MEMS device

Abstract

The MEMS device comprises a device structure and a limiting structure, the device structure comprises a rigid structure, a flexible structure and a frame, the flexible structure is used for driving the rigid structure to deflect, and the frame is used for supporting and driving the flexible structure; the limiting structure comprises an upper limiting structure and a lower limiting structure, the upper limiting structure is used for providing a reverse force for the device structure when the device structure moves towards the first direction, the third direction and the fourth direction, and the lower limiting structure is used for providing a reverse force for the device structure when the device structure moves towards the second direction; therefore, the deformation quantity of the device structure is prevented from exceeding the maximum allowable deformation quantity. According to the MEMS device, the limiting structure provides a reverse force for the device structure when the device structure moves towards the first direction, the third direction and the fourth direction, so that the impact resistance of the MEMS device in the X / Y direction is improved; and the lower limiting structure provides a reverse force for the device structure when the device structure moves towards the second direction, so that the product yield of the MEMS device is further improved.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor technology, and particularly relates to a MEMS device. Background Technology

[0002] Micro-electro-mechanical systems (MEMS) integrate micromechanical structures, microsensors, microactuators, and electrical systems onto a single chip, playing a crucial role in modern technology and being widely used in various industries such as consumer electronics, medical devices, aerospace, and the Internet of Things (IoT).

[0003] Due to their small size, intricate structure, and high sensitivity to external shocks, the shock resistance of micro-devices directly affects their stability and lifespan. In the automotive industry, micro-devices such as sensors / actuators need to withstand shocks such as bumps and vibrations during vehicle operation to ensure the stable operation of automotive electronic systems. For example, automotive sensors need to ensure normal operation of vehicles under long-term vibration. In the aerospace and military fields, micro-devices often need to operate in extreme environments, such as high acceleration and high vibration, making shock resistance and reliability key factors in ensuring mission success and equipment safety. For example, micro-devices on satellites need to withstand the enormous acceleration during launch.

[0004] like Figure 1 As shown, existing limiting structures lack X / Y direction limiting. The gap between the micromirror and the limiting structure is mainly controlled by two methods: one is by relying on the size of the silicon particles in the adhesive, such as... Figure 1 As shown in Figure (a), particle stacking can occur, and the randomness of stacking can lead to inconsistent adhesive thickness, resulting in inconsistent gap dimensions. Furthermore, the thickness of commonly used silicon particles in the industry is often a multiple of 10µm, so the error in gap dimensions is also often a multiple of 10µm. Another possibility is... Figure 1 The etched step structure shown in Figure (b) still requires adhesive to connect the micromirror and the limiting structure. The consistency of the adhesive thickness is greatly affected by the equipment used during die bonding, and the thickness error is generally on the order of 10µm. Considering the etching error on the limiting device (1µm (good industry level) to 5µm (average industry level)), the error of the gaps at various points is at least >11µm. Moreover, the travel distance of the microdevice itself is on the order of µm. If the gap is smaller than the design value, it may cause the normal movement of the microdevice to be obstructed and unable to complete its function. If the gap is larger than the design value, it may cause the limiting device to fail to prevent excessive movement of the microdevice.

[0005] Therefore, improving the shock resistance of MEMS devices in the X / Y direction and controlling the gap error within a few micrometers has become an urgent problem to be solved. Summary of the Invention

[0006] This application provides a MEMS device, including: a device structure and a limiting structure; the limiting structure consists of an upper limiting structure and a lower limiting structure. The upper limiting structure is used to provide a reverse force to the device structure when it moves in a first direction, a third direction, and a fourth direction, thereby improving the impact resistance of the MEMS device in the X / Y direction; the lower limiting structure is used to provide a reverse force to the device structure when it moves in a second direction, so as to prevent the deformation of the device structure from exceeding the maximum allowable deformation, and the gap between the limiting structure and the device structure is precisely controlled within 5µm, further improving the product yield of the MEMS device.

[0007] Other objects and advantages of the present invention can be further understood from the technical features disclosed herein.

[0008] To achieve one or more of the above objectives or other objectives, the present invention provides a MEMS device.

[0009] A MEMS device includes: a device structure and a limiting structure; The device structure includes a rigid structure, a flexible structure, and a frame. The flexible structure is used to drive the rigid structure to deflect, and the frame is used to support and drive the flexible structure. The limiting structure includes an upper limiting structure and a lower limiting structure. The upper limiting structure is used to provide a reverse force to the device structure when it moves toward the first direction, the third direction, and the fourth direction. The lower limiting structure is used to provide a reverse force to the device structure when it moves toward the second direction, so as to prevent the deformation of the device structure from exceeding the maximum allowable deformation.

[0010] The limiting structure is bonded to the upper and lower surfaces of the frame, respectively. The bonding method is one of metal bonding, hydrophilic bonding, or silicon-silicon bonding, and the bonding error is <1µm.

[0011] The upper limit structure includes a limiting part arranged in a ring shape. The limiting part includes a limiting post. The left and right sides of the limiting post are respectively etched with a first step and a second step of different heights. The height of the first step is greater than that of the second step.

[0012] The upper limit structure is bonded to the top of the device structure, and the limiting post passes through the gap between the rigid structure and the frame, with the height of the limiting post being less than the depth of the gap.

[0013] The lower limit structure is bonded directly below the device structure. The main body is U-shaped, the width of the groove is at least the same as the width of the flexible structure, and the depth of the groove is no more than 2 / 3 of the height of the lower limit structure.

[0014] The limiting structure is made of silicon, silicon carbide, diamond, or SOI wafer; The SOI wafer includes a bottom silicon layer, a buried oxide layer, and a device layer arranged sequentially from bottom to top. The first step of the upper limit structure is etched in the device layer, and the second step is etched at the buried oxide layer.

[0015] The lower limiting structure is etched to form a second groove arranged in a circumferential shape, and the depth of the second groove is not greater than 2 / 3 of the height of the lower limiting structure.

[0016] A through hole is etched at the center of the groove of the lower limiting structure.

[0017] The upper limit structure is provided with several protruding structures that cover the edge of the rigid structure to block the rigid structure.

[0018] The upper limit structure is provided with several elastic beam structures, which are connected to the main body of the upper limit structure. The upper limit structure and the rigid structure achieve flexible contact through the elastic beam structures.

[0019] Compared with the prior art, the beneficial effects of the present invention mainly include: This application provides a MEMS device, including: a device structure and a limiting structure; the limiting structure consists of an upper limiting structure and a lower limiting structure. The upper limiting structure is used to provide a reverse force to the device structure when it moves in a first direction, a third direction, and a fourth direction, thereby improving the impact resistance of the MEMS device in the X / Y direction; the lower limiting structure is used to provide a reverse force to the device structure when it moves in a second direction, so as to prevent the deformation of the device structure from exceeding the maximum allowable deformation, and the gap between the limiting structure and the device structure is precisely controlled within 5µm, further improving the product yield of the MEMS device.

[0020] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic diagram of the micromirror limiting structure provided for the background technology of this application.

[0023] Figure 2 This is a top view of the device structure provided in Embodiment 1 of this application.

[0024] Figure 3 This is a cross-sectional view of the device structure provided in Embodiment 1 of this application.

[0025] Figure 4 This is a cross-sectional view of the MEMS device provided in Embodiment 1 of this application.

[0026] Figure 5 This is a cross-sectional view of the upper limit structure provided in Embodiment 1 of this application.

[0027] Figure 6 This is a cross-sectional view of the upper limit structure provided in Embodiment 2 of this application.

[0028] Figure 7 This is a cross-sectional view of the lower limit structure provided in Embodiment 2 of this application.

[0029] Figure 8 This is a cross-sectional view of the upper limit structure provided in Embodiment 3 of this application.

[0030] Figure 9 This is a cross-sectional view of the upper limit structure provided in Embodiment 4 of this application.

[0031] Figure 10 This is a top view of the MEMS device provided in Embodiment 5 of this application.

[0032] Figure 11 This is a top view of the MEMS device provided in Embodiment 6 of this application.

[0033] Figure 12 This is a cross-sectional view of the upper limit structure provided in Embodiment 7 of this application.

[0034] Figure 13 This is a flowchart illustrating the fabrication process of the lower limit structure provided in Embodiment 1 of this application.

[0035] Figure 14 The flowchart shows the preparation process of the upper limit structure provided in Embodiment 1 of this application.

[0036] Figure 15The flowchart for the preparation of the upper limit structure provided in Embodiment 2 of this application is shown.

[0037] Figure 16 This is a flowchart illustrating the fabrication process of the lower limit structure provided in Embodiment 2 of this application.

[0038] Figure 17 This is a flowchart illustrating the preparation process of the lower limit structure provided in Embodiment 3 of this application.

[0039] Figure 18 This is a flowchart illustrating the preparation process of the lower limit structure provided in Embodiment 4 of this application.

[0040] Figure 19 This is a cross-sectional view of the upper limit structure provided in Embodiment 8 of this application. Detailed Implementation

[0041] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of a preferred embodiment with reference to the accompanying drawings. The directional terms mentioned in the following embodiments, such as up, down, left, right, front, or back, are merely for reference to the accompanying drawings. Therefore, the directional terms used are for illustrative purposes and not for limiting the present invention.

[0042] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.

[0043] Example 1 A MEMS device includes: a device structure and a limiting structure; such as Figure 2 As shown, the device structure includes a rigid structure 1, a flexible structure 2, and a frame 3. The flexible structure 2 is used to drive the rigid structure 1 to deflect, and the frame 3 is used to support and drive the flexible structure 2. Specifically, the frame 3 is used to support the rest of the structure and may contain circuitry to drive the flexible structure 2 or transmit electrical signals. It tends to have high stiffness and is not easily deformed. The flexible structure 2 is often composed of a combination of beams, membranes, and other structures. It tends to have low stiffness and is easily deformed. The rigid structure 1 is often composed of a structure with a certain mass to accomplish a specific purpose. For example, the deflection of the flexible structure 2 causes the mirror of the rigid structure 1 to deflect; or the deflection of the flexible structure 2 causes the rigid structure 1, which acts as a mass block, to deflect, thereby forming stress concentration areas in certain parts of the flexible structure 2.

[0044] The device structure is made of semiconductor materials, preferably silicon; it may contain metals for electrical connection with the outside world, such as aluminum, gold, platinum, molybdenum, copper, titanium, etc.; it may have different driving methods to actuate the flexible structure 2, such as piezoelectric, electrostatic, electromagnetic, and electrothermal driving; it may also have a passivation layer to protect a specific structure, which is composed of a single layer of silicon dioxide / silicon nitride or a composite silicon dioxide / silicon nitride film.

[0045] like Figure 4 As shown, the limiting structure includes an upper limit structure 4 and a lower limit structure 5. The upper limit structure 4 is used to provide a reverse force to the device structure when it moves toward the first direction, the third direction, and the fourth direction. The lower limit structure 5 is used to provide a reverse force to the device structure when it moves toward the second direction, so as to prevent the deformation of the device structure from exceeding the maximum allowable deformation.

[0046] Specifically, the limiting structure is made of semiconductor material, preferably silicon. In this embodiment, the first direction is the +Z direction, the second direction is the -Z direction, and the third and fourth directions are the X / Y directions. The upper limiting structure 4 primarily improves impact resistance in the +Z and X / Y directions, while the lower limiting structure 5 primarily improves impact resistance in the -Z direction. Figure 3 As shown; When an impact occurs, the flexible structure 2 deforms, causing the rigid structure 1 to deform as well. The greater the deformation, the greater the stress generated, and the easier it is for the material to break. The presence of the limiting structure can limit the deformation of each component of the device structure, keeping the stress within a safe range and thus ensuring the integrity of the device structure.

[0047] like Figure 5 As shown, the upper limit structure 4 includes a limiting part 41 arranged in a ring shape. The limiting part 41 includes a limiting post 411. The left and right sides of the limiting post 411 are respectively etched with a first step 412 and a second step 413 of different heights. like Figure 4 As shown, the limiting structure is made of silicon substrate; the upper limiting structure 4 is bonded to the frame 3, and the limiting post 411 passes through the gap between the rigid structure 1 and the frame 3, and the height of the limiting post 411 is less than the depth of the gap; the lower limiting structure 5 is bonded to the bottom of the device structure, and the main body is U-shaped. The width of the groove 51 is the same as the width of the flexible structure 2, and the depth of the groove 51 is not greater than 2 / 3 of the height of the lower limiting structure 5.

[0048] A method for fabricating a MEMS device, comprising: Fabricate the lower limit structure 5 and the upper limit structure 4, and bond the upper limit structure 4, the device structure and the lower limit structure 5 simultaneously or stepwise; In a preferred embodiment of the present invention, the limiting structure is bonded to the upper and lower surfaces of the frame 3 respectively. The bonding method is one of metal bonding, hydrophilic bonding, and silicon-silicon bonding. The bonding error is <1µm. Considering that the etching error of the upper limit structure 4 is (1µm (good level in the industry) to 5µm (general level in the industry)), the error of the gaps at each place can often be controlled to <5µm.

[0049] like Figure 13 As shown, the fabrication process of the lower limit structure 5 is as follows: Step S1: Provide a semiconductor substrate 111; Step S2: An oxide layer 112 is formed on the surface of the semiconductor substrate 111 by thermal oxidation, LPCVD, and PECVD processes. The oxide layer 112 is silicon dioxide and has a thickness of <3µm. Step S3: Photolithography and etching are performed on the front side of the semiconductor substrate 111 to form a groove 51; Step S4: Remove oxide layer 112; like Figure 14 As shown, the fabrication process of the upper limit structure 4 is as follows: Step S1: Provide a semiconductor substrate 111; Step S2: An oxide layer 112 is formed on the surface of the semiconductor substrate 111 by thermal oxidation, LPCVD, and PECVD processes. The oxide layer 112 is silicon dioxide and has a thickness of <3µm. Step S3: Perform multiple photolithography and etching processes on the front side of the semiconductor substrate 111 to form the first step 412 and the second step surface; Step S4: Photolithography and etching are performed on the back side of the semiconductor substrate 111 to etch through the semiconductor substrate 111 and form the second step 413; Step S5: Remove oxide layer 112.

[0050] Example 2 like Figure 6 As shown, the limiting structure is made of SOI wafer; the upper limiting structure 4 includes a ring-shaped limiting part 41, the limiting part 41 includes a limiting post 411, and the left and right sides of the limiting post 411 are respectively etched with a first step 412 and a second step 413 of different heights. The preparation process of upper limit structure 4 is as follows Figure 15 As shown, the preparation process is as follows: Step S1: Provide an SOI wafer, which includes a bottom silicon layer 6, a buried oxide layer 7, and a device layer 8 arranged sequentially from bottom to top; Step S2: An oxide layer is formed on the surface of the SOI wafer through thermal oxidation, LPCVD, and PECVD processes. The oxide layer is silicon dioxide with a thickness of <3µm. Steps S3-S4: Multiple photolithography and etching processes are performed on the front side of the SOI wafer to form the first step 412 and the second step 413; the first step 412 is etched and formed on the device layer 8, and the second step 413 is etched and stopped at the buried oxide layer 7. Step S5: Perform photolithography and etching on the back side of the SOI wafer to etch through the oxide layer, the bottom silicon layer 6 and the buried oxide layer 7; Step S6: Remove the oxide layer.

[0051] The buried oxide layer 7 of the SOI wafer is silicon dioxide, with a thickness typically <3µm. During the fabrication of the SOI wafer itself, the thickness error of the device layer 8 can be controlled to <1µm. During the etching process for fabricating the limiting structure, the buried oxide layer 7 itself acts as a barrier layer to prevent over-etching. Therefore, the etching depth can be defined by defining the thickness of the device layer 8. Finally, considering that the gap error caused by the bonding method is often <1µm, the overall gap error can be controlled to <2µm. like Figure 7 As shown, the limiting structure is made of an SOI wafer, which includes a bottom silicon layer 6, a buried oxide layer 7, and a device layer 8 arranged sequentially from bottom to top; the main body of the lower limiting structure 5 is U-shaped, and the groove 51 is etched and formed on the device layer 8. The preparation process of the lower limit structure 5 is as follows: Figure 16 As shown, the specific process is as follows: Step S1: Provide an SOI wafer, which includes a bottom silicon layer 6, a buried oxide layer 7, and a device layer 8 arranged sequentially from bottom to top; Step S2: An oxide layer is formed on the surface of the SOI wafer through thermal oxidation, LPCVD, and PECVD processes. The oxide layer is silicon dioxide with a thickness of <3µm. Step S3: Photolithography is performed on the front side of the SOI wafer, and the oxide layer and device layer 8 are etched. The etching stops at the buried oxide layer 7 to form a groove 51. Step S4: Remove the oxide layer.

[0052] Example 3 like Figure 8 As shown, the lower limiting structure 5 is etched to form a second groove 52 arranged in a ring shape. The depth of the groove 52 is no more than 2 / 3 of the height of the lower limiting structure 5 body. This is suitable for situations where the beam or membrane structure on the flexible structure 2 is relatively fragile and cannot directly make hard contact with the lower limiting structure 5, and needs to be avoided. Therefore, the gap between the lower limiting structure 5 part corresponding to the more fragile beam or membrane structure needs to be larger. The fabrication process of the lower limiting structure 5 is as follows: Figure 17 As shown.

[0053] Example 4 like Figure 9As shown, the lower limiting structure 5 is U-shaped, and a through hole 53 penetrating the lower limiting structure 5 is etched at the center of the groove 51. The fabrication process of the lower limiting structure 5 is as follows. Figure 18 As shown, this applies to the following three situations: 1. Align the lower limit structure 5 with the device structure; 2. The flexible structure is easy to observe during use; 3. Reduce the stiffness of the lower limit structure 5 so that the contact between the lower limit structure 5 and the flexible structure 2 is a soft contact.

[0054] Example 5 like Figure 10 As shown, the upper limit structure 4 is provided with several protruding structures 40 covering the edge of the rigid structure 1 to block the rigid structure. The upper limit structure 4 does not completely wrap the edge of the rigid structure 1, but uses the protruding structures 40 to cover part of the edge of the rigid structure 1. The number of protruding structures 40 can be determined according to actual needs. The protruding structures 40 can be conventional structures or irregular structures such as squares, rectangles, triangles, and semicircles. They only need to cover the edge of the rigid structure 1 to play a blocking role.

[0055] Applicable to the following two situations: 1. Align the upper limit structure 4 with the device structure; 2. The rigid structure 1 should be kept as unobstructed as possible.

[0056] Example 6 like Figure 11 As shown, the upper limit structure 4 uses a number of flexible and discontinuous elastic beam structures 42, which connect the main body of the upper limit structure 4. The elastic beam structures 42 reduce the stiffness, allowing the upper limit structure 4 and the rigid structure 1 to make flexible contact through the elastic beam structures 42, reducing the possibility of damage to both. The length, width and shape of the elastic beam structures 42 can be designed according to actual needs.

[0057] Example 7 like Figure 12 As shown, the upper limit structure 4 undergoes back-side photolithography and etching processes. The upper limit structure 4 completely covers the rigid structure 1 below, making it suitable for devices that do not need to contact the outside world. The fully enclosed structure can resist the impact force of the rigid structure 1 to the maximum extent.

[0058] Example 8 like Figure 19 As shown, the upper limit structure 4 does not have a limit post 411, but only a second step 413 formed by etching, which is suitable for situations where it is not necessary to limit the third / fourth direction.

[0059] In summary, this application provides a MEMS device, including: a device structure and a limiting structure; the limiting structure consists of an upper limiting structure and a lower limiting structure. The upper limiting structure is used to provide a reverse force to the device structure when it moves in the first direction, the third direction, and the fourth direction, thereby improving the impact resistance of the MEMS device in the X / Y direction; the lower limiting structure is used to provide a reverse force to the device structure when it moves in the second direction, so as to prevent the deformation of the device structure from exceeding the maximum allowable deformation, and the gap between the limiting structure and the device structure is precisely controlled within 5µm, further improving the product yield of the MEMS device.

[0060] The common English terms or letters used in this invention for clarity of description are for illustrative purposes only and are not limiting interpretations or specific uses. They should not be used to limit the scope of protection of this invention based on their possible Chinese translations or specific letters.

[0061] It should also be noted that in this article, relational terms such as “first” and “second” are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

Claims

1. A MEMS device, characterized in that, include: Device structure and limiting structure; The device structure includes a rigid structure, a flexible structure, and a frame. The flexible structure is used to drive the rigid structure to deflect, and the frame is used to support and drive the flexible structure. The limiting structure includes an upper limiting structure and a lower limiting structure. The upper limiting structure is used to provide a reverse force to the device structure when it moves toward the first direction, the third direction, and the fourth direction. The lower limiting structure is used to provide a reverse force to the device structure when it moves toward the second direction, so as to prevent the deformation of the device structure from exceeding the maximum allowable deformation.

2. A MEMS device according to claim 1, characterized in that, The limiting structure is bonded to the upper and lower surfaces of the frame, respectively. The bonding method is one of metal bonding, hydrophilic bonding, or silicon-silicon bonding, and the bonding error is <1µm.

3. A MEMS device according to claim 2, characterized in that, The upper limit structure includes a limiting part arranged in a ring shape. The limiting part includes a limiting post. The left and right sides of the limiting post are respectively etched with a first step and a second step of different heights. The height of the first step is greater than that of the second step.

4. A MEMS device according to claim 3, characterized in that, The upper limit structure is bonded to the top of the device structure, and the limiting post passes through the gap between the rigid structure and the frame, with the height of the limiting post being less than the depth of the gap.

5. A MEMS device according to claim 2, characterized in that, The lower limit structure is bonded directly below the device structure. The main body is U-shaped, the width of the groove is at least the same as the width of the flexible structure, and the depth of the groove is no more than 2 / 3 of the height of the lower limit structure.

6. A MEMS device according to claim 3, characterized in that, The limiting structure is made of silicon, silicon carbide, diamond, or SOI wafer; The SOI wafer includes a bottom silicon layer, a buried oxide layer, and a device layer arranged sequentially from bottom to top. The first step of the upper limit structure is etched in the device layer, and the second step is etched at the buried oxide layer.

7. A MEMS device according to claim 5, characterized in that, The lower limiting structure is etched to form a second groove arranged in a circumferential shape, and the depth of the second groove is not greater than 2 / 3 of the height of the lower limiting structure.

8. A MEMS device according to claim 5, characterized in that, A through hole is etched at the center of the groove of the lower limiting structure.

9. A MEMS device according to claim 3, characterized in that, The upper limit structure is provided with several protruding structures that cover the edge of the rigid structure to block the rigid structure.

10. A MEMS device according to claim 3, characterized in that, The upper limit structure is provided with several elastic beam structures, which are connected to the main body of the upper limit structure. The upper limit structure and the rigid structure achieve flexible contact through the elastic beam structures.

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