Multifunctional MEMS sensor and preparation method thereof

Abstract

The invention discloses a multifunctional MEMS sensor and a preparation method thereof, and belongs to the technical field of semiconductor chips. The device layer is suspended between the upper cover plate and the lower cover plate; the device layer comprises a first acceleration sensing unit, a second acceleration sensing unit and a pressure sensing unit, the two acceleration sensing units jointly form a square structure, and the pressure sensing unit is located in a middle cavity of the square structure; the middle area of the upper cover plate is hollow and used for sensing pressure signals by the pressure sensing unit. An outer packaging ring and an inner packaging ring are arranged between the upper cover plate and the lower cover plate, the pressure sensing unit is located in the inner packaging ring, and the first acceleration sensing unit and the second acceleration sensing unit are located in an annular cavity between the outer packaging ring and the inner packaging ring. According to the invention, synchronous measurement of an acceleration signal and a pressure signal under one chip is realized. Meanwhile, the influence of a pressure sensitive signal on an acceleration sensitive signal can be effectively isolated, signal crosstalk is effectively avoided, the structure is compact, and the occupied space is small.

Description

Technical Field

[0001] This invention relates to MEMS sensors, specifically to a multifunctional MEMS sensor and its fabrication method, belonging to the field of semiconductor chip technology. Background Technology

[0002] Tire pressure monitoring systems (TPMS) for automobiles, as well as aircraft monitoring, seismic structure and bridge monitoring, often require simultaneous monitoring of various types of dynamic environmental signals to improve system safety and energy efficiency. These signals include pressure signals, acceleration signals, and more. In existing technologies, these signals are detected using separate sensors; for example, pressure signals require a separate pressure sensor, and acceleration signals require a separate acceleration sensor. This results in numerous monitoring system components, a large footprint, complex wiring, and higher requirements for installation and layout. It can even affect the accuracy of signal acquisition by the sensing units and the actual performance of the monitoring system. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a multifunctional MEMS sensor and its fabrication method. This multifunctional sensor can simultaneously sense acceleration and pressure signals, achieving synchronous measurement of both signals on a single chip. Furthermore, it effectively isolates the influence of pressure signals on acceleration signals, effectively avoiding signal crosstalk. The multifunctional sensor features a highly integrated, compact structure and small footprint.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A multifunctional MEMS sensor includes an upper cover plate, a device layer, and a lower cover plate, with the device layer suspended between the upper and lower cover plates. The device layer includes a first acceleration sensing unit, a second acceleration sensing unit, and a pressure sensing unit. The acceleration direction sensed by the first acceleration sensing unit is perpendicular to the acceleration direction sensed by the second acceleration sensing unit. The first and second acceleration sensing units together form a U-shaped structure, and the pressure sensing unit is located in the central cavity of the U-shaped structure. The upper cover plate, corresponding to the pressure sensing unit, is hollowly disposed in the central area for the pressure sensing unit to sense pressure signals.

[0005] Furthermore, anchor connection parts are provided at the four corners of the square structure formed by the first acceleration sensing unit and the second acceleration sensing unit. The first acceleration sensing unit and the second acceleration sensing unit are suspended to the upper cover plate through the upper ends of the four anchor connection parts, and suspended to the lower cover plate through the lower ends of the four anchor connection parts; the pressure sensing unit is suspended to the lower cover plate through the support part.

[0006] Furthermore, the pressure-sensitive unit is rectangular in shape, and the support consists of four support plates that extend along the four sides of the rectangle and are connected end to end. The pressure-sensitive unit, the four support plates, and the lower cover plate are connected to form a closed cavity.

[0007] Furthermore, an outer encapsulation ring and an inner encapsulation ring are provided between the upper cover plate and the lower cover plate, the pressure-sensitive unit is located inside the inner encapsulation ring, and the first acceleration-sensitive unit and the second acceleration-sensitive unit are located in the annular cavity between the outer encapsulation ring and the inner encapsulation ring.

[0008] Furthermore, the first acceleration sensing unit and the second acceleration sensing unit are integrally formed and include a common rectangular annular mass frame. Near the ends of the outer sides of two opposite frames of the mass frame, one end of a folded beam of the first sensing unit is connected to each other. At the points of maximum stress in the four folded beams of the first sensing units, four first sensing resistors with equal resistance are formed through doping, and these four first sensing resistors are connected to form a first Wheatstone bridge. Near the ends of the other two opposite frames of the mass frame, one end of a folded beam of the second sensing unit is connected to each other. At the points of maximum stress in the four folded beams of the second sensing units, four second sensing resistors with equal resistance are formed through doping, and these four second sensing resistors are connected to form a second Wheatstone bridge. Each anchor area connection portion is respectively connected to the other end of the folded beam of the first sensing unit and the other end of the folded beam of the second sensing unit at the corresponding position.

[0009] Furthermore, the pressure-sensitive unit includes a pressure-sensitive membrane with four pressure-sensitive resistors of equal resistance, which are connected to form a third Wheatstone bridge.

[0010] Furthermore, the first Wheatstone bridge, the second Wheatstone bridge, and the third Wheatstone bridge share a common ground transmission signal.

[0011] Furthermore, the inner sides of the four sides of the mass frame are respectively provided with protrusions extending inwardly to the encapsulation ring for buffering impact.

[0012] Furthermore, the four sides of the mass frame are provided with a number of damping holes that run vertically through each other.

[0013] The present invention also provides a method for fabricating the aforementioned multifunctional MEMS sensor, comprising the following steps: Step 1: Prepare three silicon wafers, clean and dry them, and use them as the device layer silicon wafer, the top cover silicon wafer, and the bottom cover silicon wafer, respectively. Step 2: Ion implantation is performed on the front side of the device layer silicon wafer at predetermined positions. These ion implantation positions correspond to the locations of the four sensitive resistors of the first acceleration sensitive unit, the second acceleration sensitive unit, and the pressure sensitive unit, respectively; a total of 12 ion implantation positions are formed, thereby creating 12 sensitive resistors. Step 3: Prepare an oxide layer on the front side of the device layer silicon wafer to fully cover the ion implantation surface of the device layer silicon wafer; Step 4: Etch the oxide layer to expose the 12 ion implantation sites; Step 5: Sputter metal pads and leads to connect the ion-implanted sensitive resistors according to the preset circuit structure, forming three independent Wheatstone bridges; Step 6: Deposit SiO2 to cover the front side of the device layer silicon wafer; Step 7: Etch SiO2 to expose the metal pad windows to facilitate the extraction of the three Wheatstone bridge signals; Step 8: Perform wet etching on the back side of the device layer silicon wafer to obtain the pressure-sensitive film corresponding to the pressure-sensitive unit; at the same time, pre-etch the areas corresponding to the two acceleration-sensitive units; the part left around the back side of the pressure-sensitive film in this step forms the support plate of the pressure-sensitive film. Step 9: Based on step 8, further wet etching is performed on the pre-etched area on the back of the device layer silicon wafer to make the pre-etched area continuous from top to bottom, resulting in four disconnected parts of the device layer, namely the outer packaging ring, the inner packaging ring, the pressure sensitive unit and the two acceleration sensitive units. The two acceleration sensitive units include an integrally formed mass frame, a folded beam, a protruding structure, a damping hole and an anchor area connection. Step 10: Etch anchor areas, inner encapsulation rings, outer encapsulation rings, and support plate encapsulation rings on the lower cover silicon wafer. Then, deposit SiO2 on the anchor areas, inner encapsulation rings, outer encapsulation rings, and support plate encapsulation rings. The anchor areas, inner encapsulation rings, and outer encapsulation rings on the lower cover silicon wafer are vertically aligned with the anchor area connection, inner encapsulation ring, and outer encapsulation ring formed by etching the device layer silicon wafer. The support plate encapsulation ring is vertically aligned with the support plate of the pressure-sensitive membrane. Then, perform silicon-silicon bonding with the back side of the device layer silicon wafer obtained in Step 9, so that the anchor areas, the upper surface of the inner encapsulation ring, and the upper surface of the outer encapsulation ring on the lower cover silicon wafer are bonded to the corresponding anchor area connection, the lower surface of the inner encapsulation ring, and the lower surface of the outer encapsulation ring on the device layer silicon wafer, respectively. At the same time, connect the bottom support plate of the pressure-sensitive membrane to the support plate encapsulation ring of the lower cover. Step 11: Etch a central cavity structure, anchor area, inner encapsulation ring and outer encapsulation ring on the lower surface of the upper cover silicon wafer. The central cavity structure is directly opposite the pressure-sensitive membrane. The anchor area, inner encapsulation ring and outer encapsulation ring on the upper cover silicon wafer are directly opposite the anchor area, inner encapsulation ring and outer encapsulation ring formed by etching the device layer silicon wafer. Step 12: The anchor area, lower surface of the inner packaging ring, and lower surface of the outer packaging ring of the top cover silicon wafer obtained in Step 11 are bonded to the anchor area connection part, upper surface of the inner packaging ring, and upper surface of the outer packaging ring formed by etching the device layer silicon wafer to form a multifunctional sensitive device.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. The multifunctional sensor of this invention can simultaneously sense acceleration-sensitive signals and pressure-sensitive signals, realizing synchronous measurement of acceleration and pressure signals on a single chip.

[0015] 2. The multifunctional sensor packaging ring of this invention has a hollow structure. Using this packaging ring for wafer-level packaging, the pressure-sensitive unit and the acceleration-sensitive unit are physically isolated. This allows the middle part to effectively sense the pressure signal, while effectively avoiding the problem of pressure signal crosstalk affecting the acquisition of acceleration signal.

[0016] 3. The pressure-sensitive unit of the multifunctional sensor of the present invention is embedded in the U-shaped cavity formed by the first acceleration-sensitive unit and the second acceleration-sensitive unit. The structure is highly integrated and compact, effectively reducing space, chip area and installation requirements.

[0017] 4. The multifunctional sensor of this invention has three independent Wheatstone bridges for signal transmission, but can be connected to the same ground signal, making the wiring layout simple.

[0018] 5. This invention eliminates the need for pre-designing and fabricating components such as inner and outer isolation rings, mass frames, folded beams, and connecting parts. A multifunctional sensor is fabricated using only three silicon wafers through etching and mature bonding techniques. The related processes are mature and reliable, the fabrication route is clear, the fabrication process is easy to operate, and it offers good controllability. This invention completes device design while avoiding process complexity, effectively reducing process difficulty, increasing process compatibility, and saving time and reducing costs. Attached Figure Description

[0019] Figure 1 A schematic diagram of a multifunctional sensor provided in an embodiment of the present invention; Figure 2 An exploded view of a multifunctional sensor provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of a multifunctional sensor provided in an embodiment of the present invention; Figure 4 A Wheatstone bridge diagram for a multifunctional sensor provided in an embodiment of the present invention; Figure 5 A process flow chart for manufacturing a multifunctional sensor provided in an embodiment of the present invention; In the figure: 101, upper cover plate; 102, device layer; 103, lower cover plate; 201, first sensitive unit folded beam; 202, first sensitive resistor; 203, damping hole; 204, mass frame; 205, protruding structure; 206, anchor area connection; 207, second sensitive unit folded beam; 208, second sensitive resistor; 209, outer encapsulation ring; 210, pressure sensitive resistor; 211, inner encapsulation ring; 212, pressure sensitive membrane. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be understood that the terms "center", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0022] The terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature; in the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0023] See Figure 1 and Figure 2 As shown in the figure, the present invention discloses a multifunctional MEMS sensor, comprising an upper cover plate 101, a device layer 102, and a lower cover plate 103. The device layer 102 is suspended between the upper cover plate 101 and the lower cover plate 103. The device layer includes a first acceleration sensing unit, a second acceleration sensing unit, and a pressure sensing unit. The first and second acceleration sensing units are capable of sensing acceleration in a first direction and a second direction, respectively. The pressure sensing unit is capable of sensing pressure changes in the environment. The acceleration direction sensed by the first and second acceleration sensing units is perpendicular to the acceleration direction sensed by the second acceleration sensing unit. The first and second acceleration sensing units are integrally formed and together form a U-shaped structure. The pressure sensing unit is located in the central cavity of the U-shaped structure. The upper cover plate 101, corresponding to the pressure sensing unit, is hollowly disposed in the central area for the pressure sensing unit to sense pressure signals.

[0024] This invention provides a multifunctional sensor that can simultaneously detect acceleration signals in two directions and changes in atmospheric pressure signals in the environment, achieving synchronous measurement of acceleration and pressure signals on a single chip. The multifunctional sensor features a highly integrated, compact structure with a small footprint.

[0025] Specifically, anchor connection parts 206 are provided at the four corners of the square structure formed by the first acceleration sensing unit and the second acceleration sensing unit. The first acceleration sensing unit and the second acceleration sensing unit are suspended to the upper cover plate 101 through the upper ends of the four anchor connection parts 206, and suspended to the lower cover plate 103 through the lower ends of the four anchor connection parts; the pressure sensing unit is suspended to the lower cover plate through the support part.

[0026] Furthermore, the pressure-sensitive unit is rectangular in shape, and the support consists of four support plates extending along the four sides of the rectangle and connected end to end. The pressure-sensitive unit, the four support plates, and the lower cover plate are connected to form a closed cavity. After installation, a closed structure is formed, which can ensure the reliable detection of atmospheric pressure signals by the pressure-sensitive unit.

[0027] Furthermore, an outer encapsulation ring 209 and an inner encapsulation ring 211 are provided between the upper cover plate 101 and the lower cover plate 103. The pressure-sensitive unit is located within the inner encapsulation ring 211, and the first acceleration-sensitive unit and the second acceleration-sensitive unit are located within the annular cavity between the outer encapsulation ring 209 and the inner encapsulation ring 211. This invention physically isolates the pressure-sensitive unit and the acceleration-sensitive unit, which not only allows the intermediate part to effectively sense the pressure signal but also effectively avoids the problem of pressure signal crosstalk affecting acceleration signal acquisition. Moreover, the inner and outer encapsulation rings form a wafer-level packaged entity.

[0028] See Figure 3 The first and second acceleration sensing units are integrally formed and include a common rectangular annular mass frame 204. Two opposite sides of the mass frame 204 are connected to one end of a first sensing unit folded beam 201 near their ends. Four first sensing resistors 202 with equal resistance are formed by doping at the points of maximum stress in the four first sensing unit folded beams 201. The four first sensing resistors 202 are connected to form a first Wheatstone bridge. Two other opposite sides of the mass frame are connected to one end of a second sensing unit folded beam 207 near their ends. Four second sensing resistors 208 with equal resistance are formed by doping at the points of maximum stress in the four second sensing unit folded beams 207. The four second sensing resistors 208 are connected to form a second Wheatstone bridge. Each anchor connection 206 is connected to the other end of the first sensing unit folded beam 201 and the other end of the second sensing unit folded beam 207 at the corresponding positions.

[0029] The first acceleration sensing unit and the second acceleration sensing unit of the present invention are integrally formed and arranged together on the same mass frame. The pressure sensing unit is embedded in the cavity formed by the first acceleration sensing unit and the second acceleration sensing unit. The structure is highly integrated and compact, effectively reducing space, chip area and installation and layout requirements.

[0030] In this invention, the first acceleration sensing unit senses the first direction of motion through the first folded beams on both the left and right sides and oscillates accordingly to generate an acceleration response. In this embodiment, the number of first folded beams is relatively small (…). Figure 3 It consists of three beams, but one of them is relatively long, which can effectively suppress movement in the second sensitive direction. The second acceleration sensing unit senses the second direction of movement through the second folded beams on the upper and lower sides and swings accordingly to provide an acceleration response. In this embodiment, although all the folded beams have the same length, the number of folded beam segments is relatively large ( Figure 3 (The beam is a five-segment beam), which can effectively suppress movement in the first sensitive direction. Of course, the folded beams in the two directions can be exactly the same, as long as they can respond to the acceleration in the detected direction and suppress the acceleration in the other direction, they will meet the usage requirements.

[0031] The inner sides of the four sides of the mass frame 204 are respectively provided with protruding structures 205 extending inward towards the encapsulation ring for buffering impact. There are two symmetrical protruding structures 205 on each side. When the external force impact is large, the protruding structures can contact the inner encapsulation ring before the mass frame, thereby buffering the mass frame and preventing the mass frame from being damaged due to excessive force.

[0032] The mass frame 204 has several vertically penetrating damping holes 203 on its four sides. The damping structure of the sensitive unit can be effectively adjusted through the damping holes 203 to prevent impacts from the third acceleration sensitive direction (i.e., simultaneously perpendicular to the first and second acceleration directions) and reduce stress.

[0033] The pressure-sensitive unit includes a pressure-sensitive membrane 212, on which four pressure-sensitive resistors 210 with equal resistance are connected to form a third Wheatstone bridge.

[0034] See Figure 4 The first, second, and third Wheatstone bridges share a common ground transmission signal. This invention's multifunctional sensor uses three independent Wheatstone bridges for signal transmission, yet they collectively form a Wheatstone bridge group with a common grounding point, meaning they are connected to the same ground signal, simplifying wiring and layout.

[0035] This invention also provides a method for fabricating the above-mentioned multifunctional MEMS sensor, the specific steps of which are as follows, and the processing flow is also available in [link to relevant documentation]. Figure 5 .

[0036] Step 1: Prepare three silicon wafers, clean and dry them, and use them as the device layer silicon wafer, the top cover silicon wafer, and the bottom cover silicon wafer, respectively. Step 2: Ion implantation is performed on the front side of the device layer silicon wafer at predetermined positions. These ion implantation positions correspond to the locations of the four sensitive resistors of each of the first acceleration-sensitive unit, the second acceleration-sensitive unit, and the pressure-sensitive unit; a total of 12 ion implantation positions are established, forming 12 sensitive resistors; see [link to relevant documentation]. Figure 5 The status indicated by Institute 302; Step 3: Fabricate an oxide layer on the front side of the device layer silicon wafer to fully cover the ion implantation surface of the device layer silicon wafer, achieving electrical isolation; see Figure 5 The status indicated by Institute 303; Step 4: Etch the oxide layer to expose the 12 ion implantation sites for subsequent interconnection to form a Wheatstone bridge; see [link to relevant documentation]. Figure 5 The status indicated by Institute 304; Step 5: Sputter metal pads (PADs) and leads to connect the ion-implanted sensitive resistors according to the pre-defined circuit structure, forming three independent Wheatstone bridges; see Figure 5 The status indicated by Institute 305; Step 6: Deposit SiO2 to cover the front side of the device layer silicon wafer; see Figure 5 The status indicated by Institute 306; Step 7: Etch SiO2 to expose the PAD window for easy extraction of the three Wheatstone bridge signals; see Figure 5 The status indicated by Institute 307; Step 8: Perform wet etching on the back side of the device layer silicon wafer to obtain the pressure-sensitive film corresponding to the pressure-sensitive unit; simultaneously, pre-etch the areas corresponding to the two acceleration-sensitive units; the portion left around the back side of the pressure-sensitive film in this step forms the support plate for the pressure-sensitive film; see... Figure 5 The status indicated by Institute 308; Step 9: Based on Step 8, further wet etching is performed on the pre-etched areas on the back of the device layer silicon wafer to make the pre-etched areas continuous from top to bottom, resulting in four disconnected parts of the device layer: the outer packaging ring, the inner packaging ring, the pressure-sensitive unit, and two acceleration-sensitive units. The two acceleration-sensitive units include an integrally formed mass frame, a folded beam, a raised structure, a damping hole, and an anchor area connection; see [link to relevant documentation]. Figure 5 The status indicated by Institute 309; Step 10: Etch anchor areas, inner encapsulation rings, outer encapsulation rings, and support plate encapsulation rings on the lower cover silicon wafer. Then, deposit SiO2 on the anchor areas, inner encapsulation rings, outer encapsulation rings, and support plate encapsulation rings. The anchor areas, inner encapsulation rings, and outer encapsulation rings on the lower cover silicon wafer are vertically aligned with the anchor area connection portions, inner encapsulation rings, and outer encapsulation rings etched on the device layer silicon wafer. The support plate encapsulation rings are vertically aligned with the support plate of the pressure-sensitive membrane. Then, perform silicon-silicon bonding with the back side of the device layer silicon wafer obtained in Step 9, so that the upper surfaces of the anchor areas, inner encapsulation rings, and outer encapsulation rings on the lower cover silicon wafer are bonded to the corresponding anchor area connection portions, lower surfaces of the inner encapsulation rings, and lower surfaces of the outer encapsulation rings on the device layer silicon wafer, respectively. At the same time, connect the bottom support plate of the pressure-sensitive membrane to the corresponding support plate encapsulation ring of the lower cover. See Figure 5 The status indicated by Institute 310; Step 11: Etch a central cavity structure, anchor area, inner encapsulation ring, and outer encapsulation ring on the lower surface of the upper cover silicon wafer. The central cavity structure faces the pressure-sensitive membrane. The anchor area, inner encapsulation ring, and outer encapsulation ring on the upper cover silicon wafer are vertically aligned with the anchor area, inner encapsulation ring, and outer encapsulation ring formed by etching the device layer silicon wafer. See [link to relevant documentation]. Figure 5 The status indicated by 311; Step 12: Bond the anchor area, lower surface of the inner packaging ring, and lower surface of the outer packaging ring of the top cover silicon wafer obtained in Step 11 to the anchor area connection portion, upper surface of the inner packaging ring, and upper surface of the outer packaging ring formed by etching the device layer silicon wafer, thus forming a multifunctional sensing device. See [link to relevant documentation]. Figure 5 The status indicated by 312.

[0037] In this fabrication process, all three silicon wafers are formed with inner and outer encapsulation rings and interconnections to maximize wafer utilization. During final bonding, the inner and outer encapsulation rings and interconnections are bonded together to form a single unit.

[0038] This invention provides a multifunctional MEMS sensor that can simultaneously sense dual-axis acceleration and pressure signals. Its compact structure significantly increases space utilization. The sensor's encapsulation ring is hollow, allowing for wafer-level packaging that physically isolates the pressure-sensitive and acceleration-sensitive units. This ensures effective pressure signal sensing in the middle section while effectively preventing pressure signal crosstalk. The three sensing units of the multifunctional sensor have independent Wheatstone bridges for signal transmission, but can be connected to the same ground signal, simplifying the fabrication and wiring process.

[0039] The above embodiments of the present invention are merely illustrative examples and are not intended to limit the implementation of the invention. Those skilled in the art can make other variations and modifications based on the above description. It is impossible to exhaustively list all possible implementations here. All obvious variations or modifications derived from the technical solutions of the present invention are still within the protection scope of the present invention.

Claims

1. A multifunctional MEMS sensor, characterized in that: The device includes an upper cover plate, a device layer, and a lower cover plate, with the device layer suspended between the upper and lower cover plates. The device layer includes a first acceleration sensing unit, a second acceleration sensing unit, and a pressure sensing unit. The acceleration direction sensed by the first acceleration sensing unit is perpendicular to the acceleration direction sensed by the second acceleration sensing unit. The first and second acceleration sensing units together form a U-shaped structure, and the pressure sensing unit is located in the central cavity of the U-shaped structure. The upper cover plate, corresponding to the pressure sensing unit, is hollowly disposed in the central area for the pressure sensing unit to sense pressure signals.

2. The multifunctional MEMS sensor according to claim 1, characterized in that: Anchor connection parts are provided at the four corners of the "U" structure formed by the first acceleration sensing unit and the second acceleration sensing unit. The first acceleration sensing unit and the second acceleration sensing unit are suspended to the upper cover plate through the upper ends of the four anchor connection parts, and suspended to the lower cover plate through the lower ends of the four anchor connection parts; the pressure sensing unit is suspended to the lower cover plate through the support part.

3. A multifunctional MEMS sensor according to claim 2, characterized in that: The pressure-sensitive unit is rectangular in shape, and the support consists of four support plates that extend along the four sides of the rectangle and are connected end to end. The pressure-sensitive unit, the four support plates, and the lower cover plate are connected to form a closed cavity.

4. A multifunctional MEMS sensor according to claim 2, characterized in that: An outer encapsulation ring and an inner encapsulation ring are provided between the upper cover plate and the lower cover plate. The pressure-sensitive unit is located inside the inner encapsulation ring, and the first acceleration-sensitive unit and the second acceleration-sensitive unit are located in the annular cavity between the outer encapsulation ring and the inner encapsulation ring.

5. A multifunctional MEMS sensor according to claim 4, characterized in that: The first and second acceleration sensing units are integrally formed and include a common rectangular annular mass frame. Two opposite sides of the mass frame are connected to one end of a folded beam of the first sensing unit near their ends. Four first sensing resistors with equal resistance are formed by doping at the points of maximum stress in the four first sensing unit folded beams. These four first sensing resistors are connected to form a first Wheatstone bridge. The other two opposite sides of the mass frame are connected to one end of a folded beam of the second sensing unit near their ends. Four second sensing resistors with equal resistance are formed by doping at the points of maximum stress in the four second sensing unit folded beams. These four second sensing resistors are connected to form a second Wheatstone bridge. Each anchor area connection is connected to the other end of the first and second sensing unit folded beams at the corresponding positions.

6. A multifunctional MEMS sensor according to claim 5, characterized in that: The pressure-sensitive unit includes a pressure-sensitive membrane with four pressure-sensitive resistors of equal resistance, which are connected to form a third Wheatstone bridge.

7. A multifunctional MEMS sensor according to claim 6, characterized in that: The first, second, and third Wheatstone bridges share a common ground transmission signal.

8. A multifunctional MEMS sensor according to claim 5, characterized in that: The inner sides of the four sides of the mass frame are provided with protruding structures extending inwardly towards the encapsulation ring for cushioning impact.

9. A multifunctional MEMS sensor according to claim 5, characterized in that: The mass frame has several vertically penetrating damping holes on its four sides.

10. A method for fabricating the multifunctional MEMS sensor of claim 6, characterized in that: The steps are as follows: Step 1: Prepare three silicon wafers, clean and dry them, and use them as the device layer silicon wafer, the top cover silicon wafer, and the bottom cover silicon wafer, respectively. Step 2: Ion implantation is performed on the front side of the device layer silicon wafer at predetermined positions. These ion implantation positions correspond to the locations of the four sensitive resistors of the first acceleration sensitive unit, the second acceleration sensitive unit, and the pressure sensitive unit, respectively; a total of 12 ion implantation positions are formed, thereby creating 12 sensitive resistors. Step 3: Prepare an oxide layer on the front side of the device layer silicon wafer to fully cover the ion implantation surface of the device layer silicon wafer; Step 4: Etch the oxide layer to expose the 12 ion implantation sites; Step 5: Sputter metal pads and leads to connect the ion-implanted sensitive resistors according to the preset circuit structure, forming three independent Wheatstone bridges; Step 6: Deposit SiO2 to cover the front side of the device layer silicon wafer; Step 7: Etch SiO2 to expose the metal pad windows to facilitate the extraction of the three Wheatstone bridge signals; Step 8: Perform wet etching on the back side of the device layer silicon wafer to obtain the pressure-sensitive film corresponding to the pressure-sensitive unit; at the same time, pre-etch the areas corresponding to the two acceleration-sensitive units. The portion left around the back of the pressure-sensitive membrane in this step forms the support plate for the pressure-sensitive membrane. Step 9: Based on step 8, further wet etching is performed on the pre-etched area on the back of the device layer silicon wafer to make the pre-etched area continuous from top to bottom, resulting in four disconnected parts of the device layer, namely the outer packaging ring, the inner packaging ring, the pressure sensitive unit and the two acceleration sensitive units. The two acceleration sensitive units include an integrally formed mass frame, a folded beam, a protruding structure, a damping hole and an anchor area connection. Step 10: Etch anchor area, inner packaging ring, outer packaging ring and support plate packaging ring on the lower cover plate silicon wafer, and then deposit SiO2 on the anchor area, inner packaging ring, outer packaging ring and support plate packaging ring. The anchor area, inner packaging ring and outer packaging ring on the lower cover plate silicon wafer are directly opposite the anchor area, inner packaging ring and outer packaging ring formed by etching the device layer silicon wafer. The support plate encapsulation ring and the support plate of the pressure-sensitive membrane are aligned vertically; then silicon-silicon bonding is performed with the back side of the device layer silicon wafer obtained in step 9, so that the anchor area, the upper surface of the inner encapsulation ring, and the upper surface of the outer encapsulation ring on the lower cover plate silicon wafer are bonded to the anchor area connection part, the lower surface of the inner encapsulation ring, and the lower surface of the outer encapsulation ring corresponding to the device layer silicon wafer, respectively. At the same time, the bottom support plate of the pressure-sensitive membrane is connected to the support plate encapsulation ring corresponding to the lower cover plate. Step 11: Etch a central cavity structure, anchor area, inner encapsulation ring and outer encapsulation ring on the lower surface of the upper cover silicon wafer. The central cavity structure is directly opposite the pressure-sensitive membrane. The anchor area, inner encapsulation ring and outer encapsulation ring on the upper cover silicon wafer are directly opposite the anchor area, inner encapsulation ring and outer encapsulation ring formed by etching the device layer silicon wafer. Step 12: The anchor area, lower surface of the inner packaging ring, and lower surface of the outer packaging ring of the top cover silicon wafer obtained in Step 11 are bonded to the anchor area connection part, upper surface of the inner packaging ring, and upper surface of the outer packaging ring formed by etching the device layer silicon wafer to form a multifunctional sensitive device.

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