harmonic oscillator

Abstract

The present invention relates to a resonator. The resonator (10) comprises: a piezoelectric layer having a first surface and a second surface facing each other; an IDT electrode (7) disposed on the first surface side of the piezoelectric layer (5); and a high-velocity substrate (1) disposed on the second surface side of the piezoelectric layer (5). The piezoelectric layer (5) is made of crystal with a cut angle obtained by rotating a surface orthogonal to the crystal X-axis about the crystal X-axis. In the propagation direction (PD) of 90°±10° relative to the crystal X-axis of the piezoelectric layer (5), the sound speed of the high-velocity substrate (1) is faster than the sound speed of the piezoelectric layer (5). The IDT electrode (7) has a comb-shaped electrode having a plurality of electrode fingers (7b) arranged in the propagation direction (PD).

Description

Technical Field

[0001] This invention relates to harmonic oscillators. Background Technology

[0002] Previously, surface acoustic wave (SAW) resonators were known as elastic wave devices used in resonators, bandpass filters, etc. With the development of mobile communication systems such as mobile phones, there is a demand for improvements in various properties of SAW resonators, such as Q-value and frequency-temperature characteristics.

[0003] Patent document 1 discloses a surface acoustic wave device, which has a piezoelectric substrate and an IDT disposed on the piezoelectric substrate, and uses the excitation wave as an SH wave. The Q value is improved by forming a groove in the space between the electrodes of the IDT.

[0004] Patent document 2 discloses an elastic wave device comprising a high-velocity support substrate, a piezoelectric film, and an IDT electrode. When the wavelength of the elastic wave, determined by the electrode period of the IDT electrode, is set to λ, a low-velocity film with a thickness in the range of 0.1λ to 0.5λ is provided between the high-velocity support substrate and the piezoelectric film to improve the Q value.

[0005] Patent document 3 discloses a surface acoustic wave device, which is a surface acoustic wave device with a crystal layer, an amorphous silicon oxide layer, a piezoelectric layer and a comb-shaped electrode stacked in sequence. By setting the thickness of the amorphous silicon oxide layer and the thickness of the piezoelectric layer to appropriate values, the frequency temperature characteristics and other characteristics are improved.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2006-203408

[0007] Patent Document 2: Japanese Patent No. 5910763

[0008] Patent Document 3: Japanese Patent Application Publication No. 2019-149724

[0009] However, in the surface acoustic wave device described in Patent Document 1, it is sometimes difficult to control the depth of the groove in the space between the electrode fingers, thus failing to sufficiently improve the Q value.

[0010] In the elastic wave device described in Patent Document 2 and the surface acoustic wave device described in Patent Document 3, although the first-order frequency temperature coefficient has been improved, there is still room for further improvement in the frequency temperature characteristics. Summary of the Invention

[0011] The present invention was made in view of the following circumstances, and its purpose is to provide a resonator with excellent frequency-temperature characteristics or resonance characteristics.

[0012] The harmonic oscillator according to one aspect of the present invention comprises:

[0013] A piezoelectric layer having a first side and a second side that are opposite to each other;

[0014] An IDT electrode is disposed on the first side of the piezoelectric layer; and

[0015] A high-velocity substrate is disposed on the second side of the piezoelectric layer.

[0016] The piezoelectric layer is composed of crystal with a cut angle obtained by rotating a plane orthogonal to the crystal's Y-axis about the crystal's X-axis.

[0017] In the propagation direction at 90°±10° relative to the crystal X-axis of the piezoelectric layer, the sound velocity in the high-velocity substrate is faster than that in the piezoelectric layer.

[0018] The IDT electrode has a comb-shaped electrode with multiple electrode fingers arranged in the propagation direction.

[0019] According to the present invention, a harmonic oscillator with excellent frequency-temperature characteristics or resonance characteristics can be provided. Attached Figure Description

[0020] Figure 1 This is a top view schematically illustrating the structure of a harmonic oscillator in one embodiment.

[0021] Figure 2 It is a schematic representation Figure 1 The diagram shows a cross-sectional view of the structure of the harmonic oscillator.

[0022] Figure 3 This is an explanation Figure 1 The diagram shows the crystal axis orientation of the piezoelectric layer.

[0023] Figure 4 This is a schematic cross-sectional view showing the structure of a harmonic oscillator in a modified example.

[0024] Figure 5 This is a schematic cross-sectional view showing the structure of a harmonic oscillator in a modified example.

[0025] Figure 6 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the speed of sound.

[0026] Figure 7 This is a graph showing the relationship between the rotation angle of the piezoelectric layer and the electromechanical coupling coefficient in the first embodiment.

[0027] Figure 8 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the Q value.

[0028] Figure 9This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the temperature coefficient of the first-order frequency.

[0029] Figure 10 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the temperature coefficient of the second-order frequency.

[0030] Figure 11 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the temperature coefficient of the third-order frequency.

[0031] Figure 12 This is a graph showing the frequency-temperature characteristics of the first embodiment.

[0032] Figure 13 This is a graph illustrating the effect of the sound velocity of the high-velocity substrate of the first embodiment on the Q value.

[0033] Figure 14 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the second embodiment and the speed of sound.

[0034] Figure 15 This is a graph showing the relationship between the rotation angle of the piezoelectric layer and the electromechanical coupling coefficient in the second embodiment.

[0035] Figure 16 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the second embodiment and the Q value.

[0036] Figure 17 This is a graph showing the relationship between the rotation angle of the high-speed acoustic substrate in the third embodiment and the speed of sound.

[0037] Figure 18 This is a graph showing the relationship between the rotation angle of the hypersonic substrate in the third embodiment and the electromechanical coupling coefficient.

[0038] Figure 19 This is a graph showing the relationship between the rotation angle and the Q value of the hypersonic substrate in the third embodiment.

[0039] Figure 20 This is a graph showing the relationship between the rotation angle of the hypersonic substrate in the third embodiment and the temperature coefficient of the first-order frequency.

[0040] Figure 21 This is a graph showing the relationship between the rotation angle of the hypersonic substrate in the third embodiment and the temperature coefficient of the second-order frequency.

[0041] Figure 22 This is a graph showing the relationship between the rotation angle of the hypersonic substrate in the third embodiment and the temperature coefficient of the third-order frequency. Detailed Implementation

[0042] The embodiments of the present invention will be described below. In the following drawings, the same or similar constituent elements are indicated by the same or similar reference numerals. The drawings are illustrative, and the dimensions and shapes of the parts are schematic and should not be interpreted as limiting the scope of the present invention to these embodiments.

[0043] First, refer to Figures 1-3 The general structure of the resonator 10 according to one embodiment of the present invention will be described. Figure 1 This is a top view schematically illustrating the structure of a harmonic oscillator in one embodiment. Figure 2 It is a schematic representation Figure 1 The diagram shows a cross-sectional view of the structure of the harmonic oscillator. Figure 3 This is an explanation Figure 1 The diagram shows the crystal axis orientation of the piezoelectric layer.

[0044] The resonator 10 is a type of SAW resonator, specifically a STW (Surface Transverse Wave) element used for guiding SSBW (Surface Skimming Bulk Wave). For example... Figure 1 As shown in Figure 2, the resonator 10 includes: a high-velocity substrate 1, a low-velocity layer 3, a piezoelectric layer 5, an IDT (Inter Digital Transducer) electrode 7, and a pair of reflectors 9.

[0045] The high-velocity acoustic substrate 1 is a substrate capable of suppressing the leakage of vibrational energy of the piezoelectric layer 5 as bulk acoustic waves, thus reducing the Q value. Specifically, for example, as... Figure 2 As shown, the high-velocity acoustic substrate 1 is a single-layer substrate in which the velocity of sound (the propagation speed of elastic waves) in the propagation direction PD is faster than the velocity of sound in the propagation direction PD of the piezoelectric layer 5. Hereinafter, the "velocity of sound in the propagation direction PD" will be referred to simply as "velocity of sound". Preferably, the velocity of sound in the high-velocity acoustic substrate 1 is 10% or more faster than the velocity of sound in the piezoelectric layer 5, more preferably 20% or more faster, and even more preferably 40% or more faster.

[0046] The hypersonic substrate 1 may be made of, for example, a single crystal of silicon, but is not limited thereto. The hypersonic substrate 1 may also be formed from any of the following: monocrystalline silicon (amorphous silicon, polycrystalline silicon, etc.), silicon compounds (silicon oxide, silicon nitride, silicon carbide, etc.), and aluminum compounds (aluminum nitride, aluminum oxide, etc.). As described later, the piezoelectric layer 5 is formed of crystal, but the hypersonic substrate 1 may also be formed of crystal as long as the crystallization axis direction can be set to ensure a sufficient sound velocity difference between the hypersonic substrate 1 and the piezoelectric layer 5 in the propagation direction PD. In this case, the hypersonic substrate 1 and the piezoelectric layer 5 may also be formed of crystals with different cutting angles. For example, the crystal of the piezoelectric layer 5 may be BT-cut as described later, with the crystallization X-axis set to 90°±10° relative to the propagation direction PD, and the crystal of the hypersonic substrate 1 may be AT-cut as described later, with the crystallization X-axis set to 90°±10° relative to the propagation direction PD. That is, the cut angle of the crystal in the hypersonic substrate 1 can also be expressed by Euler angles as (λ, μ, θ) = (0°, 125°±10°, 90°±10°), and the cut angle of the crystal in the piezoelectric layer 5 can be expressed by Euler angles as (λ, μ, θ) = (0°, 31°±10°, 90°±10°). Accordingly, the sound velocity difference between the hypersonic substrate 1 and the piezoelectric layer 5 can be increased. Furthermore, the cut angle of the crystal constituting the hypersonic substrate 1 is not limited to the above, as long as the sound velocity of the hypersonic substrate 1 is sufficiently faster than the sound velocity of the piezoelectric layer 5 in the propagation direction PD. The hypersonic substrate 1 can also be formed from a crystal with a cut angle obtained by rotating the plane orthogonal to the crystal Y-axis counterclockwise within a range of 0° to 60° when viewed from the positive direction of the crystal X-axis.

[0047] High-speed acoustic substrates are not limited to Figure 2 The single-layer structure shown can also be a multi-layer structure. In the case of a multi-layer hypersonic substrate, if the sound velocity of the layer closest to the piezoelectric layer 5 is faster than the sound velocity of the piezoelectric layer 5, then the sound velocities of the other layers in the multi-layer structure can also be lower than the sound velocity of the piezoelectric layer 5. Preferably, the sound velocity of the layer closest to the piezoelectric layer 5 in the multi-layer hypersonic substrate is the same as that of the hypersonic substrate 1 described above, and preferably it is formed of the same material as the hypersonic substrate 1 described above.

[0048] The greater the thickness T1 of the hypersonic substrate 1, the better it can suppress the leakage of vibrational energy from the piezoelectric layer 5. Furthermore, it is preferable that the hypersonic substrate 1 has the mechanical strength to support the laminated structure having the low-velocity layer 3, the piezoelectric layer 5, the IDT electrode 7, and the reflector 9. Therefore, when the wavelength of the elastic wave is set to λ, it is preferable that the thickness T1 of the hypersonic substrate 1 is 50λ or more, more preferably 100λ or more, and even more preferably 500λ or more.

[0049] The low-velocity layer 3 is used to contain vibrational energy that is inherently concentrated in a low-velocity medium, suppressing the leakage of vibrational energy from the piezoelectric layer 5 to the high-velocity substrate 1. Specifically, the low-velocity layer 3 is a layer where the sound velocity in the propagation direction PD is lower than the sound velocity in the propagation direction PD of the piezoelectric layer 5. The low-velocity layer 3 is directly stacked on the high-velocity substrate 1. This means that there are no functional components such as adhesives between the high-velocity substrate 1 and the low-velocity layer 3, and the high-velocity substrate 1 is in contact with the low-velocity layer 3. For example, direct stacking can be achieved through direct bonding based on diffusion bonding, room temperature bonding, etc., or direct film formation based on PVD, CVD, etc. At the boundaries between directly stacked components, the composition ratio can change either abruptly or slowly. The same applies to direct stacking in other layers and substrates.

[0050] The low-velocity layer 3 is made of silicon oxide, for example, thereby improving the frequency temperature characteristics through temperature compensation. However, the material of the low-velocity layer 3 is not limited to silicon oxide; for example, it can also be formed from silicon oxynitride, tantalum oxide, or compounds obtained by adding fluorine, carbon, or boron to these materials.

[0051] Preferably, the thickness T3 of the low-velocity layer 3 is set in the range of 0.01λ or more and 2.0λ or less, more preferably in the range of 0.1λ or more and 0.5λ or less. By setting the thickness T3 in the range of 2.0λ or less, the electromechanical coupling coefficient can be easily adjusted. In addition, by setting the thickness T3 in the range of 0.01λ or more, the leakage of vibrational energy from the piezoelectric layer 5 can be sufficiently suppressed. Furthermore, from the viewpoint of reducing the warping of the resonator 10 caused by the stress of the low-velocity layer 3, it is preferable that the thickness T3 of the low-velocity layer 3 is less than 1 / 100 of the thickness T1 of the high-velocity substrate 1. In addition, the low-velocity layer 3 can also be omitted. That is, the piezoelectric layer 5 and the high-velocity substrate 1 can also be directly stacked.

[0052] Piezoelectric layer 5 is used to convert electrical vibration energy into mechanical vibration energy, allowing mechanical vibration energy to propagate as SSBW. Piezoelectric layer 5 is directly stacked on top of low-velocity sound layer 3. (As...) Figure 3 As shown, the piezoelectric layer 5 is composed of a crystal (rotationally Y-cut crystal substrate) with a cut angle obtained by rotating a plane orthogonal to the crystal X-axis around the crystal X-axis by a rotation angle θ1. Furthermore, the piezoelectric layer 5 is configured such that the direction relative to the crystal X-axis is 90° ± 10°, which is designated as the propagation direction PD. That is, the propagation direction PD is along the Z' axis after rotating the crystal Z-axis around the crystal X-axis by a rotation angle θ1. Here, for the rotation angle θ1, when viewed from the positive direction of the crystal X-axis (from... Figure 3 When observing the inside from the front side of the paper, counterclockwise is set to positive (+), and clockwise is set to negative (-), including 0. The cut angle of the crystal is (0°, θ1+90°, 90°±10°) when displayed using Euler angles.

[0053] As an example, the crystal of piezoelectric layer 5 is BT-cut, with θ1 = -59° ± 10°. The cut angle of this crystal, expressed in Euler angles, is (λ, μ, θ) = (0°, θ1 + 90°, 90° ± 10°) = (0°, 31° ± 10°, 90° ± 10°). Alternatively, as another example, the crystal of piezoelectric layer 5 is AT-cut, with θ1 = 35° ± 10°. The cut angle of this crystal, expressed in Euler angles, is (λ, μ, θ) = (0°, θ1 + 90°, 90° ± 10°) = (0°, 125° ± 10°, 90° ± 10°).

[0054] Preferably, the thickness T5 of the piezoelectric layer 5 is set in the range of 0.02λ or more and 1.0λ or less, more preferably in the range of 0.05λ or more and 0.5λ or less, and even more preferably in the range of 0.1λ or more and 0.5λ or less. Accordingly, the electromechanical coupling coefficient can be easily adjusted over a wide range. In addition, from the viewpoint of suppressing the leakage of vibrational energy from the piezoelectric layer 5, it is preferable that the thickness T5 of the piezoelectric layer 5 is less than 1 / 100 of the thickness T1 of the hypersonic substrate 1.

[0055] IDT electrode 7 is a comb-shaped electrode. Figure 1 In the example shown, the IDT electrode 7 has a pair of busbars 7a and a plurality of electrode fingers 7b. The pair of busbars 7a are configured to extend respectively along the propagation direction PD and are separated from each other in a direction orthogonal to the propagation direction PD. The plurality of electrode fingers 7b extend from the pair of busbars 7a in a direction orthogonal to the propagation direction PD and are arranged along the propagation direction PD. The plurality of electrode fingers 7b extending from one busbar 7a and the plurality of electrode fingers 7b extending from the other busbar 7a are alternately arranged along the propagation direction PD. If the crystal axis direction of the piezoelectric layer 5 is taken as a reference, then as Figure 3 As shown, multiple electrode fingers 7b extend along the X-axis direction of the crystal and are arranged along the Z'-axis direction after rotating the Z-axis around the X-axis by an angle θ1. The electrode period of the electrode fingers 7b determines the wavelength of the elastic wave. In other words, the edges of two adjacent electrode fingers 7b that are electrically connected to each other are separated by a distance λ along the Z'-axis direction.

[0056] A pair of reflectors 9 are grating reflectors used to reflect SAW and improve the Q value. The pair of reflectors 9 are configured to be separated by IDT electrodes 7 in the propagation direction PD. Each pair of reflectors 9 has: a pair of reflector busbars 9a configured to extend along the propagation direction PD and be separated in a direction orthogonal to the propagation direction PD, and a plurality of reflector electrode fingers 9b connecting the pair of reflector busbars 9a and arranged in the propagation direction PD.

[0057] The IDT electrode 7 and reflector 9 are disposed on the piezoelectric layer 5. The IDT electrode 7 and reflector 9 are made of a metal with aluminum as the main component, for example, but are not limited thereto. The IDT electrode 7 and reflector 9 may also be formed of copper, platinum, gold, silver, titanium, nickel, chromium, molybdenum, tungsten, or an alloy of any of these metals as the main component. Preferably, the thickness T7 of the IDT electrode 7 and reflector 9 is set in the range of 0.01λ or more and 0.2λ or less, more preferably in the range of 0.02λ or more and 0.15λ or less, and even more preferably in the range of 0.04λ or more and 1.0λ or less.

[0058] Next, refer to Figure 4 as well as Figure 5 A variation of this embodiment will be described below. Figure 4 as well as Figure 5 This is a schematic cross-sectional view showing the structure of a harmonic oscillator in a modified example.

[0059] like Figure 4 As shown, the hypersonic substrate 1 and the piezoelectric layer 5 of the resonator 20 can also be directly stacked together. In this case, the low-velocity layer is omitted, so in order to suppress the leakage of vibrational energy from the piezoelectric layer 5 to the hypersonic substrate 1, the sound velocity of the hypersonic substrate 1 is preferably more than 20% faster than the sound velocity of the piezoelectric layer 5.

[0060] like Figure 5 As shown, the hypersonic substrate 31 of the resonator 30 may also have a support substrate 31a and a hypersonic layer 31b stacked on the support substrate 31a. Although the hypersonic layer 31b is stacked directly on the support substrate 31a, for example, it is not limited to this and may also be stacked via bonding members such as adhesives.

[0061] The material of the support substrate 31a is not limited as long as it can support the stacked structure having the high-velocity layer 31b, the low-velocity layer 3, the piezoelectric layer 5, the IDT electrode 7, and the reflector 9. For example, the support substrate 31a can be formed from piezoelectric materials such as sapphire, lithium tantalate, lithium niobate, and crystal; various ceramics such as alumina, magnesium oxide, silicon nitride, aluminum nitride, silicon carbide, zirconium oxide, cordierite, mullite, block talc, and forsterite; dielectric materials such as glass; semiconductor materials such as silicon and gallium nitride; and resin substrates.

[0062] A high-velocity acoustic layer 31b is disposed between the support substrate 31a and the low-velocity acoustic layer 3. The sound velocity in the propagation direction PD of the high-velocity acoustic layer 31b is faster than the sound velocity in the propagation direction PD of the piezoelectric layer 5. The high-velocity acoustic layer 31b can be formed of the same material as the high-velocity acoustic substrate 1. The greater the thickness of the high-velocity acoustic layer 31b, the better it can suppress the leakage of vibrational energy from the piezoelectric layer 5. Therefore, it is preferable that the thickness of the high-velocity acoustic layer 31b is 0.5λ or more, more preferably 1.5λ or more. In addition, from a manufacturability point of view, it is preferable that the thickness of the high-velocity acoustic layer 31b is 10λ or less.

[0063] Next, refer to Figures 6-8 The resonance characteristics in one embodiment of this implementation will be explained. Figure 6 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the speed of sound. Figure 7 This is a graph showing the relationship between the rotation angle of the piezoelectric layer and the electromechanical coupling coefficient in the first embodiment. Figure 8 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the Q value.

[0064] The resonator 10 according to the first embodiment includes: a high-velocity substrate 1, a low-velocity layer 3 stacked on the high-velocity substrate 1, a piezoelectric layer 5 stacked on the low-velocity layer 3, an IDT electrode 7 formed on the piezoelectric layer 5, and a reflector 9.

[0065] Elastic wave: wavelength λ = 4 μm, frequency f = 1 GHz

[0066] High-speed acoustic substrate 1: Silicon (single crystal), T1 = 300 μm

[0067] Low-velocity layer 3: silicon oxide (amorphous), T3 = 0.8 μm

[0068] Piezoelectric layer 5: Crystal, Euler angles (0°, θ1+90°, 90°), T5=2μm

[0069] IDT electrode 7: Aluminum, T7 = 0.2 μm

[0070] The resonator involved in the comparative example is a resonator composed of a single-layer piezoelectric layer 5, with the high-velocity substrate 1 and low-velocity layer 3 omitted from the structure of the first embodiment. Simulations of various resonance characteristics in the first embodiment and the comparative example were performed.

[0071] Figure 6The horizontal axis of the graph represents the rotation angle of the piezoelectric layer, θ1, and the vertical axis represents the SAW sound velocity (phase velocity) (unit: m / s). Within the ranges of -90° ≤ θ1 ≤ 0° and 60° ≤ θ1 ≤ 90°, the SAW sound velocity of the first embodiment increases compared to the comparative example. That is, within this range, the first embodiment is more advantageous for high-frequency operation compared to the comparative example. Particularly, the increase in SAW sound velocity is greater within the range of θ1 = -59° ± 10°. For example, at θ1 = -59°, the SAW sound velocity of the comparative example is below 3300 m / s, while the SAW sound velocity of the first embodiment increases to above 3500 m / s.

[0072] Figure 7 The horizontal axis of the graph represents the rotation angle of the piezoelectric layer, θ1, and the vertical axis represents the electromechanical coupling coefficient (unit: %). Within the ranges of -90° ≤ θ1 ≤ 0° and 70° ≤ θ1 ≤ 90°, the electromechanical coupling coefficient of the first embodiment increases compared to that of the comparative example. That is, within this range, the first embodiment exhibits superior oscillation characteristics as an oscillator compared to the comparative example, enabling broadband operation as a filter.

[0073] Figure 8 The horizontal axis of the graph represents the rotation angle of the piezoelectric layer, θ1, and the vertical axis represents the Q value (Q). Throughout the entire range of θ1, the Q value of the first embodiment is higher than that of the comparative example. That is, throughout the entire range of θ1, the first embodiment exhibits superior oscillation characteristics as an oscillator compared to the comparative example, and can reduce phase noise and insertion loss as a filter. Particularly, the increase in Q value is significant within the range of θ1 = -59° ± 10°. For example, at θ1 = -59°, the Q value of the comparative example is below 1000, while the Q value of the first embodiment rises to above 8000.

[0074] Next, refer to Figures 9-12 The temperature characteristics of one embodiment of this invention will be described. Simulations of the temperature characteristics in the first embodiment and the comparative example were performed. Figure 9 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the temperature coefficient of the first-order frequency. Figure 10 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the temperature coefficient of the second-order frequency. Figure 11 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the first embodiment and the temperature coefficient of the third-order frequency. Figure 12 This is a graph showing the frequency-temperature characteristics of the first embodiment.

[0075] Figure 9 The horizontal axis of the graph represents the rotation angle of the piezoelectric layer, θ1, and the vertical axis represents the first-order temperature coefficient of frequency (1st TCF). The unit of the vertical axis is ppm / K. Figure 10 The horizontal axis of the graph represents the rotation angle of the piezoelectric layer, θ1, and the vertical axis represents the second-order temperature coefficient (2nd TCF). The unit of the vertical axis is ppb / K. 2 . Figure 11 The horizontal axis of the graph represents the rotation angle of the piezoelectric layer θ1, and the vertical axis represents the third-order temperature coefficient (3rd TCF). The unit of the vertical axis is ppt / K. 3 Throughout the entire range of θ1, the absolute value of the first-order frequency temperature coefficient of the first embodiment is smaller than that of the comparative example. The same applies to the second-order and third-order frequency temperature coefficients. In particular, the absolute value of the third-order frequency temperature coefficient decreases significantly within the range of θ1 = -59° ± 10°. For example, at θ1 = -59°, the third-order frequency temperature coefficient of the comparative example is 80 ppt / K. 3 In contrast, the absolute value of the third-order frequency temperature coefficient in the first embodiment is reduced to 40 ppt / K. 3 the following.

[0076] Figure 12 The horizontal axis of the graph represents temperature (°C), and the vertical axis represents the frequency change (dF) (ppm) with the frequency at 25°C as a reference. The curves in the graph represent the frequency-temperature characteristics of the first embodiment and the comparative example when θ1 = -59°, and the frequency-temperature characteristics of the first embodiment and the comparative example when θ1 = 35°. Regardless of whether θ1 = -59° or 35°, the frequency-temperature characteristics of the first embodiment are superior to those of the comparative example. In particular, the frequency-temperature characteristics of the first embodiment when θ1 = -59° are excellent, with the absolute value of the frequency change in the high-temperature region above 40°C and below 100°C being less than 10 ppm.

[0077] Next, refer to Figure 13 The effect of sound velocity difference on Q value is explained. Figure 13This is a graph illustrating the effect of the sound velocity of the high-velocity substrate on the Q value in the first embodiment. It shows the change in Q value obtained through simulation of changing the sound velocity of the high-velocity substrate 1 in the structure of the first embodiment.

[0078] Figure 13 The horizontal axis of the graph represents the phase velocity of the substrate 1 (unit: m / s), and the vertical axis represents the Q value. The curves in the graph represent the Q values ​​of the first embodiment when θ1 = -59° and when θ1 = 35°, respectively. The Q value increases when the sound velocity of the substrate 1 is more than 10% faster than the sound velocity of the piezoelectric layer 5, exceeds 8000 when it is more than 20% faster, and stops increasing when it is more than 40% faster.

[0079] Next, refer to Figures 14-16 The resonance characteristics of one embodiment of this implementation will be described. Figure 14 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the second embodiment and the speed of sound. Figure 15 This is a graph showing the relationship between the rotation angle of the piezoelectric layer and the electromechanical coupling coefficient in the second embodiment. Figure 16 This is a graph showing the relationship between the rotation angle of the piezoelectric layer in the second embodiment and the Q value.

[0080] The second embodiment differs from the first embodiment in that it omits the low-velocity layer 3, and the piezoelectric layer 5 is directly bonded to the high-velocity substrate 1. Otherwise, it has the same structure as the first embodiment.

[0081] Figure 14 The horizontal axis of the graph represents the rotation angle of the piezoelectric layer, θ1, and the vertical axis represents the SAW sound velocity (unit: m / s). Throughout the range of θ1, the SAW sound velocity of the second embodiment increases compared to that of the comparative example. Particularly within the range of θ1 = -59° ± 10°, the increase in SAW sound velocity is significant. For example, at θ1 = -59°, the SAW sound velocity of the comparative example is below 3300 m / s, while the SAW sound velocity of the second embodiment increases to above 4200 m / s. Furthermore, throughout the range of θ1, the SAW sound velocity of the second embodiment is greater than that of the first embodiment.

[0082] Figure 15The horizontal axis of the graph represents the rotation angle of the piezoelectric layer, θ1, and the vertical axis represents the electromechanical coupling coefficient (unit: %). Within the range of -70° ≤ θ1 ≤ 30°, the electromechanical coupling coefficient of the second embodiment is higher than that of the comparative example. In particular, the increase in the electromechanical coupling coefficient is larger within the range of θ1 = 0° ± 10°. For example, when θ1 = 0°, the electromechanical coupling coefficient of the comparative example is less than 2.5%, while the electromechanical coupling coefficient of the second embodiment increases to more than 3.8%. Furthermore, within the range of -40° ≤ θ1 ≤ 40°, the electromechanical coupling coefficient of the second embodiment is larger than that of the first embodiment.

[0083] Figure 16 The horizontal axis of the graph represents the rotation angle of the piezoelectric layer, θ1, and the vertical axis represents the Q value (Q). Within the ranges of -90° ≤ θ1 ≤ 10° and 50° ≤ θ1 ≤ 90°, the Q value of the second embodiment is higher than that of the comparative example. Particularly within the range of θ1 = -59° ± 10°, the increase in Q value is significant. For example, at θ1 = -59°, the Q value of the comparative example is below 1000, while the Q value of the second embodiment rises to above 8000. Furthermore, across the entire range of θ1, the Q value of the first embodiment is larger than that of the second embodiment.

[0084] Next, refer to Figures 17-22 The temperature characteristics of one embodiment of this implementation will be described. Simulations of the resonance characteristics and temperature characteristics in the third embodiment were performed. Figure 17 This is a graph showing the relationship between the rotation angle of the high-speed acoustic substrate in the third embodiment and the speed of sound. Figure 18 This is a graph showing the relationship between the rotation angle of the hypersonic substrate in the third embodiment and the electromechanical coupling coefficient. Figure 19 This is a graph showing the relationship between the rotation angle and the Q value of the hypersonic substrate in the third embodiment. Figure 20 This is a graph showing the relationship between the rotation angle of the hypersonic substrate in the third embodiment and the temperature coefficient of the first-order frequency. Figure 21 This is a graph showing the relationship between the rotation angle of the hypersonic substrate in the third embodiment and the temperature coefficient of the second-order frequency. Figure 22 This is a graph showing the relationship between the rotation angle of the hypersonic substrate in the third embodiment and the temperature coefficient of the third-order frequency.

[0085] The third embodiment differs from the second embodiment in that the hypersonic substrate 1 is formed of crystal. Otherwise, it has the same structure as the second embodiment. The hypersonic substrate 1 is a crystal obtained by rotating a plane orthogonal to the crystal Y-axis about the crystal X-axis by an angle θ2. The piezoelectric layer 5 is stacked with the hypersonic substrate 1 such that their crystal X-axis are parallel. The cut angle of the crystal in the hypersonic substrate 1 is represented by Euler angles (0°, θ2 ± 90°, 90°). In the third embodiment, the changes in resonance or temperature characteristics when the rotation angle θ1 of the crystal in the piezoelectric layer 5 is -59° or 35° are simulated as the rotation angle θ2 of the crystal in the hypersonic substrate 1 varies. In the comparative example, a hypersonic substrate composed of a single layer of crystal, represented by Euler angles (0°, θ2 ± 90°, 90°), is used as the resonator of the piezoelectric layer. Therefore, the rotation angle θ2 in the comparative example corresponds to the rotation angle θ1 in the third embodiment. In the comparative example, the changes in resonance or temperature characteristics when the rotation angle θ2 varies are simulated.

[0086] Figure 17 The horizontal axis of the graph represents the rotation angle of the substrate, θ2, and the vertical axis represents the SAW phase velocity (unit: m / s). In the comparative example, when θ2 = -59°, the SAW velocity is below 3300 m / s. In contrast, the SAW velocity of the third embodiment (θ1 = -59°) increases to above 3400 m / s within the range of -30° ≤ θ2 ≤ 90°.

[0087] Figure 18 The horizontal axis of the graph represents the rotation angle of the substrate, θ2, and the vertical axis represents the electromechanical coupling coefficient (unit: %). The electromechanical coupling coefficient of the comparative example (θ2 = -59°) is approximately 4.0%. In contrast, the electromechanical coupling coefficient of the third embodiment (θ1 = -59°) increases to over 4.5% in the range of -30° ≤ θ2 ≤ 90°, and particularly increases to over 5.0% in the range of -20° ≤ θ2 ≤ 80°.

[0088] Figure 19 The horizontal axis of the graph represents the rotation angle of the substrate, θ2, and the vertical axis represents the Q value (Q). In the comparative example where θ2 = -59°, the Q value is below 1000. In contrast, the Q value of the third embodiment (θ1 = -59°) increases to over 2000 within the range of -30° ≤ θ2 ≤ 90°. Particularly in the range of 0° ≤ θ2 ≤ 60°, the increase in Q value is significant, with the Q value of the third embodiment (θ1 = -59°) exceeding 8500.

[0089] The Q value of the comparative example with θ2 = 35° is below 8000, while the Q value of the third embodiment (θ1 = 35°) increases to around 8500 in the range of 20° ≤ θ2 ≤ 40°. That is, even when θ2 = 35°, at least the Q value is improved.

[0090] Figure 20 The horizontal axis of the graph represents the rotation angle of the substrate θ2, and the vertical axis represents the first-order frequency temperature coefficient (1st TCF). Figure 21 The horizontal axis of the graph represents the rotation angle of the substrate θ2, and the vertical axis represents the second-order frequency temperature coefficient (2nd TCF). Figure 22 The horizontal axis of the graph represents the rotation angle of the substrate θ2, and the vertical axis represents the third-order temperature coefficient (3rd TCF).

[0091] The third-order frequency temperature coefficient of the comparative example at θ2 = -59° is 80 ppt / K. 3 In contrast, the absolute value of the third-order frequency temperature coefficient of the third embodiment (θ1 = -59°) decreases across the entire range of the rotation angle θ2, particularly in the range of -40° ≤ θ2 ≤ 80°, decreasing to 40 ppt / K. 3 The second-order frequency temperature coefficient of the comparative example at θ2 = 35° is -50 ppb / K. 2 In contrast, the absolute value of the second-order frequency temperature coefficient in the third embodiment (θ1 = 35°) decreases to 40 ppb / K in the range of 20° ≤ θ2 ≤ 60°. 2 The following, especially at θ2 = 60°, it decreases to 10 ppb / K. 2 The temperature coefficient of the third frequency of the comparative example at θ2 = 35° is -130 ppt / K. 3 In contrast, the absolute value of the third-order frequency temperature coefficient in the third embodiment (θ1 = 35°) decreases to 120 ppt / K in the range of 20° ≤ θ2 ≤ 60°. 3 The following, especially at θ2 = 60°, decreases to 100 ppt / K. 3 about.

[0092] The exemplary embodiments of the present invention have been described above. According to one aspect of the present invention, a resonator comprises: a piezoelectric layer having a first surface and a second surface facing each other, an IDT electrode disposed on the first surface side of the piezoelectric layer, and a high-velocity acoustic substrate disposed on the second surface side of the piezoelectric layer. The piezoelectric layer is made of crystal with a cut angle obtained by rotating a surface orthogonal to the crystal X-axis about the crystal X-axis. In a propagation direction of 90°±10° relative to the crystal X-axis of the piezoelectric layer, the sound velocity of the high-velocity acoustic substrate is faster than the sound velocity of the piezoelectric layer. The IDT electrode has a comb-shaped electrode having a plurality of electrode fingers arranged in the propagation direction.

[0093] Accordingly, a resonator with superior temperature coefficient of at least the third frequency and Q value compared to a resonator composed of a single-layer piezoelectric layer is provided. Furthermore, by appropriately selecting the rotation angle of the plane of the piezoelectric layer orthogonal to the crystal Y-axis about the crystal X-axis, any one of the electromechanical coupling coefficient, SAW sound velocity, first-order temperature coefficient, and second-order temperature coefficient can be improved.

[0094] According to one aspect of the invention, the piezoelectric layer may also be composed of a crystal with a cut angle obtained by rotating a plane orthogonal to the crystal Y-axis counterclockwise within a range of -59°±10° when viewed from the positive direction of the crystal X-axis.

[0095] Accordingly, a resonator with superior SAW sound velocity and electromechanical coupling coefficient is provided compared to a resonator composed of a single-layer piezoelectric layer.

[0096] According to one aspect of the invention, the piezoelectric layer may also be composed of crystal with a cut angle obtained by rotating the plane orthogonal to the crystal Y-axis counterclockwise within a range of 35°±10° when viewed from the positive direction of the crystal X-axis.

[0097] According to one aspect of the present invention, the piezoelectric layer and the hypersonic substrate can also be directly stacked.

[0098] According to one aspect of the present invention, a low-velocity layer may also be provided between the piezoelectric layer and the high-velocity substrate, wherein the velocity of sound in the low-velocity layer is lower than the velocity of sound in the piezoelectric layer in the propagation direction.

[0099] According to one aspect of the present invention, when the wavelength of the elastic wave, which is determined by the electrode period of the IDT electrode, is set to λ, the thickness of the low-velocity layer can also be set in the range of 0.1λ or more and 0.5λ or less.

[0100] According to one aspect of the present invention, the thickness of the low-velocity layer can also be less than 1 / 100 of the thickness of the high-velocity substrate.

[0101] According to one aspect of the present invention, when the wavelength of the elastic wave determined by the electrode period of the IDT electrode is set to λ, the thickness of the piezoelectric layer may be set in the range of 0.05λ or more and 0.5λ or less.

[0102] According to one aspect of the present invention, the thickness of the piezoelectric layer can also be less than 1 / 100 of the thickness of the hypersonic substrate.

[0103] According to one aspect of the present invention, the sound velocity of the high-velocity substrate can also be more than 20% faster than the sound velocity of the piezoelectric layer in the propagation direction.

[0104] According to one aspect of the present invention, the sound velocity of the high-velocity substrate can also be more than 40% faster than the sound velocity of the piezoelectric layer in the propagation direction.

[0105] According to one aspect of the present invention, the hypersonic substrate may also be composed of any one of silicon, silicon compounds, and aluminum compounds.

[0106] According to one aspect of the present invention, the hypersonic substrate can also be made of silicon single crystal.

[0107] According to one aspect of the invention, the hypersonic substrate may also be made of crystal with a cut angle obtained by rotating the plane orthogonal to the crystal Y-axis counterclockwise in a range of 0° to 60° when viewed from the positive direction of the crystal X-axis, and the piezoelectric layer and the hypersonic substrate are arranged to be parallel to each other on their respective crystal X-axis.

[0108] According to one aspect of the present invention, the IDT electrode may also be made of a metal with aluminum as the main component.

[0109] As explained above, according to one aspect of the present invention, it is possible to provide a resonator with excellent frequency-temperature characteristics or resonance characteristics.

[0110] Furthermore, the embodiments described above are intended to facilitate understanding of the present invention and are not intended to limit the scope of the invention. The present invention can be modified / improved without departing from its spirit, and its equivalents are also included. That is, any embodiment that incorporates the features of the present invention, and whose design modifications are appropriate to those skilled in the art, is also included within the scope of the present invention. For example, the elements, their configurations, materials, conditions, shapes, and dimensions of the embodiments and / or modifications are not limited to the examples and can be appropriately modified. Additionally, the embodiments and modifications are illustrative; naturally, different substitutions or combinations of parts of the structures shown in the embodiments and / or modifications are possible, and these substitutions are also included within the scope of the present invention as long as they incorporate the features of the present invention.

[0111] Explanation of reference numerals in the attached figures

[0112] 1… High-velocity substrate, 3… Low-velocity layer, 5… Piezoelectric layer, 7… IDT electrode, 7b… Electrode finger, 9… Reflector, 10… Resonator, PD… Propagation direction.

Claims

1. A harmonic oscillator, possessing: A piezoelectric layer having a first side and a second side that are opposite to each other; An IDT electrode is disposed on the first surface side of the piezoelectric layer; and A high-velocity acoustic substrate is disposed on the second side of the piezoelectric layer. The aforementioned piezoelectric layer is composed of crystal with a cut angle obtained by rotating a plane orthogonal to the crystal's Y-axis around the crystal's X-axis. In a propagation direction at a crystal X-axis angle of 90° ± 10° relative to the piezoelectric layer, the sound velocity of the high-velocity substrate is faster than that of the piezoelectric layer. The aforementioned IDT electrode has a comb-shaped electrode, which has a plurality of electrode fingers arranged in the aforementioned propagation direction. The aforementioned high-speed acoustic substrate is made of crystal with a cut angle obtained by rotating the plane orthogonal to the crystal Y-axis counterclockwise within a range of 0° to 60° when viewed from the positive direction of the crystal X-axis. The piezoelectric layer and the hypersonic substrate are configured to be parallel to each other's crystal X-axis.

2. The harmonic oscillator according to claim 1, wherein, The piezoelectric layer described above is made of crystal with a cut angle obtained by rotating the plane orthogonal to the Y-axis of the crystal counterclockwise within a range of -59°±10° when viewed from the positive direction of the crystal X-axis.

3. The harmonic oscillator according to claim 1, wherein, The piezoelectric layer described above is made of crystal with a cut angle obtained by rotating the plane orthogonal to the Y-axis of the crystal counterclockwise within a range of 35°±10° when viewed from the positive direction of the crystal X-axis.

4. The harmonic oscillator according to any one of claims 1 to 3, wherein, The piezoelectric layer and the hypersonic substrate are directly stacked.

5. The harmonic oscillator according to any one of claims 1 to 3, wherein, It also has a low-velocity layer disposed between the piezoelectric layer and the high-velocity substrate. In the aforementioned propagation direction, the sound velocity of the low-velocity layer is lower than that of the piezoelectric layer.

6. The harmonic oscillator according to claim 5, wherein, When the wavelength of the elastic wave, determined by the electrode period of the aforementioned IDT electrode, is set as λ, The thickness of the aforementioned low-velocity layer is set in the range of 0.1λ or more and 0.5λ or less.

7. The harmonic oscillator according to claim 5, wherein, The thickness of the aforementioned low-velocity layer is less than 1 / 100 of the thickness of the aforementioned high-velocity substrate.

8. The harmonic oscillator according to any one of claims 1 to 3, wherein, When the wavelength of the elastic wave, determined by the electrode period of the aforementioned IDT electrode, is set as λ, The thickness of the piezoelectric layer is set in the range of 0.05λ or more and 0.5λ or less.

9. The harmonic oscillator according to any one of claims 1 to 3, wherein, The thickness of the piezoelectric layer is less than 1 / 100 of the thickness of the hypersonic substrate.

10. The harmonic oscillator according to any one of claims 1 to 3, wherein, In the aforementioned propagation direction, the sound velocity of the high-velocity substrate is more than 20% faster than the sound velocity of the piezoelectric layer.

11. The harmonic oscillator according to claim 10, wherein, In the aforementioned propagation direction, the sound velocity of the high-velocity substrate is more than 40% faster than that of the piezoelectric layer.

12. The harmonic oscillator according to any one of claims 1 to 3, wherein, The aforementioned hypersonic substrate is composed of any one of silicon, silicon compounds, and aluminum compounds.

13. The harmonic oscillator according to any one of claims 1 to 3, wherein, The aforementioned hypersonic substrate is made of silicon single crystal.

14. The harmonic oscillator according to any one of claims 1 to 3, wherein, The aforementioned IDT electrode is made of a metal with aluminum as the main component.

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