MEMS device and preparation method thereof
By performing a first wet cleaning process to remove part of the surface protective layer during MEMS device fabrication, followed by a second wet cleaning process, the problem of residual adhesive on the substrate surface was solved, product yield and cleaning efficiency were improved, and costs were reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-26
- Publication Date
- 2026-03-31
AI Technical Summary
During the fabrication of MEMS devices, a large amount of photoresist remains on the substrate surface, affecting product yield, and existing technologies are unable to effectively remove it.
After adopting the dry adhesive removal process, a first wet cleaning process is performed to remove part of the surface protective layer, followed by a second wet cleaning process. The batch processing tank cleaning equipment with different cleaning solutions is used for immersion cleaning to avoid substrate breakage and secondary contamination caused by single-wafer transfer.
It improves the efficiency of residual adhesive removal, reduces cleaning costs, increases product yield and work efficiency, and avoids substrate breakage and secondary contamination.
Smart Images
Figure CN121757797A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of integrated circuit manufacturing technology, and in particular to a MEMS device and its fabrication method. Background Technology
[0002] Microelectromechanical systems (MEMS) are microsystems that integrate micromechanical components, microsensors, microactuators, signal processing and control circuits. In the fabrication of MEMS devices, such as MEMS microphones, after forming a back cavity on the back side of the substrate using photolithography and etching processes, a dry etching process is needed to remove the photoresist layer. Studies have found that a significant amount of residual photoresist remains on the substrate surface, affecting product yield. Summary of the Invention
[0003] The purpose of this application is to provide a MEMS device and its fabrication method, which improves the efficiency of residual adhesive removal and increases the product yield.
[0004] To achieve the above objectives, one embodiment of this application provides a method for fabricating a MEMS device, comprising:
[0005] A substrate is provided, the substrate including a first surface and a second surface disposed opposite to each other, and a surface protective layer is formed on the first surface of the substrate;
[0006] A photoresist layer is formed on the second surface of the substrate, and the second surface of the substrate is etched using the photoresist layer as a mask to form a back cavity on the second surface of the substrate;
[0007] Perform a dry stripping process to remove the photoresist layer;
[0008] The substrate undergoes a first wet cleaning process to remove a portion of the surface protective layer; and,
[0009] The substrate is subjected to a second wet cleaning process using an EKC solution, and the cleaning solution used in the first wet cleaning process is different from that used in the second wet cleaning process.
[0010] Optionally, the thickness of the surface protective layer removed by the first wet cleaning process is less than or equal to 10% of the total thickness of the surface protective layer.
[0011] Optionally, the surface protective layer is made of silicon dioxide.
[0012] Optionally, the first wet cleaning process uses hydrofluoric acid solution or BOE solution.
[0013] Optionally, the first wet cleaning process uses hydrofluoric acid with a concentration of less than or equal to 1%.
[0014] Optionally, before performing the first wet cleaning process on the substrate, the substrate is transferred from the first wafer carrier to the second wafer carrier, the second wafer carrier being a corrosion-resistant carrier; after performing the second wet cleaning process on the substrate, the substrate is transferred from the second wafer carrier to the first wafer carrier.
[0015] Optionally, a die pusher is used to transfer the substrate from the first wafer carrier to the second wafer carrier, and a die pusher is used to transfer the substrate from the second wafer carrier to the first wafer carrier.
[0016] Optionally, the first wafer carrier is made of polypropylene, and the second wafer carrier is made of polytetrafluoroethylene.
[0017] Optionally, the MEMS device is a MEMS microphone device.
[0018] To achieve the above objectives, one embodiment of this application provides a MEMS device, and the MEMS device can be fabricated using the method described above.
[0019] Compared with the prior art, this application performs a dry adhesive removal process, followed by a first wet cleaning process on the substrate, and then a second wet cleaning process on the substrate. The cleaning solutions used in the second wet cleaning process and the first wet cleaning process are different. In this way, by first using the first wet cleaning process to remove part of the thickness of the surface protective layer, the residual adhesive adhering to the surface protective layer is fully released, and then the second wet cleaning process is performed, which helps to improve the removal efficiency of residual adhesive.
[0020] Furthermore, in the first and second wet cleaning processes, batch tank cleaning equipment is used to immerse and clean the substrate, avoiding substrate breakage caused by single-wafer transfer, reducing the probability of secondary contamination, and reducing the amount of cleaning solution used, which helps to improve cleaning efficiency and reduce cleaning costs.
[0021] Furthermore, before the first wet cleaning process, the substrate is transferred from the first wafer carrier to the corrosion-resistant second wafer carrier. After the second wet cleaning process, the substrate is transferred from the second wafer carrier to the first wafer carrier. This eliminates the need for a Sorter machine for wafer transfer, avoids contamination during the Sorter machine's wafer transfer process, and improves wafer transfer efficiency. Attached Figure Description
[0022] The accompanying drawings provide a more in-depth understanding of embodiments of this application and are incorporated herein by reference as a whole. These drawings and descriptions are used to illustrate the principles of some embodiments. It should be noted that all drawings are schematic diagrams and are for illustrative and drawing convenience, and relative sizes and proportions have been adjusted. The same symbols represent corresponding or similar features in different embodiments.
[0023] Figure 1 This is a schematic flowchart illustrating a method for fabricating a MEMS device according to an embodiment of this application.
[0024] Figure 2 This is a schematic diagram of the structure of a MEMS device fabrication method provided in this application after performing a dry resist removal process.
[0025] Figure 3 This is a schematic diagram of the structure of a MEMS device fabrication method provided in this application after the first wet cleaning process.
[0026] Figure 4 This is a schematic diagram of the wafer carrier structure used in a method for fabricating a MEMS device according to an embodiment of this application.
[0027] Figure 5 This is a schematic diagram of the pusher structure used in a method for fabricating a MEMS device according to an embodiment of this application.
[0028] In the attached image:
[0029] 100 - Substrate, 110 - First sacrificial layer, 120 - First conductive layer, 130 - Second sacrificial layer, 140 - Second conductive layer, 150 - Surface protective layer; 11 - First wafer carrier, 12 - Second wafer carrier, 20 - Wafer pusher. Detailed Implementation
[0030] To make the technical solutions and advantages of the embodiments of this application clearer, the technical solutions of this application will be further described in detail below with reference to the accompanying drawings and embodiments. Although exemplary implementation methods of this application are shown in the accompanying drawings, it should be understood that this application can be implemented in various forms and should not be limited to the implementation methods described herein. Rather, these implementation methods are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art.
[0031] The present application is described in more detail below by way of example with reference to the accompanying drawings. The advantages and features of the present application will become clearer from the following description and claims. It should be noted that the drawings are in a very simplified form and use non-precise proportions, intended only to facilitate and clarify the illustration of the embodiments of the present application. It is understood that the terms "on," "above," and "over" in this application should be interpreted in the broadest sense, such that "on" means not only "on" something without any intervening feature or layer (i.e., directly on something), but also includes "on" something with an intervening feature or layer.
[0032] Furthermore, for ease of description, regional relative terms such as “on,” “above,” “above,” “upper,” “above,” “upper,” etc., may be used herein to describe the relationship between one element or feature and another element or feature as shown in the figures. In addition to the orientations depicted in the figures, regional relative terms are intended to cover different orientations of the device in use or operation. The device may be oriented in other ways (rotated 90 degrees or in other orientations) and the regional relative descriptive terms used herein may be interpreted accordingly.
[0033] In the embodiments of this application, the terms "first," "second," etc., are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.
[0034] It should be noted that the technical solutions described in the embodiments of this application can be combined arbitrarily without conflict.
[0035] In the following embodiments, abbreviations and key terms are defined as follows:
[0036] MEMS (Micro-Electro-Mechanical Systems): MEMS is a technology that integrates micro-mechanical structures (such as cantilever beams, gears, thin films, cavities), micro-sensors, micro-actuators, and electronic circuits onto a single chip.
[0037] Sorter equipment: refers to wafer sorting machines, also known as wafer sorters or wafer transfer machines. It is a key piece of semiconductor manufacturing equipment primarily used for the handling, transfer, and sorting of wafers. It ensures the continuity and efficiency of the production process and is crucial for meeting the material flow needs of wafer fabs.
[0038] EKC chamber cleaning equipment: a very important type of specialized cleaning equipment in semiconductor manufacturing; EKC is an abbreviation of the initials of the three founders of American Chemical Company (Estreich, Krell, and Collins), and chamber refers to the reaction chamber of the cleaning equipment.
[0039] Batch processing equipment refers to equipment capable of processing multiple wafers at once. In semiconductor manufacturing, batch processing equipment improves production efficiency by processing multiple wafers simultaneously (also known as batch processing of multiple wafers). This type of equipment is typically used for process steps that can be processed in batches, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), or chemical mechanical polishing (CMP).
[0040] The applicant's research found that in current MEMS device fabrication processes, a dry etching process to remove photoresist is typically performed first, followed by the transfer of substrates one by one using a wafer transfer device (usually a Sorter) to a cleaning machine for wet cleaning with a spray solution to remove residual photoresist from the substrate surface. Taking MEMS device fabrication as an example, after etching the substrate to form a back cavity using the photoresist layer as a mask, a dry photoresist removal process is performed. After this process, a significant amount of photoresist remains on the substrate surface. Analysis revealed the following main reasons for this residual photoresist:
[0041] (1) The chuck of the photoresist stripping machine presses down on the edge of the substrate, making it easy for photoresist to remain at the edge of the substrate. The cleaning method using spray wet cleaning solution and the hardware structure have limited ability to clean the residual photoresist at the edge of the substrate. Furthermore, the substrate of MEMS devices is relatively thin and cannot be washed, resulting in the inability to completely remove the residual photoresist at the edge of the substrate.
[0042] (2) An additional Sorter machine is required for wafer transfer. Single wafer transfer can easily cause substrate breakage. Moreover, the Sorter machine handles a large number of wafers, which can easily cause contamination and thus contaminate the substrate.
[0043] (3) During the cleaning process of the substrate, the residual adhesive attached to it is easy to fall into the cleaning machine, causing secondary pollution.
[0044] To address the aforementioned issues, this application provides a MEMS device fabrication method. After a dry adhesive removal process, the substrate undergoes a first wet cleaning process, followed by a second wet cleaning process (using different cleaning solutions in the two processes). The first wet cleaning process removes a portion of the surface protective layer, fully releasing residual adhesive adhering to the protective layer and improving adhesive removal efficiency. The second wet cleaning process then thoroughly removes the remaining adhesive. Furthermore, both the first and second wet cleaning processes utilize a batch cleaning tank to immerse the substrate, avoiding substrate breakage caused by single-wafer transfer, reducing the probability of secondary contamination, and decreasing the amount of cleaning solution used, thus improving cleaning efficiency and reducing cleaning costs. In addition, before the first wet cleaning process, the substrate is transferred from the first wafer carrier to the corrosion-resistant second wafer carrier. After the second wet cleaning process, the substrate is transferred from the second wafer carrier to the first wafer carrier. This eliminates the need for a Sorter machine for wafer transfer, avoids contamination during the Sorter machine transfer process, and improves work efficiency.
[0045] The fabrication method of the MEMS device provided in the embodiments of this application will be described in detail below.
[0046] Figure 1 This is a schematic flowchart illustrating a method for fabricating a MEMS device according to an embodiment of this application. Figure 1 As shown, the fabrication method of the MEMS device may include at least the following steps:
[0047] Step S101: A substrate is provided, the substrate including a first surface and a second surface disposed opposite to each other, and a surface protective layer is formed on the first surface of the substrate.
[0048] Step S102: A photoresist layer is formed on the second surface of the substrate, and the second surface of the substrate is etched using the photoresist layer as a mask to form a back cavity on the second surface of the substrate.
[0049] Step S103: Perform a dry photoresist stripping process to remove the photoresist layer.
[0050] Step S104: Perform a first wet cleaning process on the substrate to remove a portion of the surface protective layer.
[0051] Step S105: Perform a second wet cleaning process on the substrate. The second wet cleaning process uses an EKC solution, and the cleaning solution used in the first wet cleaning process is different from that used in the second wet cleaning process.
[0052] The following explanation uses a MEMS microphone as an example of the MEMS device.
[0053] Figure 2 This is a schematic diagram of a partial structure formed on a substrate using the fabrication method provided in this application. (See attached diagram.) Figure 2 As shown, the substrate 100 includes a first side (also referred to as the front side of the substrate) and a second side (also referred to as the back side of the substrate) disposed opposite to each other. In one embodiment, the substrate 100 serves as a platform for subsequently forming components such as a first conductive layer (e.g., a diaphragm structure), a second conductive layer (e.g., a backplate structure), and a back cavity. The material of the substrate 100 can be any suitable substrate material well known to those skilled in the art, such as at least one of the following materials: silicon, silicon-on-insulator (SOI), silicon-on-insulator stacked (SSOI), silicon-on-insulator stacked (S-SiGeOI), silicon-on-insulator (SiGeOI), and germanium-on-insulator (GeOI), etc. This application does not limit the material of the substrate 100.
[0054] Next, a first sacrificial layer 110, a first conductive layer 120, a second sacrificial layer 130, a second conductive layer 140, and a protective layer 150 can be formed on the first surface of the substrate 100 by means of deposition, photolithography, and etching processes, stacked sequentially from bottom to top.
[0055] In one embodiment, the first sacrificial layer 110 and the second sacrificial layer 130 are made of the same material, so that they can be removed simultaneously in a subsequent sacrificial layer release process; their materials, for example, both include silicon oxide. The first conductive layer 120 and the second conductive layer 140 are, for example, polycrystalline silicon layers, and more specifically, N-doped polycrystalline silicon layers.
[0056] In one embodiment, the surface protective layer 150 can be used to isolate the MEMS device from other devices and also to fix the second conductive layer 120, avoiding problems with flexible circuit boards due to the second conductive layer 120 being too thin. The surface protective layer 150 can be formed of a different material than both the first sacrificial layer 110 and the second sacrificial layer 130; for example, the material of the surface protective layer 150 may be silicon dioxide or silicon nitride. Preferably, the surface protective layer 150 is made of the same material as the first sacrificial layer 110 and the second sacrificial layer 130 so that it can be removed synchronously in a subsequent sacrificial layer release process.
[0057] Then, the substrate 100 can be flipped so that the second side of the substrate 100 faces upward, and a photoresist layer (not shown) can be formed on the second side of the substrate 100 using a photolithography process. Then, using the photoresist layer as a mask, etching is performed along the second side of the substrate 100 to form a back cavity 101 in the substrate 100, and then the photoresist layer is removed.
[0058] Optionally, before flipping the substrate 100, a photoresist layer (not shown) can be formed on the first side of the substrate 100, i.e., the surface protective layer 150, and then the substrate 100 can be flipped, and a photoresist layer can be formed on the second side of the substrate 100. In this way, when the photoresist layer on the substrate is removed by the dry photoresist removal process, the photoresist layers on both the first and second sides of the substrate 100 can be removed by the dry photoresist removal process, as detailed in the following description.
[0059] In one specific embodiment, a dry photoresist stripping process can be used to remove the photoresist layer on the substrate 100. Specifically, dry photoresist stripping is performed on the first side (specifically, the surface of the surface protective layer 150) and the second side of the substrate 100. This is achieved by introducing a specific gas, such as oxygen, into a reaction chamber to generate plasma. Then, the active atoms in the plasma, such as oxygen atoms, react violently with elements in the photoresist, such as carbon and hydrogen, to generate carbon dioxide and water vapor. These gaseous products are subsequently removed by a vacuum system, but this is not a limitation.
[0060] However, due to the limitations of dry photoresist stripping processes, residual photoresist (also known as "residual photoresist") inevitably remains on the first and second surfaces of the substrate 100, such as... Figure 2 As shown in the elliptical region. To ensure the product performance of MEMS devices (such as capacitive microphones) and reduce the difficulty of subsequent processes, the photoresist remaining on the first and second surfaces of the substrate 100 needs to be removed.
[0061] Therefore, after performing the dry adhesive removal process, a first wet cleaning process is performed to remove a portion of the surface protective layer 150. During the first wet cleaning process, while removing a portion of the surface protective layer 150, residual adhesive adhering to the surface protective layer 150 is released, and damage to the second conductive layer 140 beneath the surface protective layer 150 is avoided.
[0062] In this embodiment, the surface protective layer 150 is made of silicon dioxide, and the first wet cleaning process uses a hydrofluoric acid (HF) solution or a BOE solution. Specifically, a hydrofluoric acid solution can be used, with a concentration of, for example, less than or equal to 1%.
[0063] like Figure 3As shown, the thickness of the surface protective layer 150 is reduced after the first wet cleaning process. In a preferred embodiment, the thickness of the surface protective layer removed by the first wet cleaning process is less than or equal to 10% of the total thickness of the surface protective layer, thus ensuring that the remaining surface protective layer 150 can still provide good protection for the second conductive layer 140. Specifically, the removal height of the surface protective layer 150 can be controlled by adjusting parameters such as the immersion time of the substrate 100 and the concentration of the acidic agent. Based on the disclosure of this application, those skilled in the art should know how to control the thickness of the surface protective layer 150 removed in the first wet cleaning process, and will not be elaborated upon here.
[0064] In a preferred embodiment, during the first wet cleaning process, the substrate 100 can be immersed and cleaned using a batch cleaning equipment (Batch machine). This avoids substrate breakage caused by single-wafer transfer, reduces the probability of secondary contamination, and also reduces the amount of cleaning solution used, which helps to improve cleaning efficiency and reduce cleaning costs.
[0065] In this embodiment, before performing the first wet cleaning process on the substrate 100, such as Figure 4 As shown, a batch of substrates 100 is transferred from a first wafer carrier 11 (typically a black cassette, a carrier and transport container) to a second wafer carrier 12 (typically a white cassette, a carrier and transport container), the second wafer carrier 12 being a corrosion-resistant carrier. The first wafer carrier 11 is made of, for example, polypropylene (PP). The second wafer carrier 12 is made of, for example, high-temperature and corrosion-resistant polytetrafluoroethylene (PTFE, also known as "Teflon").
[0066] In this embodiment, the following can be used: Figure 5 The wafer pusher 20 shown transfers the substrate 100 from the first wafer carrier 11 to the second wafer carrier 12, completing the cassette replacement. This eliminates the need for a sorter, avoiding contamination during sorter transfer and improving work efficiency. It is understood that other types of wafer pushers can be used in practice, and the system is not limited to these types. Figure 5 As shown.
[0067] Next, a second wet cleaning process is performed using an EKC solution. Preferably, the EKC cleaning equipment includes a cleaning tank in which the substrate 100 is immersed for cleaning. The EKC solution referred to in this application can be any of the EKC series cleaning solutions developed by a subsidiary of DuPont EKC Technology. This company develops a dedicated series of EKC cleaning solutions, which includes several sub-products of EKC solutions with different product numbers. The EKC solution used in this application can be any sub-product of the EKC cleaning solution series. Depending on the specific EKC product, its active ingredient can be hydroxylamine hydrochloride, hydroxylamine and ammonia, or a solution containing -NH2-OH groups. After immersion or rinsing with the EKC solution, the substrate 100 typically has areas with stubborn components removed, with a removal thickness usually less than 200 angstroms, and minimal damage to other areas of the substrate 100 surface.
[0068] After performing a second wet cleaning process on the substrate 100, it can be used as follows: Figure 5 The pusher 20 shown transfers the substrate 100 from the second wafer carrier 12 to the first wafer carrier 11. This eliminates the need for a sorter, avoids contamination during sorter transfer, and improves work efficiency.
[0069] More specifically, in the aforementioned first wet cleaning process, the corrosion-resistant second wafer carrier is immersed in a hydrofluoric acid (HF) solution to remove a portion of the surface protective layer 150. Then, the second wafer carrier, carrying multiple substrates, is transferred to another tank, where EKC cleaning agent is used to rinse away residual hydrofluoric acid and adhesive residue on the substrate 100. In practice, a clamp-type robotic arm can be used to transfer the substrates from one tank to another.
[0070] In one specific embodiment, the MEMS device is, for example, a MEMS microphone device. After efficient and precise removal of the adhesive from the substrate 100, subsequent process technologies can be performed on the substrate 100, such as a sacrificial layer release process on the first and second surfaces of the substrate 100 to remove the first sacrificial layer 110 and the second sacrificial layer 130, and to form a vibration gap communicating with the back cavity 101. It is understood that the above is only an example and can be adjusted accordingly based on specific device requirements.
[0071] Furthermore, based on the fabrication method described above, other embodiments of this application can also provide a MEMS device, which will not be elaborated here. Because it is fabricated using the above method, the first and second surfaces of the substrate of this MEMS device can be efficiently cleaned of residual adhesive, which is beneficial for improving product yield.
[0072] In summary, this application employs a dry adhesive removal process followed by a first wet cleaning process on the substrate, and then a second wet cleaning process using different cleaning solutions. This allows for the removal of a portion of the surface protective layer during the first wet cleaning process, effectively releasing residual adhesive adhering to the protective layer, before the second wet cleaning process, thus improving the efficiency of residual adhesive removal. Furthermore, the use of batch cleaning equipment in both the first and second wet cleaning processes avoids substrate breakage caused by single-wafer transfer, reduces the probability of secondary contamination, and decreases the amount of cleaning solution used, thereby improving cleaning efficiency and reducing cleaning costs. Furthermore, before the first wet cleaning process, the substrate is transferred from the first wafer carrier to the corrosion-resistant second wafer carrier. After the second wet cleaning process, the substrate is transferred from the second wafer carrier to the first wafer carrier. This eliminates the need for a Sorter machine for wafer transfer, avoids contamination during the Sorter machine's wafer transfer process, and improves wafer transfer efficiency.
[0073] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the embodiments of apparatus, electronic devices, and computer-readable storage media are basically similar to the method embodiments, and therefore the descriptions are relatively simple; relevant parts can be referred to the descriptions of the method embodiments.
[0074] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.
Claims
1. A method of fabricating a MEMS device, characterized by, The method comprises: providing a substrate, the substrate comprising a first surface and a second surface arranged oppositely, a surface protection layer being formed on the first surface of the substrate; forming a photoresist layer on the second surface of the substrate, and etching the second surface of the substrate with the photoresist layer as a mask to form a back cavity on the second surface of the substrate; performing a dry stripping process to remove the photoresist layer; performing a first wet cleaning process on the substrate to remove part of the thickness of the surface protection layer; and performing a second wet cleaning process on the substrate, the second wet cleaning process using an EKC solution, and the cleaning solution used in the first wet cleaning process being different from that used in the second wet cleaning process. The thickness of the surface protection layer removed by the first wet cleaning process is less than or equal to 10% of the total thickness of the surface protection layer.
2. The method of manufacturing a MEMS device according to claim 1, wherein The material of the surface protection layer is silicon dioxide.
3. The method of claim 1, wherein the MEMS device is a micro-mirror device. The first wet cleaning process uses a hydrofluoric acid solution or a BOE solution.
4. The method of claim 3, wherein the step of forming the MEMS device is performed by a method comprising: The first wet cleaning process uses a hydrofluoric acid solution with a concentration less than or equal to 1%.
5. The method of claim 4, wherein the MEMS device is a micro-mirror device. Before the first wet cleaning process is performed on the substrate, the substrate is transferred from a first wafer carrier to a second wafer carrier, the second wafer carrier being a corrosion-resistant carrier; and after the second wet cleaning process is performed on the substrate, the substrate is transferred from the second wafer carrier to the first wafer carrier.
6. The method of fabricating a MEMS device of claim 1, wherein, The substrate is transferred from the first wafer carrier to the second wafer carrier using a pusher, and the substrate is transferred from the second wafer carrier to the first wafer carrier using the pusher.
7. The method of claim 6, wherein the MEMS device is a micro-mirror device. The material of the first wafer carrier is polypropylene, and the material of the second wafer carrier is polytetrafluoroethylene.
8. The method of claim 7, wherein the MEMS device is a micro-mirror device. The MEMS device is a MEMS microphone device.
9. The method of manufacturing a MEMS device according to any one of claims 1 to 8, wherein The MEMS device is prepared by the method of any one of claims 1-9.
10. A MEMS device, characterized by