A MEMS device and a method of manufacturing the same

Abstract

The application provides a MEMS device and a preparation method thereof. A back cavity is formed on a substrate, so that a part of a diaphragm is suspended to form a suspended part, and a gap exists between the suspended part and the substrate. A viscoelastic film layer is arranged on the diaphragm and the substrate, covers at least part of the gap, and is connected to the substrate and the suspended part. The viscoelastic film layer covers and seals at least part of the gap, so that the uncovered gap in the device is reduced, which helps to establish a stable pressure difference, reduces the fluctuation and drift of the signal output, and at the same time, the viscoelastic film layer can reduce the influence on the deformation of the diaphragm based on the viscous part of the viscoelastic film layer, so that the diaphragm still has the sensitivity in the ideal interval, thereby capturing a weak signal, and the viscoelastic film layer can reduce the fluidity of the viscoelastic film layer based on the elastic part of the viscoelastic film layer, and maintain the stability of the structure. Finally, stable signal output, high sensitivity and stability of the device structure are realized.

Description

Technical Field

[0001] This application relates to the field of microelectromechanical technology, and more specifically, to a MEMS device and its fabrication method. Background Technology

[0002] Micro-Electro-Mechanical Systems (MEMS) technology enables high-precision sensing and measurement of various physical and chemical quantities. Its core mechanism lies in utilizing the deformation or displacement of a sensitive diaphragm within a MEMS device to convert and output a detection signal. Therefore, the sensitivity and stability of the sensitive diaphragm's response to external signals directly determine the overall performance of the device.

[0003] To address the sensitivity limitations of traditional sensitive membranes that employ a single, complete membrane layer, the current mainstream optimization approach involves introducing gaps to divide the membrane into cantilevered sub-membrane structures. This design grants the ends of the cantilevered sub-membranes greater freedom, enabling them to more sensitively capture weak signals and thus significantly improving the device's detection sensitivity.

[0004] However, when such MEMS devices with gaps operate in fluid media (such as gas or liquid) environments, the fluid medium on both sides of the diaphragm flows through the gaps due to the pressure difference. As the pressure difference increases, the gaps may dynamically expand, making it difficult to establish and maintain a stable pressure gradient on both sides of the diaphragm, which in turn causes large fluctuations and drift in the output signal. Summary of the Invention

[0005] The purpose of this application is to address the shortcomings of the prior art by providing a MEMS device and its fabrication method. The improved MEMS device has both good sensitivity and can improve the fluctuation amplitude of its output signal.

[0006] To achieve the above objectives, the technical solutions adopted in the embodiments of this application are as follows: In one aspect of this application, a MEMS device is provided, comprising: a substrate having a back cavity; a diaphragm disposed on the substrate, the diaphragm having a suspended portion suspended in the back cavity, a gap forming between the suspended portion and the substrate, the gap communicating with the back cavity; and a viscoelastic membrane layer connected to the suspended portion and the substrate respectively, the viscoelastic membrane layer at least covering a portion of the gap.

[0007] Optionally, the viscoelastic membrane layer includes a viscoelastic body and an elastic skeleton, with the viscoelastic body filling the elastic skeleton.

[0008] Optionally, the elastic skeleton is a solid network structure that encapsulates the viscous body.

[0009] Optionally, a viscoelastic membrane layer covers all gaps to seal the back cavity at the diaphragm.

[0010] Optionally, the viscoelastic membrane layer includes an interconnected cover portion and a connecting portion, the cover portion being located at the gap, and the connecting portion being connected to the suspended portion and the substrate respectively, the thickness of the cover portion being greater than the thickness of the connecting portion.

[0011] Optionally, the width of the slit ranges from 0.5 μm to 10 μm; and / or, the viscoelastic membrane layer has an arched structure.

[0012] Another aspect of this application provides a method for fabricating a MEMS device, the method comprising: A diaphragm is formed on the substrate; The substrate is etched to form a back cavity, and the diaphragm is suspended in the part of the back cavity as a suspended part. A gap is formed between the suspended part and the substrate, and the gap is connected to the back cavity. A viscoelastic membrane layer is formed on the suspended portion and the substrate, and the viscoelastic membrane layer at least covers part of the gap.

[0013] Optionally, forming a viscoelastic film layer on the suspended portion and the substrate includes: A liquid film layer is formed on the suspended part and the substrate; The liquid film layer is cured to form a viscoelastic film layer.

[0014] Optionally, forming a liquid film on the suspended portion and the substrate includes: A liquid is formed on the diaphragm and substrate using a dispensing or spraying process. The liquid diffuses outwards to form a liquid film.

[0015] Optionally, the liquid film layer is cured to form a viscoelastic film layer, including: In a heated environment, part of the liquid film crosslinks to form a solid network structure, while another part forms a viscous body. The solid network structure encapsulates the viscous body to form a viscoelastic film layer.

[0016] The beneficial effects of this application include: A seamless diaphragm presents both sensitivity and residual stress issues. Therefore, creating a gap within the diaphragm that connects to the back cavity improves sensitivity and effectively releases residual stress. However, because the gap allows communication between the gap and the side of the diaphragm opposite to the back cavity, a stable pressure differential cannot be established across the diaphragm when operating in fluid media (such as gas or liquid). Based on this, this application addresses device structures where a gap forms between the diaphragm and the substrate. By utilizing the back cavity of the substrate and the gap, the residual stress inside the diaphragm is first fully released. Then, a viscoelastic membrane layer is installed, connecting to both the substrate and the suspended portion. This viscoelastic membrane layer at least covers and seals part of the gap, reducing the number of uncovered gaps in the device. This helps establish a stable pressure difference, reducing signal output fluctuations and drift. Simultaneously, the viscous component of the viscoelastic membrane layer reduces the impact on diaphragm deformation, allowing the diaphragm to maintain a sensitivity within an ideal range, thus capturing weak signals. The elastic component of the viscoelastic membrane layer reduces its fluidity, maintaining structural stability. Ultimately, this achieves stable signal output, high sensitivity, and device structural stability. Attached Figure Description

[0017] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a MEMS device provided in an embodiment of this application; Figure 2 This is one of the top view structural schematic diagrams of a MEMS device provided in the embodiments of this application; Figure 3 A second top view of a MEMS device provided in an embodiment of this application; Figure 4 This is the third top view schematic diagram of a MEMS device provided in the embodiments of this application; Figure 5 A comparative schematic diagram of a planar structure and an arched structure of a viscoelastic membrane layer provided in an embodiment of this application; Figure 6 This is a schematic diagram comparing the signal output of three devices under the same operating conditions.

[0019] Icons: 100-Base; 111-Back cavity; 200-Diaphragm; 210-Suspended part; 211-Fixed end; 212-Free end; 220-Gap; 300-Viscoelastic membrane layer. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. It should be understood that the fluid medium in this application can be gas, liquid, etc.

[0021] In one aspect of this application, a MEMS device is provided, comprising: a substrate having a back cavity; a diaphragm disposed on the substrate, the diaphragm having a suspended portion suspended in the back cavity, a gap forming between the suspended portion and the substrate, the gap communicating with the back cavity; and a viscoelastic membrane layer connected to the suspended portion and the substrate respectively, the viscoelastic membrane layer at least covering a portion of the gap.

[0022] A seamless diaphragm presents both sensitivity and residual stress issues. Therefore, creating a gap in the diaphragm that communicates with the back cavity improves sensitivity and effectively releases residual stress. However, because the gap connects to the side of the diaphragm opposite to the back cavity, a stable pressure difference cannot be established across the diaphragm when operating in a fluid medium (such as gas or liquid). Therefore, the MEMS device in this application creates a back cavity on the substrate, suspending a portion of the diaphragm and forming a suspended section. A gap exists between the side of this suspended section and the substrate, allowing the gap and the back cavity to effectively release residual stress in the diaphragm and improve the sensitivity limitation caused by residual stress.

[0023] A viscoelastic membrane connects the suspended portion and the substrate, its purpose being to at least cover and seal some of the gaps. Given that the viscoelastic membrane itself possesses both viscosity and elasticity, it reduces uncovered gaps, which helps establish a stable pressure differential and reduces signal output fluctuations and drift. Simultaneously, the viscous portion of the viscoelastic membrane reduces the overall membrane's influence on the deformation of the suspended portion, ensuring the suspended portion still possesses ideal sensitivity for capturing weak signals. The elastic portion of the viscoelastic membrane reduces its fluidity, maintaining its structural stability.

[0024] Figure 1 This is a schematic diagram of the structure of a MEMS device provided in an embodiment of this application. Figure 1 The image shows a substrate 100, a diaphragm 200, and a viscoelastic membrane layer 300.

[0025] A diaphragm 200 is provided on a substrate 100, wherein a back cavity 111 is formed on the substrate 100, so that a portion of the diaphragm 200 is exposed through the back cavity 111, and the exposed portion of the diaphragm 200 is suspended relative to the substrate 100, forming a suspended portion 210.

[0026] A gap 220 is formed between the suspended portion 210 of the diaphragm 200 and the substrate, and the gap 220 is directly connected to the back cavity 111. The portion of the diaphragm 200 located at the gap 220 can freely extend and deform, thus fully releasing the stress in the diaphragm 200. It should be understood that this application does not limit the number of suspended portions 210 included in the diaphragm 200, for example... Figures 2 to 4 Only one suspended portion 210 is shown in the figure. In other examples, the suspended portion 210 may include two or more.

[0027] The presence of the gap 220 allows the suspended portion 210 to have a free end 212 and a fixed end 211. The free end 212 has a gap 220 between it and the base 100, and the fixed end 211 is the end where the suspended portion 210 connects to the base 100. Figures 1 to 4 As shown, the free end 212 and the fixed end 211 are usually the two opposite ends of the suspended part 210.

[0028] A viscoelastic membrane layer 300 is located in the slit 220 and connects the suspended portion 210 and the substrate 100. This allows the viscoelastic membrane layer 300 to cover at least a portion of the slit 220, meaning the covered slit 220 cannot serve as a channel for fluid medium to flow through the diaphragm. Thus, the viscoelastic membrane layer 300 reduces the number of interconnecting channels on both sides of the diaphragm 200, helping to establish a stable pressure difference across the diaphragm 200 and reducing large fluctuations and drift in the output signal of the MEMS device, making its output signal usable.

[0029] Based on this, the viscoelastic membrane layer 300 itself possesses both viscosity and elasticity. Therefore, the material properties of the viscoelastic membrane layer 300 are between those of a solid and a liquid. Furthermore, during the deformation of the suspended portion 210 under external force: due to the presence of the viscous portion in the viscoelastic membrane layer 300, it applies resistance to the suspended portion 210 during the initial deformation process. Then, within a very short time, this resistance rapidly decreases to a negligible or disappears due to stress relaxation and energy dissipation. At this point, the suspended portion 210... The deformation will hardly be hindered by the viscous part and will continue to deform to the maximum value. The purpose of the elastic part in the viscoelastic membrane layer 300 is to reduce the flow capacity of the viscoelastic membrane layer 300 and maintain its positional stability on the diaphragm 200 and the substrate 100. Therefore, although the elastic part may exert resistance during the deformation of the suspended part 210, the resistance it can exert is almost negligible in order to reduce the flow capacity of the viscous part. In other words, its binding effect on the deformation of the suspended part 210 is very weak.

[0030] In summary, the presence of the viscous portion in the viscoelastic membrane layer 300 reduces the resistance applied during the initial deformation of the suspended portion 210 to a negligible or non-existent level in a short time. For example, the suspended portion 210 can almost deform to a position that is in balance with the elastic stress of the diaphragm 200 itself, thereby giving the diaphragm 200 good sensitivity and the ability to capture weak signals. The presence of the elastic portion helps to reduce the fluidity of the viscoelastic membrane layer 300 and maintain its structural stability.

[0031] It should be understood that the main purpose of the viscoelastic membrane layer 300 is to, as far as possible, block the flow of fluid medium through the gap 220 on both sides of the diaphragm 200 without significantly affecting the deformation amplitude of the suspended portion 210. Therefore, the main part of the viscoelastic membrane layer 300 is the viscous part, not the elastic part.

[0032] The resistance exerted by the viscous portion of the viscoelastic membrane layer 300 on the suspended portion 210 during deformation does not follow Hooke's law like the elastic portion, but is directly proportional to the strain rate. Therefore, once the pressure difference across the membrane stabilizes, the strain rate becomes zero, and the resistance of the viscous portion also becomes zero. This explains why the viscous portion exhibits resistance in the initial stage of deformation of the suspended portion 210 (when the pressure difference across the membrane is not yet stable), which then weakens and disappears (as the pressure difference across the membrane tends to stabilize), thus not limiting the deformation amplitude of the suspended portion (ensuring that the sensitivity of the MEMS device is almost unaffected).

[0033] In some possible implementations, the viscoelastic film layer 300 includes a viscous body and an elastic skeleton, wherein the viscous body is the aforementioned viscous portion and the elastic skeleton is the aforementioned elastic portion. The viscous body is a fluid with flow capability, while the elastic skeleton can constrain the flow capability of the viscous body. The viscous body fills into the elastic skeleton based on the elastic skeleton, so as to facilitate the connection between the viscous body and the elastic skeleton, making the position of the viscous body relatively stable, improving the yield of MEMS devices in the fabrication process and the reliability and stability in long-term use.

[0034] In some possible implementations, the elastic skeleton is a network, i.e., a solid network structure. The solid network structure has an internal hollow portion, which can be filled with viscous material to encapsulate the viscous material. This can improve the constraint of the elastic skeleton on the flow capacity of the viscous material from a structural perspective, and help to achieve a better constraint effect with a lower proportion of elastic skeleton, thereby reducing the obstruction generated by the elastic skeleton during the deformation of the suspended part 210.

[0035] The hollow portion of a solid network structure results in extremely low overall stiffness, meaning the network's equivalent modulus is much lower than its material modulus. Therefore, the solid network structure functions to constrain the flowability of the viscous portion while minimizing its impact on the resistance to the suspended portions.

[0036] When a viscoelastic membrane layer covers a gap, it can cover only part of the gap or cover all the gaps. For ease of understanding, some examples will be explained below with reference to the accompanying drawings: Covering the gaps Please refer to Figure 2 As shown, gaps are formed between the free end of the suspended portion and the two adjacent sides of the free end and the substrate. The viscoelastic membrane layer is positioned closer to the free end of the suspended portion than the fixed end, extending from the free end to the substrate around it, thus connecting the suspended portion and the substrate. Simultaneously, the viscoelastic membrane layer covers the gaps adjacent to the free end, but not the gaps adjacent to the fixed end. During device operation, because the gaps near the free end are covered by the viscoelastic membrane layer, these gaps are blocked, preventing the back cavity from communicating with the space on the other side of the diaphragm through these gaps, thus contributing to the establishment of a stable pressure differential.

[0037] Please refer to Figure 3As shown, gaps are formed between the free end of the suspended portion and the two adjacent sides of the free end and the substrate. The viscoelastic membrane layer is positioned closer to the fixed end of the suspended portion than the free end, extending from the fixed end to the substrate around it, thus connecting the suspended portion and the substrate. Simultaneously, the viscoelastic membrane layer covers the gaps adjacent to the fixed end, but not the gaps adjacent to the free end. During device operation, because the gaps near the fixed end are covered by the viscoelastic membrane layer, these gaps are blocked, preventing the back cavity from communicating with the space on the other side of the diaphragm through these gaps, thus contributing to the establishment of a stable pressure differential.

[0038] It should be understood that, in an optional embodiment, when the viscoelastic membrane layer covers part of the gap, the covered gap should be more than the uncovered gap.

[0039] Cover all gaps Please refer to Figure 4 As shown, gaps are formed between the free end of the suspended portion and the two adjacent sides of the free end and the substrate. A viscoelastic membrane layer is located in the suspended portion and extends towards the substrate around the suspended portion, connecting with the substrate. The extended viscoelastic membrane layer covers all gaps between the suspended portion and the substrate. During device operation, because all gaps are covered, the back cavity and the space on the other side of the diaphragm are completely blocked and no longer connected, thus enabling a more stable pressure differential to be established.

[0040] During the deformation of the suspended portion 210, the free end 212 exerts a greater force on the viscoelastic membrane layer 300, forcing it to withstand more impact. This includes the fact that the viscoelastic membrane layer 300 is located at the gap 220, thus needing to directly block the fluid medium from passing through the gap 220 and directly face the impact of the fluid medium. However, because the viscoelastic membrane layer 300 needs to minimize the resistance of its elastic portion, it is prone to undesirable rupture under the impact of the fluid medium. Therefore, it is necessary to improve the impact resistance of the viscoelastic membrane layer 300 to prevent it from failing during use. Examples of methods to increase the impact resistance of the viscoelastic membrane layer 300 will be explained below: In some examples, please refer to Figure 1A gap 220 is formed between the free end 212 of the suspended portion 210 and the substrate 100. The viscoelastic film layer 300 includes a cover portion and a connecting portion, which are connected. The cover portion is located at the gap 220 and its purpose is to seal the gap at that location. The connecting portion is located at the top surface of the suspended portion and the substrate and its purpose is to connect the cover portion to the suspended portion and the substrate. The thickness of the cover portion of the viscoelastic film layer 300 is greater than the thickness of the connecting portion. Thus, for the cover portion, because it is subjected to the impact of the free end 212 and the fluid medium directly at the gap 220, the greater thickness can increase its structural stability and improve the ultimate withstand voltage performance of the MEMS device. For the connecting portion, its thinner thickness can weaken its impact on the suspended portion 210.

[0041] In particular, when the connection extends to the fixed end 211 of the suspended part 210, the thickness of the connection at this point should be thinner. This can further reduce the adverse effects of the elastic part in the viscoelastic film layer 300 on the deformation of the suspended part 210, optimize the sensitivity of the MEMS device, and make it closer to the sensitivity state without the viscoelastic film layer 300.

[0042] In some possible implementations, please refer to Figure 2 The width w of the slit 220 ranges from 0.5 μm to 10 μm. When the width of the slit 220 meets this range, it can both allow the suspended portions 210 to fully release the internal stress present during the preparation process and fully consider the fluidity of the viscoelastic membrane layer 300, avoiding the viscoelastic membrane layer 300 from easily flowing away from the diaphragm 200 from the slit 220 due to the slit 220 being too wide.

[0043] In some possible implementations, the viscoelastic membrane layer 300 has an arched structure. Please refer to... Figure 5 This shows a comparison between the planar structure and the arched structure of the viscoelastic membrane layer 300, from... Figure 5 As can be seen, when the viscoelastic membrane layer 300 has an arched structure, it can meet the aforementioned requirements for the thickness of the viscoelastic membrane layer 300. Therefore, the viscoelastic membrane layer 300 can minimize the restriction of the strain at the fixed end of the suspended portion 210, ensuring its high sensitivity. At the same time, it can also ensure good structural stability of the viscoelastic membrane layer 300 at the free end 212. Please refer to... Figure 1 The viscoelastic membrane layer 300 has an arched cross-section along its thickness direction, and the highest point of the arch corresponds to the gap 220, for example... Figure 2 In the middle, the upper surface of the viscoelastic membrane layer 300 is curved, and the highest point of the curved surface is where the gap 220 is located.

[0044] In some possible implementations, the viscoelastic film layer 300 is a cured film layer, which, after undergoing a curing process, can relatively reduce its flowability, thereby providing flow constraint together with the elastic portion. It should be understood that it can be cured at room temperature or at high temperature.

[0045] In some possible implementations, the viscoelastic film layer 300 is a semi-solidified film layer, such as a hydrogel or silicone gel. It should be understood that silicone gel is better suited to high-temperature environments than hydrogel, for example, it is better adapted to the high-temperature curing process experienced during the preparation of the viscoelastic film layer 300.

[0046] In some possible implementations, although the viscoelastic membrane layer 300 can be constrained in terms of flow capacity, it still has low fluidity. Therefore, during the MEMS device fabrication process, after the diaphragm 200 undergoes a high-temperature process, the weak fluidity of the viscoelastic membrane layer 300 can be used to release the internal stress (the lower the internal stress of the diaphragm 200, the better the sensitivity), thereby improving the sensitivity of the diaphragm 200.

[0047] In some possible implementations, the orthographic projection of the back cavity 111 in the thickness direction of the substrate 100 can be a circle, a square, a triangle, etc.

[0048] In some possible implementations, the orthographic projection of the suspended portion 210 in the thickness direction of the substrate 100 can be a sector, a triangle, a square, etc.

[0049] In some possible implementations, the MEMS device can be a piezoelectric device, a piezoresistive device, etc. For example, when the MEMS device is a piezoelectric device, the diaphragm 200 is a piezoelectric structure (e.g., a single piezoelectric stack, i.e., an electrode / piezoelectric / electrode stack, or a double piezoelectric stack, i.e., an electrode / piezoelectric / electrode / piezoelectric / electrode stack, etc.); when the MEMS device is a piezoresistive device, a piezoresistor is provided in the diaphragm 200, and the piezoresistor is located at the fixed end 211 of the suspended part.

[0050] The piezoelectric effect is bidirectional; therefore, when a MEMS device is a piezoelectric device, it can be divided into piezoelectric actuators (such as loudspeakers, sound wave emitters, etc.) or piezoelectric sensors (such as sound sensors, pressure sensors, flow sensors, etc.). It should be understood that, based on the characteristics of the viscous portion in the viscoelastic film layer of this application, when a MEMS device is used as a pressure sensor, since the signal involved is essentially steady-state or metastable, the resistance of the viscous portion can be eliminated.

[0051] Please refer to Figure 6The diagram illustrates the signal output of three devices under the same operating conditions. The differences between the three devices are: a seamless diaphragm (no viscoelastic film layer), a slit diaphragm (no viscoelastic film layer), and the MEMS device of this application (a slit diaphragm with a viscoelastic film layer covering all slits). Figure 6 It can be seen that for devices without gaps in the diaphragm, because the diaphragm is a complete membrane layer, its sensitivity is low, making it difficult to capture weak signals, resulting in almost no effective signal output. For devices with gaps in the diaphragm, because the gaps allow the diaphragm to have free ends, its sensitivity is significantly improved, enabling it to capture weak signals. However, because the gaps are not closed, they directly connect the spaces on both sides of the diaphragm. The fluid medium on both sides of the diaphragm flows through the gaps due to the pressure difference, making it impossible to establish a stable pressure difference on both sides of the diaphragm. The diaphragm is prone to vibration, resulting in large fluctuations and drift in the output signal, making it unable to work stably. For the MEMS device of this application, a viscoelastic membrane layer 300 can be used to separate the two sides of the diaphragm 200 at the gap 220, thereby establishing a stable pressure difference. This allows the output signal to be maintained within a small fluctuation range, improving the accuracy and reliability of the sensing results.

[0052] Another aspect of this application provides a method for fabricating a MEMS device, the method comprising: S10: Form a septum on the substrate.

[0053] A substrate 100 is provided, on which the back cavity 111 is not formed. This makes the surface of the substrate 100 relatively flat, which makes it easier to form the diaphragm 200 on the substrate 100, resulting in better quality of the diaphragm 200.

[0054] A diaphragm 200 is formed by deposition on the surface of a substrate 100 and in conjunction with a photolithography process. For example, when the diaphragm 200 is a piezoelectric stack, the electrodes can be deposited by processes such as magnetron sputtering and vacuum deposition, and then patterned by a photolithography process to form electrodes of the desired shape. The piezoelectric layer can be formed by chemical vapor deposition.

[0055] S20: The substrate is etched to form a back cavity. The diaphragm is suspended in the part of the back cavity as a suspended part. A gap is formed between the suspended part and the substrate, and the gap is connected to the back cavity.

[0056] Please refer to Figure 1 A back cavity 111 is formed on the back side of the substrate 100 by etching the substrate 100 from the back. This exposes a portion of the diaphragm 200 within the back cavity 111, creating a suspended portion. A gap is formed between the suspended portion and the substrate, directly communicating with the back cavity. During this process, residual stress in the diaphragm 200 can be fully released through the deformation and expansion of the free end 212 of the suspended portion, minimizing sensitivity loss caused by residual stress in the diaphragm 200. Deep silicon etching processes, among others, can be used to etch the substrate 100 to form the back cavity 111.

[0057] S30: A viscoelastic membrane layer is formed on the suspended portion and the substrate, the viscoelastic membrane layer at least covering part of the gap.

[0058] Please refer to Figure 1 A viscoelastic membrane layer 300 is formed on the suspended portion of the diaphragm 200 and on the substrate, wherein the viscoelastic membrane layer 300 at least covers part of the gap. S30 is located after S20, which enables the suspended portion 210 to be released first, so that the diaphragm 200 can fully release residual stress through the deformation and expansion of the suspended portion 210. Then, the viscoelastic membrane layer 300 is set on the diaphragm 200 after the stress has been released. In this way, the stress of the diaphragm 200 and the viscoelastic membrane layer 300 as a whole can be sufficiently low, such as close to a zero stress state.

[0059] Furthermore, to avoid over-etching during the etching of the back cavity 111, in S10, an etching stop layer can be formed on the surface of the substrate 100 first. For example, an oxide layer can be formed on the surface of the silicon substrate 100 using a thermal oxidation process to serve as an etching stop layer. Then, a diaphragm 200 is formed on the etching stop layer.

[0060] It should be understood that S10 to S20 fall under the category of microelectronic processes and can be completed in a wafer fab, but S30 involves packaging processes and needs to be completed in a packaging plant.

[0061] Optionally, forming a viscoelastic film layer on the suspended portion and the substrate includes: S31: A liquid film layer is formed on the suspended part and the substrate.

[0062] S32: A viscoelastic film layer is formed by a curing process from a liquid film layer.

[0063] First, a liquid film is formed on the suspended portion and the substrate. At this point, the liquid film has a certain flow capacity and also facilitates the formation of an arched cross-section that is thicker in the middle and thinner at the edges, for example... Figure 1 As shown.

[0064] Then, the fluidity of the liquid film layer is reduced through a curing process, such as forming a semi-solid state, which serves as a viscoelastic film layer 300, thereby improving its structural stability.

[0065] The curing process can be either room temperature curing or high temperature curing. When high temperature curing is used, since the viscoelastic film layer 300 does not affect the sensitivity of the suspended part 210 as much as possible, the suspended part 210 can still release residual stress through deformation and expansion after high temperature curing, without being affected by the viscoelastic film layer 300.

[0066] Optionally, forming a liquid film layer on the suspended portion and the substrate includes: forming a liquid body in the area surrounding the gap above the suspended portion and the substrate using a dispensing or spraying process; the liquid body then diffuses outwards to form a liquid film layer. Compared to microelectronic processes such as spin coating, dry film deposition, and chemical vapor deposition, dispensing or spraying the liquid body above the diaphragm 200 allows the liquid body to adhere to the diaphragm and substrate from top to bottom, and then diffuse outwards to cover the gap 220. This provides better compatibility with uneven surfaces, such as unevenness in the suspended portion due to the release of residual stress, or a step between the suspended portion and the substrate, which facilitates the complete sealing of the gap 220.

[0067] When using a dispensing process, the needle inner diameter can be 0.5mm, the dispensing pressure can be 0.4MPa, the dispensing speed can be 3mm / s, and the vertical distance from the needle tip to the surface of the suspended part can be 0.5mm, thereby improving the dispensing effect.

[0068] Optionally, the liquid film layer is cured to form a viscoelastic film layer by means of: curing in a heated environment, such as at 100°C for 30 minutes, wherein a portion of the liquid film layer crosslinks to form a solid network structure and another portion forms a viscous body, and the solid network structure encapsulates the viscous body as a semi-solid viscoelastic film layer.

[0069] It should be understood that the MEMS device fabrication method in this application can also be used to fabricate the aforementioned MEMS devices.

[0070] The basic principles of this application have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in this application are merely examples and not limitations, and should not be considered as essential features of each embodiment of this application. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the application to the necessity of employing the aforementioned specific details for implementation.

[0071] The block diagrams of devices, apparatuses, devices, and systems involved in this application are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0072] It should also be noted that in the apparatus, equipment, and methods of this application, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered as equivalent solutions of this application.

[0073] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use this application. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of this application. Therefore, this application is not intended to be limited to the aspects shown herein, but rather to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[0074] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of this application to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations thereof.

Claims

1. A MEMS device, characterized in that, include: The base has a dorsal cavity; A diaphragm is disposed on the substrate, the diaphragm having a suspended portion suspended at the back cavity, a gap being formed between the suspended portion and the substrate, the gap communicating with the back cavity; A viscoelastic membrane layer is connected to the suspended portion and the substrate respectively, and the viscoelastic membrane layer at least covers part of the gap.

2. The MEMS device as described in claim 1, characterized in that, The viscoelastic membrane layer covers all the gaps to seal the back cavity at the diaphragm.

3. The MEMS device as described in claim 1, characterized in that, The viscoelastic membrane layer includes an interconnected cover portion and a connecting portion. The cover portion is located at the gap, and the connecting portion is connected to the suspended portion and the substrate, respectively. The thickness of the cover portion is greater than the thickness of the connecting portion.

4. The MEMS device as described in claim 1, characterized in that, The viscoelastic membrane layer includes a viscous body and an elastic skeleton, wherein the viscous body fills the elastic skeleton.

5. The MEMS device as described in claim 4, characterized in that, The elastic skeleton is a solid network structure, which encapsulates the viscous body.

6. The MEMS device according to any one of claims 1 to 5, characterized in that, The width of the gap ranges from 0.5 μm to 10 μm; And / or, the viscoelastic membrane layer has an arched structure.

7. A method for fabricating a MEMS device, characterized in that, The method includes: A diaphragm is formed on the substrate; The substrate is etched to form a back cavity, and the portion of the diaphragm suspended in the back cavity serves as a suspended portion. A gap is formed between the suspended portion and the substrate, and the gap communicates with the back cavity. A viscoelastic membrane layer is formed on the suspended portion and the substrate, the viscoelastic membrane layer at least covering part of the gap.

8. The MEMS device fabrication method according to claim 7, characterized in that, The formation of a viscoelastic film layer on the suspended portion and the substrate includes: A liquid film layer is formed on the suspended portion and the substrate; The liquid film layer is solidified to form the viscoelastic film layer.

9. The MEMS device fabrication method as described in claim 8, characterized in that, The formation of the liquid film layer on the suspended portion and the substrate includes: A liquid is formed on the diaphragm and the substrate by dispensing or spraying adhesive. The liquid diffuses outwards to form the liquid film layer.

10. The MEMS device fabrication method as described in claim 8, characterized in that, The viscoelastic film layer is formed by a curing process of the liquid film layer, comprising: In a heated environment, a portion of the liquid film layer crosslinks to form a solid network structure, and another portion forms a viscous body. The solid network structure encapsulates the viscous body as the viscoelastic film layer.

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