CN111381073B

CN111381073B - MEMS accelerometer and method for improving shock resistance thereof

Info

Publication number: CN111381073B
Application number: CN202010368578.8A
Authority: CN
Inventors: 邹波; 郭梅寒
Original assignee: Shendi Semiconductor Shaoxing Co ltd
Current assignee: Shendi Semiconductor Shaoxing Co ltd
Priority date: 2020-05-01
Filing date: 2020-05-01
Publication date: 2021-11-30
Anticipated expiration: 2040-05-01
Also published as: CN111381073A

Abstract

The invention provides an MEMS accelerometer and a method for improving shock resistance of the MEMS accelerometer, wherein the MEMS accelerometer comprises damping comb teeth, the damping comb teeth comprise movable comb teeth and fixed comb teeth, electric signals are loaded on the movable comb teeth and the fixed comb teeth to generate electrostatic force suitable for attraction of the movable comb teeth and the fixed comb teeth, and the movable comb teeth are suitable for generating deformation under the action of the electrostatic force so as to enable the movable comb teeth to be closer to the fixed comb teeth than before deformation.

Description

MEMS accelerometer and method for improving shock resistance thereof

Technical Field

The invention relates to the field of semiconductor manufacturing, in particular to an MEMS accelerometer and a method for improving shock resistance of the MEMS accelerometer.

Background

MEMS (Micro Electro Mechanical System) devices have been widely used in consumer electronics, medical treatment, and automobiles due to their small size, low cost, and good integration. The MEMS accelerometer is one of the most common MEMS devices at present, and is widely applied to smart phones, unmanned aerial vehicles, smart bracelets, weighing cars, somatosensory remote controllers and the like.

The current most mainstream MEMS accelerometer adopts a capacitive detection principle, and generally includes a sensitive unit part and a capacitance signal processing circuit part, wherein when the sensitive unit part is in an external acceleration environment, acceleration changes are converted into capacitance changes, and then the capacitance signal is converted into a voltage signal by the capacitance signal processing circuit, and then the voltage signal is converted into a digital form by an analog-to-digital converter so as to be compatible with various application environments.

The sensitive unit part typically comprises the following components: fixed anchor point, movable quality piece, elastic beam, detection broach. The movable mass block is connected to the fixed anchor point through the elastic beam, when the movable mass block is in an external acceleration environment, the movable mass block can generate displacement due to the influence of inertia force, and the moving amplitude of the movable mass block in different directions can be controlled by adjusting the rigidity. The detection comb teeth comprise a movable part and a fixed part, the movable part is overlapped with the fixed part, the overlapped part generates capacitance, the movable part is directly connected to the movable mass block, and the fixed part is connected to a fixed anchor point with different anchor point potentials connected with the movable mass block. When external acceleration is detected, the movable part of the detection comb teeth generates displacement along with the movable mass block, the fixed part does not move, the capacitance between the two parts of the detection comb teeth changes corresponding to the acceleration amplitude, and the sensitivity of the detection comb teeth shows that the change rate of the capacitance between the detection comb teeth along with the external acceleration.

In order to improve the sensitivity of capacitive MEMS accelerometers of the type described above, obvious alternatives include increasing the mass of the movable mass, increasing the logarithm of the detection comb or reducing the stiffness of the spring beam. The former two methods require increasing the size of the structure, and are limited by the chip size requirement and the cost control requirement, and the size cannot be increased endlessly, so the rigidity of the elastic beam is often reduced in practical devices.

When the rigidity of the elastic beam is low, when the accelerometer detects external acceleration, the movement amplitude of the movable mass block is large, and one side effect is that when the chip is in overload acceleration, the movement amplitude of the movable mass block is often too large, so that impact between structures or excessive bending of the elastic beam is caused to damage the movable mass block.

In view of the above problems, one solution commonly adopted in the industry is to process a sensitive unit in a sealed cavity, increase the air pressure in the cavity to increase the air damping of the overlapping portion of the detection comb teeth, and reduce the displacement caused by a part of external impact by a reverse damping force, as shown in fig. 1. Some sensitive unit structure designs can increase extra damping broach, also movable part is connected on movable mass block, and the fixed part is connected on the anchor point, further increases damping force, improves the ability of resisting external impact. However, the damping force of the damping comb teeth is also proportional to the area opposite to the comb teeth, and the damping comb teeth also occupy extra chip area and cannot be designed too large.

On the other hand, as the sensitive cell structure of the MEMS accelerometer, including the damping comb teeth, is usually formed by Deep Reactive Ion Etching (DRIE) on a silicon structure, the process has certain requirements on the depth/width ratio of the processing target structure, such as 50/1, 100/1. The sensitive unit structure of the capacitive MEMS accelerometer has requirements on the thickness of the structure in order to increase the mass of the movable mass and the capacitance of the comb teeth of the detection comb, and the thickness of the structure is usually 10-60 um. The depth-to-width ratio and the etched side wall morphology of the DRIE process are comprehensively considered, and the structural spacing is usually more than or equal to 1.5 um. In the case of damping combs, the damping is greater when the spacing in the direction of their relative movement is smaller, this spacing again being limited to the DRIE machining minimum spacing described above.

Disclosure of Invention

In view of the problems in the prior art, the present invention aims to improve the shock resistance of a MEMS accelerometer, in particular to improve the actual effective damping of the damping comb teeth without additionally increasing the occupied area of the damping comb.

In order to achieve the above object, the present invention provides an MEMS accelerometer, which comprises a damping comb, wherein the damping comb comprises a movable comb and a fixed comb, and the movable comb and the fixed comb are loaded with electrical signals suitable for attracting each other.

Further, the MEMS accelerometer also comprises a limiting structure, and the limiting structure limits the limit position of the movable comb teeth close to the fixed comb teeth corresponding to the movable comb teeth.

Further, the limit structure is loaded with the same electric signal as the movable comb teeth.

Further, the movable comb teeth comprise a first part and a second part, the first part is closer to the corresponding fixed comb teeth relative to the second part, and the second part is used for cooperating with the limiting structure to limit the limit position of the movable comb teeth close to the corresponding fixed comb teeth.

Further, the fixed comb teeth are loaded with direct current voltage.

Further, when the MEMS accelerometer and the gyroscope are simultaneously applied by the device, the direct-current voltage loaded by the fixed comb teeth is shared with the gyroscope.

Further, the MEMS accelerometer and the gyroscope are disposed within the same package.

Further, a direct-current voltage pin of the gyroscope is connected to an electric signal input end of the fixed comb teeth.

Furthermore, the same fixed comb teeth correspond to the two movable comb teeth and are respectively used for providing damping forces in opposite directions.

The invention also provides a method for improving the impact resistance of the MEMS accelerometer, which loads electric signals on the movable comb teeth and the fixed comb teeth of the damping comb teeth to generate electrostatic force suitable for the attraction of the movable comb teeth and the fixed comb teeth, wherein the movable comb teeth are suitable for generating deformation under the action of the electrostatic force, so that the movable comb teeth are closer to the fixed comb teeth than before deformation.

Further, a limiting structure is arranged, and the limiting structure limits the limit position of the movable comb teeth close to the fixed comb teeth corresponding to the movable comb teeth.

Further, the fixed comb teeth are loaded with direct current voltage.

Furthermore, the same fixed comb teeth are arranged corresponding to the two movable comb teeth and are respectively used for providing damping forces in opposite directions.

The technical effects are as follows:

compared with the prior art, the MEMS accelerometer and the method for improving the shock resistance of the MEMS accelerometer further improve the shock resistance of the MEMS accelerometer by using the existing damping comb teeth on the premise of not increasing the area of a chip; meanwhile, the limit of the processing process limit on the comb tooth spacing can be made up, and a wider process window is provided for the process; the whole scheme is easy to realize.

The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.

Drawings

FIG. 1 is a schematic view of inter-comb air damping;

FIG. 2 is a schematic diagram of a MEMS accelerometer of one embodiment of the invention;

FIG. 3 is a schematic diagram of the configuration of the movable part of the damping comb when deformed in one embodiment of the present invention;

fig. 4 is a partially enlarged schematic view of fig. 2.

Detailed Description

In the description of the embodiments of the present invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the invention. The drawings are schematic diagrams or conceptual diagrams, and the relationship between the thickness and the width of each part, the proportional relationship between the parts and the like are not completely consistent with actual values.

FIG. 2 shows a schematic structural diagram of a MEMS accelerometer according to an embodiment of the present invention, which includes fixed anchors 101-110, elastic beams 201-204, and a movable mass 300. The fixed anchor 101, the movable mass block 300 and the fixed anchor 102 are arranged along the X-axis direction; one end of the movable mass block 300 is connected with the fixed anchor point 101 through the

elastic beams

201 and 202, and the other end is connected with the fixed anchor point 102 through the

elastic beams

203 and 204, in the embodiment, the elastic beams 201 to 204 are all in a U-shaped structure, and the U-shaped openings are arranged along the Y-axis direction, so that the movable mass block 300 can move along the X-axis direction.

The

fixed anchors

103, 105, 107, 109 are disposed on the upper and lower sides of the movable mass 300 symmetrically to the fixed

anchors

104, 106, 108, 110. The fixed anchor point 103 is provided with a fixed comb 103 a; the fixed anchor 104 is provided with a fixed comb 104 a; the fixed anchor points 105 are provided with fixed comb teeth 105 a; fixed anchor 106 is last to be provided with fixed broach 106a, and the quantity of the fixed broach that sets up on fixed anchor 103 ~ 106 in this embodiment is 3. The movable mass 300 is provided with a movable comb tooth 303a fitted to the fixed comb tooth 103a, a movable comb tooth 304a fitted to the fixed comb tooth 104a, a movable comb tooth 305a fitted to the fixed comb tooth 105a, and a movable comb tooth 306a fitted to the fixed comb tooth 106a, respectively. The fixed comb teeth 103a and the movable comb teeth 303a, the fixed comb teeth 104a and the movable comb teeth 304a, the fixed comb teeth 105a and the movable comb teeth 305a, and the fixed comb teeth 106a and the movable comb teeth 306a form a set of detection comb teeth, respectively, and form a detection capacitor, and the displacement of the movable mass 300 in the X-axis direction can be reflected by the detection capacitor.

The fixed anchor point 107 is provided with fixed

comb teeth

107a and 107 b; the fixed anchor point 108 is provided with

fixed comb teeth

108a and 108 b; the fixed anchor point 109 is provided with

fixed comb teeth

109a and 109 b; the fixed anchor 110 is provided with

fixed combs

110a and 110 b. The movable mass 300 is provided with movable comb teeth 307a to 307d that fit with the fixed

comb teeth

107a and 107b, movable comb teeth 308a to 308d that fit with the

fixed comb teeth

108a and 108b, movable comb teeth 309a to 309d that fit with the

fixed comb teeth

109a and 109b, and movable comb teeth 310a to 310d that fit with the

fixed comb teeth

110a and 110b, respectively. Specifically,

movable comb teeth

307a, 307c are fitted to fixed comb tooth 107a,

movable comb teeth

307b, 307d are fitted to fixed comb tooth 107b,

movable comb teeth

308a, 308c are fitted to fixed comb tooth 108a,

movable comb teeth

308b, 308d are fitted to fixed comb tooth 108b,

movable comb teeth

309a, 309c are fitted to fixed comb tooth 109a,

movable comb teeth

309b, 309d are fitted to fixed comb tooth 109b,

movable comb teeth

310a, 310c are fitted to fixed comb tooth 110a,

movable comb teeth

310b, 310d are fitted to fixed comb tooth 110b, and each of the fixed comb teeth on fixed anchors 107 to 110 is disposed between its corresponding pair of movable comb teeth.

The fixed

comb teeth

107a, 107b and the movable comb teeth 307 a-307 d, the

fixed comb teeth

108a, 108b and the movable comb teeth 308 a-308 d, the

fixed comb teeth

109a, 109b and the movable comb teeth 309 a-309 d, the fixed

comb teeth

110a, 110b and the movable comb teeth 310 a-310 d respectively form a set of damping comb teeth, so as to provide reverse damping force when the movable mass block 300 moves in the X-axis direction, specifically, the excessive displacement of the movable mass block 300 is avoided through air damping, if the MEMS accelerometer is overloaded, the air damping between the extra damping comb teeth can play a certain role in buffering, and the instantaneous speed and the maximum displacement amplitude of each movable structure at the moment are reduced.

When the MEMS accelerometer of the embodiment works, a voltage is applied to the fixed end of the damping comb teeth, that is, a voltage is applied to the fixed anchor points 107-110, so that a potential difference is generated between the fixed comb teeth and the movable comb teeth in the damping comb teeth, and for the movable comb teeth, the same potential as the movable mass block 300 depends on the voltage applied to the

fixed anchor points

101 and 102, for example, in some embodiments, the potential difference between the

fixed anchor points

101 and 102 and the fixed anchor points 107-110 is set to be 5-20V. When the potential difference is generated between the fixed comb teeth and the movable comb teeth matched with each other in the damping comb teeth, the electrostatic force between the fixed comb teeth and the movable comb teeth can cause the movable comb teeth to bend, so that the distance between the fixed comb teeth and the movable comb teeth can be further shortened, and the damping provided by the matching of the fixed comb teeth and the movable comb teeth can be further improved.

Taking the fixed anchor 107 and the fixed comb teeth 107a thereon and the

movable comb teeth

307a and 307c engaged with the fixed comb teeth 107a in fig. 2 as an example, the fixed anchor 107 and the

fixed anchors

101 and 102 are applied with electric signals to generate a potential difference between the fixed comb teeth 107a and the

movable comb teeth

307a and 307 c. When the movable mass 300 moves in the positive X-axis direction (i.e., horizontally to the right in fig. 2) under the action of the input acceleration, the movable comb teeth 307a approach the fixed comb teeth 107a along with the movement of the movable mass 300, and the movable comb teeth 307c move away from the fixed comb teeth 107a along with the movement of the movable mass 300, for the movement of the movable mass 300 in the positive X-axis direction, the fixed comb teeth 107a and the movable comb teeth 307a provide a reverse damping force to prevent the movable mass 300 from being excessively displaced in the positive X-axis direction. As described above, the air damping amount formed by the fixed comb-tooth 107a and the movable comb-tooth 307a is larger as the distance between the fixed comb-tooth 107a and the movable comb-tooth 307a is smaller. The fixed comb teeth 107a and the movable comb teeth 307a have a potential difference, and the movable comb teeth 307a bend towards the fixed comb teeth 107a under the action of electrostatic force, so that when the movable comb teeth 307a move along with the movable mass block 300, the movable comb teeth are closer to the fixed comb teeth 107a than before deformation occurs, the distance between the movable comb teeth and the fixed comb teeth is further reduced, and the damping provided by matching the movable comb teeth and the fixed comb teeth is further improved.

Similarly, when the movable mass 300 moves in the negative X-axis direction (i.e., horizontally to the left in fig. 2) under the action of the input acceleration, the movable comb teeth 307c approach the fixed comb teeth 107c along with the movement of the movable mass 300, the movable comb teeth 307a move away from the fixed comb teeth 107a along with the movement of the movable mass 300, and the fixed comb teeth 107c and the movable comb teeth 307c provide a reverse damping force for the movement of the movable mass 300 in the negative X-axis direction, so as to prevent the movable mass 300 from being excessively displaced in the negative X-axis direction. The fixed comb teeth 107c and the movable comb teeth 307c have a potential difference, and the movable comb teeth 307c bend towards the fixed comb teeth 107c under the action of electrostatic force, so that when the movable comb teeth 307c move along with the movable mass block 300, the movable comb teeth are closer to the fixed comb teeth 107c than before deformation occurs, the distance between the movable comb teeth and the fixed comb teeth is further reduced, and the damping provided by matching the movable comb teeth and the fixed comb teeth is further improved.

The degree of curvature of the movable comb teeth in the damping comb teeth affects the magnitude of the potential difference, the structures (shapes, sizes, etc.) of the fixed comb teeth and the movable comb teeth, the positions at which the fixed comb teeth and the movable comb teeth are engaged, and the like. Also, there may be some corresponding arrangements to avoid bending of the fixed comb teeth, such as making the fixed comb teeth wider relative to the movable comb teeth to increase their stiffness. The above can be adjusted according to the actual product conditions, and the invention is not limited thereto.

The MEMS accelerometer of the embodiment is further provided with limiting blocks 401 to 416, and the limiting blocks 401 to 416 are respectively matched with the movable comb teeth 307a to 307d, 308a to 308d, 309a to 309d and 310a to 310d, and are specifically arranged between the movable comb teeth matched with the limiting blocks and the fixed comb teeth matched with the movable comb teeth. As shown in FIG. 3, when the movable comb teeth 307a bend toward the fixed comb teeth 107a under the action of electrostatic force, to avoid the attraction or sticking between the comb teeth, the limit block 401 limits the movable comb teeth 307a to approach the fixed comb teeth 107a, so that the two are not in contact. Meanwhile, the potential connected to the stopper 401 needs to be consistent with the movable comb teeth 307a, so that even if the movable comb teeth 307a collide with the stopper 401, the potential signal on the movable comb teeth 307a is not affected.

In this embodiment the movable comb teeth of the damping comb teeth are arranged in a stepped shape, as shown in fig. 4, the movable comb tooth 307a comprises a first part 501, a second part 502 and a third part 503, which are connected in sequence, wherein the first part 501 and the third part 503 are arranged in parallel and the second part 502 is arranged perpendicular to the first part 501 and the third part 503. The first portion 501 is closer to the fixed comb tooth 107a, which cooperates with the movable comb tooth 307a, than the third portion 503. The position of the stopper 401 is limited such that it will only contact the third portion 503 of the movable comb teeth 307a and not the first portion 501, so that the stopper function is achieved while the first portion 501 is as close as possible to the fixed comb teeth 107a, thereby increasing the damping as much as possible. Meanwhile, the position of the limiting block 401 does not need to be too close to the fixed comb teeth 107a, and the difficulty in the process is reduced.

In another embodiment, the MEMS accelerometer of the present invention is a part of a six-axis sensor, i.e. the accelerometer and the gyroscope are integrated in a single chip, and since a relatively high dc voltage is required to increase the gyro motion amplitude when driving a typical capacitive MEMS gyroscope, the dc voltage signal can be directly applied to the MEMS accelerometer as a voltage loading signal at the fixed end of the damping comb, thereby avoiding adding an external circuit or a chip pin.

The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.

Claims

1. An MEMS accelerometer is characterized by comprising damping comb teeth and a limiting structure, wherein the damping comb teeth comprise movable comb teeth and fixed comb teeth, electric signals are loaded on the movable comb teeth and the fixed comb teeth to generate electrostatic force suitable for the movable comb teeth and the fixed comb teeth to attract each other, and the movable comb teeth are suitable for being deformed under the action of the electrostatic force so as to enable the movable comb teeth to be closer to the fixed comb teeth than before the movable comb teeth are deformed; the movable comb teeth comprise a first part, a second part and a third part, the second part is respectively connected with the first part and the third part, the first part is closer to the fixed comb teeth relative to the third part, and the third part is used for being matched with the limiting structure so as to avoid the movable comb teeth from contacting with the fixed comb teeth.

2. The MEMS accelerometer according to claim 1, wherein the limiting structure is loaded with the same electrical signal as the movable comb.

3. The MEMS accelerometer of claim 1, wherein the fixed comb is loaded with a dc voltage.

4. The MEMS accelerometer of claim 3, wherein the dc voltage applied by the fixed comb is common to the gyroscope when the MEMS accelerometer and gyroscope are simultaneously applied by the device.

5. The MEMS accelerometer of claim 4, wherein the MEMS accelerometer and the gyroscope are disposed within a same package.

6. The MEMS accelerometer according to claim 5, wherein a dc voltage pin of the gyroscope is connected to an electrical signal input of the fixed comb.

7. The MEMS accelerometer according to claim 1, wherein the same fixed comb teeth corresponds to two movable comb teeth for providing damping forces in opposite directions.

8. A method for improving the shock resistance of an MEMS accelerometer is characterized in that electric signals are loaded on movable comb teeth and fixed comb teeth of damping comb teeth to generate electrostatic force suitable for the movable comb teeth and the fixed comb teeth to attract each other, and the movable comb teeth are suitable for being deformed under the action of the electrostatic force so as to enable the movable comb teeth to be closer to the fixed comb teeth than before the movable comb teeth are deformed; arranging a limiting structure; the movable comb teeth comprise a first part, a second part and a third part, the second part is respectively connected with the first part and the third part, the first part is closer to the fixed comb teeth relative to the third part, and the third part is used for being matched with the limiting structure so as to avoid the movable comb teeth from contacting with the fixed comb teeth.