JP2024003636A - Acoustic wave device, filter, multiplexer, and wafer - Google Patents

Abstract

To provide an acoustic wave device capable of reducing the difference in TCF between a resonant frequency and an anti-resonant frequency.SOLUTION: An acoustic wave device includes a support substrate 10, at least a pair of comb-shaped electrodes 20 provided on the support substrate 10 and having a plurality of electrode fingers 18 arranged in the arrangement direction, a piezoelectric layer 14 that is provided on the support substrate 10, has a pair of comb-shaped electrodes 20 on its upper surface, has a linear expansion coefficient in the arrangement direction that is larger than the linear expansion coefficient of the support substrate 10, and has a Young's modulus that is less than or equal to the Young's modulus of the support substrate 10, and an intermediate layer that is provided between the support substrate 10 and the piezoelectric layer 14 and has a linear expansion coefficient that is 3 ppm/°C or more larger than that of the support substrate 10.SELECTED DRAWING: Figure 1

Description

The present invention relates to acoustic wave devices, filters, multiplexers, and wafers.

Acoustic wave elements such as surface acoustic wave resonators are used in communication devices such as smartphones. It is known to bond a piezoelectric layer forming an acoustic wave element to a support substrate (for example, Patent Document 1). It is known that in a surface acoustic wave resonator, the resonant frequency and the anti-resonant frequency have different temperature coefficients of frequency (TCF) (for example, Patent Document 2). It is known that when the stress on the top surface of the piezoelectric layer due to the difference in linear expansion coefficient between the piezoelectric layer and the support substrate increases, the difference between the TCF of the resonant frequency and the TCF of the anti-resonant frequency increases (for example, Patent Document 1).

Japanese Patent Application Publication No. 2005-252550 JP 2017-152868 Publication

S. Inoue and M. Solal, "Layered SAW Resonators with Near-Zero TCF at Both Resonance and Anti-resonance," 2019 IEEE International Ultrasonics Symposium (IUS), 2019, pp. 2079-2082, doi: 10.1109/ULTSYM.2019.8925592 .

There is a need to reduce the difference in TCF between the resonant frequency and the anti-resonant frequency.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce the difference in TCF between the resonant frequency and the anti-resonant frequency.

The present invention provides a supporting substrate, at least a pair of comb-shaped electrodes provided on the supporting substrate and having a plurality of electrode fingers arranged in an arrangement direction, and a pair of comb-shaped electrodes provided on the supporting substrate and having a plurality of comb-shaped electrodes arranged on an upper surface. a piezoelectric layer provided with an electrode, having a linear expansion coefficient greater than that of the support substrate in the arrangement direction and a Young's modulus equal to or less than the Young's modulus of the support substrate, and between the support substrate and the piezoelectric layer; and an intermediate layer having a linear expansion coefficient that is 3 ppm/°C or more larger than the linear expansion coefficient of the supporting substrate.

In the above configuration, the linear expansion coefficient of the intermediate layer may be smaller than the linear expansion coefficient of the piezoelectric layer in the arrangement direction.

In the above configuration, the supporting substrate is a sapphire substrate, a silicon carbide substrate, or a spinel substrate, and the piezoelectric layer is a single crystal rotating Y-cut X-propagating lithium tantalate substrate or a single-crystal rotating Y-cut X-propagating lithium niobate substrate. It is possible to have a certain configuration.

In the above structure, the intermediate layer may be a metal layer.

The present invention provides a supporting substrate that is a sapphire substrate, a silicon carbide substrate, or a spinel substrate, and a single crystal rotating Y-cut X-propagating lithium tantalate substrate or a single-crystal rotating Y-cut X-propagating lithium niobate substrate; a piezoelectric layer provided on the piezoelectric layer; at least a pair of comb-shaped electrodes provided on the piezoelectric layer and including a plurality of electrode fingers; , an intermediate layer containing at least one of cobalt and palladium as a main component.

In the above structure, the thickness of the intermediate layer may be 0.05 times or more and 1 times or less the thickness of the supporting substrate.

In the above structure, the thickness of the piezoelectric layer may be twice or less the average pitch of the plurality of electrode fingers.

In the above structure, an insulating layer may be provided between the intermediate layer and the piezoelectric layer.

The present invention is a filter including the above elastic wave device.

The present invention is a multiplexer including the above filter.

The present invention provides a support substrate, a piezoelectric layer provided on the support substrate and having a coefficient of linear expansion larger than that of the support substrate and a Young's modulus equal to or less than the Young's modulus of the support substrate; The wafer is provided with an intermediate layer provided between the piezoelectric layer and having a coefficient of linear expansion that is 3 ppm/°C or more larger than a coefficient of linear expansion of the support substrate.

According to the present invention, it is possible to reduce the difference in TCF between the resonant frequency and the anti-resonant frequency.

FIG. 1(a) is a plan view of an acoustic wave device according to Example 1, and FIG. 1(b) is a cross-sectional view of the acoustic wave device according to Example 1. FIG. 2 is a cross-sectional view of an acoustic wave device according to Comparative Example 1. FIG. 3 is a diagram showing ΔTCF versus T4/T0 in Experiment 1. FIG. 4 is a diagram showing the normalized stress on the top surface of the piezoelectric layer with respect to the Young's modulus E0 of the support substrate in simulation 1. FIG. 5(a) shows the normalized stress on the top surface of the piezoelectric layer with respect to the thickness ratio T2/T0 in simulation 2, and FIG. 5(b) shows the warpage of the support substrate with respect to the thickness ratio T2/T0. It is a diagram. FIGS. 6A and 6B are cross-sectional views of acoustic wave devices according to Modifications 1 and 2 of Example 1, respectively. FIGS. 7A and 7B are cross-sectional views of acoustic wave devices according to Modifications 3 and 4 of Example 1, respectively. FIG. 8 is a cross-sectional view of an acoustic wave device according to a fifth modification of the first embodiment. 9(a) and 9(b) are a plan view and a cross-sectional view showing a wafer according to a sixth modification of the first embodiment. 10(a) is a circuit diagram of a filter according to a second embodiment, and FIG. 10(b) is a circuit diagram of a duplexer according to a first modification of the second embodiment.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1(a) is a plan view of an acoustic wave device according to Example 1, and FIG. 1(b) is a cross-sectional view of the acoustic wave device according to Example 1. The direction in which the electrode fingers are arranged is the X direction, the direction in which the electrode fingers extend is the Y direction, and the direction in which the supporting substrate and the piezoelectric layer are laminated is the Z direction. The X direction, Y direction, and Z direction do not necessarily correspond to the X-axis direction and Y-axis direction of the crystal orientation of the piezoelectric layer. When the piezoelectric layer is a rotating Y-cut X-propagation substrate, the X direction is the X-axis direction of the crystal orientation.

As shown in FIGS. 1A and 1B, in the acoustic wave device of Example 1, a piezoelectric layer 14 is provided on a support substrate 10. A stress relaxation layer 12 is provided between the support substrate 10 and the piezoelectric layer 14. The thicknesses of support substrate 10, stress relaxation layer 12, and piezoelectric layer 14 are T0, T2, and T4, respectively. An elastic wave resonator 26 is provided on the piezoelectric layer 14. The elastic wave resonator 26 has an IDT 22 and a reflector 24. The reflectors 24 are provided on both sides of the IDT 22 in the X direction. IDT 22 and reflector 24 are formed by metal film 16 provided on piezoelectric layer 14 .

The IDT 22 includes a pair of comb-shaped electrodes 20 facing each other. The comb-shaped electrode 20 includes a plurality of electrode fingers 18 and a bus bar 19 to which the plurality of electrode fingers 18 are connected. The area where the electrode fingers 18 of the pair of comb-shaped electrodes 20 intersect is the intersection area 25 when viewed from the X direction. The length of the crossing region 25 is the opening length. In the pair of comb-shaped electrodes 20, electrode fingers 18 are alternately provided in at least a portion of the crossing region 25. The elastic waves mainly excited by the plurality of electrode fingers 18 in the intersection region 25 propagate mainly in the X direction. The pitch of the electrode fingers 18 of one of the pair of comb-shaped electrodes 20 is approximately equal to the wavelength λ of the elastic wave. If the pitch of the plurality of electrode fingers 18 (the pitch between the centers of the electrode fingers 18) is D, then the pitch of the electrode fingers 18 of one comb-shaped electrode 20 is equal to the pitch D of two electrode fingers 18. The reflector 24 reflects the elastic waves (surface acoustic waves) excited by the electrode fingers 18 of the IDT 22 . As a result, the elastic waves are confined within the intersection area 25 of the IDT 22.

The piezoelectric layer 14 is, for example, a single-crystal lithium tantalate (LiTaO ₃ ) substrate or a single-crystal lithium niobate (LiNbO ₃ ) substrate, such as a rotating Y-cut X-propagating lithium tantalate substrate or a rotating Y-cut X-propagating lithium niobate substrate. It is. When the elastic waves mainly excited by the pair of comb-shaped electrodes 20 are SH (shear horizontal) waves, the piezoelectric layer 14 is a Y-cut, X-propagating lithium tantalate substrate rotated by 36° or more and 50° or less. The thickness T4 of the piezoelectric layer 14 is preferably 1λ or less, more preferably 0.5λ or less, from the viewpoint of suppressing spurious and loss. If the piezoelectric layer 14 becomes too thin, it becomes difficult to excite elastic waves, so the thickness T4 is preferably 0.1λ or more.

Support substrate 10 is, for example, a sapphire substrate, a spinel substrate, or a silicon carbide substrate. The sapphire substrate is a single crystal Al ₂ O ₃ substrate, the spinel substrate is a polycrystalline or amorphous MgAl ₂ O ₄ substrate, and the silicon carbide substrate is a polycrystalline or single crystal SiC substrate. The linear expansion coefficient of the support substrate 10 in the X direction is smaller than that of the piezoelectric layer 14 in the X direction. Thereby, the TCF of the elastic wave resonator can be reduced. Further, the Young's modulus of the support substrate 10 is larger than that of the piezoelectric layer 14. Thereby, the support substrate 10 functions as a substrate that supports the piezoelectric layer 14, and its strength can be increased.

The stress relaxation layer 12 is, for example, a metal layer such as a copper layer, a nickel layer, an iron layer, a gold layer, a cobalt layer, or a palladium layer. The coefficient of linear expansion of the stress relaxation layer 12 is smaller than the coefficient of linear expansion in the X direction of the piezoelectric layer 14 and larger than the coefficient of linear expansion of the support substrate 10. Thereby, the difference between the TCF of the resonant frequency and the TCF of the anti-resonant frequency can be reduced.

[Comparative example 1]
FIG. 2 is a cross-sectional view of an acoustic wave device according to Comparative Example 1. As shown in FIG. 2, in Comparative Example 1, the stress relaxation layer 12 is not provided between the support substrate 10 and the piezoelectric layer 14. The other configurations are the same as in the first embodiment.

[experiment]
The relationship between the difference ΔTCF between TCF@fr at the resonant frequency fr and TCF@fa at the anti-resonant frequency fa in Comparative Example 1 and the thickness of the piezoelectric layer 14 was investigated. The experimental conditions are as follows.
Support substrate 10: Single crystal sapphire substrate with a thickness T0 of 125 μm to 148.7 μm Piezoelectric layer 14: 42° rotated Y cut X propagation lithium tantalate substrate with a thickness T4 of 1.3 μm to 25 μm 2 of the pitch of the electrode fingers 18 Double λ: approximately 4 μm
T0+T4 is constant at 150 μm.

FIG. 3 is a diagram showing ΔTCF versus T4/T0 in Experiment 1. Dots indicate measurement points, and straight lines indicate approximate straight lines. As shown in FIG. 3, when the ratio T4/T0 of the thickness T4 of the piezoelectric layer 14 to the thickness T0 of the support substrate 10 increases, ΔTCF decreases. This is thought to be because, as described in Non-Patent Document 1, as the thickness T4 increases, the stress on the upper surface of the piezoelectric layer 14 due to the linear expansion coefficient of the support substrate 10 and the piezoelectric layer 14 decreases. It will be done.

[Simulation 1]
In Comparative Example 1, the Young's modulus of the support substrate 10 was changed, and thermal stress on the upper surface of the piezoelectric layer 14 was simulated using a two-dimensional finite element method. The simulation conditions are as follows.
Support substrate 10
Thickness T0: 100μm
Linear expansion coefficient α0: 7ppm/℃
Young's modulus: E0
Piezoelectric layer 14:
Material: 42° rotation Y cut X propagation lithium tantalate substrate Thickness T4: 3μm
X-axis linear expansion coefficient α4x: 16.1 ppm/°C
Z-axis linear expansion coefficient α4z: 10.7ppm/℃
Young's modulus E4: 230GPa
No electrode finger 18 Width: 1000 μm
Temperature difference: 60℃

FIG. 4 is a diagram showing the normalized stress on the upper surface of the piezoelectric layer 14 with respect to the Young's modulus E0 of the support substrate 10 in simulation 1. Dots indicate measurement points. The vertical axis is the normalized stress normalized by the stress on the top surface of the piezoelectric layer 14 when E0=470 GPa. The stress is negative. This indicates that the stress is compressive stress. As shown in FIG. 4, when the Young's modulus E0 of the supporting substrate 10 is 200 GPa or more, the stress on the upper surface of the piezoelectric layer 14 remains almost unchanged at −1. When Young's modulus E0 becomes smaller than 200 GPa, the absolute value of stress becomes smaller. As described above, when the Young's modulus E0 of the support substrate 10 is large, the stress on the surface of the piezoelectric layer 14 becomes large, and ΔTCF becomes large.

The problems of the above comparative example 1 are summarized. By providing the supporting substrate 10 having a coefficient of linear expansion smaller than the linear expansion coefficient α4x of the piezoelectric layer 14 in the X direction (the direction in which the electrode fingers 18 are arranged), linear expansion on the upper surface of the piezoelectric layer 14 when the temperature changes can be reduced. Can be made smaller. This allows the TCF to be reduced. However, as the thickness T4 of the piezoelectric layer 14 becomes smaller, the thermal stress on the upper surface of the piezoelectric layer 14 becomes larger. This increases ΔTCF. As ΔTCF increases, it becomes difficult to reduce both TCF@Tr at the resonant frequency and TCF@fa at the anti-resonant frequency. The support substrate 10 has a Young's modulus greater than or equal to the Young's modulus of the piezoelectric layer 14 because of its function of supporting the piezoelectric layer 14 . Therefore, as shown in FIG. 4, the stress on the upper surface of the piezoelectric layer 14 increases. Therefore, ΔTCF increases. For example, in a ladder filter, the high frequency end of the passband is formed by the anti-resonant frequency of the series resonator, and the low frequency end of the passband is formed by the resonant frequency of the parallel resonator. For this reason, when ΔTCF is large, the temperature characteristics of the passband deteriorate. Therefore, an elastic wave device with a small ΔTCF is required.

[Simulation 2]
Therefore, in Example 1, the ratio T2/T0 of the thickness T2 of the stress relaxation layer 12 to the thickness T0 of the support substrate 10 and the difference between the linear expansion coefficient α2 of the stress relaxation layer 12 and the linear expansion coefficient α0 of the support substrate 10 are The stress on the upper surface of the piezoelectric layer 14 and the warpage of the support substrate 10 were simulated using the two-dimensional finite element method by changing Δα=α2−α0. The simulation conditions are as follows.
Support substrate 10
Thickness T0: 100μm
Linear expansion coefficient α0: 7ppm/℃
Young's modulus E0: 470GPa
Stress relaxation layer 12
Thickness T2: 0μm to 50μm
Linear expansion coefficient α2: 2ppm/°C to 22ppm/°C
Young's modulus E2: 200GPa
Piezoelectric layer 14:
Material: 42° rotation Y cut X propagation lithium tantalate substrate Thickness T4: 0.5 μm
Linear expansion coefficient α4x in the X-axis direction: 16.1 ppm/°C
Linear expansion coefficient α4z in Z-axis direction: 10.7 ppm/°C
Young's modulus E4: 230GPa
No electrode finger 18 Width: 1000 μm
Temperature difference: 60℃
α0 is fixed at 7 ppm/°C, and α2 is varied.

FIG. 5(a) is a diagram showing the normalized stress on the top surface of the piezoelectric layer with respect to the thickness ratio T2/T0 in simulation 2, and FIG. 5(b) is a diagram showing the warpage of the support substrate with respect to the thickness ratio T2/T0. It is. Δα is α2−α0. The normalized stress is the stress on the upper surface of the piezoelectric layer 14 normalized by the stress when the stress relaxation layer 12 is not provided. The normalized stress is negative. This indicates compressive stress. The warpage is the difference between the maximum value and the minimum value based on the least squares plane of a chip having a width of 1000 μm.

As shown in FIG. 5(a), when Δα=0, the normalized stress remains -1 even if the thickness ratio T2/T0 changes. When Δα is positive, as the thickness ratio T2/T0 increases, the normalized stress changes from −1 to the positive side. At Δα=+15 ppm/° C., the normalized stress becomes 0 when the thickness ratio T2/T0 is around 0.43. When Δα is +10 ppm/°C, the normalized stress becomes more negative than when α is +15 ppm/°C. When Δα is +5 ppm/°C, the normalized stress is between when Δα is +10 ppm/°C and when Δα is 0. When Δα becomes negative, the absolute value of the normalized stress increases. From the above, in order to bring the normalized stress close to 0, it is preferable to increase Δα positively and increase the thickness ratio T2/T0.

As shown in FIG. 5(b), when Δα=0, the warpage is 0 and does not change even if the thickness ratio T2/T0 changes. When Δα is positive, the warpage increases as the thickness ratio T2/T0 increases. As Δα increases, the warpage at the same thickness ratio T2/T0 increases. When Δα is negative, the warpage increases as the thickness ratio T2/T0 increases. The warpage is about the same when Δα=+5 ppm/°C and when Δα=−5 ppm/°C. From the above, when the absolute value of Δα is increased and the thickness ratio T2/T0 is increased, the warpage increases. If the warpage increases, problems arise, such as the wafer not being able to be picked up in manufacturing equipment, for example. From the viewpoint of warpage, it is preferable that the absolute value of Δα is small and the thickness ratio T2/T0 is small.

According to the first embodiment, the linear expansion coefficient α0 of the support substrate 10 is made smaller than the linear expansion coefficient α4x of the piezoelectric layer 14 in the X direction (the arrangement method in which the electrode fingers 18 are arranged). As a result, the temperature dependence of the pitch D of the electrode fingers 18 on the upper surface of the piezoelectric layer 14 becomes smaller, and the absolute value of TCF becomes smaller. Further, the Young's modulus E0 of the support substrate 10 is set to be equal to or higher than the Young's modulus E4 of the piezoelectric layer 14. Thereby, the support substrate 10 can better exhibit the function of supporting the piezoelectric layer 14. For example, if the Young's modulus of the support substrate 10 is small, the warpage of the support substrate 10 due to thermal stress between the support substrate 10 and the piezoelectric layer 14 will increase. By setting the Young's modulus E0 to be equal to or greater than E4, warping of the support substrate 10 due to thermal stress can be suppressed. However, on the upper surface of the piezoelectric layer 14, thermal stress due to the difference in linear expansion coefficient between the support substrate 10 and the piezoelectric layer 14 increases. In particular, when the Young's modulus of the support substrate 10 is greater than or equal to the Young's modulus of the piezoelectric layer 14, the thermal stress on the upper surface of the piezoelectric layer 14 is large, as shown in FIG. Therefore, ΔTCF increases. Therefore, a stress relaxation layer 12 (intermediate layer) is provided between the support substrate 10 and the piezoelectric layer 14. The linear expansion coefficient α2 of the stress relaxation layer 12 is made larger than the linear expansion coefficient α0 of the supporting substrate 10 by 3 ppm/°C or more. That is, the linear expansion coefficient α2 is larger than α0, and the difference between α2 and α0 is 3 ppm/°C or more. This reduces the thermal stress on the upper surface of the piezoelectric layer 14, as shown in FIG. 5(a). Therefore, ΔTCF can be reduced.

From the viewpoint of reducing the absolute value of TCF, the linear expansion coefficient α0 of the support substrate 10 is preferably 2/3 or less, more preferably 1/2 or less, of the linear expansion coefficient α4x of the piezoelectric layer 14 in the X direction. The difference between the linear expansion coefficients α0 and α4x is preferably 5 ppm/°C or more, more preferably 10 ppm/°C or more. From the viewpoint of the support substrate 10 supporting the piezoelectric layer 14, the Young's modulus E0 of the support substrate 10 is preferably 1.2 times or more, more preferably 1.5 times or more, the Young's modulus E4 of the piezoelectric layer 14. The difference between Young's modulus E0 and E4 is preferably 50 GPa or more, more preferably 100 GPa or more. The Young's modulus E0 is preferably 200 GPa or more, more preferably 300 GPa or more, and even more preferably 400 GPa or more.

From the viewpoint of reducing stress on the upper surface of the piezoelectric layer 14, it is preferable that the linear expansion coefficient α2 of the stress relaxation layer 12 is larger than the linear expansion coefficient α0 of the support substrate 10 by 5 ppm/°C or more. Further, the linear expansion coefficient α2 of the stress relaxation layer 12 is preferably 1.2 times or more, more preferably 1.5 times or more, and even more preferably 2 times or more the linear expansion coefficient α0 of the support substrate 10. If the linear expansion coefficient α2 of the stress relaxation layer 12 is too large, the temperature dependence of the pitch D of the electrode fingers 18 on the upper surface of the piezoelectric layer 14 becomes large, and the absolute value of TCF becomes large. From this point of view, it is preferable that the linear expansion coefficient α2 of the stress relaxation layer 12 is smaller than the linear expansion coefficient α4x of the piezoelectric layer 14 in the X direction. The linear expansion coefficient α2 is more preferably 0.9 times or less of α4x. The linear expansion coefficient α2 is preferably smaller than α4 by 1 ppm/°C or more, more preferably 2 ppm/°C or more smaller.

As shown in FIG. 5A, in order to reduce the stress on the upper surface of the piezoelectric layer 14, the thickness T2 of the stress relaxation layer 12 is preferably 0.05 times or more the thickness T0 of the support substrate 10, and 0.05 times or more. More preferably, it is 1 times or more. As shown in FIG. 5(b), from the viewpoint of reducing warpage of the support substrate 10, the thickness T2 of the stress relaxation layer 12 is preferably 0.5 times or less, and 0.3 times or less, the thickness T0 of the support substrate 10. is more preferable. The thickness T0 of the supporting substrate 10 is, for example, 50 μm to 200 μm, and the thickness T2 of the stress relaxation layer 12 is, for example, 0.5 μm to 100 μm.

In order to suppress spurious noise and loss, the thickness T4 of the piezoelectric layer 14 is set to be equal to or less than twice the average pitch D of the plurality of electrode fingers 18. In this case, ΔTCF becomes large as shown in FIG. Therefore, it is preferable to provide the stress relaxation layer 12. The thickness T4 of the piezoelectric layer 14 is more preferably 1.6 times or less, and even more preferably 1.2 times or less, the average pitch D of the plurality of electrode fingers 18. From the viewpoint of exciting surface acoustic waves in the piezoelectric layer 14, the thickness T4 of the piezoelectric layer 14 is preferably 0.1 times or more, and more preferably 0.2 times or more, the average pitch D of the plurality of electrode fingers 18. The average pitch D of the electrode fingers 18 can be calculated by dividing the length of the intersection region 25 in the X direction by the number of electrode fingers 18.

Table 1 is a table showing examples of each member.

As shown in Table 1, when a single-crystal rotating Y-cut, X-propagating lithium tantalate substrate or a single-crystal rotating Y-cut, The coefficient of linear expansion is 16.1 ppm/°C or 15.4 ppm/°C. Materials for the support substrate 10 having a coefficient of linear expansion smaller than that of the piezoelectric layer 14 include a sapphire substrate, a silicon carbide substrate, a spinel substrate, a quartz substrate, an alumina substrate, and a silicon substrate. The supporting substrate 10 having a higher Young's modulus than the piezoelectric layer 14 is a sapphire substrate, a silicon carbide substrate, or a spinel substrate.

A material with a coefficient of linear expansion 3 ppm/℃ or more greater than that of a sapphire substrate, silicon carbide substrate, or spinel substrate, and a coefficient of linear expansion smaller than that of a rotating Y-cut X-propagating lithium tantalate substrate or a rotating Y-cut X-propagating lithium niobate substrate is When used as the relaxation layer 12, the stress relaxation layer 12 is, for example, a copper layer, a nickel layer, an iron layer, a gold layer, a cobalt layer, or a palladium layer, and includes at least one metal element of copper, nickel, iron, gold, cobalt, and palladium. It is an alloy whose main component is Note that a layer containing a certain element as its main component means that it may contain impurities either intentionally or unintentionally, and the concentration of a certain element in a layer is, for example, 50 atomic % or more, and 80 atomic % or more. Yes, it is 90 atomic % or more. As the stress relaxation layer 12, lithium tantalate or lithium niobate may be used. For example, by appropriately selecting the crystal orientation of lithium tantalate or lithium niobate, the linear expansion coefficient α2 of the stress relaxation layer 12 in the X direction is greater than the linear expansion coefficient α0 of the supporting substrate 10 in the X direction by 3 ppm/°C or more, and It may be made smaller than the linear expansion coefficient α4x of the piezoelectric layer 14 in the X direction.

[Modification 1 of Example 1]
FIG. 6A is a cross-sectional view of an acoustic wave device according to Modification 1 of Example 1. As shown in FIG. 6A, in the first modification of the first embodiment, an insulating layer 13 is provided between the stress relaxation layer 12 and the piezoelectric layer 14. The insulating layer 13 is, for example, a silicon oxide layer, an aluminum nitride layer, an aluminum oxide layer, an aluminum nitride layer, or a stacked layer thereof. The other configurations are the same as those in Example 1, and their explanation will be omitted.

When the stress relaxation layer 12 is a metal layer, current leakage can be suppressed through the stress relaxation layer 12 by providing the insulating layer 13. In addition, when the stress relaxation layer 12 is a dielectric material with a high dielectric constant (for example, lithium tantalate or lithium niobate, and the X direction is other than the X-axis direction), the dielectric constant of the insulating layer 13 is By making it smaller than the ratio, parasitic capacitance can be suppressed and dielectric loss can be suppressed.

The insulating layer 13 is, for example, a temperature compensation film. In this case, the sign of the temperature coefficient of the elastic constant of the insulating layer 13 is opposite to the sign of the elastic constant of the piezoelectric layer 14. By providing the insulating layer 13 as a temperature compensation film, TCF can be suppressed. When the insulating layer 13 is used as a temperature compensation film, the insulating layer 13 is a silicon oxide layer containing silicon oxide as a main component or a silicon oxide layer containing fluorine or the like. The total thickness T3+T4 of the piezoelectric layer 14 and the insulating layer 13 is, for example, four times or less, and three times or less, the average pitch D of the electrode fingers 18.

The insulating layer 13 is, for example, a high sonic film. In this case, the bulk sound velocity of the insulating layer 13 is faster than the bulk sound velocity of the piezoelectric layer 14 . Thereby, elastic waves can be confined within the piezoelectric layer 14. Further, when the sound velocity of the bulk of the stress relaxation layer 12 is lower than the sound velocity of the bulk of the piezoelectric layer 14, elastic waves are likely to propagate to the stress relaxation layer 12. Therefore, by providing the insulating layer 13 as a high sound velocity film, the elastic waves can be confined in the piezoelectric layer 14. When the insulating layer 13 is made of a high sonic velocity film, the insulating layer 13 is, for example, an aluminum oxide film or an aluminum nitride oxide film.

[Modification 2 of Example 1]
FIG. 6(b) is a cross-sectional view of an acoustic wave device according to a second modification of the first embodiment. As shown in FIG. 6(b), in the second modification of the first embodiment, as the insulating layer 13, an insulating layer 13a is provided on the stress relaxation layer 12, and an insulating layer 13b is provided on the insulating layer 13a. . The insulating layer 13a is, for example, a high sonic film, and is an aluminum oxide film or an aluminum nitride oxide film. The insulating layer 13b is, for example, a temperature compensation film, and is a silicon oxide film. The other configurations are the same as Modification 1 of Embodiment 1, and the explanation will be omitted.

As in Modifications 1 and 2 of Example 1, an insulating layer 13 may be provided between the stress relaxation layer 12 and the piezoelectric layer 14. If the thickness T3 of the insulating layer 13 is large, the ability of the stress relaxation layer 12 to relieve the stress on the upper surface of the piezoelectric layer 14 is reduced. From this viewpoint, the thickness T3 of the insulating layer 13 is preferably equal to or less than the thickness T2 of the stress relaxation layer 12, more preferably equal to or less than 1/2 of the thickness T2, and even more preferably equal to or less than 1/10.

[Modification 3 of Example 1]
FIG. 7A is a cross-sectional view of an acoustic wave device according to Modification Example 3 of Example 1. As shown in FIG. 7A, in the third modification of the first embodiment, the interface 30 between the support substrate 10 and the stress relaxation layer 12 is a rough surface. The other configurations are the same as those in Example 1, and their explanation will be omitted.

[Modification 4 of Example 1]
FIG. 7(b) is a cross-sectional view of an acoustic wave device according to a fourth modification of the first embodiment. As shown in FIG. 7B, in the fourth modification of the first embodiment, the interface 32 between the stress relaxation layer 12 and the insulating layer 13 is a rough surface. The other configurations are the same as Modification 1 of Embodiment 1, and the explanation will be omitted.

[Modification 5 of Example 1]
FIG. 8 is a cross-sectional view of an acoustic wave device according to a fifth modification of the first embodiment. As shown in FIG. 8, in the fifth modification of the first embodiment, the insulating layer 13 includes insulating layers 13a and 13b. The interface 30 between the support substrate 10 and the stress relaxation layer 12 and the interface 32 between the stress relaxation layer 12 and the insulating layer 13 are both rough surfaces. The other configurations are the same as Modification 2 of Embodiment 1, and their explanation will be omitted.

As in Modifications 3 to 5 of Example 1, the interface 30 between the support substrate 10 and the stress relaxation layer 12 and/or the interface 32 between the stress relaxation layer 12 and the insulating layer 13 may have a rough surface. As a result, unnecessary waves are scattered at the interfaces 30 and 32, so spurious waves caused by unnecessary waves can be suppressed. As in Example 1 and Modifications 1 and 2 thereof, the interface 30 and/or 32 may be a flat surface. When the interfaces 30 and 32 are rough surfaces, the arithmetic mean roughness Ra of the interfaces 30 and 32 is, for example, 0.1 μm or more. When the interfaces 30 and 32 are flat surfaces, the arithmetic mean roughness Ra of the interfaces 30 and 32 is, for example, 0.01 μm or less.

Although a surface acoustic wave (SAW) device has been mainly described as an example of an acoustic wave device, the acoustic wave device may be a bulk acoustic wave (BAW) device or a lamb wave device.

[Modification 6 of Example 1]
9(a) and 9(b) are a plan view and a cross-sectional view showing a wafer according to a sixth modification of the first embodiment. As shown in FIG. 9(a), the planar shape of the wafer 35 is approximately circular, and an orientation flat indicating the crystal orientation is provided. As shown in FIG. 9(b), the cross section of the wafer is the same as FIG. 1(b) of Example 1, except that no acoustic wave resonator is provided on the piezoelectric layer 14. By forming the metal film 16 such as the IDT 22 and the reflector 24 on the piezoelectric layer 14 of the wafer of the sixth modification of the first embodiment, an acoustic wave resonator is formed on the wafer 35. Thereafter, by cutting the wafer 35, the acoustic wave device of Example 1 can be manufactured. The other configurations are the same as those in Example 1, and their explanation will be omitted. The wafer may be a wafer corresponding to Modifications 1 to 5 of the first embodiment.

FIG. 10(a) is a circuit diagram of a filter according to the second embodiment. As shown in FIG. 10(a), one or more series resonators S1 to S3 are connected in series between the input terminal Tin and the output terminal Tout. One or more parallel resonators P1 and P2 are connected in parallel between the input terminal Tin and the output terminal Tout. The elastic wave resonator of Example 1 and its modifications can be used for at least one of the one or more series resonators S1 to S3 and the one or more parallel resonators P1 and P2. The number of resonators of the ladder filter can be set as appropriate. The filter may be a multimode filter having two or more pairs of comb-shaped electrodes.

In the ladder filter, the high frequency end of the passband is mainly formed by the anti-resonant frequencies of the series resonators S1 to S3, and the low frequency end of the passband is mainly formed by the parallel resonators P1 and P2. Therefore, by using the series resonators S1 to S3 and the parallel resonators P1 and P2 as the elastic wave resonators of the first embodiment and its modified examples, it is possible to suppress changes in passband characteristics due to temperature changes.

[Modification 1 of Example 2]
FIG. 10(b) is a circuit diagram of a duplexer according to a first modification of the second embodiment. As shown in FIG. 10(b), a transmission filter 40 is connected between the common terminal Ant and the transmission terminal Tx. A reception filter 42 is connected between the common terminal Ant and the reception terminal Rx. The transmission filter 40 passes a signal in the transmission band among the high frequency signals inputted from the transmission terminal Tx to the common terminal Ant as a transmission signal, and suppresses signals of other frequencies. The reception filter 42 passes a signal in the reception band among the high-frequency signals inputted from the common terminal Ant to the reception terminal Rx as a reception signal, and suppresses signals at other frequencies. At least one of the transmission filter 40 and the reception filter 42 can be the filter of the second embodiment.

Although a duplexer has been described as an example of a multiplexer, a triplexer or a quadplexer may also be used.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and variations can be made within the scope of the gist of the present invention as described in the claims. Changes are possible.

10 Support substrate 12 Stress relaxation layer 13, 13a, 13b Insulating layer 14 Piezoelectric layer 16 Metal film 18 Electrode finger 20 Comb-shaped electrode 26 Acoustic wave resonator 30, 32 Interface 40 Transmission filter 42 Reception filter

Claims (11)

a support substrate;
at least a pair of comb-shaped electrodes provided on the support substrate and including a plurality of electrode fingers arranged in the arrangement direction;
provided on the support substrate, the pair of comb-shaped electrodes are provided on the upper surface, the coefficient of linear expansion in the arrangement direction is greater than the coefficient of linear expansion of the support substrate, and the Young's modulus is equal to or less than the Young's modulus of the support substrate. a piezoelectric layer;
an intermediate layer provided between the support substrate and the piezoelectric layer and having a linear expansion coefficient that is 3 ppm/°C or more larger than the linear expansion coefficient of the support substrate;
An elastic wave device equipped with The acoustic wave device according to claim 1, wherein the linear expansion coefficient of the intermediate layer is smaller than the linear expansion coefficient of the piezoelectric layer in the arrangement direction. The supporting substrate is a sapphire substrate, a silicon carbide substrate, or a spinel substrate,
3. The acoustic wave device according to claim 1, wherein the piezoelectric layer is a single-crystal rotating Y-cut, X-propagating lithium tantalate substrate or a single-crystal rotating Y-cut, X-propagating lithium niobate substrate. The acoustic wave device according to claim 1 or 2, wherein the intermediate layer is a metal layer. a support substrate which is a sapphire substrate, a silicon carbide substrate or a spinel substrate;
a single crystal rotating Y-cut X-propagating lithium tantalate substrate or a single-crystal rotating Y-cut X-propagating lithium niobate substrate, a piezoelectric layer provided on the support substrate;
at least a pair of comb-shaped electrodes provided on the piezoelectric layer and including a plurality of electrode fingers;
an intermediate layer provided between the support substrate and the piezoelectric layer and containing at least one of copper, nickel, iron, gold, cobalt, and palladium as a main component;
An elastic wave device equipped with 6. The acoustic wave device according to claim 1, wherein the thickness of the intermediate layer is 0.05 times or more and 1 times or less the thickness of the support substrate. The acoustic wave device according to any one of claims 1, 2 and 5, wherein the thickness of the piezoelectric layer is twice or less the average pitch of the plurality of electrode fingers. The acoustic wave device according to claim 1 , further comprising an insulating layer between the intermediate layer and the piezoelectric layer. A filter comprising the elastic wave device according to any one of claims 1, 2 and 5. A multiplexer comprising a filter according to claim 9. a support substrate;
a piezoelectric layer provided on the support substrate, having a linear expansion coefficient greater than that of the support substrate and a Young's modulus less than or equal to the Young's modulus of the support substrate;
an intermediate layer provided between the support substrate and the piezoelectric layer and having a linear expansion coefficient that is 3 ppm/°C or more larger than the linear expansion coefficient of the support substrate;
A wafer comprising:

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