Multilayer film substrates, acoustic wave devices using the multilayer film substrates, and methods for manufacturing the same.

Abstract

To provide a multilayer film substrate, an elastic wave device using such the multilayer film substrate, and a method for manufacturing, which are not affected by the flatness of the support substrate and have no voiding problems in substrate bonding.SOLUTION: A multilayer substrate has a piezoelectric substrate, a first low-sonic speed layer formed on the piezoelectric substrate, a high-sonic speed layer formed on the first low-sonic speed layer, a second low-sonic speed layer formed on the high-sonic speed layer, and a thick film layer on the second low-sonic speed layer, where the amount of voids in the thick film layer is greater in the region away from the second low-sonic speed layer than in the region near the second low-sonic speed layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a multilayer film substrate, an elastic wave device using the multilayer film substrate, and methods for manufacturing them. More specifically, it relates to a multilayer film substrate including a piezoelectric substrate, and 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 for mobile communication terminals represented by smartphones, high-frequency filters and the like are used to remove unnecessary signals outside the frequency band used for communication.

[0003] For high-frequency filters and the like, elastic wave devices having an elastic surface wave (SAW: Surface acoustic wave) element or the like are 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, an elastic surface wave device is manufactured as follows. First, a multilayer film substrate is created by bonding a piezoelectric substrate that propagates elastic waves and a support substrate having a smaller coefficient of thermal expansion than this piezoelectric substrate. Next, a large number of IDT electrodes are formed on the multilayer film substrate using photolithography technology, and then it is cut into a predetermined size by dicing to obtain an elastic surface wave device. In this manufacturing method, by using a multilayer film substrate, the change in the size of the piezoelectric substrate when the temperature changes is suppressed by the support substrate, so that the frequency characteristics as an elastic wave device are stabilized.

[0005] For example, as described in Patent Document 1 and the like, as a method for manufacturing a multilayer film substrate, a method of thinning a piezoelectric substrate after bonding the piezoelectric substrate and the support substrate is known.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2009-278610 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As disclosed in Patent Document 1, a multilayer film substrate used in an elastic wave device is formed by joining a piezoelectric substrate and a support substrate by an adhesive or van der Waals forces.

[0008] However, when bonding substrates together, the flatness of the substrates themselves has an effect, such as the support substrate having a concave or convex shape in its center. As a result, thickness adjustment of the piezoelectric substrate is necessary during the thinning process of the piezoelectric substrate after bonding. Alternatively, frequency adjustment is necessary to accommodate variations in the thickness of the piezoelectric substrate.

[0009] Furthermore, when joining circuit boards together, voids may be introduced, which can affect the frequency adjustment characteristics.

[0010] This disclosure was made to solve the above-mentioned problems. The object of this disclosure is to provide a multilayer film substrate that is not affected by the flatness of the support substrate and does not have the problem of voids in substrate bonding, an elastic wave device using the multilayer film substrate, and a method for manufacturing the same. [Means for solving the problem]

[0011] The multilayer film substrate relating to this disclosure is Piezoelectric substrate and Formed on the piezoelectric substrate , having a sound velocity lower than the speed of sound in the piezoelectric substrate The first low-sound layer, Formed on the first low-sound layer , having a sound velocity higher than the sound velocity in the piezoelectric substrate High-speed layer, Formed on the aforementioned high-sound-velocity layer , having a sound velocity lower than the speed of sound in the piezoelectric substrate The second low-sound layer, On the second low-sound layer Formed, and thicker than the piezoelectric substrate, the first low-sonic layer, the high-sonic layer, and the second low-sonic layer. Thick film layer and Equipped with, The amount of voids present in the thick film layer is larger in the region farther from the second low sound velocity layer than in the region closer to the second low sound velocity layer. 、 A multilayer film substrate was used.

[0012] In one embodiment of the present disclosure, the average crystal grain size of the thick film layer is larger in the horizontal direction than in the vertical direction with respect to the main surface of the second low sound velocity layer.

[0013] In one embodiment of the present disclosure, the thick film layer is aluminum nitrided, alumina or spinel.

[0015] In one embodiment of the present invention, the thick film layer is formed with a thickness of 100 μm or more.

[0016] Multilayer film substrate The main surface on which the first low-sonic layer of the piezoelectric substrate is formed is In one embodiment of the present invention, an elastic wave device includes a plurality of resonators formed on another main surface.

[0022] The method for manufacturing an elastic wave device according to the present disclosure includes the method for manufacturing a multilayer film substrate according to the present disclosure, and is a method for manufacturing an elastic wave device including a step of forming a plurality of resonators on another main surface of the piezoelectric substrate.

Advantages of the Invention

[0023] According to the present disclosure, it is possible to provide a multilayer film substrate that is not affected by the flatness of the support substrate and has no problem of voids in substrate bonding, an elastic wave device using the multilayer film substrate, and methods for manufacturing them.

Brief Description of the Drawings

[0024] [Figure 1] FIG. 1 is a cross-sectional view showing a multilayer film substrate according to Embodiment 1. [Figure 2] FIG. 2 is a diagram for explaining a method for manufacturing a multilayer film substrate according to Embodiment 1. [Figure 3] FIG. 3 is a cross-sectional view of an elastic wave device 20 according to Embodiment 2. [Figure 4]FIG. 4 is a diagram showing an example of an elastic wave element of an elastic wave device in Embodiment 2. [Figure 5] FIG. 5 is a longitudinal sectional view of a module to which the elastic wave device of Embodiment 2 is applied. Embodiments for Carrying Out the Invention

[0025] The embodiments will be described with reference to the accompanying drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions of such parts are appropriately simplified or omitted.

[0026] Embodiment 1. FIG. 1 is a sectional view showing a multilayer substrate according to Embodiment 1.

[0027] As shown in FIG. 1, the multilayer substrate 1 includes a piezoelectric substrate 11, a first low acoustic velocity layer 12, a high acoustic velocity layer 13, a second low acoustic velocity layer 14, and a thick film layer 15.

[0028] The piezoelectric substrate 11 is a substrate formed of a piezoelectric single crystal such as, for example, lithium tantalate, lithium niobate, or quartz. In another example, the piezoelectric substrate 11 is a substrate formed of piezoelectric ceramics.

[0029] The thickness of the piezoelectric substrate 11 can be, for example, from 0.3 μm to 5 μm.

[0030] The first low acoustic velocity layer 12 and the second low acoustic velocity layer 14 can be appropriately formed of a material having a bulk acoustic velocity lower than that of the bulk wave propagating through the piezoelectric substrate 11. Such materials can be formed, for example, of silicon oxide, glass, silicon oxynitride, tantalum oxide, or a compound obtained by adding fluorine, carbon, or boron to silicon oxide, depending on the material constituting the piezoelectric substrate 11.

[0031] The thickness of the first low acoustic velocity layer 12 and the second low acoustic velocity layer 14 can be, for example, from 0.5 μm to 5 μm.

[0032] The high-sound-velocity layer 13 can be appropriately formed from a material having a bulk wave velocity higher than the bulk wave propagating through the piezoelectric substrate 11. Such materials can be silicon nitride, aluminum nitride, aluminum oxide, silicon carbide, silicon oxynitride, spinel, diamond, etc., depending on the material constituting the piezoelectric substrate 11.

[0033] The thickness of the high-sound-velocity layer 13 can be, for example, 0.5 μm to 5 μm. A thicker high-sound-velocity layer 13 is preferable in order to confine the surface acoustic waves to the portion where the piezoelectric substrate 11 and the first low-sound-velocity layer 12 are laminated. The thickness of the high-sound-velocity layer 13 should be at least 0.5 times, more preferably 1.5 times, the wavelength λ of the surface acoustic waves. By confining the energy of SH waves, the Q factor can be improved.

[0034] The thick film layer 15 can be formed from, for example, aluminum nitride, alumina, aluminum oxide, aluminum alloy, glass, etc.

[0035] The thick film layer 15 has very few voids in the region close to the second low-sound-velocity layer 14. There are more voids in the region further away from the second low-sound-velocity layer 14. As the region close to the second low-sound-velocity layer 14 is more densely formed, heat in the piezoelectric substrate 11 is dissipated more efficiently.

[0036] The thick film layer 15 can be formed by the aerosol deposition method.

[0037] The material for forming the thick film layer 15 is first prepared as fine or ultrafine particles and mixed with gas to form an aerosol. This aerosol is then accelerated by gas transport and injected onto the second low-sonic layer 14.

[0038] The fine or ultrafine particles that are initially ejected and collide with the second low-sonic layer 14 mostly form a crystalline film, which is the densest film in the thick film layer 15 (15A). As time passes after ejection, some of the ejected fine or ultrafine particles bounce back, and the roughness of the thick film layer 15 during film formation gradually increases. As a result, very small voids are formed.

[0039] Within the thick film layer 15, the amount of voids in region 15B, which is further from the second low-speed layer 14 than region 15A, is greater than the amount of voids in region 15A, which is closest to the second low-speed layer 14. The amount of voids in region 15C, which is further from the second low-speed layer 14 than region 15B, is greater than the amount of voids in region 15B. The amount of voids in region 15D, which is further from the second low-speed layer 14 than region 15C, is greater than the amount of voids in region 15C.

[0040] The injection angle can be perpendicular or non-perpendicular to the planar direction of the second low-sonic layer 14. By selectively making it non-perpendicular, fine particles or ultrafine particles that collide with the surface of the second low-sonic layer 14 or the thick film layer 15 during deposition undergo plastic deformation and become crystalline films. As a result, the thick film layer 15 has a structure in which the crystal grain size is larger in the horizontal direction than in the direction perpendicular to the main surface of the second low-sonic layer 14.

[0041] This allows for the formation of a thick film layer 15 using a low-temperature process. This avoids the problem of poor thermal conductivity caused by the thick film layer 15 becoming amorphous.

[0042] Next, a method for manufacturing a multilayer film substrate according to Embodiment 1 will be described.

[0043] Figure 2 is a diagram illustrating the manufacturing method of a multilayer film substrate according to Embodiment 1.

[0044] First, the piezoelectric substrate is mirror-polished on both sides (S1). At this stage, the thickness of the piezoelectric substrate is, for example, 200 μm, and can be adjusted as appropriate according to the handling performance of the manufacturing equipment.

[0045] Next, a first low-sonic layer is formed on the piezoelectric substrate S2. The first low-sonic layer can be formed, for example, by sputtering, thermal spraying, or atomic layer deposition. The first low-sonic layer can be formed, for example, from silicon oxide, glass, silicon oxynitride, tantalum oxide, silicon oxide with fluorine, or a compound with carbon or boron added.

[0046] Next, a high-velocity layer is formed on the first low-velocity layer S3. The high-velocity layer can be formed, for example, by sputtering, thermal spraying, or atomic layer deposition. The high-velocity layer can be formed from, for example, silicon nitride, aluminum nitride, aluminum oxide, silicon carbide, silicon oxynitride, spinel, diamond, etc.

[0047] Next, a second low-sonic layer is formed on the high-sonic layer S4. The second low-sonic layer can be formed, for example, by sputtering, thermal spraying, or atomic layer deposition. The second low-sonic layer can be formed, for example, by silicon oxide, glass, silicon oxynitride, tantalum oxide, silicon oxide with fluorine, or a compound with carbon or boron added.

[0048] Next, a thick film layer is formed on the second low-sound-velocity layer (S5). The thick film layer can be formed, for example, by the aerosol deposition method. The thick film layer can be formed from, for example, aluminum nitride, alumina, aluminum oxide, aluminum alloy, or glass. The thick film layer can be formed with a thickness of 100 μm or more.

[0049] Next, step S6 is performed to thin the piezoelectric substrate. Thinning can be done using methods such as CMP or smartcut.

[0050] The above describes the multilayer film substrate and its manufacturing method according to Embodiment 1. The multilayer film substrate and its manufacturing method according to Embodiment 1 described above does not include a step of bonding the substrates together. This eliminates problems that arise from the influence of the flatness of the substrate itself, such as the center of the support substrate being concave or convex, which occurs when piezoelectric substrates and support substrates are bonded together as in the conventional method. Furthermore, voids are not incorporated. In addition, if aluminum nitride is used for the thick film layer, the thermal conductivity of aluminum nitride is approximately 180 to 230 W / mK, resulting in a multilayer film substrate with higher heat dissipation characteristics compared to a common support substrate such as sapphire (thermal conductivity of approximately 35.1 W / mK).

[0051] Embodiment 2. Figure 3 is a cross-sectional view of the elastic wave device 20 according to Embodiment 2.

[0052] As shown in Figure 3, the elastic wave device 20 comprises a wiring board 23, external connection terminals 24, a device chip 25, electrode pads 26, bumps 27, and a sealing portion 28.

[0053] For example, the wiring board 23 is a multilayer substrate made of resin. For example, the wiring board 23 is a low-temperature co-fired ceramics (LTCC) multilayer substrate made of multiple dielectric layers.

[0054] Multiple external connection terminals 24 are formed on the lower surface of the wiring board 23.

[0055] Multiple electrode pads 26 are formed on the main surface of the wiring board 23. For example, the electrode pads 26 are made of copper or a copper-containing alloy. For example, the thickness of the electrode pads 26 is 10 μm to 20 μm.

[0056] The bumps 27 are formed on the upper surface of each electrode pad 26. For example, the bumps 27 are gold bumps. For example, the height of the bumps 27 is between 10 μm and 50 μm.

[0057] A gap 29 is formed between the wiring board 23 and the device chip 25.

[0058] The device chip 25 is mounted on the wiring board 23 via bumps 27 by flip-chip bonding. The device chip 25 is electrically connected to multiple electrode pads 26 via multiple bumps 27.

[0059] The device chip 25 is a substrate on which elastic wave elements 52 are formed on a piezoelectric substrate 11 of the multilayer film substrate 1 according to Embodiment 1. For example, a transmitting filter and a receiving filter, each containing a plurality of elastic wave elements 52, are formed on the main surface of the device chip 25.

[0060] A transmitting filter is designed to allow electrical signals within a desired frequency band to pass through. For example, a transmitting filter is a ladder filter consisting of multiple series resonators and multiple parallel resonators.

[0061] A receiving filter is designed to allow electrical signals of a desired frequency band to pass through. For example, a receiving filter is a ladder filter.

[0062] The sealing portion 28 is formed to cover the device chip 25. For example, the sealing portion 28 is formed of an insulator such as a synthetic resin. For example, the sealing portion 28 is formed of metal.

[0063] When the sealing portion 28 is formed of a synthetic resin, the synthetic resin may be an epoxy resin, polyimide, or the like. Preferably, the sealing portion 28 is made of an epoxy resin and formed using a low-temperature curing process.

[0064] Next, an example of an elastic wave element 52 formed on the device chip 25 will be described using Figure 4. Figure 4 is a diagram showing an example of an elastic wave element of an elastic wave device in Embodiment 2.

[0065] As shown in Figure 4, the IDT (Interdigital Transducer) 52a and the pair of reflectors 52b are formed on the main surface of the device chip 25. The IDT 52a and the pair of reflectors 52b are arranged to excite elastic waves (mainly SH waves).

[0066] For example, the IDT52a and the pair of reflectors 52b are made of an aluminum-copper alloy. For example, the IDT52a and the pair of reflectors 52b are made of suitable metals or alloys thereof, such as aluminum, molybdenum, iridium, tungsten, cobalt, nickel, ruthenium, chromium, strontium, titanium, palladium, and silver.

[0067] For example, the IDT 52a and the pair of reflectors 52b are formed from a laminated metal film in which multiple metal layers are stacked. For example, the thickness of the IDT 52a and the pair of reflectors 52b is between 150 nm and 450 nm.

[0068] The IDT52a comprises a pair of comb-shaped electrodes 52c. The pair of comb-shaped electrodes 52c face each other. The comb-shaped electrodes 52c comprises a plurality of electrode fingers 52d and a busbar 52e.

[0069] Multiple electrode fingers 52d are arranged with their longitudinal directions aligned. A busbar 52e connects the multiple electrode fingers 52d.

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

[0071] According to Embodiment 2 described above, it is possible to provide an elastic wave device with small variations in the thickness of the piezoelectric substrate and fewer voids between the piezoelectric substrate and other layers. Furthermore, by using aluminum nitride for the thick film layer, since the thermal conductivity of aluminum nitride is approximately 180-230 W / mK, it is possible to provide an elastic wave device with superior heat dissipation characteristics compared to a common support substrate such as sapphire (thermal conductivity of approximately 35.1 W / mK).

[0072] Embodiment 3. Figure 5 is a longitudinal cross-sectional view of a module to which the elastic wave device of Embodiment 2 is applied. Parts identical or corresponding to those in Embodiment 2 are denoted by the same reference numerals. Descriptions of these parts are omitted.

[0073] In Figure 5, the module 100 comprises a wiring board 130, a plurality of external connection terminals 131, an integrated circuit component IC, an elastic wave device 20, an inductor 111, and a sealing portion 117.

[0074] Multiple external connection terminals 131 are formed on the underside of the wiring board 130. The multiple external connection terminals 131 are mounted on the motherboard of a pre-configured mobile communication terminal.

[0075] For example, the integrated circuit component IC is mounted inside the wiring board 130. The integrated circuit component IC includes a switching circuit and a low-noise amplifier.

[0076] The elastic wave device 20 is mounted on the main surface of the wiring board 130.

[0077] The inductor 111 is mounted on the main surface of the wiring board 130. The inductor 111 is mounted for impedance matching. For example, the inductor 111 is an Integrated Passive Device (IPD).

[0078] The sealing portion 117 seals multiple electronic components, including the elastic wave device 20.

[0079] According to Embodiment 2 described above, the module 100 includes an elastic wave device 20. Therefore, it is possible to provide a module that has an elastic wave device with small variations in the thickness of the piezoelectric substrate and with few voids between the piezoelectric substrate and other layers.

[0080] While several aspects of at least one embodiment have been described, it should be understood that various modifications, alterations, and improvements will be readily conceivable to those skilled in the art. Such modifications, alterations, and improvements are intended to be part of and within the scope of this disclosure.

[0081] It should be understood that the embodiments of the methods and apparatus described herein are not limited to their application to the structural and arrangement details of the components described above or illustrated in the accompanying drawings. The methods and apparatus can be implemented in other embodiments and carried out or performed in various ways.

[0082] Specific implementation examples are provided here for illustrative purposes only and are not intended to be limiting.

[0083] The expressions and terms used in this disclosure are for illustrative purposes only and should not be considered limiting. The use herein of “includes,” “equips,” “possesses,” “contains,” and variations thereof means the inclusion of the items listed herein and their equivalents, as well as the supplementary items.

[0084] The use of "or" can be interpreted as meaning that any term used with "or" refers to one, more than one, or all of the terms described.

[0085] References to front / back, left / right, top / bottom / top / bottom, width / height, and front / back are all intended for convenience of description. Such references do not mean that the components of this disclosure are limited to any single positional or spatial orientation. Accordingly, the above description and drawings are illustrative only. [Explanation of Symbols]

[0086] 1 Multilayer film substrate 11 Piezoelectric substrate 12 1st low sound speed layer 13 High-sonic layer 14 2nd low sound speed layer 15 Thick film layer 20 Elastic wave devices 23 Wiring board 24 External connection terminals 25 device chips 26 electrode pads 27 Bump 28 Sealing part 29 void 52 Elastic wave element, 52a IDT, 52b Reflector, 52c Comb electrode, 52d Electrode finger 100 Module, 111 Inductor, 117 Encapsulation, 130 Wiring board, 131 External connection terminal, IC integrated circuit component

Claims

1. Piezoelectric substrate and A first low-sound-velocity layer formed on the piezoelectric substrate and having a sound velocity lower than the sound velocity in the piezoelectric substrate, A high-speed layer formed on the first low-speed layer and having a sound velocity higher than the sound velocity in the piezoelectric substrate, A second low-sound-velocity layer is formed on the high-sound-velocity layer and has a sound velocity lower than the sound velocity in the piezoelectric substrate, A thick film layer formed on the second low-sound-velocity layer, which is thicker than the piezoelectric substrate, the first low-sound-velocity layer, the high-sound-velocity layer, and the second low-sound-velocity layer. Equipped with, A multilayer substrate in which the amount of voids present in the thick film layer is greater in regions further from the second low-speed layer than in regions closer to the second low-speed layer.

2. The multilayer substrate according to claim 1, wherein the average grain size of the thick film layer is greater in the horizontal direction than in the direction perpendicular to the main surface of the second low-sound-velocity layer.

3. The multilayer substrate according to claim 1, wherein the thick film layer is aluminite, alumina, or spinel.

4. The multilayer substrate according to claim 1, wherein the thick film layer is formed to have a thickness of 100 μm or more.

5. An elastic wave device comprising a multilayer film substrate according to any one of claims 1 to 4, and a plurality of resonators formed on a main surface of the piezoelectric substrate other than the main surface on which the first low-sound-velocity layer is formed.

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