A MEMS accelerometer anti-shock stop structure

Abstract

The present invention discloses a MEMS accelerometer anti-impact stop structure, including a stop convex block, a support beam, a fixed frame, a hollow structure and an elastic beam; the support beam and the fixed frame form a rectangular frame, a hollow structure is arranged inside the rectangle, the hollow structure is composed of a parallelogram structure and a triangle structure, the stop convex block and the support beam are fixed on a substrate layer, the fixed frame and the hollow structure are suspended, and the two sides of the fixed frame are connected to the MEMS accelerometer through elastic beams. When there is a strong impact from the outside world causing a large displacement of the movable mass block, the hollow structure converts the work done by the impact force into the plasticity required for the deformation of its own structure, reduces the displacement and stress of the elastic beam, avoids the breakage of the elastic beam, and then reduces the displacement of the movable mass block, reduces the stress on the stop convex block, accurately controls the stop distance, and effectively avoids the problem of the movable comb teeth on the mass block hitting the fixed comb teeth to cause the MEMS accelerometer to fail.

Description

Technical Field

[0001] The invention relates to the field of MEMS accelerometers, and in particular to an anti-shock stop structure of a MEMS accelerometer. Background Art

[0002] Micro-Electro-Mechanical Systems (MEMS) accelerometers are a common sensor element in MEMS. Since they were first proposed, they have experienced nearly half a century of development and evolution. With the gradual expansion of the scope of application, MEMS accelerometers have also been gradually applied to electronic devices, medical equipment, and automotive safety, etc., from being limited to military and aerospace fields at the earliest.

[0003] The most mainstream MEMS accelerometer currently uses the capacitive detection principle, which usually includes a sensitive unit part and a capacitive signal processing circuit part. The mass block of the sensitive unit part is connected to a fixed anchor point through an elastic beam. When the external acceleration impacts, the mass block shifts or moves along a specific axis. The displacement can be detected by the change in capacitance to achieve the measurement of the input acceleration. However, when the external impact force is too large, the large displacement or deflection of the mass block will cause the movable comb teeth on the mass block to collide with the fixed comb teeth on the corresponding detection electrode, or cause the beam structure connected to the mass block to break. To avoid this situation, it is necessary to limit the displacement or deflection of the mass block under strong impact conditions.

[0004] There are currently two main types of displacement limiting structures: the first structure is to symmetrically distribute fixed blocks with anti-collision bumps on the outside of the fixed anchor points of the connecting beam, or to set a central fixed mass block with anti-collision bumps in the hollowed-out area in the center of the mass block. The central fixed mass block can limit the movement range to about a few microns. Although this method can limit the displacement of the mass block, when the mass block collides with the fixed stop block, the fixed stop block is not easy to deform, which will cause it to break and fail under strong impact conditions. The second method is to set a suspended honeycomb stop structure supported by an anchor point close to one side of the mass block. Although this method can use the honeycomb structure to disperse the impact stress, the design cannot accurately control the stop distance, and it is difficult to determine whether the detection comb teeth on the mass block hit the fixed comb teeth under a large impact, causing failure. Summary of the invention

[0005] In view of the above problems, the present invention provides a MEMS accelerometer anti-impact stop structure to limit the displacement of the mass block under strong impact conditions and convert the work done by the impact force into the plasticity required for its own structural deformation.

[0006] The present invention adopts the following technical solutions:

[0007] A MEMS accelerometer anti-impact stop structure, characterized in that it includes a stop bump, a support beam, a fixed frame, a hollow structure and an elastic beam; one end of the stop bump is parallel to the mass block of the MEMS accelerometer, and the other end is connected to the middle of the support beam; both ends of the support bridge are connected to the fixed frame; the support beam and the fixed frame form a rectangular frame; a hollow structure is provided inside the rectangle; the stop bump and the support beam are fixed to the MEMS accelerometer substrate layer; the fixed frame and the hollow structure are suspended; both sides of the fixed frame are connected to the MEMS accelerometer through elastic beams; the hollow structure is composed of a parallelogram structure and a triangular structure, and the wall thickness and side length of the parallelogram structure and the triangular structure are the same.

[0008] The hollow structure includes three rows of hollows, the top row of hollows is composed of a triangular structure and two parallelogram structures alternately arranged in sequence, the middle row of hollows is composed of parallelogram structures, and a triangular structure is arranged on the right side of the top row of hollows and the middle row of hollows; the bottom row of hollows is composed of two parallelogram structures and a triangular structure alternately arranged in sequence, and a triangular structure is arranged on the left side of the bottom row of hollows and the middle row of hollows;

[0009] The directions of two adjacent triangular structures in the top row of hollows and the bottom row of hollows are opposite.

[0010] Furthermore, there is a gap between the stop protrusion and the movable mass block of the MEMS accelerometer.

[0011] Furthermore, the gap is smaller than the comb teeth spacing of the MEMS accelerometer.

[0012] Furthermore, the stop structures are symmetrically distributed with mass blocks.

[0013] Furthermore, the relationship between the dynamic peak stress of the hollow structure and the wall thickness side length is:

[0014] σ p =σ ys B(t / L) k

[0015] In the formula, σ p is the dynamic peak stress, MPa; σ ys is the yield stress of the hollow structure substrate, MPa; B is the relationship coefficient between the dynamic peak stress and the wall thickness side length ratio, ranging from 4.10 to 7.06; k is the relationship index between the dynamic peak stress and the wall thickness side length ratio, with a value of 1; t is the wall thickness of the parallelogram structure and the triangle structure; L is the side length of the parallelogram structure and the triangle structure.

[0016] Furthermore, the relationship between the dynamic peak stress of the hollow structure and the acute angle of the parallelogram structure is:

[0017] σ p =A′θ 2 +B′θ+C′

[0018] In the formula, σ p is the dynamic peak stress, MPa; A′, B′, and C′ are determined by the specific materials and structural parameters of the hollow structure, the wall thickness to side length ratio, A′ and C′ are positive numbers, and B′ is a negative number; θ is the acute angle of the parallelogram structure, 0°<θ<90°.

[0019] The beneficial effect of the present invention is that when there is a strong impact from the outside world causing the movable mass block to deviate significantly, the hollow structure can help the elastic beam connected to the movable mass block resist the external impact force, that is, convert the work done by the impact force into the plasticity required for its own structural deformation to reduce the displacement and stress of the elastic beam, avoid the elastic beam from breaking, and then reduce the displacement of the movable mass block, and reduce the stress on the stopper protrusion. Limiting the displacement of the mass block under strong impact conditions and accurately controlling the stopper distance effectively avoids the problem of the movable comb teeth on the mass block hitting the fixed comb teeth, causing the MEMS accelerometer to fail. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of the present invention, but are not intended to limit the present invention.

[0021] Figure 1 It is a schematic diagram of the structure of the present invention;

[0022] Figure 2 A schematic diagram of the connection between the present invention and a MEMS accelerometer;

[0023] Figure 3 It is a schematic diagram of the connection between the solid stop structure and the MEMS accelerometer;

[0024] Figure 4 It is a schematic diagram of displacement simulation of the present invention under strong impact;

[0025] Figure 5 This is a schematic diagram of the displacement simulation of the solid stop structure under strong impact;

[0026] Figure 6 It is a schematic diagram of stress simulation of the present invention under strong impact;

[0027] Figure 7 It is a schematic diagram of stress simulation of solid stopper structure under strong impact;

[0028] Figure 8 This is a schematic diagram of displacement simulation when all hollow structures are parallelograms under strong impact;

[0029] Fig. 9 This is a schematic diagram of displacement simulation when all hollow structures are triangles under strong impact;

[0030] Fig.10 Schematic diagram of displacement simulation when all hollow structures are hexagonal under strong impact.

[0031] In the figure: 1-stop convex block, 2-support beam, 3-parallelogram structure, 4-triangular structure, 5-fixed frame, 6-hollow structure, 7-elastic beam, 8-movable frame, 9-movable mass block, 10-fixed mass block. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure shall have the usual meanings understood by persons with ordinary skills in the field to which the present disclosure belongs. The words "include" or "comprise" and the like used in the present disclosure mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0034] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0035] like Figure 1As shown, a MEMS accelerometer anti-impact stop structure is characterized in that it includes a stop bump 1, a support beam 2, a fixed frame 5, a hollow structure 6 and an elastic beam 7; one end of the stop bump 1 is parallel to the mass block of the MEMS accelerometer, and the other end is connected to the middle of the support beam 2; both ends of the support beam 2 are connected to the fixed frame 5; the support beam 2 and the fixed frame 5 form a rectangular frame; a hollow structure 6 is provided inside the rectangle; the stop bump 1 and the support beam 2 are fixed to the substrate layer of the MEMS accelerometer to support the entire structure; the fixed frame 5 and the hollow structure 6 are suspended; the hollow structure 6 is composed of a parallelogram structure 3 and a triangular structure 4, and the wall thickness and side length of the parallelogram structure 3 and the triangular structure 4 are the same; the fixed frame 5 is connected to the MEMS accelerometer on both sides through the elastic beam 7. In this embodiment, the elastic beam 7 is connected to the movable frame 8 of the MEMS accelerometer, as shown in FIG. Figure 2 As shown, since the structure of the MEMS accelerometer is not the focus of the present invention, only the upper half of the structure is shown to illustrate the present invention; the displacement of the movable comb teeth on the movable mass block 9 and the fixed comb teeth on the fixed mass block 10 of the MEMS accelerometer changes, and the external acceleration is measured by detecting the capacitance change.

[0036] The hollow structure includes three rows of hollows, the top row of hollows is composed of a triangular structure and two parallelogram structures alternately arranged in sequence, the middle row of hollows is composed of parallelogram structures, and a triangular structure is arranged on the right side of the top row of hollows and the middle row of hollows; the bottom row of hollows is composed of two parallelogram structures and a triangular structure alternately arranged in sequence, and a triangular structure is arranged on the left side of the bottom row of hollows and the middle row of hollows;

[0037] The directions of two adjacent triangular structures in the top row of hollows and the bottom row of hollows are opposite.

[0038] There is a gap between the stopper convex block 1 and the movable mass block of the MEMS accelerometer, and the gap is smaller than the comb teeth spacing of the MEMS accelerometer to prevent the movable comb teeth on the movable mass block 9 from colliding with the fixed comb teeth on the fixed mass block 10. The size of the gap is adjusted according to actual conditions to accurately control the moving distance of the movable mass block under a large impact.

[0039] The stop structure can be used in plurality at the same time, with the masses being symmetrically distributed.

[0040] Figure 3 The figure is a schematic diagram of the structure of most current impact-resistant stopper structures, which are solid stopper structures. Figure 2 The present invention Figure 3The solid stop structure is subjected to displacement and stress simulation under strong impact. The simulation material of this embodiment is Si_100, the fixing point is the bottom surface in contact with the substrate layer, the impact acceleration direction is vertically upward, and the impact value is 5000g.

[0041] Figure 4 , Figure 5 They are schematic diagrams of the displacement of the hollow and solid stopper structures under strong impact. Figure 4 As shown, the maximum moving distance of the present invention under strong impact is 3.14um, and the moving distance decreases from the outside of the elastic beam 7 to the middle. Figure 5 As shown, the maximum displacement of the solid stop structure under strong impact is 5um, and the moving distance still decreases from the outside to the middle of the elastic beam.

[0042] Figure 6 , 7 are schematic diagrams of stress of hollow and solid stopper structures with elastic beams under strong impact. Figure 6 It can be seen that the maximum stress of the elastic beam 7 connecting the hollow structure 6 is 8.4Mpa, and the stress borne by the hollow structure 6 is 3E-03Mpa. Figure 7 It can be seen that the maximum stress of the elastic beam 7 connected to the solid stop structure is 23Mpa, and the stress borne by the solid structure part is 2.7E-05Mpa, which means that the hollow structure 6 helps the elastic beam resist most of the impact energy by buffering deformation.

[0043] The energy absorption of the hollow structure 6 designed by the present invention is mainly determined by the size and material of the internal unit. By reasonably designing the side length, number of layers, and thickness of the internal unit and adjusting the deformation of the hollow structure 6 under impact conditions, the accelerometer can accurately limit the moving distance of the movable mass block under strong impact conditions and avoid damage to the stop block. Dynamic peak stress is an important variable that determines the buffering performance of the hollow material under dynamic impact loads. The relationship between the dynamic peak stress of the hollow structure 6 and the wall thickness side length is:

[0044] σ p =σ ys B(t / L) k

[0045] In the formula, σ p is the dynamic peak stress, MPa; σ ys is the yield stress of the hollow structure substrate, MPa; B is the relationship coefficient between the dynamic peak stress and the wall thickness side length ratio, ranging from 4.10 to 7.06; k is the relationship index between the dynamic peak stress and the wall thickness side length ratio, with a value of 1; t is the wall thickness of the parallelogram structure and the triangle structure; L is the side length of the parallelogram structure and the triangle structure.

[0046] The relationship between the dynamic peak stress of the hollow structure 6 and the acute angle of the parallelogram structure 3 is:

[0047] σ p =A′θ 2 +B′θ+C′

[0048] In the formula, σ p is the dynamic peak stress, MPa; A′, B′, and C′ are determined by the specific materials and structural parameters of the hollow structure, the wall thickness to side length ratio, A′ and C′ are positive numbers, and B′ is a negative number; θ is the acute angle of the parallelogram structure 3, 0°<θ<90°.

[0049] The hollow structure 6 designed in the present invention has a triangular structure 4 interspersed with the parallelogram structure 3. The triangular structure is more stable than the parallelogram structure, and can prevent the stopper structure from entering the densification stage under strong impact and causing damage.

[0050] Figure 8 , Fig. 9 , Fig.10 This is the impact displacement simulation of different hollow stopper structures, and the simulation conditions are the same as above. Figure 8 As shown, when all hollow structures 6 are parallelograms, the displacement is 5.03um; Fig. 9 As shown, when all the hollow structures 6 are triangles, the displacement is 5.11 um; Fig.10 As shown in Figure 2, when all hollow structures are hexagonal, the displacement is 5.05um, while the displacement of the hollow structure with mixed parallelograms and triangles is only 3.14um (as shown in Figure 2). Figure 4 It is proved that the mixture of parallelogram and triangle structures is more conducive to reducing the stress borne by the elastic beam under large impact.

[0051] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with the profession can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A MEMS accelerometer anti-shock stop structure, characterized in that: The invention comprises a stopper protrusion (1), a support beam (2), a fixed frame (5), a hollow structure (6) and an elastic beam (7); one end of the stopper protrusion (1) is parallel to the mass block of the MEMS accelerometer, and the other end is connected to the middle of the support beam (2); both ends of the support beam (2) are connected to the fixed frame (5); the support beam (2) and the fixed frame (5) form a rectangular frame; a hollow structure (6) is provided inside the rectangle; the stopper protrusion (1) and the support beam (2) are fixed to the substrate layer of the MEMS accelerometer; the fixed frame (5) and the hollow structure (6) are suspended; both sides of the fixed frame (5) are connected to the MEMS accelerometer via the elastic beam (7); the hollow structure (6) is composed of a parallelogram structure (3) and a triangle structure (4), and adjacent parallelogram structures (3) and triangle structures (4) have the same wall thickness and the same side length; The hollow structure (6) comprises three rows of hollows, the top row of hollows is composed of a triangular structure (4) and two parallelogram structures (3) arranged alternately, the middle row of hollows is composed of parallelogram structures (3), and a triangular structure (4) is arranged on the right side of the top row of hollows and the middle row of hollows; the bottom row of hollows is composed of two parallelogram structures (3) and a triangular structure (4) arranged alternately, and a triangular structure (4) is arranged on the left side of the bottom row of hollows and the middle row of hollows; The directions of two adjacent triangular structures (4) in the top row of hollows and the bottom row of hollows are opposite.

2. The MEMS accelerometer anti-shock stop structure according to claim 1, characterized in that: There is a gap between the stop convex block (1) and the movable mass block of the MEMS accelerometer.

3. The MEMS accelerometer anti-shock stop structure according to claim 2, characterized in that: The gap is smaller than the comb teeth spacing of the MEMS accelerometer.

4. The MEMS accelerometer anti-shock stop structure according to claim 1, characterized in that: The stop structures are symmetrically distributed with mass blocks.

5. The MEMS accelerometer anti-shock stop structure according to claim 1, characterized in that: The relationship between the dynamic peak stress of the hollow structure (6) and the wall thickness and side length is: In the formula, is the dynamic peak stress, MPa; is the yield stress of the hollow structure substrate, MPa; is the coefficient of the relationship between dynamic peak stress and wall thickness to side length ratio, with a value range of 4.10-7.06; is the relationship index between dynamic peak stress and wall thickness side length ratio, and takes the value of 1; is the wall thickness of the parallelogram structure and the triangle structure; is the side length of the parallelogram and triangle structures.

6. The MEMS accelerometer anti-shock stop structure according to claim 1, characterized in that: The relationship between the dynamic peak stress of the hollow structure (6) and the acute angle of the parallelogram structure (3) is: In the formula, is the dynamic peak stress, MPa; , , It is determined by the specific materials and structural parameters of the hollow structure, such as the wall thickness to side length ratio. , is a positive number, is a negative number; is the acute angle of the parallelogram structure (3), 0°< <90°.

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