Piezoelectric micro electro mechanical system acoustic sensor

Abstract

The invention discloses a piezoelectric micro electro mechanical system acoustic sensor, which comprises a substrate, a device layer, an oxide layer, a piezoelectric layer and an electrode layer, sequentially laminating the device layer, the oxide layer, the piezoelectric layer and the electrode layer on the substrate; the device layer comprises a cantilever beam array, and the oxide layer is arranged on at least one part of the cantilever beam array; the substrate comprises a cavity, and the cavity penetrates through the substrate. The cantilever beam array can be utilized to form the acoustic sensor with high sensitivity, the acoustic sensor is suitable for various voice application scenes to realize sound sensing in most hearing ranges of human beings, the controllability of the sensitivity of the acoustic sensor is realized, and the acoustic sensor can be widely applied to the technical field of micro electro mechanical systems.

Description

Technical Field

[0001] This application relates to the technical field of microelectromechanical systems, and particularly to a piezoelectric microelectromechanical system acoustic sensor. Background Art

[0002] As one of the most commercially valuable microelectromechanical systems (MEMS) sensors, microphones have been deeply and widely studied since the first prototype device was proposed. Currently, the sensing mechanisms of mainstream commercial microphones are mainly divided into piezoresistive, capacitive, and piezoelectric. Among them, capacitive and piezoelectric microphones have gradually occupied the mainstream microphone market because of their strong compatibility with CMOS processes, high sensitivity, and wide response frequency.

[0003] Piezoelectric MEMS microphones have the following advantages compared with capacitive microphones: higher durability and reliability. Since piezoelectric microphones adopt a solid-state design, compared with the flexible diaphragm in capacitive microphones, they are not easily affected by mechanical stress, dust, or moisture, and are more suitable for harsh environments. In addition, piezoelectric microphones do not require a bias voltage, which simplifies the circuit design. Due to the absence of the common overload distortion phenomenon in capacitive microphones, MEMS piezoelectric microphones perform better when processing high sound pressure level signals. These characteristics make MEMS piezoelectric microphones have significant advantages in certain specific application scenarios, such as wearable devices, Internet of Things sensors, and industrial monitoring.

[0004] Since microphones need to collect sound signals evenly, they need a structure to match their requirements, forming a flat frequency response curve and meeting the 20 kHz bandwidth of human hearing. Therefore, most microphones operate in the flat response range of their vibration structures.

[0005] With the development of artificial intelligence algorithms, voice applications have put forward higher requirements for the signal-to-noise ratio and acquisition directivity of the collected signals. Microphones operating in the flat region of the frequency response range, although able to collect sound signals, cannot meet the higher requirements of technological development and are not applicable to a variety of voice application scenarios.

[0006] Therefore, the above technical problems need to be solved urgently. Summary of the Invention

[0007] The main purpose of the embodiments of this application is to propose a piezoelectric microelectromechanical system acoustic sensor, which can be applicable to a variety of voice application scenarios and achieve controllability of the sensitivity of the acoustic sensor.

[0008] The embodiments of this application propose a piezoelectric microelectromechanical system acoustic sensor, including: a substrate, a device layer, an oxide layer, a piezoelectric layer, and an electrode layer;

[0009] The device layer, the oxide layer, the piezoelectric layer, and the electrode layer are sequentially stacked on the substrate; the device layer includes a cantilever beam array, and the oxide layer is disposed on at least a part of the area of the cantilever beam array; the substrate includes a cavity that penetrates the substrate.

[0010] In some embodiments, the substrate includes a substrate bottom layer, a substrate intermediate layer, and a substrate oxide layer; the substrate intermediate layer and the substrate oxide layer are sequentially stacked on the substrate bottom layer, and the substrate oxide layer is connected to the device layer.

[0011] In some embodiments, the device layer includes a plurality of cantilever beams, and the plurality of cantilever beams are arranged in parallel or crosswise to form the cantilever beam array, and the cantilever beam array is connected to the substrate oxide layer.

[0012] In some embodiments, the oxide layer, the piezoelectric layer, and the electrode layer are sequentially stacked on at least a part of the area of the cantilever beam array, and the piezoelectric layer is disposed on at least another part of the area.

[0013] In some embodiments, the electrode layer includes an acoustic signal readout electrode and a modulation voltage electrode;

[0014] The acoustic signal readout electrode is disposed at a first position on the anchor end of each cantilever beam, and the piezoelectric layer and the acoustic signal readout electrode are sequentially stacked at the first position; the modulation voltage electrode is disposed at a second position on the free end of each cantilever beam, and the piezoelectric layer and the modulation voltage electrode are sequentially stacked at the second position.

[0015] In some embodiments, the material of the piezoelectric layer includes at least any one of aluminum nitride, zinc oxide, or lead zirconate titanate.

[0016] In some embodiments, the cavity penetrates the substrate bottom layer, the substrate oxide layer, and the substrate intermediate layer.

[0017] In some embodiments, the material of the substrate intermediate layer includes at least silicon dioxide, and the material of the substrate bottom layer includes at least an n-type doped silicon wafer.

[0018] In some embodiments, the piezoelectric layer covers the oxide layer and at least a part of the cantilever beam array.

[0019] In some embodiments, the electrode layer includes a ground electrode, the ground electrode is disposed at a third position on the anchor end of the cantilever beam, the acoustic signal readout electrode is located between the ground electrode and the modulation voltage electrode, and the piezoelectric layer and the ground electrode are sequentially stacked at the third position.

[0020] The embodiments of the present application at least include the following beneficial effects: A piezoelectric microelectromechanical system acoustic sensor provided by the present application includes: a substrate, a device layer, an oxide layer, a piezoelectric layer, and an electrode layer. The device layer, the oxide layer, the piezoelectric layer, and the electrode layer are sequentially stacked on the substrate. The device layer includes a cantilever beam array, and an oxide layer is provided on at least a part of the area of the cantilever beam array. The present application can form a highly sensitive acoustic sensor by using the cantilever beam array, which is applicable to a variety of voice application scenarios to realize sound sensing within most of the human auditory range and achieve controllability of the sensitivity of the acoustic sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present invention and used together with the specification to explain the principles of the present invention.

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 is a schematic structural diagram of a piezoelectric microelectromechanical system sensor provided by an embodiment of the present application;

[0024] Figure 2 is a schematic structural diagram of a single cantilever beam in the device layer in an embodiment of the present application;

[0025] Figure 3 is a schematic structural diagram of the device layer in an embodiment of the present application;

[0026] Figure 4 is a schematic preparation process diagram of a preparation method provided by an embodiment of the present application;

[0027] Figure 5 is another schematic preparation process diagram of a preparation method provided by an embodiment of the present application

[0028] Figure 6 is another schematic preparation process diagram of a preparation method provided by an embodiment of the present application;

[0029] Figure 7 is another schematic preparation process diagram of a preparation method provided by an embodiment of the present application;

[0030] Figure 8 is another schematic preparation process diagram of a preparation method provided by an embodiment of the present application;

[0031] Figure 9 is another schematic preparation process diagram of a preparation method provided by an embodiment of the present application. Detailed implementation manners

[0032] To make the objectives, technical solutions and advantages of the present application clearer and more understandable, the present application 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 only used to explain the present application and are not used to limit the present application. When the following description involves the accompanying drawings, unless otherwise indicated, the same numerals in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all implementation manners consistent with the embodiments of the present application. They are only examples of devices and methods consistent with some aspects of the embodiments of the present application as detailed in the appended claims.

[0033] It can be understood that the terms "first", "second", etc. used in the present application can be used in this document to describe various concepts, but unless otherwise specified, these concepts are not limited by these terms. These terms are only used to distinguish one concept from another. For example, without departing from the scope of the embodiments of the present application, the first information can also be referred to as the second information, and similarly, the second information can also be referred to as the first information. Depending on the context, the words "if", "when" as used herein can be interpreted as "when...", "while...", or "in response to determining".

[0034] The terms "at least one", "a plurality of", "each", "any one", etc. used in the present application, at least one includes one, two or more than two, a plurality of includes two or more than two, each refers to each of the corresponding plurality, and any one refers to any one of the plurality.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present application belongs. The terms used herein are only for the purpose of describing the embodiments of the present application and are not intended to limit the present application.

[0036] A piezoelectric microelectromechanical system acoustic sensor provided by an embodiment of the present application, as Figure 1 shown, includes: a substrate 1, a device layer 2, an oxide layer 3, a piezoelectric layer 4, and an electrode layer 5; the device layer 2, the oxide layer 3, the piezoelectric layer 4, and the electrode layer 5 are sequentially stacked on the substrate 1; the device layer 1 includes a cantilever beam array, and the oxide layer 3 is provided on at least a part of the area of the cantilever beam array.

[0037] In some embodiments, as Figure 1As shown, the substrate 1 includes a substrate bottom layer 101, a substrate intermediate layer 102, and a substrate oxide layer 103. The substrate intermediate layer 102 and the substrate oxide layer 103 are stacked in sequence on the substrate bottom layer 101. The substrate oxide layer 103 is connected to the device layer 2. The material of the substrate intermediate layer 102 at least includes silicon dioxide, and the material of the substrate bottom layer 101 at least includes an n-type doped silicon wafer. The substrate 1 includes a cavity 104 that penetrates the substrate 1. Optionally, the cavity 104 penetrates the substrate bottom layer, the substrate oxide layer, and the substrate intermediate layer. Specifically, the RIE etching and DRIE etching are used to etch the substrate oxide layer 103 and the substrate bottom layer 101 to form a partial cavity, and the wet oxidation etching is used to etch the substrate intermediate layer 102 to finally form the cavity 104 to release the cantilever beam array.

[0038] The substrate intermediate layer 102 and the substrate bottom layer 101 are bonded together. Among them, the substrate intermediate layer 102 serves to connect the device layer 2 and the substrate bottom layer 101, and the cavity 104 is used to form a vibration space.

[0039] In some embodiments, as Figure 2 and Figure 3 shown, the device layer 2 includes a plurality of cantilever beams 201. The plurality of cantilever beams 201 are arranged in parallel or crosswise to form a cantilever beam array. The cantilever beam array is connected to the substrate oxide layer 103. As Figure 4 shown, an oxide layer 3, a piezoelectric layer 4, and an electrode layer 5 are stacked in sequence on at least a part of the area of the cantilever beam array, and a piezoelectric layer 4 is provided on at least another part of the area. Specifically, the oxide layer 3 is grown on the device layer 2, a photoresist is covered on the oxide layer 3, and the photoresist is patterned using a mask. The oxide layer 3 is patterned by RIE etching, and a piezoelectric layer 4 is deposited on the oxide layer 3 by reactive sputtering. Through the oxide layer 3 and the piezoelectric layer 4, electrical isolation between the electrode layer 5 and the device layer 2 is achieved.

[0040] The device layer 2 includes a cantilever beam array for realizing the conversion between acoustic energy and mechanical energy and being able to sensitively respond to the change of sound pressure. Exemplarily, the material of the cantilever beam device is an n-type doped silicon wafer, the shape of the cantilever beam 201 is rectangular, and the rectangular properties are controlled by different aspect ratios to control the resonant frequency of the cantilever beam 201. The cantilever beam array is composed of a plurality of cantilever beams 201 with different aspect ratios arranged in parallel.

[0041] The oxide layer 3 is used to achieve electrical isolation, so that the signals output by the acoustic signal readout electrode 502 and the modulation voltage electrode 503 are independent of each other. The oxide layer 3 is patterned and has etching trenches.

[0042] In some embodiments, the material of the piezoelectric layer 4 at least includes any one of aluminum nitride, zinc oxide, or lead zirconate titanate. The piezoelectric layer 4 covers the oxide layer 3 and at least a part of the cantilever beam array.

[0043] The piezoelectric layer 4 is used to realize the conversion between mechanical energy and electrical energy by using the direct and inverse piezoelectric effects. The piezoelectric layer 4 is patterned and covers a part of the cantilever beam array, so that the subsequent electrode layer will not adhere to cause unnecessary connection, and at the same time, the sensitivity is improved.

[0044] In some embodiments, as Figures 1 to 3 shown, the electrode layer 5 includes a ground electrode 501, an acoustic signal readout electrode 502, and a modulation voltage electrode 503. The acoustic signal readout electrode 502 is disposed at a first position on the anchor end of each cantilever beam 201. The piezoelectric layer 4 and the acoustic signal readout electrode 201 are sequentially stacked at the first position. The modulation voltage electrode 503 is disposed at a second position on the free end of each cantilever beam 201. The piezoelectric layer 4 and the modulation voltage electrode 503 are sequentially stacked at the second position. The ground electrode is disposed at a third position on the anchor end of the cantilever beam. The acoustic signal readout electrode 502 is located between the ground electrode 501 and the modulation voltage electrode 503. The piezoelectric layer 4 and the ground electrode 501 are sequentially stacked at the third position.

[0045] Optionally, the electrode layer 5 includes a ground electrode 501, an acoustic signal readout electrode 502, and a modulation voltage electrode 503. Since the cantilever beam generates opposite curvatures near the anchor end during vibration, due to the piezoelectric effect, the opposite curvatures will cause opposite potential differences to be generated on the piezoelectric surface. Therefore, the acoustic signal readout electrode 502 is located at the anchor end on the piezoelectric layer 103, and the modulation voltage electrode 503 is located at the free end position on the piezoelectric layer 4. When the modulation voltage electrode 503 is not connected to an external input, it can be regarded as an acoustic signal detection electrode. At this time, the modulation voltage electrode 503 and the ground electrode 501 receive differential electrical signals, which are generated due to the opposite curvatures generated during the acoustic vibration process. The modulation voltage electrode 503 and the ground electrode 501 read the signals in series or separately, so as to realize the reading of the differential electrical signals caused by the opposite curvatures; when a bias voltage is applied to the modulation voltage electrode 503, the inverse piezoelectric effect is generated, thereby adjusting the internal stress of the cantilever beam and changing its vibration mode, so as to adjust the sensitivity of the acoustic sensor unit; when an AC signal is applied to the modulation voltage electrode 503, while generating the inverse piezoelectric effect, the parametric modulation principle is used to adjust the first local oscillation mode of the cantilever beam. Through parametric modulation, the modulation of the device quality factor is realized. For example, the quality factor of the target resonance peak is enhanced by using Blue Sideband Excitation, or the quality factor of the target resonance peak is reduced by using Red Sideband Excitation. The parametric modulation principle refers to a method of using a specific frequency AC signal loaded on the modulation electrode to form a modulation that can adjust the intrinsic parameters (such as stiffness) of the device through the amplitude and frequency of the modulation signal, thereby adjusting the sensitivity of the device. Red Sideband Excitation refers to that the frequency of the modulation signal is the difference between the first two local oscillation frequencies of the smallest sensing unit of the device, and Blue Sideband Excitation refers to that the frequency of the modulation signal is the sum of the first two local oscillation frequencies of the smallest sensing unit of the device.

[0046] An embodiment of the present application provides a preparation method of a piezoelectric microelectromechanical system acoustic sensor for preparing the above-mentioned microelectromechanical system acoustic sensor. The method may include but is not limited to the following steps:

[0047] Step 1: The piezoelectric microelectromechanical system sensor is prepared based on an N-doped SOI wafer. The layer structure is successively a substrate bottom layer 101, a substrate intermediate layer 102, a substrate oxide layer 103, and a device layer 2. An oxide layer 3 is grown on the device layer 2, a photoresist is covered on the oxide layer 3, and the photoresist is patterned using a mask. The oxide layer 3 is patterned using RIE etching so that the oxide layer 3 can achieve electrical isolation between the electrode layer 2 and the device layer 1, as Figure 4 shown;

[0048] Step 2: Deposit a piezoelectric layer 4 on the oxide layer 3 by reactive sputtering, as Figure 5 shown;

[0049] Step 3: Cover the piezoelectric layer 4 with photoresist, pattern the photoresist using the piezoelectric layer mask, and pattern the piezoelectric thin film by wet etching to prevent unnecessary electrical interconnection due to process tolerance when using a hard mask during the subsequent preparation of the electrode layer 5, and form a contact window that allows the grounded ground electrode 503 to be exposed on the front side. The piezoelectric layer 4 only covers a part of the total length of the cantilever beam, as Figure 6 shown;

[0050] Step 4: Pattern the photoresist with a mask for metal deposition, and deposit the electrode layer 5 by electron beam evaporation. The electrode layer 5 includes a ground electrode 501, an acoustic signal readout electrode 502, and a modulation voltage electrode 503, as Figure 7 shown;

[0051] Step 5: Coat photoresist on the top of the wafer of the N-doped SOI wafer again, then pattern the photoresist using a light field SOI mask, complete the etching of the oxide layer under the guidance of the patterned photoresist using RIE, complete the etching of the device layer 2 under the guidance of the patterned photoresist using DRIE, remove the photoresist, and form an array structure of cantilever beams of the device layer, as Figure 8 shown;

[0052] Step 6: Use RIE etching and DRIE etching to etch the substrate oxide layer 101 and the substrate bottom layer 102 in the substrate 1 to form partial cavities. Then, use wet oxidation etching to etch the substrate intermediate layer 103 in the substrate 1 to finally form a cavity 104 to release the array structure of cantilever beams, as Figure 9 shown.

[0053] A piezoelectric microelectromechanical system acoustic sensor provided by an embodiment of the present application has the characteristics of both high sensitivity and adjustable performance. Compared with traditional diaphragm piezoelectric acoustic sensors, it can effectively adjust the sensitivity and working range of the acoustic sensor by controlling the applied bias voltage and modulation signal, has adjustable characteristics, can selectively suppress or enhance the sensitivity, can be applied to a variety of voice application scenarios, the manufacturing process is simple and easy to implement, it can be applied to noisy environments, and occasions that require high audio fidelity. It improves the performance and fidelity of MEMS-sized acoustic sensors to electret acoustic sensors, expands the application scenarios of MEMS acoustic sensors. For example, combined with artificial intelligence algorithms, the performance of the acoustic sensor is further adjusted using subsequent circuits, greatly expanding the voice application scenarios of the acoustic sensor, and can be used in new technology scenarios such as intelligent human voice detection and recognition, hearing aid whistle detection and suppression, and frequency-shifting hearing aids.

[0054] A piezoelectric microelectromechanical system acoustic sensor provided by an embodiment of the present application is based on the principle of the combined action of the direct and inverse piezoelectric effects and the parameter modulation principle, uses a combination of new sensing mechanisms, combines acoustic detection and mechanical drive with a simple structure, can read differential acoustic signals through opposite curvatures through electrode settings, and applies a voltage to adjust the strain stress of the cantilever beam of the acoustic sensor, change the vibration mode of the cantilever beam, or adjust the quality factor or operating frequency band of the device through parameter modulation, thereby realizing the adjustability of the performance of the acoustic sensor at the mechanical level and greatly expanding the voice application scenarios of the acoustic sensor.

[0055] The embodiments described in the embodiments of the present application are for more clearly explaining the technical solutions of the embodiments of the present application and do not constitute a limitation on the technical solutions provided by the embodiments of the present application. Those skilled in the art know that with the evolution of technology and the emergence of new application scenarios, the technical solutions provided by the embodiments of the present application are equally applicable to similar technical problems.

[0056] Those skilled in the art can understand that the technical solutions shown in the figures do not constitute a limitation on the embodiments of the present application, and may include more or fewer steps than those shown, or combine certain steps, or different steps.

[0057] The preferred embodiments of the embodiments of the present application have been described above with reference to the drawings, but this does not limit the scope of rights of the embodiments of the present application. Any modifications, equivalent replacements, and improvements made by those skilled in the art without departing from the scope and essence of the embodiments of the present application shall be within the scope of rights of the embodiments of the present application.

Claims

1. A piezoelectric microelectromechanical system acoustic sensor, characterized in that, Comprising: a substrate, a device layer, an oxide layer, a piezoelectric layer, and an electrode layer; The device layer, the oxide layer, the piezoelectric layer, and the electrode layer are sequentially stacked on the substrate; the device layer includes a cantilever beam array, and the oxide layer is provided on at least a part of the area of the cantilever beam array; the substrate includes a cavity that penetrates the substrate.

2. The piezoelectric MEMS acoustic sensor according to claim 1, wherein The substrate includes a substrate bottom layer, a substrate intermediate layer, and a substrate oxide layer; the substrate intermediate layer and the substrate oxide layer are sequentially stacked on the substrate bottom layer, and the substrate oxide layer is connected to the device layer.

3. The piezoelectric MEMS acoustic sensor according to claim 2, wherein, The device layer includes a plurality of cantilever beams, and the plurality of cantilever beams are arranged in parallel or crosswise to form the cantilever beam array, and the cantilever beam array is connected to the substrate oxide layer.

4. The piezoelectric MEMS acoustic sensor according to claim 3, wherein The oxide layer, the piezoelectric layer, and the electrode layer are sequentially stacked on at least a part of the area of the cantilever beam array, and the piezoelectric layer is provided on at least another part of the area.

5. The piezoelectric MEMS acoustic sensor according to claim 4, characterized in that The electrode layer includes an acoustic signal readout electrode and a modulation voltage electrode; The acoustic signal readout electrode is disposed at a first position on the anchor end of each cantilever beam, and the piezoelectric layer and the acoustic signal readout electrode are sequentially stacked at the first position; the modulation voltage electrode is disposed at a second position on the free end of each cantilever beam, and the piezoelectric layer and the modulation voltage electrode are sequentially stacked at the second position.

6. The piezoelectric MEMS acoustic sensor according to claim 1, characterized in that, The material of the piezoelectric layer includes at least any one of aluminum nitride, zinc oxide, or lead zirconate titanate.

7. The piezoelectric MEMS acoustic sensor according to claim 2, wherein, The cavity penetrates the substrate bottom layer, the substrate oxide layer, and the substrate intermediate layer.

8. The piezoelectric MEMS acoustic sensor according to claim 2, wherein The material of the substrate intermediate layer includes at least silicon dioxide, and the material of the substrate bottom layer includes at least an n-type doped silicon wafer.

9. The piezoelectric MEMS acoustic sensor according to claim 4, wherein The piezoelectric layer covers the oxide layer and at least a part of the cantilever beam array.

10. The piezoelectric MEMS acoustic sensor according to claim 4, characterized in that The electrode layer includes a ground electrode, the ground electrode is disposed at a third position on the anchor end of the cantilever beam, the acoustic signal readout electrode is located between the ground electrode and the modulation voltage electrode, and the piezoelectric layer and the ground electrode are sequentially stacked at the third position.

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