JP2025103590A - Acoustic wave device and module using the same - Google Patents

Abstract

[Problem] To provide an acoustic wave device and a module using the acoustic wave device, which suppresses transverse mode spurious and high frequency spurious while reducing the number of processes after forming a resonator and reducing damage to the resonator due to the processes. [Solution] An acoustic wave device comprising a piezoelectric substrate, a resonator formed on a main surface of the piezoelectric substrate, a spurious absorption layer formed on the other main surface of the piezoelectric substrate, and a high acoustic velocity film layer formed between the piezoelectric substrate and the spurious absorption layer, the spurious absorption layer being made of a tetragonal crystal substrate and having a slower acoustic velocity than the piezoelectric substrate. [Selected Figure] Figure 2

Description

This disclosure relates to an acoustic wave device and a module using the acoustic wave device. In particular, this disclosure relates to a surface acoustic wave device using SH waves, such as a filter, a duplexer, or a multiplexer.

In high-frequency communication systems for mobile communication terminals, such as smartphones, high-frequency filters are used to remove unnecessary signals outside the frequency band used for communication.

High frequency filters and the like use acoustic wave devices that have surface acoustic wave (SAW) elements. A SAW element is an element in which an IDT (Interdigital Transducer) with a pair of comb-shaped electrodes is formed on a piezoelectric substrate.

For example, a surface acoustic wave device is manufactured as follows. First, a multilayer film substrate is created by bonding a piezoelectric substrate that propagates acoustic waves to a support substrate that has a smaller thermal expansion coefficient than the piezoelectric substrate. Next, multiple IDT electrodes are formed on the multilayer film substrate using photolithography technology, and then the substrate is cut to a specified size by dicing to create a surface acoustic wave device. In this manufacturing method, by using a multilayer film substrate, changes in size of the piezoelectric substrate when the temperature changes are suppressed by the support substrate, stabilizing the frequency characteristics of the acoustic wave device.

For example, in Patent Document 1 and other publications, it is known that in order to suppress transverse mode spurious emissions in acoustic wave devices, grooves are formed in the intersection regions of the electrode fingers, and additional films are formed, thereby varying the sound speed transversely relative to the propagation direction of the surface acoustic wave, thereby suppressing transverse mode spurious emissions.

JP 2019-50544 A

As disclosed in Patent Document 1, forming grooves in the intersection regions of the electrode fingers and forming additional films to suppress transverse mode spurious in acoustic wave devices makes the process complicated. In particular, the process of forming these after forming the resonator causes damage to the resonator and accelerates the deterioration of the filter characteristics.

The present disclosure has been made to solve the above-mentioned problems. The purpose of the present disclosure is to provide an acoustic wave device and a module using the acoustic wave device in which transverse mode spurious and high frequency spurious are suppressed while reducing the number of processes after the formation of the resonator and reducing damage to the resonator due to the processes.

The acoustic wave device according to the present disclosure comprises:
A piezoelectric substrate;
a resonator formed on a main surface of the piezoelectric substrate and a spurious absorption layer formed on another main surface of the piezoelectric substrate;
a high acoustic velocity film layer having an acoustic velocity faster than that of the piezoelectric substrate, the high acoustic velocity film layer being formed between the piezoelectric substrate and the spurious absorption layer;
The spurious absorption layer is an acoustic wave device made of a tetragonal crystal substrate, and has a slower acoustic velocity than the piezoelectric substrate.

One aspect of the present disclosure is to have a temperature characteristic improving layer formed between the piezoelectric substrate and the spurious absorption layer.

In one embodiment of the present disclosure, the thickness of the spurious absorption layer is 3λ or more and 20λ or less, where λ is the wavelength of the wave of the main mode excited by the resonator, and a support substrate is provided on the main surface of the spurious absorption layer opposite the piezoelectric substrate.

It is one aspect of the present disclosure that the thickness of the high acoustic velocity film layer is smaller than the thickness of the piezoelectric substrate.

It is one aspect of the present disclosure that the thickness of the high acoustic velocity film layer is smaller than the thickness of the temperature characteristic improving layer.

In one embodiment of the present disclosure, the thickness of the high acoustic velocity film layer is 0.1λ or more and 0.3λ or less, where λ is the wavelength of the wave of the main mode excited by the resonator.

It is one aspect of the present disclosure that the spurious absorption layer has a lower crystal density than the piezoelectric substrate.

In one aspect of the present disclosure, the spurious absorption layer is a Li ₂ B ₄ O ₇ single crystal substrate.

In one aspect of the present disclosure, the support substrate is a substrate made of sapphire, silicon, alumina, or spinel.

The cut angle of the principal surface of the spurious absorption layer is such that the Euler angles (φ, θ, ψ) are:
φ=0°±2° or 90°±2°,
θ=90°±2°,
It is one aspect of the present disclosure that ψ=80° to 100°.

A module including the above-described acoustic wave device is one aspect of the present invention.

According to the present disclosure, it is possible to provide an acoustic wave device and a module using the acoustic wave device in which transverse mode spurious and high frequency spurious are suppressed while reducing the number of processes after the formation of the resonator and reducing damage to the resonator due to the processes.

FIG. 1 is a cross-sectional view of an acoustic wave device 1 according to a first embodiment. FIG. 2 is a cross-sectional view showing the device chip 5 of the acoustic wave device 1 according to the first embodiment. FIG. 3 is a cross-sectional view showing another example of the device chip 5 of the acoustic wave device 1 according to the first embodiment. FIG. 4 is a top view of the functional element 50 of the acoustic wave device 1 according to the first embodiment. FIG. 5 is a diagram showing the resonance characteristics of the resonator of the acoustic wave device 1 according to the first embodiment. FIG. 6 is an enlarged view of the resonance characteristics of the acoustic wave device 1 shown in region R in FIG. FIG. 7 is a diagram illustrating the resonance characteristics of the resonator of the acoustic wave device 1 according to the first embodiment. FIG. 8 is a diagram illustrating the resonance characteristics of the resonator of the acoustic wave device 1 according to the first embodiment. FIG. 9 is a diagram illustrating the resonance characteristics of a resonator as a comparative example of the acoustic wave device 1 according to the first embodiment. FIG. 10 is a cross-sectional view showing the device chip 5 of the acoustic wave device 1 according to the second embodiment. FIG. 11 is a diagram illustrating the resonance characteristics of the resonator of the acoustic wave device 1 according to the second embodiment. FIG. 12 is an enlarged view of the resonance characteristics of the acoustic wave device 1 shown in region R2 of FIG. FIG. 13 is a vertical cross-sectional view of a module to which the acoustic wave device 1 according to the first or second embodiment is applied.

The embodiment will be described with reference to the attached drawings. In each drawing, the same or corresponding parts are given the same reference numerals. Duplicate explanations of the parts will be appropriately simplified or omitted.

Embodiment 1.
FIG. 1 is a cross-sectional view of an acoustic wave device 1 according to a first embodiment.

As shown in FIG. 1, the acoustic wave device 1 includes a package substrate 3, an external connection terminal 31, a device chip 5, electrode pads 9, bumps 15, and a sealing portion 17.

For example, the package substrate 3 is a multi-layer substrate made of resin. For example, the package substrate 3 is a low temperature co-fired ceramics (LTCC) multi-layer substrate made of multiple dielectric layers.

Multiple external connection terminals 31 are formed on the underside of the package substrate 3.

Multiple electrode pads 9 are formed on the main surface of the package substrate 3. For example, the electrode pads 9 are formed of copper or an alloy containing copper. For example, the thickness of the electrode pads 9 is 10 μm to 20 μm.

The bumps 15 are formed on the upper surface of each of the electrode pads 9. For example, the bumps 15 are gold bumps. For example, the height of the bumps 15 is 10 μm to 50 μm.

A gap 16 is formed between the package substrate 3 and the device chip 5.

The device chip 5 is mounted on the package substrate 3 by flip-chip bonding via the bumps 15. The device chip 5 is electrically connected to the multiple electrode pads 9 via the multiple bumps 15.

The device chip 5 is a substrate on which the acoustic wave elements 50 are formed. For example, a transmission filter and a reception filter including a plurality of acoustic wave elements 50, which are mainly resonators, are formed on the main surface of the device chip 5.

The transmit filter is formed so that electrical signals in the desired frequency band can pass through. For example, the transmit filter is a ladder-type filter consisting of multiple series resonators and multiple parallel resonators.

The receiving filter is formed so that electrical signals in the desired frequency band can pass through. For example, the receiving filter is a ladder filter.

The sealing portion 17 is formed so as to cover the device chip 5. For example, the sealing portion 17 is formed of an insulating material such as a synthetic resin. For example, the sealing portion 17 is formed of a metal.

When the sealing portion 17 is formed of a synthetic resin, the synthetic resin is an epoxy resin, a polyimide, or the like. Preferably, the sealing portion 17 is formed of an epoxy resin using a low-temperature curing process.

Figure 2 is a cross-sectional view showing the device chip 5 of the acoustic wave device 1 according to the first embodiment.

As shown in FIG. 2, the device chip 5 includes a piezoelectric substrate 11, a high acoustic velocity film layer 12, and a spurious absorption layer 13. An acoustic wave element 50 is formed on the piezoelectric substrate 11.

The piezoelectric substrate 11 is, for example, a substrate formed of a piezoelectric single crystal such as lithium tantalate, lithium niobate, or quartz. In another example, the piezoelectric substrate 11 is a substrate formed of a piezoelectric ceramic.

The thickness of the piezoelectric substrate 11 can be, for example, 0.1λ to 0.9λ, where λ is the wavelength of the elastic wave determined by the electrode pitch of the IDT electrodes.

The high acoustic velocity film layer 12 is a material with a faster acoustic velocity than the piezoelectric substrate 11. This allows for the trapping of fast acoustic waves and suppression of spurious noise that occurs on the high frequency side. For example, it can be made of SiN. The thickness of the high acoustic velocity film layer 12 can be, for example, 0.1λ to 0.3λ, where λ is the wavelength of the elastic wave determined by the electrode pitch of the IDT electrodes.

The spurious absorption layer 13 can be formed of, for example, a Li ₂ B ₄ O ₇ single crystal substrate. The Li ₂ B ₄ O ₇ single crystal is a tetragonal crystal with a crystal density of 2.44 g/cm ^3. The lithium tantalate single crystal has a crystal density of 7.45 g/cm ^3. The _{Li 2} B ₄ O ₇ single crystal substrate has a lower density than the lithium tantalate single crystal substrate, but the sound velocity of the shear wave is slower.

Although the sound velocity of the Li ₂ B ₄ O ₇ single crystal substrate is slow, when the vibration of the SAW reaches the Li ₂ B ₄ O ₇ single crystal substrate, the energy is trapped on the surface without leaking in the substrate depth direction due to the presence of the inherent vibration of the SH wave. The inherent vibration of the _{Li 2} B ₄ O ₇ single crystal substrate is faster than the sound velocity of the wave generated by the inherent vibration of the lithium tantalate single crystal substrate. This makes it possible to trap the resonance energy of the main mode wave.

In addition, it is preferable to use a Li ₂ B ₄ O ₇ single crystal substrate with a non-piezoelectric orientation as the spurious absorption layer 13. Since the _{Li 2} B ₄ O ₇ single crystal is a tetragonal crystal, the wave propagation speed has little directional dependency, so the wave does not spread horizontally. On a tetragonal crystal, the wave has a linearity that travels straight along the crystal direction. This reduces so-called transverse mode waves that occur in a direction perpendicular to the SAW propagation direction. Therefore, transverse mode spurious is reduced.

Fig. 3 is a cross-sectional view showing another example of the device chip 5 of the acoustic wave device 1 according to the first embodiment. As shown in Fig. 3, the device chip 5 includes a temperature characteristic improving layer 14 between the piezoelectric substrate 11 and the high acoustic velocity film layer 12. The temperature characteristic improving layer 14 is preferably made of a material having a temperature characteristic curve in the opposite direction to that of the piezoelectric substrate 11. The temperature characteristic improving layer 14 is made of, for example, silicon dioxide ( _SiO2 ).

The thickness of the temperature characteristic improving layer 14 can be, for example, 0.05λ to 0.45λ, where λ is the wavelength of the elastic wave determined by the electrode pitch of the IDT electrodes. The total thickness of the piezoelectric substrate 11 and the temperature characteristic improving layer 14 can be, for example, 1.0λ or less, where λ is the wavelength of the elastic wave determined by the electrode pitch of the IDT electrodes.

A semiconductor layer may be provided between the piezoelectric substrate 11 and the temperature characteristic improvement layer 14. The semiconductor layer may be made of, for example, silicon. By using silicon with a thickness of, for example, 5 nm to 20 nm to bond the piezoelectric substrate 11 and the temperature characteristic improvement layer 14, the bond can be achieved without increasing unnecessary spurious signals.

Next, an example of an acoustic wave element 50 formed on a piezoelectric substrate 11 will be described with reference to FIG. 4. FIG. 3 is a top view of the functional element 50 of the acoustic wave device 1 according to the first embodiment.

As shown in FIG. 4, an elastic wave element 50 including an IDT (Interdigital Transducer) electrode 51 and a pair of reflectors 52 is formed on the main surface of the piezoelectric substrate 11. The IDT electrode 51 and the pair of reflectors 52 are arranged so as to excite elastic waves (mainly SH waves).

For example, the IDT electrode 51 and the pair of reflectors 52 are formed of an alloy of aluminum and copper. For example, the IDT electrode 51 and the pair of reflectors 52 are formed of an appropriate metal such as aluminum, molybdenum, iridium, tungsten, cobalt, nickel, ruthenium, chromium, strontium, titanium, palladium, silver, or an alloy of these metals.

For example, the IDT electrode 51 and the pair of reflectors 52 are formed from a laminated metal film in which multiple metal layers are stacked. For example, the thickness of the IDT electrode 51 and the pair of reflectors 52 is 150 nm to 450 nm.

The IDT electrode 51 has a pair of comb electrodes 51a. The pair of comb electrodes 51a face each other. The comb electrode 51a has a plurality of electrode fingers 51b and a bus bar 51c.

The multiple electrode fingers 51b are arranged with their longitudinal directions aligned. The bus bar 51c connects the multiple electrode fingers 51b.

One of the pair of reflectors 52 is adjacent to one side of the IDT electrode 51. The other of the pair of reflectors 52 is adjacent to the other side of the IDT electrode 51.

Figure 5 is a diagram showing the resonance characteristics of the resonator of the acoustic wave device 1 according to the first embodiment. Single crystal lithium tantalate was used for the piezoelectric substrate 11. The thickness of the piezoelectric substrate 11 was set to 0.3λ.

Here, the IDT electrode 51 had a thickness of 0.1λ and was made of aluminum. The temperature characteristic improving layer 14 had a thickness of 0.4λ and was made of SiO _2. The spurious absorption layer 13 had a thickness of 15λ and was made of a Li ₂ B ₄ O ₇ single crystal substrate. The high acoustic velocity film layer 12 was made of SiN.

Figure 6 is an enlarged view of the resonance characteristics of the acoustic wave device 1 shown in region R in Figure 5. As shown in Figure 5, spurious signals occur in the frequency band from 1550 MHz to 1650 MHz.

Here, the solid line represents the characteristics when the thickness of the high acoustic velocity film layer 12 is 0.25λ. The long chain line represents the characteristics when the thickness of the high acoustic velocity film layer 12 is 0.2λ. The long dashed line represents the characteristics when the thickness of the high acoustic velocity film layer 12 is 0.15λ. The dashed and dotted line represents the characteristics when the thickness of the high acoustic velocity film layer 12 is 0.1λ. The dashed line represents the characteristics when the thickness of the high acoustic velocity film layer 12 is 0.05λ. The dotted line represents the characteristics when the thickness of the high acoustic velocity film layer 12 is 0λ.

As shown in FIG. 6, when the thickness of the high acoustic velocity film layer 12 is 0.05λ, the spurious suppression effect is slight, but the spurious is shifted to the higher frequency side. When the thickness of the high acoustic velocity film layer 12 is 0.1λ, the spurious suppression effect is clearly apparent, and the spurious is shifted further to the higher frequency side.

When the thickness of the high acoustic velocity film layer 12 is 0.15λ or 0.2λ, the spurious suppression effect is most pronounced. When the thickness of the high acoustic velocity film layer 12 is 0.25λ, the spurious suppression effect is more pronounced than when the thickness of the high acoustic velocity film layer 12 is 0.1λ, but is slightly inferior to when the thickness of the high acoustic velocity film layer 12 is 0.15λ or 0.2λ.

Therefore, it is desirable that the thickness of the high acoustic velocity film layer 12 be, for example, 0.1λ to 0.3λ. More desirably, the thickness of the high acoustic velocity film layer 12 be 0.15λ to 0.25λ. Even more desirably, the thickness of the high acoustic velocity film layer 12 be 0.15λ to 0.2λ.

7 to 9 show the resonance characteristics of the resonator of the acoustic wave device. The dependency of the resonance characteristics of the acoustic wave device on the cut angle of the main surface of the Li ₂ B ₄ O ₇ single crystal substrate does not change depending on whether or not the high acoustic velocity film layer 12 is present. Regardless of the presence or absence of the high acoustic velocity film layer 12, the vibration reaches the Li ₂ B ₄ O ₇ single crystal substrate, so the spurious from the Li ₂ B ₄ O ₇ single crystal substrate depends directly on the cut angle. In FIG. 7 to FIG. 9, the calculation of the resonance characteristics of the resonator of the acoustic wave device is performed assuming that the thickness of the high acoustic velocity film layer 12 is 0λ.

Figure 7 is a diagram showing the resonance characteristics of the resonator of the acoustic wave device 1 according to the first embodiment. Single crystal lithium tantalate was used for the piezoelectric substrate 11. The thickness of the piezoelectric substrate 11 was set to 0.3λ.

Here, the IDT electrode 51 had a thickness of 0.1λ and was made of aluminum. The temperature characteristic improving layer 14 had a thickness of 0.4λ. The spurious absorption layer 13 was made of a Li ₂ B ₄ O ₇ single crystal substrate.

In Fig. 7(a), the cut angles of the main surface of the Li ₂ B ₄ O ₇ single crystal substrate are Euler angles (φ, θ, ψ) of (0°, 90°, 90°). In Fig. 7(b), the cut angles of the main surface of the Li ₂ B ₄ O ₇ single crystal substrate are Euler angles (φ, θ, ψ) of (0°, 90°, 88°). In Fig. 7(c), the cut angles of the main surface of the Li ₂ B ₄ O ₇ single crystal substrate are Euler angles (φ, θ, ψ) of (0°, 90°, 86°).

The resonance characteristics shown in Figures 7(a) and (b) show almost no transverse mode spurious emissions. In this way, a deviation in the cut angle of about ±2% can be tolerated as an error range if there is no substantial problem with the quality of the resonance characteristics. The resonance characteristics shown in Figure 7(c) show slight transverse mode spurious emissions, but the transverse mode spurious emissions are suppressed to a considerable extent.

Here, the Euler angle φ has the same effect at both 0° and 90° because the crystal is symmetric. Similarly, the Euler angle ψ has the same effect at both 80° and 100° because the crystal is symmetric.

8 is a diagram showing the resonance characteristics of the resonator of the acoustic wave device 1 according to the first embodiment. In FIG. 8(a), the cut angle of the main surface of the Li ₂ B ₄ O ₇ single crystal substrate is the Euler angle (φ, θ, ψ) of (0°, 90°, 84°). In FIG. 8(b), the cut angle of the main surface of the Li ₂ B ₄ O ₇ single crystal substrate is the Euler angle (φ, θ, ψ) of (0°, 90°, 82°). In FIG. 8(c), the cut angle of the main surface of the Li ₂ B ₄ O ₇ single crystal substrate is the Euler angle (φ, θ, ψ) of (0°, 90°, 80°).

The resonance characteristics shown in Figures 8(a) to (c) show slight transverse mode spurious emissions. It can also be seen that the transverse mode spurious emissions worsen as the Euler angle ψ approaches 80°. If the resonance characteristics deteriorate further beyond the transverse mode spurious emissions shown in Figure 8(c), it would be difficult to use this device as an acoustic wave device, especially in the high-end smartphone market.

9A and 9B are diagrams showing the resonance characteristics of a resonator of a comparative example of the acoustic wave device 1 according to the first embodiment. In Fig. 9A, the cut angles of the main surface of _{the Li2B4O7 single} crystal substrate are Euler angles (φ, θ, ψ) of (0°, 90°, 70°). In Fig. 9B, the cut angles of the main surface of _{the Li2B4O7 single} crystal substrate are Euler angles (φ, θ, ψ) of (0°, 90°, 60°).

In Fig. 9(c), the cut angles of the main surface of the Li ₂ B ₄ O ₇ single crystal substrate are Euler angles (φ, θ, ψ) of (0°, 90°, 50°). In Fig. 9(d), the cut angles of the main surface of the Li ₂ B ₄ O ₇ single crystal substrate are Euler angles (φ, θ, ψ) of (0°, 90°, 45°). The rest is as explained in Fig. 7.

As shown in Fig. 9, the comparative example has a large transverse mode spurious response. It was found that as the cut angle of the main surface of _{the Li2B4O7 single} crystal substrate increases from the Euler angles (φ, θ, ψ) (0°, 90°, 45° to 70°) to the crystal plane, the resonance characteristics become separated and are combined with the spurious response.

In addition, as the propagation direction changes from the crystal plane, the resonant impedance also increases, causing energy leakage in the direction of the substrate. Strong spurious signals can cause significant degradation of characteristics when combining resonators to create filters, etc., so the smaller the height of the spurious peak and the depth of the valley, the better the characteristics.

According to the first embodiment described above, it is possible to provide an acoustic wave device in which the number of processes after the formation of the resonator is reduced, and damage to the resonator caused by the processes is reduced, while suppressing transverse mode spurious emissions.

Embodiment 2.
Fig. 10 is a cross-sectional view showing the device chip 5 of the acoustic wave device 1 according to the second embodiment. As shown in Fig. 10, the device chip 5 of the acoustic wave device 1 according to the second embodiment includes a support substrate 20 on the other main surface of the spurious absorption layer 13 opposite to the piezoelectric substrate 11.

The support substrate 20 can be formed of, for example, sapphire, silicon, alumina, spinel, silicon nitride, aluminum nitride, silicon carbide, silicon oxynitride, diamond, quartz, glass, etc. The support substrate 20 should have a small thermal expansion coefficient and a high Young's modulus, as this improves the temperature characteristics of the acoustic wave device 1.

A sapphire substrate, which is a typical substrate that satisfies these conditions, is hard and chemically stable, so processing the surface to have an uneven or jagged shape is difficult and reduces yield. Therefore, it is desirable for the support substrate 20 to have a flat, plate-like rectangular parallelepiped shape.

The thickness of the support substrate 20 can be, for example, 50 μm to 200 μm.

Figure 11 is a diagram showing the resonance characteristics of the resonator of the acoustic wave device 1 according to the second embodiment. Single crystal lithium tantalate was used for the piezoelectric substrate 11. The thickness of the piezoelectric substrate 11 was set to 0.3λ. The IDT electrode 51 had a thickness of 0.1λ and was made of aluminum. The thickness of the temperature characteristic improving layer 14 was set to 0.4λ.

_{A Li2B4O7 single} crystal substrate was used for the spurious absorption layer 13. The cut angles of the main surface of _{the Li2B4O7 single} crystal substrate were Euler angles (φ, θ, ψ) of (0°, 90°, 90°). The thicknesses of the spurious absorption layer 13 were 2λ, 5λ, and 10λ.

Figure 12 is an enlarged view of the resonance characteristics of the acoustic wave device 1 shown in region R2 of Figure 11. As shown in Figure 12, spurious signals occur in the frequency band from 1500 MHz to 1650 MHz. Here, the solid line represents the characteristics when the thickness of the spurious absorption layer 13 is 10λ. The dashed line represents the characteristics when the thickness of the spurious absorption layer 13 is 5λ. The dashed line represents the characteristics when the thickness of the spurious absorption layer 13 is 2λ.

As shown in FIG. 12, when the thickness of the spurious absorption layer 13 is 10λ, spurious is most suppressed. When the thickness of the spurious absorption layer 13 is 2λ, spurious occurs the most. When the thickness of the spurious absorption layer 13 is 5λ, spurious is suppressed more than when it is 2λ, but more spurious occurs than when it is 10λ.

From this, it can be seen that the thicker the spurious absorption layer 13, the greater the spurious suppression effect tends to be. Therefore, it is desirable that the thickness of the spurious absorption layer 13 be, for example, 3λ to 20λ. It is even more desirable that the thickness of the spurious absorption layer 13 be, for example, 5λ to 20λ. It is even more desirable that the thickness of the spurious absorption layer 13 be, for example, 10λ to 20λ. The other configurations are the same as in embodiment 1, so a description thereof will be omitted.

According to the second embodiment described above, it is possible to produce an acoustic wave device in which the resonance characteristics and transverse mode spurious on the high frequency side are suppressed while reducing damage to the resonator due to the process.

Embodiment 3.
13 is a vertical cross-sectional view of a module to which the acoustic wave device 1 according to the first or second embodiment is applied. Note that the same reference numerals are used to designate the same or corresponding parts as those in the first or second embodiment, and a description of these parts will be omitted.

In FIG. 13, the module 100 includes a package substrate 130, a plurality of external connection terminals 131, an integrated circuit component IC, an acoustic wave device 1, an inductor 111, and a sealing portion 117.

The multiple external connection terminals 31 are formed on the underside of the package substrate 130. The multiple external connection terminals 131 are mounted on a motherboard of a pre-set mobile communication terminal.

For example, the integrated circuit component IC is mounted inside the package substrate 130. The integrated circuit component IC includes a switching circuit and a low-noise amplifier.

The acoustic wave device 1 is mounted on the main surface of the package substrate 130.

The inductor 111 is mounted on the main surface of the package substrate 130. The inductor 111 is mounted for impedance matching. For example, the inductor 111 is an integrated passive device (IPD).

The sealing portion 117 seals multiple electronic components including the acoustic wave device 1.

The module 100 described above includes an acoustic wave device 1. This makes it possible to provide a module using an acoustic wave device that reduces the number of processes after the formation of the resonator, reduces damage to the resonator due to the processes, and suppresses transverse mode spurious emissions.

While several aspects of at least one embodiment have been described, it should be understood that various alterations, modifications, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the scope of this disclosure.

It should be understood that the embodiments of the methods and apparatus described herein are not limited in their application to the details of construction and arrangement of components set forth in the above description or illustrated in the accompanying drawings. The methods and apparatus may be implemented in other embodiments and practiced or carried out in various ways.

The specific implementation examples are provided here for illustrative purposes only and are not intended to be limiting.

The phraseology and terminology used in this disclosure are for purposes of description and should not be regarded as limiting. The use herein of "including," "comprising," "having," "including" and variations thereof means the inclusion of the items listed thereafter and equivalents thereof as well as additional items.

References to "or" may be construed as meaning that any term described using "or" refers to one, more than one, and all of those described terms.

All references to front, back, left, right, top, bottom, top, bottom, width, length, front and back are intended for convenience of description. Such references are not intended to limit the components of this disclosure to any one positional or spatial orientation. Accordingly, the above description and drawings are by way of example only.

REFERENCE SIGNS LIST 1 acoustic wave device, 3 package substrate, 5 device chip, 17 sealing portion 11 piezoelectric substrate, 12 high acoustic velocity film layer 13 spurious absorption layer 14 temperature characteristic improving layer, 20 support substrate, 50 acoustic wave element 100 module, 111 inductor, 117 sealing portion 130 package substrate

Claims (11)

A piezoelectric substrate;
a resonator formed on a main surface of the piezoelectric substrate and a spurious absorption layer formed on another main surface of the piezoelectric substrate;
a high acoustic velocity film layer having an acoustic velocity faster than that of the piezoelectric substrate, the high acoustic velocity film layer being formed between the piezoelectric substrate and the spurious absorption layer;
The spurious absorption layer is an acoustic wave device made of a tetragonal crystal substrate and has a slower acoustic velocity than the piezoelectric substrate. The acoustic wave device of claim 1, further comprising a temperature characteristic improving layer formed between the piezoelectric substrate and the spurious absorption layer. The acoustic wave device of claim 1, wherein the thickness of the spurious absorption layer is 3λ or more and 20λ or less, where λ is the wavelength of the wave of the main mode excited by the resonator, and a support substrate is provided on the main surface of the spurious absorption layer opposite the piezoelectric substrate. The acoustic wave device of claim 1, wherein the thickness of the high acoustic velocity film layer is smaller than the thickness of the piezoelectric substrate. The acoustic wave device of claim 2, wherein the thickness of the high acoustic velocity film layer is smaller than the thickness of the temperature characteristic improving layer. The acoustic wave device according to claim 1, wherein the thickness of the high acoustic velocity film layer is 0.1λ or more and 0.3λ or less, where λ is the wavelength of the wave of the main mode excited by the resonator. The acoustic wave device of claim 1, wherein the spurious absorption layer has a lower crystal density than the piezoelectric substrate. 2. The acoustic wave device of claim 1, wherein the spurious absorption layer is a _{Li2B4O7 single} crystal _substrate . The acoustic wave device according to claim 1, wherein the support substrate is a substrate made of sapphire, silicon, alumina or spinel. The cut angle of the principal surface of the spurious absorption layer is such that the Euler angles (φ, θ, ψ) are:
φ=0°±2° or 90°±2°,
θ=90°±2°,
2. The acoustic wave device of claim 1, wherein ψ=80° to 100°. A module comprising the acoustic wave device according to claim 1 .

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