Transducer having piezoelectric element and method for manufacturing the same

Abstract

To provide a transducer having a piezoelectric element in which a plurality of vibration units by the piezoelectric element can be configured by a simple structure, and a method for manufacturing the same.SOLUTION: In a transducer 1, a piezoelectric sheet 2 has a piezoelectric element formed on a surface of a flexible substrate. In a support member 3, a plurality of holes 35 having the same inner diameter are formed on a support plate 30 such as a metal plate. The piezoelectric sheet 2 is overlapped on a first surface 31 of the support plate 30 and bonded and fixed thereto. A region of an element region DA of the piezoelectric sheet 2, which is opposed to the holes 35, is a vibration portion (v), and a region other than the holes 35 is a restraint portion(s) to which the piezoelectric sheet 2 is fixed without moving. A plurality of the vibration portions (v) has the same resonance frequency, and an ultrasonic wave can be synchronously generated from the vibration portions (v).SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a transducer using a piezoelectric element that can be used as a speaker, a sensor, or the like. [Background technology]

[0002] Patent Document 1 describes an invention related to an ultrasonic transducer. This ultrasonic transducer has an elastic plate having elasticity capable of vibrating in the plate thickness direction. The elastic plate is made of stainless steel, Ni-Fe alloy, aluminum alloy, titanium alloy, carbon fiber reinforced plastic, ceramic, or the like. A plurality of piezoelectric elements are fixed in parallel in the plate surface direction to a first surface of the elastic plate. The piezoelectric element has a piezoelectric body made of PZT, and a pair of upper and lower electrode layers arranged on both sides in the thickness direction of the piezoelectric body. In addition, the ultrasonic transducer is provided with a sealing member having a plurality of cylindrical parts surrounding each of the plurality of piezoelectric elements in a plan view, and a flexible wiring board that serves as a voltage supply path to the plurality of piezoelectric elements.

[0003] The elastic plate has vibration regions in which a plurality of piezoelectric elements are respectively attached, a plurality of low-rigidity regions surrounding each of the vibration regions, and a restraining region surrounding each of the plurality of low-rigidity regions. In a boundary region located radially outward from the restraining regions, a slit portion is formed in the elastic plate. By providing piezoelectric elements in the plurality of vibration regions surrounded by the low-rigidity regions, the plurality of vibration regions can be arranged in close proximity to each other. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication WO2020 / 202351 Summary of the Invention [Problem to be solved by the invention]

[0005] The ultrasonic transducer described in Patent Document 1 has multiple vibration areas arranged closely adjacent to each other on a first surface of an elastic plate. However, it is necessary to individually attach a piezoelectric element to each vibration area, and furthermore, it is necessary to provide a flexible wiring board on the surface of the elastic plate and wire the flexible wiring board individually to each piezoelectric element, making the manufacturing process very complicated.

[0006] The present invention is devised to solve the above-mentioned problems of the conventional technology, and aims to provide a transducer using a piezoelectric element, which can form multiple vibration sections using piezoelectric elements without the need to provide a large number of individual piezoelectric elements, and a method for manufacturing the same. [Means for solving the problem]

[0007] The present invention provides a transducer having a flexible substrate and a piezoelectric element formed on a surface of the flexible substrate, an element region in which the piezoelectric elements are continuous in a planar direction is formed on a surface of the flexible substrate; a support member having a higher rigidity than the flexible substrate and having a plurality of holes formed therein is provided, the flexible substrate is overlaid on the support member, and the plurality of holes face the element region; The flexible substrate is free inside the holes, and is fixed to the support member in the areas other than the holes.

[0008] In the transducer having a piezoelectric element of the present invention, it is preferable that the inner diameters of the plurality of holes overlapping the element region are the same.

[0009] The transducer having a piezoelectric element of the present invention may be configured such that the support members are superimposed on each of two surfaces of the flexible substrate, and the areas of the support members where the holes are not formed are fixed to the respective surfaces of the flexible substrate with the centers of the holes of the two support members aligned.

[0010] A transducer having a piezoelectric element of the present invention may be constructed such that the support member overlapping the element region is curved.

[0011] The present invention also provides a method for manufacturing a transducer having a flexible substrate and a piezoelectric element formed on a surface of the flexible substrate, the method comprising the steps of: forming an element region on a surface of the flexible substrate, the piezoelectric elements being continuous in a planar direction; forming a support member having a plurality of holes formed therein using a material that is more rigid than the flexible substrate; a step of overlapping the flexible substrate on the support member, arranging the holes so as to face the element region, placing the flexible substrate in a free state inside the holes, and fixing the flexible substrate to the support member in a region other than the holes; The present invention is characterized in that it has the following features.

[0012] The method for producing a transducer having a piezoelectric element of the present invention comprises the steps of: In the step of forming the element region, A lower electrode layer, a piezoelectric material layer, and an upper electrode layer are laminated in this order on the surface of the flexible substrate.

[0013] The method for producing a transducer having a piezoelectric element of the present invention comprises the steps of: In the step of forming the element region, A piezoelectric element is formed by laminating a lower electrode layer on the lower surface of a piezoelectric material layer formed of a polymeric piezoelectric material and an upper electrode layer on the upper surface of the piezoelectric material layer. The piezoelectric element is fixed to the surface of a flexible substrate.

[0014] The method for producing a transducer having a piezoelectric element of the present invention comprises the steps of: Before or after the step of overlapping the flexible substrate and the support member, The method may further include a step of bending the support member. Effect of the Invention

[0015] In the converter of the present invention, an element region in which piezoelectric elements are continuous in the planar direction is formed on the surface of a flexible substrate, and a support member having a plurality of holes is superimposed on the surface of the flexible substrate, with the portion of the element region where the plurality of holes face each other functioning as a vibration section. Since a single element region can be used to form a plurality of vibration sections that are substantially separated, there is no need to form a plurality of small piezoelectric elements. There is also no need to connect wiring members individually to each vibration section. Therefore, a converter having a plurality of vibration sections can be constructed at low cost. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is an exploded perspective view showing a first embodiment of a transducer having a piezoelectric element of the present invention; [Diagram 2] FIG. 2 is a partial cross-sectional view taken along line II-II of FIG. 1 showing the assembled state of the converter; [Diagram 3] FIG. 2 is a partial cross-sectional view of a second embodiment of a transducer having a piezoelectric element of the present invention; [Figure 4] FIG. 3 is an enlarged cross-sectional view showing details of the construction of a piezoelectric sheet used in the transducer shown in FIG. [Diagram 5] FIG. 3 is an enlarged cross-sectional view showing a variation of the configuration of the piezoelectric sheet used in the transducer shown in FIG. [Figure 6] FIG. 13 is an exploded perspective view showing a third embodiment of a transducer having a piezoelectric element according to the present invention; [Figure 7] FIG. 13 is a perspective view showing a state in which the converter of the third embodiment is assembled; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] 1 and 2 show a converter 1 according to a first embodiment of the present invention. The converter 1 is configured by stacking a piezoelectric sheet 2 and a support member 3. The piezoelectric sheet 2 has a flexible substrate 10. The flexible substrate 10 is an organic resin film having elasticity and capable of bending and deforming, such as a polyimide film. As shown in the enlarged cross-sectional view of FIG. 4, the flexible substrate 10 has a first surface 11 facing the Z1 direction and a second surface 12 facing the Z2 direction, and a piezoelectric element 20 is fixed to the first surface 11. As shown in FIG. 1, the flexible substrate 10 is rectangular in plan view, and the piezoelectric element 20 fixed to the first surface 11 is also rectangular. The piezoelectric element 20 is formed continuously in the surface direction over a wide area on the first surface 11 of the flexible substrate 10. The region on the first surface 11 where the piezoelectric element 20 is formed continuously in the surface direction is the element region DA.

[0018] As shown in Fig. 4, the piezoelectric element 20 has a lower electrode layer 21 fixed to the first surface 11 of the flexible substrate 10, a piezoelectric material layer 23 laminated on the surface of the lower electrode layer 21, and an upper electrode layer 22 laminated on the surface of the piezoelectric material layer 23. The manufacturing method of the piezoelectric element 20 is to manufacture the lower electrode layer 21 by forming a conductive metal layer such as a copper layer, a silver layer, or a gold layer on the first surface 11 of the flexible substrate 10 by a method such as vapor deposition or sputtering. A ferroelectric ceramic such as barium titanate, barium zirconate, or lead zirconate titanate is fired on the surface to form a piezoelectric material layer 23, and the upper electrode layer 22 is formed on the surface by a method such as vapor deposition or sputtering. An electric field is applied to the piezoelectric material layer 23, and a polarization process is performed in which the film thickness direction (Z direction) is the polarization direction. Alternatively, the piezoelectric material layer 23 may be formed from a polymeric piezoelectric material such as polyvinylidene fluoride, the lower electrode layer 21 and the upper electrode layer 22 may be laminated on this film-like piezoelectric material layer 23 to form the piezoelectric element 20, and this piezoelectric element 20 may be bonded to the first surface 11 of the flexible substrate 10. In this case as well, an electric field is applied to the piezoelectric material layer 23 to perform a polarization process in which the film thickness direction (Z direction) is the polarization direction.

[0019] As shown in Fig. 1, extensions 13 and 14 are formed on a flexible substrate 10. A bottom terminal 24 is formed on a first surface of extension 13, and a top terminal 25 is formed on a first surface of extension 14. The bottom terminal 24 is a conductive metal layer and is formed integrally and continuously with the bottom electrode layer 21, or is formed separately from the bottom electrode layer 21 and connected to the bottom electrode layer 21. The top electrode layer 25 is also a conductive metal layer and is formed integrally and continuously with the top electrode layer 22, or is formed separately from the top electrode layer 22 and connected to the top electrode layer 22.

[0020] The support member 3 shown in FIG. 1 and FIG. 2 has a support plate 30. The support plate 30 has higher rigidity than the flexible substrate 10 and is sufficiently thicker than the flexible substrate 10. The support plate 30 is a metal plate such as a stainless steel plate, or a synthetic resin plate such as an epoxy-based plate. The support plate 30 has a first surface 31 facing the Z1 side and a second surface 32 facing the opposite Z2 side. A piezoelectric sheet 2 is overlaid on the first surface 31. A plurality of holes 35 are formed in the support plate 30. The center line of each hole 35 is perpendicular to the first surface 31 and the second surface 32, and the holes 35 are formed penetrating the support plate 30. The plurality of holes 35 are arranged at a constant pitch in a first direction (X direction) along the first surface 31, and are also arranged at a constant pitch in a second direction (Y direction) perpendicular to the first direction.

[0021] The holes 35 are cylindrical holes with a constant inner diameter from the first surface 31 to the second surface 32 of the support plate 30, and all the holes 35 have the same inner diameter. Alternatively, the holes 35 may have a tapered shape in which the inner diameter gradually widens from the first surface 31 to which the piezoelectric sheet 2 is fixed to the second surface 32 on the opposite side. In this case, the opening diameter of all the holes 35 that appear on the first surface 31 is the same.

[0022] 2, the transducer 1 is formed by adhering and fixing the piezoelectric sheet 2 to a first surface 31 of a support plate 30 constituting the support member 3. The element area DA of the piezoelectric sheet 2 is continuous over a predetermined area along the sheet surface, and the support plate 30 and the piezoelectric sheet 2 are adhered and fixed such that a plurality of holes 35 face the element area DA.

[0023] In the region of the support member 3 where the holes 35 are not formed, the element region DA of the piezoelectric sheet 2 is bonded and fixed to the first surface 31 of the support plate 30. The element region DA in the region of the support member 3 facing the holes 35 is not fixed to the first surface 31 and is in a free state. That is, the flexible substrate 10 and the piezoelectric element 20 are in a free state inside the hole 35. In the element region DA of the piezoelectric sheet 2, the portion facing the region where the holes 35 are formed functions as a vibration part (v), and the region where the holes 35 are not formed becomes a restraint part (s) where the piezoelectric sheet 2 is fixed to the first surface 31 of the support plate 30. When focusing on a group of multiple vibration parts (v), all the vibration parts (v) are circular and have the same diameter. In the restraint part (s), the element region DA is fixed and restrained to the first surface 31 of the support plate 30 over the entire area between the adjacent holes 35, and the movement of the flexible substrate 10 and the piezoelectric element 20 is restricted.

[0024] Next, the operation of the converter 1 will be described. When an AC voltage is applied between the bottom terminal portion 24 and the top terminal portion 25 of the piezoelectric sheet 2, in the element region DA, the voltage between the bottom electrode layer 21 and the top electrode layer 22 acts on the piezoelectric material layer 23 in the thickness direction. Since the thickness direction of the piezoelectric material layer 23 is the polarization direction, a distortion occurs in the piezoelectric material layer 23 on which the voltage acts. In the vibration portion (v), the piezoelectric sheet 2 is in a free state inside the hole 35, so that the difference in volume change between the piezoelectric element 20 in which distortion occurs and the flexible substrate 10 causes the piezoelectric sheet 2 to bend and deform, and vibrate, as shown by the dashed line in Fig. 2. In the restraint portion (s), the element region DA is fixed to the first surface 31 of the support plate 30, so that the piezoelectric sheet 2 does not bend in the thickness direction.

[0025] When the converter 1 is used as a piezoelectric speaker, pressure waves are generated from the multiple vibration parts (v) due to the flexural vibration of the piezoelectric sheet 2. In each vibration part (v), the piezoelectric sheet 2 located inside the hole 35 has a predetermined resonance frequency based on its mass and elastic coefficient, so that the piezoelectric sheet 2 can be vibrated with high sensitivity by applying an AC voltage in a specific frequency band including the resonance frequency to the piezoelectric sheet 2. Although the output of pressure waves from only one vibration part (v) is low, multiple vibration parts (v) with the same diameter and the same resonance frequency vibrate in synchronously, so that the converter 1 as a whole can generate pressure waves with a large output.

[0026] The converter 1 is used, for example, as a parametric speaker that constitutes a highly directional acoustic system. This speaker applies FM modulation or AM modulation to, for example, 40 kHz ultrasonic waves, reproducing audible sounds in the space where two ultrasonic waves intersect, or producing audible sounds due to the nonlinear characteristics of ultrasonic waves propagating through the air. The converter 1 of the embodiment can emit ultrasonic waves synchronized with each other from multiple vibration parts (v), so that the output of ultrasonic waves can be increased and audible sounds can be reproduced at a relatively high output.

[0027] 1 and 2, the Z1 side on which the piezoelectric sheet 2 is provided may be used as the sound generation direction (the transmission direction of the pressure wave), or the Z2 side on which the support member 3 is provided may be used as the sound generation direction. When the Z2 side is used as the sound generation direction, the directionality of the pressure wave can be further increased by making the hole 35 a cylindrical hole that is long in the Z direction. Also, when the Z2 side is used as the sound generation direction, the shape of the hole 35 may be a tapered shape in which the inner diameter gradually increases in the Z2 direction.

[0028] The converter 1A shown in FIG. 5 uses a modified piezoelectric sheet 102. The piezoelectric sheet 102 is overlaid and fixed on the first surface 31 of the support plate 30 constituting the support member 3. In this piezoelectric sheet 102, a piezoelectric element 20A is overlaid on the first surface 11 of the flexible substrate 10, and a piezoelectric element 20B is overlaid on the second surface 12. Both the piezoelectric element 20A and the piezoelectric element 20B have a structure in which a piezoelectric material layer 23 is sandwiched between a lower electrode layer 21 and an upper electrode layer 22. In this converter 1A, AC voltages with inverted phases are applied to the piezoelectric element 20A and the piezoelectric element 20B of the piezoelectric sheet 102. When a positive strain is generated in the piezoelectric element 20A, a negative strain is generated in the piezoelectric element 20B, and when a negative strain is generated in the piezoelectric element 20A, a positive strain is generated in the piezoelectric element 20B. This makes it possible to vibrate the piezoelectric sheet 102 with good sensitivity in the vibration section (v).

[0029] In the converter 101 of the second embodiment of the present invention shown in FIG. 3, the piezoelectric sheet 2 shown in FIG. 4 or the piezoelectric sheet 102 shown in FIG. 5 is sandwiched between the support member 3A and the support member 3B. The hole 35 formed in the support plate 30 of the support member 3A and the hole 35 formed in the support plate 30 of the support member 3B have the same inner diameter. As shown in FIG. 3, the support members 3A and 3B are positioned so that the centers of the hole 35 of the support member 3A and the hole 35 of the support member 3B coincide in the Z direction. The element region DA of the piezoelectric sheet 2 is bonded and fixed to both the support member 3A and the support member 3B at the restraint portion (s). Since the converter 101 can fix and restrain the element region DA with the two support members 3A and 3B, it is possible to suppress the occurrence of distortion in the thickness direction of the piezoelectric material layer 23 at the restraint portion (s), and to prevent the distortion from affecting the vibration of the piezoelectric sheet 2 at the vibration portion (v).

[0030] 6 and 7 show a converter 201 according to a third embodiment of the present invention. In the converter 201, the support member 103 has a curved support plate 30, and a plurality of holes 35 are formed in the support plate 30. The support plate 30 is curved so that the first surface 31 can form a part of a cylindrical surface. That is, the support plate 30 is curved two-dimensionally so that the radius from a virtual center line extending in the Y direction parallel to the first surface 31 is constant. The piezoelectric sheet 2 is overlapped and fixed on the first surface 31, which is the concave side of the support plate 30. The support plate 30 is formed by curving a metal plate in which a plurality of holes 35 are formed in advance, in a press process. Alternatively, the support plate 30 may be molded into a curved shape using a synthetic resin material. The piezoelectric sheet 2 is bonded to the concave side of the support plate 30 so as to follow the concave surface. At this time, the piezoelectric sheet 2 and the support member 3 are positioned relative to each other, bonded, and fixed so that the plurality of holes 35 are located within the element area DA of the piezoelectric sheet 2.

[0031] In the converter 201 of the third embodiment shown in FIG. 7, the Z1 side, which is the concave side of the support member 3, is used as the sound generation direction (the transmission direction of the pressure wave). When the piezoelectric element 20 of the converter 201 is operated, pressure waves are emitted from the multiple vibration parts (v), and since the multiple vibration parts (v) are arranged along the concave curved surface, it is easy to concentrate the pressure waves at a predetermined position in the Z1 direction. When the piezoelectric sheet 2 coincides with a part of the cylindrical surface, the pressure waves are concentrated near the center line of the curvature of the cylindrical surface. When the converter 201 is used as a parametric speaker, it is possible to increase the listening sensitivity at the listening position.

[0032] The transducer 201 of the third embodiment may be structured such that the piezoelectric sheet 2 is overlapped and adhered to the second surface 32, which is the convex side of the curved support plate 30. Alternatively, the transducer 201 may be structured such that the piezoelectric sheet 2 is sandwiched between two curved support members 103, similar to the transducer 101 shown in FIG. 3. In the transducer 201 of the third embodiment, the curved shape of the support member 103 may have a constant curvature in the X direction, but the curvature may vary depending on the location in the X direction, for example, to be curved in a quadratic function curve. Furthermore, the support member 103 may have a three-dimensional curved shape having curvatures in both the X direction and the Y direction.

[0033] In the converter of each of the above-mentioned embodiments, the piezoelectric element 20 (or 20A, 20B) is formed continuously along the surface of the piezoelectric sheet 2 (or 102), and a plurality of vibration parts (v) are formed in a single element area DA where the piezoelectric element 20 is formed. Therefore, the process of forming the piezoelectric element 20 is easier than a structure in which a plurality of independent piezoelectric elements are arranged side by side on the surface of the substrate. In addition, since there is no need to provide individual wiring paths for each vibration part (v) and the wiring structure can be made single, the manufacturing process is simple and the converter can be manufactured at low cost. In addition, the size of the piezoelectric element 20 that contributes to the vibration in each vibration part (v) is determined by the inner diameter of the hole 35. By processing the holes 35 with high precision so that the inner diameters of the plurality of holes 35 are the same, the variation in the dimensions of the piezoelectric element 20 that can be deformed in each vibration part (v) can be extremely reduced, and the vibration characteristics of each vibration part (v) can be uniformly configured.

[0034] The transducers of the above embodiments can also be used as piezoelectric sensors or ultrasonic sensors. When ultrasonic waves of about 40 kHz are applied to the transducer, the pressure waves cause distortion in the piezoelectric element 20 at each vibration portion (v). By measuring the voltage generated between the lower electrode layer 21 and the upper electrode layer 22 of the piezoelectric element at that time, it becomes possible to detect the ultrasonic waves.

[0035] In the converter of the embodiment, a plurality of holes 35 having the same inner diameter are opposed to the element area DA of the piezoelectric element 20 continuous in the surface direction, so that a plurality of vibration parts (v) having the same resonance frequency are formed. However, a plurality of first holes having the same inner diameter and a plurality of second holes having the same inner diameter but different from the first holes may be formed in the vibration plate, and the plurality of first holes and the plurality of second holes may be opposed to the same element area DA. In this case, a plurality of first vibration parts opposed to the first holes and a plurality of second vibration parts opposed to the second holes can be configured in the same element area DA. Since the first vibration part and the second vibration part have different resonance frequencies, ultrasonic waves of different frequencies can be generated simultaneously or alternately from the first vibration part and the second vibration part by applying a driving voltage corresponding to the resonance frequency of each hole. The number of types of holes may be three or more. [Explanation of symbols]

[0036] 1,101,201 Converter 1,102 Piezoelectric sheet 3,3A,3B,103 Support member 10 Flexible substrate 20, 20A, 20B Piezoelectric element 21 Bottom electrode layer 22 Top electrode layer 23 Piezoelectric material layer 30 Support plate 35 holes DA element area (s) Restraint part (v) Vibrating part

Claims

1. 1. A transducer having a flexible substrate and a piezoelectric element formed on a surface of the flexible substrate, an element region in which the piezoelectric elements are continuous in a planar direction is formed on a surface of the flexible substrate; a support member having a higher rigidity than the flexible substrate and having a plurality of holes formed therein is provided, the flexible substrate is overlaid on the support member, and the plurality of holes face the element region; A transducer having a piezoelectric element, characterized in that the flexible substrate is free inside the plurality of holes, and the flexible substrate is fixed to the support member in areas other than the holes.

2. 2. A transducer having a piezoelectric element according to claim 1, wherein the inner diameters of the holes overlapping the element region are the same.

3. A transducer having a piezoelectric element as described in claim 1, wherein the support members are superimposed on each of the two surfaces of the flexible substrate, and the areas of the support members where the holes are not formed are fixed to each surface of the flexible substrate with the centers of the holes of the two support members aligned.

4. 4. A transducer having a piezoelectric element according to claim 1, wherein the support member overlapping the element region is curved.

5. A method for manufacturing a transducer having a flexible substrate and a piezoelectric element formed on a surface of the flexible substrate, comprising the steps of: forming an element region on a surface of the flexible substrate, the piezoelectric elements being continuous in a planar direction; forming a support member having a plurality of holes formed therein using a material that is more rigid than the flexible substrate; a step of overlapping the flexible substrate on the support member, arranging the holes so as to face the element region, placing the flexible substrate in a free state inside the holes, and fixing the flexible substrate to the support member in a region other than the holes; A method for manufacturing a transducer having a piezoelectric element, comprising:

6. In the step of forming the element region, 6. The method for producing a transducer having a piezoelectric element according to claim 5, further comprising laminating a lower electrode layer, a piezoelectric material layer and an upper electrode layer in that order on the surface of said flexible substrate.

7. In the step of forming the element region, A piezoelectric element is formed by laminating a lower electrode layer on the lower surface of a piezoelectric material layer formed of a polymeric piezoelectric material and an upper electrode layer on the upper surface of the piezoelectric material layer.

6. The method for producing a transducer having a piezoelectric element according to claim 5, wherein the piezoelectric element is fixed to a surface of a flexible substrate.

8. Before or after the step of overlapping the flexible substrate and the support member, 8. The method for producing a transducer having a piezoelectric element according to claim 5, further comprising a step of bending the support member.

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