Bulk elastic wave filter device

Abstract

Provided is a bulk elastic wave filter device having a good heat dissipation property. The bulk elastic wave filter device comprises: an acoustic multilayer film that includes, on a supporting substrate, a first layer and a second layer layered in an alternating pattern, the first layer having a prescribed characteristic acoustic impedance, the second layer having a lower characteristic acoustic impedance than the first layer; and an active element that is provided on the opposite side of the acoustic multilayer film from the supporting substrate. The active element includes a first electrode layer provided on the acoustic multilayer film, a piezoelectric layer provided on the first electrode layer, and a second electrode layer provided on the piezoelectric layer. A portion of or the entirety of the acoustic multilayer film has electrical conductivity. An insulating layer is provided between the acoustic multilayer film and the first electrode layer. In a preferable configuration example, the second layer, which has electric conductivity, has an electric resistivity of 1.0×10^-3 Ω cm or less.

Description

Bulk Acoustic Wave Filter Devices

[0001] The present invention relates to bulk acoustic wave filter devices.

[0002] High-frequency radio waves, such as microwaves, millimeter waves, and terahertz waves, enable high-speed, high-capacity communications. The 5G mobile communication standard uses the "sub-6" frequency band, close to 6 GHz, and the 28 GHz band, with the 100 GHz band also being considered for future use. Therefore, resonators and bandpass filters suitable for frequencies exceeding several GHz are required. Bulk Acoustic Wave (BAW) resonators or BAW filters are used in resonators for electronic devices such as smartphones and high-frequency filters for communication devices. The thickness of the functional layer constituting a BAW device is determined by the target frequency, with thinner layers becoming thinner as the frequency increases. Functional elements (or active elements) such as BAW resonators change their acoustic and electrical properties due to heat, so they require a configuration that can reduce the effects of heat.

[0003] A known configuration is one in which an acoustic mirror layer made of alternating low thermal conductive layers and high thermal conductive layers is provided between a resonator and a support substrate, and the resonator and support substrate are connected by a heat bridge (see, for example, Patent Document 1).

[0004] Patent No. 6668347

[0005] As electronic and communication devices become increasingly high-frequency, their components are becoming smaller, posing a problem of temperature rise during device operation, resulting in a decline in device performance. Known heat bridge configurations require complex processing steps to form the heat bridge. In configurations where the heat bridge surrounds the sides of the acoustic mirror, a heat transfer path is created through the low thermal conductivity layer, preventing efficient heat dissipation. In configurations where the beat bridge is located directly below the resonator, the heat bridge interferes with the acoustic mirror's reflection of the elastic waves, resulting in a decline in resonance characteristics.

[0006] In one aspect, the present invention aims to provide a bulk acoustic wave filter device with good heat dissipation properties.

[0007] In one embodiment, the bulk acoustic wave filter device comprises an acoustic multilayer film in which first layers having a predetermined specific acoustic impedance and second layers having a lower specific acoustic impedance than the first layers are alternately stacked on a support substrate; and an active element provided on the side of the acoustic multilayer film opposite the support substrate, wherein the active element has a first electrode layer provided on the acoustic multilayer film, a piezoelectric layer provided on the first electrode layer, and a second electrode layer provided on the piezoelectric layer, and part or all of the second layer in the acoustic multilayer film is conductive, and an insulating layer is provided between the acoustic multilayer film and the first electrode layer.

[0008] In a preferred configuration example, the second layer having electrical conductivity has an electrical resistivity of 1.0×10 −3 Ωcm or less.

[0009] A laminate having good heat dissipation properties and a high frequency filter device using the same are realized.

[0010] 1 is a schematic diagram of a laminate used in a bulk acoustic wave filter device according to an embodiment; FIG. 2 is a schematic diagram of a bulk acoustic wave filter device using the laminate of FIG. 1; FIG. 3 is a schematic diagram of a modified example of the laminate of FIG. 1; FIG. 4 is a schematic diagram of a bulk acoustic wave filter device using the laminate of FIG. 3; FIG. 5 is a diagram showing the structure and thermal characteristics of a laminate of an example; FIG. 6 is a diagram showing the structure and thermal characteristics of a laminate of an example; and FIG. 7 is a diagram showing the structure and thermal characteristics of a laminate of a comparative example.

[0011] Thermal conduction in thin films is primarily due to thermal conduction caused by phonons (lattice vibrations) and thermal conduction caused by carriers. Silicon oxide (SiO2) films, which have traditionally been used in low acoustic impedance layers of acoustic mirrors, are insulating materials, and thermal conduction caused by phonons is dominant. Generally, thermal conduction caused by carriers is more efficient than thermal conduction caused by phonons because the mean free path of the carriers is long. While thermal conduction caused by carriers is affected by carrier density, thermal conduction caused by phonons is not directly affected by carrier density. Therefore, in the present embodiment, the heat dissipation effect of functional devices that utilize vibrations is enhanced by making thermal conduction caused by carriers dominant.

[0012] Specific configurations of bulk acoustic wave filter devices according to embodiments are described below with reference to the drawings. The following embodiments are merely examples for embodying the technical concepts of the present disclosure and are not intended to limit the scope of the disclosure. The sizes, positional relationships, and other aspects of components shown in the drawings may be exaggerated to facilitate understanding of the invention. Identical components or functions may be given the same names or symbols to minimize redundant explanations. When referring to positional relationships, "above" or "below" refers to the top and bottom of the stacking direction or film formation direction, unless otherwise specified, and is not an absolute direction.

[0013] FIG. 1 is a schematic diagram of a laminate 20 used in a bulk acoustic wave filter device according to an embodiment. The laminate 20 includes an acoustic multilayer film 18 and an insulating layer 19 disposed on a support substrate 11. The acoustic multilayer film 18 is a multilayer film formed by alternately stacking two or more pairs of first layers 16 having a predetermined specific acoustic impedance and second layers 17 having a lower specific acoustic impedance than the first layers. Because the first layers 16 have a higher specific acoustic impedance than the second layers 17, the first layers are referred to as "high acoustic impedance layers 16" and the second layers are referred to as "low acoustic impedance layers 17" for convenience. A feature of this embodiment is that at least one low acoustic impedance layer 17 is formed of a conductive oxide.

[0014] When resonant vibrations are transmitted to the acoustic multilayer film 18 via the insulating layer 19, the vibration energy of the resonance is reflected by the acoustic multilayer film 18. The speed at which the vibration waves (elastic waves) propagate through the high acoustic impedance layer 16 differs from the speed at which they propagate through the low acoustic impedance layer 17. By designing the film thickness so that the reflected waves reinforce each other due to interference at the interfaces of the layers that make up the acoustic multilayer film 18, the vibration energy of the resonance is returned in the direction of incidence of the elastic waves without being affected by the support substrate 11, while dissipating thermal energy in the direction of the support substrate 11.

[0015] The high acoustic impedance layer 16 is formed of a material with a high density or bulk modulus, such as tungsten (W), molybdenum (Mo), tantalum oxide (Ta2O5), or zinc oxide (ZnO). The low acoustic impedance layer 17 is formed of a material with a lower density or bulk modulus than the high acoustic impedance layer 16, and by selecting a conductive material, the carrier can be responsible for heat conduction. The range of its electrical resistivity is preferably 1.0 x 10^-3 Ωcm or less, more preferably 8.0 x 10^-4 Ωcm or less, and even more preferably 5.0 x 10^-4 Ωcm or less. In the following description, "electrical resistivity" may be simply referred to as "resistivity."

[0016] The low acoustic impedance layer 17 may be made of a conductive oxide such as ITO (indium tin oxide), AZO (aluminum-doped zinc oxide), IZO (indium-doped zinc oxide), FTO (fluorine-doped tin oxide), GZO (gas-doped zinc oxide), ATO (antimony-doped tin oxide), or PTO (phosphorus-doped tin oxide). These materials are generally used as transparent conductive films. As described below, the thermal conductivity of the low acoustic impedance layer 17 is 3 W / mK or higher, and more preferably 3.35 W / mK or higher. The low acoustic impedance layer 17 may be an amorphous layer or a layer predominantly composed of an amorphous phase. By making the low acoustic impedance layer 17 a layer predominantly composed of an amorphous phase, stress increase in the high acoustic impedance layer 16 can be suppressed.

[0017] The high acoustic impedance layer 16 and the low acoustic impedance layer 17 are formed by sputtering or the like on the support substrate 11. By using a conductive oxide as the low acoustic impedance layer 17, heat diffusion by carriers becomes possible, and complicated processing steps such as providing a heat bridge are not required.

[0018] The support substrate 11 is any substrate capable of supporting the acoustic multilayer film 18. A semiconductor substrate such as silicon (Si) may be used, an inorganic dielectric substrate such as MgO or sapphire may be used, or a plastic substrate may be used. When a flexible substrate is used as the support substrate 11, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polycarbonate (PC), acrylic resin, cycloolefin polymer, polyimide (PI), thin film glass, etc. may be used. An insulating layer 19 provided on the surface opposite the support substrate 11 electrically insulates the acoustic multilayer film 18 from active elements (resonators, etc.) connected to the acoustic multilayer film 18.

[0019] 2 is a schematic diagram of a bulk acoustic wave filter device 10 using the laminate 20 of Fig. 1. The bulk acoustic wave filter device 10 has a first electrode layer 12, a second electrode layer 14, and a piezoelectric layer 13 provided between the first electrode layer 12 and the second electrode layer 14 on an insulating layer 19 of the laminate 20. The first electrode layer 12, the second electrode layer 14, and the piezoelectric layer 13 form a resonator 15, which is an active element.

[0020] The first electrode layer 12 and the second electrode layer 14 are formed of a conductive material. For example, Mo, W, Pr, Au, Ru, Ir, Al, Cu, etc. may be used as the conductive material. The piezoelectric layer 13 may be made of a wurtzite crystal, a perovskite crystal, etc. These crystal materials may be used as the main component, with a predetermined amount of impurity elements added as a secondary component. Examples of wurtzite piezoelectric materials include zinc oxide (ZnO), aluminum nitride (AlN), and gallium nitride (GaN).

[0021] When a high frequency wave is input to the resonator 15, a resonant vibration occurs at a specific frequency corresponding to the film thickness of the piezoelectric layer 13. When the resonator 15 is driven, resonant vibration energy is generated, and heat is generated due to electrical driving. The resonant vibration energy transmitted to the acoustic multilayer film 18 via the insulating layer 19 is reflected by the acoustic multilayer film 18, returns to the resonator 15, and is trapped between the first electrode layer 12 and the second electrode layer 14. The trapped vibration is extracted as an electrical signal by the first electrode layer 12 and the second electrode layer 14.

[0022] Heat generated by driving the resonator 15 is transferred to the support substrate 11 by the acoustic multilayer film 18. The low acoustic impedance layer 17 has a thermal conductivity of 3 W / mK or more, and can transfer heat to the support substrate 11 efficiently.

[0023] Fig. 3 is a schematic diagram of a laminate 40, which is a modified example of the laminate 20 of Fig. 1. In the laminate 20 of Fig. 1, all of the low acoustic impedance layers 17 in the acoustic multilayer film 18 are formed from conductive oxides, and an insulating layer 19 is provided on the acoustic multilayer film 18. In the laminate 40 of Fig. 3, some of the low acoustic impedance layers are formed from conductive oxides, and some are formed from conventional insulating materials. At least the low acoustic impedance layer 27-2 provided as the uppermost layer of the acoustic multilayer film 28 is formed from an insulating material. The insulating material is SiO2, Al2O3, or the like.

[0024] The laminate 40 includes an acoustic multilayer film 28 formed by alternately stacking high acoustic impedance layers 26 and low acoustic impedance layers 27-1 or 27-2 on a support substrate 11. The low acoustic impedance layer 27-2 of the acoustic multilayer film 28, which is connected to an active element such as a piezoelectric element or resonator on the side opposite the support substrate 11, may be formed of an insulating material, while the other low acoustic impedance layer 27-1 may be formed of a conductive oxide. This configuration eliminates the need for a separate insulating layer on the acoustic multilayer film 28. Because the insulating low acoustic impedance layer 27-2 accounts for only a small proportion of the acoustic multilayer film 28, heat is efficiently transferred to the support substrate 11 by the high acoustic impedance layer 26 and the conductive oxide low acoustic impedance layer 27-1.

[0025] 4 is a schematic diagram of a bulk acoustic wave filter device 30 using the laminate 40 of FIG. 3. The bulk acoustic wave filter device 30 has a first electrode layer 12, a second electrode layer 14, and a piezoelectric layer 13 provided between the first electrode layer 12 and the second electrode layer 14 on the laminate 40. The first electrode layer 12, the second electrode layer 14, and the piezoelectric layer 13 form a resonator 15, which is an active element.

[0026] The configuration of the resonator 15 is the same as that of the resonator 15 shown in Fig. 2. The piezoelectric layer 13 may be made of a perovskite crystal or a wurtzite crystal.

[0027] When a high frequency wave is input to the resonator 15, a resonant vibration occurs at a specific frequency corresponding to the film thickness of the piezoelectric layer 13. When the resonator 15 is driven, resonant vibration energy is generated, and heat is generated due to electrical driving. The resonant vibration energy transmitted from the resonator 15 to the acoustic multilayer film 28 is reflected by the acoustic multilayer film 28, returns to the resonator 15, and is trapped between the first electrode layer 12 and the second electrode layer 14. The trapped vibration is extracted as an electrical signal by the first electrode layer 12 and the second electrode layer 14.

[0028] In the configurations of FIGS. 3 and 4, at least one low acoustic impedance layer 28-1 of the low acoustic impedance layers included in the acoustic multilayer film 28 is formed of a conductive oxide, so that the heat dissipation effect is high.

[0029] 5A and 5B show the structure and thermal characteristics of the laminate of the example. FIG. 5C shows the structure and thermal characteristics of the laminate of the comparative example. For ease of illustration, the low acoustic impedance layer and the high acoustic impedance layer are sometimes referred to as "low acoustic imp. layer" and "high acoustic imp. layer," respectively, in FIGS. 5A to 5C. A common structure between the example and the comparative example is that three high acoustic impedance layers and three low acoustic impedance layers are alternately stacked. The thermal conductivity and thermal resistance of the low acoustic impedance layer and the high acoustic impedance layer were measured by varying the frequency of the high frequency applied to the laminate, the thickness of the material of the low acoustic impedance layer, and the material and thickness of the high acoustic impedance layer. The thermal conductivity and thermal resistance were measured by calculating the thermal diffusivity λ using the thermoreflectance method, and then calculating the thermal conductivity κ using the following formula:

[0030] κ=ρcλ where ρ is density and c is specific heat. The thermal resistance R was calculated using the following formula.

[0031] R=d / κ where d is the film thickness.

[0032] Example 1 In Example 1, a silicon substrate is used as the substrate, with the high acoustic impedance layer made of W and the low acoustic impedance layer made of ITO. When the center frequency of the applied high frequency is 2 GHz, the center wavelength of the elastic wave propagating through the high acoustic impedance layer is approximately 2600 nm. The thickness of the high acoustic impedance layer is set to 650 nm, which is ¼ of the center wavelength of the elastic wave. The center wavelength of the elastic wave propagating through the ITO low acoustic impedance layer is approximately 2165 nm, and the thickness of the ITO layer is set to 541 nm. The resistivity of ITO is 3.3 x 10^-4 Ωcm, and it has sufficient conductivity to cause heat conduction by carriers. Here, the thermal conductivity of the high acoustic impedance layer is 5.06 x 10 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 5.95 (W / mK). The thermal resistance of the low acoustic impedance layer is 9.08 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 1.28×10^-8 (m ２ K / W), and the total thermal resistance is 1.04 x 10^-7 (m ２ It can be seen that the thermal conductivity of ITO is very good, and the acoustic multilayer film as a whole has low thermal resistance and good thermal conductivity.

[0033] Example 2 In Example 2, a silicon substrate is used as the substrate, with the high acoustic impedance layer made of W and the low acoustic impedance layer made of IZO. The thickness of the high acoustic impedance layer is set to 650 nm, the same as in Example 1. The center wavelength of the acoustic waves propagating through the IZO low acoustic impedance layer is approximately 2035 nm, and the thickness of the IZO layer is set to 509 nm. The resistivity of IZO is 4.1 x 10^-4 Ωcm, and it has sufficient conductivity to cause heat conduction by carriers. Here, the thermal conductivity of the high acoustic impedance layer is 5.06 x 10 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 3.35 (W / mK). The thermal resistance of the low acoustic impedance layer is 1.52 x 10^-7 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 1.28×10^-8 (m ２ K / W), total thermal resistance is 1.65 x 10^-7 (m ２ The acoustic multilayer film as a whole has low thermal resistance and good thermal conductivity.

[0034] Example 3 In Example 3, a silicon substrate is used as the substrate, with the high acoustic impedance layer made of W and the low acoustic impedance layer made of AZO. The thickness of the high acoustic impedance layer is set to 650 nm, the same as in Example 1. The center wavelength of the acoustic wave propagating through the AZO low acoustic impedance layer is approximately 2052 nm, and the thickness of the AZO layer is set to 538 nm. The resistivity of AZO is 4.0 x 10^-4 Ωcm, and it has sufficient conductivity to cause heat conduction by carriers. Here, the thermal conductivity of the high acoustic impedance layer is 5.06 x 10 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 4.89 (W / mK). The thermal resistance of the low acoustic impedance layer is 1.10 x 10^-7 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 1.28×10^-8 (m ２ K / W), and the total thermal resistance is 1.23 x 10^-7 (m ２ AZO has good thermal conductivity, and the acoustic multilayer film as a whole has low thermal resistance and good thermal conductivity.

[0035] Example 4 In Example 4, as in Example 1, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using ITO. Unlike Example 1, the center frequency of the applied high frequency is set to 6 GHz. In this case, the center wavelength of the acoustic wave propagating through the high acoustic impedance layer is approximately 868 nm, and the thickness of the high acoustic impedance layer is set to 217 nm. The center wavelength of the acoustic wave propagating through the ITO layer is approximately 720 nm, and the thickness of the ITO layer is set to 180 nm. The resistivity of ITO is 3.3 x 10^-4 Ωcm, and it has sufficient conductivity to cause heat conduction by carriers. Here, the thermal conductivity of the high acoustic impedance layer is 5.06 x 10 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 5.95 (W / mK). The thermal resistance of the low acoustic impedance layer is 3.03 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 4.28×10^-9 (m ２ K / W), total thermal resistance is 3.64 x 10^-8 (m ２ITO has a good thermal conductivity, and the entire acoustic multilayer film has low thermal resistance to 6 GHz resonant vibration and good thermal conductivity.

[0036] <Example 5> In Example 5, as in Example 2, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using IZO. Unlike Example 2, the center frequency of the applied high frequency is set to 6 GHz. The thickness of the high acoustic impedance layer is set to 217 nm and the thickness of the IZO layer is set to 170 nm. The resistivity of IZO is 4.1 x 10^-4 Ωcm, and it has sufficient conductivity to cause heat conduction by carriers. Here, the thermal conductivity of the high acoustic impedance layer is 5.06 x 10^-4 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 3.35 (W / mK). The thermal resistance of the low acoustic impedance layer is 5.06 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 4.28×10^-9 (m ２ K / W), total thermal resistance is 5.49 x 10^-8 (m ２ The acoustic multilayer film as a whole has low thermal resistance to 6 GHz resonant vibration and good thermal conductivity.

[0037] Example 6 In Example 6, as in Example 3, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using AZO. Unlike Example 3, the center frequency of the applied high frequency is set to 6 GHz. The thickness of the high acoustic impedance layer is set to 217 nm and the thickness of the AZO layer is set to 170 nm. The resistivity of AZO is 4.0 x 10^-4 Ωcm, and it has sufficient conductivity to cause heat conduction by carriers. Here, the thermal conductivity of the high acoustic impedance layer is 5.06 x 10 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 4.89 (W / mK). The thermal resistance of the low acoustic impedance layer is 3.47 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 4.28×10^-9 (m ２ K / W), total thermal resistance is 3.90 x 10^-8 (m ２ AZO has good thermal conductivity, and the entire acoustic multilayer film has low thermal resistance to 6 GHz resonant vibration and good thermal conductivity.

[0038] <Example 7> In Example 7, as in Example 1, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using ITO. Unlike Example 1, the center frequency of the applied high frequency is set to 3 GHz. The thickness of the high acoustic impedance layer is 433 nm. The thickness of the low acoustic impedance (ITO) layer is 360 nm. The materials of the low acoustic impedance layer and the high acoustic impedance layer are ITO and W, as in Example 1, and the thermal conductivity of each is the same as in Example 1. The thermal resistance of the low acoustic impedance layer is 6.06 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 8.56×10^-9 (m ２ K / W), total thermal resistance is 6.91 x 10^-8 (m ２ ITO has a good thermal conductivity, and the entire acoustic multilayer film has low thermal resistance to 6 GHz resonant vibration and good thermal conductivity.

[0039] <Example 8> In Example 8, as in Example 2, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using IZO. Unlike Example 2, the center frequency of the applied high frequency is set to 3 GHz. The thickness of the high acoustic impedance layer is 433 nm and the thickness of the IZO layer is 339 nm. The materials of the low acoustic impedance layer and the high acoustic impedance layer are IZO and W, as in Example 2, and the thermal conductivity of each is the same as in Example 2. The thermal resistance of the low acoustic impedance layer is 1.01 x 10^-7 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 8.56×10^-9 (m ２ K / W), total thermal resistance is 1.10 x 10^-7 (m ２ The acoustic multilayer film as a whole has low thermal resistance to 3 GHz resonant vibration and good thermal conductivity.

[0040] <Example 9> In Example 9, as in Example 3, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using AZO. Unlike Example 3, the center frequency of the applied high frequency is set to 3 GHz. The thickness of the high acoustic impedance layer is 433 nm and the thickness of the AZO layer is 358 nm. The materials of the low acoustic impedance layer and the high acoustic impedance layer are AZO and W, as in Example 3, and the thermal conductivity of each is the same as in Example 3. The thermal resistance of the low acoustic impedance layer is 7.33 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 8.56×10^-9 (m ２ K / W), and the total thermal resistance is 8.18 x 10^-8 (m ２ AZO has good thermal conductivity, and the entire acoustic multilayer film has low thermal resistance to 3 GHz resonant vibration and good thermal conductivity.

[0041] Example 10 In Example 10, as in Example 1, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using ITO. Unlike Example 1, the center frequency of the applied high frequency is set to 4 GHz. The thickness of the high acoustic impedance layer is 325 nm. The thickness of the low acoustic impedance (ITO) layer is 270 nm. The materials of the low acoustic impedance layer and the high acoustic impedance layer are ITO and W, as in Example 1, and the thermal conductivity of each is the same as in Example 1. The thermal resistance of the low acoustic impedance layer is 4.54 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 6.42 × 10^-9 (m ２ K / W), total thermal resistance is 5.18 x 10^-8 (m ２ ITO has a good thermal conductivity, and the entire acoustic multilayer film has low thermal resistance to 4 GHz resonant vibration and good thermal conductivity.

[0042] <Example 11> In Example 8, as in Example 2, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using IZO. Unlike Example 2, the center frequency of the applied high frequency is set to 4 GHz. The thickness of the high acoustic impedance layer is 325 nm and the thickness of the IZO layer is 254 nm. The materials of the low acoustic impedance layer and the high acoustic impedance layer are IZO and W, as in Example 2, and the thermal conductivity of each is the same as in Example 2. The thermal resistance of the low acoustic impedance layer is 7.58 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 6.42 × 10^-9 (m ２ K / W), total thermal resistance is 8.23 ​​x 10^-8 (m ２ The acoustic multilayer film as a whole has low thermal resistance to 4 GHz resonant vibration and good thermal conductivity.

[0043] <Example 12> In Example 12, as in Example 3, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using AZO. Unlike Example 3, the center frequency of the applied high frequency is set to 4 GHz. The thickness of the high acoustic impedance layer is 325 nm and the thickness of the AZO layer is 269 nm. The materials of the low acoustic impedance layer and the high acoustic impedance layer are AZO and W, as in Example 3, and the thermal conductivity of each is the same as in Example 3. The thermal resistance of the low acoustic impedance layer is 5.50 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 6.42 × 10^-9 (m ２ K / W), total thermal resistance is 6.14 x 10^-8 (m ２ AZO has good thermal conductivity, and the entire acoustic multilayer film has low thermal resistance to 4 GHz resonant vibration and good thermal conductivity.

[0044] Example 13 In Example 13, as in Example 1, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using ITO. Unlike Example 1, the center frequency of the applied high frequency is set to 5 GHz. The thickness of the high acoustic impedance layer is 260 nm. The thickness of the low acoustic impedance (ITO) layer is 216 nm. The materials of the low acoustic impedance layer and the high acoustic impedance layer are ITO and W, as in Example 1, and the thermal conductivity of each is the same as in Example 1. The thermal resistance of the low acoustic impedance layer is 3.63 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 5.14×10^-9 (m ２ K / W), total thermal resistance is 4.15 x 10^-8 (m ２ ITO has a good thermal conductivity, and the entire acoustic multilayer film has low thermal resistance to 5 GHz resonant vibration and good thermal conductivity.

[0045] Example 14 In Example 14, as in Example 2, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using IZO. Unlike Example 2, the center frequency of the applied high frequency is set to 5 GHz. The thickness of the high acoustic impedance layer is set to 260 nm and the thickness of the IZO layer is set to 204 nm. The materials of the low acoustic impedance layer and the high acoustic impedance layer are IZO and W, as in Example 2, and the thermal conductivity of each is the same as in Example 2. The thermal resistance of the low acoustic impedance layer is 6.07 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 5.14×10^-9 (m ２ K / W), total thermal resistance is 6.58 x 10^-8 (m ２ The acoustic multilayer film as a whole has low thermal resistance to 5 GHz resonant vibration and good thermal conductivity.

[0046] <Example 15> In Example 15, as in Example 3, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer is formed using AZO. Unlike Example 3, the center frequency of the applied high frequency is set to 5 GHz. The thickness of the high acoustic impedance layer is set to 260 nm and the thickness of the AZO layer is set to 215 nm. The materials of the low acoustic impedance layer and the high acoustic impedance layer are AZO and W, as in Example 3, and the thermal conductivity of each is the same as in Example 3. The thermal resistance of the low acoustic impedance layer is 4.40 x 10^-8 (m ２ K / W), and the thermal resistance of the high acoustic impedance layer is 5.14×10^-9 (m ２ K / W), and the total thermal resistance is 4.91 x 10^-8 (m ２ AZO has good thermal conductivity, and the entire acoustic multilayer film has low thermal resistance to 4 GHz resonant vibration and good thermal conductivity.

[0047] <Comparative Example 1> Referring to FIG. 5C, in Comparative Example 1, a silicon substrate is used as the substrate, the high acoustic impedance layer is made of W, and the low acoustic impedance layer is made of SiO2. When the center frequency of the applied high frequency is 2 GHz, the thickness of the high acoustic impedance layer is set to 650 nm. The center wavelength of the elastic wave propagating through the SiO2 low acoustic impedance layer is approximately 2980 nm, and the thickness of the SiO2 layer is set to 745 nm. SiO2 is generally an insulator, and since its resistivity is 10^6 Ωcm or more, no heat conduction occurs due to carriers. Here, the thermal conductivity of the high acoustic impedance layer is 5.06 x 10 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 1.31 (W / mK), which is low. The thermal resistance of the high acoustic impedance layer is 1.28 x 10^-8 (m ２ K / W), but the thermal resistance of the low acoustic impedance layer is 5.68×10^-7 (m ２ K / W), and the total thermal resistance is 5.81 x 10^-7 (m ２ The thermal conductivity of SiO2 is poor and the thermal resistance is high, so the acoustic multilayer film as a whole has high thermal resistance and poor thermal conductivity. This acoustic multilayer film cannot dissipate heat sufficiently, which may result in a deterioration of the resonance characteristics.

[0048] <Comparative Example 2> In Comparative Example 2, similar to Comparative Example 1, a high acoustic impedance layer is formed on a silicon substrate using W and a low acoustic impedance layer using SiO2, but a high frequency with a center frequency of 6 GHz is applied. The thickness of the high acoustic impedance layer is set to 217 nm, and the thickness of the SiO2 layer, which is the low acoustic impedance layer, is set to 248 nm. SiO2 is generally an insulator, and since its resistivity is 10^6 Ωcm or more, no heat conduction occurs due to carriers. Here, the thermal conductivity of the high acoustic impedance layer is 5.06 x 10 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 1.31 (W / mK), which are low. The thermal resistance of the high acoustic impedance layer is 4.28 x 10^-9 (m ２ K / W), but the thermal resistance of the low acoustic impedance layer is 1.89 × 10^-7 (m ２ K / W), and the total thermal resistance is 1.94 x 10^-7 (m ２ The thermal conductivity of SiO2 is low and the thermal resistance is high, resulting in a high thermal resistance for the entire acoustic multilayer. This acoustic multilayer cannot dissipate heat sufficiently for the 6 GHz resonant vibration, which may result in a deterioration of the resonance characteristics.

[0049] Comparative Example 3 In Comparative Example 3, a silicon substrate is used as the substrate, the high acoustic impedance layer is made of Mo, and the low acoustic impedance layer is made of SiO2, and a high frequency with a center frequency of 2 GHz is applied. The center wavelength of the elastic wave propagating through Mo is approximately 3096 nm, and the thickness of the Mo layer is set to 774 nm. The thickness of the SiO2 low acoustic impedance layer is set to 745 nm, as in Comparative Example 1. SiO2 is generally an insulator, and since its resistivity is 10^6 Ωcm or more, no heat conduction occurs due to carriers. Here, the thermal conductivity of the high acoustic impedance layer is 3.53 x 10 (W / mK), which is sufficiently high, but the thermal conductivity of the low acoustic impedance layer is low at 1.31 (W / mK). The thermal resistance of the high acoustic impedance layer is 2.19 x 10^-8 (m ２ K / W), but the thermal resistance of the low acoustic impedance layer is 5.68×10^-7 (m ２ K / W), and the total thermal resistance is 5.90 x 10^-7 (m ２The thermal conductivity of SiO2 is low and the thermal resistance is high, so the thermal resistance of the entire acoustic multilayer is also high. This acoustic multilayer cannot dissipate heat sufficiently for the 2 GHz resonant vibration, which may result in a deterioration of the resonance characteristics.

[0050] Comparative Example 4 In Comparative Example 4, a silicon substrate is used as the substrate, the high acoustic impedance layer is made of ZnO, and the low acoustic impedance layer is made of SiO2, and a high frequency with a center frequency of 2 GHz is applied. The center wavelength of the acoustic wave propagating through ZnO is approximately 3776 nm, and the thickness of the ZnO layer is set to 944 nm. The thickness of the SiO2 low acoustic impedance layer is set to 745 nm, as in Comparative Examples 1 and 3. SiO2 is generally an insulator, and its resistivity is 10 ６ Since the thermal conductivity of the high acoustic impedance layer is 1.94×10 (W / mK) or more, heat conduction by the carrier does not occur. Here, the thermal conductivity of the high acoustic impedance layer is 1.94×10 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 1.31 (W / mK). The thermal resistance of the high acoustic impedance layer is 4.97×10 －８ (m ２ K / W), but the thermal resistance of the low acoustic impedance layer is 5.68×10 －７ (m ２ K / W), and the total thermal resistance is 6.18 x 10 －７ (m ２ The thermal conductivity of SiO2 is poor and the thermal resistance is high, so the thermal resistance of the entire acoustic multilayer is also high. This acoustic multilayer cannot dissipate heat sufficiently for the 2 GHz resonant vibration, and there is a risk that the resonance characteristics will deteriorate.

[0051] Comparative Example 5 In Comparative Example 5, a silicon substrate is used as the substrate, the high acoustic impedance layer is made of W, and the low acoustic impedance layer is made of Al2O3, and a high frequency with a center frequency of 2 GHz is applied. The thickness of the W layer is set to 650 nm, the same as in Comparative Example 1. The center wavelength of the acoustic wave propagating through Al2O3 is approximately 5552 nm, and the thickness of the low acoustic impedance layer is set to 1388 nm. Al2O3 is generally an insulator, and since its resistivity is 10^6 Ωcm or more, no heat conduction occurs due to carriers. Here, the thermal conductivity of the high acoustic impedance layer is 5.06 x 10 (W / mK), and the thermal conductivity of the low acoustic impedance layer is 2.81 (W / mK), which are somewhat higher than those of SiO2. The thermal resistance of the high acoustic impedance layer is 1.28 x 10^-8 (m ２ K / W), but the thermal resistance of the low acoustic impedance layer is 4.94 × 10^-7 (m ２ K / W), and the total thermal resistance is 5.07 x 10^-7 (m ２ In Al2O3, thermal conduction by phonons is dominant, and thermal resistance is high. The entire acoustic multilayer film cannot dissipate heat sufficiently for the 2 GHz resonant vibration, which may result in a deterioration of the resonance characteristics.

[0052] Based on Examples 1 to 15 and Comparative Examples 1 to 5, it can be seen that by forming the low acoustic impedance layer from a conductive oxide such as ITO, IZO, or AZO instead of an insulating layer such as SiO2 or Al2O3, the carrier is responsible for heat conduction, improving thermal conductivity. In addition to ITO, IZO, or AZO, conductive oxides such as FTO, GZO, ATO, or PTO may also be used, or a composite of one or more conductive oxides may be used. By using a conductive oxide with a resistivity of 1.0 x 10^-3 Ωcm or less in the low acoustic impedance layer, the thermal conductivity of the low acoustic impedance layer can be maintained at 3 W / mK or more, improving the heat dissipation of the entire acoustic multilayer film.

[0053] Although the present invention has been described above based on specific examples, the present invention is not limited to the above-described configuration examples. For example, the high acoustic impedance layer may be formed of Ta2O5, Ru, Ir, or a composite thereof in addition to W, Mo, or ZnO, and the low acoustic impedance layer may be formed of a transparent electrode material. Furthermore, the uppermost low acoustic impedance layer of the acoustic multilayer may be formed of an insulating layer such as SiO2 or Al2O3. As long as heat conduction via carriers is predominant throughout the low acoustic impedance layer of an oxide conductor, an insulating layer may be used in part of the low acoustic impedance layer in addition to the uppermost low acoustic impedance layer. In either case, the thermal conductivity of the entire acoustic multilayer is improved. When connecting active elements such as resonators or piezoelectric elements to the acoustic multilayer, heat generated by the active elements can be efficiently dissipated from the acoustic multilayer to the support substrate. In the laminate of the embodiment, the low acoustic impedance layer enables heat diffusion via carriers, achieving high heat dissipation without the need for complex processing. In a high frequency filter device using a laminate, deterioration of the characteristics of the acoustic multilayer film due to heat generation in the active element is suppressed, improving the reliability of device operation.

[0054] This application claims priority from Patent Application No. 2022-058815 filed with the Japan Patent Office on March 31, 2022, the entire contents of which are incorporated by reference.

[0055] REFERENCE SIGNS LIST 10, 30 Bulk acoustic wave filter device 11 Support substrate 12 First electrode layer 13 Piezoelectric layer 14 Second electrode layer 15 Resonator (active element) 16, 26 High acoustic impedance layer (first layer) 17, 27-1, 27-2 Low acoustic impedance layer (second layer) 18, 28 Acoustic multilayer film 19 Insulating layer 20, 40 Laminate

Claims

1. an acoustic multilayer film in which a first layer having a predetermined specific acoustic impedance and a second layer having a specific acoustic impedance lower than that of the first layer are alternately laminated on a support substrate; an active element provided on the opposite side of the acoustic multilayer film from the support substrate; and the active element has a first electrode layer provided on the acoustic multilayer film, a piezoelectric layer provided on the first electrode layer, and a second electrode layer provided on the piezoelectric layer; a part or the whole of the second layer in the acoustic multilayer is electrically conductive; A bulk acoustic wave filter device, comprising: an insulating layer provided between the acoustic multilayer film and the first electrode layer.

2. the second conductive layer has an electrical resistivity of 1.0×10^-3 Ωcm or less; 10. The bulk acoustic wave filter device of claim 1.

3. the second conductive layer has a thermal conductivity of 3 W / mK or more; 3. The bulk acoustic wave filter device according to claim 1 or 2.

4. the second layer having conductivity is formed of a conductive oxide or a transparent electrode material; 3. The bulk acoustic wave filter device according to claim 1 or 2.

5. the second conductive layer is ITO, AZO, IZO, FTO, GZO, ATO, PTO, or a composite thereof; 5. The bulk acoustic wave filter device of claim 4.

6. the first layer is W, Mo, Ta2O5, ZnO, Ru, Ir, or a composite thereof; 3. The bulk acoustic wave filter device according to claim 1 or 2.

7. the second layer provided on the top layer of the acoustic multilayer is insulating; 3. The bulk acoustic wave filter device according to claim 1 or 2.

8. the entire second layer is electrically conductive; an insulating layer provided on the acoustic multilayer film; 3. The bulk acoustic wave filter device according to claim 1, further comprising: