Elastic wave device and module using same

Abstract

The invention discloses an elastic wave device and a module including the elastic wave device. The elastic wave device includes a piezoelectric substrate, a resonator formed on a main surface of the piezoelectric substrate and used for exciting an elastic surface wave; the stray absorbing layer is formed on the other main surface of the piezoelectric substrate, and a temperature characteristic improving layer or a high-sound-speed layer is further arranged on the stray absorbing layer. The stray absorbing layer is composed of a tetragonal crystal substrate, and the sound velocity of the stray absorbing layer is slower than that of the piezoelectric substrate; the sound velocity of the high-sound-velocity layer is higher than that of the piezoelectric substrate. According to the invention, the process steps after the resonator is formed can be reduced, the damage of the process to the resonator is reduced, and meanwhile, the elastic wave device for inhibiting the transverse-mode stray waves and the module using the elastic wave device are provided.

Description

Technical Field

[0001] The present invention relates to an elastic wave device and a module using the elastic wave device. More specifically, it relates to an elastic surface wave device using SH waves, such as a filter, a duplexer, or a multiplexer. Background Art

[0002] In a high-frequency communication system of a mobile communication terminal represented by a smartphone, devices such as high-frequency filters are used to remove unnecessary signals outside the frequency band used for communication.

[0003] In devices such as high-frequency filters, an elastic wave device having an elastic surface wave (SAW: Surface acoustic wave) element is used. A SAW element is an element in which an IDT (Interdigital Transducer) having a pair of comb-shaped electrodes is formed on a piezoelectric substrate.

[0004] For example, the manufacturing method of an elastic surface wave device is as follows. First, a multilayer film substrate formed by bonding a piezoelectric substrate that transmits elastic waves and a support substrate having a smaller coefficient of thermal expansion than the piezoelectric substrate is prepared. Then, a plurality of IDT electrodes are formed on the multilayer film substrate using a lithography technique, and then it is cut into a specified size by a cutting process to manufacture an elastic surface wave device. In this manufacturing method, by using a multilayer film substrate, changes in the size of the piezoelectric substrate due to temperature changes can be suppressed, thereby stabilizing the frequency characteristics of the elastic wave device.

[0005] For example, according to Patent Document 1 (Japanese Patent Application Laid-Open No. 2019-50544), in order to suppress lateral mode spurious waves of an elastic wave device, it is known to change the sound velocity of the lateral mode in the lateral direction of the propagation direction of the elastic surface wave by forming a groove or an additional film in the crossing region of the electrode fingers, thereby suppressing lateral mode spurious waves.

[0006] As disclosed in Patent Document 1, forming a groove or an additional film in the crossing region of the electrode fingers to suppress lateral mode spurious waves of an elastic wave device makes the process complicated. Especially when these processes are performed after forming a resonator, the resonator may be damaged, thereby accelerating the deterioration of the filter characteristics. Summary of the Invention

[0007] The present disclosure aims to solve the above problems. An object of the present disclosure is to reduce the process steps after forming a resonator, reduce the damage to the resonator by the process, and at the same time provide an elastic wave device that suppresses lateral mode spurious waves and a module using the elastic wave device.

[0008] The present invention discloses an elastic wave device, which includes: a piezoelectric substrate, a resonator formed on the main surface of the piezoelectric substrate for exciting elastic surface waves; a stray absorption layer formed on the other main surface of the piezoelectric substrate; the stray absorption layer is composed of a tetragonal crystal substrate, and its sound velocity is slower than that of the piezoelectric substrate.

[0009] Further, in an embodiment of the present invention, the cutting angle of the main surface of the stray absorption layer is the Euler angle (φ, θ, ψ), where φ = 0° ± 2° or 90° ± 2°, θ = 90° ± 2°, and ψ ranges from 80° to 100°.

[0010] Further, in an embodiment of the present invention, when the wavelength of the main mode wave excited by the resonator is λ, the thickness of the stray absorption layer is not less than 3λ and not more than 20λ.

[0011] Further, in an embodiment of the present invention, the crystal density of the stray absorption layer is lower than that of the piezoelectric substrate.

[0012] Further, in an embodiment of the present invention, the stray absorption layer is a Li2B4O7 single crystal substrate.

[0013] Further, in another embodiment of the present invention, a support substrate is provided on the main surface of the stray absorption layer opposite to the piezoelectric substrate; the support substrate is a substrate composed of sapphire, silicon, alumina, spinel, silicon nitride, aluminum nitride, silicon carbide, silicon oxynitride, diamond, quartz, or glass.

[0014] Further, in another embodiment of the present invention, a temperature characteristic improvement layer is further formed between the piezoelectric substrate and the stray absorption layer. The temperature characteristic curve of the material constituting the temperature characteristic improvement layer is opposite to the direction of the temperature characteristic curve of the material constituting the piezoelectric substrate.

[0015] Further, in another specific embodiment of the present invention, the temperature characteristic improvement layer is SiO2. When the elastic wave wavelength is λ, the thickness of the temperature characteristic improvement layer is 0.05λ to 0.45λ; the thickness of the piezoelectric substrate is 0.1λ to 0.9λ; the total thickness of the piezoelectric substrate and the temperature characteristic improvement layer does not exceed 1.0λ.

[0016] Further, in an embodiment of the present invention, a semiconductor layer is further provided between the piezoelectric substrate and the temperature characteristic improvement layer, and the semiconductor layer is silicon with a thickness of 5 to 20 nm.

[0017] Further, in an embodiment of the present invention, a high acoustic velocity layer is formed between the piezoelectric substrate and the spurious absorption layer, and the acoustic velocity thereof is higher than that of the piezoelectric substrate. Further, the thickness of the high acoustic velocity layer is smaller than the thickness of the piezoelectric substrate. When the wavelength of the main mode wave excited by the resonator is λ, the thickness of the high acoustic velocity layer is between 0.1λ or more and 0.3λ or less.

[0018] Further, in an embodiment of the present invention, a temperature characteristic improvement layer and a high acoustic velocity layer are further included. The temperature characteristic improvement layer is disposed between the piezoelectric substrate and the high acoustic velocity layer, and the high acoustic velocity layer is disposed between the temperature characteristic improvement layer and the spurious absorption layer; the thickness of the high acoustic velocity layer is smaller than the thickness of the temperature characteristic improvement layer.

[0019] Correspondingly, the present invention further provides a module, which is the above-mentioned elastic wave device.

[0020] According to the present disclosure, the process steps after the formation of the resonator can be reduced, the damage to the resonator caused by the process can be reduced, and at the same time, an elastic wave device for suppressing transverse mode spurious waves and a module using the elastic wave device are provided. Description of the Drawings

[0021] Figure 1 It is a cross-sectional view showing the elastic wave device 1 in Embodiment 1.

[0022] Figure 2 It is a cross-sectional view showing the device chip 5 of the elastic wave device 1 in Embodiment 1.

[0023] Figure 3 It is a cross-sectional view showing another example of the device chip 5 of the elastic wave device 1 in Embodiment 1.

[0024] Figure 4 It is a top view showing the functional element 50 of the elastic wave device 1 in Embodiment 1.

[0025] Figure 5 It is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 in Embodiment 1.

[0026] Figure 6 It is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 in Embodiment 1.

[0027] Figure 7 It is a diagram showing the resonance characteristics of the resonator of the comparative example of the elastic wave device 1 in Embodiment 1.

[0028] Figure 8 It is a cross-sectional view showing the device chip 5 of the elastic wave device 1 in Embodiment 2.

[0029] Figure 9This is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 in Embodiment 2.

[0030] Figure 10 is an enlarged Figure 9 diagram of the resonance characteristics of the elastic wave device 1 shown in the region R0 in

[0031] Figure 11 This is a cross-sectional view of the device chip 5 of the elastic wave device 1 according to Embodiment 3.

[0032] Figure 12 This is a cross-sectional view of another example of the device chip 5 of the elastic wave device 1 according to Embodiment 3.

[0033] Figure 13 This is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 according to Embodiment 3.

[0034] Figure 14 is Figure 13 an enlarged diagram of the resonance characteristics of the elastic wave device 1 in the shown region R1.

[0035] Figure 15 This is a cross-sectional view of the device chip 5 of the elastic wave device 1 according to Embodiment 4.

[0036] Figure 16 This is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 according to Embodiment 4.

[0037] Figure 17 is Figure 16 an enlarged diagram of the resonance characteristics of the elastic wave device 1 in the shown region R2.

[0038] Figure 18 This is a longitudinal cross-sectional view of the module to which the elastic wave device 1 in Embodiments 1 to 4 is applied.

[0039] The main reference numerals are as follows: 1 - elastic wave device, 3 - package substrate, 5 - device chip, 17 - sealing portion, 11 - piezoelectric substrate, 12 - high-velocity layer, 13 - spurious absorption layer, 14 - temperature characteristic improvement layer, 20 - support substrate, 50 - elastic wave element, 100 - module, 111 - coil, 117 - sealing portion, 130 - package substrate. Specific embodiments The embodiments will be described with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals. The repeated description of these parts will be appropriately simplified or omitted.

[0041] Embodiment 1 Figure 1 This is a cross-sectional view of the elastic wave device 1 in Embodiment 1.

[0042] As Figure 1 shown, 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.

[0043] 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.

[0044] A plurality of external connection terminals 31 are formed on the lower surface of the package substrate 3.

[0045] A plurality of electrode pads 9 are formed on the upper surface of the package substrate 3. For example, the electrode pads 9 are formed of copper or a copper-containing alloy. For example, the thickness of the electrode pads 9 is 10 μm to 20 μm.

[0046] 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.

[0047] A gap 16 is formed between the package substrate 3 and the device chip 5.

[0048] The device chip 5 is mounted on the package substrate 3 in a flip-chip bonding manner through the bumps 15. The device chip 5 is electrically connected to the plurality of electrode pads 9 through the plurality of bumps 15.

[0049] The device chip 5 is an elastic wave element 50 formed on a piezoelectric substrate. For example, a transmission filter and a reception filter including a plurality of elastic wave elements 50 mainly composed of resonators are formed on the main surface of the device chip 5.

[0050] The transmission filter is designed to allow an electrical signal in a desired frequency band to pass through. For example, the transmission filter is a ladder filter composed of a plurality of series resonators and a plurality of parallel resonators.

[0051] The reception filter is designed to allow an electrical signal in a desired frequency band to pass through. For example, the reception filter is a ladder-type filter.

[0052] The sealing portion 17 is designed to cover the device chip 5. For example, the sealing portion 17 is formed of an insulating material such as synthetic resin. In other embodiments, for example, the sealing portion 17 is formed of metal.

[0053] When the sealing portion 17 is formed of synthetic resin, the synthetic resin is epoxy resin, polyimide, etc. The sealing portion 17 preferably uses epoxy resin and is formed by a low-temperature curing process using epoxy resin.

[0054] Figure 2 This is a cross-sectional view of the device chip 5 of the elastic wave device 1 in Embodiment 1.

[0055] As Figure 2 shown, the device chip 5 includes a piezoelectric substrate 11 and a stray absorption layer 13. An elastic wave element 50 is formed on the piezoelectric substrate 11.

[0056] 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 piezoelectric ceramic substrate.

[0057] When the elastic wave wavelength determined by the electrode pitch of the IDT electrode (the distance between adjacent electrode fingers 51b) is λ, the thickness of the piezoelectric substrate 11 is set to 0.1λ to 0.9λ.

[0058] The stray absorption layer 13 can be formed, for example, of a Li2B4O7 single crystal substrate or the like. The Li2B4O7 single crystal is a tetragonal crystal, and the crystal density is 2.44 g / cm³. The crystal density of the lithium tantalate single crystal is 7.45 g / cm³. Although the density of the Li2B4O7 single crystal substrate is lower than that of the lithium tantalate single crystal substrate, the sound velocity of its transverse wave is slower.

[0059] Although the sound velocity of the Li2B4O7 single crystal substrate is slower, when the SAW vibration reaches the Li2B4O7 single crystal substrate, due to the existence of the inherent vibration of the SH wave (Shear Horizontal wave), the energy does not leak into the depth direction of the substrate but is confined to the surface. The inherent vibration of the Li2B4O7 single crystal substrate generates a wave with a faster sound velocity than the inherent vibration of the lithium tantalate single crystal substrate. This enables better confinement of the resonance energy of the main mode wave.

[0060] In addition, as the stray absorption layer 13, the Li2B4O7 single crystal substrate preferably uses an orientation that does not have piezoelectricity. Since the Li2B4O7 single crystal is tetragonal, the wave propagation speed has little dependence on the orientation, so the wave is not easily laterally diffused. On a tetragonal crystal, the wave has the characteristic of propagating linearly along the crystal direction. Therefore, the so-called transverse mode wave generated perpendicular to the SAW propagation direction is reduced, thereby reducing the transverse mode stray wave.

[0061] Figure 3 This is a cross-sectional view of another example of the device chip 5 of the elastic wave device 1 in Embodiment 1. As Figure 3 shown, a temperature characteristic improvement layer 14 is provided between the piezoelectric substrate 11 and the stray absorption layer 13 in the device chip 5. The temperature characteristic improvement layer 14 preferably uses a material having a temperature characteristic opposite to the direction of the temperature characteristic curve of the piezoelectric substrate 11. The temperature characteristic improvement layer 14 is formed of, for example, silicon dioxide (SiO2).

[0062] When the elastic wave wavelength determined by the electrode pitch of the IDT electrode is λ, the thickness of the temperature characteristic improvement layer 14 can be, for example, 0.05λ to 0.45λ. The total thickness of the piezoelectric substrate 11 and the temperature characteristic improvement layer 14 can be set to not exceed 1.0λ when the elastic wave wavelength determined by the electrode pitch of the IDT electrode is λ.

[0063] A semiconductor layer may also be provided between the piezoelectric substrate 11 and the temperature characteristic improvement layer 14. Silicon can be used for the semiconductor layer, for example. By using silicon with a thickness of 5 nm to 20 nm at the junction of the piezoelectric substrate 11 and the temperature characteristic improvement layer 14, bonding can be performed without increasing unnecessary stray waves.

[0064] Next, Figure 4 An example of the elastic wave element 50 formed on the piezoelectric substrate 11 will be described. Figure 3 FIG. is a plan view showing the functional element 50 of the elastic wave device 1 in Embodiment 1.

[0065] As Figure 4 shown, 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 can excite elastic waves (mainly SH waves).

[0066] For example, the IDT electrode 51 and the pair of reflectors 52 are formed of an aluminum and copper alloy. For example, the IDT electrode 51 and the pair of reflectors 52 can also be formed of appropriate metals such as aluminum, molybdenum, iridium, tungsten, cobalt, nickel, ruthenium, chromium, strontium, titanium, palladium, silver or alloys thereof.

[0067] For example, the IDT electrode 51 and the pair of reflectors 52 are constituted by a laminated metal film formed by laminating a plurality of metal layers. For example, the thickness of the IDT electrode 51 and the pair of reflectors 52 is 150 nm to 450 nm.

[0068] The IDT electrode 51 includes a pair of comb-shaped electrodes 51a. The pair of comb-shaped electrodes 51a are symmetric with each other. The comb-shaped electrode 51a is composed of a plurality of electrode fingers 51b and bus bars 51c.

[0069] The plurality of electrode fingers 51b are arranged in the long side direction. The bus bar 51c is used to connect the plurality of electrode fingers 51b.

[0070] One side of the pair of reflectors 52 is adjacent to one side of the IDT electrode 51. The other pair of reflectors 52 is adjacent to the other side of the IDT electrode 51.

[0071] Figure 5It is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 in Embodiment 1. The piezoelectric substrate 11 uses single-crystal lithium tantalate. The thickness of the piezoelectric substrate 11 is 0.3λ.

[0072] Here, the thickness of the IDT electrode 51 is set to 0.1λ and is formed of aluminum. The thickness of the temperature characteristic improvement layer 14 is 0.4λ. The stray absorption layer 13 uses a Li2B4O7 single-crystal substrate.

[0073] The upper surface of the Li2B4O7 single-crystal substrate is the main surface, that is, the surface where the Li2B4O7 single-crystal substrate contacts the temperature characteristic improvement layer 14 is the main surface. Figure 5 (a), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single-crystal substrate are (0°, 90°, 90°). Temperature Figure 5 (b), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single-crystal substrate are (0°, 90°, 88°). Figure 5 (c), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single-crystal substrate are (0°, 90°, 86°). Figure 5 (a) and (b) show that the resonance characteristics hardly generate transverse mode stray waves. Therefore, a cutting angle deviation of ±2% has no problem in the quality of the actual resonance characteristics and can be regarded as an allowable error range. Figure 5 (c) shows that the resonance characteristics slightly generate transverse mode stray waves, but the transverse mode stray waves are suppressed to a considerable extent. Here, due to the symmetry of the crystal, the Euler angle φ has the same effect at 0° and 90°. Similarly, due to the symmetry of the crystal, the Euler angle ψ also has the same effect at 80° and 100°.

[0074] Figure 6 It is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 in Embodiment 1. Figure 6 (a), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single-crystal substrate are (0°, 90°, 84°). Figure 6 (b), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single-crystal substrate are (0°, 90°, 82°). Figure 6 (c), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single-crystal substrate are (0°, 90°, 80°). Figure 6 (a) to (c) show that the resonance characteristics slightly generate transverse mode stray waves. In addition, as the Euler angle ψ approaches 80°, the situation of transverse mode stray waves becomes more serious. If Figure 6(c) The lateral mode spurious waves shown are further intensified, and the resonance characteristics will deteriorate, so it will be difficult to be used as an elastic wave device, especially in the application in the high-end smartphone market.

[0075] Figure 7 It is a diagram showing the resonance characteristics of the resonator of the comparative example of the elastic wave device 1 in Embodiment 1. Figure 7 (a) In (a), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single crystal substrate are (0°, 90°, 70°). Figure 7 (b) In (b), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single crystal substrate are (0°, 90°, 60°). Figure 7 (c) In (c), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single crystal substrate are (0°, 90°, 50°). Figure 7 (d) In (d), the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single crystal substrate are (0°, 90°, 45°). The other parts are the same as those Figure 5 described in.

[0076] As Figure 7 shown, the generation of lateral mode spurious waves in the comparative example is large. As the Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single crystal substrate are (0°, 90°, 45° to 70°), with the increase of the crystal plane angle, the resonance characteristics are separated and combined with the spurious waves. In addition, with the change of the propagation direction, the resonance impedance also increases significantly, resulting in energy leakage in the substrate direction. When there are strong spurious waves, when combining resonators to form a filter, etc., it will cause significant characteristic deterioration. Therefore, the smaller the peak height and valley depth of the spurious waves, the better the characteristics.

[0077] According to the above Embodiment 1, it is possible to reduce the process steps after the formation of the resonator, reduce the damage of the process to the resonator, and at the same time provide an elastic wave device that suppresses lateral mode spurious waves.

[0078] Embodiment 2 Figure 8 It is a cross-sectional view of the device chip 5 of the elastic wave device 1 in Embodiment 2. As Figure 8 shown, on the other main surface of the spurious absorption layer on the side opposite to the piezoelectric substrate 11 of the device chip 5 of the elastic wave device 1 in Embodiment 2, a support substrate 20 is provided.

[0079] The support substrate 20 can be made of materials such as sapphire, silicon, alumina, spinel, silicon nitride, aluminum nitride, silicon carbide, silicon oxynitride, diamond, quartz, glass, etc. The smaller the thermal expansion coefficient and the higher the Young's modulus of the support substrate 20, the better. This is because it can improve the temperature characteristics of the elastic wave device 1. However, typical substrates that meet these conditions, such as sapphire substrates, although hard and chemically stable, will encounter difficulties in processing with uneven shapes or serrated surfaces, resulting in a reduction in yield. Therefore, the support substrate 20 is preferably a flat plate-shaped cuboid.

[0080] The thickness of the support substrate 20 can be set to, for example, 50 μm to 200 μm.

[0081] Figure 9 It is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 in Embodiment 2. The piezoelectric substrate 11 uses single-crystal lithium tantalate. The thickness of the piezoelectric substrate 11 is set to 0.3λ. The thickness of the IDT electrode 51 is set to 0.1λ and is formed of aluminum. The thickness of the temperature characteristic improvement layer 14 is set to 0.4λ. The stray absorption layer 13 uses a Li2B4O7 single-crystal substrate. The Euler angles (φ, θ, ψ) of the cutting angle of the main surface of the Li2B4O7 single-crystal substrate are set to (0°, 90°, 90°). The thickness of the stray absorption layer 13 is set to 2.5λ, 5λ, 10λ, and 20λ.

[0082] Figure 10 It is a diagram for Figure 9 enlarging the resonance characteristics of the elastic wave device 1 shown in the region R0 in Figure 10 As shown, in the frequency band of 1700 MHz to 1950 MHz, stray waves appear. Here, the solid line represents the characteristics when the thickness of the stray absorption layer 13 is 20λ. The dashed line represents the characteristics when the thickness of the stray absorption layer 13 is 10λ. The long dashed line represents the characteristics when the thickness of the stray absorption layer 13 is 5λ. The dotted line represents the characteristics when the thickness of the stray absorption layer 13 is 2.5λ.

[0083] As Figure 10 shown, when the thickness of the stray absorption layer 13 is 20λ, the stray waves are most effectively suppressed. When the thickness of the stray absorption layer 13 is 2.5λ, the generation of stray waves is the most obvious. Therefore, the thickness of the stray absorption layer 13 is preferably, for example, 3λ to 20λ. In addition, it is more preferably that the thickness of the stray absorption layer 13 is, for example, 5λ to 20λ. Further preferably, the thickness of the stray absorption layer 13 is, for example, 10λ to 20λ. Other structures are the same as those in Embodiment 1, so the description is omitted.

[0084] According to the above Embodiment 2, it is possible to provide an elastic wave device that suppresses the resonance characteristics and the lateral mode stray waves on the high-frequency side while reducing the damage to the resonator by the process.

[0085] Embodiment 3 Figure 1 FIG. 4 is a cross-sectional view showing the surface acoustic wave device 1 in Embodiment 3.

[0086] As shown in Figure 1 FIG. 4, the surface acoustic 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.

[0087] 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.

[0088] A plurality of external connection terminals 31 are formed on the lower surface of the package substrate 3.

[0089] 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 a copper-containing alloy. For example, the thickness of the electrode pads 9 is 10 μm to 20 μm.

[0090] Bumps 15 are formed on the upper surfaces of the respective 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.

[0091] A gap 16 is formed between the package substrate 3 and the device chip 5.

[0092] The device chip 5 is mounted on the package substrate 3 in a flip chip bonding manner through the bumps 15. The device chip 5 is electrically connected to a plurality of electrode pads 9 through a plurality of bumps 15.

[0093] The device chip 5 is a substrate on which a surface acoustic 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 surface acoustic wave elements 50 mainly composed of resonators are formed.

[0094] The transmission filter is designed to allow an electric signal in a desired frequency band to pass through. For example, the transmission filter is a ladder filter composed of a plurality of series resonators and a plurality of parallel resonators.

[0095] The reception filter is designed to allow an electric signal in a desired frequency band to pass through. For example, the reception filter is a ladder type filter.

[0096] The sealing portion 17 is designed 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 metal.

[0097] When the sealing portion 17 is formed of a synthetic resin, the synthetic resin is an epoxy resin, polyimide, or the like. The sealing portion 17 preferably uses an epoxy resin and is formed by a low-temperature curing process of the epoxy resin.

[0098] Figure 11 It is a cross-sectional view of the device chip 5 of the surface acoustic wave device 1 in Embodiment 3.

[0099] As Figure 11 shown, the device chip 5 includes a piezoelectric substrate 11 and a spurious absorption layer 13. The surface acoustic wave element 50 is formed on the piezoelectric substrate 11.

[0100] 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 piezoelectric ceramic substrate.

[0101] The thickness of the piezoelectric substrate 11 can be, for example, set to 0.1λ to 0.9λ when the elastic wave wavelength determined by the electrode pitch (distance between adjacent electrode fingers 51b) of the IDT electrode is λ.

[0102] The high acoustic velocity layer 12 is provided between the piezoelectric substrate 11 and the spurious absorption layer 13 and is a material with a higher acoustic velocity than that of the piezoelectric substrate 11. With this structure, waves with a higher propagation speed can be restricted, thereby suppressing spurious signals generated on the high-frequency side. For example, SiN can be used to form the high acoustic velocity layer 12. The thickness of the high acoustic velocity layer 12 can be set to 0.1λ to 0.3λ, for example, when the elastic wave wavelength determined by the electrode pitch of the IDT electrode is λ.

[0103] The spurious absorption layer 13 can be formed of, for example, a Li2B4O7 single crystal substrate or the like. The Li2B4O7 single crystal is a tetragonal crystal, and the crystal density is 2.44 g / cm³. The crystal density of the lithium tantalate single crystal is 7.45 g / cm³. Although the density of the Li2B4O7 single crystal substrate is lower than that of the lithium tantalate single crystal substrate, its shear wave acoustic velocity is slower.

[0104] Although the acoustic 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 intrinsic vibration of the SH wave, the energy does not leak into the depth direction of the substrate but is restricted to the surface. The intrinsic vibration of the Li2B4O7 single crystal substrate generates waves with a higher acoustic velocity than the intrinsic vibration of the lithium tantalate single crystal substrate. This enables better restriction of the resonance energy of the main mode wave.

[0105] In addition, as the stray absorption layer 13, a Li2B4O7 single crystal substrate is preferably used in an orientation that does not have piezoelectricity. Since the Li2B4O7 single crystal is tetragonal, the wave propagation speed has little dependence on the orientation, so the wave is not easily diffused laterally. On a tetragonal crystal, the wave has the characteristic of propagating linearly along the crystal direction. Therefore, the so-called lateral mode wave generated perpendicular to the SAW propagation direction is reduced, thereby reducing the lateral mode stray wave.

[0106] Figure 12 is a cross-sectional view showing another example of the device chip 5 of the elastic wave device 1 in Embodiment 3. As Figure 12 shown, a temperature characteristic improvement layer 14 is provided between the piezoelectric substrate 11 and the high acoustic velocity layer 12 in the device chip 5. The temperature characteristic improvement layer 14 is preferably made of a material having a temperature characteristic opposite to the direction of the temperature characteristic curve of the piezoelectric substrate 11. The temperature characteristic improvement layer 14 is composed of, for example, silicon dioxide (SiO2).

[0107] The thickness of the temperature characteristic improvement layer 14 can be set, for example, to be 0.05λ to 0.45λ when the elastic wave wavelength determined by the electrode pitch of the IDT electrode (the distance between adjacent electrode fingers 51b) is λ. The total thickness of the piezoelectric substrate 11 and the temperature characteristic improvement layer 14 can be set, for example, to not exceed 1.0λ when the elastic wave wavelength determined by the electrode pitch of the IDT electrode is λ.

[0108] A semiconductor layer can also be provided between the piezoelectric substrate 11 and the temperature characteristic improvement layer 14. Silicon can be used for the semiconductor layer, for example. By using silicon with a thickness of 5 nm to 20 nm at the junction of the piezoelectric substrate 11 and the temperature characteristic improvement layer 14, bonding can be performed without increasing unnecessary stray waves.

[0109] Next, in combination with Figure 4 an example of the elastic wave element 50 formed on the piezoelectric substrate 11 will be described. Figure 12 is a top view showing the functional element 50 of the elastic wave device 1 in Embodiment 3.

[0110] As Figure 4 shown, 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 can excite elastic waves (mainly SH waves).

[0111] For example, the IDT electrode 51 and the pair of reflectors 52 are formed of an aluminum and copper alloy. For example, the IDT electrode 51 and the pair of reflectors 52 can also be formed of an appropriate metal such as aluminum, molybdenum, iridium, tungsten, cobalt, nickel, ruthenium, chromium, strontium, titanium, palladium, silver or an alloy thereof.

[0112] For example, the IDT electrode 51 and a pair of reflectors 52 are composed of a laminated metal film formed by stacking multiple metal layers. For example, the thickness of the IDT electrode 51 and a pair of reflectors 52 is 150 nm to 450 nm.

[0113] The IDT electrode 51 includes a pair of comb-shaped electrodes 51a. This pair of comb-shaped electrodes 51a are symmetric to each other. The comb-shaped electrode 51a is composed of multiple electrode fingers 51b and bus bars 51c.

[0114] The multiple electrode fingers 51b are arranged along the long side direction. The bus bar 51c is used to connect the multiple electrode fingers 51b.

[0115] One side of a pair of reflectors 52 is adjacent to one side of the IDT electrode 51. The other pair of reflectors 52 on the other side is adjacent to the other side of the IDT electrode 51.

[0116] Figure 13 It is a diagram showing the resonance characteristics of the resonator of the surface acoustic wave device 1 in Embodiment 3. The piezoelectric substrate 11 uses single crystal lithium tantalate. The thickness of the piezoelectric substrate 11 is 0.3λ.

[0117] Here, the thickness of the IDT electrode 51 is set to 0.1λ and is made of aluminum. The thickness of the temperature characteristic improvement layer 14 is set to 0.4λ and is made of SiO2. The thickness of the spurious absorption layer 13 is set to 15λ, and a Li2B4O7 single crystal substrate is used. The high acoustic velocity layer 12 is made of SiN.

[0118] Figure 14 Is Figure 13 A diagram in which the resonance characteristics of the surface acoustic wave device 1 shown in the region R1 in Figure 13 As shown, spurious signals are generated in the frequency band range of 1550 MHz to 1650 MHz.

[0119] Here, the solid line represents the characteristics when the thickness of the high acoustic velocity layer 12 is 0.25λ. The long dashed line represents the characteristics when the thickness of the high acoustic velocity layer 12 is 0.2λ. The long chain line represents the characteristics when the thickness of the high acoustic velocity layer 12 is 0.15λ. The dotted line represents the characteristics when the thickness of the high acoustic velocity layer 12 is 0.1λ. The dashed line represents the characteristics when the thickness of the high acoustic velocity layer 12 is 0.05λ. The dotted line represents the characteristics when the thickness of the high acoustic velocity layer 12 is 0λ.

[0120] As Figure 14 Shown, when the thickness of the high acoustic velocity layer 12 is 0.05λ, the suppression effect of the spurious signal is weak, but the spurious signal has shifted to the high frequency side. When the thickness of the high acoustic velocity layer 12 is 0.1λ, the suppression effect of the spurious signal is significantly enhanced, and the spurious signal further shifts to the high frequency side.

[0121] When the thickness of the high-velocity layer 12 is 0.15λ or 0.2λ, the suppression effect of the spurious signal is the most significant. When the thickness of the high-velocity layer 12 is 0.25λ, although the effect of suppressing the spurious signal is more obvious than when the thickness is 0.1λ, the suppression effect slightly decreases compared with the case when the thickness is 0.15λ or 0.2λ.

[0122] Therefore, the thickness of the high-velocity layer 12 is preferably set to be from 0.1λ to 0.3λ. More preferably, the thickness of the high-velocity layer 12 is set to be from 0.15λ to 0.25λ. Further preferably, the thickness of the high-velocity layer 12 is set to be from 0.15λ to 0.2λ.

[0123] Figures 5 to 7 shows the resonance characteristics of the resonator of the elastic wave device. The dependence of the resonance characteristics of the elastic wave device on the cutting angle of the main surface of the Li2B4O7 single crystal substrate is not affected by the presence or absence of the high-velocity layer 12. Whether the high-velocity layer 12 exists or not, the vibration is transmitted to the Li2B4O7 single crystal substrate, so the spurious signal still depends on the cutting angle of the Li2B4O7 single crystal substrate. In Figures 5 to 7 it shows the calculation result when the thickness of the high-velocity layer 12 is set to 0λ in calculating the resonance characteristics of the resonator of the elastic wave device.

[0124] Figure 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 uses single crystal lithium tantalate. The thickness of the piezoelectric substrate 11 is set to 0.3λ.

[0125] Here, the thickness of the IDT electrode 51 is set to 0.1λ and is made of aluminum. The thickness of the temperature characteristic improvement layer 14 is set to 0.4λ. The spurious absorption layer 13 uses a Li2B4O7 single crystal substrate.

[0126] Figure 5 In (a), the cutting angle of the main surface of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 90°). Figure 5 In (b), the cutting angle of the main surface of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 88°). Figure 5 In (c), the cutting angle of the main surface of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 86°).

[0127] Figure 5 Almost no transverse mode spurious signals are generated in the resonance characteristics shown in (a) and (b). It can be seen that a cutting angle deviation of about ±2% can be accepted as an error range when there are no substantial problems with the resonance characteristic quality. Figure 7In the resonance characteristics shown in (c), transverse mode spurious signals slightly appeared, but the transverse mode spurious signals were suppressed to a considerable extent.

[0128] Here, due to the symmetry of the crystal, the Euler angle φ has the same effect at 0° and 90°. Similarly, due to the symmetry of the crystal, the Euler angle ψ also has the same effect at 80° and 100°.

[0129] Figure 6 It is a diagram showing the resonance characteristics of the resonator of the elastic wave device 1 according to Embodiment 1. Figure 6 In (a), the cutting angle of the main plane of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 84°). Figure 6 In (b), the cutting angle of the main plane of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 82°). Figure 6 In (c), the cutting angle of the main plane of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 80°).

[0130] Figure 6 In the resonance characteristics shown in (a) to (c), transverse mode spurious signals slightly appeared. In addition, it can be seen that as the Euler angle ψ approaches 80°, the transverse mode spurious signals gradually deteriorate. If the resonance characteristics deteriorate further, exceeding Figure 6 the transverse mode spurious signals shown in (c), it will be difficult to apply as an elastic wave device, especially in the high-end smartphone market.

[0131] Figure 7 It is a diagram showing the resonance characteristics of the resonator of the comparative example of the elastic wave device 1 according to Embodiment 1. Figure 7 In (a), the cutting angle of the main plane of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 70°). Figure 7 In (b), the cutting angle of the main plane of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 60°).

[0132] Figure 7 In (c), the cutting angle of the main plane of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 50°). Figure 7 In (d), the cutting angle of the main plane of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 45°). Other parts are as Figure 5 described.

[0133] As Figure 7As shown, in the comparative example, a large transverse mode spurious signal appeared. When the cutting angle of the main surface of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 45° to 70°), as the angle with the crystal plane increases, the resonance characteristics gradually separate and couple with the spurious signal, forming such characteristics.

[0134] In addition, as the propagation direction changes with respect to the crystal plane, the resonance impedance also increases, resulting in energy leakage towards the substrate direction. When there is a strong spurious signal, it will cause significant characteristic degradation when combining resonators into structures such as filters. Therefore, the lower the peak value and the shallower the valley value of the spurious signal, the better the characteristics.

[0135] According to the above-described embodiment, the process steps after forming the resonator can be reduced, while reducing the damage to the resonator caused by the process, and an elastic wave device with suppressed transverse mode spurious signals can be provided.

[0136] Embodiment 4 Figure 15 is a cross-sectional view of the device chip 5 of the elastic wave device 1 according to Embodiment 4. As Figure 15 shown, the device chip 5 of the elastic wave device 1 according to Embodiment 4 is provided with a support substrate 20 on the other main surface of the spurious absorption layer 13 opposite to the piezoelectric substrate 11. A high-velocity layer 12 is provided on the spurious absorption layer 13, a temperature characteristic improvement layer 14 is provided on the high-velocity layer 12, and a piezoelectric substrate 11 is provided on the temperature characteristic improvement layer 14.

[0137] The support substrate 20 can be formed of materials such as sapphire, silicon, alumina, spinel, silicon nitride, aluminum nitride, silicon carbide, silicon oxynitride, diamond, quartz, glass, etc. The smaller the thermal expansion coefficient and the higher the Young's modulus of the support substrate 20, the better, because this can improve the temperature characteristics of the elastic wave device 1.

[0138] A typical substrate that satisfies these conditions is a sapphire substrate. Due to its high hardness and stable chemical properties, it is difficult to perform surface processing with concave-convex shapes or serrations, resulting in a decrease in the yield. Therefore, the support substrate 20 is preferably a flat plate-shaped rectangular parallelepiped shape.

[0139] The thickness of the support substrate 20 can be set to, for example, 50 μm to 200 μm.

[0140] Figure 16 is a graph showing the resonance characteristics of the resonator of the elastic wave device 1 according to Embodiment 4. The piezoelectric substrate 11 uses single crystal lithium tantalate, and the thickness is set to 0.3λ. The thickness of the IDT electrode 51 is set to 0.1λ and is made of aluminum. The thickness of the temperature characteristic improvement layer 14 is set to 0.4λ.

[0141] The stray absorption layer 13 uses a Li2B4O7 single crystal substrate. The cutting angle of the main surface of the Li2B4O7 single crystal substrate is the Euler angle (φ, θ, ψ) = (0°, 90°, 90°). The thickness of the stray absorption layer 13 is set to 2λ, 5λ, and 10λ.

[0142] Figure 17 Is Figure 16 A diagram showing the amplification of the resonance characteristics of the elastic wave device 1 shown in region R2 in. As Figure 17 Shown, spurious signals are generated in the frequency band range of 1500 MHz to 1650 MHz. Here, the solid line represents the characteristics when the thickness of the stray absorption layer 13 is 10λ; the dashed line represents the characteristics when the thickness of the stray absorption layer 13 is 5λ; the dotted line represents the characteristics when the thickness of the stray absorption layer 13 is 2λ.

[0143] As Figure 17 Shown, when the thickness of the stray absorption layer 13 is 10λ, the spurious signal is suppressed to the greatest extent. When the thickness of the stray absorption layer 13 is 2λ, the generation of the spurious signal is the most obvious. When the thickness of the stray absorption layer 13 is 5λ, the spurious signal is suppressed compared to 2λ, but is still more than the case of 10λ.

[0144] From this, it can be seen that the larger the thickness of the stray absorption layer 13, the more obvious the stray suppression effect. Therefore, the thickness of the stray absorption layer 13 is preferably set to, for example, 3λ to 20λ. More preferably, the thickness of the stray absorption layer 13 is set to, for example, 5λ to 20λ. Further preferably, the thickness of the stray absorption layer 13 is set to, for example, 10λ to 20λ. Other structures are the same as those in Embodiment 1, so the description is omitted.

[0145] According to the above Embodiment 2, it is possible to provide an elastic wave device with excellent resonance characteristics and suppressed high-frequency side transverse mode spurious signals while reducing the damage to the resonator caused by the process.

[0146] Embodiment 5 Figure 11 Is a longitudinal sectional view showing a module to which the elastic wave device 1 in Embodiments 1 to 4 is applied. Parts that are the same as or similar to those in Embodiments 1 to 4 are marked with the same symbols, so the description of this part is omitted.

[0147] In Figure 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, a coil 111, and a sealing portion 117.

[0148] A plurality of external connection terminals 131 are formed on the bottom surface of the package substrate 130. These external connection terminals 131 will be mounted on the main board of a preset mobile communication terminal.

[0149] For example, the integrated circuit component IC is installed inside the packaging substrate 130. The integrated circuit component IC includes a switching circuit and a low noise amplifier.

[0150] The surface acoustic wave device 1 is installed on the main surface of the packaging substrate 130.

[0151] The coil 111 is installed on the main surface of the packaging substrate 130. The coil 111 is used to achieve impedance matching. For example, the coil 111 is an integrated passive device (abbreviated as IPD).

[0152] The sealing portion 117 seals a plurality of electronic components including the surface acoustic wave device 1.

[0153] The above-mentioned module 100 is equipped with the surface acoustic wave device 1. Therefore, a module of a surface acoustic wave device can be provided, which reduces the process steps after the resonator is formed, reduces the damage of the process to the resonator, and suppresses the transverse mode spurious waves at the same time.

[0154] Although several aspects of at least one embodiment have been described, it should be understood that many changes, modifications, and improvements are readily conceivable to those skilled in the art. These changes, modifications, and improvements are intended to be part of the present disclosure and are intended to fall within the scope of the present disclosure.

[0155] It should be understood that the embodiments of the methods and apparatuses described herein are not limited to the details of the structures and arrangements of the components described in the above description or shown in the drawings. The methods and apparatuses can be implemented in other embodiments and implemented or executed in various forms.

[0156] Specific embodiments are provided herein only by way of example and are not intended to be limiting.

[0157] The expressions and terms used in the present disclosure are for illustrative purposes only and should not be construed as limiting. The use of "including", "having", "owning", "containing" and their variants herein means the inclusion of the items listed hereinafter and their equivalents as well as additional items.

[0158] The "or" mentioned can be interpreted as any term described using "or" can mean one, more than one or all of the terms.

[0159] The front, back, left, right, up, down, horizontal, vertical, inside, and outside mentioned are for convenience of description. This mention does not mean that the components of the present disclosure are limited to a specific orientation or spatial orientation. Therefore, the above description and illustration are only examples.

Claims

1. An elastic wave device, comprising: A piezoelectric substrate, and a resonator for exciting a surface acoustic wave formed on a main surface of the piezoelectric substrate; characterized in that: a stray absorption layer formed on the other main surface of the piezoelectric substrate; The stray absorption layer is composed of a tetragonal crystal substrate, and its acoustic velocity is slower than that of the piezoelectric substrate.

2. The elastic wave device according to claim 1, characterized in that: The cutting angle of the main surface of the stray absorption layer is the Euler angle (φ, θ, ψ), wherein φ=0°±2° or 90°±2°, θ=90°±2°, and ψ ranges from 80° to 100°.

3. The elastic wave device according to claim 1, characterized in that: When the wavelength of the main mode wave excited by the resonator is λ, the thickness of the stray absorption layer is greater than 3λ and less than 20λ.

4. The elastic wave device according to claim 1, characterized in that: The stray absorption layer has a lower crystal density than the piezoelectric substrate.

5. The elastic wave device according to claim 1, characterized in that: The stray absorption layer is a Li2B4O7 single crystal substrate.

6. The elastic wave device according to claim 1, characterized in that: A supporting substrate is provided on the main surface of the stray absorption layer opposite to the piezoelectric substrate; the supporting substrate is a substrate made of sapphire, silicon, aluminum oxide, spinel, silicon nitride, aluminum nitride, silicon carbide, acid silicon nitride, diamond, quartz, or glass.

7. The elastic wave device according to claim 1, characterized in that: It also includes a temperature characteristic improving layer formed between the piezoelectric substrate and the stray absorption layer; the temperature characteristic curve of the material constituting the temperature characteristic improving layer is opposite to the temperature characteristic curve of the material constituting the piezoelectric substrate.

8. The elastic wave device according to claim 7, characterized in that: The temperature characteristic improvement layer is SiO2, and when the elastic wave wavelength is λ, the thickness of the temperature characteristic improvement layer is 0.05λ to 0.45λ; the thickness of the piezoelectric substrate is 0.1λ to 0.9λ; the total thickness of the piezoelectric substrate and the temperature characteristic improvement layer does not exceed 1.0λ.

9. The elastic wave device according to claim 7, characterized in that: A semiconductor layer is further provided between the piezoelectric substrate and the temperature characteristic improving layer, and the semiconductor layer is 5-20 nm of silicon.

10. The elastic wave device according to claim 1, wherein: A high-sound-velocity layer is formed between the piezoelectric substrate and the stray absorption layer, and the sound velocity of the high-sound-velocity layer is higher than that of the piezoelectric substrate.

11. The elastic wave device according to claim 10, characterized in that: The thickness of the high-sonic velocity layer is smaller than the thickness of the piezoelectric substrate.

12. The elastic wave device according to claim 10, characterized in that: When the wavelength of the main mode wave excited by the resonator is λ, the thickness of the high-speed acoustic layer is between 0.1λ and 0.3λ.

13. The elastic wave device according to claim 1, wherein: It also includes a temperature characteristic improvement layer and a high sonic velocity layer, wherein the temperature characteristic improvement layer is arranged between the piezoelectric substrate and the high sonic velocity layer, and the high sonic velocity layer is arranged between the temperature characteristic improvement layer and the stray absorption layer; the thickness of the high sonic velocity layer is smaller than the thickness of the temperature characteristic improvement layer.

14. A module, characterized in that: The module includes the elastic wave device according to any one of claims 1 to 13.

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