Elastic Wave Device

Abstract

This elastic wave device (100) comprises a support substrate (110), a piezoelectric layer (121) positioned on the support substrate (110), and a functional element (130) positioned on the piezoelectric layer (121). The support substrate (110) and the piezoelectric layer (121) have a substantially square shape when viewed from a direction normal to the support substrate (110). At least one of the corners of the piezoelectric layer (121) is formed in a curved or polygonal shape.

Description

[Technical field]

[0001] The present disclosure relates to an acoustic wave device, and more particularly to a technique for suppressing peeling of a piezoelectric layer in an acoustic wave device having a wafer level package (WLP) structure or a chip size package (CSP) structure. [Background technology]

[0002] In recent years, communication devices such as mobile terminals, typified by mobile phones and smartphones, communicate using high-frequency signals in multiple frequency bands. When processing signals in multiple frequency bands, filters are used to selectively pass signals in each frequency band.

[0003] As such a filter, for example, a filter using a surface acoustic wave (SAW) resonator is known. WO 2015 / 098679 (Patent Document 1) discloses an acoustic wave device having a WLP structure or a CSP structure and used as a bandpass filter. In the acoustic wave device disclosed in WO 2015 / 098679 (Patent Document 1), a piezoelectric thin film is not disposed below a pad electrode portion that is joined to an external connection terminal, thereby preventing peeling and cracking of the piezoelectric thin film from the support substrate when the external connection terminal is joined or when the acoustic wave device is mounted. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2015 / 098679 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-described elastic wave device, if the elastic wave device is subjected to reflow or other thermal shock when mounted on a mounting substrate, stress may be generated due to the difference in thermal expansion coefficient between the support substrate and the piezoelectric layer during the subsequent temperature drop process, which may cause the piezoelectric layer to peel off from the support substrate. In particular, depending on the planar shape of the piezoelectric layer, stress may be concentrated at the corners of the piezoelectric layer, making it more likely to peel off.

[0006] The present disclosure has been made to solve such problems, and its purpose is to suppress peeling of a piezoelectric layer arranged on a supporting substrate in an acoustic wave device having a WLP structure or a CSP structure. [Means for solving the problem]

[0007] The elastic wave device according to the present disclosure includes a support substrate, a piezoelectric layer disposed on the support substrate, and a functional element disposed on the piezoelectric layer. When viewed in a plan view from a normal direction of the support substrate, the support substrate and the piezoelectric layer have a substantially rectangular shape. At least one corner of the piezoelectric layer is curved or polygonal. Effect of the Invention

[0008] In the elastic wave device according to the present disclosure, the corners of the substantially rectangular piezoelectric layer disposed on the support substrate are curved or polygonal. Therefore, even when thermal stress is applied, stress concentration at the corners is mitigated. Therefore, in the elastic wave device, peeling of the piezoelectric layer disposed on the support substrate can be suppressed. [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of an elastic wave device according to an embodiment. [Diagram 2] 2 is a plan view of the acoustic wave device of FIG. 1. [Diagram 3] 11A and 11B are diagrams for explaining the shape of corners of an electrode pad. [Figure 4] FIG. 1 is a plan view of an elastic wave device according to a comparative example. [Diagram 5] 2A to 2C are diagrams illustrating a manufacturing process for the acoustic wave device of FIG. 1. [Figure 6] 1 is a cross-sectional view of an elastic wave device according to a first modification. [Figure 7] 11 is a cross-sectional view of an elastic wave device according to a second modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference characters and their description will not be repeated.

[0011] (Structure of Elastic Wave Device) A detailed configuration of elastic wave device 100 according to an embodiment will be described with reference to Fig. 1 and Fig. 2. Fig. 2 is a plan view of elastic wave device 100, and Fig. 1 is a cross-sectional view taken along line II in Fig. 2.

[0012] 1 and 2, acoustic wave device 100 includes support substrate 110, laminated film 120, functional element 130, electrode pad 140, wiring electrode 145, support 160, connection electrode 150 provided in support 160, solder bump 170, and resin layer 180. Laminated film 120 includes piezoelectric layer 121, low acoustic velocity layer 122, and high acoustic velocity layer 123. In the following description, low acoustic velocity layer 122 and high acoustic velocity layer 123 are collectively referred to as "intermediate layer." In the following description, the positive direction of the Z axis in the lamination direction in the figures may be referred to as the upper surface side, and the negative direction may be referred to as the lower surface side.

[0013] The support substrate 110 is a semiconductor substrate made of silicon (Si). The support substrate 110 has a substantially rectangular shape when viewed in a plan view from the normal direction (Z-axis direction). A high acoustic velocity layer 123, a low acoustic velocity layer 122, and a piezoelectric layer 121 are laminated in this order on the support substrate 110 toward the positive direction of the Z-axis. The material of the support substrate 110 is not limited to silicon, and may be silicon carbide (SiC) or quartz crystal.

[0014] The piezoelectric layer 121 is formed of, for example, a piezoelectric single crystal material such as lithium tantalate (LiTaO3), lithium niobate (LiNbO3), and quartz, or a piezoelectric laminate material made of LiTaO3, LiNbO3, or aluminum nitride (AlN).

[0015] A plurality of functional elements 130 are disposed on the upper surface (the surface in the positive direction of the Z axis) of the piezoelectric layer 121. The functional elements 130 include a pair of IDT (Interdigital Transducer) electrodes and a reflector, which are made of an electrode material such as an elemental metal made of at least one of aluminum, copper, silver, gold, titanium, tungsten, platinum, chromium, nickel, and molybdenum, or an alloy containing these metals as main components. The piezoelectric layer 121 and the IDT electrodes form a surface acoustic wave (SAW) resonator.

[0016] The low acoustic velocity layer 122 is made of a material that causes a bulk wave to propagate through the low acoustic velocity layer 122 to have a slower acoustic velocity than a bulk wave to propagate through the piezoelectric layer 121. In the acoustic wave device 100, the low acoustic velocity layer 122 is made of silicon oxide (SiO2). However, the low acoustic velocity layer 122 is not limited to silicon oxide and may be made of other dielectric materials such as glass, silicon oxynitride, and tantalum oxide, or compounds in which fluorine, carbon, boron, or the like is added to silicon oxide.

[0017] Moreover, high acoustic velocity layer 123 is formed of a material that allows the acoustic velocity of a bulk wave propagating through high acoustic velocity layer 123 to be higher than the acoustic velocity of an elastic wave propagating through piezoelectric layer 121. In acoustic wave device 100, high acoustic velocity layer 123 is formed of silicon nitride (SiN). However, high acoustic velocity layer 123 is not limited to silicon nitride, and may be formed of a material such as aluminum nitride, aluminum oxide (alumina), silicon oxynitride, silicon carbide, diamond-like carbon (DLC), or diamond.

[0018] By stacking the low acoustic velocity layer 122 and the high acoustic velocity layer 123 below the piezoelectric layer 121, the low acoustic velocity layer 122 and the high acoustic velocity layer 123 function as a reflective layer (mirror layer) 120. That is, surface acoustic waves leaking from the piezoelectric layer 121 in the direction of the support substrate 110 are reflected by the high acoustic velocity layer 123 due to the difference in the propagating sound velocities, and are trapped within the low acoustic velocity layer 122. In this way, the loss of acoustic energy of the propagating surface acoustic waves is suppressed by the intermediate layer, so that the surface acoustic waves can be propagated efficiently.

[0019] 1, an example in which one low acoustic velocity layer 122 and one high acoustic velocity layer 123 are arranged as the intermediate layer has been described, but the intermediate layer may be configured with a plurality of low acoustic velocity layers 122 and high acoustic velocity layers 123 arranged alternately. The intermediate layer is not an essential component, and the laminated film 120 may include only the piezoelectric layer 121. Alternatively, either the low acoustic velocity layer 122 or the high acoustic velocity layer 123 may be provided as the intermediate layer. When only the low acoustic velocity layer 122 is provided as the intermediate layer, the support substrate 110 functions as the high acoustic velocity layer.

[0020] The laminated film 120 including the piezoelectric layer 121 and the intermediate layers (low acoustic velocity layer 122, high acoustic velocity layer 123) has a substantially rectangular shape when viewed in a plan view from the normal direction (Z-axis direction) of the support substrate 110, and is disposed inside the outer shape of the support substrate 110. In the portion of the support substrate 110 where the laminated film 120 is not disposed (i.e., around the laminated film 120), a resin layer 180 using a material such as polyimide, polybenzoxazole (PBO), benzocyclobutene (BCB), or epoxy is disposed. Note that the laminated film 120 does not necessarily need to be disposed inside the support substrate 110, and may have the same outer shape as the support substrate 110 as long as the corners are curved rather than right angles, as described later.

[0021] A plurality of electrode pads 140 are arranged on the surface of the piezoelectric layer 121 on which the functional elements 130 are arranged. The electrode pads 140 are arranged along the periphery of the approximately rectangular support substrate 110. In addition, wiring electrodes 145 are provided on the upper surface of the piezoelectric layer 121 for electrically connecting between the functional elements 130 and between the functional elements 130 and the electrode pads 140.

[0022] The connection electrodes 150 are columnar electrodes that protrude in the positive direction of the Z axis from the electrode pads 140. The connection electrodes 150 electrically connect the solder bumps 170 to the electrode pads 140. The acoustic wave device 100 is mounted on an external device via the solder bumps 170.

[0023] The support 160 has a wall shape surrounding the periphery of the functional element 130, and protrudes from the upper surface of the piezoelectric layer 121 in the positive direction of the Z axis. The support 160 is made of an insulating resin such as epoxy or polyimide and / or a photosensitive resin material. A part of the support 160 covers the connection electrode 150. The support 160 forms a space around the functional element 130.

[0024] In elastic wave device 100 according to the present embodiment, the corners of laminate film 120 are curved rather than right-angled, and are arc-shaped with a predetermined radius of curvature (for example, 25 to 200 μm) in the example of Fig. 2. Alternatively, the corners of laminate film 120 may be polygonal.

[0025] In addition, the shape of the portion of the electrode pad 140 facing the corner of the laminated film 120 is also arc-shaped, similar to the shape of the corner of the piezoelectric layer 121 (FIG. 3(a)). Alternatively, the shape of the corner of the electrode pad may be polygonal, like the electrode pad 140A in FIG. 3(b).

[0026] As described above, acoustic wave device 100 is mounted on an external device (mounting board) by solder bumps 170. At this time, in the reflow process for melting solder bumps 170, heat is applied to the entire acoustic wave device 100, and the temperatures of supporting substrate 110 and laminate film 120 increase.

[0027] Thereafter, acoustic wave device 100 is cooled to solidify solder bumps 170. However, stress is applied to acoustic wave device 100 during the cooling process due to differences in the thermal expansion coefficients of the materials constituting mounting substrate and supporting substrate 110. For example, when the mounting substrate is made of glass epoxy, the thermal expansion coefficient is approximately 5 to 15×10 -5 (1 / K), whereas when the support substrate 110 is made of silicon, the thermal expansion coefficient is about 2.5 to 3×10 -5 Since the force is (1 / K), a force is applied to acoustic wave device 100 in the direction indicated by arrow AR1 in FIG.

[0028] As a result, stress may be generated between the support substrate 110 and the laminated film 120, between the layers in which the laminated film 120 is disposed, and / or between the piezoelectric layer 121 and the electrode pad 140, which may cause peeling between the elements. When the corners of the laminated film 120X and the electrode pad 140X are right-angled or nearly right-angled, as in the comparative elastic wave device 100X shown in Fig. 4, stress tends to be concentrated at the apex of the corner. Therefore, with a shape like that of the comparative example, peeling is likely to occur from the corners of the laminated film 120X or the electrode pad 140X.

[0029] On the other hand, in elastic wave device 100 of the present embodiment, the corners of laminated film 120 on supporting substrate 110 and the portions of electrode pads 140 facing the corners are curved (or polygonal). With this configuration, even when thermal stress such as reflow is applied, stress concentration at the corners is mitigated, thereby preventing peeling between the elements.

[0030] It is also possible to curve only the corners of the laminated film 120 and leave the corners of the electrode pad 140 as right angles, but in that case, the electrode pad 140 needs to be positioned inside the outer edge of the laminated film 120, narrowing the area of ​​the region in which the functional element 130 can be placed. By curving the portion of the electrode pad 140 facing the corner of the curved laminated film 120, the electrode pad 140 can be positioned closer to the edge of the laminated film 120, making it possible to expand the region in which the functional element 130 can be placed.

[0031] (Manufacturing Process) Next, a manufacturing process of acoustic wave device 100 according to the present embodiment will be described with reference to Fig. 5. Note that, for ease of explanation, one acoustic wave device will be described in Fig. 5, but in reality, a plurality of acoustic wave devices are simultaneously formed on one silicon wafer (support substrate 110) and then separated into individual acoustic wave devices by dicing.

[0032] 5, first, in the step of Fig. 5(a), high acoustic velocity layer 123, low acoustic velocity layer 122, and piezoelectric layer 121 are laminated in this order on silicon support substrate 110 to form laminated film 120. Then, as shown in Fig. 5(b), portions of laminated film 120 between adjacent acoustic wave devices (region PG1 in Fig. 5) are removed by etching. At this time, as shown in Fig. 2, patterning is performed so that corners of laminated film 120 in each acoustic wave device are curved or polygonal.

[0033] 5(c), a resin layer 180 is disposed in the region PG1 from which the laminate film 120 has been removed. By disposing the resin layer 180 in this region, peeling and / or cracking at the end of the laminate film 120 can be suppressed when the laminate film 120 is divided into individual acoustic wave devices by dicing.

[0034] When the placement of the resin layer is completed, in the step of Fig. 5(d), a conductive layer such as copper is laminated on the piezoelectric layer 121, and the functional element 130, the electrode pad 140, and the wiring electrode 145 are arranged by patterning. At this time, as described in Fig. 2 and Fig. 3, the portion of the electrode pad 140 facing the corner of the laminated film 120 is curved or polygonal.

[0035] 5(e), the support 160 is disposed so as to surround the functional element 130 and the electrode pad 140. Then, in FIG. 5(f), an opening V1 is formed using a laser or the like in a portion of the support 160 disposed above the electrode pad 140. The opening V1 is formed to a depth at which the electrode pad 140 is exposed.

[0036] After the opening V1 is formed, in the step of Fig. 5(g), a conductor such as copper is injected into the opening V1 to form a connection electrode 150. Then, a solder bump 170 is disposed on the connection electrode 150 (Fig. 5(h)). Thereafter, the boundary portion between adjacent acoustic wave devices (region PG1 in Fig. 5(b)) is diced to separate the acoustic wave devices into individual devices.

[0037] In this manner, in the steps of Figures 5(b) and 5(d), by making the corners of the laminate film 120 and the portions of the electrode pads 140 facing the corners curved or polygonal, peeling of the laminate film 120 and the electrode pads 140 that may occur when thermal stress is applied can be suppressed.

[0038] (Variation 1) 1, a space is formed around functional element 130 by support 160, but the space is configured to communicate with the outside of the device in an area without solder bumps 170. Therefore, changes in the environment surrounding acoustic wave device 100 (e.g., humidity, corrosive gases, etc.) may affect functional element 130.

[0039] In the first modification, a configuration will be described in which a cover portion is provided on the upper portion of the support 160, thereby disposing the functional element 130 in a space isolated from the outside of the device, thereby reducing the influence of changes in the surrounding environment.

[0040] Fig. 6 is a cross-sectional view of elastic wave device 100A of Modification 1. Elastic wave device 100A in Fig. 6 has a configuration in which a cover 190 is added to the configuration of elastic wave device 100 in Fig. 1. In the description of Fig. 6, description of elements that overlap with Fig. 1 will not be repeated.

[0041] 6, in acoustic wave device 100A, cover portion 190 that covers functional element 130 is disposed on top of support 160. Cover portion 190 is formed of an insulating material such as epoxy, and is supported by support 160. Support 160 and cover portion 190 form a hollow space 200 between cover portion 190 and piezoelectric layer 121. Hollow space 200 is an enclosed space and is isolated from the surrounding environment of acoustic wave device 100A. Therefore, even if the surrounding environment of acoustic wave device 100A changes, the effect on functional element 130 can be suppressed.

[0042] Furthermore, even in a configuration having such a cover portion, peeling of the laminated film 120 and the electrode pad 140 that faces the corners can be made curved or polygonal in shape, thereby preventing peeling of the laminated film 120 and the electrode pad 140 that can occur when thermal stress is applied.

[0043] (Variation 2) Fig. 7 is a cross-sectional view of an acoustic wave device 100B of Modification 2. The acoustic wave device 100B of Fig. 7 is a so-called CSP component that can be surface-mounted on a circuit board or the like.

[0044] 7, acoustic wave device 100B has a configuration in which support 160, connection electrodes 150, and solder bumps 170 in acoustic wave device 100 shown in Fig. 1 are replaced with external connection terminals 175. In Fig. 7, description of the same elements as those in acoustic wave device 100 in Fig. 1 will not be repeated.

[0045] The external connection terminals 175 are stud bumps made of a conductive material such as gold (Au), and are electrically connected to the electrode pads 140. Note that the material of the external connection terminals 175 may be a metal material other than Au.

[0046] When mounted on a circuit board or the like, external connection terminal 175 is connected to a terminal on the circuit board. After being mounted on the circuit board, the periphery of acoustic wave device 100B is sealed with resin or the like as necessary.

[0047] Even in the case of the elastic wave device 100B formed as such a CSP component, by making the corners of the laminated film 120 and the portions of the electrode pads 140 facing the corners curved or polygonal, peeling of the laminated film 120 and the electrode pads 140 that may occur when thermal stress is applied can be suppressed.

[0048] In the above description, a SAW resonator is used as the functional element. However, other acoustic wave devices such as a bulk acoustic wave (BAW) resonator may be used as the functional element arranged in a hollow space.

[0049] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not by the description of the embodiments described above, and is intended to include all modifications within the scope and meaning equivalent to the claims. [Explanation of symbols]

[0050] 100, 100A, 100B, 100X acoustic wave device, 110 supporting substrate, 120, 120X laminated film, 121 piezoelectric layer, 122 low acoustic velocity layer, 123 high acoustic velocity layer, 130 functional element, 140, 140A, 140X electrode pad, 145 wiring electrode, 150 connection electrode, 160 support, 170 solder bump, 175 external connection terminal, 180 resin layer, 190 cover portion, 200 hollow space, V1 opening.

Claims

1. A support substrate; a piezoelectric layer disposed on the support substrate; a functional element disposed on the piezoelectric layer, When viewed in a plan view from a normal direction of the support substrate, the support substrate and the piezoelectric layer have a substantially rectangular shape, An acoustic wave device, wherein at least one corner of the piezoelectric layer is formed in an outwardly convex curved or polygonal shape.

2. an electrode pad provided on the piezoelectric layer and connected to the functional element; The acoustic wave device according to claim 1 , wherein a portion of the electrode pad facing a corner of the piezoelectric layer has a curved or polygonal shape when viewed in a plan view from a normal direction of the support substrate.

3. 3 . The acoustic wave device according to claim 1 , wherein the piezoelectric layer is disposed inside an outer shape of the support substrate when viewed in a plan view from a normal direction of the support substrate.

4. The acoustic wave device according to claim 3 , further comprising a resin layer provided between an outline of the support substrate and an outline of the piezoelectric layer when viewed in a plan view from a normal direction of the support substrate.

5. 5. The acoustic wave device according to claim 1, further comprising an intermediate layer disposed between the piezoelectric layer and the support substrate.

6. The acoustic wave device according to claim 5 , wherein the intermediate layer includes a low acoustic velocity layer disposed on the support substrate and propagating an acoustic bulk wave having a velocity slower than that of a bulk wave propagating in the piezoelectric layer.

7. The acoustic wave device according to claim 5 , wherein the intermediate layer is disposed on the support substrate and includes a high acoustic velocity layer that propagates an acoustic bulk wave having a velocity faster than that of the acoustic wave propagating in the piezoelectric layer.

8. The acoustic wave device according to claim 7 , wherein the intermediate layer further includes a low acoustic velocity layer disposed between the high acoustic velocity layer and the piezoelectric layer, and propagating an acoustic bulk wave having a speed slower than that of a bulk wave propagating in the piezoelectric layer.

9. The intermediate layer has a generally rectangular shape, The acoustic wave device according to claim 5, wherein at least one corner of the intermediate layer is curved or polygonal.

10. A support; A cover portion supported by the support body, 10. The acoustic wave device according to claim 1, wherein the functional element is provided in a space defined by the support body and the cover portion.

11. 11. The acoustic wave device according to claim 1, wherein the functional element includes a surface acoustic wave element.

12. The acoustic wave device according to claim 1, wherein the supporting substrate includes silicon.

13. A support substrate; a piezoelectric layer disposed on the support substrate; A functional element disposed on the piezoelectric layer; an electrode pad provided on the piezoelectric layer and connected to the functional element; When viewed in a plan view from a normal direction of the support substrate, the support substrate and the piezoelectric layer have a substantially rectangular shape, At least one corner of the piezoelectric layer is curved or polygonal. An acoustic wave device, wherein a portion of the electrode pad facing a corner of the piezoelectric layer is curved or polygonal.

Images