Acoustic wave device

Abstract

To appropriately improve adhesiveness between an encapsulation part which encapsulates a resonator and a device chip without increasing the number of steps in a manufacturing process in an acoustic wave device.SOLUTION: A pattern 5 includes a first layer 5a consisting of a conductive material, a second layer 5b consisting of polyimide, and a third layer 5c consisting of a conductive material. A resonator 3 consists of the first layer 5a, and a wire 4 consists of both or any one of the first layer 5a and the third layer 5c. An encapsulation part 6 consists of a support layer 6a which is formed so as to enclose a formation region of the resonator 3 and consists of an insulating synthetic resin and a cover layer 6b which is supported on the support layer 6a. At least a part of a functional surface 2a and the first layer 5a is covered by a coating 5d consisting of silicon dioxide. In a single-layer region where only the second layer is positioned on the functional surface 2a, the coating 5b and the support layer 6a are fixed by the second layer 5b.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to an improvement in an acoustic wave device suitable for use as a frequency filter in a mobile communication device or the like. [Background technology]

[0002] An acoustic wave device with a WLP (Wafer Level Package) structure has the structure shown in Patent Document 1. That is, such an acoustic wave device has a support layer formed so as to surround an IDT electrode formed on the main surface of a piezoelectric substrate, and a cover layer disposed on this support layer to cover the IDT electrode, with the IDT electrode positioned in an internal space formed by the piezoelectric substrate, the support layer, and the cover layer. Here, when this type of acoustic wave device is to have a three-dimensional wiring structure, that is, when two metal films that will become wiring are stacked in a direction perpendicular to the main surface of the piezoelectric substrate without being electrically connected, a metal film that will become the lower layer wiring is formed, then an insulating resin layer is formed on top of that, and then a metal film that will become the upper layer wiring is formed on this resin layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2016 / 185866 Summary of the Invention [Problem to be solved by the invention]

[0004] The main problem that this invention aims to solve is to appropriately improve the adhesion between the sealing part that seals the resonator and the device chip (piezoelectric substrate) in an elastic wave device with a WLP structure having this type of three-dimensional wiring structure, without increasing the number of steps in the manufacturing process. [Means for solving the problem]

[0005] In order to achieve the above object, the present invention provides an acoustic wave device, which is formed by forming a pattern including a resonator and wiring on a functional surface of a device chip that is made of a piezoelectric material, and a sealing portion that seals the resonator between the functional surface and the pattern, the pattern has at least a first layer made of a conductive material, a second layer made of polyimide, and a third layer made of a conductive material; In the three-layer region where the three layers overlap, the second layer is located on top of the first layer, and the third layer is located on top of the second layer, The resonator is formed by the first layer, The wiring is made up of both or either of the first layer and the third layer, the sealing portion is composed of a support layer made of insulating synthetic resin formed so as to surround a region where the resonator is formed, and a cover layer supported on the support layer, the functional surface and at least a portion of the first layer are covered with a coating made of silicon dioxide; In a single-layer region where only the second layer is located on the functional surface, the coating and the support layer are fixed together by the second layer.

[0006] In addition to the above configuration, one aspect of the present invention is that in a two-layer region where the second layer is located on the first layer, the coating and the support layer are fixed together by the second layer. [Effects of the Invention]

[0007] The second layer, made of polyimide, has insulating properties and insulates the first and second layers in the three-layer region. This allows a WLP-structured acoustic wave device to have a three-dimensional wiring structure. Furthermore, the polyimide constituting the second layer has been shown to have excellent adhesion to the silicon dioxide constituting the coating, and also to the synthetic resin support layer constituting the encapsulation portion. This allows for appropriately improved adhesion between the device chip and the support layer constituting the encapsulation portion that encapsulates the resonator in the single-layer region or the two-layer region where the second layer is located on the functional surface, without adding an additional step in the manufacturing process of the acoustic wave device due to the second layer. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of an acoustic wave device according to one embodiment of the present invention. [Figure 2] FIG. 2 is a plan view of the main part of the acoustic wave device, taken along line AA in FIG. [Figure 3] FIG. 3 is a cross-sectional view of the essential parts taken along line BB in FIG. [Figure 4] FIG. 4 is a cross-sectional view of the essential parts taken along line CC in FIG. [Figure 5] FIG. 5 is a cross-sectional view of the essential parts taken along line DD in FIG. [Figure 6] FIG. 6 is a perspective view showing an example of a main part of a three-dimensional wiring structure formed on the functional surface of a device chip that constitutes the acoustic wave device. [Figure 7] FIG. 7 is a cross-sectional view of the essential part taken along line EE in FIG. [Figure 8] FIG. 8 is a configuration diagram showing an example of a circuit formed on the functional surface of a device chip that constitutes the acoustic wave device. DETAILED DESCRIPTION OF THE INVENTION

[0009] Exemplary embodiments of the present invention will now be described with reference to Figures 1 to 8. An acoustic wave device 1 according to this embodiment is suitable for use as a frequency filter in mobile communication devices and the like. Such an acoustic wave device 1 is formed by forming a pattern 5 including a resonator 3 and wiring 4 on a functional surface 2a of a device chip 2 made of a piezoelectric material, and a sealing portion 6 that seals the resonator 3 between the functional surface 2a and the pattern 5.

[0010] The device chip 2 has the function of propagating elastic waves. The surface of the device chip 2 that has the function of propagating elastic waves is the functional surface 2a. The device chip 2 typically uses lithium tantalate or lithium niobate as a piezoelectric material, and the device chip 2 may also be configured by laminating sapphire, silicon, alumina, spinel, quartz, glass, or the like on top of these. Typically, the device chip 2 is configured to have a rectangular plate shape with a side of 0.5 to 1 mm and a thickness of 0.15 to 0.2 mm. Therefore, when the device chip 2 is viewed from a direction perpendicular to the functional surface 2 a, the outline of the functional surface 2 a is rectangular.

[0011] The pattern 5 has at least a first layer 5a made of a conductive material, a second layer 5b made of polyimide, and a third layer 5c made of a conductive material. Furthermore, the functional surface 2a and at least a part of the first layer 5a are covered with a coating 5d made of silicon dioxide (SiO2), which has insulating properties and also functions to adjust the frequency of the resonator. Specifically, on the functional surface 2a of the device chip 2, there are formed an area where the pattern 5 is not formed, a single-layer area where any one of the first layer 5a, the second layer 5b and the third layer 5c is formed, a two-layer area where two of the first layer 5a, the second layer 5b and the third layer 5c overlap, and a three-layer area where all of the first layer 5a, the second layer 5b and the third layer 5c overlap.

[0012] Typically, such an acoustic wave device 1 is produced by the following process. First, a first layer 5a is formed on a wafer that will become the device chip 2. The first layer 5a is typically made of Al, Cu, Ti, or the like, and is formed by a method such as vapor deposition and lift-off. Next, the coating 5d made of silicon dioxide is formed on the wafer on which the first layer 5a has been formed. The coating 5d is typically formed by sputtering or the like. Next, the second layer 5b made of polyimide is formed on the wafer on which the first layer 5a and the coating film 5d have been formed. The second layer 5b is typically formed by a spin coating photolithography method. Next, a third layer 5c is formed on the wafer on which the first layer 5a, the coating 5d, and the second layer 5b have been formed. The third layer 5c is typically made of Al, Cu, Ti, or the like, and is formed by a method such as vapor deposition or lift-off. Thereafter, a support layer 6a (described later) is formed to constitute the sealing portion 6, followed by a cover layer 6b (described later) to constitute the sealing portion 6. The support layer 6a and the cover layer 6b are typically made of insulating synthetic resin, and are formed by photolithography and etching.

[0013] Therefore, in the three-layer region, the second layer 5b is located on top of the first layer 5a, and the third layer 5c is located on top of the second layer 5b. In the two-layer region, the second layer 5b is located on top of the first layer 5a, the third layer 5c is located on top of the first layer 5a, or the third layer 5c is located on top of the second layer 5b. The second layer 5b made of polyimide has insulating properties and insulates the first layer 5a from the second layer 5b in the three-layer region, which makes it possible to provide a three-dimensional wiring structure in an acoustic wave device with a WLP structure, as shown in Figures 6 and 7.

[0014] The resonator 3 is formed from the first layer 5a. A plurality of resonators 3 are formed on the functional surface 2a. The formation area of ​​each resonator 3 on the functional surface 2a is surrounded by a support layer 6a (described later) and is covered with a cover layer 6b formed on the support layer 6a. This provides the acoustic wave device 1 with a plurality of internal spaces 7. Each of the plurality of resonators 3 is adapted to be positioned within the internal space 7 .

[0015] The resonator 3 includes an IDT electrode 3a. The resonator 3 may also include a reflector (not shown). The IDT electrode 3a is composed of an electrode pair, and each electrode pair has multiple electrode fingers 3b arranged in parallel so that their length direction intersects with the propagation direction x of the elastic wave. The electrode fingers 3b are connected at one end of the electrode pairs by a bus bar 3c.

[0016] The wiring 4 is composed of both or either one of the first layer 5a and the third layer 5c. As shown in Fig. 5, in the portion where the wiring 4 is composed of both the first layer 5a and the third layer 5c, the coating 5d is removed from the first layer 5a, and the first layer 5a and the third layer 5c are connected through the removed portion 5e.

[0017] 8 shows the concept of an example of a circuit 8 provided on one device chip 2. Reference numeral 30 denotes a resonator 3 connected in series between input / output ports 8a, reference numeral 31 denotes a resonator 3 connected in parallel between input / output ports 8a, and reference numeral 8b denotes a ground. FIG. 2 shows one specific embodiment of the resonators 30, 31 shown in FIG. The number and arrangement of the resonators 3 can be changed as needed. In the example shown in Fig. 8, a ladder-type filter is configured.

[0018] The sealing portion 6 is composed of a support layer 6a made of insulating synthetic resin formed so as to surround the region where the resonator 3 is formed, and a cover layer 6b supported on the support layer 6a.

[0019] The support layer 6a is formed so as to surround the formation region of the resonator 3 when the device chip 2 is viewed in a direction perpendicular to the functional surface 2a. The internal space 7 is formed inside each of the support layers 6a. 3 and 4, the upper end 6ab of the support layer 6a, opposite to the lower end 6aa facing the functional surface 2a, is formed so as to be positioned on an imaginary plane S parallel to the functional surface 2a at any position on the functional surface 2a. The upper surfaces of the single-layer region, two-layer region, and three-layer region, i.e., the upper surface 5f of the pattern, are positioned closer to the functional surface 2a than the imaginary plane S, i.e., lower, at any position on the functional surface 2a. The lower end 6aa of the support layer 6a is fixed to the functional surface 2a in the region where the pattern 5 is not formed, and is fixed to the upper surface 5f of the pattern in the single-layer region, two-layer region, and three-layer region.

[0020] The cover layer 6b is fixed to the upper end of the support layer 6a with one surface facing the functional surface 2a aligned with the imaginary plane S. The cover layer 6b thus formed airtightly closes the frame-shaped opening formed by the upper end 6ab of the support layer 6a, thereby forming the internal space 7.

[0021] The circuit 8 provided on the device chip 2 as described above is typically electrically connected to the outside using a pad 4b that constitutes part of the wiring 4 formed outside the internal space 7.

[0022] 3, in the single-layer region where only the second layer 5b is located on the functional surface 2a and where the coating 5d is formed on the functional surface 2a, the coating 5d and the support layer 6a are fixed to each other by the second layer 5b. In other words, the coating 5d is used to firmly fix the functional surface 2a and the support layer 6a to each other by the second layer 5b at the location where the coating 5d is formed.

[0023] 4, in the two-layer region where the second layer 5b is located on the first layer 5a and where the coating 5d is formed on the first layer 5a, the coating 5d and the support layer 6a are fixed together by the second layer 5b. In other words, the coating 5d is used to firmly fix the first layer 5a and the support layer 6a together by the second layer 5b at the location of the first layer 5a where the coating 5d is formed.

[0024] The polyimide constituting the second layer 5b has been found to have excellent adhesion to the silicon dioxide constituting the coating 5d, and also has excellent adhesion to the synthetic resin support layer 6a constituting the sealing portion 6. As a result, in a single-layer region where only the second layer 5b is located on the functional surface 2a and a two-layer region where the second layer 5b is located on the first layer 5a, it is possible to appropriately improve adhesion between the support layer 6a constituting the sealing portion 6 that seals the resonator 3 and the device chip 2 without increasing the number of steps in the manufacturing process of the acoustic wave device by using the second layer 5b.

[0025] Typically, the first layer 5a has a thickness in a direction perpendicular to the functional surface 2a of the device chip 2 of 150 to 400 nm. The thickness of the coating 5d in the direction perpendicular to the functional surface 2a of the device chip 2 is set to about 15 to 50 nm. The second layer 5b has a thickness in a direction perpendicular to the functional surface 2a of the device chip 2 of 300 to 1000 nm. The third layer 5c has a thickness in the direction perpendicular to the functional surface 2a of the device chip 2 of 2 to 4 μm. Furthermore, the support layer 6a is typically configured so that its thickness in the direction perpendicular to the functional surface 2a of the device chip 2 is 15 to 20 μm. Furthermore, the cover layer 6b is typically configured so that its thickness in the direction perpendicular to the functional surface 2a of the device chip 2 is 20 to 25 μm. The acoustic wave device 1 configured in this manner typically has a thickness of about 0.2 to 0.25 mm. In each drawing, the thickness of the components of the acoustic wave device 1 is exaggerated to make it easier to understand the configuration of the device.

[0026] It should be noted that the present invention is not limited to the above-described embodiments, but includes all embodiments that can achieve the object of the present invention. [Explanation of symbols]

[0027] x Propagation direction S Virtual plane 1. Acoustic wave devices 2. Device chip 2a Functional aspect 3, 30, 31 resonator 3a IDT electrode 3b Electrode finger 3c busbar 4 Wiring 4a 3D wiring structure part 4b pad 5 patterns 5a 1st layer 5b 2nd layer 5c 3rd layer 5d coating 5e Removal section 5f top surface 6 Sealing part 6a Support layer 6aa bottom end 6ab top edge 6b Cover Layer 7. Interior Space 8 circuits 8a I / O port 8b Grand

Claims

1. An acoustic wave device comprising: a device chip having a functional surface made of a piezoelectric body, on which a pattern including a resonator and wiring is formed; and a sealing portion that seals the resonator between the functional surface and the pattern; the pattern has at least a first layer made of a conductive material, a second layer made of polyimide, and a third layer made of a conductive material; In the three-layer region where the three layers overlap, the second layer is located on top of the first layer, and the third layer is located on top of the second layer; The resonator is formed by the first layer, The wiring is made up of both or either of the first layer and the third layer, the sealing portion is composed of a support layer made of insulating synthetic resin formed so as to surround a region where the resonator is formed, and a cover layer supported on the support layer, the functional surface and at least a portion of the first layer are covered with a coating made of silicon dioxide; An acoustic wave device, wherein the coating and the support layer are fixed together by the second layer in a single-layer region where only the second layer is located on the functional surface.

2. The acoustic wave device according to claim 1 , further comprising: a two-layer region in which the second layer is located on the first layer, and the coating and the support layer are fixed together by the second layer.

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