Piezoelectric Devices

Abstract

To provide a piezoelectric device that can prevent a change in resonance frequency due to an adhesive.SOLUTION: A piezoelectric device 1 comprises: a first substrate 4 that includes a first surface 4a on which a piezoelectric element 7 and a common terminal 12 connected with the piezoelectric element 7 are arranged; a second substrate 2 that includes a second surface 2a on which a common connection terminal 22 connected with a control circuit 29 is arranged; a third substrate 3 that is arranged between the first substrate 4 and the second substrate 2, and includes a third surface 3a joined to the first surface 4a and a fourth surface 3b opposite to the second surface 2a; and a bonding part 32 that bonds the second substrate 2 and the third substrate 3 to each other. The third substrate 3 includes a first through hole 14 penetrating from the third surface 3a to the fourth surface 3b, and a first through electrode 16 provided in the first through hole 14 and connected with the common terminal 12. The common connection terminal 22 is connected with the first through electrode 16 and electrically connected with the common terminal 12 via the first through electrode 16. The second substrate 2 has a wall part 33 for preventing flow out of adhesive on the second surface 2a opposite to the third substrate 3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric device. [Background technology]

[0002] Conventionally, piezoelectric devices in which piezoelectric elements are arranged in a matrix are known. For example, Patent Document 1 discloses a piezoelectric device that includes a sealing plate with an opening, a vibration plate that closes the opening, and a piezoelectric element that is mounted on the vibration plate and has a piezoelectric body sandwiched between an upper electrode and a lower electrode.

[0003] According to this, a diaphragm and a sealing plate are arranged opposite each other. The sealing plate limits the range in which the diaphragm vibrates. The frequency at which the diaphragm vibrates is determined by the size of the diaphragm surrounded by the opening in the sealing plate.

[0004] A pair of through electrodes is arranged on the sealing plate. The upper electrode and the lower electrode are each electrically connected to the through electrodes. The sealing plate is arranged opposite the wiring substrate. The wiring substrate has pads. The through electrodes protrude toward the wiring substrate. The pads and the through electrodes are in electrical contact. The upper electrode and the lower electrode are each electrically connected to the pads.

[0005] The through electrodes are formed using a resin adhesive containing a metal filler, and the sealing plate and the wiring substrate are bonded together using an insulating adhesive. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2021-106183 Summary of the Invention [Problem to be solved by the invention]

[0007] In the piezoelectric device of Patent Document 1, variations occur in the area of ​​adhesive spreading between the sealing plate and the wiring substrate. In this case, the adhesive area between the sealing plate and the wiring substrate affects the rigidity of the sealing plate. The rigidity of the sealing plate then affects the vibration characteristics of the diaphragm. Therefore, variations in the area of ​​adhesive spreading between the sealing plate and the wiring substrate change the resonance frequency of the piezoelectric element and the diaphragm. Therefore, a piezoelectric device that can suppress changes in resonance frequency caused by adhesive has been desired. [Means for solving the problem]

[0008] The piezoelectric device comprises a first substrate including a first surface on which a plurality of piezoelectric elements and first electrodes connected to the piezoelectric elements are arranged, a second substrate including a second surface on which a second electrode connected to a control circuit is arranged, a third substrate arranged between the first substrate and the second substrate and including a third surface joined to the first surface and a fourth surface opposite the second surface, and an adhesive portion for adhering the second substrate to the third substrate, wherein the third substrate has a through hole penetrating from the third surface to the fourth surface and a third electrode provided in the through hole and connected to the first electrode, the second electrode being connected to the third electrode and electrically connected to the first electrode via the third electrode, and the second substrate has a wall portion on the second surface opposite the third substrate for preventing adhesive from flowing out. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic exploded perspective view showing the configuration of a piezoelectric device according to a first embodiment. [Figure 2] FIG. 1 is a schematic cross-sectional side view showing a configuration of a piezoelectric device. [Figure 3] FIG. 1 is a schematic cross-sectional side view showing a configuration of a piezoelectric device. [Figure 4] FIG. 2 is a schematic plan view showing the configuration of a first substrate. [Figure 5] FIG. 2 is a schematic cross-sectional side view showing the configuration of a through electrode. [Figure 6] FIG. 1 is a schematic cross-sectional side view showing a configuration of a piezoelectric device. [Figure 7] FIG. 4 is a schematic cross-sectional side view of a main portion for explaining an adhesive and a wall portion. DETAILED DESCRIPTION OF THE INVENTION

[0010] First embodiment In this embodiment, a characteristic example of a piezoelectric device will be described.

[0011] As shown in Figure 1, in piezoelectric device 1, second substrate 2, third substrate 3, first substrate 4, and fourth substrate 5 are stacked in this order in the Z direction. In the Z direction, the fourth substrate 5 side is the Z positive direction, and the second substrate 2 side is the Z negative direction. The direction along the Z positive direction is called first direction 6. First direction 6 is the stacking direction of first substrate 4, third substrate 3, and second substrate 2.

[0012] When viewed from the first direction 6, the second substrate 2, the third substrate 3, the first substrate 4, and the fourth substrate 5 are rectangular. The longitudinal directions of the second substrate 2, the third substrate 3, the first substrate 4, and the fourth substrate 5 are in the same direction. The third substrate 3, the first substrate 4, and the fourth substrate 5 have the same shape. The second substrate 2 is larger than the third substrate 3, the first substrate 4, and the fourth substrate 5.

[0013] The longitudinal direction of the second substrate 2 is defined as the X direction, and the lateral direction of the second substrate 2 is defined as the Y direction. The X direction, Y direction, and Z direction are perpendicular to each other.

[0014] The first substrate 4 includes a first surface 4a on the side facing the third substrate 3. A plurality of piezoelectric elements 7 are arranged in a matrix on the first surface 4a. By applying an AC voltage to the piezoelectric elements 7, the piezoelectric device 1 can vibrate the first substrate 4 and emit ultrasonic waves. The first substrate 4 is also called a diaphragm. The plurality of piezoelectric elements 7 are arranged in an array to form an element array 8.

[0015] There is no particular limitation on the number of piezoelectric elements 7. In this embodiment, for example, the piezoelectric elements 7 are arranged in 4 rows and 4 columns, so the number of piezoelectric elements 7 is 16.

[0016] The fourth substrate 5 has four fourth holes 9 that are long in the Y direction. When viewed from the first direction 6, the shape of the fourth holes 9 is a parallelogram. The fourth substrate 5 is formed from a silicon single crystal substrate. The fourth holes 9 are formed by wet etching. The side surfaces of the fourth holes 9 are crystal planes with a slow etching rate. In a silicon single crystal substrate, the crystal planes with a slow etching rate are parallelograms, so the shape of the fourth holes 9 is a parallelogram. The fourth holes 9 penetrate the fourth substrate 5. The fourth holes 9 are arranged in positions facing the arrangement of the piezoelectric elements 7. The number of fourth holes 9 is not particularly limited.

[0017] The third substrate 3 is disposed between the first substrate 4 and the second substrate 2. The third substrate 3 has a third surface 3a and a fourth surface 3b. The third surface 3a faces the positive Z direction. The fourth surface 3b faces the negative Z direction. The third surface 3a is bonded to the first surface 4a of the first substrate 4. The third substrate 3 has four second grooves 11 on the third surface 3a as sealed spaces that are long in the X direction. When viewed from the first direction 6, the second grooves 11 have a parallelogram shape. The third substrate 3 is formed from a silicon single crystal substrate. The second grooves 11 are formed by wet etching. Therefore, the second grooves 11 have a parallelogram shape. The second grooves 11 are disposed in a position facing the arrangement of the piezoelectric elements 7.

[0018] When viewed from the first direction 6, the piezoelectric element 7 is disposed at the location where the fourth hole 9 and the second groove 11 intersect. Therefore, at the location where the piezoelectric element 7 is disposed, the first substrate 4 can vibrate in the positive Z direction and the negative Z direction.

[0019] The first substrate 4 and the fourth substrate 5 are integrated together. The material of the first substrate 4 is silicon oxide, and the first substrate 4 is formed by oxidizing the fourth substrate 5.

[0020] A common terminal 12 as a first electrode and a drive terminal 13 as a first electrode are arranged on a first surface 4a of the first substrate 4. The common terminal 12 and the drive terminal 13 are electrically connected to the piezoelectric element 7.

[0021] The third substrate 3 has a first through hole 14 as a through hole that penetrates from the third surface 3a to the fourth surface 3b at a position corresponding to the common terminal 12. The third substrate 3 has a second through hole 15 as a through hole that penetrates from the third surface 3a to the fourth surface 3b at a position corresponding to the drive terminal 13. The thickness of the third substrate 3 is approximately 400 μm.

[0022] A first through electrode 16 serving as a third electrode is provided in the first through hole 14 of the third substrate 3 on the negative Z direction side of the common terminal 12. The first through electrode 16 is electrically connected to the common terminal 12. A second through electrode 17 serving as a third electrode is provided in the second through hole 15 of the third substrate 3 on the negative Z direction side of the drive terminal 13. The second through electrode 17 is electrically connected to the drive terminal 13.

[0023] The third substrate 3 has an open hole 18 on the X-positive side of the second groove 11. The open hole 18 penetrates from the third surface 3a to the fourth surface 3b. The open hole 18 and the second groove 11 are connected by a first communicating groove 19. The four second grooves 11 are connected to one another by a second communicating groove 21.

[0024] The third substrate 3 and the first substrate 4 are adhesively fixed together. The second groove 11 is not sealed because it is connected to the open hole 18, the first communicating groove 19, and the second communicating groove 21. When the first substrate 4 vibrates, the air pressure does not easily fluctuate because the air in the second groove 11 is connected to the outside air. For this reason, the first substrate 4 is prone to vibrating.

[0025] The second substrate 2 includes a second surface 2a facing the fourth surface 3b of the third substrate 3. A common connection terminal 22 serving as a second electrode is arranged on the second surface 2a of the second substrate 2 at a position corresponding to the first through-hole electrode 16. The common connection terminal 22 is connected to the first through-hole electrode 16 and is electrically connected to the common terminal 12 via the first through-hole electrode 16. A drive connection terminal 23 serving as a second electrode is arranged on the second surface 2a of the second substrate 2 at a position corresponding to the second through-hole electrode 17. The drive connection terminal 23 is connected to the second through-hole electrode 17 and is electrically connected to the drive terminal 13 via the second through-hole electrode 17. Power can be supplied to the piezoelectric element 7 by supplying power to the common connection terminal 22 and the drive connection terminal 23. The third substrate 3 and the second substrate 2 are flip-chip mounted.

[0026] The second substrate 2 has an external common terminal 24 on the negative X side of the common connection terminal 22. The external common terminal 24 and the common connection terminal 22 are electrically connected by a common connection wiring 25. The second substrate 2 has an external drive terminal 26 on the negative X side of the drive connection terminal 23. The external drive terminal 26 and the drive connection terminal 23 are electrically connected by a drive connection wiring 27.

[0027] The external common terminal 24 and the external drive terminal 26 are electrically connected to a control circuit 29 by external wiring 28. Therefore, the common connection terminal 22 and the drive connection terminal 23 are electrically connected to the control circuit 29.

[0028] The common connection wiring 25 and the drive connection wiring 27 are covered with resist 31. The common connection terminal 22, the drive connection terminal 23, the external common terminal 24, and the external drive terminal 26 are exposed without being covered with resist 31. The common connection terminal 22 is electrically connected to the first through electrode 16. The drive connection terminal 23 is electrically connected to the second through electrode 17.

[0029] The piezoelectric device 1 includes an adhesive portion 32 on the second surface 2a of the second substrate 2, which bonds the second substrate 2 and the third substrate 3 together. The adhesive portion 32 includes a first adhesive portion 32a and a second adhesive portion 32b. The second adhesive portion 32b is arranged on the second substrate 2 at a location that overlaps the Y-positive corner and the Y-negative corner of the X-positive end of the third substrate 3 when viewed from the first direction 6. The first adhesive portion 32a is arranged around the first through electrode 16 and the second through electrode 17 on the second substrate 2 corresponding to the X-negative end of the third substrate 3. The common connection terminal 22 and the drive connection terminal 23 face the first through electrode 16 and the second through electrode 17, respectively. Therefore, the first adhesive portion 32a is arranged around the common connection terminal 22 and the drive connection terminal 23. Because the first adhesive portion 32a and the second adhesive portion 32b are spaced apart, bending of the third substrate 3 due to adhesion is suppressed.

[0030] In the assembly process of the second substrate 2 and the third substrate 3, adhesive is applied to the location where the adhesive portion 32 will be formed. The adhesive is applied to either the second substrate 2 or the third substrate 3. The adhesive is sandwiched between the second substrate 2 and the third substrate 3. The first through electrode 16 and the common connection terminal 22 are pressed against each other. The second through electrode 17 and the drive connection terminal 23 are pressed against each other. The adhesive spreads as it is pressed by the first through electrode 16, the second through electrode 17, the common connection terminal 22, and the drive connection terminal 23. The second substrate 2 has a wall portion 33 on its second surface 2a facing the third substrate 3 that prevents the adhesive from flowing out. The wall portion 33 prevents the adhesive from spreading. The adhesive is non-conductive. A non-conductive adhesive is called NCP (Non-Conductive Paste). The adhesive solidifies to become the adhesive portion 32.

[0031] According to this configuration, the second substrate 2 has a wall portion 33. When the second substrate 2 and the third substrate 3 are bonded together, an adhesive is applied to the second substrate 2. The wall portion 33 prevents the adhesive from leaking out. The second substrate 2 and the third substrate 3 are bonded and fixed together at the adhesive portion 32. When the adhesive leaks out to the area that overlaps with the element array 8 in a planar view of the piezoelectric device 1, internal stress is generated in the third substrate 3 due to the bonding, which affects the resonant frequency of the piezoelectric device 1. Because the wall portion 33 is arranged, the adhesive does not reach the area that overlaps with the element array 8 in a planar view of the piezoelectric device 1. Therefore, the piezoelectric device 1 can suppress changes in the resonant frequency caused by the adhesive.

[0032] The wall portions 33 are made of resist 31. According to this configuration, the common connection terminals 22 and the drive connection terminals 23 are arranged on the second substrate 2. A common connection wiring 25 is connected from the common connection terminal 22 to the external common terminal 24. A drive connection wiring 27 is connected from the drive connection terminal 23 to the external drive terminal 26. The common connection wiring 25 and the drive connection wiring 27 are coated with resist 31. Because the wall portions 33 are made of resist 31, the wall portions 33 and the resist 31 that coats the common connection wiring 25 and the drive connection wiring 27 can be formed simultaneously. Therefore, the piezoelectric device 1 can be manufactured with better productivity than when the wall portions 33 and the resist 31 for the common connection wiring 25 and the drive connection wiring 27 are formed in separate processes.

[0033] Fig. 2 is a cross-sectional view taken along line AA in Fig. 1. Fig. 3 is a cross-sectional view taken along line BB in Fig. 1. As shown in Figs. 2 and 3, a piezoelectric element 7 is disposed at the location where the fourth hole 9 and the second groove 11 intersect when viewed from the first direction 6. The piezoelectric element 7 is disposed on the first surface 4a of the first substrate 4. The piezoelectric element 7 is composed of a drive electrode 7a, a piezoelectric film 7b, and a common electrode 7c that are stacked in the negative Z direction from the first surface 4a.

[0034] The piezoelectric film 7b is made of, for example, a transition metal oxide having a perovskite structure, specifically, lead zirconate titanate containing Pb, Ti, and Zr.

[0035] The plurality of drive electrodes 7a are electrically connected to drive wiring 34 extending in the X direction. The drive electrodes 7a and the drive wiring 34 are made of the same material. The plurality of common electrodes 7c are electrically connected to common wiring 35 extending in the Y direction. The common electrodes 7c and the common wiring 35 are made of the same material.

[0036] The first substrate 4 and the piezoelectric element 7 form an ultrasonic transducer 36. The drive electrode 7a and the common electrode 7c are electrically connected to the control circuit 29. The common electrode 7c is maintained at a predetermined reference potential. When a drive pulse signal is input to the drive electrode 7a, the piezoelectric element 7 deforms and the first substrate 4 vibrates. This causes the ultrasonic transducer 36 to transmit ultrasonic waves in the positive Z direction. If an object is present on the positive Z side of the piezoelectric device 1, the ultrasonic waves are reflected by the object. When the reflected ultrasonic waves pass through the fourth hole 9 in the fourth substrate 5 and reach the ultrasonic transducer 36, the first substrate 4 vibrates in response to the sound pressure of the ultrasonic waves. The vibration of the first substrate 4 deforms the piezoelectric film 7b, generating a potential difference between the drive electrode 7a and the common electrode 7c. As a result, a reception signal corresponding to the sound pressure of the received ultrasonic waves is output from the drive electrode 7a of the ultrasonic transducer 36. In other words, ultrasonic waves are detected.

[0037] 4 is a view of the first substrate 4 viewed from the third substrate 3 side. As shown in FIG. 4, four drive wires 34 extending in the X direction are arranged on the first surface 4a. The drive wires 34 are integrated on the negative X direction side and electrically connected to the drive terminals 13. Four common wires 35 extending in the Y direction are arranged on the first surface 4a. The common wires 35 are integrated on the negative Y direction side and electrically connected to the common terminals 12.

[0038] The region where the element array 8 is arranged is referred to as an array region 37. The region surrounding the array region 37 is referred to as a non-array region 38. In the non-array region 38, the common terminal 12 and the drive terminal 13 are arranged.

[0039] A signal output from the control circuit 29 to the external common terminal 24 is supplied to the common electrode 7c through the common connection wiring 25, the common connection terminal 22, the first through electrode 16, the common terminal 12, and the common wiring 35. A signal output from the control circuit 29 to the external drive terminal 26 is supplied to the drive electrode 7a through the drive connection wiring 27, the drive connection terminal 23, the second through electrode 17, the drive terminal 13, and the drive wiring 34. The control circuit 29 is electrically connected to the piezoelectric element 7. The control circuit 29 outputs a drive signal to the piezoelectric element 7.

[0040] Fig. 5 is a cross-sectional view taken along line CC in Fig. 1. As shown in Fig. 5, the first through electrode 16 electrically connects the common terminal 12 and the common connection terminal 22. The second through electrode 17 electrically connects the drive terminal 13 and the drive connection terminal 23.

[0041] The second substrate 2 is disposed opposite the fourth surface 3b of the third substrate 3. The second substrate 2 has a common connection terminal 22 that is electrically connected to the first through-electrode 16. The second substrate 2 has a drive connection terminal 23 that is electrically connected to the second through-electrode 17. By supplying power to the common connection terminal 22 and the drive connection terminal 23, power is supplied to the piezoelectric element 7.

[0042] The first through electrode 16 and the second through electrode 17 are made of a conductive resin adhesive that has been heated, dried, and solidified. Specifically, the first through electrode 16 and the second through electrode 17 are made of a resin containing silver filler. Examples of the resin adhesive that can be used include epoxy resin, urethane resin, and silicone resin adhesives. Silver bumps may be formed on the common connection terminal 22 and the drive connection terminal 23. This can improve adhesion between the first through electrode 16 and the common connection terminal 22. This can improve adhesion between the second through electrode 17 and the drive connection terminal 23.

[0043] Fig. 6 is a cross-sectional view taken along line DD in Fig. 1. As shown in Fig. 6, a second groove 11 that allows the first substrate 4 to vibrate is disposed between the first substrate 4 and the third substrate 3. The third substrate 3 has an open hole 18 that connects the second groove 11 with the fourth surface 3b. A wall portion 33 is disposed between the first through hole 14 and the second through hole 15 and the open hole 18.

[0044] With this configuration, the wall portion 33 suppresses the flow of adhesive. Therefore, the flow of adhesive does not reach the open hole 18 in a plan view of the piezoelectric device 1. When the open hole 18 is blocked, vibration of the first substrate 4 causes the air pressure in the second groove 11 to fluctuate. As a result, vibration of the first substrate 4 is suppressed, and the resonant frequency changes. The piezoelectric device 1 of this embodiment can suppress changes in resonant frequency caused by adhesive entering the open hole 18.

[0045] In a plan view from the first direction 6, the wall portion 33 is disposed between the first through hole 14 and the second through hole 15 and the element array 8. When the adhesive spreads to the array region 37, the rigidity of the third substrate 3 increases. This changes the resonance frequency of the piezoelectric device 1. As shown in FIG. 7, when the amount of adhesive in the adhesive portion 32 is large, the adhesive reaches the wall portion 33. The wall portion 33 then stops the flow of the adhesive. The wall portion 33 then prevents the adhesive from spreading.

[0046] With this configuration, the wall portion 33 suppresses the flow of the adhesive. Therefore, in a plan view from the first direction 6 in which the first substrate 4, the second substrate 2, and the third substrate 3 are stacked, the adhesive does not reach the array region 37 that overlaps with the element array 8. Therefore, the piezoelectric device 1 can suppress changes in the resonant frequency caused by the adhesive. [Explanation of symbols]

[0047] 1...piezoelectric device, 2...second substrate, 2a...second surface, 3...third substrate, 3a...third surface, 3b...fourth surface, 4...first substrate, 4a...first surface, 7...piezoelectric element, 8...element array, 11...second groove as sealed space, 12...common terminal as first electrode, 13...drive terminal as first electrode, 14...first through hole as through hole, 15...second through hole as through hole, 16...first through electrode as third electrode, 17...second through electrode as third electrode, 18...open hole, 22...common connection terminal as second electrode, 23...drive connection terminal as second electrode, 29...control circuit, 32...adhesive portion, 33...wall portion.

Claims

1. a first substrate including a first surface on which a plurality of piezoelectric elements and first electrodes connected to the piezoelectric elements are disposed; a second substrate including a second surface on which a second electrode connected to a control circuit is disposed; a third substrate disposed between the first substrate and the second substrate, the third substrate including a third surface bonded to the first surface and a fourth surface facing the second surface; an adhesive portion provided on the second surface and adhering the second substrate and the third substrate together; The plurality of piezoelectric elements are arranged in an array, the third substrate includes a through hole extending from the third surface to the fourth surface, and a third electrode provided in the through hole and connected to the first electrode; the second electrode is connected to the third electrode and is electrically connected to the first electrode via the third electrode; the second substrate includes, on the second surface facing the third substrate, a wall portion that suppresses the adhesive portion from flowing out into an area overlapping with the element array; A piezoelectric device characterized in that, when viewed in a planar view from the stacking direction of the first substrate, the second substrate, and the third substrate, the wall portion is arranged between the through hole and the element array.

2. 2. The piezoelectric device according to claim 1, a sealed space that allows the first substrate to vibrate is disposed between the first substrate and the third substrate; the third substrate has an open hole that communicates the sealed space with the fourth surface, The piezoelectric device, wherein the wall portion is disposed between the through hole and the open hole.

3. 3. The piezoelectric device according to claim 1, The piezoelectric device is characterized in that the wall portion is made of resist.

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