Piezoelectric micro electro mechanical system microphone and preparation method and application thereof

Abstract

The invention discloses a piezoelectric micro-electro-mechanical system microphone and a preparation method and application thereof, and belongs to the technical field of micro-electro-mechanical systems. The piezoelectric micro-electro-mechanical system microphone provided by the invention comprises a substrate, a vibrating diaphragm, an oxide layer, a piezoelectric layer and an electrode layer which are stacked in sequence, a cavity is formed in the base, and the cavity penetrates through the base; the electrode layer comprises an inner electrode, an outer electrode, a strip-shaped electrode and a bias applying electrode; the outer electrode is arranged outside the inner electrode in a surrounding mode, the strip-shaped electrode is arranged between the inner electrode and the outer electrode in a surrounding mode, and the bias applying electrode is connected with the strip-shaped electrode. Based on the principle of combined action of positive and inverse piezoelectric effects, bias voltage can be applied through the strip-shaped electrodes to adjust the strain stress of the vibrating diaphragm of the microphone and change the vibration mode of the vibrating diaphragm, so that the sensitivity of the microphone at the mechanical level is improved, and the microphone has the advantage of wide band and can output stronger electric signals.

Description

Technical Field

[0001] The present invention belongs to the technical field of micro-electromechanical systems, and in particular relates to a piezoelectric micro-electromechanical system microphone and a preparation method and application thereof. Background Art

[0002] As one of the most commercially valuable micro-electro-mechanical systems (MEMS) sensors, microphones have been studied in depth and extensively since the first prototype device was proposed. At present, 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 due to their strong compatibility with CMOS processes, high sensitivity, and wide response frequency. Generally speaking, capacitive MEMS microphones are composed of gap-closed sensing electrodes (including deformable / movable electrodes and fixed reference electrodes). Therefore, the air damping effect is a design consideration for gap-closed electrodes. The design of capacitive sensing electrodes trades off between the sensing area and the vent area to reduce air damping. In addition, the small air gap of capacitive sensing is very susceptible to water and dust particles. This is a critical design issue for the growing microphone array application, because damage to a single microphone may cause the entire array to lose its function. In addition to capacitive sensing MEMS microphones, piezoelectric MEMS microphones that do not require a backplate and a sensing gap have also attracted attention in recent years. For piezoelectric microphones, although many designs are currently used to improve the sensitivity of the microphone, such as increasing the sensitivity by adding gaps on the thin film structure or the fixed beams at both ends, or increasing the local strain through cantilever beams (fixed at one end), the gap structure is also an effective way to release the residual stress generated by the thin film process. However, since the gap structure causes the pressure difference on both sides of the membrane to decrease, the gap structure on the plane inevitably reduces the performance of the microphone in the low-frequency area. In summary, for traditional microphones, whether using piezoelectric or capacitive sensing mechanisms, how to balance high sensitivity, bandwidth, and device energy consumption is always a topic for microphone designers. Summary of the invention

[0003] In order to overcome at least one of the problems existing in the above-mentioned prior art, one of the objectives of the present invention is to provide a piezoelectric micro-electromechanical system microphone, which can enhance the linear sensitivity by adjusting the membrane structure stress without sacrificing the bandwidth.

[0004] A second objective of the present invention is to provide a method for preparing the above-mentioned piezoelectric MEMS microphone.

[0005] A third objective of the present invention is to provide an application of the above-mentioned piezoelectric MEMS microphone.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A first aspect of the present invention provides a piezoelectric micro-electromechanical system microphone, comprising: a substrate, a diaphragm, an oxide layer, a piezoelectric layer and an electrode layer stacked in sequence;

[0008] A cavity is provided in the substrate, and the cavity penetrates the substrate;

[0009] The electrode layer includes an inner electrode, an outer electrode, a strip electrode and a bias electrode; the outer electrode is arranged around the outside of the inner electrode, the strip electrode is arranged around between the inner electrode and the outer electrode, and the bias electrode is connected to the strip electrode.

[0010] The inventive concept of the present invention is: a bias voltage can be applied using a strip electrode, thereby utilizing the inverse piezoelectric effect to adjust the internal stress of the diaphragm, change the vibration mode of the diaphragm, and thus adjust the sensitivity of the microphone. The enhancement of the sensitivity of the microphone of the present invention is different from the common method of adding gaps to the microphone diaphragm. The microphone structure of the present invention retains the integrity of the diaphragm, and therefore has the advantage of a wide bandwidth. Due to the introduction of the inverse piezoelectric effect, the defect of low sensitivity of traditional diaphragm microphones and cantilever beam microphones is overcome. The microphone of the present invention can effectively adjust the sensitivity of the microphone by controlling the external bias voltage through the combined action of the positive and inverse piezoelectric effects. Without sacrificing the bandwidth, the linear sensitivity is enhanced by adjusting the stress of the membrane structure, providing more possibilities for the application scenarios of the microphone.

[0011] Preferably, the inner electrode is located at the center of the piezoelectric layer, and the outer electrode is located at the periphery of the piezoelectric layer, and a differential electrical signal is received through the inner electrode and the outer electrode, and the differential electrical signal is generated due to the opposite curvature generated during the acoustic vibration process.

[0012] Preferably, the strip electrode is used to apply a bias voltage to generate an inverse piezoelectric effect, thereby adjusting the diaphragm stress.

[0013] Preferably, the substrate comprises a substrate oxide layer, a substrate bottom layer and a substrate intermediate layer which are stacked in sequence. The substrate intermediate layer is connected to the diaphragm.

[0014] Preferably, the material of the base oxide layer is selected from silicon dioxide.

[0015] Preferably, the material of the substrate bottom layer is selected from n-type doped silicon wafer.

[0016] Preferably, the material of the substrate intermediate layer is selected from silicon dioxide.

[0017] Preferably, the material of the diaphragm is selected from n-type doped silicon wafer.

[0018] Preferably, the material of the oxide layer is selected from silicon dioxide.

[0019] Preferably, the material of the piezoelectric layer includes at least one of aluminum nitride, zinc oxide or lead zirconate titanate.

[0020] Preferably, the material of the electrode layer is selected from metals.

[0021] Preferably, the shape of the diaphragm is at least one of circular, rectangular, hexagonal and octagonal.

[0022] Preferably, the shape of the cavity is at least one of a cylinder, a cuboid, a truncated cone or a polygonal column.

[0023] Preferably, the number of turns of the strip electrode is 1 to 10.

[0024] Preferably, the oxide layer has an etched groove, and the piezoelectric layer is connected to the diaphragm through the etched groove.

[0025] The second aspect of the present invention provides a method for preparing the piezoelectric micro-electromechanical system microphone described in the first aspect of the present invention, comprising the following steps: providing a substrate, and sequentially stacking a diaphragm, an oxide layer, a piezoelectric layer and an electrode layer on the substrate; forming a cavity in the substrate, and the cavity passes through the substrate.

[0026] In some specific embodiments of the present invention, the diaphragm, oxide layer, piezoelectric layer and electrode layer are formed by conventional semiconductor process technologies such as low pressure chemical vapor deposition (LPCVD) or ion enhanced chemical vapor deposition (PECVD).

[0027] In some specific embodiments of the present invention, the cavity is formed by dry etching or wet etching. Dry etching includes conventional processes such as reactive ion etching (RIE) or deep reactive ion etching (DRIE), and wet etching includes conventional processes such as wet oxidation etching.

[0028] In some specific embodiments of the present invention, after the oxide layer is formed, the oxide layer is also patterned. By patterning the oxide layer, it is ensured that the oxide layer and the piezoelectric layer can electrically isolate the electrode layer from the substrate. The patterning of the oxide layer is performed by photolithography and dry etching, and the dry etching can be a conventional process such as reactive ion etching (RIE) or deep reactive ion etching (DRIE).

[0029] In some specific embodiments of the present invention, after the piezoelectric layer is formed, the piezoelectric layer is also patterned. By patterning the piezoelectric layer, unnecessary electrical interconnection due to process tolerance is prevented when a hard mask is used in the subsequent electrode layer preparation; and a contact window is formed to expose the grounded bottom electrode to the front. The patterning of the piezoelectric layer is performed by photolithography and wet etching, and the wet etching can be a conventional process such as wet oxidation etching.

[0030] A third aspect of the present invention provides an application of the piezoelectric MEMS microphone described in the first aspect of the present invention in the fields of music production, speech recognition or sound monitoring.

[0031] In some specific embodiments of the present invention, the music production field includes the field of singer sound recording or musical instrument sound recording; for example, it can be used as a professional microphone for singers or a microphone for musical instruments.

[0032] In some specific embodiments of the present invention, the speech recognition field includes keyword wake-up, human voice localization or human voice recognition.

[0033] In some specific embodiments of the present invention, the sound monitoring field includes the field of internal human body sound monitoring, environmental sound monitoring or industrial equipment monitoring.

[0034] The beneficial effects of the present invention are: the present invention is based on the principle of the combined action of the positive and negative piezoelectric effects, uses a combination of new sensing mechanisms, and combines acoustic detection and mechanical drive with a simple structure. A bias voltage can be applied through a strip electrode to adjust the strain stress of the microphone diaphragm and change the vibration mode of the diaphragm, thereby achieving an improvement in the sensitivity of the microphone at the mechanical level. Since there is no need to add a gap to the diaphragm, the integrity of the diaphragm is retained in the structure, and therefore it has the advantage of a wide bandwidth, thereby being able to output a stronger electrical signal.

[0035] Specifically, compared with the prior art, the present invention has the following advantages:

[0036] 1. The microphone of the present invention has the characteristics of high sensitivity and wide bandwidth, integrating the wide-band characteristics of traditional diaphragm microphones and the high-sensitivity characteristics of traditional cantilever beam array microphones. At the same time, it can effectively adjust the sensitivity of the microphone by controlling the external bias voltage. It has adjustable characteristics and can selectively suppress or enhance the sensitivity. Therefore, the application scenarios of the microphone of the present invention are more flexible.

[0037] 2. The manufacturing process of the piezoelectric MEMS microphone of the present invention is simple and easy, and can be used in noisy environments and in sound recording occasions that require high audio reproduction. The performance and reproduction of MEMS-sized microphones are improved to those of electret microphones, expanding the application scenarios of MEMS microphones. For example, in music production fields such as singer sound recording or musical instrument sound recording, it can be used as a professional microphone for singers, a musical instrument microphone, etc. In addition, it also provides more application options for speech recognition fields such as keyword wake-up, voice positioning or voice recognition, and sound monitoring fields such as internal human body sound monitoring, environmental sound monitoring or industrial equipment monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 Schematic diagram of the structure of the microphone in Embodiment 1 of the present invention.

[0039] Figure 2 It is a schematic diagram of the three-dimensional structure of the microphone in Embodiment 1 of the present invention.

[0040] Figure 3 Schematic diagram of a top view of the microphone in Embodiment 1 of the present invention and description of design parameters.

[0041] Figure 4 It is a schematic diagram of the structure after an oxide layer is deposited on a substrate and the oxide layer is patterned in Example 1 of the present invention.

[0042] Figure 5 It is a schematic diagram of the structure after a piezoelectric layer is deposited on the oxide layer in Example 1 of the present invention.

[0043] Figure 6 This is a schematic diagram of the structure after the piezoelectric layer is patterned in Example 1 of the present invention.

[0044] Figure 7 It is a schematic diagram of the structure after depositing an electrode layer on the piezoelectric layer in Example 1 of the present invention.

[0045] Figure 8 It is a schematic diagram of the structure after etching the substrate bottom layer and the substrate oxide layer in the substrate in Example 1 of the present invention.

[0046] Fig. 9 This is the infinite element model simulation result of the microphone in Example 1 of the present invention.

[0047] The figures are marked as follows: 1-substrate, 2-diaphragm, 3-oxide layer, 4-piezoelectric layer, 5-electrode layer; 101-substrate oxide layer, 102-substrate bottom layer, 103-substrate middle layer, 104-cavity, 501-inner electrode, 502-bias electrode, 503-strip electrode, 504-outer electrode, 505-ground electrode. DETAILED DESCRIPTION

[0048] The content of the present invention is further described in detail below through specific examples. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the principles set forth in the present invention all belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific data exemplified below. The raw materials, reagents or devices used in the following examples and comparative examples, unless otherwise specified, can all be obtained from conventional commercial sources, or can be obtained by existing known methods.

[0049] Example 1

[0050] A piezoelectric MEMS microphone, the structural schematic diagram of which is shown in Figure 1 As shown, the three-dimensional structure diagram is as follows Figure 2 As shown, the top view and design parameter description are as follows Figure 3 , specifically composed of the following layers:

[0051] The substrate 1 comprises a substrate oxide layer 101, a substrate bottom layer 102 and a substrate intermediate layer 103 which are stacked in sequence, and a cavity 104. The substrate oxide layer 101 is made of silicon dioxide, the substrate bottom layer 102 is made of an n-type doped silicon wafer, the substrate intermediate layer 103 is made of silicon dioxide, the silicon wafer and the silicon dioxide are bonded to each other, wherein the substrate intermediate layer 103 serves to connect the diaphragm 2 and the substrate bottom layer 102, and the cavity 104 is used to form a vibration space;

[0052] Diaphragm 2, used to achieve the conversion of acoustic energy and mechanical energy, can sensitively respond to changes in sound pressure, the material of the diaphragm is n-type doped silicon wafer, the shape of the diaphragm is at least one of circular, rectangular, hexagonal, and octagonal, and the shape of the diaphragm in this example is circular;

[0053] The oxide layer 3 is used to achieve electrical isolation, ensure that the readout signals of the inner and outer electrodes are independent of each other, and ensure the polarization direction of the piezoelectric material. The oxide layer 3 is patterned and has etched grooves. The piezoelectric layer 4 is connected to the diaphragm 2 through the etched grooves.

[0054] The piezoelectric layer 4 is used to realize the conversion of mechanical energy and electrical energy by using the positive and reverse piezoelectric effects. The piezoelectric layer 4 is patterned to ensure that the subsequent electrode layer will not adhere to cause unnecessary connection, and to form a contact window between the inner electrode 501 and the outer electrode 504;

[0055] The electrode layer 5 includes an inner electrode 501, a bias electrode 502, a strip electrode 503, an outer electrode 504, and a ground electrode 505; Figures 2-3It can be seen that the inner electrode 501 is located at the center of the piezoelectric layer 4, and the outer electrode 504 is located at the peripheral position of the piezoelectric layer 4. The outer electrode 504 is arranged around the inner electrode 501. The differential electrical signal is received by the inner electrode 501 and the outer electrode 504. The differential electrical signal is generated due to the opposite curvature generated during the acoustic vibration process. The inner electrode 501 and the outer electrode 504 are connected in series or separately to read out the signal, thereby ensuring the reading of the differential electrical signal caused by the opposite curvature; the strip electrode 503 is located on the piezoelectric layer 4 and is spaced at a certain distance. The gap is arranged between the inner electrode 501 and the outer electrode 504. The strip electrode 503 is used to apply a bias voltage to generate an inverse piezoelectric effect, thereby adjusting the stress of the diaphragm 2, changing the vibration mode of the film, and thus adjusting the sensitivity of the microphone. The strip electrode 503 can be arranged in a single circle, a double circle, or multiple circles, such as 1 to 10 circles, and a single circle in this example. The bias electrode 502 is connected to the strip electrode 503, and the bias electrode 502 is used to apply a bias voltage to the strip electrode 503. Under the assumption of statistical process control (SPC), considering that most piezoelectric materials will have better piezoelectric performance when polarized in the Z-axis direction, the diaphragm is grounded through the ground electrode 505, so that the piezoelectric MEMS microphone in this example works in an electric field direction perpendicular to the radius of the diaphragm. The diaphragm generates vibrations perpendicular to the radius of the membrane under the drive of sound pressure, and the acoustic vibration is converted into a change in charge through the piezoelectric material to read the voice signal.

[0056] The method for preparing the piezoelectric MEMS microphone in this example includes the following steps:

[0057] Step 1: Provide a substrate 1 having a substrate oxide layer 101, a substrate bottom layer 102 and a substrate intermediate layer 103 stacked in sequence, and stack a diaphragm 2 on the substrate 1, grow an oxide layer 3 on the diaphragm 2, cover the oxide layer 3 with a photoresist, and pattern the photoresist using a mask, and pattern the oxide layer 3 using RIE etching; this step is to ensure that the oxide layer 3 and the piezoelectric layer 4 can electrically isolate the electrode layer 5 from the grounded silicon substrate (including the substrate 1 and the diaphragm 2). The structure formed in this step is shown in FIG. Figure 4 shown.

[0058] Step 2: Depositing a piezoelectric layer 4 on the oxide layer 3 by reactive sputtering. The structure formed in this step is shown in FIG. Figure 5 shown.

[0059] Step 3: Cover the piezoelectric layer 4 with photoresist, and pattern the photoresist using the piezoelectric layer mask, and pattern the piezoelectric film using wet etching to prevent unnecessary electrical interconnection due to process tolerance when a hard mask is used in the subsequent preparation of the electrode layer 5, and form a contact window that allows the grounded ground electrode 505 to be exposed to the front. The structure formed in this step is shown in FIG. Figure 6 shown.

[0060] Step 4: Using a method similar to steps 1 and 3, the photoresist is patterned with a metal deposition mask, and an electrode layer (including an inner electrode 501, a bias electrode 502, a strip electrode 503, an outer electrode 504, and a ground electrode 505) is deposited by electron beam evaporation. The structure formed in this step is shown in FIG. Figure 7 shown.

[0061] Step 5: Using RIE etching and DRIE etching, the base oxide layer 101 and the base bottom layer 102 in the base 1 are etched to form a partial cavity 104. The structure formed in this step is shown in FIG. Figure 8 shown.

[0062] Step 6: Use wet oxidation etching to etch the substrate intermediate layer 103 in the substrate 1 to form a cavity 104 to release the diaphragm structure. Figure 1 The piezoelectric MEMS microphone shown.

[0063] The piezoelectric MEMS microphone prepared in this example was tested and studied, and it was found that the circular clamped membrane that generates resonance in the first flexural mode has a zero point of curvature at 60% of the radius direction with the center of the circular membrane as the center point, so the stress values ​​at the center and edge of the membrane have opposite signs, which leads to the piezoelectric effect generating opposite charges. If the same electrode covers the opposite charge distribution area, it will cause charge neutralization and reduce sensitivity. Therefore, the electrode is divided into two parts, the inner electrode 501 and the outer electrode 504, which are arranged at the center and the periphery of the membrane respectively to detect the electrical signals generated by different curvatures, and the inner electrode 501 and the outer electrode 504 are connected in series or the differential electrical signals of the two are read separately.

[0064] By applying a bias voltage to the strip electrode 503 through the bias electrode 502, the piezoelectric layer under the strip electrode will be deformed due to the inverse piezoelectric effect, resulting in a change in the stress in the membrane caused by the sound pressure. The bias voltage applied by the strip electrode and the strain generated by the inverse piezoelectric effect are linearly positively correlated within a certain range. Fig. 9 : is the infinite element model simulation result of the microphone in Example 1 of the present invention. Fig. 9As shown in the figure, the lower and left axes represent the vibration displacement of the diaphragm at different radial positions under different bias voltages (-1V to 1V) (where R = 0 is the center of the diaphragm and R = 500 is the edge of the diaphragm); the upper and right axes represent the influence of different bias voltages on the output voltage under the same input sound pressure. Fig. 9 It can be seen that applying a bias voltage is conducive to introducing greater mechanical sensitivity. By modulating the bias electrode, the strain stress of the microphone diaphragm 2 is increased, and a stronger electrical signal can be output. By adjusting the bias voltage applied to the bias electrode 502, the microphone sensitivity can be modulated according to the actual usage scenario.

[0065] The piezoelectric MEMS microphone prepared in Example 1 of the present invention has the characteristics of high sensitivity and wide bandwidth, integrating the wide-band characteristics of traditional diaphragm microphones and the high-sensitivity characteristics of traditional cantilever beam array microphones. At the same time, it can effectively adjust the microphone sensitivity by controlling the external bias voltage, has adjustable characteristics, and can selectively suppress or enhance the sensitivity, so the application scenario of the microphone of the present invention is more flexible. In addition, the piezoelectric MEMS microphone in Example 1 of the present invention has a simple and easy manufacturing process, can be applied to noisy environments, and sound recording occasions requiring high audio reproduction, improves the performance and reproduction of MEMS size microphones to electret microphones, expands the application scenarios of MEMS microphones, such as music production fields such as singers' sound recording or musical instrument sound recording, and can be used as professional singer microphones, musical instrument microphones, etc. In addition, it also provides more application options for speech recognition fields such as keyword wake-up, human voice positioning or human voice recognition, and sound monitoring fields such as human body internal sound monitoring, environmental sound monitoring or industrial equipment monitoring.

[0066] In summary, the present invention is based on the principle of the combined action of the positive and negative piezoelectric effects, uses a combination of new sensing mechanisms, and utilizes a simple structure to combine acoustic detection and mechanical drive. A bias voltage can be applied through a strip electrode to adjust the strain stress of the microphone diaphragm and change the vibration mode of the diaphragm, thereby achieving an improvement in the sensitivity of the microphone at the mechanical level. Furthermore, since there is no need to add a gap to the diaphragm and the integrity of the diaphragm is retained in the structure, it has the advantage of a wide bandwidth and can output a stronger electrical signal.

Claims

1. A piezoelectric micro-electromechanical system microphone, characterized in that: It includes: a substrate, a diaphragm, an oxide layer, a piezoelectric layer and an electrode layer which are stacked in sequence; A cavity is provided in the substrate, and the cavity penetrates the substrate; The electrode layer includes an inner electrode, an outer electrode, a strip electrode and a bias electrode; the outer electrode is arranged around the outside of the inner electrode, the strip electrode is arranged around between the inner electrode and the outer electrode, and the bias electrode is connected to the strip electrode.

2. The piezoelectric MEMS microphone according to claim 1, characterized in that: The inner electrode is located at the center of the piezoelectric layer, and the outer electrode is located at the periphery of the piezoelectric layer. A differential electrical signal is received through the inner electrode and the outer electrode, and the differential electrical signal is generated due to opposite curvatures generated during acoustic vibration.

3. The piezoelectric MEMS microphone according to claim 1, characterized in that: The strip electrode is used to apply a bias voltage to generate an inverse piezoelectric effect, thereby adjusting the diaphragm stress.

4. The piezoelectric MEMS microphone according to claim 1, characterized in that: The substrate comprises a substrate oxide layer, a substrate bottom layer and a substrate intermediate layer which are stacked in sequence; Preferably, the material of the base oxide layer is selected from silicon dioxide; And / or, the material of the bottom layer of the substrate is selected from n-type doped silicon wafer; And / or, the material of the substrate intermediate layer is selected from silicon dioxide.

5. The piezoelectric MEMS microphone according to claim 1, characterized in that: The material of the diaphragm is selected from n-type doped silicon wafer; And / or, the material of the oxide layer is selected from silicon dioxide; and / or, the material of the piezoelectric layer includes at least one of aluminum nitride, zinc oxide or lead zirconate titanate; And / or, the material of the electrode layer is selected from metals.

6. The piezoelectric MEMS microphone according to claim 1, characterized in that: The shape of the diaphragm is at least one of circular, rectangular, hexagonal, and octagonal; And / or, the shape of the cavity is at least one of a cylinder, a cuboid, a truncated cone or a polygonal column.

7. The piezoelectric MEMS microphone according to claim 1, characterized in that: The number of turns of the strip electrode is 1 to 10.

8. The piezoelectric MEMS microphone according to claim 1, characterized in that: The oxide layer has an etched groove, and the piezoelectric layer is connected to the diaphragm through the etched groove.

9. A method for preparing a piezoelectric micro-electromechanical system microphone according to any one of claims 1 to 8, characterized in that: The following steps are involved: Providing a substrate, on which a diaphragm, an oxide layer, a piezoelectric layer and an electrode layer are sequentially stacked; A cavity is formed in the substrate, the cavity penetrating the substrate.

10. Application of the piezoelectric MEMS microphone according to any one of claims 1 to 8 in the fields of music production, speech recognition or sound monitoring.

Images