JP2011097137A - Piezoelectric sound generating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain flat frequency characteristics by decreasing variations in sound pressure level of a piezoelectric sound generating device in a low frequency band. <P>SOLUTION: The piezoelectric sound generating device includes: a vibrating membrane composed of resin; a supporter that supports an outer peripheral part of the vibrating membrane; and a center unit that is connected with a center part of the vibrating membrane separated from the supporter and where a piezoelectric element and reinforced membrane are laminated. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a piezoelectric sounding device.

  2. Description of the Related Art Conventionally, a piezoelectric sounding device that generates sound by vibrating a piezoelectric element integrated with a vibrating membrane is known. Patent Documents 1 and 3 disclose a technique for forming a vibration film with a resin film. When a piezoelectric sound generator is configured by connecting a piezoelectric element to the center of a vibration film made of resin, resonance in a low frequency band is obtained in a plurality of low-order modes including the lowest-order mode. Pressure level increases. Patent Documents 2 and 3 disclose techniques for forming a diaphragm in a rectangular shape in order to obtain flat frequency characteristics. Patent Document 4 discloses a technique in which the vibration film is made of silicon.

JP 2002-112391 A JP 2003-219499 A Japanese Patent No. 4203911 Japanese Patent No. 3945292

In order to obtain a flat frequency characteristic, it is necessary to suppress a drop in sound pressure between resonance frequencies to reduce variations in sound pressure level.
An object of the present invention is to obtain flat frequency characteristics by reducing variations in sound pressure level of a piezoelectric sounding device in a low frequency band.

  (1) A piezoelectric sounding element for achieving the above object is coupled to a vibration film made of resin, a support part supporting an outer peripheral part of the vibration film, and a central part of the vibration film separated from the support part And a center unit in which the piezoelectric element and the reinforcing film are laminated.

  In the lowest order mode in which one antinode appears in the entire diaphragm unit and the center unit coupled to the center part thereof, the Young's modulus of the diaphragm made of resin is a dominant factor for determining the resonance frequency. In the next low-order mode, two antinodes appear in the diaphragm and one antinode in the center unit, and the Young's modulus of the center unit has a greater influence on the resonance frequency than in the lowest-order mode. Since the resonance frequency increases as the Young's modulus increases, the difference between the resonance frequency of the lowest order mode and the resonance frequency of the next lower order mode increases as the difference between the Young's modulus of the center unit and the Young's modulus of the diaphragm increases. Becomes larger. According to the present invention, since the piezoelectric element and the reinforcing film are laminated in the center unit coupled to the central portion of the vibration film made of resin, the resonance of the lowest order mode compared to the case where the center unit is made of only the piezoelectric element. The difference between the frequency and the resonance frequency of the next lower-order mode increases. Therefore, according to the present invention, the frequency at which the amplitude drops most between the lowest-order mode and the next lower-order mode is higher than that in the case where the center unit is composed only of piezoelectric elements. Since the sound pressure is proportional to the square of the frequency and proportional to the amplitude, the drop in the sound pressure level due to the drop in amplitude becomes smaller as the frequency at which the amplitude falls becomes higher. Further, when the vibration film is made of resin, the resonance frequency of the lowest order mode is lowered, so that the sound pressure level in the low frequency band can be increased. On the other hand, as the resonance frequency of the lowest order mode becomes lower, the drop in sound pressure level due to the drop in amplitude in the band up to the next lower order mode becomes more prominent. However, according to the present invention, the difference between the resonance frequency of the lowest-order mode and the resonance frequency of the next lower-order mode becomes large, so the amplitude increases in the band from the resonance frequency of the lowest-order mode to the resonance frequency of the next lower-order mode. The frequency that falls most becomes high, and the variation in the sound pressure level can be reduced in a low frequency band.

(2) In the piezoelectric sounding element for achieving the above object, the reinforcing film preferably has a Young's modulus greater than that of the vibrating film.
According to the present invention, flatter frequency characteristics can be obtained as compared with the case where the Young's modulus of the reinforcing membrane is smaller than that of the vibrating membrane.

(3) In the piezoelectric sounding element for achieving the above object, the reinforcing film may have a Young's modulus larger than that of the piezoelectric element.
According to the present invention, a flatter frequency characteristic can be obtained as compared with the case where the Young's modulus of the reinforcing film is smaller than that of the piezoelectric element.

(4) In the piezoelectric sounding element for achieving the above object, the reinforcing film preferably has a density lower than that of the piezoelectric element.
The resonance frequency increases as the density of the object decreases. Then, the influence of the vibration characteristics of the center unit on the resonance frequency is greater in the lower order mode than in the lowest order mode. Therefore, according to the present invention, a flatter frequency characteristic can be obtained as compared with the case where the density of the reinforcing film is larger than that of the piezoelectric element.

1A is a cross-sectional view according to the first embodiment of the present invention, and is a cross-sectional view taken along line 1A-1A shown in FIG. 1B. FIG. 1B is a plan view according to the first embodiment of the present invention. It is a line graph concerning a first embodiment of the present invention. It is a line graph concerning a comparative example. It is sectional drawing concerning 1st embodiment of this invention. It is sectional drawing concerning 1st embodiment of this invention. It is sectional drawing concerning 1st embodiment of this invention. It is sectional drawing concerning 1st embodiment of this invention. It is sectional drawing concerning 1st embodiment of this invention. It is sectional drawing concerning 1st embodiment of this invention. It is sectional drawing concerning 1st embodiment of this invention. It is sectional drawing concerning 1st embodiment of this invention. It is a top view concerning a first embodiment of the present invention. It is sectional drawing concerning 2nd embodiment of this invention. It is sectional drawing concerning 2nd embodiment of this invention. It is sectional drawing concerning 2nd embodiment of this invention. It is sectional drawing concerning 2nd embodiment of this invention. It is sectional drawing concerning 2nd embodiment of this invention. It is sectional drawing concerning 2nd embodiment of this invention. It is sectional drawing concerning 3rd embodiment of this invention. It is sectional drawing concerning 3rd embodiment of this invention. It is sectional drawing concerning 3rd embodiment of this invention. It is sectional drawing concerning 3rd embodiment of this invention. It is sectional drawing concerning 3rd embodiment of this invention. It is sectional drawing concerning 3rd embodiment of this invention. It is sectional drawing concerning 3rd embodiment of this invention. It is sectional drawing concerning 4th embodiment of this invention. It is sectional drawing concerning 4th embodiment of this invention. It is sectional drawing concerning 4th embodiment of this invention. It is sectional drawing concerning 4th embodiment of this invention. It is sectional drawing concerning 4th embodiment of this invention. It is sectional drawing concerning 4th embodiment of this invention. It is sectional drawing concerning 5th embodiment of this invention. It is sectional drawing concerning 5th embodiment of this invention. It is sectional drawing concerning 5th embodiment of this invention. It is sectional drawing concerning 5th embodiment of this invention. It is sectional drawing concerning 5th embodiment of this invention. It is sectional drawing concerning 5th embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in the following order with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the corresponding component in each figure, and the overlapping description is abbreviate | omitted.

1. First embodiment (Configuration)
FIG. 1 shows a piezoelectric sounding device 1 according to a first embodiment of the present invention. The piezoelectric sounding device 1 is a micro device manufactured using a semiconductor manufacturing process, and is housed in a case (not shown) and used as a speaker of a portable electronic device. For this reason, the piezoelectric sounding device 1 is configured to be thinner than a dynamic speaker. The piezoelectric sounding device 1 includes a support portion 10, a vibration film 12, and a center unit 15.

  The support 10 has a rectangular frame shape as shown in FIG. 1B. The support portion 10 is made of a bulk material such as single crystal silicon or glass, and has sufficient rigidity so as not to be deformed when the vibration film 12 vibrates.

  The vibration film 12 is a rectangular thin film made of resin. The outer peripheral portion of the vibration film 12 is annularly coupled to the support portion 10. That is, the vibration film 12 is supported at the outer peripheral portion by the support portion 10 and is stretched inside the support portion 10. Therefore, the vibration end of the vibration film 12 is rectangular. The vibration film 12 is made of a resin such as polyimide, PVDF (PolyVinylidene DiFluoride), or rubber having a thickness of 0.5 μm to 100 μm, and has a Young's modulus set to 0.01 GPa or more and 5 GPa or less.

The center unit 15 is a driving element that vibrates the vibrating membrane 12, has a rectangular plate or membrane shape, and is coupled to a central portion of the vibrating membrane 12 that is separated from the support portion 10. The center unit 15 includes a reinforcing film 14 and a piezoelectric element 16 laminated in the thickness direction, and is coupled to the vibration film 12 in the reinforcing film 14. The piezoelectric element 16 has a structure in which a piezoelectric layer such as lead zirconate titanate (PZT) is sandwiched between two layers (not shown), and is bonded to the reinforcing film 14 in the lower layer electrode. The thickness of the piezoelectric layer is set to about 3 μm, for example. The reinforcing film 14 has a rectangular plate shape and is coupled to the lower electrode of the piezoelectric element 16 and the vibration film 12. The reinforcing film 14 is preferably configured to be hard and light. Specifically, for example, the thickness of 1μm or 100μm or less, the Young's modulus in 300GPa the range above 50 GPa, single crystal silicon, silicon oxide, polycrystalline silicon, ceramic (zirconia _(ZrO 2), alumina _(Al 2 _{O 3} And the like, and a reinforcing film 14 is formed from a metal (such as Cu). The reinforcing film 14 preferably has a higher Young's modulus than the piezoelectric element 16 and a density lower than that of the piezoelectric element 16 than the vibrating film 12. In addition, since the ceramic material has high heat resistance, it becomes easier to handle the material of the reinforcing film 14 when manufactured.

  The piezoelectric sounding device 1 configured as described above operates as follows. When a drive signal is applied to the piezoelectric element 16 via a lead wire (not shown), the piezoelectric element 16 contracts or expands in an in-plane direction (a direction parallel to the paper surface in FIG. 1B). As a result, the reinforcing film 14 and the vibration film 12 are bent together with the piezoelectric element 16, and sound is generated.

FIG. 2 is a line graph showing the frequency characteristics of the piezoelectric sounding device 1, with the horizontal axis representing frequency and the vertical axis representing sound pressure level. The lowest order resonance frequency is _denoted by f ₀ , the next lower order resonance frequency is _denoted by f ₁ , and the frequency at which the sound pressure level falls most between f ₀ and f ₁ is _denoted by f ₀₁ . The dimensions of the piezoelectric sounding device 1 showing the characteristics of the polygonal lines (1), (2), and (3) were set as shown in Table 1 below.

FIG. 3 is a line graph showing the frequency characteristics of the piezoelectric sound producing device in the example in which the reinforcing film is laminated in the center unit 15 and the comparative example in which the reinforcing film is not laminated. The sound pressure level is taken on the axis. The dimensions of the piezoelectric sounding device showing the characteristics of the broken lines (4) and (5) were set as shown in Table 2 below. For items not listed in Table 2, the piezoelectric sounding device 1 showing the characteristics of the polygonal lines (1), (2), and (3) and the characteristics of the polygonal lines (4) and (5) were shown. Other forms, dimensions, drive voltages, and the like of the piezoelectric sounding device are matched.

Polygonal line (1), (2), (3) Comparing the properties of the difference d between the lowest-order resonance frequency f ₀ and the next lower order resonance frequency f ₁ as the reinforcing layer 14 becomes thicker that increases Recognize. As a result, the frequency f ₀₁ at which the sound pressure level falls most between f ₀ and f ₁ when the lowest-order resonance frequency is almost the same as in the characteristics of the broken line (1) and the broken line (3). The thicker the reinforcing film 14, the higher it becomes. Further, comparing the characteristics of the broken lines (4) and (5), it can be seen that the frequency f ₀₁ is increased by adding the reinforcing film. From these facts, it can be seen that the addition of the reinforcing film 14 to the center unit 15 suppresses the drop in the sound pressure level between f ₀ and f ₁ .

The drop in the sound pressure level becomes more noticeable as the frequency is lower. Therefore, if the drop in the sound pressure level between f ₀ and f ₁ is suppressed, the drop in the sound pressure level at a higher frequency tends to be suppressed. That is, if the drop in the sound pressure level between f ₀ and f ₁ is suppressed, the variation in the sound pressure level can be reduced as a whole, and a flat frequency characteristic can be obtained.

  Further, since the forms of the piezoelectric element 16 and the reinforcing film 14 having different material characteristics can be designed separately, the degree of freedom in design is high and the frequency characteristics can be optimized as compared with the case where the center unit 15 is composed of only the piezoelectric elements 16. . Further, by using single crystal silicon or the like having a density smaller than that of the piezoelectric element 16 and a large Young's modulus as the material of the reinforcing film 14, the Young's modulus of the center unit 15 as a whole is increased while suppressing the strength burden of the center unit 15 on the vibration film 12. can do.

(Production method)
Next, a method for manufacturing the piezoelectric sounding device 1 described above will be described with reference to FIGS.
First, as shown in FIG. 4, a platinum layer 110 serving as a lower layer electrode, a piezoelectric layer 111, and a platinum layer 112 serving as an upper layer electrode are sequentially stacked on the surface of a wafer 100 made of single crystal silicon using a sputtering method or the like.

  Next, as shown in FIG. 5, the piezoelectric element 16 including the platinum layer 110, the piezoelectric layer 111, and the platinum layer 112 is formed by etching using a protective film.

  Next, as shown in FIG. 6, the wafer 100 is thinly processed to the thickness of the reinforcing film 14 by grinding, polishing, wet etching or RIE.

  Next, as shown in FIG. 7, the wafer 100 is divided by dicing to obtain the center unit 15.

  On the other hand, a supporting portion 10 produced by processing a single crystal silicon or glass wafer is prepared separately, and a vibrating membrane 12 is bonded to the supporting portion 10 as shown in FIG. At this time, for example, the vibration film 12 and the support portion 10 are joined by thermocompression bonding a dry film to be the vibration membrane 12 to the support portion 10.

  Then, as shown in FIG. 9, when the center unit 15 is bonded to the surface of the central portion of the vibration film 12, the piezoelectric sounding device 1 shown in FIG. 1 is completed. At this time, since the center unit 15 is not a single piezoelectric element 16, the center unit 15 is easy to handle.

(Modification)
The vibration ends of the vibration film 12 and the center unit 15 may be circular. In the center unit 15, the reinforcing film 14 may protrude outward from the piezoelectric element 16, or the piezoelectric element 16 may protrude outward from the reinforcing film 14.
Further, as in the piezoelectric sounding device 2 shown in FIG. 10, the center unit 15 may be configured by laminating monomorph piezoelectric elements 16 a, 16 b, 16 c and the reinforcing film 14.
Moreover, like the piezoelectric sounding device 3 shown in FIG. 11, the piezoelectric elements 16a and 16b driven in opposite phases may be coupled to both the front and back sides of the reinforcing film 14, and the center unit 15 may be driven in a bimorph type. Further, as in the piezoelectric sound producing device 3 shown in FIG. 11, an opening may be formed at the center of the vibration film 12, and the center unit 15 may be coupled to the vibration film 12 so as to close the opening.
Further, like the piezoelectric sounding device 4 shown in FIG. 12, the four sides of the center unit 15 and the support portion 10 may be independently connected to each other by four vibration films 12a, 12b, 12c, and 12d.

2. Second Embodiment As shown in FIGS. 13 to 18, the piezoelectric sounding device 5 may be manufactured. The manufacturing method of the piezoelectric sounding device 5 is as follows.
First, as shown in FIG. 13, a platinum layer 110, a piezoelectric layer 111, and a platinum layer 112 are formed on the surface of an SOI (Silicon On Insulator) wafer in which a thick single crystal silicon layer 101, a silicon oxide layer 102, and a thin single crystal silicon layer 103 are stacked. Are stacked using a sputtering method or the like.

  Next, by patterning the platinum layer 110, the piezoelectric layer 111, the platinum layer 112, and the single crystal silicon layer 103 by etching using a protective film, a single crystal is formed together with a recess 110a corresponding to the vibration film 12 as shown in FIG. A reinforcing film 14 made of the silicon layer 103 and the piezoelectric element 16 are formed.

  Next, as shown in FIG. 15, a resin layer R to be the vibration film 12 is formed, and the recess 110 a is filled with the resin layer R. At this time, the resin layer R is formed by spin coating, vapor deposition polymerization, CVD (Chemical Vapor Deposition), spray coating, thermocompression bonding of a dry film, printing, bonding of various resin films or rubber films. The resin layer R may be left only in the recess 110a by photolithography, or may be formed so as to overlap the center unit 15. When the resin layer R overlapping the center unit 15 is left, the Q value can be lowered.

  Next, after forming through holes in the resin layer R, the platinum layer 112, and the piezoelectric layer 111, conductive wires 17 and 18 made of a conductive layer 114 are formed by sputtering or the like as shown in FIG. A resin-based composite material having excellent flexibility can be used for the conductive wires 17 and 18.

Next, as shown in FIG. 17, through-holes 100 a are formed in the single crystal silicon layer 101 and the silicon oxide layer 102 by Deep-RIE (Reactive Ion Etching), wet etching, or the like from the back surface of the SOI wafer. The inner peripheral surface is formed and the vibration end of the vibration film 12 is determined.
Further, when a post-process such as dicing is performed, the piezoelectric sounding device 5 shown in FIG. 18 is completed. According to this manufacturing method, an alignment error does not occur in the joining process, so that variations in characteristics of the piezoelectric sounding device 5 can be reduced.

3. Third Embodiment The piezoelectric sounding device 6 may be manufactured as shown in FIGS. The manufacturing method of the piezoelectric sounding device 6 is as follows.
First, as shown in FIG. 19, a platinum layer 110, a piezoelectric layer 111, and a platinum layer 112 are laminated on the surface of a wafer 120 made of single crystal silicon by sputtering or the like.
Next, as in the second embodiment, the piezoelectric element 16 and the recess 120a are formed as shown in FIG.
Next, as in the second embodiment, the vibrating membrane 12 and the conducting wires 17 and 18 are formed as shown in FIGS.
Next, as shown in FIG. 23, the wafer 120 is thinly processed to the thickness of the reinforcing film 14 by grinding, polishing, wet etching, or RIE while the back surface of the wafer 120 is temporarily bonded to the shape holding member 190. As a result, a reinforcing film 14 made of single crystal silicon is formed.
Next, as shown in FIG. 24, the wafer 120 held by the shape holding member 190 and diced is bonded to the support 10 manufactured in advance by a wafer direct bonding method, an anodic bonding method, or the like.
When the shape holding member 190 is further separated and the subsequent process is performed, the piezoelectric sounding device 6 shown in FIG. 25 is completed.

4). Fourth Embodiment The piezoelectric sounding device 7 may be manufactured as shown in FIGS. The manufacturing method of the piezoelectric sounding device 7 is as follows.
First, as shown in FIG. 26, a reinforcing layer 130 made of silicon oxide, polycrystalline silicon, metal, ceramics or the like is formed on the surface of a wafer 100 made of single crystal silicon by a CVD method or the like. Subsequently, a platinum layer 110, a piezoelectric layer 111, and a platinum layer 112 are laminated on the surface of the reinforcing layer 130 as in the second embodiment.
Next, as in the second embodiment, the recess 130a is formed as shown in FIG. 27, the vibrating membrane 12 is formed as shown in FIG. 28, and the conducting wires 17 and 18 are formed as shown in FIG.
Next, as shown in FIG. 30, the through hole 100 a is formed in the wafer 100 by Deep-RIE, wet etching, or the like from the back surface of the wafer 100 to form the inner peripheral surface of the support portion 10 and the vibration end of the vibration film 12. To confirm. In order to avoid the vibration film 12 made of resin from being etched in this step, a thin silicon oxide film is formed on the bottom surface of the recess 130a using a sputtering method or the like after the recess 130a is formed in the process of FIG. Also good.
When a post-process such as dicing is further performed, the piezoelectric sounding device 7 shown in FIG. 31 is completed. By manufacturing in this way, the reinforcing film 14 of the piezoelectric sounding device 7 can be made of silicon oxide, polycrystalline silicon, metal, ceramics, or the like.

5. Fifth Embodiment A piezoelectric sounding device 8 may be manufactured as shown in FIGS. The manufacturing method of the piezoelectric sounding device 8 is as follows.
First, similarly to the first embodiment, a platinum layer 110, a piezoelectric layer 111, and a platinum layer 112 are laminated on the surface of a wafer 100 made of single crystal silicon, and the reinforcing film 14 and the surface of the platinum layer 112 are formed as shown in FIG. The resulting metal layer 140 is formed by CVD, sputtering, or the like.
Next, as shown in FIG. 33, etching is performed to form a recess 140a in the metal layer 140, and the reinforcing film 14 made of the piezoelectric element 16 and the metal layer 140 is formed.
Next, as shown in FIG. 34, the vibration film 12 is formed as in the second embodiment.
Next, as shown in FIG. 35, after forming through holes in the metal layer 140, the platinum layer 112, and the piezoelectric layer 111, conductive wires 17 and 18 made of the conductive layer 114 are formed by sputtering or the like.
Next, as shown in FIG. 36, as in the fourth embodiment, by forming a through hole 100a in the wafer 100, the inner peripheral surface of the support portion 10 is formed and the vibration end of the vibration film 12 is determined.
When further post-processes such as dicing are performed, the piezoelectric sounding device 8 shown in FIG. 37 is completed. By manufacturing in this way, the reinforcing film 14 is laminated on the piezoelectric element 16. In this case, the center unit 15 is coupled to the vibration film 12 in the piezoelectric element 16.

6). Other Embodiments The technical scope of the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the scope of the present invention. For example, the materials, dimensions, shapes, film formation methods, and pattern transfer methods shown in the above embodiment are merely examples, and descriptions of addition and deletion of processes and replacement of process order that are obvious to those skilled in the art are omitted. Has been.

1: Piezoelectric sound generating device, 2: Piezoelectric sound generating device, 3: Piezoelectric sound generating device, 4: Piezoelectric sound generating device, 5: Piezoelectric sound generating device, 6: Piezoelectric sound generating device, 7: Piezoelectric sound generating device, 8 : Piezoelectric sound generating device, 10: support part, 12: vibration film, 12a: vibration film, 12b: vibration film, 12c: vibration film, 12d: vibration film, 14: reinforcement film, 15: center unit, 16: piezoelectric element 16a, 16b, 16c: piezoelectric element, 17: conducting wire, 18: conducting wire, 100: wafer, 100a: through hole, 101: single crystal silicon layer, 102: silicon oxide layer, 103: single crystal silicon layer, 110: platinum 110a: recess, 111: piezoelectric layer, 112: platinum layer, 114: conductive layer, 120: wafer, 120a: recess, 130: reinforcing layer, 130a: recess, 140: metal layer, 140a: recess, 190: shape Holding member, R: Tree Layer

Claims (4)

A vibrating membrane made of resin;
A support portion for supporting an outer peripheral portion of the vibration membrane;
A center unit that is coupled to the central portion of the vibration film away from the support part, and in which a piezoelectric element and a reinforcing film are laminated,
A piezoelectric sounding device. The reinforcing membrane has a Young's modulus greater than that of the vibrating membrane,
The piezoelectric sounding device according to claim 1. The reinforcing film has a larger Young's modulus than the piezoelectric element,
The piezoelectric sounding device according to claim 1 or 2. The reinforcing film has a lower density than the piezoelectric element,
The piezoelectric sounding device according to any one of claims 1 to 3.

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