US-12623899-B2 - Absolute pressure sensing MEMS microphone, microphone unit and electronic device

US12623899B2US 12623899 B2US12623899 B2US 12623899B2US-12623899-B2

Abstract

Embodiments of the present disclosure provides an absolute pressure sensing MEMS microphone, a microphone unit and an electronic device. The absolute pressure sensing MEMS microphone includes: a diaphragm; a back electrode plate; a spacer between the diaphragm and the back electrode plate, wherein the diaphragm, the back electrode plate and the spacer form a vacuum cavity, an air pressure in the vacuum cavity is a first air pressure, wherein a gap separating the diaphragm from the back electrode plate by the spacer is a fabrication gap, wherein in a state where the air pressure inside and outside the diaphragm are both the first air pressure, an effective vacuum gap between the diaphragm and the back electrode plate is the first vacuum gap, and wherein the first vacuum gap is larger than the fabrication gap.

Inventors

Quanbo Zou
DeXin Wang
Huabin Fang

Assignees

GOERTEKMICROELECTRONICS CO., LTD.

Dates

Publication Date: 20260512
Application Date: 20200630
Priority Date: 20200616

Claims (11)

1 . An absolute pressure sensing MEMS microphone, comprising: a diaphragm; a back electrode plate; a spacer between the diaphragm and the back electrode plate, wherein, the diaphragm, the back electrode plate and the spacer form a vacuum cavity having a first air pressure, wherein, the spacer forms a fabrication gap between the diaphragm and the back electrode plate, wherein, in a state where an air pressures outside the diaphragm is at the first air pressure, an effective vacuum gap between the diaphragm and the back electrode plate is a first vacuum gap, wherein, the first vacuum gap is larger than the fabrication gap, and wherein, at a standard atmospheric pressure without an operating bias, the effective vacuum gap between the diaphragm and the back electrode plate is a second vacuum gap, and the second vacuum gap is larger than the fabrication gap.
2 . The absolute pressure sensing MEMS microphone according to claim 1 , wherein the first vacuum gap is greater than twice the fabrication gap or equal to twice the fabrication gap.
3 . The absolute pressure sensing MEMS microphone according to claim 2 , wherein the first vacuum gap is less than or equal to 10 times the fabrication gap.
4 . The absolute pressure sensing MEMS microphone according to claim 1 , wherein, at standard atmospheric pressure, under a state that an operating bias is applied, the effective vacuum gap between the diaphragm and the back electrode plate is a third vacuum gap, and the third vacuum gap is greater than or equal to 80% of the fabrication gap and less than or equal to 120% of the fabrication gap.
5 . The absolute pressure sensing MEMS microphone according to claim 1 , wherein the diaphragm is pre-deviated by a stress structure, so that the first vacuum gap is larger than the fabrication gap.
6 . The absolute pressure sensing MEMS microphone according to claim 5 , wherein the stress structure comprises the diaphragm and a compressive stress component, wherein, the diaphragm has a tensile stress along a surface direction of the diaphragm surface, and wherein, the compressive stress component is attached to outside of the diaphragm relative to the vacuum cavity, and has a compressive stress along the surface direction of the diaphragm.
7 . The absolute pressure sensing MEMS microphone according to claim 5 , wherein said stress structure comprises a composite layer of the diaphragm, wherein, the composite layer includes an inner film located inside the vacuum cavity and an outer film located outside, wherein, the inner film has a tensile stress along a surface direction of the diaphragm and the outer film has a compressive stress along the surface direction of the diaphragm.
8 . The absolute pressure sensing MEMS microphone according to claim 5 , wherein the stress structure includes the spacer and a fixing member securing the diaphragm to the spacer, wherein, the fixing member has a tensile stress along a surface direction of the diaphragm and is attached to an upper surface of the diaphragm, and the spacer has a compressive stress along the surface direction of the diaphragm and is attached to a lower surface of the diaphragm.
9 . The absolute pressure sensing MEMS microphone according to claim 5 , wherein the stress structure comprises a corrugated membrane structure on the diaphragm, so that the diaphragm bulges outwards relative to the vacuum cavity.
10 . A microphone unit, comprising a unit shell, the absolute pressure sensing MEMS microphone according to claim 1 and an integrated circuit chip, wherein the absolute pressure sensing MEMS microphone and the integrated circuit chip are arranged in the unit shell.
11 . An electronic device comprising the microphone unit according to claim 10 .

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a National Stage of International Application No. PCT/CN2020/099439, filed on Jun. 30, 2020, which claims priority to Chinese Patent Application No. 202010547998.2, filed on Jun. 16, 2020, both of which are hereby incorporated by reference in their entireties. TECHNICAL FIELD The present disclosure relates to the technical field of MEMS microphones, and in particular, to an absolute pressure sensing MEMS microphone, a microphone unit and an electronic device. BACKGROUND In an absolute pressure sensor, one side of a pressure sensing membrane is a vacuum and the other side is a pressure environment to be sensed. The vacuum here refers to an approximate vacuum, which can be an environment where the air pressure is much lower than the standard atmospheric pressure. FIG. 1 shows different states of a microelectromechanical system (MEMS) absolute pressure sensor. The MEMS absolute pressure sensor shown in FIG. 1 may be a capacitive type sensor. In FIG. 1, a pressure sensing membrane 11, an electrode plate 12 and a spacer 13 form a vacuum cavity 14. FIG. 1(A) shows a state of the MEMS absolute pressure sensor in a vacuum environment with no operating bias applied. As shown in FIG. 1(A), the pressure sensing membrane 11 is located at a flat position P. FIG. 1(A) may be the state when the MEMS absolute pressure sensor is fabricated. FIG. 1(B) shows a state of the MEMS absolute pressure sensor in an atmospheric pressure environment with no operating bias applied. As shown in FIG. 1(B), due to the effect of atmospheric pressure, the pressure sensing membrane 11 deviates from the flat position P and is concavely depressed downwards. FIG. 1(B) may be the state when the MEMS absolute pressure sensor is not used. FIG. 1(C) shows a state of the MEMS absolute pressure sensor in an atmospheric pressure environment under the condition of applying a working bias. As shown in FIG. 1(C), due to the atmospheric pressure and the working bias, the pressure sensing membrane 11 deviates from the flat position P and is further concavely depressed downwards. FIG. 1(C) may be the state of the MEMS absolute pressure sensor when it is used. Since the pressure referenced by the absolute pressure sensor for sensing is vacuum pressure, the absolute pressure sensor is not susceptible to atmospheric pressure changes and/or temperature changes. However, the pressure sensing membrane 11 of the absolute pressure sensor needs to resist the atmospheric pressure Po, and will be greatly deformed. Therefore, the absolute pressure sensor is generally used for pressure sensing and is not suitable for microphones. If it is desired to achieve the same sensitivity as a traditional MEMS microphone (for example, about 5-10 mV/Pa), then the initial vacuum gap of the absolute pressure sensor (the gap between the pressure sensing membrane 11 and the electrode plate 12 shown in FIG. 1(A), where the inside and outside of the pressure sensing membrane 11 are vacuum) needs to be set relatively large, about 15-20 μm or more. This not only greatly increases the difficulty of fabricating processes, but also makes the area of the diaphragm (pressure sensing membrane) very large due to the requirement that the effective capacitance Cmic of the MEMS microphone matches the MEMS microphone, which further increases the cost of the MEMS microphone. In addition, when the flat diaphragm is displaced/warped towards the back electrode plate, the center of the diaphragm has the greatest deflection, while most of the surrounding area of the diaphragm contributes little to the performance of the microphone, which increases the difficulty of improving performance. Therefore, a new MEMS microphone needs to be provided. SUMMARY Embodiments of the present disclosure provide new technical solutions for MEMS microphones. According to a first aspect of the present disclosure, there is provided an absolute pressure sensing MEMS microphone, including: a diaphragm; a back electrode plate; a spacer between the diaphragm and the back electrode plate, wherein the diaphragm, the back electrode plate and the spacer form a vacuum cavity, and an air pressure in the vacuum cavity is a first air pressure, wherein a gap separating the diaphragm from the back electrode plate by the spacer is a fabrication gap, wherein, in a state where air pressures inside and outside the diaphragm both are the first air pressure, an effective vacuum gap between the diaphragm and the back electrode plate is a first vacuum gap, and wherein the first vacuum gap is larger than the fabrication gap. According to a second aspect of the present disclosure, a microphone unit is provided, including a unit shell, the absolute pressure sensing MEMS microphone disclosed here and an integrated circuit chip, wherein the absolute pressure sensing MEMS microphone and the integrated circuit chip are arranged in the unit shell. According to a third aspect of the present disclos