A MEMS stress isolation mechanism and design method thereof

Abstract

The present invention discloses a MEMS stress isolation mechanism and a design method thereof, which belongs to the field of MEMS mechanical design, and is mainly composed of an annular or regular polygonal structure and anchor points distributed at antinodes and node points. During the processing or working process of MEMS devices, due to the mismatch of expansion coefficients of various materials and temperature effects, MEMS devices will be affected by residual stress and thermal stress. Based on the standing wave characteristics of the annular or regular polygonal structure, the antinode points are connected to the substrate anchor points, and the node points are connected to the anchor points of the protected MEMS device, so that stress isolation between the MEMS device substrate and the internal protected MEMS device can be achieved. The present invention has a simple structure and a good stress isolation effect, and can be applied to the mechanical design of various MEMS devices.

Description

Technical Field

[0001] The present invention belongs to the field of MEMS mechanical design, and more specifically, relates to a MEMS stress isolation mechanism and a design method thereof. Background Art

[0002] During the processing or working process of MEMS devices, due to the mismatch of expansion coefficients of various materials or temperature effects, MEMS devices are usually affected by residual stress or thermal stress. At present, the commonly used stress isolation mechanism is composed of a rigid outer frame and an external elastic beam. The protected MEMS device is connected to the rigid outer frame, and the rigid outer frame is connected to the substrate anchor point through the elastic beam. The stress on the substrate is absorbed by the elastic beam during the conduction process, and the rigid outer frame ensures that the protected device is not affected by the stress. There are two main problems with the design of this stress isolation mechanism: 1. The elastic beam absorbs almost all the stress, so the stiffness of the elastic beam cannot be too large, thereby limiting the mechanical bandwidth of the protected MEMS device; 2. The symmetrically distributed elastic beams outside the rigid outer frame are difficult to ensure consistency during the processing process, and the asymmetry will cause the center of the entire outer frame to shift, thereby affecting the positioning of the protected MEMS device, and will have an adverse effect on some multi-layer MEMS devices (such as sandwich devices). In addition, there are also reports that the rigid outer frame is cantilevered directly without elastic beams to achieve stress release and isolation effects. This method will introduce cross-coupling effects and increase the processing process.

[0003] Annular or regular polygonal structures are often used as sensitive elements of MEMS resonant gyroscopes. The degenerate mode energy transfer generated by the Coriolis force coupling can be used as the angular velocity detection principle. The free vibration mode of the annular or regular polygon has an Nθ standing wave vibration mode, including antinodes and node points, which serve as the driving and detection modes of the gyroscope respectively. The present invention utilizes the standing wave characteristics of the annular or regular polygonal structure, connects the antinode points with the substrate anchor point, and connects the node points with the anchor point of the protected MEMS device, thereby forming a simple stress isolation mechanism. Summary of the invention

[0004] In view of the shortcomings and deficiencies of the existing MEMS stress isolation mechanism, the present invention provides a MEMS stress isolation mechanism and a design method thereof, which is mainly composed of a ring or regular polygon structure and anchor points distributed at the antinodes and node points. Based on the standing wave characteristics of the ring or regular polygon structure, the present invention connects the antinode points with the substrate anchor points, and connects the node points with the anchor points of the protected MEMS device, so as to achieve stress isolation between the MEMS device substrate and the internal protected MEMS device, effectively reduce the stress influence caused by the MEMS processing process and temperature effect, and at the same time be compatible with the protected MEMS device in terms of processing technology, so that the manufacturing cost can be effectively controlled.

[0005] The technical solution adopted by the present invention is as follows:

[0006] One of the objects of the present invention is to provide a MEMS stress isolation mechanism, wherein the MEMS includes a substrate and an internally protected MEMS device, wherein the stress isolation mechanism is composed of a ring structure or a regular polygonal structure equipped with anchor points, wherein the anchor points are distributed at anti-node points and node points, and the anchor points distributed at the anti-node points are connected to the substrate anchor points, and the anchor points distributed at the node points are connected to the internally protected MEMS device anchor points.

[0007] As a preferred embodiment of the present invention, the number of sides of the regular polygon structure is not less than 8.

[0008] As a preferred embodiment of the present invention, the MEMS stress isolation mechanism and the internally protected MEMS device have synchronous and compatible processing techniques.

[0009] As a preferred embodiment of the present invention, the free vibration mode of the annular structure or regular polygonal structure includes Nθ standing wave modes, N>1; under each standing wave mode, there are antinode points and node points that are centrally symmetrically distributed.

[0010] As a preferred embodiment of the present invention, the resonance frequency corresponding to the Nθ standing wave mode is more than three to five times the mechanical bandwidth of the internally protected MEMS device itself.

[0011] As a preferred embodiment of the present invention, the substrate anchor points are symmetrically distributed on the anti-node points, and the protected MEMS device anchor points are symmetrically or asymmetrically distributed on all or part of the node points.

[0012] Another object of the present invention is to provide a design method for the above-mentioned MEMS stress isolation mechanism, comprising the following steps:

[0013] 1) According to the structure and shape of the target substrate and the MEMS device to be protected inside, the stress isolation mechanism is selected to be a ring structure or a regular polygon structure;

[0014] 2) According to the number of anchor points m that need to be fixed on the target substrate, determine the order of the Nθ standing wave mode, that is, determine the value of N so that N=m;

[0015] 3) Designing anchor point positions on the annular structure or regular polygonal structure according to the determined standing wave vibration mode, wherein the anchor points are distributed at antinodes and node points, and the antinodes and node points are distributed at intervals on the annular structure or regular polygonal structure; for the Nθ standing wave vibration mode, two adjacent antinodes and node points are spaced 90° / N;

[0016] 4) Connecting the substrate anchor points to a group of anti-node points on the annular structure or the regular polygonal structure, so that the substrate anchor points are symmetrically distributed on the anti-node points; connecting the internal protected MEMS device anchor points to the node points on the annular structure or the regular polygonal structure, so that the protected MEMS device anchor points are symmetrically or asymmetrically distributed on all or part of the node points.

[0017] Furthermore, the resonant frequency corresponding to the Nθ standing wave mode determined in step 2) is more than three to five times the mechanical bandwidth of the internally protected MEMS device itself.

[0018] In general, the technical solution conceived by the present invention has the following beneficial effects compared with the prior art:

[0019] (1) The present invention utilizes the standing wave characteristics of the annular or regular polygonal structure. Under the action of stress, the antinode of the structure is deformed, while the position of the node remains unchanged, so that the protected MEMS device connected to the node is not affected by the stress. The overall structure is simple and the isolation effect is obvious.

[0020] (2) The stress isolation mechanism of the present invention includes a variety of structural designs, which can be flexibly adapted to a variety of MEMS devices. For example, the structure can be annular, regular octagonal, regular hexadecagonal, etc. The substrate anchor points can be symmetrically distributed on the antinode points of the Nθ vibration mode, and the connection points of the protected device can be flexibly distributed on the node points;

[0021] (3) The stress isolation mechanism of the present invention is compatible with the processing technology of the protected MEMS device and can be processed synchronously. At the same time, by adjusting the structural dimensions, the mechanical bandwidth of the protected MEMS device can be kept unaffected, thereby effectively reducing the coupling effect caused by the stress isolation mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagrams of two annular stress isolation mechanisms according to embodiments of the present invention, wherein (a) corresponds to a 2θ vibration mode, and (b) corresponds to a 4θ vibration mode;

[0023] Figure 2 Schematic diagrams of two regular octagonal stress isolation mechanisms according to embodiments of the present invention, wherein (a) corresponds to a 2θ vibration mode, and (b) corresponds to a 4θ vibration mode;

[0024] Figure 3 is a standing wave vibration mode diagram of an annular stress isolation mechanism according to an embodiment of the present invention;

[0025] Figure 4 is a standing wave vibration mode diagram of the ring structure in an embodiment of the present invention;

[0026] Figure 5 is a standing wave vibration mode diagram of a regular octagonal structure in an embodiment of the present invention;

[0027] In all the drawings, the anchor region represents the region connected to the substrate anchor point, and the protected MEMS device is equivalently represented as a system consisting of a mass and a spring. DETAILED DESCRIPTION

[0028] In order to more clearly express the purpose, technical solutions and advantages of the present invention, further explanation is given below in conjunction with the accompanying drawings and formula derivations. It should be understood that the principles herein are used to explain the present invention, but are not limited to the present invention.

[0029] The present invention utilizes the standing wave characteristics of annular or regular polygonal structures to connect the anti-wave points with the substrate anchor points, and connects the node points with the anchor points of the protected MEMS device, and proposes a MEMS stress isolation mechanism with simple structure and good stress isolation effect and a design method thereof, which can be applied to the mechanical design of various MEMS devices.

[0030] The MEMS includes a substrate and an internally protected MEMS device, and the stress isolation mechanism is composed of a ring structure or a regular polygonal structure configured with anchor points, and the anchor points are distributed at antinode points and node points;

[0031] The annular structure or regular polygonal structure is deformed by stress during processing or operation, and the deformation mainly occurs at the anti-trend points, while the node points remain unchanged. Therefore, the anti-trend point positions of the annular or regular polygon in the stress isolation mechanism are connected to the substrate anchor points, and the node points of the annular or regular polygon are connected to the internal protected MEMS device anchor points. Therefore, the stress cannot be transmitted to the protected MEMS device, thereby achieving a stress isolation effect.

[0032] like Figure 1 and Figure 2 As shown, the MEMS stress isolation mechanism provided by the present invention includes a ring or a regular polygon. Generally, the number of sides of the regular polygon structure is not less than 8. Figure 1 and Figure 2 A ring and a regular octagonal structure are shown respectively. A group of antinode points of the ring or regular octagon are connected to the substrate anchor point to form an anchor area. The number and position of the anchor area determine the standing wave vibration mode. The node point is connected to the anchor point of the protected MEMS device. The spring-mass system is used to represent the protected MEMS device in the figure.

[0033] In a specific implementation of the present invention, the thickness of the ring-shaped structure and the regular polygonal structure are consistent, and the axial ring width thereof can be uniform or non-uniform according to different crystal orientations of the silicon wafer.

[0034] The annular or regular polygonal free vibration modes in the stress isolation mechanism include Nθ standing wave modes (N>1), and there are antinodes and node points under each mode, and the antinodes and node points are symmetrically distributed, thereby ensuring that the antinode points can be deformed freely during processing or working, while the positions of the node points remain unchanged. Figure 1 and Figure 2 The middle ring structure has two anchoring methods corresponding to different standing wave vibration modes: Figure 1 (a) and Figure 2 (a) Corresponding to the 2θ vibration mode, the node and antinode are 45° apart; Figure 1 (b) and Figure 2 (b) Corresponding to the 4θ vibration mode, the node and the antinode are 22.5° apart.

[0035] In a specific implementation of the present invention, the stress isolation mechanism is a ring structure (the vibration mode is a 2θ standing wave vibration mode). Figure 3 It is a stress isolation mechanism with a 2θ standing wave vibration mode provided by the present invention. It can be seen that under the action of the tensile stress or compressive stress of the substrate, the wave node connected to the anchor point of the protected MEMS device is not affected.

[0036] In a specific implementation of the present invention, the anchor point distribution of the annular structure in the stress isolation mechanism can be of various designs, and the design range covers all standing wave vibration modes of the annular structure. Figure 4 It is the simulation result of the 2θ~8θ standing wave vibration mode of the annular structure provided by the present invention, and the Nθ standing wave vibration mode corresponds to the deformation caused by the residual stress or thermal stress of processing. In the result diagram, the white circle represents the annular structure without applied stress, and the dark vibration mode diagram represents the simulation of different standing wave vibration modes. It can be seen that under all standing wave vibration modes, the position of the node does not change. The antinode points corresponding to each standing wave vibration mode are connected to the substrate anchor points to achieve stress release and ensure free deformation, and the anchor points on the substrate are symmetrically distributed on the antinode points to ensure that the annular force is uniform and its deformation will not affect the node points; and the anchor points of the protected MEMS device can be selectively connected to the node points, without the need to be fully connected, to ensure that the protected MEMS device is not affected by stress deformation.

[0037] In a specific implementation of the present invention, the regular polygon in the stress isolation mechanism can be any regular polygon, such as a regular octagon, a regular hexadecagon, etc., and the anchor point design also covers all standing wave vibration modes. Figure 5These are the simulation results of several typical standing wave modes (2θ, 4θ and 8θ) of regular octagonal structures. In the result diagram, the white regular polygons represent regular polygonal structures without applied stress, and the dark vibration mode diagrams represent the simulation of different standing wave modes. Similarly, under all standing wave modes, the positions of the wave nodes remain unchanged. Same as the above content, the antinode points corresponding to each standing wave mode are connected to the substrate anchor points, and the anchor points on the substrate are symmetrically distributed on the antinode points; while the anchor points of the protected MEMS device can be selectively connected to the wave nodes, without having to be connected completely.

[0038] The annular structure or regular polygonal structure has a synchronous and compatible processing technology with the internally protected MEMS device and can be processed synchronously. At the same time, by adjusting the structural dimensions, the mechanical bandwidth of the protected MEMS device is not affected, effectively reducing the coupling effect caused by the stress isolation mechanism.

[0039] The design method of the stress isolation mechanism comprises the following steps:

[0040] 1) According to the structure and shape of the target substrate and the MEMS device to be protected inside, the stress isolation mechanism is selected to be a ring structure or a regular polygon structure;

[0041] 2) According to the number m of anchor areas to be fixed on the target substrate, determine the order of the Nθ standing wave mode, that is, determine the value of N, so that N = m;

[0042] 3) Designing anchor point positions on the annular structure or regular polygonal structure according to the determined standing wave vibration mode, wherein the anchor points are distributed at antinodes and node points, and the antinodes and node points are distributed at intervals on the annular structure or regular polygonal structure; for the Nθ standing wave vibration mode, two adjacent antinodes and node points are spaced 90° / N;

[0043] 4) Connect the substrate anchor area to a group of wave antinodes on the annular structure or regular polygon structure, so that the substrate anchor area is symmetrically distributed on the wave antinodes, thereby ensuring that the force on the ring or regular polygon is uniform and its deformation will not affect the wave nodes; connect the internal protected MEMS device anchor area to the wave node on the annular structure or regular polygon structure, so that the anchor area of ​​the protected MEMS device is symmetrically or asymmetrically distributed on all or part of the wave nodes. The specific layout depends on the mechanical design requirements of the protected MEMS device.

[0044] In a specific implementation of the present invention, the resonant frequency corresponding to the Nθ standing wave mode depends on the size parameters of the annular or regular polygonal structure. In order not to affect the mechanical bandwidth of the internally protected MEMS device, the resonant frequency corresponding to the Nθ standing wave mode determined in step 2) is more than three to five times the mechanical bandwidth of the internally protected MEMS device itself.

[0045] Those skilled in the art should understand that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A design method for a MEMS stress isolation mechanism, wherein the MEMS comprises a substrate and an internally protected MEMS device, characterized in that: The stress isolation mechanism is composed of an annular structure or a regular polygonal structure equipped with anchor points, the anchor points are distributed at antinodes and node points, and the anchor points distributed at the antinodes are connected to the substrate anchor points, and the anchor points distributed at the node points are connected to the internally protected MEMS device anchor points; the free vibration mode of the annular structure or regular polygonal structure includes Nθ standing wave vibration modes, N>1; under each standing wave vibration mode, there are antinodes and node points that are centrally symmetrically distributed; the substrate anchor points are symmetrically distributed on the antinodes, and the protected MEMS device anchor points are symmetrically or asymmetrically distributed on all or part of the node points; The design method comprises the following steps: 1) According to the structure and shape of the target substrate and the MEMS device to be protected inside, the stress isolation mechanism is selected to be a ring structure or a regular polygon structure; 2) According to the number of anchor points m that need to be fixed on the target substrate, determine the order of the Nθ standing wave mode, that is, determine the value of N so that N=m; 3) Designing anchor point positions on the annular structure or regular polygonal structure according to the determined standing wave vibration mode, wherein the anchor points are distributed at antinodes and node points, and the antinodes and node points are distributed at intervals on the annular structure or regular polygonal structure; for the Nθ standing wave vibration mode, two adjacent antinodes and node points are spaced 90° / N; 4) Connecting the substrate anchor points to a group of anti-node points on the annular structure or the regular polygonal structure, so that the substrate anchor points are symmetrically distributed on the anti-node points; connecting the internal protected MEMS device anchor points to the node points on the annular structure or the regular polygonal structure, so that the protected MEMS device anchor points are symmetrically or asymmetrically distributed on all or part of the node points.

2. The design method of the MEMS stress isolation mechanism according to claim 1, characterized in that: The resonant frequency corresponding to the Nθ standing wave mode determined in step 2) is more than three times the mechanical bandwidth of the internally protected MEMS device itself.

3. The design method of the MEMS stress isolation mechanism according to claim 1, characterized in that: The number of sides of the regular polygon structure is not less than 8.

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