Piezoelectric speaker

Abstract

This invention provides a piezoelectric speaker that optimizes the stress of each layer during displacement, increases the displacement of the 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 provided, 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 provided through the support unit to divide it into a first support portion 201 and a second support portion 202 located in the direction of its outer circumference. In the vibration direction of the piezoelectric speaker, the first support portion protrudes towards the back cavity more than the second support portion. The piezoelectric unit is provided with a first piezoelectric portion 301 through which a second slit 34 is provided and which is supported by the first support portion and protrudes towards the back cavity more than the second piezoelectric portion in the vibration direction, and a second piezoelectric portion 302 located in the direction of the outer circumference 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 particularly to piezoelectric speakers.

Background Art

[0002] In a silicon-based microelectromechanical speaker, by using an organic film for the diaphragm, air leakage can be prevented, the sound pressure level (SPL) can be improved, and moreover, the total harmonic distortion (THD) can be reduced. However, since the displacement of the diaphragm of the speaker is restricted by the organic film, the achievable sound pressure level is limited.

Summary of the Invention

Problems to be Solved by the Invention

[0003] An object of the present invention is to provide a piezoelectric speaker that solves the technical problems in the prior art.

Means for Solving the Problems

[0004] The present invention provides a piezoelectric speaker comprising a substrate, a support unit, a piezoelectric unit, and an additional film layer, wherein a back cavity is provided through the substrate, the support unit is provided on the substrate and covers the back cavity, a first slit is provided 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 the outer peripheral direction of the first support portion, and in the vibration direction of the piezoelectric speaker, the first support portion protrudes further toward the back cavity than the second support portion, and the pressure The electrical unit is provided on the support unit, and a second slit is provided through a part of the piezoelectric unit, dividing the piezoelectric unit into a first piezoelectric part and a second piezoelectric part, the second piezoelectric part is located in the direction of the outer circumference of the first piezoelectric part, the first piezoelectric part is supported on the first support unit, the second piezoelectric part is supported on the second support unit, in the vibration direction of the piezoelectric speaker, the first piezoelectric part protrudes further toward the back cavity than the second piezoelectric part, and the additional film layer is provided on the piezoelectric unit and is also formed at a position corresponding to the second slit.

[0005] In the piezoelectric speaker 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 part and the second piezoelectric part.

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

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

[0008] In the piezoelectric speaker described above, preferably, the second support portion includes a plurality of sub-support portions surrounding the first support portion and separated from each other by a first partition groove, the second piezoelectric portion includes a plurality of sub-piezoelectric portions surrounding the first piezoelectric portion and separated from each other by a second partition groove, the sub-piezoelectric portions are provided in one-to-one correspondence with the sub-support portion, the first slit communicates with the second slit, and the additional film layer covers only the gaps between the plurality of sub-piezoelectric portions and the second slit.

[0009] In the piezoelectric speaker described above, preferably, the plurality of sub-supports and the first support are connected by a first elastic beam, the first elastic beam being provided in the first slit, and the plurality of sub-piezoelectric units and the first piezoelectric unit are connected by a second elastic beam, the second elastic beam being provided in the second slit.

[0010] In the piezoelectric speaker described above, preferably, the piezoelectric unit includes a first electrode layer, a piezoelectric layer, and a second electrode layer, which are sequentially stacked on the support unit along the vibration direction of the piezoelectric speaker. In the piezoelectric speaker described above, preferably, the piezoelectric speaker has a first opening and a second opening. The first opening penetrates the additional film layer, the second electrode layer, and the piezoelectric layer in that order, and a first metal pad is laminated 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 at the second opening.

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

[0012] In the piezoelectric speaker described above, preferably, the substrate includes a first silicon layer and a first oxide layer laminated in order along the vibration direction of the piezoelectric speaker, the support unit includes a second silicon layer and a second oxide layer laminated in order on the first oxide layer along the vibration direction of the piezoelectric speaker, the back cavity penetrates 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 described above, preferably, the additional film layer is added by a dry film roll press method, spin coating method, spray method, inkjet method, vapor phase deposition method, etc., and formed by an etching method, molding method, laser processing method, etc. [Effects of the Invention]

[0014] Compared to conventional technology, the present invention bends the piezoelectric unit downward (towards the back cavity) in its initial state by adjusting the stress of the support unit, piezoelectric unit, additional film layer, or stress adjustment layer. 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 single stress adjustment layer between the piezoelectric unit and the additional film layer, the support unit and piezoelectric unit can also be bent downward in their initial state. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic cross-sectional view of a piezoelectric speaker according to an embodiment of the present invention. [Figure 2] This is a schematic diagram of the exploded structure of a piezoelectric speaker according to an embodiment of the present invention. [Figure 3] This is a schematic plan view of the support unit of an embodiment related to the present invention. [Figure 4] This is a schematic plan view of the piezoelectric unit according to an embodiment of the present invention. [Figure 5]This is a schematic diagram of the planar structure of the added film layer in an embodiment related to the present invention. [Modes for carrying out the invention]

[0016] The following description will be given with reference to the drawings. The examples provided are illustrative and are intended solely to illustrate the present invention and should not be construed as limitations on the invention.

[0017] As shown in Figures 1 to 5, embodiments of the present invention provide 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. Here, the substrate 10 includes a first silicon layer 12 and a first oxide layer 13 that are sequentially laminated along the vibration direction of the piezoelectric speaker, for example, as shown in Figure 1, the first silicon layer 12 and the first oxide layer 13 are sequentially laminated 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 is a circular groove structure. The back cavity 11 penetrates the first silicon layer 12 and the first oxide layer 13 in sequence, and in a viable embodiment, the first oxide layer 13 made of SiO2 material is formed on the first silicon layer 12 made of silicon material by methods such as vapor deposition, 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 that are stacked sequentially along the vibration direction of the piezoelectric speaker. For example, as shown in Figure 1, the second silicon layer 21 and the second oxide layer 22 are stacked sequentially from bottom to top. At least a portion of the second silicon layer 21 is exposed to the back cavity 11 side. 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 methods such as bonding a silicon wafer to the first oxide layer 13. The second oxide layer 22 can be formed by growing at least one layer of the 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 the material of the first silicon layer 12. The first oxide layer 13 is located beneath the second silicon layer 21 and has a significantly lower etching rate than the second silicon layer 21, ensuring that when etching is performed to form a slit or back cavity 11, the etching stops precisely 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 that are stacked in order along the vibration direction of the piezoelectric speaker. For example, as shown in Figure 1, the first electrode layer 31, the piezoelectric layer 32, and the second electrode layer 33 are stacked in 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 deposition or magnetron sputtering). The first electrode layer 31 is also 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, and ZrN, or other materials with good conductivity. In a feasible embodiment, the material of the first electrode layer 31 is platinum (Pt) and molybdenum (Mo).

[0020] The piezoelectric layer 32 is formed by depositing on the first electrode layer 31. The piezoelectric layer 32 vibrates mechanically under an alternating current electric field. The material of the piezoelectric layer 32 may be lead zirconate titanate, aluminum nitride, barium titanate, or any other piezoelectric material. In an executable 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 (for example, 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 any other material with good electrical conductivity. In an executable embodiment, the material of the second electrode layer 33 is platinum (Pt) and molybdenum (Mo).

[0022] The additional film layer 40 is provided on the piezoelectric unit 30 and on the side surface between the first piezoelectric part 301 and the second piezoelectric part 302 that form the piezoelectric unit 30. The additional film layer 40 serves as a diaphragm. The stress adjustment layer 50 is provided between the piezoelectric unit 30 and the additional film layer 40, and the stress adjustment layer 50 covers the surfaces of the first piezoelectric part 301 and the second piezoelectric part 302. The stress adjustment layer 50 also serves as a passivation. The stress adjustment layer 50 has a compressive stress, and for example, the material is composed of SiN, Al2O3, TiO2.

[0023] A through hole is provided in the substrate 10, thereby forming a cavity 11. A first slit 23 is made through the support unit 20, leaving a plurality of first elastic beams 2022 (described later) intact, thereby dividing the support unit 20 into a first support section 201 and a second support section 202 via the plurality of first elastic beams 2022. The first support section 201 is located in the central part of the support unit 20, and the second support section 202 is located in the outer circumferential direction of the first support section 201. Due to the action of the additional film layer 40 and the stress adjustment layer 50, the first support section 201 and the second support section 202 are initially located in different planes. Therefore, in the vibration direction of the piezoelectric speaker, the first support section 201 is positioned to protrude into the back cavity 11.

[0024] A second slit 34 is made through the piezoelectric unit 30, leaving a plurality of first elastic beams 3022 (described later) intact, thereby dividing the piezoelectric unit 30 into a first piezoelectric section 301 and a second piezoelectric section 302 via the plurality of first elastic beams 3022. The first piezoelectric section 301 is located in the central part of the piezoelectric unit 30, and the second piezoelectric section 302 is located in the outer circumferential direction of the first piezoelectric section 301. The first piezoelectric section 301 is supported on the first support section 201, and the second piezoelectric section 302 is supported on the second support section 202. Due to the action of the additional film layer 40 and the stress adjustment layer 50, the first piezoelectric section 301 and the second piezoelectric section 302 are initially located in different planes. Therefore, in the vibration direction of the piezoelectric speaker, the first piezoelectric section 301, together with the first support section 201, protrudes towards the back cavity 11. The presence of the second slit 34 allows for adjustment of the overall rigidity of the piezoelectric unit 30, thereby improving the speaker's maximum sound pressure output and frequency characteristics.

[0025] The additional film layer 40 forms a bent portion 43 at a position corresponding to the second slit 34 due to the action of the additional film layer 40 and the stress adjustment layer 50 on the first support portion 201 and the first piezoelectric portion 301. The bent portion 43 has an inner first end and an outer second end. In the vibration direction of the piezoelectric speaker, the first end of the bent portion 43 protrudes towards the back cavity 11 side than the second end of the bent portion 43. 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 thereby effectively improving the SPL.

[0026] By providing a stress adjustment layer 50 between the piezoelectric unit 30 and the additional film layer 40, the additional film layer 40 can be made convex downwards, dramatically improving the SPL. Also, initially, the first piezoelectric part 301 and the first support part 201 are both recessed downwards relative to the second piezoelectric part 302 and the second support part 202. Therefore, when an electric field is applied to the piezoelectric film 32, it deforms in the tensile direction, causing the support unit 20, the piezoelectric unit 30, and the additional film layer 40 to bend upwards. As a result, the movement (displacement) of the additional film layer 40 increases, effectively improving the SPL. In this invention, the stress adjustment layer 50 is provided to make the additional film layer 40 convex downwards in conjunction with its action. However, if the additional film layer 40 can be made convex downwards by adjusting the additional film layer 40, then the stress adjustment layer 50 does not need to be provided.

[0027] In embodiments relating to the present invention, a portion of the additional film layer 40 is filled into the second slit 34 and not into the first slit 23. The additional film layer 40 is partially filled into the second slit 34, reducing sound pressure loss caused by air leakage through the second slit 34 and increasing the adhesion force of the additional film layer 40. Furthermore, since it is not filled into the first slit 23, the restrictions on the movement of the first support portion 201 and the first piezoelectric portion 301 are reduced.

[0028] As shown in Figures 3 and 4, the second support section 202 includes a plurality of sub-support sections 2021 that surround the first support section 201 and are separated from each other by a first partition groove 24 that extends from the first support section 201 to near the end of the second support section 202. The second support section 202 is provided at a certain distance from the first support section 201 by a first elastic beam 2022 between the sub-support sections 2021, thereby improving the maximum sound pressure output and frequency characteristics of the speaker.

[0029] The second piezoelectric section 302 includes a plurality of sub-piezoelectric sections 3021 that surround the first piezoelectric section 301 and are separated from each other by a second partition groove 35 that extends from the first piezoelectric section 301 to near the end of the second piezoelectric section 302. The second piezoelectric section 302 is provided at a certain distance from the first piezoelectric section 301 by a second elastic beam 3022 between the sub-piezoelectric sections 3021, thereby improving the maximum sound pressure output and frequency characteristics of the speaker.

[0030] The sub-piezoelectric section 3021 is provided in a one-to-one correspondence with the sub-support section 2021, the first slit 23 communicates with the second slit 34, and the additional film layer 40 covers at least the slits and their vicinity extending from the first piezoelectric section 301 to the vicinity of the end of the second piezoelectric section 302 between the multiple sub-piezoelectric sections 3021, and the second slit 34 and the second elastic beam 3022 and their vicinity. This reduces the restrictions on the movement of the piezoelectric unit 30, and when the first piezoelectric section 301 undergoes bending deformation, the surrounding area is not excessively restricted, further improving SPL and structural reliability.

[0031] Continuing to refer to Figures 3 and 4, the multiple sub-supports 2021 and the first support 201 are connected by a first elastic beam 2022, which is located within the first slit 23. The installation of the first elastic beam 2022 reduces the overall rigidity of the second support 202.

[0032] Multiple sub-piezoelectric units 3021 and the first piezoelectric unit 301 are connected by a second elastic beam 3022, which is located within the second slit 34. The installation of the second elastic beam 3022 reduces the overall rigidity of the second piezoelectric unit 302.

[0033] Preferably, the Young's modulus of the additional film layer 40 is 2 GPa or less. Furthermore, the additional film layer 40 has a certain degree of flexibility. These characteristics reduce the limitations on the movement of the piezoelectric unit 30.

[0034] In a feasible embodiment, the additional film layer 40 is made of an elastomer, specifically an epoxy resin or silicone rubber (for example, PDMS (polydimethylpolysiloxane)). Methods for forming and shaping the additional film layer 40 include forming the film by spin coating or roll pressing, and then patterning it by photolithography or lift-off.

[0035] Furthermore, the additional film layer 40 is not filled into the second slit 34, nor into the first slit 23. This allows the deformation of the additional film layer 40 to be more flexible, reducing the vibration limitations of the piezoelectric unit 30, and preventing excessive restriction of the surrounding area when the piezoelectric unit 30 undergoes bending deformation, thereby further improving SPL and structural reliability.

[0036] In embodiments relating to the present invention, a first opening 41 and a second opening 42 are provided in the 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. Subsequently, a first opening 41 is formed in the through-hole again, reaching the first electrode layer 31 without contacting the second electrode layer 33, etc. A first metal pad 60 is provided on the first electrode layer 31 located in the first opening 41 so as to be electrically connected to the first electrode layer 31. In a feasible embodiment, a patterned hard mask is fabricated on the additional film layer 40, excluding the area that will become the first opening 41. 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. The first metal pad 60 is then deposited on the exposed first electrode layer 31 to form an electrical connection.

[0037] The second opening 42 penetrates the addition layer 40 and the stress adjustment layer 50. A second metal pad 70 is laminated on the second electrode layer 33 located at the second opening 42 so as to be electrically connected to the second electrode layer 33. In a feasible embodiment, a patterned hard mask is fabricated on the addition layer 40 except for the area that will become the second opening 42, and the second opening 42 is etched into the addition layer 40 and the stress adjustment layer 50 by dry etching or wet etching, exposing a portion of the second electrode layer 33, and the second metal pad 70 is deposited on the exposed second electrode layer 33 to form an electrical connection.

[0038] With respect to the piezoelectric speaker described above, the present invention further provides a preferred manufacturing method, which includes the following flow.

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

[0040] In S102, a silicon wafer is bonded or a second silicon layer 21 is formed on the first oxide layer 13 using a method such as 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 step S103, the first electrode layer 31, the piezoelectric layer 32, and the second electrode layer 33 are deposited on top of the second oxide layer 22 in the direction of vibration 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 the bottom electrode pad via a bottom electrode lead, and the piezoelectric layer 32 is formed by depositing it on the first electrode layer 31, leaving a portion that will become the first aperture 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 aperture 41. The second electrode layer 33 is patterned using a photolithography process. The second electrode layer 33 is connected to the top electrode pad via an top electrode lead.

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

[0043] In step S105, a stress adjustment layer 50 is formed at a predetermined location on the second electrode layer 33. The stress adjustment layer 50 is formed on the surface of the second electrode layer 33, the inner wall surface of the second slit 34, and the side wall surface of the first opening 41.

[0044] In S106, an additional film layer 40 is formed in the stress adjustment layer 50. When epoxy resin is used for the additional film layer 40, it is formed by spin coating or roll pressing and then patterned by photolithography. When silicone rubber is used for the additional film layer 40, it is formed by spin coating or roll pressing and then patterned by lift-off. Some of the additional film layer 40 is filled into the second slit 34, while the additional film layer 40 is not filled into the first slit 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, exposing the first electrode layer 31 and the second electrode layer 33. Dry etching or wet etching is preferred for the etching process.

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

[0047] In step S109, a back cavity 11 is formed by etching the bottom of the first silicon layer 12. 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, a second slit 34 is formed by etching the bottom of the second silicon layer 21. 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 and the additional film layer 40, and optionally the stress adjustment layer 50, are initially bent downward. However, if the additional film layer 40 can be formed to be bent downward initially by adjusting it, 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 shown in the drawings. Modifications made based on the concept of the present invention, or equivalent embodiments modified to equivalents, should all be included within the scope of protection of the present invention, as long as they do not depart from the gist contained in the specification and drawings. [Explanation of Symbols]

[0050] 10 circuit boards 11 Back Cavity 12. First silicon layer 13. First Oxide Layer 20 support units 201 1st support part 202 Second support part 2021 Sub-support section 2022 1st Elastic Beam 21 Second silicon layer 22 Second Oxide Layer 23. First Slit 24. First partition groove 30 Piezoelectric Units 301 First piezoelectric section 302 Second piezoelectric section 3021 Sub-piezoelectric unit 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. Bending section 50 Stress adjustment layer 60 First metal pad 70 Second metal pad

Claims

1. It is a piezoelectric speaker, It includes a substrate, a support unit, a piezoelectric unit, and an additional film layer. A back cavity is provided through the aforementioned substrate. The support unit is provided on the substrate and covers the back cavity, and a first slit is provided through a part of the support unit, dividing the support unit into a first support portion and a second support portion, the second support portion is located in the outer peripheral direction of the first support portion, and in the vibration direction of the piezoelectric speaker, the first support portion protrudes further toward the back cavity than the second support portion. The piezoelectric unit is provided on the support unit, and a second slit is provided through a part of the piezoelectric unit, dividing the piezoelectric unit into a first piezoelectric section and a second piezoelectric section, the second piezoelectric section is located in the direction of the outer circumference of the first piezoelectric section, the first piezoelectric section is supported on the first support section, the second piezoelectric section is supported on the second support section, and in the vibration direction of the piezoelectric speaker, the first piezoelectric section protrudes further toward the back cavity than the second piezoelectric section. A piezoelectric speaker 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. A piezoelectric speaker according to claim 1, characterized in that 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 part and the second piezoelectric part.

3. The piezoelectric speaker according to claim 1, characterized in that a portion of the additional film layer is filled into the second slit.

4. The piezoelectric speaker according to claim 3, characterized in that the additional film layer is not filled inside the first slit.

5. The piezoelectric speaker according to claim 1, characterized in that the second support portion includes a plurality of sub-support portions surrounding the first support portion and separated from each other by a first partition groove, the second piezoelectric portion includes a plurality of sub-piezoelectric portions surrounding the first piezoelectric portion and separated from each other by a second partition groove, the sub-piezoelectric portions are provided in one-to-one correspondence with the sub-support portion, the first slit communicates with the second slit, and the additional film layer covers only the gaps between the plurality of sub-piezoelectric portions and the second slit.

6. The piezoelectric speaker according to claim 5, characterized in that the plurality of sub-supports and the first support are connected by a first elastic beam, the first elastic beam is provided in the first slit, and the plurality of sub-piezoelectric units and the first piezoelectric unit are connected by a second elastic beam, the second elastic beam is provided in the second slit.

7. The piezoelectric speaker according to any one of claims 1 to 6, characterized in that the Young's modulus of the added film layer is 2 GPa or less.

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

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