CN109270298B

CN109270298B - MEMS accelerometer

Info

Publication number: CN109270298B
Application number: CN201811241269.3A
Authority: CN
Inventors: 尹永刚; 韩丰田; 方政翔; 吴秋平; 董景新; 刘云峰
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2018-10-24
Filing date: 2018-10-24
Publication date: 2020-04-07
Anticipated expiration: 2038-10-24
Also published as: CN109270298A

Abstract

The invention relates to a MEMS accelerometer, which comprises a substrate, two supporting bodies, a first sensitive structure, a second sensitive structure and a bearing beam for connecting the second sensitive structure and the first sensitive structure. The two supports are fixed on the surface of the substrate and are oppositely arranged at intervals. The spandrel girder erects between two supporters, and with two supporter difference fixed connection. The straight line of the two supporting bodies is vertical to the bearing beam. The invention reduces the number of anchor points and avoids the influence of the thermal stress among a plurality of anchor points on the first sensitive structure and the second sensitive structure. When the thermal stress generated by the substrate is transmitted to the bearing beam through the two supporting bodies, the trend of the thermal stress on the bearing beam is shown on the straight line of the two supporting bodies and is vertical to the measuring direction of the first sensitive structure and the second sensitive structure, so that the influence on the measuring result can be avoided.

Description

MEMS accelerometer

Technical Field

The invention relates to the technical field of MEMS, in particular to an MEMS accelerometer.

Background

Micro Electro Mechanical Systems (MEMS) refers to a mechanical electronic system with critical structure size in micron order, integrates a Micro mechanical structure, a signal processing and control circuit, and a high-performance electronic integrated device, and is known as a revolutionary high-tech technology in the 21 st century. With the development of micro-machining technology, micro-mechanical inertial sensors play more and more important roles in the field of inertial navigation. Micromechanical accelerometers have gradually replaced traditional accelerometers in many fields by virtue of their advantages of small size, low power consumption, low cost, etc.

The MEMS accelerometer is usually made of Silicon, Silicon dioxide, Glass, etc. as a structural material, and is micro-machined in a structural form of Silicon-Glass (SOG) or Silicon-On-Insulator (SOI) and a related process, and finally fixed in a package by bonding or welding. Due to the fact that thermal expansion coefficients of materials of components such as silicon, glass, adhesives, a tube shell substrate and the like are not consistent, when the ambient temperature changes, a sensitive structure of the accelerometer is subjected to thermal stress, and temperature drift of an output signal is caused (the change of parameters of a semiconductor device caused by the temperature change is a main reason for generating the output drift phenomenon of the device, namely the temperature drift). Therefore, the conventional MEMS accelerometer suffers from thermal stress and suffers from long-term stability.

Disclosure of Invention

In view of the above, it is necessary to provide a MEMS accelerometer, which can solve the problem that the long-term stability of the conventional MEMS accelerometer is impaired by the influence of thermal stress.

A MEMS accelerometer, comprising:

a substrate;

the two supporting bodies are fixed on the surface of the substrate and are oppositely arranged at intervals;

the bearing beam is erected between the two supporting bodies and is respectively and fixedly connected with the two supporting bodies, and the straight line of the two supporting bodies is perpendicular to the bearing beam.

In one embodiment, the first sensitive structure and the second sensitive structure are the same in structure and are symmetrically arranged.

In one embodiment, the two supporting bodies are arranged on the symmetry axis of the first sensitive structure and the second sensitive structure.

In one embodiment, the first sensitive structure comprises a first isolation frame arranged on the periphery of the first sensitive structure;

the second sensitive structure comprises a second isolation frame which is arranged at the periphery of the second sensitive structure, and the second isolation frame is connected with the first isolation frame through the bearing beam.

In one embodiment, the first sensitive structure further includes a mass block and at least one pair of support beams, the mass block is connected with the first isolation frame through the support beams, the at least one pair of support beams are oppositely arranged on two sides of the mass block far away from the bearing beams, and the deformation direction of the support beams is parallel to the extension direction of the bearing beams.

In one embodiment, the first sensitive structure further comprises a lever and a resonator, one end of the resonator is connected with the first isolation frame, the other end of the resonator is connected with the lever, one end of the lever, far away from the resonator, is connected with the mass block, and the lever is used for transmitting the force of the mass block to the resonator after being amplified.

In one embodiment, the number of the levers is two and the levers are symmetrically arranged, and the levers include:

one end of the lever input beam is connected with the mass block;

one end of the lever main body beam is connected with the end part, far away from the mass block, of the lever input beam, and the extending direction of the lever main body beam is perpendicular to the deformation direction of the supporting beam;

one end of the lever output beam is connected to the other end, far away from the lever input beam, of the lever main body beam, and the other end of the lever output beam is connected with the resonator;

a lever fulcrum disposed proximate to the lever output beam on the lever body beam; and

and the fulcrum fixing beam is connected between the lever fulcrum and the first isolation frame.

In one embodiment, the resonator comprises:

one end of each of the two parallel resonance beams is connected with the lever output beam, and the other end of each of the two parallel resonance beams is connected with the first isolation frame;

the two connecting beams are respectively arranged at two ends of the resonance beam and connected between the two resonance beams;

the first movable comb teeth are arranged on the resonant beam; and

and the first static comb teeth are fixed on the substrate and distributed with the moving comb teeth in a finger shape.

In one embodiment, the MEMS accelerometer includes a plurality of fixed blocks fixed to the substrate, and the first stationary comb is disposed on the fixed blocks.

In one embodiment, the first sensitive structure includes:

the second movable comb teeth are arranged on the mass block; and

and the second static comb teeth are fixed on the substrate and distributed with the second moving comb teeth in a finger shape.

In one embodiment, the MEMS accelerometer includes:

the first metal layer is clamped between the support body and the substrate and is used for connecting the substrate and the support body;

and the second metal layer is clamped between the fixed block and the substrate and is used for connecting the substrate and the fixed block.

The MEMS accelerometer comprises a substrate, two supporting bodies, a first sensitive structure, a second sensitive structure and a bearing beam. The first sensitive structure, the second sensitive structure and the substrate are connected through the two support bodies, the number of connection points between the first sensitive structure, the second sensitive structure and the substrate is reduced, and the influence of thermal stress among multiple connection points on the first sensitive structure and the second sensitive structure is avoided. When the thermal stress generated by the substrate is transmitted to the bearing beam through the two supporting bodies, the trend of the thermal stress on the bearing beam is shown on the straight line of the two supporting bodies and is vertical to the measuring direction of the first sensitive structure and the second sensitive structure, so that the influence on the measuring result can be avoided. And this application adopts two supporters, makes first sensitive structure with second sensitive structure is more firm at the production tape-out in-process, has increased the yield.

Drawings

FIG. 1 is a schematic top view of a MEMS accelerometer according to an embodiment of the present application;

FIG. 2 is a schematic front view of a MEMS accelerometer according to an embodiment of the present application;

FIG. 3 is a schematic side view of a MEMS accelerometer according to an embodiment of the present application;

fig. 4 is a schematic top view of a MEMS accelerometer according to another embodiment of the present application.

Description of the reference numerals

10 MEMS accelerometer

100 substrate

200 support

300 first sensitive structure

310 first isolation frame

320 mass block

330 support beam

340 lever

341 lever input beam

342 lever body beam

343 lever output beam

344 fulcrum of lever

345 fixed beam of fulcrum

350 resonator

351 resonant beam

352 connecting beam

353 first moving comb tooth

354 first static comb teeth

360 second movable comb teeth

370 second static comb teeth

400 second sensitive structure

410 second isolation frame

500 spandrel girder

600 fixed block

710 first metal layer

720 second metal layer

Detailed Description

In order to make the aforementioned objects, features and advantages of the present application more comprehensible, embodiments accompanying the present application are described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. This application is capable of embodiments in many different forms than those described herein and those skilled in the art will be able to make similar modifications without departing from the spirit of the application and it is therefore not intended to be limited to the embodiments disclosed below.

It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present.

Unless defined otherwise, 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 terminology used herein in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Please refer to fig. 1. An embodiment of the present application provides a MEMS accelerometer 10, which includes a substrate 100, two supporting bodies 200, a first sensitive structure 300, a second sensitive structure 400, and a load-bearing beam 500 for connecting the second sensitive structure 400 and the first sensitive structure 300. The two supporting bodies 200 are fixed on the surface of the substrate 100 and are oppositely arranged at intervals. The load-bearing beam 500 is erected between the two support bodies 200 and is respectively and fixedly connected with the two support bodies 200. The straight line of the two supporting bodies 200 is perpendicular to the bearing beam 500.

In one embodiment, the substrate 100 may be glass or silicon dioxide. In one embodiment, a metal lead layer may be disposed on the surface of the substrate 100 and electrically connected to the first sensitive structure 300 and the second sensitive structure 400 through the two supporting bodies 200. In one embodiment, the two supporting bodies 200 and the load-bearing beam 500 may be integrally provided. In one embodiment, the first sensitive structure 300, the second sensitive structure 400 and the load-bearing beam 500 may be integrally disposed. In an embodiment, the first sensitive structure 300, the second sensitive structure 400, and the load-bearing beam 500 may be made of silicon, and are etched to obtain corresponding shapes. It will be appreciated that the first sensitive structure 300 and the second sensitive structure 400 are used to detect acceleration.

It can be understood that the two supporting bodies 200 are used for suspending the first sensitive structure 300, the second sensitive structure 400 and the load-bearing beam 500. The two supports 200 are two anchor points. The shape and size of the two supporting bodies 200 are not limited, and can be set according to actual needs. In one embodiment, the support 200 may have a cylindrical shape. It is understood that the first sensitive structure 300 and the second sensitive structure 400 are differential structures adopted by the MEMS accelerometer 10 to reduce common mode errors. The detection results of the first sensitive structure 300 and the second sensitive structure 400 are compared or cooperatively processed, so that the detection results can be more accurate.

In this embodiment, the first sensitive structure 300 and the second sensitive structure 400 are connected to the substrate 100 through the two supports 200, so that the number of anchor points is reduced, and the influence of thermal stress between a plurality of anchor points on the first sensitive structure 300 and the second sensitive structure 400 is avoided. When the thermal stress generated by the substrate 100 is transferred to the load-bearing beam 500 through the two supporting bodies 200, the trend of the thermal stress on the load-bearing beam 500 is shown on the straight line of the two supporting bodies 200, which is perpendicular to the measuring direction of the first sensitive structure 300 and the second sensitive structure 400, so that the influence on the measuring result can be avoided. The first sensitive structure 300 and the second sensitive structure 400 are connected only through the load-bearing beam 500, so that the contact area is small, and the mechanical coupling between the first sensitive structure 300 and the second sensitive structure 400 can be avoided as much as possible.

In one embodiment, the number of the bearing beams 500 is two and the bearing beams 500 are arranged at intervals, one of the bearing beams 500 is connected between the first sensitive structure 300 and the two supporting bodies 200, and the other bearing beam 500 is connected between the second sensitive structure 400 and the two supporting bodies 200. In this embodiment, the first sensing structure 300 and the second sensing structure 400 are completely isolated, so that the mechanical coupling between the first sensing structure 300 and the second sensing structure 400 is avoided, and the measurement result is more accurate.

In one embodiment, the first sensing structure 300 and the second sensing structure 400 have the same structure and are symmetrically arranged. In this embodiment, after the measurement structures of the first sensitive structure 300 and the second sensitive structure 400 are obtained, the common mode error can be reduced through subtraction, so that the measurement result is more accurate. It is understood that the first sensing structure 300 is disposed axisymmetrically with the second sensing structure 400. In the case where the second sensitive structure 400 is the same as the first sensitive structure 300, only the first sensitive structure 300 needs to be explained.

In one embodiment, the two supporting bodies 200 are disposed on the symmetry axis of the first sensitive structure 300 and the second sensitive structure 400. It is understood that the center point of the load-bearing beam 500 is set at the center point of the symmetry axis of the first sensitive structure 300 and the second sensitive structure 400. The symmetry axis of the first sensitive structure 300 and the second sensitive structure 400 is the straight line where the two supporting bodies 200 are located. In this embodiment, on one hand, the structure of the MEMS accelerometer 10 can be more regular, thereby facilitating simplification of the production process. On the other hand, the structure of the MEMS accelerometer 10 can be made more stable.

In one embodiment, the first sensitive structure 300 includes a first isolation frame 310. The first isolation frame 310 is disposed on the periphery of the first sensitive structure 300. The second sensitive structure 400 comprises a second isolation frame 410. The second isolation frame 410 is disposed on the periphery of the second sensitive structure 400. The second isolation frame 410 is connected to the first isolation frame 310 through the load-bearing beam 500. In this embodiment, the first isolation frame 310 and the second isolation frame 410 may be used to isolate thermal stress transferred by the substrate 100, and may also be used to isolate an influence between the first sensitive structure 300 and the second sensitive structure 400, so that the measurement result is more accurate.

In one embodiment, the first sensing structure 300 further comprises a mass 320 and at least one pair of support beams 330. The mass 320 is connected to the first isolation frame 310 through the support beams 330. The at least one pair of support beams 330 are oppositely disposed on two sides of the mass 320 far away from the load-bearing beam 500. The deformation direction of the support beam 330 is parallel to the extending direction of the bearing beam 500. In one embodiment, the support beam 330 may be a U-beam. In one embodiment, the first sensing structure 300 further includes two pairs of the supporting beams 330, which are respectively disposed on two sides of the mass 320 away from the bearing beam 500.

In this embodiment, the support beams 330 may move the mass 320 in the deformation direction of the support beams 330 according to the change of the acceleration, so that the acceleration is obtained according to the moving distance of the mass 320.

In one embodiment, the end of the support beam 330 connected to the first isolation frame 310 is perpendicular to the first isolation frame 310 and parallel to the symmetry axes of the first sensitive structure 300 and the second sensitive structure 400. A coordinate system may be established on the plane where the first sensitive structure 300 is located, a straight line where the symmetry axes of the first sensitive structure 300 and the second sensitive structure 400 are located is an X axis, and a direction perpendicular to the symmetry axes is a Y axis. In this embodiment, the stiffness of the support beam 330 in the Y direction is small, and the stiffness in the X direction is large, so that the loss of the inertial force in the Y direction on the support beam 330 can be reduced, and the inter-axis coupling in the direction X, Y can be reduced, so that the acceleration measurement result is more accurate.

In one embodiment, the first sensitive structure 300 further comprises a lever 340 and a resonator 350. The resonator 350 has one end connected to the first isolation frame 310 and the other end connected to the lever 340. The end of the lever 340 remote from the resonator 350 is connected to the mass 320. The lever 340 is used to amplify the force of the mass 320 and transmit the amplified force to the resonator 350. In this embodiment, the lever 340 may amplify the force generated by the mass 320 due to the movement to the resonator 350, so that the resonator 350 may detect the deformation more easily, and the sensitivity may be enhanced.

In one embodiment, the number of the levers 340 is two and symmetrically arranged. The lever 340 includes a lever input beam 341, a lever body beam 342, a lever output beam 343, a lever fulcrum 344, and a fulcrum fixing beam 345. One end of the lever input beam 341 is connected to the mass block 320. One end of the lever body beam 342 is connected to the end of the lever input beam 341 away from the mass 320. The lever body beam 342 extends in a direction perpendicular to the deformation direction of the support beam 330. The lever output beam 343 has one end connected to the other end of the lever body beam 342 remote from the lever input beam 341 and the other end connected to the resonator 350. The lever fulcrum 344 is disposed on the lever body beam 342 near the lever output beam 343. The fulcrum fixing beam 345 is connected between the lever fulcrum 344 and the first barrier frame 310.

In this embodiment, the force applied by the mass 320 is transferred through the lever input beam 341 to the lever body beam 342. The lever body beam 342 transmits the force to the lever output beam 343 after increasing the force by the lever fulcrum 344. The lever output beam 343 transmits the increased force to the resonator 350, affecting the resonant frequency of the resonator 350. By measuring the change in the resonant frequency, the acceleration can be obtained.

In one embodiment, the resonator 350 may be a double-ended fixed tuning fork structure. In one embodiment, the resonator 350 includes two parallel resonant beams 351, two connecting beams 352, a plurality of first movable comb teeth 353, and a plurality of first stationary comb teeth 354. The resonance beam 351 has one end connected to the lever output beam 343 and the other end connected to the first isolation frame 310. The two connecting beams 352 are respectively disposed at two ends of the resonant beams 351 and connected between the two resonant beams 351. The plurality of first movable comb teeth 353 are provided to the resonance beam 351. The plurality of first stationary comb teeth 354 are fixed to the substrate 100 and are distributed in a finger-like manner with the plurality of moving comb teeth.

It is understood that the first movable comb 353 and the first stationary comb 354 are respectively connected to positive and negative electrodes. In one embodiment, the resonant beam 351 has a plurality of pairs of moving and static comb teeth on two sides. It will be appreciated that each of the first movable fingers 353 forms a differential capacitance with the adjacent first stationary fingers 354. The first static comb 354 may serve as a driving electrode (for driving the resonance beam 351 to vibrate) and a detecting electrode (for detecting the resonance frequency of the resonance beam 351), and specific signals may be separated by an external circuit. In one embodiment, the plurality of first movable comb teeth 353 may be fixed to the resonance beam 351 by a comb rack. The resonance beam 351 may vibrate in the extending direction of the first movable comb teeth 353.

In this embodiment, the resonance frequency of the resonance beam 351 changes after receiving the force transmitted by the lever output beam 343, so that the acceleration is measured.

Please refer to fig. 3. In one embodiment, the MEMS accelerometer 10 includes a plurality of fixed blocks 600 fixed to the substrate 100. It is understood that the first stationary comb 354 is disposed on the fixed block 600. The fixing block 600 is used for fixing the position of the first stationary comb 354. The fixed block 600 may further connect the first stationary comb teeth 354 to a conductive line of the substrate 100 to connect electrodes. In one embodiment, the fixing block 600 may be a conductor. In one embodiment, the surface of the fixing block 600 is provided with a metal coating.

Please refer to fig. 4. In one embodiment, the first sensing structure 300 includes a plurality of second moving comb teeth 360 and a plurality of second stationary comb teeth 370. The plurality of second movable comb teeth 360 are disposed on the mass block 320. The plurality of second stationary comb teeth 370 are fixed to the substrate 100 and interdigitate with the plurality of second moving comb teeth 360. In one embodiment, the second stationary comb teeth 370 may be fixed to the substrate 100 by anchor points and electrically connected to metal leads on the surface of the substrate 100. The anchor point may also be the fixed block 600.

In this embodiment, a MEMS capacitive accelerometer may be formed to measure acceleration by the movement of the mass 320 causing a change in capacitance.

In one embodiment, the MEMS accelerometer 10 includes a first metal layer 710 and a second metal layer 720. The first metal layer 710 is interposed between the support 200 and the substrate 100, and connects the substrate 100 and the support 200. The second metal layer 720 is sandwiched between the fixed block 600 and the substrate 100, and is used for connecting the substrate 100 and the fixed block 600. In one embodiment, the first metal layer 710 and the second metal layer 720 may be sputtered on the surface of the substrate 100. In one embodiment, the support 200 may be fixed on the first metal layer 710 by bonding. The fixed block 600 may be bonded to the second metal layer 720. In one embodiment, the first metal layer 710 and the second metal layer 720 may be made of the same material. In one embodiment, the first metal layer 710 and the second metal layer 720 may be pure metals (e.g., copper, gold, nickel) or alloys.

In this embodiment, the first metal layer 710 and the second metal layer 720 are used to fix the supporting body 200 and the fixing block 600 to the substrate 100, so that the upper and lower layers are more firm and the stability of the whole structure is improved.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A MEMS accelerometer, comprising:

a substrate (100);

two supporting bodies (200) fixed on the surface of the substrate (100) and arranged oppositely and at intervals;

the sensing device comprises a first sensing structure (300), a second sensing structure (400) and a bearing beam (500) used for connecting the second sensing structure (400) and the first sensing structure (300), wherein the bearing beam (500) is erected between the two supporting bodies (200) and is respectively and fixedly connected with the two supporting bodies (200), a straight line where the two supporting bodies (200) are located is perpendicular to the bearing beam (500), and the measuring directions of the first sensing structure (300) and the second sensing structure (400) are consistent with the extending direction of the bearing beam (500).

2. The MEMS accelerometer according to claim 1, wherein the first sensitive structure (300) and the second sensitive structure (400) are structurally identical and symmetrically arranged.

3. The MEMS accelerometer according to claim 2, wherein the two supports (200) are arranged at the symmetry axes of the first sensitive structure (300) and the second sensitive structure (400).

4. The MEMS accelerometer according to claim 2, wherein the first sensitive structure (300) comprises a first isolation frame (310) disposed at a periphery of the first sensitive structure (300);

the second sensitive structure (400) comprises a second isolation frame (410) which is arranged on the periphery of the second sensitive structure (400), and the second isolation frame (410) is connected with the first isolation frame (310) through the bearing beam (500).

5. The MEMS accelerometer according to claim 4, wherein the first sensing structure (300) further comprises a mass (320) and at least one pair of support beams (330), the mass (320) is connected to the first isolation frame (310) through the support beams (330), the at least one pair of support beams (330) is oppositely disposed on two sides of the mass (320) far away from the load-bearing beam (500), and the deformation direction of the support beams (330) is parallel to the extension direction of the load-bearing beam (500).

6. The MEMS accelerometer according to claim 5, wherein the first sensing structure (300) further comprises a lever (340) and a resonator (350), the resonator (350) is connected to the first isolation frame (310) at one end and to the lever (340) at the other end, the lever (340) is connected to the mass (320) at the end away from the resonator (350), and the lever (340) is configured to transmit the amplified force of the mass (320) to the resonator (350).

7. The MEMS accelerometer according to claim 6, wherein the number of levers (340) is two and arranged symmetrically, the levers (340) comprising:

a lever input beam (341) having one end connected to the mass (320);

the lever main body beam (342) is connected with the end part, away from the mass block (320), of the lever input beam (341) at one end, and the extending direction of the lever main body beam (342) is perpendicular to the deformation direction of the support beam (330);

a lever output beam (343) having one end connected to the other end of the lever body beam (342) away from the lever input beam (341) and the other end connected to the resonator (350);

a lever fulcrum (344) disposed on the lever body beam (342) proximate to the lever output beam (343); and

a fulcrum fixing beam (345) connected between the lever fulcrum (344) and the first isolation frame (310).

8. The MEMS accelerometer according to claim 7, wherein the resonator (350) comprises:

two parallel resonance beams (351) with one end connected with the lever output beam (343) and the other end connected with the first isolation frame (310);

two connecting beams (352) respectively arranged at two ends of the resonance beams (351) and connected between the two resonance beams (351);

a plurality of first movable comb teeth (353) provided to the resonance beam (351); and

a plurality of first stationary comb teeth (354) fixed to the substrate (100) and interdigitating with the plurality of first moving comb teeth (353).

9. The MEMS accelerometer according to claim 8, comprising a plurality of fixed blocks (600) fixed to the substrate (100), the first stationary comb teeth (354) being arranged on the fixed blocks (600).

10. The MEMS accelerometer according to claim 5, wherein the first sensitive structure (300) comprises:

a plurality of second movable comb teeth (360) arranged on the mass block (320); and

a plurality of second stationary comb teeth (370) fixed to the substrate (100) and interdigitating with the plurality of second moving comb teeth (360).

11. The MEMS accelerometer of claim 9, comprising:

a first metal layer (710) interposed between the support body (200) and the substrate (100) and connecting the substrate (100) and the support body (200);

and the second metal layer (720) is clamped between the fixed block (600) and the substrate (100) and is used for connecting the substrate (100) and the fixed block (600).