Membrane microelectromechanical system piezoelectric speaker

Abstract

The application provides a MEMS piezoelectric loudspeaker, which comprises a substrate with a cavity; a vibrating structure comprising a structure layer, a piezoelectric composite layer and a flexible layer; the structure layer comprises a structure plate, a structure fixing part and a plurality of structure springs with slits; the piezoelectric composite layer comprises a piezoelectric film and a first electrode layer and a second electrode layer; wherein the mutually coinciding areas of the piezoelectric film, the first electrode layer and the second electrode layer in the orthographic projection of the substrate are piezoelectric driving functional areas, and the flexible layer is arranged in the stacking direction of the layers of the vibrating structure and is spaced apart from the structure layer and its orthographic projection completely covers the slits of the plurality of structure springs. The stress of the piezoelectric composite layer can be released through the elastic effect of the structure springs, the rigidity of the overall structure is ensured and the rigidity of the overall structure is not too low, so that the sound pressure level of the MEMS piezoelectric loudspeaker is improved and the harmonic distortion is reduced, and the performance of the MEMS piezoelectric loudspeaker is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of acoustoelectricity, and particularly relates to a MEMS piezoelectric loudspeaker. BACKGROUND

[0002] As one of main components of mobile terminals such as mobile phones and tablet computers, the MEMS piezoelectric loudspeaker is mainly used for converting electrical signals into sound signals and is a key to realize a human-machine interaction interface. Especially with the emergence of TWS earphones, the demand for small and high-performance loudspeakers is increasingly urgent. The MEMS piezoelectric loudspeaker has become a main component combined with a traditional loudspeaker and bearing high-frequency vibration due to its small size, light weight and low power consumption.

[0003] The existing MEMS piezoelectric loudspeaker mainly comprises a substrate, a structure layer fixed on the substrate and a piezoelectric functional layer placed on the structure layer. The piezoelectric functional layer comprises a piezoelectric layer and electrode layers arranged on opposite sides of the piezoelectric layer. The working principle is that the piezoelectric functional layer will deform after being electrified, thereby driving the overall structure to vibrate and emit sound.

[0004] The existing MEMS piezoelectric loudspeaker mainly has two structures. One is to directly stack the whole structure layer and the piezoelectric functional layer on the substrate in sequence. This way will cause a large harmonic distortion (THD) due to the stress limitation of the process and the structure of each layer, and the sound pressure level (SPL) improvement ability is also limited. The other is to directly set the middle driving area of the piezoelectric energy supply layer on the flexible membrane connected with the substrate. This way will reduce the stiffness of the whole device, so that the first-order resonance frequency of the loudspeaker moves to the low frequency, and the higher-order high-frequency resonance frequency also moves to the low frequency, thereby causing the high-order high-frequency resonance frequency to appear in the human ear hearing range (20Hz-20kHz), which not only reduces the sound pressure level, but also increases the harmonic distortion, affecting the listening experience. SUMMARY

[0005] The technical problem to be solved by the application is how to provide a MEMS piezoelectric loudspeaker to solve the problem of poor harmonic distortion and sound pressure level performance of the existing MEMS piezoelectric loudspeaker due to its structural design.

[0006] The application is implemented by providing a MEMS piezoelectric loudspeaker, comprising:

[0007] a substrate, the substrate having a cavity;

[0008] a vibration structure, the vibration structure comprising a structure layer, a piezoelectric composite layer and a flexible layer stacked in sequence above the substrate;

[0009] The structural layer includes a structural plate, a structural fixing part surrounding and spaced apart from the structural plate, and a plurality of structural springs having slits connecting the structural plate and the structural fixing part; the structural fixing part is supported and fixed to the base, and the orthographic projection of the structural springs and the structural plate onto the base is entirely within the range of the cavity;

[0010] The piezoelectric composite layer includes a piezoelectric thin film, a first electrode layer formed on the side of the piezoelectric thin film near the structural layer, and a second electrode layer formed on the side of the piezoelectric thin film away from the structural layer; wherein, the regions in which the piezoelectric thin film, the first electrode layer, and the second electrode layer overlap in their orthogonal projections onto the substrate serve as piezoelectric driving functional regions, and the flexible layer is spaced apart from the structural layer in the stacking direction of each layer of the vibrating structure, and its orthogonal projection completely covers the slits of the plurality of structural springs.

[0011] Furthermore, the first electrode layer includes a first electrode functional part fixed to the structural plate, a first electrode fixing part fixed to the structural fixing part, and a first electrode spring connecting the first electrode functional part and the first electrode fixing part.

[0012] Furthermore, the flexible layer covers the side of the second electrode layer away from the piezoelectric film and extends at least partially to the periphery of the second electrode layer and the piezoelectric film, and is fixed to the surface of the first electrode layer away from the structural layer.

[0013] Furthermore, the piezoelectric film includes a piezoelectric functional portion fixed to the first electrode functional portion, a piezoelectric fixing portion fixed to the first electrode fixing portion, and a piezoelectric spring connecting the piezoelectric functional portion and the piezoelectric fixing portion.

[0014] Furthermore, the piezoelectric thin film, the first electrode layer, and the structural layer all have the same shape and structure.

[0015] Furthermore, the flexible layer covers the side of the second electrode layer away from the piezoelectric film and extends at least partially to the periphery of the second electrode layer and is fixed to the surface of the piezoelectric film away from the structural layer.

[0016] Furthermore, the structural spring can be any one of a U-shaped structure, a ring structure, or an S-shaped structure.

[0017] Furthermore, the piezoelectric film is made of any one of aluminum nitride, piezoelectric ceramics, and zinc oxide.

[0018] Furthermore, the flexible layer is made of a polymer material.

[0019] Furthermore, the polymer is SU-8 photoresist or polyimide.

[0020] Compared with the prior art, in the MEMS piezoelectric loudspeaker of the present invention, the structural plate of the structural layer is connected to the structural fixing part by multiple structural springs. At the same time, the areas where the piezoelectric film, the first electrode layer and the second electrode layer in the piezoelectric composite layer overlap in the orthographic projection onto the substrate are used as the piezoelectric driving functional area. In this way, the stress of the piezoelectric composite layer can be released by the elastic action of the structural springs, while ensuring the rigidity of the overall structure and preventing the overall structural rigidity from being too low. This improves the sound pressure level of the MEMS piezoelectric loudspeaker and reduces harmonic distortion, thereby improving the performance of the MEMS piezoelectric loudspeaker. [Attached Image Description]

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is an exploded structural diagram of the first MEMS piezoelectric loudspeaker provided in the embodiments of the present invention;

[0023] Figure 2 This is a schematic diagram of the overall structure of the first MEMS piezoelectric loudspeaker provided in the embodiments of the present invention;

[0024] Figure 3 yes Figure 2 A sectional view of line A-A in the middle;

[0025] Figure 4 This is an exploded structural diagram of the second MEMS piezoelectric loudspeaker provided in this embodiment of the invention;

[0026] Figure 5 This is a schematic diagram of the overall structure of the second MEMS piezoelectric loudspeaker provided in this embodiment of the invention;

[0027] Figure 6 yes Figure 5 A sectional view of line B-B in the middle;

[0028] Figure 7 This is a schematic diagram of the structure of the second type of structural layer provided in the embodiments of the present invention;

[0029] Figure 8 This is a schematic diagram of the third structural layer provided in the embodiments of the present invention;

[0030] Wherein: 100, MEMS piezoelectric loudspeaker; 1, substrate; 11, cavity; 2, vibration structure; 21, structural layer; 211, structural plate; 212, structural spring; 213, structural fixing part; 22, piezoelectric composite layer; 221, piezoelectric film; 2211, piezoelectric functional part; 2212, piezoelectric fixing part; 2213, piezoelectric spring; 222, first electrode layer; 2221, first electrode functional part; 2222, first electrode fixing part; 2223, first electrode spring; 223, second electrode layer; 2231, second electrode functional part; 2232, lead wire; 2233, connecting part; 23, flexible layer; 10, slit.

Detailed Implementation Methods

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] This invention provides a MEMS piezoelectric loudspeaker 100, combined with... Figures 1 to 8 As shown, it includes a base 1 and a vibration structure 2.

[0033] Specifically, the substrate 1 has a cavity 11; the vibration structure 2 includes a structural layer 21, a piezoelectric composite layer 22 and a flexible layer 23 stacked sequentially on the substrate 1.

[0034] Specifically, the structural layer 21 includes a structural plate 211, a structural fixing part 213 surrounding the structural plate 211 and spaced apart from the structural plate, and a plurality of structural springs 212 connecting the structural plate 211 and the structural fixing part 213 and having a slit 10; the structural fixing part 213 is supported and fixed to the base 1, and the orthogonal projection of the structural springs 212 and the structural plate 211 onto the base 1 is completely within the range of the cavity 11.

[0035] In this configuration, one end of each structural spring 212 is connected to the structural plate 211, and the other end is connected to the structural fixing part 213. The structural spring 212 can be any of a variety of structures, such as a U-shaped structure, a ring structure, or an S-shaped structure. This arrangement enhances the overall structural rigidity through the elastic action of the structural fixing part 213 and the structural spring 212, without making its rigidity too low. This improves the sound pressure level of the MEMS piezoelectric speaker and reduces harmonic distortion, thereby enhancing the performance of the MEMS piezoelectric speaker.

[0036] Specifically, the piezoelectric composite layer 22 includes a piezoelectric thin film 221, a first electrode layer 222 formed on the side of the piezoelectric thin film 221 close to the structural layer 21, and a second electrode layer 223 formed on the side of the piezoelectric thin film 221 away from the structural layer 21; wherein, the regions in which the piezoelectric thin film 221, the first electrode layer 222, and the second electrode layer 223 overlap in their respective orthogonal projections onto the substrate 1 serve as piezoelectric driving functional regions, and the flexible layer 23 is spaced apart from the structural layer 21 in the stacking direction of each layer of the vibrating structure 2, and its orthogonal projection completely covers the slits 10 of the multiple structural springs 212.

[0037] The flexible layer 23 is spaced apart from the structural layer 21 in the stacking direction of each layer of the vibration structure 2, and its orthogonal projection completely covers the slit 10 between multiple structural springs 212. This arrangement can prevent air from leaking outward from the slit 10.

[0038] In this embodiment, the piezoelectric film 221 is made of any one of the piezoelectric materials selected from aluminum nitride (AlN), piezoelectric ceramic (PZT), and zinc oxide (ZnO). Of course, it can also be made of other materials according to actual needs, which will not be listed here.

[0039] In this embodiment, the flexible layer 23 is made of a polymer material, such as SU-8 photoresist or polyimide (PI). Of course, depending on the actual needs, the flexible layer 23 can also be made of other polymer materials, which will not be listed here.

[0040] Specifically, the first electrode layer 222 includes a first electrode functional part 2221 fixed to the structural plate 211, a first electrode fixing part 2222 fixed to the structural fixing part 213, and a first electrode spring 2223 connecting the first electrode functional part 2221 and the first electrode fixing part 2222.

[0041] Among them, the end face of the substrate 1 is the part surrounding the cavity 11 at one end of the substrate 1, which is also equivalent to the planar region at one end of the substrate 1.

[0042] In this embodiment, there are multiple first electrode springs 2223 arranged around the first electrode functional part 2221, with adjacent two springs spaced apart. Of course, depending on actual needs, the first electrode layer 222 may not have the first electrode fixing part 2222 and the first electrode spring 2223, or the first electrode fixing part 2222 may be set as a point and the first electrode spring 2223 may be set as one.

[0043] Specifically, the piezoelectric film 221 includes a piezoelectric functional portion 2211 fixed to the first electrode functional portion 2221, a piezoelectric fixing portion 2212 fixed to the first electrode fixing portion 2221, and a piezoelectric spring 2213 connecting the piezoelectric functional portion 2211 and the piezoelectric fixing portion 2212. This arrangement can enhance the rigidity of the overall structure through the elastic action of the piezoelectric fixing portion 2212 and the piezoelectric spring 2213, without making its rigidity too low, thereby increasing the sound pressure level of the MEMS piezoelectric speaker and reducing harmonic distortion, thus improving the performance of the MEMS piezoelectric speaker.

[0044] Of course, depending on actual needs, the piezoelectric film 221 may only have the piezoelectric functional part 2211, without the piezoelectric fixing part 2212 and the piezoelectric spring 2213. In this way, since no other structures are set in other positions except for the piezoelectric driving functional area, the rigidity of the overall structure can be further reduced, so as to adjust the first resonant frequency of the MEMS piezoelectric speaker 100 within a certain range and expand the usable audio frequency range.

[0045] The piezoelectric fixing part 2212 can be a ring structure, and there can be multiple piezoelectric springs 2213 arranged around the piezoelectric fixing part 2212. In this case, the structure of the piezoelectric film 221 is similar to or the same as that of the structural layer 21. Of course, depending on the actual needs, the piezoelectric fixing part 2212 can also be a single point, and the piezoelectric spring 2213 can also be a single spring with a structure similar to or the same as that of the structural spring 212.

[0046] In this embodiment, the piezoelectric film 221, the first electrode layer 222, and the structural layer 21 all have the same shape and structure.

[0047] Specifically, the second electrode layer 223 includes a second electrode functional section 2231 fixed to the side of the piezoelectric functional section 2211 away from the first electrode functional section 2221, a lead wire 2233 extending outward from the periphery of the second electrode functional section 2231, and a connecting portion 2233 formed at one end of the lead wire 2233 away from the second electrode functional section 2231. This facilitates the introduction of electrical signals into the second electrode layer 223.

[0048] In this embodiment, the second electrode fixing part 2231 has the same shape and structure as the first electrode functional part 2221.

[0049] In this embodiment, as Figure 3 As shown, the flexible layer 23 covers the side of the second electrode layer 223 away from the piezoelectric film 221 and extends at least partially to the periphery of the second electrode layer 223 and is fixed to the surface of the piezoelectric film 221 away from the structural layer 21.

[0050] In another embodiment, such as Figure 6As shown, the flexible layer 23 covers the side of the second electrode layer 223 away from the piezoelectric film 221 and extends at least partially to the periphery of the second electrode layer 223 and the piezoelectric film 221 and is fixed to the surface of the first electrode layer 222 away from the structural layer 21.

[0051] Specifically, the structural layer 21 may also include multiple layers stacked sequentially, such as two layers, three layers, four layers, etc.; the piezoelectric composite layer 22 may also include multiple layers stacked sequentially, such as two layers, three layers, five layers, etc.

[0052] Compared with the prior art, in this embodiment, the structural plate 211 of the structural layer 21 of the MEMS piezoelectric loudspeaker 100 is connected to the structural fixing part 213 through multiple structural springs 212. Simultaneously, the overlapping areas of the piezoelectric film 221, the first electrode layer 222, and the second electrode layer 223 in the piezoelectric composite layer 22 projected onto the substrate 1 are designated as the piezoelectric driving functional area. This allows the elastic action of the structural springs 212 to release the stress in the piezoelectric composite layer 22, while maintaining the overall structural rigidity without causing it to be too low. This improves the sound pressure level of the MEMS piezoelectric loudspeaker and reduces harmonic distortion, thereby enhancing the performance of the MEMS piezoelectric loudspeaker. Specifically, it allows for a larger boost stage, a wider usable audio frequency range, releases the stress in the piezoelectric composite layer 22, reduces the impact of stress on harmonic distortion and device power consumption, and prevents excessive high-order resonant frequencies from appearing in the audible frequency range, while also reducing the increase in harmonic distortion caused by excessive rigidity.

[0053] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A MEMS piezoelectric loudspeaker, characterized in that, include: A substrate having a cavity; A vibration structure, comprising a structural layer, a piezoelectric composite layer, and a flexible layer sequentially stacked on the substrate; The structural layer includes a structural plate, a structural fixing part surrounding and spaced apart from the structural plate, and a plurality of structural springs having slits connecting the structural plate and the structural fixing part; the structural fixing part is supported and fixed to the base, and the orthographic projection of the structural springs and the structural plate onto the base is entirely within the range of the cavity; The piezoelectric composite layer includes a piezoelectric thin film, a first electrode layer formed on the side of the piezoelectric thin film near the structural layer, and a second electrode layer formed on the side of the piezoelectric thin film away from the structural layer; wherein, the regions in which the piezoelectric thin film, the first electrode layer, and the second electrode layer overlap in their orthographic projections onto the substrate constitute a piezoelectric driving functional region; the flexible layer is spaced apart from the structural layer in the stacking direction of each layer of the vibrating structure, and its orthographic projection completely covers the slits of the plurality of structural springs; the orthographic projection of the piezoelectric driving functional region onto the substrate is entirely within the cavity; the orthographic projection of the structural fixing portion onto the substrate in the stacking direction of each layer of the vibrating structure does not fall within the cavity; the flexible layer covers the side of the second electrode layer away from the piezoelectric thin film and extends at least partially to the periphery of the second electrode layer.

2. The MEMS piezoelectric loudspeaker as described in claim 1, characterized in that, The first electrode layer includes a first electrode functional part fixed to the structural plate, a first electrode fixing part fixed to the structural fixing part, and a first electrode spring connecting the first electrode functional part and the first electrode fixing part. The first electrode layer and the structural layer have the same shape and structure.

3. The MEMS piezoelectric loudspeaker as described in claim 2, characterized in that, The flexible layer covers the side of the second electrode layer away from the piezoelectric film and extends at least partially to the periphery of the second electrode layer and the piezoelectric film, and is fixed to the surface of the first electrode layer away from the structural layer.

4. The MEMS piezoelectric loudspeaker as described in claim 2, characterized in that, The piezoelectric film includes a piezoelectric functional part fixed to the first electrode functional part, a piezoelectric fixing part fixed to the first electrode fixing part, and a piezoelectric spring connecting the piezoelectric functional part and the piezoelectric fixing part.

5. The MEMS piezoelectric loudspeaker as described in claim 4, characterized in that, The piezoelectric thin film and the structural layer have the same shape and structure.

6. The MEMS piezoelectric loudspeaker as described in claim 1, characterized in that, The structural spring can be any one of the following structures: U-shaped, ring-shaped, or S-shaped.

7. The MEMS piezoelectric loudspeaker as described in claim 1, characterized in that, The piezoelectric thin film is made of any one of aluminum nitride, piezoelectric ceramics, and zinc oxide.

8. The MEMS piezoelectric loudspeaker as described in claim 1, characterized in that, The flexible layer is made of a polymer material.

9. The MEMS piezoelectric loudspeaker as described in claim 8, characterized in that, The polymer is SU-8 photoresist or polyimide.

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