Capacitive vibration sensor

Abstract

The utility model provides a capacitive vibration sensor, a sealed cavity is formed in the capacitive vibration sensor, and an elastic beam and a movable structure are arranged in the sealed cavity; the fixed end of the movable structure is connected to the tail end of the elastic beam, and the free end, opposite to the fixed end, of the movable structure is suspended in the sealing cavity; an upper groove is formed above the free end of the movable structure, and / or a lower groove is formed below the free end of the movable structure. According to the capacitive vibration sensor, the air flowing space in the sealing cavity, especially the air flowing space near the free end of the movable structure, can be increased by adding the upper groove and / or the lower groove, so that the air damping under high frequency is reduced, and the measurement bandwidth of the capacitive vibration sensor can be increased.

Description

Technical Field

[0001] This application relates to the technical field of vibration sensors, and in particular, to a capacitive vibration sensor. Background Art

[0002] A vibration sensor is a sensor device for detecting external vibration signals. Traditional vibration sensors generally use piezoelectric blocks as sensitive materials, and can relatively easily achieve a wide frequency measurement bandwidth above 10 kHz. However, piezoelectric vibration sensors cannot measure DC signals, and have a large volume and high cost. MEMS capacitive vibration sensors are based on silicon-based semiconductor processes to prepare sensitive structures, and use a variable capacitor to detect external vibration signals. They have the advantages of small volume and low cost, and can cover low-frequency vibration signals up to DC in the measurement frequency band, and have excellent development prospects.

[0003] The core of an MEMS capacitive vibration sensor is a vibrating system of a spring beam-mass block, and the mass block is used to sense external vibration signals. The frequency response curve of a common capacitive vibration sensor is as Figure 1 shown, and generally has a higher response amplitude at its resonant fundamental frequency f0. To ensure response consistency within the measurement frequency band, its measurable frequency range BW generally needs to be much smaller than the resonant fundamental frequency f0. To increase the measurement bandwidth BW of the vibration sensor, if the resonant fundamental frequency f0 is directly increased, an elastic beam with a greater stiffness needs to be used, resulting in a decrease in the displacement generated by the same magnitude of external vibration signal, reducing the sensitivity of the sensor and weakening the minimum vibration signal that the sensor can detect. Therefore, keeping the resonant fundamental frequency f0 unchanged and making the measurable frequency range BW as close as possible to the resonant fundamental frequency f0 is an important technical improvement direction for capacitive vibration sensors. Summary of the Invention

[0004] To solve the existing technical problems, this application provides a capacitive vibration sensor capable of improving the measurement bandwidth.

[0005] To achieve the above object, the technical solution of the embodiment of this application is implemented as follows:

[0006] The embodiment of this application provides a capacitive vibration sensor. A sealed cavity is formed inside the capacitive vibration sensor, and an elastic beam and a movable structure are provided in the sealed cavity; the fixed end of the movable structure is connected to the end of the elastic beam, and the free end of the movable structure opposite to the fixed end is suspended in the sealed cavity; an upper groove is provided above the free end of the movable structure, and / or a lower groove is provided below the free end of the movable structure.

[0007] In one embodiment, the upper groove and the lower groove are straight grooves, and the length is substantially equal to the width of the free end of the movable structure.

[0008] In one embodiment, the upper groove and the lower groove are arc grooves, and the length of the connection line at both ends is substantially equal to the width of the free end of the movable structure.

[0009] In one embodiment, a plurality of upper grooves are spaced apart in the direction from the free end to the fixed end of the movable structure, and / or a plurality of lower grooves are spaced apart in the direction from the free end to the fixed end of the movable structure.

[0010] In one embodiment, the width of the upper groove and the lower groove is 5 - 50 μm, and the depth of the upper groove and the lower groove is 5 - 50 μm.

[0011] In one embodiment, the capacitive vibration sensor includes an upper cover plate, an intermediate structural plate, a lower cover plate, and a bonding insulating layer. The bonding insulating layer is provided between the upper cover plate and the intermediate structural plate, and between the lower cover plate and the intermediate structural plate. The upper cover plate, the intermediate structural plate, and the lower cover plate are bonded through the bonding insulating layer to form the sealed cavity inside; the upper groove is opened on the side of the upper cover plate facing the sealed cavity, and the lower groove is opened on the side of the lower cover plate facing the sealed cavity.

[0012] In one embodiment, the upper cover plate and the lower cover plate are made of silicon wafers or glass substrates. The upper groove is etched on the upper cover plate, and the lower groove is etched on the lower cover plate.

[0013] In one embodiment, the intermediate structural plate is made of a silicon wafer in a frame shape, and one end of the elastic beam is connected to the inner side of the intermediate structural plate and is a cantilever beam suspended in the sealed cavity.

[0014] In one embodiment, an upper electrode region for electrical connection and leading out to the outside of the sealed cavity is provided on the outer side of the upper cover plate, a middle electrode region for electrical connection and leading out to the outside of the sealed cavity is provided on the outer side of the intermediate structural plate, and a lower electrode region for electrical connection and leading out to the outside of the sealed cavity is provided on the outer side of the lower cover plate.

[0015] In one embodiment, the air pressure value in the sealed cavity is set between 5000 - 50000 Pa.

[0016] The capacitive vibration sensor of the present application has at least the following beneficial effects: In the capacitive vibration sensor of the present application, by increasing the upper groove and / or the lower groove, the space for air flow inside the sealed cavity can be increased, especially the air flow space near the free end of the movable structure, thereby reducing the air damping at high frequencies and helping to increase the measurement bandwidth of the capacitive vibration sensor. Description of the Drawings

[0017] Figure 1 is the frequency response curve of an existing capacitive vibration sensor;

[0018] Figure 2 is a schematic perspective view of the three-dimensional structure of the capacitive vibration sensor according to an embodiment of the present application;

[0019] Figure 3 is Figure 2 the exploded structural schematic diagram of the capacitive vibration sensor in

[0020] Figure 4a , Figure 4b , Figure 4c are respectively the perspective structural schematic diagrams of the lower cover plates of three different embodiments;

[0021] Figure 5 is Figure 2 the cross-sectional structural schematic diagram of the capacitive vibration sensor in

[0022] Figure 6 is the frequency response curve of the sealed cavity of the capacitive vibration sensor at different air pressure values;

[0023] Figure 7 is the frequency response curve of the capacitive vibration sensor with and without grooves.

[0024] The reference numerals of each component in the figure are as follows:

[0025] Upper cover plate 11, intermediate structural plate 12, lower cover plate 13, bonding insulating layer 14;

[0026] Movable structure 15, elastic beam 16; upper groove 17, lower groove 18; sealed cavity 20;

[0027] Upper layer electrode region 41, middle layer electrode region 42, lower layer electrode region 43. Detailed Embodiments

[0028] The technical solution of the present application will be further elaborated in detail below in conjunction with the accompanying drawings of the specification and specific embodiments.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terms used in the description of this application herein are for the purpose of describing specific embodiments only and are not intended to limit the implementation of this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0030] In the description of this application, it should be understood that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to this application. In the description of this application, unless otherwise stated, the meaning of "a plurality of" is two or more.

[0031] In the description of this application, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0032] Please refer to Figure 2 and Figure 3 , the structure of a capacitive vibration sensor according to an embodiment of this application is shown in the figure. Sequentially from top to bottom, it includes an upper cover plate 11, an intermediate structure plate 12, and a lower cover plate 13, which are bonded by three layers of materials. Among them, the intermediate structure plate 12 is prepared from a silicon wafer, and the upper cover plate 11 and the lower cover plate 13 can be prepared from a silicon wafer or a glass substrate. A bonding insulating layer 14 is provided between the upper cover plate 11 and the intermediate structure plate 12, and a bonding insulating layer 14 is also provided between the lower cover plate 13 and the intermediate structure plate 12, which is used to form a capacitive gap and constitute electrical insulation. The upper cover plate 11, the intermediate structure plate 12, and the lower cover plate 13 form a closed structure through the bonding insulating layer 14, and a sealed cavity 20 is formed inside.

[0033] The intermediate structural plate 12 is in a frame shape, and a movable structure 15 is connected inside it through elastic beams 16. That is, one end of the elastic beam 16 is connected to the inner side of the intermediate structural plate 12 and is a cantilever beam suspended in the sealing cavity 20. One end of the movable structure 15 is connected to the end of the elastic beam 16 to form a fixed end of the movable structure 15, and the other end of the movable structure 15 opposite to the fixed end is suspended to form a free end of the movable structure 15, so that the movable structure 15 can move within the sealing cavity 20.

[0034] The upper cover plate 11, the intermediate structural plate 12, and the lower cover plate 13 each have an electrode area for electrical connection and lead-out on the outer side, which are the upper layer electrode area 41, the middle layer electrode area 42, and the lower layer electrode area 43 respectively. That is, the upper layer electrode area 41 is provided on the outer side of the upper cover plate 11 for leading out the upper layer electrical connection to the outside of the sealing cavity 20; the middle layer electrode area 42 is provided on the outer side of the intermediate structural plate 12 for leading out the middle layer electrical connection to the outside of the sealing cavity 20; the lower layer electrode area 43 is provided on the outer side of the lower cover plate 13 for leading out the lower layer electrical connection to the outside of the sealing cavity 20.

[0035] The working principle of the capacitive vibration sensor is as follows: When there is an external vibration signal to be measured, in the capacitive vibration sensor, the movable structure 15 will generate a corresponding displacement in the sealing cavity 20, thereby causing a change in capacitance. By detecting the change in the capacitance of the capacitive vibration sensor through the upper layer electrode area 41, the middle layer electrode area 42, and the lower layer electrode area 43, the change characteristics of the external vibration signal can be detected.

[0036] Please refer to Figure 4a and Figure 5 , in order to increase the measurement bandwidth of the capacitive vibration sensor, upper grooves 17 and lower grooves 18 are respectively opened on the sides of the upper cover plate 11 and the lower cover plate 13 facing the intermediate structural plate 12 (towards the inner side of the sealing cavity 20). The upper grooves 17 and the lower grooves 18 can be prepared by semiconductor processes, such as etching formed by dry etching or wet etching processes, etc.

[0037] In Figure 3 , Figure 4a and Figure 5 In the illustrated embodiments, a upper groove 17 is opened on the lower end surface of the upper cover plate 11 near the free end of the movable structure 15. The upper groove 17 is a straight groove and its length is substantially equal to (slightly larger, slightly smaller, or equal to) the width of the free end of the movable structure 15. Similarly, a lower groove 18 is opened on the upper end surface of the lower cover plate 13 near the free end of the movable structure 15. The lower groove 18 is a straight groove and its length is substantially equal to (slightly larger, slightly smaller, or equal to) the width of the free end of the movable structure 15. Thus, at the free end of the movable structure 15, there is a straight upper groove 17 above and a straight lower groove 18 below.

[0038] Please refer toFigure 4b , on the sides of the upper cover plate 11 and the lower cover plate 13 facing the intermediate structural plate 12 (towards the inside of the sealing cavity 20), a plurality of upper grooves 17 and a plurality of lower grooves 18 are respectively provided. More specifically, on the lower end surface of the upper cover plate 11, a plurality of upper grooves 17 are spaced apart in the direction from the free end to the fixed end of the movable structure 15. The upper grooves 17 are straight grooves and the length is substantially equal to (slightly larger, slightly smaller, or equal to) the width of the free end of the movable structure 15. Similarly, on the upper end surface of the lower cover plate 13, a plurality of lower grooves 18 are spaced apart in the direction from the free end to the fixed end of the movable structure 15. The lower grooves 18 are straight grooves and the length is substantially equal to (slightly larger, slightly smaller, or equal to) the width of the free end of the movable structure 15. Thus, at the free end of the movable structure 15, a plurality of straight upper grooves 17 are provided above, and a plurality of straight lower grooves 18 are provided below.

[0039] Please refer to Figure 4c , on the sides of the upper cover plate 11 and the lower cover plate 13 facing the intermediate structural plate 12 (towards the inside of the sealing cavity 20), an upper groove 17 and a lower groove 18 are respectively provided. More specifically, on the lower end surface of the upper cover plate 11, an upper groove 17 is provided near the free end of the movable structure 15. The upper groove 17 is an arc groove and the length of the line connecting both ends is substantially equal to (slightly larger, slightly smaller, or equal to) the width of the free end of the movable structure 15. Similarly, on the upper end surface of the lower cover plate 13, a lower groove 18 is provided near the free end of the movable structure 15. The lower groove 18 is an arc groove and the length of the line connecting both ends is substantially equal to (slightly larger, slightly smaller, or equal to) the width of the free end of the movable structure 15. Thus, at the free end of the movable structure 15, an arc upper groove 17 is provided above, and an arc lower groove 18 is provided below.

[0040] From the upper grooves 17 and the lower grooves 18 in the above various embodiments, it can be seen that in the capacitive vibration sensor, an upper groove 17 is provided above the movable structure 15 (on the side of the upper cover plate 11 facing the sealing cavity 20), and / or a lower groove 18 is provided below the movable structure 15 (on the side of the lower cover plate 13 facing the sealing cavity 20); the upper grooves 17 and the lower grooves 18 are provided near the free end of the movable structure 15. The upper grooves 17 and the lower grooves 18 can be straight grooves or curved grooves. The length of the line connecting both ends of the upper grooves 17 and the lower grooves 18 is close to the width dimension of the movable structure 15. The width of the upper grooves 17 and the lower grooves 18 is preferably 5 - 50 μm, and the depth of the upper grooves 17 and the lower grooves 18 is preferably 5 - 50 μm.

[0041] Please refer to in combination Figure 5 , in the sealing cavity 20 of the capacitive vibration sensor, an upper groove 17 and / or a lower groove 18 is provided, thereby increasing the space above and / or below the free end of the movable structure 15 in the sealing cavity 20. Please refer to in combination Figure 6, after there is no groove and grooves (upper groove 17, lower groove 18) are provided, the frequency response curves of the capacitive vibration sensor are compared as shown in the figure. It can be seen from the comparison of the response curves in the figure that by increasing the grooves (upper groove 17, lower groove 18) on the upper cover plate and the lower cover plate, the space for air flow inside the sealed cavity 20 can be increased, especially the air flow space near the free end of the movable structure 15, and the air damping at high frequencies can be reduced, which helps to increase the measurement bandwidth of the capacitive vibration sensor.

[0042] A specific sealed cavity 20 is formed inside the capacitive vibration sensor, and different air pressure values inside the sealed cavity 20 will affect the frequency response of the capacitive vibration sensor. Please refer to Figure 7 , the frequency response curves of the sealed cavity 20 of the capacitive vibration sensor at different air pressure values (1000 Pa, 3000 Pa, 9000 Pa respectively). It can be seen from the frequency response curves that by controlling the air pressure value inside the sealed cavity 20, the measurement bandwidth of the capacitive vibration sensor can be improved. Preferably, when the capacitive vibration sensor is bonded, the air pressure value inside the sealed cavity 20 is set between 5000 - 50000 Pa (lower than the standard atmospheric pressure), which helps to further increase the measurement bandwidth of the capacitive vibration sensor.

[0043] In summary, compared with the prior art, the capacitive vibration sensor of the present application has at least the following beneficial effects: grooves are provided in the sealed cavity of the capacitive vibration sensor to increase the air flow space above and below the free end of the movable structure, which can increase the measurement bandwidth of the capacitive vibration sensor; by controlling the air pressure value of the sealed cavity and keeping it within a specific range, the measurement bandwidth of the capacitive vibration sensor can be further increased.

[0044] It should be noted that in this article, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of another identical element in the process, method, article or device including that element.

[0045] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A capacitive vibration sensor, characterized in that: A sealed cavity (20) is formed inside the capacitive vibration sensor. An elastic beam (16) and a movable structure (15) are arranged inside the sealed cavity (20); the fixed end of the movable structure (15) is connected to the end of the elastic beam (16), and the free end of the movable structure (15) opposite to the fixed end is suspended in the sealed cavity (20); an upper groove (17) is arranged above the free end of the movable structure (15), and / or a lower groove (18) is arranged below the free end of the movable structure (15).

2. The capacitive vibration sensor according to claim 1, wherein: The upper groove (17) and the lower groove (18) are straight grooves, and the length is basically equal to the width of the free end of the movable structure (15).

3. The capacitive vibration sensor according to claim 1, characterized in that: The upper groove (17) and the lower groove (18) are arc grooves, and the length of the connecting line at both ends is basically equal to the width of the free end of the movable structure (15).

4. The capacitive vibration sensor according to claim 1, characterized in that: Multiple upper grooves (17) are spacedly arranged in the direction from the free end to the fixed end of the movable structure (15), and / or multiple lower grooves (18) are spacedly arranged in the direction from the free end to the fixed end of the movable structure (15).

5. The capacitive vibration sensor according to claim 1, characterized in that: The widths of the upper groove (17) and the lower groove (18) are 5 - 50 μm, and the depths of the upper groove (17) and the lower groove (18) are 5 - 50 μm.

6. The capacitive vibration sensor according to claim 1, wherein: The capacitive vibration sensor includes an upper cover plate (11), an intermediate structure plate (12), a lower cover plate (13) and a bonding insulating layer (14). The bonding insulating layer (14) is arranged between the upper cover plate (11) and the intermediate structure plate (12) and between the lower cover plate (13) and the intermediate structure plate (12). The upper cover plate (11), the intermediate structure plate (12) and the lower cover plate (13) are bonded through the bonding insulating layer (14) to form the sealed cavity (20) inside; the upper groove (17) is arranged on the side of the upper cover plate (11) facing the sealed cavity (20), and the lower groove (18) is arranged on the side of the lower cover plate (13) facing the sealed cavity (20).

7. The capacitive vibration sensor according to claim 6, characterized in that: The upper cover plate (11) and the lower cover plate (13) are made of silicon wafers or glass substrates. The upper groove (17) is etched on the upper cover plate (11), and the lower groove (18) is etched on the lower cover plate (13).

8. The capacitive vibration sensor according to claim 6, characterized in that: The intermediate structure plate (12) is made of a silicon wafer in a frame shape, and one end of the elastic beam (16) is connected to the inner side of the intermediate structure plate (12) to form a cantilever beam suspended in the sealed cavity (20).

9. The capacitive vibration sensor according to claim 6, wherein: An upper layer electrode region (41) for electrical connection and leading out to the outside of the sealed cavity (20) is arranged on the outer side of the upper cover plate (11), a middle layer electrode region (42) for electrical connection and leading out to the outside of the sealed cavity (20) is arranged on the outer side of the intermediate structure plate (12), and a lower layer electrode region (43) for electrical connection and leading out to the outside of the sealed cavity (20) is arranged on the outer side of the lower cover plate (13).

10. The capacitive vibration sensor according to any one of claims 1 to 9, characterized in that: The air pressure value inside the sealed cavity (20) is set between 5000 - 50000 Pa.

Images