A piezoelectric MEMS loudspeaker and a performance improvement method thereof

Abstract

The application discloses a piezoelectric MEMS loudspeaker and a performance improvement method thereof, and belongs to the field of MEMS loudspeakers. The application first proposes a cantilever beam structure with a fixed support end perforation, and the structure can change the resonant frequency of the device. Further, based on the structure, the piezoelectric MEMS loudspeaker proposed in the application is composed of a plurality of triangular cantilever beams with different fixed support end perforations. Since the displacement of the triangular cantilever beam at the resonant frequency will be phase-inverted, the driving voltages of various triangular cantilever beams at both sides of the respective resonant frequencies should be opposite. Through the optimization design of the cantilever beam structure, compared with the traditional piezoelectric MEMS loudspeaker, the application can improve the sound pressure level output at the design frequency band without additional process difficulty, make the sound pressure level spectrum curve in the human ear hearing threshold frequency band relatively flat, realize compact layout, and has a good application prospect.

Description

Technical Field

[0001] This invention belongs to the field of MEMS loudspeaker technology, and more specifically, relates to a piezoelectric MEMS loudspeaker and a method for improving its performance. Background Technology

[0002] MEMS stands for Micro-Electro-Mechanical Systems, referring to miniature systems fabricated using microfabrication techniques. These systems have structures on the micrometer or even nanometer scale and integrate components such as microsensors, microactuators, and microelectronic signal processing and control circuits. Piezoelectric MEMS loudspeakers are miniature loudspeaker devices that operate within the range of human hearing, driven by the inverse piezoelectric effect and manufactured using MEMS technology. Due to their outstanding advantages of small size, simple structure, low power consumption, high driving force, and low cost, piezoelectric MEMS loudspeakers are expected to replace traditional loudspeakers as the next generation of high-performance loudspeakers.

[0003] However, existing piezoelectric MEMS loudspeakers have low output sound pressure levels in the mid-to-low frequency range and their sound pressure level spectrum curves are not flat enough. Summary of the Invention

[0004] To address the shortcomings and improvement needs of existing technologies, this invention provides a piezoelectric MEMS loudspeaker and a method for improving its performance. Through a specific design, multiple cantilever beam structures with different resonant frequencies are combined to form a piezoelectric MEMS loudspeaker, which can solve the technical problems of low output sound pressure level and uneven sound pressure level spectrum curve in the mid-to-low frequency range of existing piezoelectric MEMS loudspeakers.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a piezoelectric MEMS loudspeaker, comprising a piezoelectric multilayer film and a substrate, wherein the piezoelectric multilayer film comprises multiple cantilever beams with different resonant frequencies.

[0006] Furthermore, the parameters of each layer of material in the thickness direction of each cantilever beam remain consistent.

[0007] Furthermore, the substrate has a cavity, the piezoelectric multilayer film is formed on the substrate, and each of the cantilever beams has a fixed end and a free end, the fixed end being connected to the substrate and the free end being suspended above the cavity.

[0008] Furthermore, by changing the contact area between the fixed end of each cantilever beam and the substrate, the resonant frequencies of each cantilever beam are made different.

[0009] Furthermore, by drilling holes at the fixed ends of each cantilever beam, the contact area between the fixed ends of each cantilever beam and the substrate is changed.

[0010] Furthermore, by changing the material parameters of each cantilever beam, the resonant frequencies of each cantilever beam are made different.

[0011] In a second aspect, the present invention provides a method for improving the performance of the piezoelectric MEMS loudspeaker described in the first aspect, wherein when each of the cantilever beams operates on both sides of its corresponding resonant frequency, the corresponding applied driving voltage is out of phase.

[0012] In summary, the above-described technical solutions conceived in this invention can achieve the following beneficial effects:

[0013] (1) Compared to traditional piezoelectric MEMS loudspeakers, which are usually composed of multiple identical cantilever beam structures, the cantilever beam structures of the piezoelectric MEMS loudspeaker in this invention do not need to be identical. They can be composed of a mixture of cantilever beam structures with different resonant frequencies. In this way, without increasing the difficulty of the manufacturing process, the sound pressure level of a single piezoelectric MEMS loudspeaker at the design frequency band can be improved by mixing, and the sound pressure level spectrum curve in the human hearing threshold frequency band is relatively flat.

[0014] (2) The cantilever beams of this invention have similar external dimensions, but the material parameters of each layer in the thickness direction must be consistent. In this way, the fabrication process of the entire piezoelectric MEMS loudspeaker is the same, easy to control, and can achieve a compact layout.

[0015] (3) Based on the provided piezoelectric MEMS loudspeaker, this invention proposes a method to improve its performance, namely, when each cantilever beam operates on both sides of its corresponding resonant frequency, the corresponding applied driving voltage is out of phase. This ensures that each cantilever beam always maintains the same direction of motion to obtain the maximum volume of air pushed. Attached Figure Description

[0016] Figure 1 This is one of the schematic diagrams of a piezoelectric MEMS loudspeaker structure provided in an embodiment of the present invention, wherein the left structure includes four different triangular cantilever beams, and the right structure includes six triangular cantilever beams with three different structures.

[0017] Figure 2 The second schematic diagram of the piezoelectric MEMS loudspeaker structure provided in the embodiment of the present invention includes four triangular cantilever beams with two different structures.

[0018] Figure 3 The third schematic diagram of the piezoelectric MEMS loudspeaker structure provided in this embodiment of the invention includes four identical triangular cantilever beams with complete fixed ends. Figure 2 The sound output performance of the example shown is compared to reference group 1.

[0019] Figure 4The fourth schematic diagram of the piezoelectric MEMS loudspeaker structure provided in this embodiment of the invention includes four identical triangular cantilever beams, each with holes drilled at its fixed end to form three sets of support structures. Figure 2 The sound output performance of the example shown is compared to reference group 2.

[0020] Figure 5 for Figure 2 The diagram shows the method of applying driving voltage to the piezoelectric MEMS speaker structure.

[0021] Figure 6 To simulate using COMSOL Multiphysics 5.6 software Figure 2 , Figure 3 , Figure 4 The sound pressure level spectrum curve of the piezoelectric MEMS loudspeaker structure shown is obtained from simulation in a human simulated ear canal model under a driving voltage of 40Vpp. Detailed Implementation

[0022] 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. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0023] In this invention, the terms "first," "second," etc. (if present) in the invention and the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0024] See Figure 1 This invention provides a piezoelectric MEMS loudspeaker, which can be composed of a mixture of multiple different types of cantilever beam structures, such as... Figure 1 The two structures shown consist of four distinct triangular cantilever beams and six triangular cantilever beams containing three different structures, respectively. This design employs a method of drilling holes at the fixed support ends of the triangular cantilever beams. That is, the fixed support ends of the triangular cantilever beams are no longer complete; instead, they are supported by structures formed between the two holes, with each set of supports corresponding to two hole structures. The only difference between the different types of triangular cantilever beams lies in the number of supports at the fixed support ends; all other aspects, such as external dimensions and material parameters for each layer in the thickness direction, remain consistent.

[0025] It is understandable that the resonant frequency of a cantilever beam with a complete fixed support end is relatively the highest. By drilling holes in the fixed support end of the cantilever beam, its resonant frequency can be changed; and, with the same hole structure, the more holes and the more supports at the fixed support end, the higher the resonant frequency will be relative to a cantilever beam with fewer supports.

[0026] Furthermore, it should be noted that besides achieving different resonant frequencies for each cantilever beam through drilling, the material parameters of each cantilever beam can also be changed to achieve different resonant frequencies. However, considering the simplicity of the manufacturing process, the preferred approach is to maintain consistent material parameters across all layers in the thickness direction for each cantilever beam and achieve different resonant frequencies through drilling.

[0027] See Figure 2 The design consists of four triangular cantilever beams with two different structures. This example also utilizes... Figure 1 The design mentioned above, involving drilling holes at the fixed support ends, involves two triangular cantilever beams using complete fixed support ends, and two other triangular cantilever beams using drilled holes at their fixed support ends to form a three-set support structure. In terms of layout, a symmetrical distribution is adopted, meaning triangular cantilever beams with different structures are placed adjacent to each other, while those with the same structure are placed alternately.

[0028] Furthermore, such as Figure 2 As shown, in terms of external dimensions, the piezoelectric MEMS loudspeaker, formed by these four cantilever beams, has a square shape with a diagonal length of 3mm and a slit width of 5μm between adjacent cantilever beams. At the perforated structure, the hole diameter is 50μm, and the support portion between two holes is 30μm wide. Regarding material selection, the piezoelectric MEMS loudspeaker in this example uses AlN as the piezoelectric layer material with a thickness of 1μm, while the support layer uses Si material with a thickness of 5μm.

[0029] The sound pressure output of a piezoelectric MEMS loudspeaker is positively correlated with the volume of air pushed by the cantilever beams. Therefore, to achieve higher sound pressure output, traditional piezoelectric MEMS loudspeakers typically use in-phase voltage driving to ensure that each cantilever beam displaces in the same direction. In this invention, the cantilever beams of different designs correspond to different resonant frequencies. At these resonant frequencies, the cantilever beam displacement exhibits phase reversal. Therefore, if the cantilever beams continue to be driven by in-phase voltage, the displacements may reverse, which is generally detrimental to the sound output performance of the piezoelectric MEMS loudspeaker. Therefore, the cantilever beams should not always be driven by in-phase voltage; instead, the driving voltages should be out of phase when the cantilever beams operate at their respective resonant frequencies. That is, if the resonant frequency of a certain cantilever beam structure is f0, then the driving voltage for the cantilever beam operating at frequencies above f0 should be out of phase with its driving voltage operating at frequencies below f0. The same principle applies to cantilever beams of other structures, driven by their respective resonant frequencies. This ensures that the cantilever beams always move in the same direction to maximize the volume of air pushed. Figure 5 for Figure 2 The diagram shows the driving voltage application method of the piezoelectric MEMS loudspeaker structure, where the driving voltages are out of phase when the two cantilever beams operate at frequencies above and below their respective resonant frequencies. Under this voltage-driven method, by designing the structure of each cantilever beam of the piezoelectric MEMS loudspeaker to have multiple resonant peaks when operating within the range of human hearing threshold, a relatively flat sound pressure level spectrum curve can be obtained.

[0030] Finally, based on the COMSOL Multiphysics 5.6 simulation software, the simulation was performed... Figure 2 , Figure 3 , Figure 4 The piezoelectric MEMS speaker structure shown was simulated in a human simulated ear canal model under a 40Vpp driving voltage, and the results were as follows. Figure 6 The sound pressure level spectrum curve is shown. Compared with the two sets of reference structures, this invention achieves a considerable improvement in the mid-frequency sound pressure level output by sacrificing a small amount of high-frequency sound pressure level, and makes the sound pressure level spectrum curve in the human hearing threshold band relatively flat, thereby improving the sound output performance of the piezoelectric MEMS loudspeaker.

[0031] In summary, this invention, through a specific design, combines various cantilever beam structures with different resonant frequencies to form a piezoelectric MEMS loudspeaker. In practical applications, the number of cantilever beams, the types of cantilever beams, and the resonant frequencies of various cantilever beams can be designed according to actual needs to achieve better sound output performance.

[0032] Those skilled in the art will readily understand that the above description is merely 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 scope of protection of the present invention.

Claims

1. A piezoelectric MEMS speaker comprising a piezoelectric multilayer film and a substrate, characterized by, The piezoelectric multilayer film includes a plurality of cantilever beams with different resonance frequencies. The contact area between the fixed end of each cantilever beam and the substrate is changed by punching a hole in the fixed end of each cantilever beam.

2. The piezoelectric MEMS loudspeaker of claim 1, wherein, The parameters of each layer of material in the thickness direction of each cantilever beam are consistent.

3. The piezoelectric MEMS loudspeaker of claim 1, wherein, The substrate has a cavity, and the piezoelectric multilayer film is formed above the substrate, each cantilever beam has a fixed end and a free end, the fixed end is connected to the substrate, and the free end is suspended above the cavity.

4. The piezoelectric MEMS loudspeaker of claim 3, wherein, The resonance frequencies of each cantilever beam are different by changing the contact area between the fixed end of each cantilever beam and the substrate.

5. The piezoelectric MEMS loudspeaker of claim 1, wherein, The resonance frequencies of each cantilever beam are different by changing the material parameters of each cantilever beam.

6. A method of improving the performance of the piezoelectric MEMS loudspeaker of any one of claims 1 to 5, characterized in that, When each cantilever beam operates on both sides of the corresponding resonance frequency, the corresponding applied driving voltage is reversed.

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