Elastic wave device and module using elastic wave device

Abstract

To provide an elastic wave device and a module using the elastic wave device in which transverse mode spurious is suppressed while reducing the number of processes after resonator formation and reducing damage to the resonator caused by the processes.SOLUTION: An elastic wave device comprises: a piezoelectric substrate; a resonator for excitation of surface acoustic waves formed on the main surface of the piezoelectric substrate; a spurious absorption layer formed on the other main surface of the piezoelectric substrate. The spurious absorption layer consists of a tetragonal crystal substrate; the sonic speed is slower than that of the piezoelectric substrate; and the cut angles of the main surface of the spurious absorption layer are Euler angles (φ, θ, ψ) where φ=0° ± 2° or 90° ± 2°, θ=90° ± 2°, ψ=80° to 100°.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to an elastic wave device and a module using the elastic wave device. Specifically, it relates to a surface acoustic wave device using SH waves, such as a filter, a duplexer, or a multiplexer.

Background Art

[0002] In a high-frequency communication system for a mobile communication terminal represented by a smartphone, a high-frequency filter or the like is used to remove unnecessary signals outside the frequency band used for communication.

[0003] For a high-frequency filter or the like, an elastic wave device having a surface acoustic wave (SAW) element or the like is used. The SAW element is an element in which an interdigital transducer (IDT) having a pair of comb-shaped electrodes is formed on a piezoelectric substrate.

[0004] For example, a surface acoustic wave device is manufactured as follows. First, a multilayer substrate is created by bonding a piezoelectric substrate that propagates elastic waves and a support substrate having a smaller coefficient of thermal expansion than the piezoelectric substrate. Next, a large number of IDT electrodes are formed on the multilayer substrate using photolithography technology, and then it is cut into a predetermined size by dicing to obtain a surface acoustic wave device. In this manufacturing method, by using the multilayer substrate, the change in the size of the piezoelectric substrate when the temperature changes is suppressed by the support substrate, so that the frequency characteristics as an elastic wave device are stabilized.

[0005] For example, according to Patent Document 1 or the like, in order to suppress the transverse mode spurious of an elastic wave device, a groove is formed in the intersection region of the electrode fingers, and an additional film is formed, etc., to vary the sound velocity in the transverse direction with respect to the propagation direction of the surface acoustic wave, thereby suppressing the transverse mode spurious.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] As disclosed in Patent Document 1, in order to suppress the lateral mode spurious of an elastic wave device, forming a groove in the intersection region of electrode fingers and forming an additional film complicates the process. In particular, the process of forming these after forming the resonator damages the resonator and accelerates the deterioration of filter characteristics.

[0008] This disclosure has been made to solve the above problems. An object of this disclosure is to provide an elastic wave device in which lateral mode spurs are suppressed while reducing the number of processes after resonator formation and reducing damage to the resonator caused by the processes, and a module using the elastic wave device.

Means for Solving the Problems

[0009] The elastic wave device according to this disclosure is a piezoelectric substrate, a resonator that excites an elastic surface wave formed on the main surface of the piezoelectric substrate, a spurious absorption layer formed on the other main surface of the piezoelectric substrate, and includes the spurious absorption layer is made of a tetragonal crystal substrate, has a slower sound velocity than the piezoelectric substrate, the cut angle of the main 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°, ψ = 80° to 100°, and it is an elastic wave device.

[0010] 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 in which the resonator vibrates. One embodiment of the present disclosure is that a support substrate is provided on the main surface of the spurious absorption layer on the side opposite to the piezoelectric substrate.

[0011] One embodiment of the present disclosure is that the spurious absorption layer has a lower crystal density than the piezoelectric substrate.

[0012] One embodiment of the present disclosure is that the spurious absorption layer is a Li2B4O7 single crystal substrate.

[0013] One embodiment of the present disclosure is that the support substrate is a substrate made of sapphire, silicon, alumina, or spinel.

[0014] One embodiment of the present disclosure is that a temperature characteristic improvement layer formed between the piezoelectric substrate and the spurious absorption layer is provided.

[0015] One embodiment of the present disclosure is that the temperature characteristic improvement layer is SiO2.

[0016] One embodiment of the present invention is a module including the elastic wave device.

Advantages of the Invention

[0017] According to the present disclosure, it is possible to provide an elastic wave device in which transverse mode spurious is suppressed while reducing the number of processes after resonator formation and reducing damage to the resonator caused by the processes, and a module using the elastic wave device.

Brief Description of the Drawings

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BEST MODE FOR CARRYING OUT THE INVENTION

[0019] The embodiments will be described with reference to the accompanying drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals. The redundant description of such parts will be simplified or omitted as appropriate.

[0020] Embodiment 1. FIG. 1 is a cross-sectional view showing the elastic wave device 1 according to Embodiment 1.

[0021] As shown in FIG. 1, the elastic wave device 1 includes a package substrate 3, external connection terminals 31, a device chip 5, electrode pads 9, bumps 15, and a sealing portion 17.

[0022] For example, the package substrate 3 is a multilayer substrate made of resin. For example, the package substrate 3 is a Low Temperature Co-fired Ceramics (LTCC) multilayer substrate composed of a plurality of dielectric layers.

[0023] A plurality of external connection terminals 31 are formed on the lower surface of the package substrate 3.

[0024] A plurality of 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 from 10 μm to 20 μm.

[0025] 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 from 10 μm to 50 μm.

[0026] A gap 16 is formed between the package substrate 3 and the device chip 5.

[0027] 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 a plurality of electrode pads 9 via a plurality of bumps 15.

[0028] The device chip 5 is a substrate on which an elastic wave element 50 is formed. For example, on the main surface of the device chip 5, a transmission filter and a reception filter including a plurality of elastic wave elements 50 mainly composed of resonators are formed.

[0029] The transmission filter is formed so that an electrical signal in a desired frequency band can pass therethrough. For example, the transmission filter is a ladder type filter composed of a plurality of series resonators and a plurality of parallel resonators.

[0030] The reception filter is formed so that an electrical signal in a desired frequency band can pass therethrough. For example, the reception filter is a ladder type filter.

[0031] The sealing portion 17 is formed so as to cover the device chip 5. For example, the sealing portion 17 is formed of an insulator such as a synthetic resin. For example, the sealing portion 17 is formed of metal.

[0032] 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.

[0033] FIG. 2 is a cross-sectional view showing the device chip 5 of the surface acoustic wave device 1 according to Embodiment 1.

[0034] As shown in FIG. 2, the device chip 5 includes a piezoelectric substrate 11 and a spurious absorption layer 13. An acoustic wave element 50 is formed on the piezoelectric substrate 11.

[0035] 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 piezoelectric ceramics.

[0036] The thickness of the piezoelectric substrate 11 can be, for example, from 0.1λ to 0.9λ, where λ is the wavelength of the acoustic wave determined by the electrode pitch of the IDT electrode.

[0037] The spurious absorption layer 13 can be formed of, for example, a Li2B4O7 single crystal substrate. The Li2B4O7 single crystal is a tetragonal crystal, and the crystal density is 2.44 g / cm 3 and is. Also, the crystal density of the lithium tantalate single crystal is 7.45 g / cm 3 and is. The Li2B4O7 single crystal substrate has a lower density than the lithium tantalate single crystal substrate, but the transverse wave sound velocity is slower.

[0038] Although the sound velocity of the Li2B4O7 single crystal substrate is slow, when the SAW vibration reaches the Li2B4O7 single crystal substrate, due to the existence of the inherent vibration of the SH wave, the energy is confined to the surface without leakage in the substrate depth direction. The inherent vibration of the Li2B4O7 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 enables the confinement of the resonance energy of the wave in the main mode.

[0039] Also, for the Li2B4O7 single crystal substrate, it is desirable to use an orientation without piezoelectricity as the spurious absorption layer 13. Since the Li2B4O7 single crystal is tetragonal, the wave propagation velocity has little orientation dependence, so the wave is less likely to spread laterally. On a tetragonal crystal, the wave has a straight - forward property of traveling straight with respect to the crystal direction. As a result, the so - called transverse mode waves generated in the direction orthogonal to the SAW propagation direction are reduced. Thus, the transverse mode spurious is reduced.

[0040] FIG. 3 is a cross - sectional view showing another example of the device chip 5 of the elastic wave device 1 according to Embodiment 1. As shown in FIG. 3, the device chip 5 includes a temperature characteristic improvement layer 12 between the piezoelectric substrate 11 and the spurious absorption layer 13. For the temperature characteristic improvement layer 12, it is desirable to use a member having a temperature characteristic opposite to that of the piezoelectric substrate 11. The temperature characteristic improvement layer 12 is made of, for example, silicon dioxide (SiO2).

[0041] The thickness of the temperature characteristic improvement layer 12 can be, for example, from 0.05λ to 0.45λ when the wavelength of the elastic wave determined by the electrode pitch of the IDT electrode is λ. The total thickness of the piezoelectric substrate 11 and the temperature characteristic improvement layer 12 can be, for example, 1.0λ or less when the wavelength of the elastic wave determined by the electrode pitch of the IDT electrode is λ.

[0042] A semiconductor layer may be provided between the piezoelectric substrate 11 and the temperature characteristic improvement layer 12. For the semiconductor layer, for example, silicon can be used. By using silicon with a thickness of, for example, 5 nm to 20 nm for the bonding between the piezoelectric substrate 11 and the temperature characteristic improvement layer 12, bonding can be achieved without increasing unnecessary spurious.

[0043] Next, an example of the elastic wave element 50 formed on the piezoelectric substrate 11 will be described with reference to FIG. 4. FIG. 3 is a top view of the functional element 50 of the elastic wave device 1 according to the first embodiment.

[0044] 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 provided so as to be able to excite elastic waves (mainly SH waves).

[0045] 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 thereof.

[0046] For example, the IDT electrode 51 and the pair of reflectors 52 are formed of a laminated metal film in which a plurality of metal layers are laminated. For example, the thickness of the IDT electrode 51 and the pair of reflectors 52 is from 150 nm to 450 nm.

[0047] The IDT electrode 51 includes a pair of comb-shaped electrodes 51a. The pair of comb-shaped electrodes 51a face each other. The comb-shaped electrode 51a includes a plurality of electrode fingers 51b and a bus bar 51c.

[0048] The plurality of electrode fingers 51b are arranged with their longitudinal directions aligned. The bus bar 51c connects the plurality of electrode fingers 51b.

[0049] 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.

[0050] FIG. 5 is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 according to Embodiment 1. The piezoelectric substrate 11 used was single crystal lithium tantalate. The thickness of the piezoelectric substrate 11 was set to 0.3λ.

[0051] Here, the IDT electrode 51 had a thickness of 0.1λ and was formed of aluminum. The thickness of the temperature characteristic improvement layer 12 was set to 0.4λ. The spurious absorption layer 13 used a Li2B4O7 single crystal substrate.

[0052] In FIG. 5(a), as the cut angle of the main surface of the Li2B4O7 single crystal substrate, the Euler angles (φ, θ, ψ) are (0°, 90°, 90°). In FIG. 5(b), as the cut angle of the main surface of the Li2B4O7 single crystal substrate, the Euler angles (φ, θ, ψ) are (0°, 90°, 88°). In FIG. 5(c), as the cut angle of the main surface of the Li2B4O7 single crystal substrate, the Euler angles (φ, θ, ψ) are (0°, 90°, 86°). The resonance characteristics shown in FIGS. 5(a) and (b) have almost no transverse mode spurious. Thus, a deviation in the cut angle of about ±2% can be tolerated as an error range when there is substantially no problem with the quality of the resonance characteristics. The resonance characteristics shown in FIG. 5(c) have a slight occurrence of transverse mode spurious, but the transverse mode spurious is suppressed to a considerable extent. Here, since the crystal is symmetric, the φ of the Euler angle has the same effect at both 0° and 90°. Similarly, since the crystal is symmetric, the ψ of the Euler angle has the same effect at both 80° and 100°.

[0053] FIG. 6 is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 according to Embodiment 1. In FIG. 6(a), the Euler angles (φ, θ, ψ) are (0°, 90°, 84°) as the cut angle of the main surface of the Li2B4O7 single crystal substrate. In FIG. 6(b), the Euler angles (φ, θ, ψ) are (0°, 90°, 82°) as the cut angle of the main surface of the Li2B4O7 single crystal substrate. In FIG. 6(c), the Euler angles (φ, θ, ψ) are (0°, 90°, 80°) as the cut angle of the main surface of the Li2B4O7 single crystal substrate. The resonance characteristics shown in FIGS. 6(a) to 6(c) have slight transverse mode spurs. Also, it can be seen that the transverse mode spurs deteriorate as ψ of the Euler angle approaches 80°. If the resonance characteristics deteriorate further beyond the transverse mode spurs shown in FIG. 6(c), it is considered difficult to use as an elastic wave device, especially in the high-end smartphone market.

[0054] FIG. 7 is a diagram showing the resonance characteristics of the resonator of the comparative example of the elastic wave device 1 according to Embodiment 1. In FIG. 7(a), the Euler angles (φ, θ, ψ) are (0°, 90°, 70°) as the cut angle of the main surface of the Li2B4O7 single crystal substrate. In FIG. 7(b), the Euler angles (φ, θ, ψ) are (0°, 90°, 60°) as the cut angle of the main surface of the Li2B4O7 single crystal substrate. In FIG. 7(c), the Euler angles (φ, θ, ψ) are (0°, 90°, 50°) as the cut angle of the main surface of the Li2B4O7 single crystal substrate. In FIG. 7(d), the Euler angles (φ, θ, ψ) are (0°, 90°, 45°) as the cut angle of the main surface of the Li2B4O7 single crystal substrate. Others are as described in FIG. 5.

[0055] As shown in FIG. 7, in the comparative example, significant horizontal-mode spurious signals occur. As the cut angles (Euler angles (φ, θ, ψ)) of the main surface of the Li2B4O7 single crystal substrate are (0°, 90°, 45° to 70°), it was found that as the angle from the crystal plane increases, the resonance characteristics separate and become characteristics combined with spurious signals. Also, since the resonance impedance increases as the propagation direction changes from the crystal plane, energy leakage occurs in the substrate direction. When there are strong spurious signals, it causes significant characteristic degradation when combining resonators to form filters etc. Therefore, it can be said that the smaller the height of the peak and the depth of the valley of the spurious signals, the better the characteristics.

[0056] According to the first embodiment described above, it is possible to provide an elastic wave device in which the horizontal-mode spurious signals are suppressed while reducing the processes after resonator formation and reducing the damage to the resonator due to the processes.

[0057] Embodiment 2. FIG. 8 is a cross-sectional view showing the device chip 5 of the elastic wave device 1 according to Embodiment 2. As shown in FIG. 8, the device chip 5 of the elastic wave device 1 according to Embodiment 2 includes a support substrate 14 on the other main surface opposite to the piezoelectric substrate 11 of the spurious signal absorption layer 13.

[0058] The support substrate 14 can be formed of, for example, sapphire, silicon, alumina, spinel, silicon nitride, aluminum oxynitride, silicon carbide, silicon oxynitride, diamond, quartz, glass, etc. The support substrate 14 preferably has a small coefficient of thermal expansion and a high Young's modulus. This is because the temperature characteristics of the elastic wave device 1 are improved. A sapphire substrate, which is a typical substrate satisfying such conditions, has high hardness and is chemically stable, so it is difficult for surface processing such as having an uneven shape or a jagged shape, and the yield decreases. Therefore, the support substrate 14 is preferably in the shape of a flat rectangular parallelepiped.

[0059] The thickness of the support substrate 14 can be, for example, from 50 μm to 200 μm.

[0060] FIG. 9 is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 according to Embodiment 2. The piezoelectric substrate 11 used was single crystal lithium tantalate. The thickness of the piezoelectric substrate 11 was set to 0.3λ. The IDT electrode 51 had a thickness of 0.1λ and was formed of aluminum. The thickness of the temperature characteristic improvement layer 12 was set to 0.4λ. The spurious absorption layer 13 used a Li2B4O7 single crystal substrate. As the cut angle of the main surface of the Li2B4O7 single crystal substrate, the Euler angles (φ, θ, ψ) were set to (0°, 90°, 90°). The thicknesses of the spurious absorption layer 13 were set to 2.5λ, 5λ, 10λ, and 20λ.

[0061] FIG. 10 is an enlarged view of the resonance characteristics of the elastic wave device 1 shown in the region R of FIG. 9. As shown in FIG. 10, spurious occurs in the frequency band from 1700 MHz to 1950 MHz. Here, the solid line is the characteristic when the thickness of the spurious absorption layer 13 is 20λ. The broken line is the characteristic when the thickness of the spurious absorption layer 13 is 10λ. The long broken line is the characteristic when the thickness of the spurious absorption layer 13 is 5λ. The long chain line is the characteristic when the thickness of the spurious absorption layer 13 is 2.5λ.

[0062] As shown in FIG. 10, when the thickness of the spurious absorption layer 13 is 20λ, spurious is most suppressed. When the thickness of the spurious absorption layer 13 is 2.5λ, spurious is most generated. Therefore, it is desirable that the thickness of the spurious absorption layer 13 be, for example, from 3λ to 20λ. More desirably, the thickness of the spurious absorption layer 13 is, for example, more desirably from 5λ to 20λ. Even more desirably, the thickness of the spurious absorption layer 13 is, for example, more desirably from 10λ to 20λ. Since other configurations are the same as those in Embodiment 1, the description thereof is omitted.

[0063] According to Embodiment 2 described above, it is possible to provide an elastic wave device in which resonance characteristics and lateral mode spurious on the high frequency side are suppressed while reducing damage to the resonator due to the process.

[0064] Embodiment 3. FIG. 11 is a longitudinal sectional view of a module to which the elastic wave device 1 according to Embodiment 1 or 2 is applied. In addition, the same or corresponding parts as those in Embodiment 1 or 2 are denoted by the same reference numerals, and the description of this part is omitted.

[0065] In FIG. 11, the module 100 includes a package substrate 130, a plurality of external connection terminals 131, an integrated circuit component IC, an elastic wave device 1, an inductor 111, and a sealing portion 117.

[0066] The plurality of external connection terminals 31 are formed on the lower surface of the package substrate 130. The plurality of external connection terminals 131 are mounted on a mother board of a preset mobile communication terminal.

[0067] 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.

[0068] The elastic wave device 1 is mounted on the main surface of the package substrate 130.

[0069] 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).

[0070] The sealing portion 117 seals a plurality of electronic components including the elastic wave device 1.

[0071] The module 100 described above includes the elastic wave device 1. Therefore, it is possible to provide a module using an elastic wave device in which the number of processes after resonator formation is reduced, damage to the resonator due to the processes is reduced, and transverse mode spurious is suppressed.

[0072] Although some aspects of at least one embodiment have been described, it should be understood that various modifications, corrections, and improvements will readily occur to those skilled in the art. Such modifications, corrections, and improvements are intended to be part of this disclosure and are intended to be within the scope of this disclosure.

[0073] It should be understood that the embodiments of the methods and apparatuses described herein are not limited to the application to the details of the structure and arrangement of the components described in the above description or illustrated in the accompanying drawings. The methods and apparatuses can be implemented in other embodiments and can be implemented or executed in various manners.

[0074] Specific implementation examples are provided herein for illustrative purposes only and are not intended to be limiting.

[0075] The expressions and terms used in this disclosure are for explanatory purposes and should not be regarded as limiting. The use of "including", "comprising", "having", "containing" and their variants herein means the inclusion of the items listed hereinafter and their equivalents as well as additional items.

[0076] The reference to "or (alternatively)" can be construed such that any term described using "or (alternatively)" indicates one, more than one, and all of the terms of the description.

[0077] References to front and back, left and right, top and bottom, vertical and horizontal, front and back are all for the convenience of description. Such references do not limit the components of this disclosure to any one positional or spatial orientation. Therefore, the above description and drawings are merely illustrative.

Description of Reference Numerals

[0078] 1 Elastic wave device, 3 Package substrate, 5 Device chip, 17 Sealing portion 11 Piezoelectric substrate, 12 Temperature characteristic improvement layer 13 Spurious absorption layer, 14 Support substrate, 50 Elastic wave element 100 module, 111 inductor, 117 sealing part 130 package substrate

Claims

1. A piezoelectric substrate, a resonator formed on a main surface of the piezoelectric substrate for exciting an elastic surface wave, a spurious absorption layer formed on the other main surface of the piezoelectric substrate, comprising: the spurious absorption layer is made of a tetragonal crystal substrate, and has a lower sound velocity than the piezoelectric substrate, the cut angle of the main surface of the spurious absorption layer has Euler angles (φ, θ, ψ) such that φ = 0° ± 2° or 90° ± 2°, θ = 90° ± 2°, ψ = 80° to 100°, an elastic wave device.

2. The thickness of the spurious absorption layer is 3λ or more and 20λ or less when the wavelength of the wave of the main mode excited by the resonator is λ, and a support substrate is provided on the main surface of the spurious absorption layer opposite to the piezoelectric substrate. An elastic wave device.

3. The elastic wave device according to claim 1, wherein the spurious absorption layer has a lower crystal density than the piezoelectric substrate.

4. The spurious absorption layer is Li ２ B ４ O ７ The elastic wave device according to claim 1, wherein the substrate is a single crystal substrate of LiBO.

5. The elastic wave device according to claim 1, wherein the support substrate is a substrate made of sapphire, silicon, alumina or spinel.

6. The elastic wave device according to claim 1, further comprising a temperature characteristic improvement layer formed between the piezoelectric substrate and the spurious absorption layer.

7. The temperature characteristic improvement layer is SiO ２ The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is ２ .

8. A module comprising the elastic wave device according to any one of claims 1 to 7.

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