PIEZOLELECTRIC SOUND-GENERATING DEVICE

Abstract

Provided is a piezoelectric sound generating device capable of obtaining a stable connection state of lead-out conductors constituted of a conductive resin layer. A piezoelectric sound generating device 10, wherein lead-out conductors 18a, 18b are so flatly formed as to extend from surface electrodes 11a, 11b1 of a piezoelectric element 11 exposed to first openings 13a1, 13b1 to terminal electrodes 15a, 15b of a terminal portion 15 exposed to second openings 13a2, 13b2 on one main surface side of a diaphragm 12, respectively. As a result, the surface electrode 11a1 of the piezoelectric element 11 and the terminal electrode 15a of the terminal portion 15, and also the surface electrode 11b1 and a surface electrode 11c of the piezoelectric element 11, and the terminal electrode 15b of the terminal portion 15 are conductively connected. Hence, poor connection caused by cracks or the like is not likely to occur in the lead-out conductors.

Description

TECHNICAL FIELD

The present invention relates to a piezoelectric sound-generating device of a square shape using a bimorph piezoelectric element.

BACKGROUND ART

Piezoelectric sound-generating bodies are used in receivers, speakers and other parts of slim electronic devices and mobile electronic devices. These piezoelectric sound-generating bodies are constituted, for example, by storing, in a cap-shaped resin case, etc., a piezoelectric vibration plate formed by adhesively attaching on the principle side of a vibration plate made of phosphor bronze, etc., a piezoelectric element having surface electrodes formed on both principle sides of a disk-shaped ceramic piezoelectric substance. In recent years, high sound pressures and improved space efficiencies are required for the aforementioned devices as LCD displays and organic EL displays, etc., have become larger. To meet this demand, piezoelectric sound-generating bodies using bimorph piezoelectric elements are proposed as a means for achieving larger amplitudes.

One example of the aforementioned bimorph piezoelectric elements is presented by Patent Literature 1, which is a piezoelectric electro-acoustic converter having a bimorph piezoelectric element 111 as shown in FIG. 15. To be specific, a layered body is formed by stacking two or three piezoelectric ceramic layers 111d1, 111d2. Surface electrodes 111b1, 1112 are formed on the two principle sides of this layered body, and an internal electrode 111a2 is formed between the ceramic layers 111d1, 111d2. Furthermore, all ceramic layers 111d1, 111d2 are polarized in the same direction, or specifically in the thickness direction, as indicated by the bold arrow. When alternating signals are applied between the surface electrodes 111b1, 111b2 and internal electrode 111a2 in the directions indicated by the thin arrows and in the opposite directions, for example, the layered body as a whole generates bending vibration.

On the other hand, Patent Literature 2 proposes a square piezoelectric electro-acoustic converter 120 having a piezoelectric element 121, as shown in FIGS. 16 and 17. This converter 120 has a pair of terminals 125a, 125b whose inner connection parts are exposed on the inner surface of the side wall of a case 124 in a direction roughly vertical to the piezoelectric element 121, and the inner connection parts of the terminals 125a, 125b are electrically connected to the surface electrodes (not illustrated) of the piezoelectric element 121 by lead conductors 128a, 128b made of conductive adhesive.

Patent Literature 1: Japanese Patent Laid-open No. 2001-95094

Patent Literature 2: Japanese Patent Laid-open No. 2004-15768

SUMMARY OF THE INVENTION

Problems to Be Solved by the Invention

In the latter piezoelectric electro-acoustic converter 120 described in “Prior Art” above, one end of the lead conductors 128a, 128b made of conductive adhesive are connected to the surface electrodes on one principle side of the piezoelectric element 121, from the surface of a vibration plate 122, in a manner passing over the thickness dimension of the piezoelectric element 121. Also, the other ends of the lead conductors 128a, 128b are connected to the inner connection parts of the terminals 125a, 125b, from the surface of the vibration plate 122, via the top surface of a seal 127 such as silicone resin seal and the step of the case 124. When conductive adhesive constituting the lead conductors 128a, 128b is formed this way in an alienating manner from the surface of the vibration plate 122 in the thickness direction, high tensile/compressive stresses are applied repeatedly to the inside of the layer of conductive adhesive constituting the lead conductors 128a, 128b when the vibration plate 122 generates flexural vibration due to driving of the piezoelectric element 121, as shown in FIG. 18. As a result, the lead conductors 128a, 128b made of conductive adhesive have a possibility of suffering from poor connection due to cracking C, etc. The object of the present invention is to provide a piezoelectric sound-generating device whose lead conductors made of conductive resin layer are resistant to poor connection due to cracking C, etc.

Means for Solving the Problems

To achieve the aforementioned object, one piezoelectric sound-generating device conforming to the present invention is (1) a piezoelectric sound-generating device of a square shape comprising:

• a vibration plate having a main square area in which multiple first openings are formed, and multiple extension parts on which second openings are formed and which are projecting from the outer periphery of the main area;
• a frame having a rim that circularly supports a vicinity of the continuous outer periphery of the main area and extension parts of the vibration plate, adhesively attached on one principle side of the vibration plate;
• a square bimorph piezoelectric element having multiple surface electrodes formed in positions corresponding to the first openings on the one principle side of the vibration plate, adhesively attached in the main area on the other principle side of the vibration plate;
• a terminal having an insulative substrate and terminal electrodes formed on one principle side of the substrate, adhesively attached on the other principle side of the extension parts of the vibration plate; and
• multiple lead conductors formed on the one principle side of the vibration plate, respectively, from the surface electrodes of the piezoelectric element exposed in the first openings, to the terminal electrodes of the terminal exposed in the second openings. (This is hereinafter referred to as the “first technical means of the present invention.”)

The operation of the above first technical means is as follows. To be specific, on this piezoelectric sound-generating device of a square shape, the multiple lead conductors are formed on the one principle side of the vibration plate, respectively, from the surface electrodes of the square bimorph piezoelectric element exposed in the first openings in the main square area of the vibration plate, to the terminal electrodes of the terminal exposed in the second openings on the extension parts projecting from the main area of the vibration plate. This way, the surface electrodes of the piezoelectric elements are connected to the terminal electrodes of the terminal via the lead conductors.

Because of the above structure, the aforementioned lead conductors are formed roughly flat on the one principle side of the vibration plate. As a result, these lead conductors do not easily have thin parts regardless of the thickness dimension of the bimorph piezoelectric element. Consequently, the lead conductors are resistant to poor connection due to cracking, etc.

In addition, another key embodiment of the aforementioned piezoelectric sound-generating device is (2) one according to the above first technical means, wherein a first cover is also provided on the other principle side of the vibration plate in a manner covering the other principle side of the piezoelectric element while also forming a ventilation hole. (This is hereinafter referred to as the “second technical means of the present invention.”)

The operation of the above second technical means is as follows. To be specific, existence of the first cover prevents the piezoelectric element from being damaged due to contact with the outside.

In addition, another key embodiment of the aforementioned piezoelectric sound-generating device is (3) one according to the above first or second technical means, wherein a second cover is also provided on the frame in a manner covering the one principle side of the vibration plate while also forming a ventilation hole. (This is hereinafter referred to as the “third technical means of the present invention.”)

The operation of the above third technical means is as follows. To be specific, existence of the second cover prevents the vibration plate from being damaged due to contact with the outside.

In addition, another key embodiment of the aforementioned piezoelectric sound-generating device is (4) one according to the above first technical means, wherein the frame also has projections extending from the rim, with edges projecting into the area overlapping with the piezoelectric element across the vibration plate. (This is hereinafter referred to as the “fourth technical means of the present invention.”)

The operation of the above fourth technical means is as follows. To be specific, because the frame has the projections the vibration of the vibration plate can be changed compared to when there are no projections, and consequently the frequency vs. sound pressure characteristics of the piezoelectric sound-generating device can be adjusted with ease.

In addition, another key embodiment of the aforementioned piezoelectric sound-generating device is (5) one according to the above first technical means, wherein the vibration plate is made of a rubber sheet. (This is hereinafter referred to as the “fifth technical means of the present invention.”)

The operation of the above fifth technical means is as follows. To be specific, because the vibration plate is made of a rubber sheet, the first-order resonance frequency can be shifted to low-frequency ranges.

EFFECTS OF THE INVENTION

According to a piezoelectric sound-generating device conforming to the present invention, lead conductors are resistant to poor connection due to cracking, etc. As a result, a piezoelectric sound-generating device offering stable connection condition can be provided. The aforementioned and other objects, configurations and characteristics, and operations and effects, of the present invention are explained below using attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective exterior view showing an overview of the first embodiment of a piezoelectric sound-generating device conforming to the present invention.

FIG. 2 is a figure showing an overview of the internal structure of the above embodiment, where FIG. 2(A) is an enlarged view of key parts in section A-A of FIG. 1 above, while FIG. 2(B) is an enlarged view of key parts in section B-B of FIG. 1 above.

FIG. 3 is a perspective exploded view showing the internal structure of the above embodiment.

FIG. 4 is a schematic section view showing the internal structure of the piezoelectric element used in the above embodiment.

FIG. 5 is a perspective exterior view showing an overview of the second embodiment of a piezoelectric sound-generating device conforming to the present invention.

FIG. 6 is an enlarged view of key parts in section C-C of FIG. 5 above, showing an overview of the internal structure of the above embodiment.

FIG. 7 is a perspective exploded view showing the internal structure of the above embodiment.

FIG. 8 is a perspective exploded view showing the internal structure of the third embodiment of a piezoelectric sound-generating device conforming to the present invention.

FIG. 9 is a graph showing the sound pressure characteristics of the piezoelectric sound-generating bodies in the above second and third embodiments.

FIG. 10 is a perspective exterior view showing an overview of the fourth embodiment of a piezoelectric sound-generating device conforming to the present invention.

FIG. 11 is a perspective exploded view showing the internal structure of the above embodiment.

FIG. 12 is a schematic section view showing the internal structure of the piezoelectric element used in the above embodiment.

FIG. 13 is a perspective exterior view showing an overview of the fifth embodiment of a piezoelectric sound-generating device conforming to the present invention.

FIG. 14 is a perspective exploded view showing the internal structure of the above embodiment.

FIG. 15 is a schematic section view showing the internal structure of an example of bimorph piezoelectric element conforming to prior art.

FIG. 16 is a section view showing an overview of the internal structure of an example of piezoelectric electro-acoustic converter conforming to prior art.

FIG. 17 is an enlarged section view of key parts, showing the internal structure of a piezoelectric electro-acoustic converter conforming to prior art.

FIG. 18 is an enlarged section view of key parts, explaining the driving condition of the aforementioned piezoelectric electro-acoustic converter conforming to prior art.

DESCRIPTION OF THE SYMBOLS

• • 10, 20, 30, 40, 50 Piezoelectric sound-generating device
  • 11, 41 Piezoelectric element
  • 11 a 1, 41a1 Surface electrode
  • 11 a 2, 41a2 Internal electrode
  • 11 a 3, 41a3 Inter-layer connection part (through hole conductor)
  • 11 b 1, 41b1 Surface electrode
  • 11 b 2, 41b2 Surface electrode
  • 11 b 3, 41b3 Inter-layer connection part (through hole conductor)
  • 11 c, 41c Surface electrode
  • 11 d 1, 11d2, 41d1, 41d2 Piezoelectric layer
  • 12, 42 Vibration plate
  • 12S, 42S Main area
  • 12 a, 12b, 42a1, 42a2, 42b1, 42b2 Extension part
  • 12 c, 42c Area overlapping with piezoelectric element
  • 12F, 42F One principle side
  • 12B, 42B Other principle side
  • 13 a 1, 13b1, 43a1, 43b1 First opening
  • 13 a 2, 13b2, 43a2, 43b2 Second opening
  • 14, 34, 44 Frame
  • 14 a, 14b, 44a, 44b Cutout
  • 14 c, 34c, 44c Rim
  • 15, 45 Terminal
  • 15 a, 15b, 45a, 45b Terminal electrode
  • 15 c, 45c Substrate
  • 18 a, 48a Lead conductor
  • 18 b, 48b Lead conductor
  • 26, 56 First cover
  • 26 a Second frame
  • 26 b Cover plate
  • 26 c Ventilation hole
  • 27, 57 Second cover
  • 27 a, 27b, 57a, 57b Cutout
  • 34 d 1, 34d2 Projection

MODE FOR CARRYING OUT THE INVENTION

The first embodiment of a piezoelectric sound-generating device conforming to the present invention is explained below by referring to FIGS. 1 to 4.

A piezoelectric sound-generating device 10 in this embodiment has a square shape on the outside, as shown in FIG. 1. As shown in FIG. 3, the constitution of the piezoelectric sound-generating device 10 is outlined by a vibration plate 12, a frame 14 adhesively attached on one principle side 12F of the vibration plate 12, a piezoelectric element 11 adhesively attached on the other principle side 12B of the vibration plate 12, a terminal 15 adhesively attached on the other principle side 12B of the vibration plate 12, and multiple lead conductors 18a, 18b formed on the one principle side 12F of the vibration plate 12.

The vibration plate 12 has a main square area 12S in which multiple first openings 13a1, 13b1 are formed, and multiple extension parts 12a, 12b projecting toward the outer periphery from one side of the main area 12S. The extension parts 12a, 12b have second openings 13a2, 13b2 formed on them, respectively.

The frame 14 has a rim 14c that circularly supports a vicinity of the continuous outer periphery of the main area 12S and extension parts 12a, 12b of the vibration plate 12 and is adhesively attached on the one principle side 12F of the vibration plate 12. The frame 14 has cutouts 14a, 14b formed in positions corresponding to the second openings 13a2, 13b2 on the extension parts 12a, 12b of the vibration plate 12, respectively.

The piezoelectric element 11 has multiple surface electrodes 11a1, 11b1, 11c formed in positions corresponding to the first openings 13a1, 13b1 on the one principle side of the vibration plate 12, and is adhesively attached in the main area 12S on the other principle side 12B of the vibration plate 12. It is of bimorph type and has a square shape on the outside.

As shown schematically in FIG. 4, the internal structure of the piezoelectric element 11 is such that there are multiple piezoelectric layers 11d1, 11d2 made of piezoelectric ceramics. The surface electrode 11a1 on the one principle side is conductively connected to an internal electrode 11a2 provided between the first piezoelectric layer 11d1 and second piezoelectric layer 11d2 via an inter-layer connection part 11a3 such as a through hole conductor penetrating through the first piezoelectric layer 11d1 in the thickness direction, a side electrode, etc. The surface electrode 11b1 on the one principle side is conductively connected to the surface electrode 11b2 on the other principle side of the piezoelectric element 11 via an inter-layer connection part 11b3 such as a through hole conductor penetrating through the first piezoelectric layer 11d1 and second piezoelectric layer 11d2 in the thickness direction, a side electrode, etc.

All of the above piezoelectric layers 11d1, 11d2 are polarized in the same direction, or specifically in the thickness direction, as indicated by the bold arrow.

The terminal 15 has an insulative substrate 15c and multiple terminal electrodes 15a, 15b formed on one principle side of the substrate 15c, and is adhesively attached on the other principle side of the extension parts 12a, 12b of the vibration plate 12. In this embodiment, the terminal 15 bridges one extension part 12a and the other extension part 12b of the vibration plate 12, with both ends adhesively attached on the other principle side 12B of the vibration plate 12, respectively.

The multiple lead conductors 18a, 18b are formed on the one principle side 12F of the vibration plate 12, respectively, from the surface electrodes 11a1, 11c of the piezoelectric element 11 exposed in the first openings 13a1, 13b1 formed in the main square area 12S of the vibration plate 12, to the terminal electrodes 15a, 15b of the terminal 15 exposed in the second openings 13a2, 13b2 formed on the extension parts 12a, 12b of the vibration plate 12.

In this embodiment, the lead conductors 18a, 18b are provided on one side of the piezoelectric sound-generating device 10, in parallel with each other, in a manner sandwiching the terminal 15.

The one lead conductor 18a is formed from the main area 12S on the one principle side 12F of the vibration plate 12 to the extension part 12a, as shown in FIG. 2(A). One end 18a1 of it is connected to the surface electrode 11a1 of the piezoelectric element 11 exposed in the first opening 13a1 as formed in the main square area 12S of the vibration plate 12, while the other end 18a2 is connected to the terminal electrode 15a of the terminal 15 exposed in the second opening 13a2 as formed on the extension part 12a of the vibration plate 12.

The other lead conductor 18b is formed from the main area 12S on the one principle side 12F of the vibration plate 12 to the extension part 12b, as shown in FIG. 2(B). The lead conductor 18b is longer than the lead conductor 18a. Also, one end 18b1 of it is connected to the surface electrodes 11b1, 11c of the piezoelectric element 11 exposed in the first opening 13b1 on the vibration plate 12, while the other end 18b2 is connected to the terminal electrode 15b of the terminal 15 exposed in the second opening 13b2 as formed on the extension part 12b of the vibration plate 12.

The other end 18a2 of the one lead conductor 18a is stored in the cutout 14a formed in the frame 14, and its periphery is guided by the frame 14. Similarly, the other end 18b2 of the other lead conductor 18b is stored in the cutout 14b formed in the frame 14, and its periphery is guided by the frame 14.

Accordingly, the piezoelectric sound-generating device 10 in this embodiment provides flat lead conductors 18a, 18b along the one principle side 12F of the vibration plate 12, regardless of the thickness dimension of the square bimorph piezoelectric element 11, and consequently achieves a stable connection condition.

Next, the second embodiment of a piezoelectric sound-generating device conforming to the present invention is explained below by referring to FIGS. 5 to 7.

As evident from FIG. 7, a piezoelectric sound-generating device 20 in this embodiment, while conforming to the constitution of the piezoelectric sound-generating device 10 in the first embodiment, also has a first cover 26 provided on the other principle side 12B of the vibration plate 12 in a manner covering the other principle side of the piezoelectric element 11 while also forming a ventilation hole 26c. The first cover 26 is constituted by a second frame 26a surrounding the periphery of the piezoelectric element 11, and a cover plate 26b adhesively attached on the second frame 26a in a manner covering the other principle side of the piezoelectric element 11, where multiple ventilation holes 26c are formed in the cover plate 26b. Accordingly, the piezoelectric sound-generating device 20 in this embodiment can prevent the piezoelectric element 11 from being damaged due to contact with the outside.

In addition, the piezoelectric sound-generating device 20 in this embodiment, while conforming to the constitution of the piezoelectric sound-generating device 10 in the first embodiment, also has a second cover 27 provided on the frame 14 in a manner covering the one principle side 12F of the vibration plate 12 while also forming a ventilation hole 27c. The second cover 27 has cutouts 27a, 27b formed in positions respectively corresponding to the lead conductors 18a, 18b. Accordingly, the piezoelectric sound-generating device 20 in this embodiment can prevent the vibration plate 12 from being damaged due to contact with the outside.

Next, the third embodiment of a piezoelectric sound-generating device conforming to the present invention is explained below by referring to FIGS. 8 and 9.

A piezoelectric sound-generating device 30 in this embodiment is the same as the piezoelectric sound-generating device 20 in the second embodiment, except that a frame 34 is used instead of the frame 14. The frame 34 of the piezoelectric sound-generating device 30 in this embodiment has projections 34d1, 34d2 extending from a rim 34c of the frame 34, with edges projecting into an area 34c overlapping with the piezoelectric element 11 across the vibration plate 12. Accordingly, the piezoelectric sound-generating device 30 in this embodiment allows the vibration of the vibration plate to be changed compared to when there are no projections. In FIG. 9, the horizontal axis represents frequency, while the vertical axis represents sound pressure level. Here, the alternately long and short dashed line represents the target level of acoustic characteristics desirable for mobile phone speakers. The dotted line represents the sound pressure characteristics of the piezoelectric sound-generating device 20 in the second embodiment, while the solid line represents the sound pressure characteristics of the piezoelectric sound-generating device 30 in the third embodiment. As evident from FIG. 9, the sound pressure drops near 4500 Hz with the piezoelectric sound-generating device 20 in the second embodiment, but it improves to the target level or above with the piezoelectric sound-generating device 30 in the third embodiment having the projections 34d1, 34d2 on the frame 34.

Next, the fourth embodiment of a piezoelectric sound-generating device conforming to the present invention is explained below by referring to FIGS. 10 and 12.

A piezoelectric sound-generating device 40 in this embodiment has a different terminal electrode layout compared to the piezoelectric sound-generating device 10 in the first embodiment explained earlier. In the piezoelectric sound-generating device 10 in the first embodiment, the multiple terminal electrodes 15a, 15b are provided adjacent to each other on one side of the piezoelectric sound-generating device of a square shape 10. The piezoelectric sound-generating device 40 in this embodiment, on the other hand, has its terminal electrodes 45a, 45b provided at the centers of two opposing sides.

To be specific, the piezoelectric sound-generating device 40 in this embodiment has a square shape on the outside, as shown in FIG. 10. As shown in FIG. 11, its constitution is outlined by a vibration plate 42, a frame 44 adhesively attached on one principle side 42F of the vibration plate 42, a piezoelectric element 41 adhesively attached on the other principle side 42B of the vibration plate 42, a pair of terminals 45, 45 adhesively attached on the other principle side 42B of the vibration plate 42, and multiple lead conductors 48a, 48b formed on the one principle side 42F of the vibration plate 42.

The vibration plate 42 has a main square area 42S in which multiple first openings 43a1, 43b1 are formed, and multiple extension parts 42a1, 42a2, 42b1, 42b2 projecting toward the outer periphery from two opposing sides of the main area 42S. The extension parts 42a1, 42b1 have second openings 43a2, 43b2 formed on them, respectively.

The frame 44 has a rim 44c that circularly supports a vicinity of the continuous outer periphery of the main area 42S and extension parts 42a1, 42a2, 42b1, 42b2 of the vibration plate 42 and is adhesively attached on the one principle side 42F of the vibration plate 42. The frame 44 has cutouts 44a, 44b formed in positions corresponding to the second openings 43a2, 43b2 on the extension parts 42a1, 42b1 of the vibration plate 42, respectively.

The piezoelectric element 41 has multiple surface electrodes 41a1, 41b1, 41c formed in positions corresponding to the first openings 43a1, 43b1 on the one principle side of the vibration plate 42, and is adhesively attached in the main area 42S on the other principle side 42B of the vibration plate 42. It is of bimorph type and has a square shape on the outside.

As shown schematically in FIG. 12, the internal structure of the piezoelectric element 41 is such that there are multiple piezoelectric layers 41d1, 41d2 made of piezoelectric ceramics. The surface electrode 41a1 on the one principle side is conductively connected to an internal electrode 41a2 provided between the first piezoelectric layer 41d1 and second piezoelectric layer 41d2 via an inter-layer connection part 41a3 such as a through hole conductor penetrating through the first piezoelectric layer 41d1 in the thickness direction, a side electrode, etc. The surface electrode 41b1 on the one principle side is conductively connected to a surface electrode 41b2 on the other principle side of the piezoelectric element 41 via an inter-layer connection part 41b3 such as a through hole conductor penetrating through the first piezoelectric layer 41d1 and second piezoelectric layer 41d2 in the thickness direction, a side electrode, etc.

All of the above piezoelectric layers 41d1, 41d2 are polarized in the same direction, or specifically in the thickness direction, as indicated by the bold arrow.

The terminals 45, 45 have an insulative substrate 45c and terminal electrodes 45a, 45b formed on one principle side of the substrate 45c, respectively, and are adhesively attached on the other principle side of the extension parts 42a1, 42a2, 42b1, 42b2 of the vibration plate 42. In this embodiment, each terminal 45 bridges one extension part 42a1 and the other extension part 42a2 on one of the two opposing sides of the main square area 42S of the vibration plate 42, or one extension part 42b1 and the other extension part 42b2 on the other side of the two opposing sides, with both ends adhesively attached on the other principle side 42B of the vibration plate 42, respectively.

The multiple lead conductors 48a, 48b are formed on the one principle side 42F of the vibration plate 42, respectively, from the surface electrodes 41a1, 41c of the piezoelectric element 41 exposed in the first openings 43a1, 43b1 formed in the main square area 42S of the vibration plate 42, to the terminal electrodes 45a, 45b of the terminal 45 exposed in the second openings 43a2, 43b2 formed on the extension parts 42a1, 42b1 of the vibration plate 42.

In this embodiment, the lead conductors 48a, 48b are provided on two opposing sides of the piezoelectric sound-generating device of a square shape 40, in parallel with each other and adjacent to the respective terminals 45, 45.

The one lead conductor 48a is formed from the main area 42S on the one principle side 42F of the vibration plate 42 to the extension part 42a1, as shown in FIG. 11. One end 48a1 of it is connected to the surface electrode 41a1 of the piezoelectric element 41 exposed in the first opening 43a1 as formed in the main square area 42S of the vibration plate 42, while the other end 48a2 is connected to the terminal electrode 45a of the terminal 45 exposed in the second opening 43a2 as formed on the extension part 42a1 of the vibration plate 42.

The other lead conductor 48b is formed from the main area 42S on the one principle side 42F of the vibration plate 42 to the extension part 42b. The lead conductor 48b is longer than the lead conductor 48a. Also, one end 48b1 of it is connected to the surface electrodes 41b1, 41c of the piezoelectric element 41 exposed in the first opening 43b1 on the vibration plate 42, while the other end 48b2 is connected to the terminal electrode 45b of the terminal 45 exposed in the second opening 43b2 as formed on the extension part 42b1 of the vibration plate 42.

The other end 48a2 of the one lead conductor 48a is stored in the cutout 44a formed in the frame 44, and its periphery is guided by the frame 44. Similarly, the other end 48b2 of the other lead conductor 48b is stored in the cutout 44b formed in the frame 44, and its periphery is guided by the frame 44.

Accordingly, the piezoelectric sound-generating device 40 in this embodiment provides flat lead conductors 48a, 48b along the one principle side 42F of the vibration plate 42, regardless of the thickness dimension of the square bimorph piezoelectric element 41, and consequently achieves a stable connection condition.

Next, the fifth embodiment of a piezoelectric sound-generating device conforming to the present invention is explained below by referring to FIGS. 13 and 14.

As is evident from FIG. 14, a piezoelectric sound-generating device 50 in this embodiment, while conforming to the constitution of the piezoelectric sound-generating device 40 in the fourth embodiment, also has a first cover 56 provided on the other principle side 42B of the vibration plate 42 in a manner covering the other principle side of the piezoelectric element 41 while also forming a ventilation hole 56c. The first cover 56 is formed by drawing of an Al or other metal plate, etc., and constituted by a second rim 56a surrounding the periphery of the piezoelectric element 41 and a cover part 56b formed integrally with the rim 56a in a manner covering the other principle side of the piezoelectric element 41, where multiple ventilation holes 56c are formed in the cover part 56b. Accordingly, the piezoelectric sound-generating device 50 in this embodiment can prevent the piezoelectric element 41 from being damaged due to contact with the outside.

In addition, the piezoelectric sound-generating device 50 in this embodiment, while conforming to the constitution of the piezoelectric sound-generating device 40 in the fourth embodiment, also has a second cover 57 provided on the frame 44 in a manner covering the one principle side 42F of the vibration plate 42 while also forming a ventilation hole 57c. The second cover 57 has cutouts 57a, 57b formed in positions respectively corresponding to the lead conductors 48a, 48b and terminal electrodes 45a, 45b. Accordingly, the piezoelectric sound-generating device 50 in this embodiment can prevent the vibration plate 42 from being damaged due to contact with the outside.

Next a favorable embodiment of each part of a piezoelectric sound-generating device conforming to the present invention is explained.

First, the piezoelectric elements should desirably be comprised of piezoelectric layers and an internal electrode that are layered alternately and sintered integrally. Also, the surface electrodes on the principle side of the piezoelectric element should desirably be formed simultaneously with the internal electrode. Note, however, that the present invention is not limited to the foregoing in any way, and surface electrodes may also be formed by, for example, alternately layering and integrally sintering piezoelectric layers and an internal electrode and then applying electrode paste on its surface, followed by baking, etc.

Also note that, while the aforementioned embodiments show examples of a bimorph piezoelectric element constituted by a total of two piezoelectric layers including one on each side, the present invention is not limited to the foregoing in any way and various variations may be permitted as long as a bimorph piezoelectric element having multiple surface electrodes is used. For example, a bimorph piezoelectric element having an odd number of layers (such as three layers) on each side may be used.

Next, a favorable embodiment of the above piezoelectric layer is as follows. To be specific, the above piezoelectric layer should ideally be made of piezoelectric ceramics such as PbZr_xTi_1-xO₃ (PZT). It may also be made of so-called lead-free piezoelectric ceramics not containing lead.

The above piezoelectric layer is formed by, for example, mixing material powder of the aforementioned piezoelectric ceramics with organic solvent, binder, plasticizer, dispersant, etc., at specific ratios to prepare a slurry and then creating a ceramic green sheet using any known method such as the doctor blade method, after which the obtained sheet is layered with the surface electrodes and internal electrode explained later and then binder is removed at 500° C. in atmosphere, followed by integral sintering at, for example, 1000° C. in atmosphere. Note that the method is not limited to the doctor blade method in any way, and it is also possible to use the so-called slurry build method, for example, where a slurry containing material powder of piezoelectric ceramics just like the slurry mentioned above is printed/layered alternately with conductive paste containing internal electrode material, which is then followed by integral sintering in the same manner as explained above.

Next, a favorable embodiment of the above surface electrodes and internal electrode is as follows. To be specific, favorable examples of the above surface electrodes and internal electrode are Ag and Ag—Pd alloy. However, the material is not limited to the foregoing in any way, and any one of Au, Pt, Pd and Au—Pd alloy may be used. The thickness of the above surface electrodes and internal electrode may be 2 μm, for example.

Next a favorable embodiment of the above inter-layer connection conductor is as follows. To be specific, the above inter-layer connection conductor should ideally be a through hole conductor formed in a manner penetrating the aforementioned piezoelectric layer in the thickness direction, or a side electrode printed on the side face of the aforementioned piezoelectric layer.

Next, a favorable embodiment of the above vibration plate is as follows. To be specific, the above vibration plate should ideally be made of a rubber insulating sheet, such as a rubber sheet constituted by polyurethane rubber, silicone rubber, chloroprene rubber, other synthetic rubber, or the like. The thickness of the above vibration plate may be 50 to 150 μm, for example. The above vibration plate should ideally have an adhesive layer applied/formed at least on the side where the above piezoelectric element is adhesively attached.

Next, a favorable embodiment of the above frame is as follows. To be specific, the above frame should ideally be an insulative film made of polybutylene terephthalate (PBT), polyethylene terephthalate (PET), liquid crystal polymer, or the like. The thickness of the above frame may be 150 to 250 μm, for example.

Next, a favorable embodiment of the above terminal is as follows. To be specific, the above terminal should ideally be an insulative substrate made of polyethylene terephthalate (PET), liquid crystal polymer, etc., on which terminal electrodes are formed by means of Cu foil etching, etc. However, the terminal is not limited to the foregoing in any way, and it is also possible to, for example, apply conductive resin paste by means of screen printing, etc., and then curing the paste to form terminal electrodes. The thickness of the above terminal electrode may be 7 to 10 μm, for example.

Next, a favorable embodiment of the above lead conductors is as follows. To be specific, the above lead conductors should ideally be made of a conductive resin layer produced by mixing powder of metal, carbon, etc., with polyester resin, for example, where a favorable production method is applying and then curing conductive resin paste. The thickness of the above lead conductors may be 100 to 150 μm, for example.

Next, a favorable embodiment of the above first cover is as follows. To be specific, the above first cover should ideally be constituted by a second frame and cover plate, for example. As with the above frame, ideally the above second frame should also be an insulative film made of polybutylene terephthalate (PBT), polyethylene terephthalate (PET), liquid crystal polymer, or the like. The thickness of the above second frame may be 188 μm, for example.

Note that the first cover is not limited to the foregoing in any way, and it is also possible to draw or otherwise process an Al or other metal plate, and then use the obtained plate to integrally form the second rim and cover part.

Next, a favorable embodiment of the above second cover is as follows. To be specific, the above second cover should ideally be an insulative film made of polybutylene terephthalate (PBT), polyethylene terephthalate (PET), liquid crystal polymer, etc., or Al or other metal plate. The thickness of the above second cover may be 150 to 250 μm, for example.

Example 1

Next, an example of a piezoelectric sound-generating device conforming to the present invention is explained by referring to FIGS. 3 and 7 according to the second embodiment.

First, a vibration plate 12 of 100 μm in thickness was prepared, wherein such plate was constituted by a rubber sheet having an adhesive layer (not illustrated) formed on the principle side 12B where a piezoelectric element 11 was to be adhesively attached, as well as first openings 13a1, 13b1 and second openings 13a2, 13b2 formed in specified positions. Also, a 188-μm thick sheet made of polyethylene terephthalate (PET), also having an adhesive layer (not illustrated) formed on one principle side beforehand as with the vibration plate 12, was irradiated with a laser beam and cut to a specified shape to obtain a frame 14. Next, the frame 14 was adhesively attached on one principle side 12F of the vibration plate 12, while a second frame 26a was adhesively attached on the other principle side 12B of the vibration plate 12. Next, a piezoelectric element 11 was adhesively attached on the other principle side 12B of the vibration plate 12 in a manner enclosed by the second frame 26. Next, a terminal 15 was adhesively attached on the other principle side 12B of extension parts 12a, 12b of the vibration plate 12. Next, a cover plate 26b was adhesively attached on the second frame 26a. Next, conductive resin paste was applied in a band shape on the one principle side 12F of the vibration plate 12 obtained above, using the screen printing method and covering the area from the first opening 13a1 to the second opening 13a2, while at the same time conductive resin paste was similarly applied in a band shape covering the area from the first opening 13b1 to the second opening 13b2, after which the paste was cured at 150° C. to form lead conductors 18a, 18b constituted by a conductive resin layer. Next, a second cover 27 was adhesively attached on the frame 14 in a manner covering the one principle side 12F of the vibration plate 12 to obtain a piezoelectric sound-generating device 20.

Industrial Field of Application

The present invention is suitable for piezoelectric sound-generating bodies used for small speakers, etc., installed in slim electronic devices, mobile electronic devices, etc.

Claims

1. A piezoelectric sound-generating device of a square shape, said piezoelectric sound-generating device characterized by comprising: a vibration plate having a main square area in which multiple first openings are formed, and multiple extension parts on which second openings are formed and which are projecting from an outer periphery of the main area;a frame having a rim that circularly supports a vicinity of a continuous outer periphery of the main area and extension parts of the vibration plate, adhesively attached on one principle side of the vibration plate;a square bimorph piezoelectric element having multiple surface electrodes formed in positions corresponding to the first openings on the one principle side of the vibration plate, adhesively attached in the main area on the other principle side of the vibration plate;a terminal having an insulative substrate and terminal electrodes formed on one principle side of the substrate, adhesively attached on the other principle side of the extension parts of the vibration plate; andmultiple lead conductors formed on the one principle side of the vibration plate, respectively, from the surface electrodes of the piezoelectric element exposed in the first openings, to the terminal electrodes of the terminal exposed in the second openings.

2. A piezoelectric sound-generating device according to claim 1, characterized by further comprising a first cover on the other principle side of the vibration plate in a manner covering the other principle side of the piezoelectric element while also forming a ventilation hole.

3. A piezoelectric sound-generating device according to claim 1, characterized by further comprising a second cover on the frame in a manner covering the one principle side of the vibration plate while also forming a ventilation hole.

4. A piezoelectric sound-generating device according to claim 1, characterized in that the frame has projections extending from the rim, with edges projecting into an area overlapping with the piezoelectric element across the vibration plate.

5. A piezoelectric sound-generating device according to claim 1, characterized in that the vibration plate is made of a rubber sheet.

6. A piezoelectric sound-generating device according to claim 2, characterized by further comprising a second cover on the frame in a manner covering the one principle side of the vibration plate while also forming a ventilation hole.

7. A piezoelectric sound-generating device according to claim 1, wherein top surfaces of the terminal electrodes are leveled with top surfaces of the surface electrodes, constituting a plane on which the vibration plate is placed.

8. A piezoelectric sound-generating device according to claim 1, wherein the vibration plate has four general peripheral sides, and the extension parts are disposed at one of the peripheral sides.

9. A piezoelectric sound-generating device according to claim 1, wherein the vibration plate has four general peripheral sides, and the extension parts are disposed at two opposite sides of the peripheral sides.