Embedded laminated beam MEMS piezoresistive acceleration sensor and preparation method thereof

Abstract

The application discloses an embedded laminated beam MEMS piezoresistive acceleration sensor and a preparation method thereof, and belongs to the technical field of micro-electro-mechanical system inertial sensors. The sensor comprises a silicon base frame, a mass block, a sensitive beam connecting the mass block and the silicon base frame, and a piezoresistor arranged on the sensitive beam. The silicon base frame, the mass block and the sensitive beam are integrally formed by silicon material. A closed groove is arranged on the mass block, the sensitive beam and / or the silicon base frame. The closed groove has a closed contour, and at least a part of the closed groove is located in a sensitive beam area or a connecting area of the sensitive beam and the mass block and the silicon base frame. A continuous silicon layer is reserved at the bottom of the closed groove. A polymer filling body is arranged in the closed groove, and the polymer filling body and the continuous silicon layer jointly form an embedded laminated structure. The application can improve the stress response of the piezoresistor arrangement area while maintaining the bearing capacity of the sensitive structure.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) inertial sensor technology, specifically relating to an embedded laminated beam MEMS piezoresistive accelerometer and its fabrication method. Background Technology

[0002] MEMS accelerometers are characterized by their small size, light weight, ease of mass production, and convenient integration, and are widely used in inertial measurement, impact testing, collision detection, aerospace, and other motion state detection fields.

[0003] Piezoresistive MEMS accelerometers typically include a fixed frame, a mass block, a sensitive beam connecting the fixed frame and the mass block, and a piezoresistor mounted on the sensitive beam. When an external acceleration occurs, the mass block generates an inertial force, causing the sensitive beam to deform. The piezoresistor then experiences a change in resistance under stress. Acceleration information can be obtained by detecting the piezoresistor or the output of a bridge circuit.

[0004] For accelerometers with large ranges or high natural frequencies, the sensing beam typically needs to have high structural stiffness and load-bearing capacity. However, increasing the stiffness of the sensing beam reduces the deformation and strain produced under the same acceleration, which can easily lead to a decrease in the sensor's output sensitivity.

[0005] In existing technologies, the range, natural frequency, and sensitivity of a sensor can be altered by adjusting the dimensions of the mass block and the sensing beam. However, these properties are mutually restrictive. While simply reducing the local thickness of the sensing beam can increase the strain response, it also changes the structural continuity and load transfer characteristics of the sensing beam.

[0006] Therefore, it is necessary to provide a new sensitive structure for MEMS piezoresistive accelerometers and a corresponding fabrication method, which adjusts the mechanical properties of the sensitive structure while maintaining its load-bearing capacity, in order to improve the problem of the difficulty in balancing structural load-bearing capacity and output sensitivity. Summary of the Invention

[0007] This invention provides an embedded laminated beam MEMS piezoresistive accelerometer and its fabrication method, in order to improve the problem that it is difficult to balance structural load-bearing capacity and output sensitivity in existing MEMS piezoresistive accelerometers.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides an embedded laminated beam MEMS piezoresistive accelerometer, comprising: Silicon-based framework, bonded to a glass substrate; The mass block is located inside the silicon-based framework; Multiple sensitive beams connect the mass block and the silicon-based frame; A varistor is mounted on the sensitive beam; The silicon-based framework, mass block, and sensitive beam are integrally formed from silicon material. A closed groove is located between the mass block and the silicon-based framework; A polymer filler is provided inside the closed groove.

[0009] Furthermore, multiple closed grooves are spaced apart from each other and arranged around the mass block.

[0010] Furthermore, there are four closed grooves, which are centrally symmetrically distributed around the center of the mass block.

[0011] Furthermore, the closed groove includes at least two types of groove segments: a groove segment disposed near the outer periphery of the mass block, a groove segment extending along the side of the sensitive beam, and a groove segment disposed near the inner periphery of the silicon-based frame.

[0012] Furthermore, the polymer filler is formed from a patternable and curable polymer material.

[0013] Furthermore, the polymer filler is SU-8 filler.

[0014] Furthermore, the varistor is formed in the near-surface layer of silicon material at the root of the sensitive beam near the silicon-based frame, and is spaced apart from the polymer filler.

[0015] Furthermore, the varistor includes multiple P-type piezoresistive segments and P+-type heavily doped connection regions disposed between adjacent P-type piezoresistive segments and / or at the ends of the varistor; the multiple P-type piezoresistive segments are connected in series through the P+-type heavily doped connection regions to form a bent varistor.

[0016] Secondly, the present invention provides a method for fabricating an embedded laminated beam MEMS piezoresistive accelerometer, comprising the following steps: A thin oxide layer is formed on both sides of the silicon wafer; A varistor is formed on the front side of the silicon wafer; A back cavity is formed by etching on the back side of the silicon wafer; Anodizing the silicon wafer to the glass substrate; Form leadholes, ohmic contact metal, metal leads, and pads on the front side of the silicon wafer; A closed groove is etched on the front side of the silicon wafer. The closed groove does not penetrate the silicon wafer so as to retain a continuous silicon layer at the bottom of the closed groove. A polymer filler is formed within the closed groove; The release positions corresponding to the mass block and the sensitive beam in the silicon wafer are etched to release the mass block and the sensitive beam, so that the polymer filler and the continuous silicon layer form an embedded laminate structure.

[0017] Furthermore, forming the polymer filler includes: defining the polymer pattern to be retained in the closed groove by photolithography, so that the polymer material is retained in the closed groove, and removing the polymer material outside the closed groove.

[0018] Compared with the prior art, the present invention has at least the following beneficial technical effects: The accelerometer provided by this invention has the following beneficial technical effects: First, the closed groove does not penetrate the sensitive structure, and a continuous silicon layer is retained at the bottom of the closed groove, so that the mass block, the sensitive beam and the silicon-based frame still maintain a continuous connection, which is beneficial for the sensor to maintain the structural load-bearing capacity under high impact acceleration.

[0019] Secondly, after the polymer filler is placed in the closed groove, the polymer filler and the continuous silicon layer at the bottom of the closed groove work together to change the local equivalent stiffness and stress transmission path of the sensitive beam and its adjacent parts, so that the part where the piezoresistor is located under the action of out-of-plane acceleration can obtain a higher stress response, which is conducive to improving the output sensitivity of the sensor, and thus achieving a balance between load-bearing capacity and output sensitivity.

[0020] Third, the varistor is formed at the root of the sensitive beam on the side of the sensitive beam close to the silicon-based framework, avoiding the closed groove and polymer filler. This can prevent the varistor from crossing the closed groove or polymer filler, which is beneficial to ensuring the reliability of the varistor fabrication and the stability of its electrical performance.

[0021] Furthermore, multiple closed grooves are spaced apart from each other and arranged around the mass block, forming a more balanced local stiffness adjustment and stress transfer effect around the mass block.

[0022] Furthermore, the closed grooves are centrally symmetrically distributed around the center of the mass block, which helps maintain structural symmetry and reduce output imbalance caused by lateral interference and off-center loading.

[0023] Furthermore, the closed groove includes at least two types of groove segments: a groove segment located near the outer periphery of the mass block, a groove segment extending along the side of the sensitive beam, and a groove segment located near the inner periphery of the silicon-based frame. This facilitates the adjustment of local stress transmission near the connection between the mass block, the sensitive beam, and the silicon-based frame.

[0024] Furthermore, the polymer filler is formed from a patternable and curable polymer material, which facilitates the patterning preparation of the polymer filler through processes such as photolithography.

[0025] Furthermore, the varistor is formed in the near-surface layer of silicon material at the root of the sensitive beam near the silicon-based frame, and is spaced apart from the polymer filler. This helps to place the varistor in a position with greater stress response, while ensuring its electrical performance is stable.

[0026] The method for fabricating an accelerometer provided by this invention has the following beneficial technical effects: First, the etching of the closed groove and the formation of the polymer filler are both completed before the release of the mass block and the sensitive beam. Since the silicon wafer still has complete mechanical support at this time, the risk of adhesion, deformation or damage to the released sensitive beam caused by the polymer coating, exposure, development and curing processes can be reduced, which is beneficial to improving the stability of the device fabrication process and the yield.

[0027] Secondly, the heat treatment steps such as varistor annealing, heavily doped connection region annealing, and silicon-glass anodic bonding are all completed before the formation of the polymer filler, which reduces the impact of subsequent high-temperature processes on the morphology and material properties of the polymer filler and helps to maintain the structural integrity and process consistency of the polymer filler in the closed groove. Attached Figure Description

[0028] Figure 1a This is a front three-dimensional structural diagram of an embedded laminated beam MEMS piezoresistive accelerometer according to an embodiment of the present invention; Figure 1b This is a front-view three-dimensional structural diagram of an embedded laminated beam MEMS piezoresistive accelerometer according to an embodiment of the present invention (excluding the polymer filler). Figure 1c This is a schematic diagram of the three-dimensional structure of the back of an embedded laminated beam MEMS piezoresistive accelerometer according to an embodiment of the present invention; Figure 2a This is a top view of the front structure of an embedded laminated beam MEMS piezoresistive accelerometer according to an embodiment of the present invention. Figure 2b As an embodiment of the present invention Figure 2a A schematic diagram of a symmetrical cross-sectional structure formed by the AA section line, without passing through a closed groove; Figure 2c As an embodiment of the present invention Figure 2a A schematic diagram of the asymmetric cross-sectional structure formed by the BB section line and passing through the closed groove; Figure 3a This is a frontal three-dimensional structural diagram of an embedded laminated beam MEMS piezoresistive accelerometer according to an embodiment of the present invention (the mass block is highlighted in color). Figure 3b This is a frontal three-dimensional structural diagram of an embedded laminated beam MEMS piezoresistive accelerometer according to an embodiment of the present invention (the sensitive beam is highlighted in color). Figure 3c This is a front-view three-dimensional structural diagram of an embedded laminated beam MEMS piezoresistive accelerometer according to an embodiment of the present invention (the silicon-based frame is highlighted in color); Figure 4This is an enlarged schematic diagram showing the arrangement of the varistor at the root of the sensitive beam in one embodiment of the present invention; Figure 5a Stress simulation cloud diagram of a sensitive structure without a closed groove under a 10000g impact load; Figure 5b Stress simulation cloud diagram of a sensitive structure with a closed groove but not filled with polymer material under a 10000g impact load; Figure 5c Stress simulation cloud diagram of a sensitive structure with a closed groove filled with polymer material (SU-8 material) under a 10000g impact load; Figure 6 This is a schematic diagram of the preparation method according to an embodiment of the present invention.

[0029] In the attached figure: 1-Silicon-based framework; 2-Mass block; 3-Sensitive beam; 4-Closed groove; 5-Continuous silicon layer; 6-Varistor; 7-Cavity; 8-Glass substrate; 9-P-type varistor segment; 10-Thin oxide layer; 11-Polymer filler. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0031] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0032] It should be noted that when an element is referred to as being "set on" another element, it can be directly on the other element or may be interposed with another element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or may be interposed with another element. The terms "upper," "lower," "front," "rear," "left," "right," "top," "bottom," "inner," and "outer," etc., used herein to indicate orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing the invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] An embedded laminated beam MEMS piezoresistive accelerometer includes a silicon-based frame, a mass block located within the silicon-based frame, multiple sensitive beams connecting the mass block and the silicon-based frame, and piezoresistors formed on the sensitive beams. Multiple closed grooves are provided on the mass block, sensitive beams, and / or silicon-based frame. These closed grooves are loop-shaped grooves with a closed profile in a plane. The closed grooves are blind grooves to retain a continuous silicon layer at the bottom. A polymer filler is disposed within the closed grooves, and the polymer filler and the continuous silicon layer together form an embedded laminated structure.

[0035] In a preferred embodiment, there are four closed grooves, which are centrally symmetrically distributed around the center of the mass block. The number of closed grooves, the shape of their closed contours, and their arrangement can also be adjusted according to the performance requirements of the sensor.

[0036] The present invention also provides a method for fabricating the above-mentioned sensor. In this method, before the release of the mass block and the sensitive beam, a closed groove that does not penetrate the sensitive structure is first formed on the front side of the silicon wafer, and a polymer filler is formed at the wafer level; subsequently, the release positions of the mass block and the sensitive beam in the silicon wafer are etched to release the mass block and the sensitive beam.

[0037] The following are specific embodiments. It should be noted that these embodiments are preferred examples of the present invention and are intended for those skilled in the art to understand the present invention, but the present invention is not limited to these embodiments.

[0038] Example 1: An Embedded Laminated Beam MEMS Piezoresistive Accelerometer like Figures 1a to 3cAs shown, this embodiment provides an embedded laminated beam MEMS piezoresistive accelerometer, including a silicon-based frame 1, a mass block 2, multiple sensitive beams 3, multiple closed grooves 4, a continuous silicon layer 5, a piezoresistor 6, metal leads, pads, and a glass substrate 8. The silicon-based frame 1, mass block 2, multiple sensitive beams 3, multiple closed grooves 4, and the continuous silicon layer 5 at the bottom of the closed grooves 4 constitute the sensor's sensitive structure. The mass block 2 is connected to the silicon-based frame 1 via multiple sensitive beams 3; the closed grooves 4 extend inward from the front of the sensitive structure but do not penetrate it, and the bottom of the closed grooves 4 retains the continuous silicon layer 5, which is the area of ​​the sensitive structure at the bottom of the closed grooves 4 that is not etched through, and maintains continuous connection with its surrounding structure. Below the continuous silicon layer 5 is a cavity 7, and all the closed grooves 4 communicate with the cavity 7. The piezoresistor 6 is disposed on the sensitive beams 3, and the metal leads are electrically connected to the piezoresistor 6, and the pads are electrically connected to the metal leads to extract the electrical signal from the piezoresistor 6. A glass substrate 8 is located on the back side of the sensitive structure and is bonded to the silicon-based framework 1 to support the sensitive structure. To highlight the sensitive structure, Figures 1a to 3c The varistor 6, metal leads, solder pads and glass substrate 8 are omitted.

[0039] In one specific embodiment, one or more of the closed groove segments are provided in the same sensitive beam, and the one or more groove segments do not fill the width direction of the sensitive beam, so that a continuous silicon material portion that has not formed the closed groove is retained on the sensitive beam, and the varistor is disposed on the upper part of the sensitive beam.

[0040] A silicon-based frame 1 is disposed around the periphery of the sensitive structure to support the mass block 2 and multiple sensitive beams 3. The mass block 2 is located in the center of the inner space enclosed by the silicon-based frame 1 and is connected to the silicon-based frame 1 through the multiple sensitive beams 3. In one specific embodiment, there are four sensitive beams 3, which are located around the mass block 2.

[0041] The silicon-based frame 1, mass block 2, and sensing beam 3 are integrally formed from the same silicon wafer, with mass block 2 being a single, solid mass block. This embodiment is a uniaxial accelerometer, with its sensing direction parallel to the sensor's thickness direction. When external acceleration acts on the sensor, mass block 2 moves along the sensor's thickness direction, causing the sensing beam 3 to bend and deform.

[0042] like Figure 6As shown, the glass substrate 8 is bonded to the back side of the silicon-based frame 1, and together with the silicon-based frame 1, the mass block 2, and the sensing beam 3, defines a cavity 7. The cavity 7 is located below the mass block 2 and the sensing beam 3, providing space for the mass block 2 to move along the sensor thickness direction. In one embodiment, the glass substrate 8 is made of borosilicate glass, the silicon-based frame 1 is anoly bonded to the glass substrate 8, and a cavity is formed between the mass block 3 and the glass substrate 8 to allow the mass block to move in a direction perpendicular to the lower end face of the glass substrate. To highlight the cross-sectional relationship of the sensing structure, the closed groove 4, and the continuous silicon layer 5, Figure 2b and Figure 2c The glass substrate is omitted in the middle.

[0043] Example 2: Closed groove and embedded laminated structure like Figures 1a to 4 As shown, multiple closed grooves 4 are provided between the mass block 2 and the silicon-based frame 1. The closed grooves 4 can pass through the sensitive beam 3, or through the connection between the sensitive beam 3 and the mass block 2, or the connection between the sensitive beam 3 and the silicon-based frame 1.

[0044] Each closed groove 4 has a closed profile. In other words, "closed" means that the closed groove 4 has a closed profile in the sensor plane; "not penetrating" means that the closed groove 4 does not penetrate the sensitive structure in the thickness direction of the sensor.

[0045] The closed groove 4 extends inward from the surface of at least one of the silicon-based frame 1, the mass block 2, and the sensitive beam 3; the closed groove 4 does not penetrate the corresponding silicon-based frame 1, the mass block 2, or the sensitive beam 3.

[0046] In one specific embodiment, there are four closed grooves 4, spaced apart from each other, and the four closed grooves 4 are centrally symmetrically distributed around the center of the mass block 2. Each closed groove 4 includes a groove segment located near the outer periphery of the mass block 2, a groove segment extending along the side of the sensitive beam 3, a groove segment located near the inner periphery of the silicon-based frame 1, and another groove segment extending along the side of the sensitive beam 3, which are connected end to end to form a closed profile. The corners of the closed grooves 4 are provided with chamfers or rounded transitions to reduce local stress concentration at the corners of the closed grooves 4 and improve the etching consistency of the closed grooves 4.

[0047] Mass block 2, closed groove 4 and sensitive beam 3 are all located above continuous silicon layer 5, and the bottom surface of closed groove 4 is the top surface of continuous silicon layer 5.

[0048] In other embodiments, the closed groove 4 can also be configured with other quantities, closed contour shapes, or arrangements according to the target range, natural frequency, sensitivity, and structural strength requirements, as long as the closed groove 4 does not penetrate the sensitive structure and forms an embedded laminated structure together with the polymer filler 11 inside it. Here, "embedded" means that the polymer filler 11 is located inside the closed groove 4, and "laminated structure" means that the polymer filler 11 and the continuous silicon layer 5 at the bottom of the closed groove 4 jointly bear the local stress transmission role in the sensor thickness direction.

[0049] like Figure 2a As shown, a silicon-based frame 1 is arranged around a mass block 2, and the mass block 2 is connected to the silicon-based frame 1 through a sensitive beam 3. A cavity 7 is formed below the mass block 2 and the sensitive beam 3, so that the mass block 2 can be displaced relative to the silicon-based frame 1 under inertial load, and the sensitive beam 3 can undergo elastic deformation. Figure 2b The AA section shown does not pass through the closed groove 4 and is used to represent the basic connection relationship between the silicon-based frame 1, the mass block 2, the sensitive beam 3, and the cavity 7.

[0050] like Figure 2c As shown, the BB section line passes through the closed groove 4. The closed groove 4 extends from the front of the sensitive structure in the thickness direction, and its depth is less than the thickness of the sensitive structure at the corresponding position, so that the closed groove 4 does not penetrate the sensitive structure, and a continuous silicon layer 5 is retained at the bottom of the closed groove 4. The continuous silicon layer 5 is the part of the sensitive structure that is not etched through at the bottom of the closed groove 4, and it is continuously connected to the silicon base frame 1, sensitive beam 3 or mass block 2 adjacent to the closed groove 4, thereby maintaining a continuous load-bearing path between the silicon base frame 1, sensitive beam 3 and mass block 2.

[0051] A polymer filler 11 is disposed within the closed groove 4, and the polymer filler 11 and the continuous silicon layer 5 at the bottom of the closed groove 4 together form an embedded laminated structure. No continuous polymer layer is disposed on the silicon surface outside the closed groove 4. In one specific embodiment, the surface of the polymer filler is substantially flush with the upper surface of the sidewall of the closed groove 4.

[0052] The polymer filler 11 can be made of a patternable and curable polymer material. In one embodiment, the polymer filler 11 is made of SU-8 material. SU-8 material can be retained within the closed groove 4 using a wafer-level patterning process. In other embodiments, other polymer materials that can be formed, cured, and stably bonded to the sensitive structure within the closed groove 4 can also be used. The depth and width of the closed groove 4, as well as the thickness of the continuous silicon layer 5, can be determined according to the sensor's target range, intrinsic frequency, sensitivity, and structural strength requirements.

[0053] Example 3: Piezoresistive Detection Structure The piezoresistive sensing structure includes a piezoresistor 6, a metal lead electrically connected to the piezoresistor 6, and a pad electrically connected to the metal lead. The piezoresistor 6 is used to convert the stress change generated by the sensitive beam 3 under acceleration into a resistance change. The metal lead and the pad are used to draw out the electrical signal of the piezoresistor 6.

[0054] like Figure 4 As shown, the varistor 6 is positioned in the beam root region of the sensitive beam 3 near the silicon-based frame 1, and is located in the continuous silicon material region of the sensitive beam 3 where the closed groove 4 is not formed (i.e., the polymer fillers 11 are spaced apart), to avoid the varistor 6 crossing the closed groove 4 or the polymer filler region. The specific position of the varistor 6 within the beam root region can be determined based on the stress distribution of the sensitive beam 3 under load, so that the varistor 6 is located in a region with a large stress response and relatively stable stress changes. Figure 4 The black area in the diagram is only used to indicate the arrangement of the varistor 6 and does not represent its actual shape, size, or quantity, nor does it limit the specific distance between the varistor 6 and the closed groove 4.

[0055] In one specific embodiment, one or more closed groove segments 4 may be provided within the same sensitive beam 3 region. These one or more groove segments do not fill the entire width direction of the sensitive beam 3 and are spaced apart from sensitive structural areas where closed grooves 4 are not formed, thus reserving an area within the sensitive beam 3 region for installing the varistor 6. This description does not limit the specific number, width, or extension length of the closed groove segments 4 within the same sensitive beam 3 region.

[0056] In one embodiment, the sensor is an N-type single-crystal silicon with a (100) crystal plane, and the main sensing direction of the varistor 6 is set along the <110> crystal direction. The varistor 6 may include one or more P-type piezoresistive segments and P+ type heavily doped connection regions for electrical connection. Its specific shape, size, number and bending form can be determined according to the stress distribution on the sensitive beam 3, the target resistance value, the output sensitivity and the ion implantation process requirements.

[0057] In one embodiment, the varistor 6 includes a plurality of P-type piezoresistive segments disposed in N-type single crystal silicon, and a P+ type heavily doped connection region disposed between adjacent P-type piezoresistive segments and / or at the end of the varistor; the plurality of P-type piezoresistive segments are connected in series through the P+ heavily doped connection region to form a bent varistor.

[0058] The varistor 6 is electrically connected to the external detection circuit via metal leads. The specific lead configuration and pad arrangement can be determined according to the sensor layout requirements. To emphasize the positional relationship between the varistor 6 and the closed groove 4, Figure 4 Metal leads and pads are omitted.

[0059] In one specific embodiment, four varistors 6 are connected by metal leads to form a Wheatstone bridge. When an external acceleration occurs, the sensitive beam 3 bends, and the varistor 6 undergoes a change in resistance under stress, causing the Wheatstone bridge to output a voltage signal related to the input acceleration. The Wheatstone bridge and its metal leads can employ connection methods commonly used in the art.

[0060] The working process and technical effects of the accelerometer provided by this invention are as follows: When external acceleration acts on the accelerometer, mass block 2 generates inertial force and moves in a direction parallel to the thickness of the sensor. The movement of mass block 2 causes the sensitive beam 3 to bend, and the piezoresistor 6 located at the beam root region experiences stress and a change in resistance. By detecting the voltage change at the output of the Wheatstone bridge, an output signal corresponding to the external acceleration can be obtained.

[0061] The continuous silicon layer 5 retained at the bottom of the closed groove 4 ensures a continuous load transfer path between the mass block 2, the sensitive beam 3, and the silicon-based frame 1. The polymer filler 11 within the closed groove 4 forms an embedded laminated structure with the continuous silicon layer 5, altering the local equivalent stiffness, neutral layer position, and stress transfer path of the sensitive beam and its adjacent areas, thereby enabling the region where the piezoresistor 6 is located to obtain a larger stress response under out-of-plane acceleration.

[0062] like Figures 5a to 5c As shown, to verify the influence of the embedded laminated structure on the stress response of the varistor arrangement area, three sensitive structure models were established for comparative analysis: the first is a conventional sensitive structure without a closed groove; the second is an empty groove sensitive structure with a closed groove but without polymer material filling the groove; and the third is an embedded laminated sensitive structure with a closed groove filled with SU-8 material. The silicon-based frame, mass block, sensitive beam, and varistor arrangement are consistent in all three sensitive structures.

[0063] Under the same boundary conditions, an impact load of 10,000g was applied to the three types of sensitive structures. Simulation results show that in the conventional sensitive structure without closed grooves, the maximum stress in the varistor arrangement area is 3.92 MPa; in the empty groove sensitive structure with closed grooves but not filled with polymer material, the maximum stress in the varistor arrangement area is 6.73 MPa; and in the embedded laminated sensitive structure with closed grooves and filled with SU-8 material, the maximum stress in the varistor arrangement area is 8.95 MPa. Compared with the conventional sensitive structure without closed grooves, the maximum stress in the varistor arrangement area of ​​the embedded laminated sensitive structure with closed grooves and filled with SU-8 material is increased by approximately 128.3%; and compared with the empty groove sensitive structure with closed grooves but not filled with polymer material, the maximum stress in the varistor arrangement area is increased by approximately 33.0%.

[0064] The simulation results show that the closed groove can improve the stress response of the varistor arrangement area under impact load. After setting the SU-8 filler in the closed groove, the embedded laminated structure formed by the polymer filler 11 and the continuous silicon layer at the bottom of the groove further improves the stress response of the varistor arrangement area, thereby helping to improve the output sensitivity of the piezoresistive accelerometer. The simulation model described above is used to illustrate the influence of the closed groove and the polymer filler 11 on the stress response of the varistor arrangement area, and is not used to limit the specific dimensions of the sensitive beam, mass block, closed groove, and continuous silicon layer.

[0065] Example 4: A method for fabricating an embedded laminated beam MEMS piezoresistive accelerometer like Figure 6 As shown, the embedded laminated beam MEMS piezoresistive accelerometer of this embodiment is prepared according to the following steps. Figure 6 include Figure 6 a to Figure 6 There are a total of eight process diagrams.

[0066] Step 1, as follows Figure 6 As shown in a, the silicon wafer is prepared and subjected to standard cleaning to form a thin oxide layer 10 on both sides of the silicon wafer.

[0067] Step two, as Figure 6 As shown in b, the piezoresistive region is defined by photolithography, and after etching the oxide layer corresponding to the piezoresistive region, the piezoresistive region is subjected to ion implantation and annealing to form a P-type piezoresistive segment 9.

[0068] Step 3, as Figure 6 As shown in Figure c, the oxide layer on the front side of the silicon wafer is removed by RIE etching, and then a silicon oxide layer is deposited by PECVD. The heavily doped connection region is defined by photolithography. After etching the mask layer corresponding to the heavily doped connection region, ion implantation and annealing are performed to form the P+ type heavily doped connection region. The P+ type heavily doped connection region is located at the end of the P-type varistor segment and between adjacent P-type varistor segments to reduce the contact resistance between the P-type varistor segment and the subsequent metal leads, and to reduce the connection resistance between adjacent P-type varistor segments. The P-type varistor segment and the P+ type heavily doped connection region together constitute varistor 6. Step four, as... Figure 6 As shown in d, the oxide layer on the back side of the silicon wafer is etched, the back cavity area is defined by photolithography, and the back cavity 7 is formed from the back side of the silicon wafer by ICP etching. Figure 6 d represents the structural state after the formation of the back cavity mask and the back cavity etching are completed.

[0069] Step 5, as Figure 6 As shown in e, a silicon wafer with a back cavity 7 is bonded to a glass substrate 8 via silicon-glass anodic bonding.

[0070] Step six, as follows Figure 6 As shown in f, firstly, the lead hole area is defined on the front side of the silicon wafer by photolithography, the lead hole is etched to form, platinum ohmic contact metal is sputtered, and the ohmic contact at the lead hole is formed by a lift-off process; then, the lead area is defined by photolithography, an aluminum metal layer is formed by magnetron sputtering, and metal leads and pads are formed by a lift-off process. Figure 6 f-combination represents the fabrication process of the ohmic contact metal and the metal lead.

[0071] Step seven, as Figure 6 As shown in g, the closed groove area is defined by photolithography, and the closed groove 4 is etched on the front side of the silicon wafer using ICP etching. The closed groove 4 does not penetrate the silicon wafer to retain a continuous silicon layer 5 at the bottom of the closed groove 4. Subsequently, a polymer material is coated on the front side of the silicon wafer to fill the closed groove 4; the polymer material is patterned by photolithography, and the polymer material outside the closed groove 4 is removed, leaving the polymer material within the closed groove 4, thereby forming a polymer filler 11. In this embodiment, the polymer material used is SU-8.

[0072] Step eight, as Figure 6 As shown in Figure h, the sensitive structure release area is defined by photolithography, and ICP etching is used to etch through the silicon wafer to release the mass block 2 and the sensitive beam 3. After release, the mass block 2 is connected to the silicon substrate frame 1 through the sensitive beam 3, and the SU-8 filler in the closed groove 4 and the continuous silicon layer 5 at the bottom of the closed groove 4 together form an embedded laminated structure.

[0073] In this embodiment, the etching of the closed groove 4 and the formation of the SU-8 filler are both completed before the mass block 2 and the sensitive beam 3 are released. At this time, the silicon wafer still has complete mechanical support, which can reduce the risk of adhesion, deformation or damage to the released sensitive structure caused by the SU-8 coating, exposure, development and curing processes.

[0074] The heat treatment steps, such as varistor annealing, P+ type heavily doped connection region annealing, and silicon-glass anodic bonding, are all completed before the formation of SU-8 filler, thereby reducing the impact of subsequent high-temperature processes on the morphology and material properties of SU-8 filler.

[0075] The term "constituting of" in describing a combination should include the identified elements, components, parts, or steps, as well as other elements, components, parts, or steps that do not substantially affect the essential novel features of the combination. The use of the terms "comprising" or "including" to describe combinations of elements, components, parts, or steps herein also contemplates embodiments that are essentially composed of such elements, components, parts, or steps. The use of the term "may" herein is intended to indicate that any described attribute included by "may" is optional.

[0076] Multiple elements, components, parts, or steps can be provided by a single integrated element, component, part, or step. Alternatively, a single integrated element, component, part, or step can be divided into multiple separate elements, components, parts, or steps. The use of "a" or "an" to describe an element, component, part, or step does not imply the exclusion of other elements, components, parts, or steps.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention.

Claims

1. An embedded laminated beam MEMS piezoresistive accelerometer, characterized in that, include: A silicon-based framework (1) is bonded to a glass substrate (8); Mass block (2) is disposed inside the silicon-based framework (1); Multiple sensitive beams (3) are connected between the mass block (2) and the silicon-based frame (1); A varistor (6) is disposed on the sensitive beam (3); The silicon-based framework (1), the mass block (2), and the sensitive beam (3) are integrally formed from silicon material; A closed groove (4) is located between the mass block (2) and the silicon-based frame (1); A polymer filler (11) is provided inside the closed groove (4).

2. The embedded laminated beam MEMS piezoresistive accelerometer according to claim 1, characterized in that, Multiple closed grooves (4) are spaced apart from each other and arranged around the mass block (2).

3. The embedded laminated beam MEMS piezoresistive accelerometer according to claim 1, characterized in that, There are four closed grooves (4), and the four closed grooves (4) are centrally symmetrically distributed around the center of the mass block (2).

4. An embedded laminated beam MEMS piezoresistive accelerometer according to claim 2 or 3, characterized in that, The closed groove (4) includes at least two types of groove segments: a groove segment located near the outer periphery of the mass block (2), a groove segment extending along the side of the sensitive beam (3), and a groove segment located near the inner periphery of the silicon-based frame (1).

5. The embedded laminated beam MEMS piezoresistive accelerometer according to claim 1, characterized in that, The polymer filler (11) is formed from a patternable and curable polymer material.

6. An embedded laminated beam MEMS piezoresistive accelerometer according to claim 5, characterized in that, The polymer filler (11) is SU-8 filler.

7. An embedded laminated beam MEMS piezoresistive accelerometer according to claim 1, characterized in that, The varistor (6) is formed on the near-surface layer of silicon material at the root of the sensitive beam (3) near the silicon-based frame (1) and is spaced apart from the polymer filler (11).

8. An embedded laminated beam MEMS piezoresistive accelerometer according to claim 1, characterized in that, The varistor (6) includes multiple P-type piezoresistive segments and P+ type heavily doped connection regions disposed between adjacent P-type piezoresistive segments and / or at the ends of the varistor; the multiple P-type piezoresistive segments are connected in series through the P+ type heavily doped connection regions to form a bent varistor (6).

9. A method for fabricating an embedded laminated beam MEMS piezoresistive accelerometer, characterized in that, Includes the following steps: A thin oxide layer is formed on both sides of the silicon wafer (10). A varistor (6) is formed on the front side of the silicon wafer; A back cavity is formed by etching on the back side of the silicon wafer; The silicon wafer is anodicly bonded to the glass substrate (8); Lead holes, ohmic contact metal, metal leads, and pads are formed on the front side of the silicon wafer; A closed groove (4) is etched on the front side of the silicon wafer. The closed groove (4) does not penetrate the silicon wafer so as to retain a continuous silicon layer (5) at the bottom of the closed groove (4). A polymer filler (11) is formed within the closed groove (4); The release positions corresponding to the mass block (2) and the sensitive beam (3) in the silicon wafer are etched to release the mass block (2) and the sensitive beam (3), so that the polymer filler (11) and the continuous silicon layer (5) form an embedded laminated structure.

10. The method for fabricating an embedded laminated beam MEMS piezoresistive accelerometer according to claim 9, characterized in that, Forming the polymer filler (11) includes: defining the polymer pattern to be retained in the closed groove (4) by photolithography, retaining the polymer material in the closed groove (4), and removing the polymer material outside the closed groove (4).

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