Piezoelectric speaker

Abstract

A piezoelectric speaker is provided that optimizes the stress of each layer during displacement, increases the displacement of an additional film layer, and effectively improves the sound pressure level. [Solution] The piezoelectric speaker includes a substrate (10) through which a back cavity (11) is formed, a support unit (20) provided on the substrate and covering the back cavity, a piezoelectric unit (30) provided on the support unit, and an additional film layer (40) provided on the piezoelectric unit. A first slit (23) is formed through the support unit, dividing the support unit into a first support portion (201) and a second support portion (202) located around the periphery of the first support portion. In the vibration direction of the piezoelectric speaker, the first support portion protrudes further toward the back cavity than the second support portion. A second slit (34) is formed through a portion of the piezoelectric unit, and the first piezoelectric portion (301) is supported by the first support portion and protrudes further toward the back cavity than the second piezoelectric portion in the vibration direction, and the second piezoelectric portion (302) is located around the periphery of the first piezoelectric portion and supported by the second support portion.

Description

[Technical Field]

[0001] The present invention relates to the technical field of speakers, and in particular to piezoelectric speakers. [Background technology]

[0002] In silicon-based microelectromechanical speakers, the use of an organic film on the diaphragm can prevent air leakage, improve sound pressure level (SPL), and reduce total harmonic distortion (THD). However, the displacement of the speaker's diaphragm is limited by the organic film, which limits the achievable sound pressure level. Summary of the Invention [Problem to be solved by the invention]

[0003] The present invention aims to provide a piezoelectric speaker that solves the technical problems in the prior art. [Means for solving the problem]

[0004] The present invention provides a piezoelectric speaker, the piezoelectric speaker including a substrate, a support unit, a piezoelectric unit, and an additional film layer, a back cavity penetrating the substrate, the support unit being provided on the substrate and covering the back cavity, a first slit penetrating a part of the support unit to divide the support unit into a first support part and a second support part, the second support part being located in a circumferential direction of the first support part, the first support part protruding further toward the back cavity than the second support part in a vibration direction of the piezoelectric speaker, and the pressure a piezoelectric unit provided on the support unit, a second slit formed through a portion of the piezoelectric unit to divide the piezoelectric unit into a first piezoelectric portion and a second piezoelectric portion, the second piezoelectric portion being located in the outer circumferential direction of the first piezoelectric portion, the first piezoelectric portion being supported on the first support portion, and the second piezoelectric portion being supported on the second support portion, the first piezoelectric portion protruding further toward the back cavity than the second piezoelectric portion in the vibration direction of the piezoelectric speaker, and the additional film layer being provided on the piezoelectric unit and also formed at a position corresponding to the second slit.

[0005] In the piezoelectric speaker as described above, a stress adjustment layer is provided between the piezoelectric unit and the additional film layer, and the stress adjustment layer covers the surfaces of the first piezoelectric portion and the second piezoelectric portion.

[0006] In the piezoelectric speaker as described above, preferably, a portion of the additional film layer fills the second slit.

[0007] In the above-described piezoelectric speaker, preferably, the first slit is not filled with the additional film layer.

[0008] In the piezoelectric speaker as described above, preferably, the second support portion includes a plurality of sub-support portions that surround the first support portion and are spaced apart from one another by first partition grooves, the second piezoelectric portion includes a plurality of sub-piezoelectric portions that surround the first piezoelectric portion and are spaced apart from one another by second partition grooves, the sub-piezoelectric portions are arranged in one-to-one correspondence with the sub-support portions, the first slits are connected to the second slits, and the additional film layer covers only the spaces between the plurality of sub-piezoelectric portions and the second slits.

[0009] In the piezoelectric speaker as described above, preferably, the plurality of sub-support portions and the first support portion are connected by a first elastic beam, and the first elastic beam is provided within the first slit, and the plurality of sub-piezoelectric portions and the first piezoelectric portion are connected by a second elastic beam, and the second elastic beam is provided within the second slit.

[0010] In the piezoelectric speaker as described above, the piezoelectric unit preferably includes a first electrode layer, a piezoelectric layer, and a second electrode layer stacked in this order on the support unit along the vibration direction of the piezoelectric speaker. In the above-described piezoelectric speaker, preferably, the piezoelectric speaker has a first opening and a second opening, the first opening passes through the additional film layer, the second electrode layer, and the piezoelectric layer in this order, and a first metal pad is stacked on the first electrode layer located in the first opening; The second opening penetrates the additional film layer, and a second metal pad is laminated on the second electrode layer located in the second opening.

[0011] In the above-described piezoelectric speaker, the Young's modulus of the additional film layer is preferably 2 GPa or less. In the piezoelectric speaker as described above, the additional film layer is preferably an elastomer.

[0012] In the piezoelectric speaker as described above, preferably, the substrate includes a first silicon layer and a first oxide layer stacked in order along the vibration direction of the piezoelectric speaker, the support unit includes a second silicon layer and a second oxide layer stacked in order on the first oxide layer along the vibration direction of the piezoelectric speaker, the back cavity passes through the first silicon layer and the first oxide layer in order, at least a portion of the second silicon layer is exposed through the back cavity, and the piezoelectric unit is provided on the second oxide layer.

[0013] In the piezoelectric speaker as described above, the additional film layer is preferably added by a dry film roll press method, a spin coating method, a spray method, an inkjet method, a vapor deposition method, or the like, and is shaped by an etching method, a molding method, a laser processing method, or the like. [Effects of the Invention]

[0014] Compared to the prior art, the present invention adjusts the stress of the support unit, piezoelectric unit, additional film layer, or stress adjustment layer to bend the piezoelectric unit downward (toward the back cavity) in the initial state. This optimizes the stress of each layer during displacement, increases the displacement of the additional film layer 40, and effectively improves the SPL. By providing a stress adjustment layer between the piezoelectric unit and the additional film layer, the support unit and piezoelectric unit can also bend downward in the initial state. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view of a piezoelectric speaker according to an embodiment of the present invention. [Figure 2] 1 is a schematic exploded view of a piezoelectric speaker according to an embodiment of the present invention; [Figure 3] 1 is a schematic plan view of a support unit according to an embodiment of the present invention; [Figure 4] 1 is a schematic plan view of a piezoelectric unit according to an embodiment of the present invention; [Figure 5]FIG. 2 is a schematic plan view of the structure of an additional film layer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following description will be given with reference to the drawings. The examples are illustrative and are for the purpose of explaining the present invention only, and should not be construed as limitations on the present invention.

[0017] As shown in FIGS. 1 to 5, an embodiment of the present invention provides a piezoelectric speaker. The piezoelectric speaker includes a substrate 10, a support unit 20, a piezoelectric unit 30, an additional film layer 40, and a stress adjustment layer 50. The substrate 10 includes a first silicon layer 12 and a first oxide layer 13 stacked in order along the vibration direction of the piezoelectric speaker. For example, as shown in FIG. 1, the first silicon layer 12 and the first oxide layer 13 are stacked in order from bottom to top. A back cavity 11 is formed in the substrate 10, and preferably, the inner contour surface of the back cavity 11 has a circular groove structure. The back cavity 11 penetrates the first silicon layer 12 and the first oxide layer 13 in order. In a possible embodiment, the first oxide layer 13 made of SiO2 is formed on the first silicon layer 12 made of silicon by a method such as evaporation, thermal oxidation, or chemical vapor deposition (CVD).

[0018] The support unit 20 is provided on the substrate 10 and covers the back cavity 11. The support unit 20 includes a second silicon layer 21 and a second oxide layer 22 stacked in order along the vibration direction of the piezoelectric speaker. For example, as shown in FIG. 1, the second silicon layer 21 and the second oxide layer 22 are stacked in order from bottom to top. At least a portion of the second silicon layer 21 is exposed to the back cavity 11. The piezoelectric unit 30 is formed on the second oxide layer 22. The second silicon layer 21 is formed on the first oxide layer 13 by, for example, bonding a silicon wafer onto the first oxide layer 13. The second oxide layer 22 can be formed by growing at least one second oxide layer 22 on the surface of the second silicon layer 21 by thermal oxidation, vapor deposition, or CVD. The material of the second silicon layer 21 may be the same as that of the first silicon layer 12. The first oxide layer 13 is located below the second silicon layer 21 and has a significantly lower etching rate than the second silicon layer 21, ensuring that when etching to form the slit or back cavity 11, the etching stops exactly at the boundary between the first oxide layer 13 and the second silicon layer 21.

[0019] The piezoelectric unit 30 is formed on the support unit 20. The piezoelectric unit 30 includes a first electrode layer 31, a piezoelectric layer 32, and a second electrode layer 33, which are stacked in this order along the vibration direction of the piezoelectric speaker. For example, as shown in FIG. 1, the first electrode layer 31, the piezoelectric layer 32, and the second electrode layer 33 are stacked in this order from bottom to top. Here, the first electrode layer 31 is formed on the second oxide layer 22 by physical vapor deposition (PVD) (electron beam evaporation or magnetron sputtering). The first electrode layer 31 is patterned using a photolithography process. The first electrode layer 31 is connected to a bottom electrode pad (not shown) via a bottom electrode lead (not shown). The material of the first electrode layer 31 may be one or more of Al, Mo, W, Pt, Cu, Ag, Au, ZrN, or other materials with good electrical conductivity. In a possible embodiment, the material of the first electrode layer 31 is platinum (Pt) and molybdenum (Mo).

[0020] The piezoelectric layer 32 is deposited on the first electrode layer 31. The piezoelectric layer 32 vibrates mechanically when an AC electric field is applied. The material of the piezoelectric layer 32 may be lead zirconate titanate, aluminum nitride, barium titanate or any other piezoelectric material. In a possible embodiment, the material of the piezoelectric layer 32 is lead zirconate titanate (PZT).

[0021] The second electrode layer 33 is formed on the piezoelectric layer 32 by PVD (e.g., electron beam evaporation or magnetron sputtering). The second electrode layer 33 is patterned using a photolithography process. The second electrode layer 33 is connected to an upper electrode pad (not shown) via an upper electrode lead (not shown). The material of the second electrode layer 33 may be one or more of Al, Mo, W, Pt, Cu, Ag, Au, ZrN, or other materials with good electrical conductivity. In a possible embodiment, the material of the second electrode layer 33 is platinum (Pt) or molybdenum (Mo).

[0022] The additional film layer 40 is provided on the piezoelectric unit 30 and on the side surface between the first piezoelectric portion 301 and the second piezoelectric portion 302 that form the piezoelectric unit 30. The additional film layer 40 functions as a vibration plate (diaphragm). The stress adjustment layer 50 is provided between the piezoelectric unit 30 and the additional film layer 40, and covers the surfaces of the first piezoelectric portion 301 and the second piezoelectric portion 302. The stress adjustment layer 50 also functions as a passivation layer. The stress adjustment layer 50 generates compressive stress and is made of, for example, SiN, Al2O3, or TiO2.

[0023] A through hole is provided in the substrate 10 to form a cavity 11 . First slits 23 are formed through the support unit 20, leaving behind a plurality of first elastic beams 2022 (described later), dividing the support unit 20 into a first support portion 201 and a second support portion 202 via the plurality of first elastic beams 2022. The first support portion 201 is located in the center of the support unit 20, and the second support portion 202 is located in the outer circumferential direction of the first support portion 201. The first support portion 201 and the second support portion 202 are initially located on different planes due to the effects of the additional film layer 40 and the stress adjustment layer 50. Therefore, the first support portion 201 is positioned so as to protrude into the back cavity 11 in the vibration direction of the piezoelectric speaker.

[0024] Second slits 34 are formed through the piezoelectric unit 30, leaving behind a plurality of first elastic beams 3022 (described later), dividing the piezoelectric unit 30 into a first piezoelectric portion 301 and a second piezoelectric portion 302 via the plurality of first elastic beams 3022. The first piezoelectric portion 301 is located at the center of the piezoelectric unit 30, and the second piezoelectric portion 302 is located on the outer periphery of the first piezoelectric portion 301. The first piezoelectric portion 301 is supported on the first support portion 201, and the second piezoelectric portion 302 is supported on the second support portion 202. The first piezoelectric portion 301 and the second piezoelectric portion 302 are initially located on different planes due to the effects of the additional film layer 40 and the stress adjustment layer 50. Therefore, in the vibration direction of the piezoelectric speaker, the first piezoelectric portion 301 protrudes toward the back cavity 11 together with the first support portion 201. The presence of the second slits 34 makes it possible to adjust the overall rigidity of the piezoelectric unit 30, thereby improving the maximum sound pressure output and frequency characteristics of the speaker.

[0025] The additional film layer 40 has a bent portion 43 formed at a position corresponding to the second slit 34 by the action of the additional film layer 40 of the first support portion 201 and the first piezoelectric portion 301, and the stress adjustment layer 50, and the bent portion 43 has a first end on the inside and a second end on the outside, and in the vibration direction of the piezoelectric speaker, the first end of the bent portion 43 protrudes further toward the back cavity 11 than the second end of the bent portion 43, and the portion of the additional film layer 40 connected to the first end of the bent portion 43 is located above the first piezoelectric portion 301, and the portion of the additional film layer 40 connected to the second end of the bent portion 43 is located above the second piezoelectric portion 302. The bent portion 43 effectively covers the gap between the first support portion 201 and the first piezoelectric portion 301 and the second support portion 202 and the second piezoelectric portion 302, preventing air leakage during vibration and effectively improving the SPL.

[0026] By providing one stress adjustment layer 50 between the piezoelectric unit 30 and the additional film layer 40, the additional film layer 40 can be made convex downward, dramatically improving the SPL. Furthermore, since the first piezoelectric portion 301 and the first support portion 201 are both initially configured to be concave downward relative to the second piezoelectric portion 302 and the second support portion 202, when an electric field is applied to the piezoelectric film 32, the piezoelectric film 32 is distorted in the tensile direction, causing the support unit 20, the piezoelectric unit 30, and the additional film layer 40 to bend upward, thereby increasing the movement (displacement) of the additional film layer 40 and effectively improving the SPL. In the present invention, the stress adjustment layer 50 is provided to achieve a downward convex shape in conjunction with the action of the additional film layer 40. However, if the additional film layer 40 can be made convex downward by adjusting the additional film layer 40, the stress adjustment layer 50 need not be provided.

[0027] In the embodiment of the present invention, a portion of the additional film layer 40 is filled in the second slits 34, and is not filled in the first slits 23. The additional film layer 40 is partially filled in the second slits 34, which reduces sound pressure loss caused by air leakage through the second slits 34 and increases the adhesive strength of the additional film layer 40. Furthermore, since the first slits 23 are not filled, restrictions on the movement of the first support portion 201 and the first piezoelectric portion 301 are reduced.

[0028] 3 and 4, the second support portion 202 includes a plurality of sub-support portions 2021 that surround the first support portion 201 and are spaced apart from each other by first partition grooves 24 that extend from the first support portion 201 to near the ends of the second support portion 202. The second support portion 202 is spaced apart from the first support portion 201 by first elastic beams 2022 that are provided between the sub-support portions 2021, thereby improving the maximum sound pressure output and frequency characteristics of the speaker.

[0029] The second piezoelectric portion 302 includes a plurality of sub-piezoelectric portions 3021 that surround the first piezoelectric portion 301 and are spaced apart from each other by second partition grooves 35 that extend from the first piezoelectric portion 301 to near the ends of the second piezoelectric portion 302. The second piezoelectric portion 302 is spaced apart from the first piezoelectric portion 301 by second elastic beams 3022 that are provided between the sub-piezoelectric portions 3021, thereby improving the maximum sound pressure output and frequency characteristics of the speaker.

[0030] The sub-piezoelectric elements 3021 are arranged in one-to-one correspondence with the sub-support elements 2021, the first slits 23 are connected to the second slits 34, and the additional film layer 40 covers at least the slits extending from the first piezoelectric element 301 between the multiple sub-piezoelectric elements 3021 to near the ends of the second piezoelectric element 302 and their vicinity, as well as the second slits 34 and the second elastic beam 3022 and their vicinity, thereby reducing restrictions on the movement of the piezoelectric unit 30, and preventing excessive restrictions from being imposed on the surrounding area when the first piezoelectric element 301 bends and deforms, thereby further improving the SPL and structural reliability.

[0031] 3 and 4, the plurality of sub-supports 2021 and the first support 201 are connected by a first elastic beam 2022, and the first elastic beam 2022 is provided in the first slit 23. The provision of the first elastic beam 2022 reduces the overall rigidity of the second support 202.

[0032] The plurality of sub-piezoelectric elements 3021 and the first piezoelectric element 301 are connected by second elastic beams 3022, which are provided within the second slits 34. By providing the second elastic beams 3022, the overall rigidity of the second piezoelectric element 302 is reduced.

[0033] Preferably, the Young's modulus of the additional film layer 40 is 2 GPa or less. The additional film layer 40 also has a certain degree of flexibility, which reduces the restriction on the movement of the piezoelectric unit 30.

[0034] In a possible embodiment, the additional film layer 40 is made of an elastomer, specifically, an epoxy resin or a silicone rubber (e.g., PDMS (polydimethylpolysiloxane)). The additional film layer 40 can be formed and shaped by a method such as spin coating or roll pressing, followed by patterning using photolithography or lift-off.

[0035] Furthermore, the additional film layer 40 is not filled in the second slits 34, and is not filled in the first slits 23. This allows the additional film layer 40 to deform more flexibly, reducing restrictions on the vibration of the piezoelectric unit 30, and preventing excessive restrictions on the periphery when the piezoelectric unit 30 bends and deforms, thereby further improving the SPL and structural reliability.

[0036] In an embodiment of the present invention, a first opening 41 and a second opening 42 are formed in a piezoelectric speaker. Here, the first opening 41 is formed by penetrating through the additional film layer 40, the second electrode layer 33, and the piezoelectric layer 32 in that order. The through-hole formed by this penetration is coated with, for example, the same material as the stress adjustment layer 50. Thereafter, a first opening 41 is formed again in the through-hole, reaching the first electrode layer 31 so as not to come into contact with the second electrode layer 33, etc. A first metal pad 60 is provided on the first electrode layer 31 located at the first opening 41 so as to be electrically connected to the first electrode layer 31. In a possible embodiment, a patterned hard mask is formed on the additional film layer 40 except for the portion that will become the first opening 41, and the first opening 41 is formed by etching through the additional film layer 40, the second electrode layer 33, and the piezoelectric layer 32 in that order using a method such as dry etching or wet etching, exposing a portion of the first electrode layer 31, and a first metal pad 60 is deposited and formed on the exposed first electrode layer 31 to form an electrical connection.

[0037] The second opening 42 penetrates the additional film layer 40 and the stress adjustment layer 50. A second metal pad 70 is laminated on the second electrode layer 33 located in the second opening 42 so as to be electrically connected to the second electrode layer 33. In a possible embodiment, a patterned hard mask is formed on the additional film layer 40 except for the portion where the second opening 42 will be formed, and the second opening 42 is etched into the additional film layer 40 and the stress adjustment layer 50 by dry etching or wet etching to expose a portion of the second electrode layer 33. The second metal pad 70 is then deposited on the exposed second electrode layer 33 to form an electrical connection.

[0038] The present invention further provides a preferred manufacturing method for the above-described piezoelectric speaker, which includes the following steps.

[0039] In S101, a substrate 10 is provided, specifically, a first silicon layer 12 is provided, and a first oxide layer 13 made of SiO2 material is formed on the first silicon layer 12 made of silicon material by using a method such as thermal oxidation, deposition, or CVD.

[0040] In S102, a second silicon layer 21 is formed on the first oxide layer 13 by using a method such as silicon wafer bonding or CVD. The material of the second silicon layer 21 may be the same as the material of the first silicon layer 12. A second oxide layer 22 is formed on the second silicon layer 21. Specifically, a single layer of the second oxide layer 22 is grown on the surface of the second silicon layer 21 by sputtering using a thermal oxidation method.

[0041] In S103, a first electrode layer 31, a piezoelectric layer 32, and a second electrode layer 33 are deposited on the second oxide layer 22 in the vibration direction of the piezoelectric speaker. The first electrode layer 31 is formed on the second oxide layer 22 by electron beam evaporation or magnetron sputtering. The first electrode layer 31 is patterned using a photolithography process. The first electrode layer 31 is connected to a bottom electrode pad via a bottom electrode lead, and the piezoelectric layer 32 is deposited on the first electrode layer 31, leaving a portion that will become the first opening 41. The second electrode layer 33 is formed on the piezoelectric layer 32 by electron beam evaporation or magnetron sputtering, leaving a portion that will become the first opening 41. The second electrode layer 33 is patterned using a photolithography process. The second electrode layer 33 is connected to an upper electrode pad via an upper electrode lead.

[0042] In S104, the second electrode layer 33 is etched to form the second slits 34. The second slits 34 are formed by sequentially penetrating the first electrode layer 31, the piezoelectric layer 32, and the second electrode layer 33. Specifically, the second slits 34 are formed by etching the second electrode layer 33 by dry etching or wet etching.

[0043] In S105, the stress adjustment layer 50 is formed in a predetermined portion of the second electrode layer 33. The stress adjustment layer 50 is formed on the surface of the second electrode layer 33, the inner wall surfaces of the second slits 34, and the side wall surfaces of the first openings 41.

[0044] In S106, the additional film layer 40 is formed on the stress adjustment layer 50. When an epoxy resin is used for the additional film layer 40, the additional film layer 40 is formed by spin coating or roll pressing and patterning by photolithography. When a silicone rubber is used for the additional film layer 40, the additional film layer 40 is formed by spin coating or roll pressing and patterning by lift-off. A portion of the additional film layer 40 fills the second slits 34, and the additional film layer 40 does not fill the first slits 23.

[0045] In S107, the additional film layer 40 and the stress adjustment layer 50 are etched to penetrate the first opening 41 and the second opening 42, thereby exposing the first electrode layer 31 and the second electrode layer 33. Dry etching or wet etching is preferably used for the etching.

[0046] In S108, a metal is deposited on the first electrode layer 31 exposed by the first opening 41 to form a first metal pad 60, and a metal is deposited on the second electrode layer 33 exposed by the second opening 42 to form a second metal pad 70. Specifically, the first metal pad 60 is formed by depositing a metal on the first electrode layer 31 by electron beam evaporation or magnetron sputtering to form an electrical connection, and the second metal pad 70 is formed by depositing a metal on the second electrode layer 33 by electron beam evaporation or magnetron sputtering to form an electrical connection.

[0047] In S109, the bottom of the first silicon layer 12 is etched to form a back cavity 11. The back cavity 11 is formed by sequentially penetrating the first silicon layer 12 and the first oxide layer 13. The second silicon layer 21 is exposed through the back cavity 11. Then, the bottom of the second silicon layer 21 is etched to form a second slit 34. The second slit 34 sequentially penetrates the second silicon layer 21 and the second oxide layer 22.

[0048] In the piezoelectric speaker manufactured by the above manufacturing method, the piezoelectric unit 30, the additional film layer 40, and, if necessary, the stress adjustment layer 50 are provided, so that the additional film layer 40 and the piezoelectric unit 30 are initially bent downward. Note that if the additional film layer 40 can be adjusted to be initially bent downward, the stress adjustment layer 50 does not need to be provided.

[0049] The above describes in detail the structure, features, and effects of the present invention based on the embodiments shown in the drawings, but these are merely preferred embodiments of the present invention. The present invention is not limited to the scope of the embodiments shown in the drawings. Any modifications made based on the concept of the present invention or equivalent embodiments modified by equivalent changes should be included in the scope of protection of the present invention as long as they do not deviate from the gist contained in the specification and drawings. [Explanation of symbols]

[0050] 10 Substrate 11 Back cavity 12 First silicon layer 13 First oxide layer 20 Support Unit 201 1st support part 202 Second support part 2021 Sub-Support Section 2022 First Elastic Beam 21 Second silicon layer 22 Second oxide layer 23 First slit 24 First partition groove 30 Piezoelectric unit 301 First piezoelectric part 302 Second piezoelectric part 3021 Sub-piezoelectric part 3022 Second Elastic Beam 31 1st electrode layer 32 Piezoelectric layer 33 Second electrode layer 34 Second slit 35 Second partition groove 40 Additional film layer 41 First Opening 42 Second Opening 43 Bend 50 Stress adjustment layer 60 First metal pad 70 Second metal pad

Claims

1. A piezoelectric speaker, a substrate, a support unit, a piezoelectric unit, and an additional film layer; The substrate has a back cavity formed therethrough, the support unit is provided on the substrate and covers the back cavity, a first slit is formed through a part of the support unit to divide the support unit into a first support portion and a second support portion, the second support portion is located in a circumferential direction of the first support portion, and the first support portion protrudes further toward the back cavity than the second support portion in a vibration direction of the piezoelectric speaker, the piezoelectric unit is provided on the support unit, a second slit is formed through a part of the piezoelectric unit to divide the piezoelectric unit into a first piezoelectric portion and a second piezoelectric portion, the second piezoelectric portion is located in a circumferential direction of the first piezoelectric portion, the first piezoelectric portion is supported on the first support portion, and the second piezoelectric portion is supported on the second support portion, and in a vibration direction of the piezoelectric speaker, the first piezoelectric portion protrudes closer to the back cavity than the second piezoelectric portion, The piezoelectric speaker is characterized in that the additional film layer is provided on the piezoelectric unit and is also formed at a position corresponding to the second slit.

2. 2. The piezoelectric speaker according to claim 1, wherein a stress adjustment layer is provided between the piezoelectric unit and the additional film layer, and the stress adjustment layer covers the surfaces of the first piezoelectric portion and the second piezoelectric portion.

3. 2. The piezoelectric speaker according to claim 1, wherein a portion of the additional film layer fills the second slit.

4. 4. The piezoelectric speaker according to claim 3, wherein the first slit is not filled with the additional film layer.

5. 2. The piezoelectric speaker of claim 1, wherein the second support portion includes a plurality of sub-support portions that surround the first support portion and are spaced apart from each other by first partition grooves, the second piezoelectric portion includes a plurality of sub-piezoelectric portions that surround the first piezoelectric portion and are spaced apart from each other by second partition grooves, the sub-piezoelectric portions are arranged in one-to-one correspondence with the sub-support portions, the first slits are connected to the second slits, and the additional film layer covers only the spaces between the plurality of sub-piezoelectric portions and the second slits.

6. The piezoelectric speaker of claim 5, characterized in that the plurality of sub-support portions and the first support portion are connected by a first elastic beam, the first elastic beam being provided within the first slit, and the plurality of sub-piezoelectric portions and the first piezoelectric portion are connected by a second elastic beam, the second elastic beam being provided within the second slit.

7. 7. The piezoelectric speaker according to claim 1, wherein the additional film layer has a Young's modulus of 2 GPa or less.

8. 8. The piezoelectric speaker according to claim 7, wherein the additional film layer is an elastomer.

Images