Surface acoustic wave devices
The innovative bump pad design in elastic surface wave devices enhances resonator formation area, enabling miniaturization by extending into the bump pad and maintaining the circuit layout, thus optimizing device size.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Patents
- Current Assignee / Owner
- SANAN JAPAN TECH CORP
- Filing Date
- 2022-05-11
- Publication Date
- 2026-05-27
AI Technical Summary
Existing elastic surface wave devices face limitations in maximizing the formation area of resonators due to the configuration of bump pads, which restricts the miniaturization of the device without altering the circuit layout.
The bump pad is designed with a specific outer shape that receives the end of the resonator, allowing it to extend into the bump pad and creating a receiving portion, with a concave or cut-off configuration, and maintaining a height ratio relative to the resonator, thereby increasing the formation area without changing the circuit layout.
This design enables a larger resonator area within the device chip, allowing for a smaller device size without altering the circuit configuration, thus optimizing the surface acoustic wave device's dimensions.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to an improvement of an elastic surface wave device.
Background Art
[0002] Elastic surface wave devices are used as frequency filters and the like in mobile communication devices and the like. Fig. 9 shows a typical configuration example thereof. In Fig. 9, reference numeral 100 denotes a device chip composed 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 the two. In Fig. 9, reference numeral 106 denotes a sealing resin, and thereby the elastic surface wave device has an internal space 107 on the resonator 101. The bump pad is typically configured to have a size of about 100 μm × 100 μm. Also, as shown in Fig. 10, the bump pad 102 is formed between the edge 100a of the device chip 100 and the resonator 101 so as not to contact the resonator 101.
Summary of the Invention
Problems to be Solved by the Invention
[0003] The main problem to be solved by this invention is to provide a structure that can increase the possible formation area of the resonator in this type of elastic surface wave device as much as possible, with a simple and reasonable configuration, in this type of elastic surface wave device.
Means for Solving the Problems
[0004] In order to solve the above problems, in this invention, the elastic surface wave device includes a device chip, a resonator formed on one surface of the device chip, comprising an IDT electrode and a reflector, The device chip comprises a bump pad formed on one surface of the device chip between the edge of the device chip and the 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 embodiment of the present invention is that the surface acoustic wave device includes a receiving portion for the end of the resonator that extends into the bump pad with the central side of the device chip as an entrance, and the end of the resonator is positioned within this receiving portion.
[0006] Furthermore, one embodiment of this invention is to make the outer shape of the bump pad resemble a shape in which one corner of a hypothetical rectangle has been cut off, and to make this cut-off portion the receiving portion.
[0007] Furthermore, one embodiment of this invention is to form the outer shape of the bump pad so that it is open on one side of a virtual rectangle and has a concave portion that extends into the other side opposite to this side, and to make the inside of this concave portion the receiving portion.
[0008] Furthermore, one embodiment of this invention is to set the height of the bump pad relative to one surface of the device chip to a height in the range of 5 to 20 times the height of the resonator relative to one surface.
[0009] Furthermore, in one embodiment of this invention, the device chip is electrically connected to the package substrate by a bump made of conductive metal interposed between the bump pad and the package substrate, and in the receiving portion, a space is formed on the resonator and to the side of the bump pad to allow for the bump to protrude. [Effects of the Invention]
[0010] According to this invention, a structure that can increase the area on which a resonator can be formed in this type of surface acoustic wave device can be provided to this type of surface acoustic wave device with a simple and rational configuration. In other words, by making the outer shape of the bump pad as described above, the resonator can be placed as close as possible to the edge of the device chip, so that the size of the device chip, and thus the surface acoustic wave device, can be made as small as possible without changing the circuit layout (configuration and placement of the resonator) itself. [Brief explanation of the drawing]
[0011] [Figure 1] Figure 1 is a configuration diagram showing one side of a device chip constituting a surface acoustic wave device (first example) according to one embodiment of the present invention, viewed from the direction of d2 in Figure 3. [Figure 2] Figure 2 is a diagram showing the configuration of the reflector that constitutes the first example. [Figure 3] Figure 3 shows the main component configuration of the first example (Figure a / the upper right corner of Figure 1) and the cross-sectional configuration of line AA (Figure b), showing the state before the formation of the bump. [Figure 4] Figure 4 shows the main components of the first example (Figure a / the upper right corner of Figure 1) and the cross-sectional structure of the BB line (Figure b), illustrating the state after the formation of the bump and sacrificial layer. [Figure 5] Figure 5 shows the main components of the first example (Figure a / the upper right corner of Figure 1) and the cross-sectional configuration of the CC line (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 shows the main component configuration diagram of the first example (Figure a / the upper right corner of Figure 1) and the DD line cross-sectional configuration diagram (Figure b), showing the state after the sacrificial layer has been removed from the state shown in Figure 5. [Figure 7] Figure 7 is a cross-sectional view of the main part of the first example. [Figure 8]Figure 8 is a diagram showing the main components 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 that surface. [Figure 9] Figure 9 is a cross-sectional diagram of a conventional surface acoustic wave device. [Figure 10] Figure 10 is a plan view of the configuration at the EE line position shown in Figure 9. [Modes for carrying out the invention]
[0012] A typical embodiment of this invention will be described below with reference to Figures 1 to 8. The surface acoustic wave device 1 according to this embodiment is suitable for use as a frequency filter in mobile communication equipment 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 in the illustration, such a 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 mm to 1.0 mm.
[0014] Figure 7 shows the main 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 Figure 7, reference numeral 2 denotes the device chip, reference numeral 3 denotes the resonator, reference numeral 4 denotes the bump pad, reference numeral 5 denotes the bump, reference numeral 6 denotes the package substrate, reference numeral 7 denotes the electrode on the package substrate side, and reference numeral 8 denotes the sealing resin.
[0015] Device chip 2 is composed of a piezoelectric substrate. Typically, lithium tantalate or lithium niobate is used for the piezoelectric substrate, and in some cases, the piezoelectric substrate may be constructed by laminating these materials with sapphire, silicon, alumina, spinel, quartz, or glass.
[0016] Fig. 2 shows the concept of the resonator 3. The resonator 3 has an IDT electrode 3a and a reflector 3b formed so as to sandwich the IDT electrode 3a. One resonator 3 is formed so as to create a substantially rectangular formation region 3d of one resonator 3 on one surface 2a of the device chip 2. That is, the resonator 3 has the IDT electrode 3a positioned in the center and the reflectors 3b positioned on both sides thereof, and reflectors 3b are respectively positioned at two end portions 3c in the elastic wave propagation direction d1 in the resonator 3. Each electrode pair constituting the IDT electrode 3a is formed by connecting a plurality of electrode fingers 3aa arranged in parallel so as to cross the length direction in the elastic wave propagation direction d1 at one end side thereof with a bus bar 3ab. The reflector 3b is formed by connecting between the end portions 3c of a plurality of electrode fingers 3ba arranged in parallel so as to cross the length direction in the elastic wave propagation direction d1 with a bus bar 3bb.
[0017] As shown in Fig. 1, a plurality of the resonators 3 are formed on one surface 2a of the device chip 2, and a filter circuit with desired characteristics is constituted thereby. Each resonator 3 is typically constituted by a conductive metal film formed by photolithography technology.
[0018] The bump pad 4 is formed between the edge 2b of the device chip 2 and the end portion 3c of the resonator 3 positioned on the edge 2b side on the one surface 2a of the device chip 2. The bump pad 4 is electrically connected to the resonator 3 by wiring not shown. The bump pad 4 and the wiring not shown are typically constituted by a conductive metal film formed by photolithography technology after the resonator 3 is formed.
[0019] The bump 5 is composed of a conductive metal and is formed on the bump pad 4. After forming the ball-shaped bump 5 on the bump pad 4, the package substrate 6 is overlapped and pressed against the device chip 2 such that the electrode 7 on the package substrate 6 side contacts the bump 5. As a result, the bump 5 is crushed, and the device chip 2 and the package substrate 6 are fixed to each other via the bump 5. Typically, the bump 5 and the electrode 7 of the package substrate 6 are made of a metal with good compatibility, for example, both are made of gold, or are composed of gold and aluminum.
[0020] Thereby, the device chip 2 is electrically connected to the package substrate 6 by the bump 5 made of a conductive metal interposed between the bump pad 4 and the package substrate 6.
[0021] A gap (clearance) corresponding to the sum of the thicknesses of the bump pad 4, the bump 5, and the electrode 7 on the package substrate 6 side 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 surface 2d extending over the entire periphery of the device chip 2 and is joined to the package substrate 6, a hollow structure portion 9 (internal space or air cavity) is formed in the surface acoustic wave device 1, and the resonator 3 is positioned within this hollow structure portion 9.
[0022] The bump pad 4 is formed to have an outer shape that receives the end portion 3c of the resonator 3. More specifically, in a state where the bump pad 4 is viewed from a direction orthogonal to one surface 2a of the device chip 2, the bump pad 4 is formed to have an outer shape that receives the end portion 3c of the resonator 3.
[0023] As a result, in the surface acoustic wave device 1 according to this embodiment, the area on one surface 2a of the device chip 2 where the resonator 3 can be formed can be increased as much as possible. In other words, by making the outer shape of the bump pad 4 as described above, the resonator 3 can be positioned as close as possible to the edge 2b of the device chip 2, so that the size of the device chip 2, and by extension the surface acoustic wave device 1, can be made as small as possible without changing the circuit layout (configuration and placement of the resonator 3) itself.
[0024] In this embodiment, the surface acoustic wave device 1 has an inlet 10a at the central side O of the device chip 2 and is provided with a receiving portion 10 for the end 3c of the resonator 3 that extends into the bump pad 4, and the end 3c of the resonator 3 is positioned within this receiving portion 10.
[0025] In the first example shown in Figures 1 to 7, the outer shape of the bump pad 4 is made to resemble a shape in which one of the corners sa of a virtual rectangle s has been cut off, and this cut-off portion is made to be the receiving portion 10. In this first example, the cut-off results in the outer shape of the bump pad 4 being bent in a hook shape so that the central side O of the device chip 2 is bent inward. In this first example, the bump pad 4 is located at the corner 2e of the device chip 2 and comprises a first side 4a formed parallel to the side 2f of the device chip 2 along the x direction in Figure 3, with a gap between it and the side 2f of the device chip 2, and a second side 4b formed parallel to the side 2g of the device chip 2 along the y direction perpendicular to the x direction in Figure 3, with a gap between it and the side 2g of the device chip 2. Furthermore, it includes a third side 4c that is located closer to the center O of the device chip 2 than the first side 4a, parallel to the first side 4a, and facing the receiving portion 10, and a fourth side 4d that is located closer to the center O of the device chip 2 than the second side 4b, parallel to the second side 4b, and facing the receiving portion 10. In this first example, gaps are formed between the third side 4c and the length-side side 3e of the resonator formation region 3d of the resonator 3, and between the fourth side 4d and the width-side side 3f of the resonator formation region 3d of the resonator 3, so that one side of the two corners 3g of the end 3c of the resonator 3 is located within the receiving portion 10. That is, within the receiving portion 10, the resonator 3 and the bump pad 4 are not in contact due to the gaps.
[0026] In the second example shown in Figure 8, the outer shape of the bump pad 4 is formed to have a recessed portion 4e that is open at one side sb of a virtual rectangle s and extends into the other side sc opposite to this side sb, with the inside of this recessed portion 4e serving as the receiving portion 10. In this second example, the bump pad 4 is located at the corner 2e of the device chip 2 and comprises a first side 4a formed parallel to the side 2f of the device chip 2 along the x-direction in Figure 8, with a gap between it and the side 2f, and a second side 4b formed parallel to the side 2g of the device chip 2 along the y-direction perpendicular to the x-direction in Figure 8, with a gap between it and the side 2g. Furthermore, the concave portion 4e includes a third side 4c and a fourth side 4d that are located closer to the center O of the device chip 2 than the first side 4a, parallel to the first side 4a, and facing the receiving portion 10, and a fifth side 4f that is located closer to the center O of the device chip 2 than the second side 4b, parallel to the second side 4b, and facing the receiving portion 10. In this second example, the end portion 3c of the resonator 3 is positioned within the receiving portion 10 such that gaps are formed between the third side 4c and the fourth side 4d and the length-side side 3e of the resonator formation region 3d, and between the fifth side 4f and the width-side side 3f of the resonator formation region 3d. That is, within the receiving portion 10, the resonator 3 and the bump pad 4 are not in contact 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 one 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 one surface 2a.
[0028] In this way, a space 11 that allows the bump 5 to protrude is formed in the receiving portion 10 on the resonator 3, more specifically on the reflector 3b that constitutes the resonator 3, and to the side of the bump pad 4. This space 11 prevents a portion of the bump 5 that is crushed and protrudes to one side 2a of the device chip 2 when the device chip 2 and the package substrate 6 are fixed together from coming 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 prior to the fixing of the device chip 2 to the package substrate 6, as shown in Figure 5, a portion of the bumps that are crushed and protrude during the fixing process is supported by this sacrificial layer 12, and as shown in Figure 6, this sacrificial layer 12 is removed after the fixing process, thereby making it possible to more effectively prevent the aforementioned situation.
[0030] Naturally, the present invention is not limited to the embodiments described above, but includes all embodiments that can achieve the objectives of the present invention. [Explanation of symbols]
[0031] 1. Surface acoustic wave devices 2 device chips 2a one side 2b Edge 2c other side 2d end face 2e corner 2f, 2g sides 3 resonator 3a IDT electrode 3b reflector 3c end 3d forming area 3e, 3f sides 3g corner 3aa, 3ba electrode finger 3ab, 3bb busbar 4 Bump pads 4a First side 4b Second side 4c Third side 4d (4th side) 4e Concave part 4f Fifth side 5 Bump 6 Package substrates 7 electrodes 8 Sealing resin 9 Hollow structure 10 Receptor part 10a Entrance 11 Allowable space 12 layers of victims d1 Propagation direction d2 Orthogonal direction O Center side s virtual quadrilateral sa corner sb one side sc other side h1, h2 height
Claims
1. Device chip and A resonator comprising an IDT electrode and a reflector, formed on one surface of the device chip, The device chip comprises a bump pad formed on one surface of the device chip between the edge of the device chip and the end of the resonator located on the edge side, The bump pad is a portion formed on one surface of the device chip on which a bump in the wiring electrically connected to the resonator is mounted. The bump pad is formed to have an outer shape that extends into the bump pad with the central side of the device chip as an entrance, and that receives the end of the resonator with a gap between it and the end, The height of the bump pad relative to 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 one surface. The device chip is electrically connected to the package substrate by the bumps, which are made of conductive metal and interposed between the bump pad and the package substrate. A surface acoustic wave device, wherein the receiving portion is configured such that a space allowing for the bump to protrude is formed on the resonator and to the side of the bump pad.
2. The surface acoustic wave device according to claim 1, wherein the outer shape of the bump pad is made to resemble a shape in which one corner of a virtual rectangle has been cut off, and this cut-off portion is made to be the receiving portion.
3. The surface acoustic wave device according to claim 1, wherein the outer shape of the bump pad is formed to have a recessed portion that is open on one side of a virtual rectangle and extends into the other side opposite to this side, and the inside of this recessed portion is made to be the receiving portion.