A piezoelectric MEMS loudspeaker

Abstract

This application discloses a piezoelectric MEMS loudspeaker, comprising: a substrate having a cavity; a vibration support layer formed above the substrate and covering the cavity; a first electrode layer formed above the vibration support layer; a piezoelectric layer formed above the first electrode layer; and a second electrode layer formed above the piezoelectric layer. A first groove extends from the upper surface of the second electrode layer to the upper surface of the vibration support layer and exposes the vibration support layer. The exposed vibration support layer has a second groove extending from the upper surface of the vibration support layer to the lower surface of the vibration support layer. The piezoelectric MEMS loudspeaker structure provided in this application is divided into two parts: an edge portion of a tweeter and a center portion of a woofer, and a hollowed-out vibration support layer connecting the two, thereby improving the auditory effect across the entire frequency range.

Description

Technical Field

[0001] This application relates to the field of micromechanical technology, and more specifically, to a piezoelectric MEMS (Micro-Electro-Mechanical System) loudspeaker. Background Technology

[0002] A piezoelectric MEMS loudspeaker is a small electroacoustic device that uses piezoelectric materials as sound conversion elements. It works by utilizing the inverse piezoelectric effect: by inputting a voltage signal to a diaphragm containing piezoelectric material, the diaphragm vibrates, causing the diaphragm and surrounding air to vibrate and radiate sound. Compared to traditional moving-coil loudspeakers, piezoelectric MEMS loudspeakers offer advantages such as small size, low power consumption, simple manufacturing process, and low cost, making them widely applicable to various portable electronic devices.

[0003] Currently, most piezoelectric MEMS loudspeakers have poor low-frequency response and uneven sound pressure level frequency response curves, which affects the user's listening experience. Summary of the Invention

[0004] In response to the problems in related technologies, this application proposes a method to obtain a flat sound pressure level frequency response curve.

[0005] The technical solution of this application is implemented as follows:

[0006] According to one aspect of this application, a piezoelectric MEMS loudspeaker is provided, comprising:

[0007] Substrate with a cavity;

[0008] A vibration support layer is formed above the substrate and covers the cavity;

[0009] A first electrode layer is formed above the vibration support layer;

[0010] A piezoelectric layer is formed above the first electrode layer;

[0011] A second electrode layer is formed above the piezoelectric layer;

[0012] The first groove extends from the upper surface of the second electrode layer to the upper surface of the vibration support layer and exposes the vibration support layer. The exposed vibration support layer has a second groove that extends from the upper surface of the vibration support layer to the lower surface of the vibration support layer.

[0013] From a top view, the first groove is annular, and the projection area of ​​the first groove is within the projection area of ​​the cavity.

[0014] The second groove is connected to the cavity.

[0015] The first groove divides the first electrode layer, the piezoelectric layer, and the second electrode layer into a central portion and an edge portion, and the exposed vibration support layer connects the central portion and the edge portion.

[0016] The piezoelectric MEMS loudspeaker further includes a blocking block formed below and / or above the exposed vibration support layer, and the blocking block is formed between the central portion and the edge portion.

[0017] The blocking block is ring-shaped.

[0018] The piezoelectric MEMS loudspeaker structure provided in this application consists of two parts: the edge part of the tweeter and the center part of the woofer, as well as a hollowed-out vibration support layer connecting the two. The tweeter part has a poor low-frequency sound pressure level response, which the woofer part can compensate for to some extent, thereby improving the overall low-frequency sound pressure level of the structure and giving it a wider and flatter sound pressure level frequency response curve, thus improving the auditory effect across the entire frequency range. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A perspective view of a piezoelectric MEMS loudspeaker structure provided according to some embodiments is shown;

[0021] Figure 2 A cross-sectional perspective view of a piezoelectric MEMS loudspeaker structure provided according to some embodiments is shown;

[0022] Figure 3 A top view of a piezoelectric MEMS loudspeaker structure provided according to some embodiments is shown;

[0023] Figure 4 The sound pressure level frequency response curves for the edge and center portions of a piezoelectric MEMS loudspeaker are shown under specific material and size parameters.

[0024] Figure 5 The sound pressure level frequency response curves of the piezoelectric MEMS loudspeaker structure are shown under specific material and size parameters. Detailed Implementation

[0025] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0026] According to embodiments of this application, a piezoelectric MEMS loudspeaker is provided, capable of improving low-frequency sound pressure levels and possessing a wider and flatter sound pressure level frequency response curve. This piezoelectric MEMS loudspeaker can, but is not limited to, use other sensors or actuators, such as microphones or ultrasonic sensors. See also Figure 1 , Figure 2 and Figure 3 The piezoelectric MEMS loudspeaker includes a substrate 10, a vibration support layer 21, a first electrode layer 22, a piezoelectric layer 23, and a second electrode layer 24. Details will be described in detail below.

[0027] The substrate 10 has a cavity 11. The substrate 10 comprises silicon or any suitable silicon-based compound or derivative (e.g., silicon wafer, SOI, polycrystalline silicon on SiO2 / Si).

[0028] A vibration support layer 21 is formed above the substrate 10 and covers the cavity 11. In some embodiments, the vibration support layer 21 includes a single-layer or multi-layer composite film structure made of silicon nitride (Si3N4), silicon oxide, monocrystalline silicon, polycrystalline silicon, or other suitable support material.

[0029] A first electrode layer 22 is formed above a vibration support layer 21. A piezoelectric layer 23 is formed above the first electrode layer 22. A second electrode layer 24 is formed above the piezoelectric layer 23. In some embodiments, the piezoelectric layer 23 includes zinc oxide, aluminum nitride, an organic piezoelectric film, lead zirconate titanate (PZT), a perovskite piezoelectric film, or other suitable materials. The first electrode layer 22 and the second electrode layer 24 include aluminum, gold, platinum, molybdenum, titanium, chromium, and composite films thereof, or other suitable materials. The first electrode layer 22 and the second electrode layer 24 can transmit voltage signals to the piezoelectric layer 23, which can convert the voltage into deformation, thereby causing the surrounding air to vibrate and radiate sound pressure.

[0030] It is worth noting that the first groove 26 extends from the upper surface of the second electrode layer 24 to the upper surface of the vibration support layer 21 and exposes the vibration support layer 21. In some embodiments, from a top view, the first groove 26 is annular, and the projected area of ​​the first groove 26 is within the projected area of ​​the cavity 11. In some embodiments, the first groove 26 may have other shapes. The first groove 26 divides the first electrode layer 22, the piezoelectric layer 23, and the second electrode layer 24 into a central portion 20b and an edge portion 20a, and the exposed vibration support layer 21 connects the central portion 20b and the edge portion 20a. The edge portion 20a is used to generate high-frequency sound pressure level, and the central portion 20b is used to improve the low-frequency sound pressure level response. This application widens the flat range of the sound pressure level frequency response curve by combining the edge portion 20a and the central portion 20b.

[0031] The exposed vibration support layer 21 has a second groove 27 extending from the upper surface to the lower surface of the vibration support layer 21. The second groove 27 communicates with the cavity 11. This application forms a perforated vibration support layer 21 by providing the second groove 27 on the vibration support layer 21. The perforated vibration support layer 21 has lower bending and tensile stiffness to prevent continuous bending moments between the edge portion 20a and the center portion 20b.

[0032] The piezoelectric MEMS loudspeaker also includes a blocking block 25 formed below or above the exposed vibration support layer 21, and the blocking block 25 is formed between the central portion 20b and the edge portion 20a. In some embodiments, the blocking block 25 is annular. In some embodiments, the blocking block 25 may be square or other suitable shapes. It is worth noting that... Figure 2 The piezoelectric MEMS loudspeaker shown only illustrates a blocking block 25 formed below the exposed vibration support layer 21. In some embodiments, the blocking block 25 may be formed above the exposed vibration support layer 21. Alternatively, the blocking block 25 may be both above and below the exposed vibration support layer 21. When the blocking block 25 is on top, the material of the blocking block 25 may be the material of the piezoelectric layer 23.

[0033] The function of the blocking block 25 is to align the edge stiffness of the central portion 20b with the fixed boundary conditions, thereby maintaining the resonant frequency of the central portion 20b consistent with that of the fixed boundary. Since the resonant frequencies of the edge portion 20a and the central portion 20b differ significantly, this application physically connects the edge portion 20a and the central portion 20b through a perforated vibration support layer 21, and uses the blocking block 25 to achieve the blocking separation of the edge portion 20a and the central portion 20b during vibration. In some embodiments, the gap width of the second groove 27 of the perforated vibration support layer 21 is less than or equal to 5 μm to prevent sound leakage. The first electrode layer 22, piezoelectric layer 23, and second electrode layer 24 of the central portion 20b are suspended above the cavity 11 to generate a larger amplitude and sound pressure level.

[0034] Figure 4 and Figure 5 represent Figure 1 The sound pressure level frequency response curves (SPR) of the low-frequency and high-frequency components of a piezoelectric MEMS loudspeaker, as well as the overall SPR of the structure, are presented under specific material and dimensional parameters. Specifically, the cavity 11 of the substrate 10 has a radius of 0.5 cm, the distance between the inner and outer edges of the edge portion 20a is 0.1 cm, the distance between the edge portion 20a and the center portion 20b is 20 μm, the gap width of the second groove 27 is 5 μm, the thickness of the vibration support layer 21 is 7 μm, the thickness of the piezoelectric layer 23 is 2 μm, and the thickness of the first electrode layer 22 and the second electrode layer 24 is 0.1 μm. The radius of the piezoelectric layer 23 in the center portion 20b is 0.27 cm, and the height and radial thickness of the blocking block 25 are both 100 μm. The vibration support layer 21 is made of silicon (Si), the piezoelectric layer 23 is made of piezoelectric ceramic (PZT), and the first electrode layer 22 and the second electrode layer 24 are made of aluminum (Al). A voltage of 2V was applied, and the sound pressure level was measured at a distance of 5cm from the center of the top surface of the central part 20b.

[0035] from Figure 4 The sound pressure level frequency response curves show that the edge portion 20a has a higher sound pressure level at high frequencies, but experiences significant attenuation at low frequencies. Conversely, the central portion 20b has a higher sound pressure level at low frequencies. Therefore, the edge portion 20a and the central portion 20b can work together, with the central portion 20b operating at frequencies from 0Hz to 3900Hz, and the edge portion 20a operating at frequencies from 3900Hz to 20000Hz. Figure 5 This corresponds to the overall sound pressure level frequency response curve of the piezoelectric MEMS loudspeaker. It can be seen that the overall sound pressure level in the low-frequency region is increased by more than 20dB, and the output sound pressure level reaches more than 80dB in the 1000Hz-20000Hz range, thereby improving the listening effect across the entire frequency band.

[0036] This only presents the sound pressure level frequency response curve for a structure with specific dimensions and material parameters. It is intended to illustrate the working principle and does not represent the optimal result. The dimensions and material parameters of the structure can be adjusted as needed to obtain higher sound pressure level output and a wider frequency range with a flatter sound pressure level frequency response curve.

[0037] The piezoelectric MEMS loudspeaker structure provided in this application consists of two parts: an edge portion 20a of a tweeter and a center portion 20b of a woofer, as well as a hollowed-out vibration support layer 21 connecting the two. The tweeter portion has a poor low-frequency sound pressure level response, which the woofer portion can compensate for to some extent, thereby improving the overall low-frequency sound pressure level of the structure and giving it a wider and flatter sound pressure level frequency response curve, thus improving the auditory effect across the entire frequency range.

[0038] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A piezoelectric MEMS loudspeaker, characterized in that, include: Substrate with a cavity; A vibration support layer is formed above the substrate and covers the cavity; A first electrode layer is formed above the vibration support layer; A piezoelectric layer is formed above the first electrode layer; A second electrode layer is formed above the piezoelectric layer; The first groove extends from the upper surface of the second electrode layer to the upper surface of the vibration support layer and exposes the vibration support layer. The exposed vibration support layer has a second groove that extends from the upper surface of the vibration support layer to the lower surface of the vibration support layer. The second groove is connected to the cavity, and a hollow vibration support layer is formed by setting the second groove on the vibration support layer. From a top view, the first groove is annular, and the projection area of ​​the first groove is within the projection area of ​​the cavity. The first groove divides the first electrode layer, the piezoelectric layer, and the second electrode layer into a central part and an edge part, and the exposed vibration support layer connects the central part and the edge part.

2. The piezoelectric MEMS loudspeaker according to claim 1, characterized in that, The piezoelectric MEMS loudspeaker also includes a blocking block formed below and / or above the exposed vibration support layer, and the blocking block is formed between the central portion and the edge portion.

3. The piezoelectric MEMS loudspeaker according to claim 2, characterized in that, The blocking block is ring-shaped.

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