Surface acoustic wave device

Abstract

To provide a surface acoustic wave device that has a structure that can increase an area where a resonator can be formed as much as possible, with a simple and rational configuration.SOLUTION: A surface acoustic wave device includes a device chip 2, a resonator 3 including an IDT electrode 3a and a reflector 3b and formed on one surface 2a of the device chip 2, and a bump pad 4 formed on the one surface 2a of the device chip 2 between an edge 2b of the device chip 2 and an end 3c of the resonator 3 located on the edge 2b side. The bump pad 4 is formed to have an outline shape that receives the end portion 3c of the resonator 3.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to improvements in surface acoustic wave devices. [Background technology]

[0002] Surface acoustic wave devices are used as frequency filters in mobile communication devices and the like. FIG. 9 shows a typical configuration example. In FIG. 9, reference numeral 100 denotes a device chip made of a piezoelectric substrate, reference numeral 101 denotes a resonator, reference numeral 102 denotes a bump pad connected to the resonator, reference numeral 103 denotes a package substrate, reference numeral 104 denotes an electrode on the package substrate side, and reference numeral 105 denotes a bump interposed between the bump pad 102 and the electrode 104 to connect them. In FIG. 9, reference numeral 106 denotes a sealing resin, which provides an internal space 107 above the resonator 101 of the surface acoustic wave device. The bump pad is typically configured to have a size of approximately 100 μm × 100 μm. As shown in FIG. 10, the bump pad 102 is formed between an edge 100 a of the device chip 100 and the resonator 101 so as not to come into contact with the resonator 101. Summary of the Invention [Problem to be solved by the invention]

[0003] The main problem that the present invention aims to solve is to provide a surface acoustic wave device of this type with a structure that can increase the area in which a resonator can be formed as much as possible, with a simple and rational configuration. [Means for solving the problem]

[0004] In order to achieve the above object, the present invention provides a surface acoustic wave device comprising: a device chip; a resonator including an IDT electrode and a reflector and formed on one surface of the device chip; a bump pad formed on the one surface of the device chip between an edge of the device chip and an end of the resonator located on the edge side; The bump pad is formed to have an outer shape that receives the end of the resonator.

[0005] One aspect of the present invention is that the surface acoustic wave device has a receiving portion for the end of the resonator, which has an entrance at the center side of the device chip and continues into the bump pad, and the end of the resonator is positioned within this receiving portion.

[0006] In one embodiment of the present invention, the outer shape of the bump pad is formed into a shape like an imaginary rectangle with one corner cut away, and this cut-out portion serves as the receiving portion.

[0007] In addition, one aspect of the present invention is to form the outer shape of the bump pad so that it has a concave portion that is open on one side of an imaginary rectangle and extends into the other side opposite this side, and to make the inside of this concave portion the receiving portion.

[0008] In addition, one aspect of the present invention is to make the height of the bump pad relative to the one surface of the device chip to be in the range of 5 to 20 times the height relative to the one surface of the resonator.

[0009] In addition, one aspect of the present invention is that the device chip is electrically connected to the package substrate by a bump made of a conductive metal interposed between the bump pad and the package substrate, and a space to allow the bump to protrude is formed in the receiving portion above the resonator and to the side of the bump pad. [Effects of the Invention]

[0010] According to this invention, a structure that can maximize the area in which a resonator can be formed in this type of surface acoustic wave device can be provided in this type of surface acoustic wave device with a simple and rational configuration. In other words, by configuring the outer shape of the bump pad as described above, it becomes possible to position the resonator as close as possible to the edge of the device chip, and therefore it becomes possible to make the size of the device chip, and ultimately the surface acoustic wave device, as small as possible without changing the circuit layout (the configuration and layout of the resonator) itself. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a configuration diagram showing one surface of a device chip constituting a surface acoustic wave device (first example) according to an embodiment of the present invention, as viewed from the direction d2 in FIG. [Figure 2] FIG. 2 is a structural diagram of a reflector constituting the first example. [Figure 3] FIG. 3 is a diagram showing the main part of the first example (Fig. 3a / the upper right corner of Fig. 1) and a cross-sectional diagram taken along line AA (Fig. 3b), showing the state before bumps are formed. [Figure 4] Figure 4 is a diagram of the main part of the first example (Figure a / the upper right corner of Figure 1) and a cross-sectional diagram along line BB (Figure b), showing the state after the bumps and sacrificial layer have been formed. [Figure 5] Figure 5 is a diagram of the main components of the first example (Figure a / the upper right corner of Figure 1) and a cross-sectional diagram along line CC (Figure b), showing the state after the package substrate and device chip have been fixed together from the state shown in Figure 4. [Figure 6] Figure 6 is a diagram of the main part of the first example (Figure a / the upper right corner of Figure 1) and a cross-sectional diagram along line DD (Figure b), showing the state after the sacrificial layer has been removed from the state shown in Figure 5. [Figure 7] FIG. 7 is a cross-sectional view of the main part of the first example. [Figure 8]FIG. 8 is a diagram showing the configuration of a main part of one surface of a device chip constituting a surface acoustic wave device (second example) according to one embodiment of the present invention, viewed from a direction perpendicular to this surface. [Figure 9] FIG. 9 is a cross-sectional view of a conventional surface acoustic wave device. [Figure 10] FIG. 10 is a plan view of the configuration taken along the line EE in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0012] A typical embodiment of the present invention will be described below with reference to Figures 1 to 8. A surface acoustic wave device 1 according to this embodiment is suitable for use as a frequency filter in mobile communication devices and the like.

[0013] The surface acoustic wave device 1 is typically configured as a rectangular plate with sides of 1 to 2 mm and a thickness of 0.4 to 0.5 mm. Although not shown, the surface acoustic wave device 1 is typically mounted together with other devices on a module substrate with a thickness of about 0.3 mm to form a module such as a front-end module with a thickness of about 0.8 to 1.0 mm.

[0014] Fig. 7 shows the cross-sectional structure of the surface acoustic wave device 1. In the illustrated example, the surface acoustic wave device 1 has a CSP (Chip Size Package) structure. In Fig. 7, reference numeral 2 denotes a device chip, reference numeral 3 denotes a resonator, reference numeral 4 denotes a bump pad, reference numeral 5 denotes a bump, reference numeral 6 denotes a package substrate, reference numeral 7 denotes an electrode on the package substrate side, and reference numeral 8 denotes a sealing resin.

[0015] The device chip 2 is made of a piezoelectric substrate. Typically, lithium tantalate or lithium niobate is used for the piezoelectric substrate, and the piezoelectric substrate may also be made by laminating sapphire, silicon, alumina, spinel, quartz, glass, or the like on the above.

[0016] FIG. 2 illustrates the concept of the resonator 3. The resonator 3 includes an IDT electrode 3a and reflectors 3b sandwiching the IDT electrode 3a. Each resonator 3 is formed on one surface 2a of the device chip 2, creating a substantially rectangular resonator formation region 3d. Specifically, the resonator 3 has the IDT electrode 3a located in the center and reflectors 3b on both sides. Reflectors 3b are also located at two ends 3c of the resonator 3 in the acoustic wave propagation direction d1. Each electrode pair constituting the IDT electrode 3a is formed by connecting multiple electrode fingers 3aa arranged in parallel with one end of the electrode fingers 3aa via a busbar 3ab. The reflector 3b is formed by connecting the ends 3c of multiple electrode fingers 3ba arranged in parallel with one end of the electrode fingers 3ba via a busbar 3bb.

[0017] 1, a plurality of the resonators 3 are formed on one surface 2a of the device chip 2, and these form a filter circuit with desired characteristics. Each resonator 3 is typically made of a conductive metal film formed by photolithography.

[0018] The bump pads 4 are formed on the one surface 2a of the device chip 2 between an edge 2b of the device chip 2 and an end 3c of the resonator 3 located on the edge 2b side. The bump pads 4 are electrically connected to the resonator 3 by wiring (not shown). The bump pads 4 and the wiring (not shown) are typically made of a conductive metal film formed by photolithography after the resonator 3 is formed.

[0019] The bumps 5 are made of a conductive metal and are formed on the bump pads 4. After the ball-shaped bumps 5 are formed on the bump pads 4, the package substrate 6 is placed on the device chip 2 and pressed together so that the electrodes 7 on the package substrate 6 come into contact with the bumps 5, crushing the bumps 5 and bonding the device chip 2 to the package substrate 6 via the bumps 5. Typically, the bumps 5 and the electrodes 7 of the package substrate 6 are made of metals that are compatible with each other, such as gold, or gold and aluminum.

[0020] As a result, the device chip 2 is electrically connected to the package substrate 6 by the bumps 5 made of a conductive metal interposed between the bump pads 4 and the package substrate 6 .

[0021] A gap (space) equal to the sum of the thicknesses of the bump pads 4, the bumps 5, and the electrodes 7 on the package substrate 6 is formed between one surface 2a of the device chip 2 and the package substrate 6. By forming a sealing resin 8 that covers the entire other surface 2c of the device chip 2 and the end faces 2d around the entire periphery of the device chip 2 and is bonded to the package substrate 6, a hollow structure 9 (internal space or air cavity) is formed within the surface acoustic wave device 1, and the resonator 3 is positioned within this hollow structure 9.

[0022] The bump pad 4 is formed to have an outer shape that receives the end 3c of the resonator 3. More specifically, when the bump pad 4 is viewed from a direction perpendicular to one surface 2a of the device chip 2, the bump pad 4 is formed to have an outer shape that receives the end 3c of the resonator 3.

[0023] As a result, in the surface acoustic wave device 1 according to this embodiment, it is possible to increase as much as possible the area in which the resonators 3 can be formed on one surface 2a of the device chip 2. In other words, by configuring the outer shape of the bump pads 4 as described above, it is possible to arrange the resonators 3 as close as possible to the edge 2b of the device chip 2, and therefore it is possible to make the device chip 2, and in turn the surface acoustic wave device 1, as small as possible without changing the circuit layout (the configuration and layout of the resonators 3) itself.

[0024] In this embodiment, the surface acoustic wave device 1 has a receiving portion 10 for the end 3c of the resonator 3, which has an entrance 10a at the center side O of the device chip 2 and continues into the bump pad 4, and the end 3c of the resonator 3 is positioned within this receiving portion 10.

[0025] 1 to 7, the outer shape of the bump pad 4 is shaped like an imaginary rectangle s with one corner sa cut away, and this cut-out portion serves as the receiving portion 10. In this first example, due to the cutout, the outer shape of the bump pad 4 is bent like a hook with the central side O of the device chip 2 on the inner side of the bend. In this first example, the bump pad 4 is provided with a first side 4a located at the corner 2e of the device chip 2 and formed parallel to an edge 2f of the device chip 2 extending along the x direction in FIG. 3 with a gap therebetween, and a second side 4b formed parallel to an edge 2g of the device chip 2 extending along the y direction perpendicular to the x direction in FIG. 3 with a gap therebetween. The resonator 3 also has a third side 4c that is closer to the center O of the device chip 2 than the first side 4a, is parallel to the first side 4a, and faces the receiving portion 10, and a fourth side 4d that is closer to the center O of the device chip 2 than the second side 4b, is parallel to the second side 4b, and faces the receiving portion 10. In this first example, gaps are formed between the third side 4c and a side 3e on the length side of the formation region 3d of the resonator 3, and between the fourth side 4d and a side 3f on the width side of the formation region 3d of the resonator 3, so that one side of two corners 3g of the end 3c of the resonator 3 is positioned within the receiving portion 10. In other words, the resonator 3 and the bump pad 4 are not in contact with each other within the receiving portion 10 due to the gaps.

[0026] 8, the outer shape of the bump pad 4 is formed so as to have a recessed portion 4e that is open at one side sb of an imaginary rectangle s and that extends into the other side sc that faces this side sb, and the inside of this recessed portion 4e serves as the receiving portion 10. In this second example, the bump pad 4 is provided with a first side 4a that is located at a corner 2e of the device chip 2 and that is formed parallel to a side 2f of the device chip 2 that runs along the x direction in FIG. 8 with a gap therebetween, and a second side 4b that is formed parallel to a side 2g of the device chip 2 that runs along the y direction orthogonal to the x direction in FIG. The recessed portion 4e also has a third side 4c and a fourth side 4d that are closer to the center O of the device chip 2 than the first side 4a, are parallel to the first side 4a, and face the receiving portion 10, and a fifth side 4f that is closer to the center O of the device chip 2 than the second side 4b, are parallel to the second side 4b, and face the receiving portion 10. In this second example, gaps are formed between the third side 4c and the fourth side 4d and the side 3e on the length side of the formation region 3d of the resonator 3, and between the fifth side 4f and the side 3f on the width side of the formation region 3d of the resonator 3, so that the end 3c of the resonator 3 is positioned within the receiving portion 10. That is, the resonator 3 and the bump pad 4 are not in contact with each other within the receiving portion 10 due to the gaps.

[0027] As shown in Figure 7, it is preferable that the height h1 of the bump pad 4 relative to the surface 2a of the device chip 2 is in the range of 5 to 20 times the height h2 of the resonator 3 relative to the surface 2a.

[0028] By doing so, in the receiving portion 10, a protrusion allowance space 11 for the bump 5 is formed above the resonator 3, more specifically above the reflector 3b constituting the resonator 3, and on the side of the bump pad 4. This protrusion allowance space 11 can prevent a situation in which a part of the bump 5, which is crushed when the device chip 2 and the package substrate 6 are fixed and protrudes toward the one surface 2a of the device chip 2, comes into contact with the resonator 3 in the receiving portion 10.

[0029] As shown in Figure 4, the resonator 3 is covered with a sacrificial layer 12 before the device chip 2 is bonded to the package substrate 6, and as shown in Figure 5, a portion of the bump that is crushed and protrudes during the bonding is supported by this sacrificial layer 12, and as shown in Figure 6, this sacrificial layer 12 is removed after the bonding, which makes it possible to prevent the above situation more effectively.

[0030] 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]

[0031] 1. Surface acoustic wave devices 2. Device chip 2a one side 2b Edge 2c other side 2d end face 2e corner 2f, 2g side 3 resonator 3a IDT electrode 3b reflector 3c end 3d forming area 3e, 3f sides 3g corner 3aa, 3ba electrode finger 3ab, 3bb busbars 4 Bump Pads 4a First side 4b Second side 4c Third side 4d Fourth side 4e Concave part 4F 5th side 5. Bump 6 Package substrate 7 electrodes 8 Sealing resin 9 Hollow structure 10 Receptor 10a Entrance 11 Allowable space 12 Sacrificial Layer d1 Propagation direction d2 Orthogonal direction O Central side s Imaginary rectangle sa corner sb One side sc other side h1, h2 height

Claims

1. A device chip; a resonator including an IDT electrode and a reflector and formed on one surface of the device chip; a bump pad formed on the one surface of the device chip between an edge of the device chip and an end of the resonator located on the edge side; The surface acoustic wave device is configured such that the bump pad has an outer shape that receives the end of the resonator.

2. 2. The surface acoustic wave device according to claim 1, further comprising a receiving portion for the end of the resonator, the receiving portion having an entrance at the center side of the device chip and continuing into the bump pad, and the end of the resonator is positioned within the receiving portion.

3. 3. The surface acoustic wave device according to claim 2, wherein the outer shape of the bump pad is an imaginary quadrangle with one corner cut away, and the cut-out portion serves as the receiving portion.

4. 3. The surface acoustic wave device according to claim 2, wherein the outer shape of the bump pad is formed so as to have a concave portion that is open at one side of an imaginary rectangle and extends into the other side opposite the one side, and the inside of this concave portion serves as the receiving portion.

5. 5. The surface acoustic wave device according to claim 1, wherein the height of the bump pads relative to the one surface of the device chip is set to a height in the range of 5 to 20 times the height of the resonator relative to the one surface.

6. The device chip is electrically connected to the package substrate by bumps made of conductive metal interposed between the bump pads and the package substrate, and 6. The surface acoustic wave device according to claim 5, wherein the receiving portion defines a space above the resonator and to the side of the bump pad to allow the bump to protrude.

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