoelectric layer changes, the changes in the Rayleigh wave mode and the plate mode are small. Therefore, the Rayleigh wave mode and the plate mode can be suppressed in a wide Y-cut range.

[0105] Fig.21 It is a graph showing the acoustic velocity, electromechanical coupling coefficient and amplitude calculated in the main mode, plate mode and Rayleigh wave mode having the admittance characteristics of the surface acoustic wave device of the present invention as a function of the thickness of the piezoelectric layer.

[0106] In the main mode, the electromechanical coupling coefficient is maximum at about 20°Y, and its Zrat io gradually decreases with the increase of the cutting angle, but it is still very large between 0 and 55°Y, exceeding 80dB, so a low-loss filter can be achieved at any cutting angle.

[0107] For the plate mode, the amplitude becomes smaller at 52°Y or less, preferably at 50°Y or less, and for the Rayleigh wave mode, the amplitude becomes smaller at 15°Y or more, preferably at 20°Y. Therefore, when the cutting angle of the piezoelectric layer is greater than or equal to 15°Y and less than or equal to 52°Y, preferably greater than or equal to 20°Y and less than or equal to 50°Y, the Rayleigh wave mode and the plate mode can be suppressed.

[0108] Although the embodiments of the present invention have been described on the basis of the accompanying drawings, it will be appreciated by those skilled in the art that the present invention can be implemented in other specific forms without changing the technical spirit or basic features. Therefore, the embodiments described above should be understood to be illustrative in all aspects and not restrictive.

Claims

1. A surface acoustic wave device, characterized in that: include: A supporting substrate; a piezoelectric layer formed on a supporting substrate; as well as IDT electrode on the piezoelectric layer, Here, when the wavelength of the surface acoustic wave excited at the IDT electrode is λ, the thickness of the piezoelectric layer is 2.4λ or less.

2. The surface acoustic wave device according to claim 1, characterized in that The support substrate comprises a sapphire substrate, The piezoelectric layer includes LiTaO3.

3. The surface acoustic wave device according to claim 2, characterized in that: The sapphire substrate is a C-plane, When the propagation direction of the surface acoustic wave of the sapphire substrate is the Euler angle (0,0,Θ), Θ is a multiple of 0° or 60°, and the thickness of the piezoelectric layer is greater than or equal to 0.15λ and less than or equal to 0.30λ.

4. The surface acoustic wave device according to claim 3, characterized in that: The thickness of the piezoelectric layer is greater than or equal to 0.20λ and less than or equal to 0.30λ.

5. The surface acoustic wave device according to claim 3, characterized in that: The cutting angle of the piezoelectric layer is greater than or equal to 15°Y and less than or equal to 52°Y.

6. The surface acoustic wave device according to claim 5, characterized in that: The cutting angle of the piezoelectric layer is greater than or equal to 20°Y and less than or equal to 50°Y.

7. The surface acoustic wave device according to claim 2, characterized in that: The sapphire substrate is surface A, When the propagation direction of the surface acoustic wave of the sapphire substrate is the Euler angle (0, 90°, Θ), Θ is 0° or 180°, and the thickness of the piezoelectric layer is 0.30λ or greater.

8. The surface acoustic wave device according to claim 7, characterized in that: The thickness of the piezoelectric layer is 0.35λ or more.

9. The surface acoustic wave device according to claim 2, characterized in that: The sapphire substrate is surface A, When the propagation direction of the surface acoustic wave is the Euler angle (0, 90°, Θ), Θ is 90° or 270°.

10. The surface acoustic wave device according to claim 9, characterized in that: The piezoelectric layer has a thickness of 0.30λ or more.

11. The surface acoustic wave device according to claim 10, characterized in that The thickness of the piezoelectric layer is 0.35λ or more.

12. The surface acoustic wave device according to claim 2, characterized in that: The sapphire substrate is an R-surface. When the surface acoustic wave propagation direction of the sapphire substrate is the Euler angle (60°, 57.6°, θ), θ is 0°, 90°, 180° or 270°. The piezoelectric layer has a thickness of 0.30λ or more.

13. The surface acoustic wave device according to claim 12, characterized in that: The thickness of the piezoelectric layer is 0.34λ or greater.

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