A shock-resistant structure and design method for a mass-discrete MEMS device

Abstract

The present invention discloses a shock-resistant structure and design method of a MEMS device with discretized mass, wherein the mass block in the sensitive structure of the MEMS device is discretized into a plurality of sub-mass blocks, each of which is supported on a substrate by an independent elastic beam; each sub-mass block is respectively provided with a sub-detection electrode for detecting its motion signal; and each sub-detection electrode located on the same deflection direction side of each sub-mass block is connected in series. The present invention reduces the mass and area of ​​each sub-mass block by discretizing the mass block into each sub-mass block, and the inertial force generated by the corresponding impact acceleration on the sub-mass block is also reduced accordingly. Through reasonable design, the shock resistance of a single sub-mass block is greatly improved compared with the original overall mass block. This method can not only improve the shock resistance of the MEMS device, but also be used to suppress the g sensitivity generated by the sensitive structure of the MEMS device under the influence of acceleration.

Description

Technical Field

[0001] The present invention relates to the field of electronics, and in particular to an impact-resistant structure and a design method of a MEMS device. Background Art

[0002] MEMS sensors measure the corresponding measured quantity by measuring certain changes in tiny sensitive structures. MEMS (Micro Electro Mechanical System) sensors have the advantages of small size, light weight, low power consumption and low cost. MEMS sensors can be divided into MEMS mechanical sensors, MEMS chemical sensors, MEMS biosensors, MEMS flow sensors, etc. according to their sensing quantity.

[0003] MEMS inertial sensors are a type of MEMS mechanical sensor that is widely used. MEMS inertial sensors include MEMS accelerometers that detect acceleration and MEMS gyroscopes that detect angular velocity, which can be widely used in military and civilian fields. In the field of industrial automation, they are mainly used in advanced automatic safety systems, high-performance navigation systems, navigation stability, rollover detection and prevention, as well as airbags and braking systems. In the field of consumer electronics, they are mainly used in digital products such as mobile phones and tablets, image stabilization in photographic equipment, virtual reality products, and computer games. In military applications, they are mainly used in inertial guidance of ammunition, navigation and attitude control of aircraft, platform stabilization, portable individual navigation, etc.

[0004] In some applications with large shock and strong vibration, MEMS sensors need to have corresponding shock resistance to ensure that the device does not fail or performance degrade, and to achieve measurement perception of the measured value in harsh environments.

[0005] Existing technology and its shortcomings:

[0006] In order to solve the problem that MEMS devices are prone to failure or performance degradation under large shock and strong vibration environments, relevant researchers at home and abroad have proposed a variety of solutions:

[0007] The invention patent application "A Capacitive Accelerometer with Acoustic Cavity" proposes to design and process a back plate with damping holes and limit bumps on the back of the sensitive structure of the accelerometer. By comprehensively using the damping holes on the back plate to adjust the system damping, and using the limit bumps to prevent adhesion during overload, the ability of the capacitive accelerometer to resist strong impact is improved.

[0008] The invention patent application "A MEMS gyroscope resistant to high overload" proposes to symmetrically distribute fixed blocks with anti-collision bumps around the gyroscope mass block, and at the same time set a central fixed block with anti-collision bumps in the hollowed-out area in the center of the mass block. The mass block adopts a grid cavity design to improve the gyroscope's ability to resist overload.

[0009] The invention patent application "Device for Preventing Excessive Movement of MEMS Components" proposes a stopping device for preventing damage to MEMS devices. The stopping device is arranged above the MEMS device to limit the excessive amplitude movement of the MEMS microphone backplate.

[0010] Invention patent application "Micro-electromechanical system device, deceleration block, method for reducing impact and gyroscope" and European patent application EP2146182A1 "Multistage Proof-mass movement deceleration within memsstructure" propose extending at least one deceleration beam from the mass block. The deceleration beam and the deceleration groove are configured as a deceleration structure, so that the gyro comb structure can be decelerated or stopped before a collision occurs under impact conditions.

[0011] US Patent 8596123B2 "MEMS Device with Impacting Structure for Enhanced Resistance Stiction" proposes a "T"-shaped vertical stop structure to achieve the purpose of limiting the vertical movement displacement of the mass block.

[0012] US Patent 5111693 "Motion Restraints for Micromechanical Devices" proposes processing a layer of special material, such as gold, between the moving structure and the stopper structure to prevent the moving structure and the stopper structure from sticking after collision contact. The stopper structure is a cantilever beam structure or a column cap structure grown by substrate deposition.

[0013] US Patent US2009 / 0194397A1 "Planar microelectromechanical device having a stopper structure for out-of-plane movements" proposes a stopper structure coupled and fixed below a mass block. When the structure detects an erroneous rotation, the stopper structure prevents the mass block from moving in a vertical direction.

[0014] US Patent US2010 / 0223997A1 "Accelerometer with over-travel stop structure" proposes a stop structure to prevent the mass block from exceeding the set motion range. The stop structure is specially designed to be fixedly connected to the connection line between the mass block anchor point of the structural substrate and the sensitive axis.

[0015] US Patent 5721377 "Angular velocity sensor with built-in limitstops", US Patent 6065341 "Semiconductor Physical Quantity Sensor With Stopper Portion", US Patent 4882933 "Accelerometer with integral bidirectional shock protection and controllable viscous damping", US Patent 4882933 "Accelerometer with integral bidirectional shock protection and controllable viscous damping", US Patent 6865944B2 "Methods and systems for decelerating proof mass movements within MEMS structures", US Patent 2002 / 0046602A1 "Micromachined devices with stop members", US Patent 2013 / 0019678A1 "Limiting travel of proof mass within frame of MEMSdevice》 and other publications have designed various types of stopper structures with different structural forms and different processing technologies from different design and manufacturing process perspectives, thereby improving the overload resistance of MEMS devices.

[0016] Almost all existing domestic and foreign patents arrange a stop structure on the periphery of the active mass block of the MEMS sensor to limit the movement displacement of the mass block, thereby achieving protection for the MEMS sensitive structure under large impact and strong vibration environments.

[0017] The stopper structure needs to be designed according to the different reliability requirements of MEMS sensors in different application scenarios. The distance between the stopper structure and the mass block must be greater than the maximum displacement of the mass block when the sensor is working normally, and it must also ensure that the mass block is limited in movement after contacting the stopper structure in a large impact and strong vibration environment, so as to avoid structural failures such as beam breakage or comb structure collision breakage caused by a large displacement of the mass block beyond the design range.

[0018] The potential of the stop structure usually also needs to be specially designed. Generally, the active mass potential of a MEMS sensor is a non-zero value, and the stop structure arranged around the active mass block needs to be designed to be insulated or have the same potential as the mass block. Because if an electric field is formed between the peripheral stop structure and the mass block, the electric field will generate an electrostatic force of mutual attraction between the mass block and the stop structure. This electrostatic attraction is not conducive to the mass block separating and returning to its original position after colliding with the stop. Therefore, the stop structure generally needs to be designed to be connected to the mass block with the same potential.

[0019] In extremely strong impact environments, the fixed stop structure is not easily deformed due to its high rigidity, which is not conducive to buffering and absorbing the inertial force generated by the impact, resulting in high stress at the contact point between the movable structure and the fixed stop, which is prone to failure such as breakage and fracture. Therefore, in extremely strong impact environments, an elastic stop structure needs to be designed, which further increases the design difficulty of MEMS sensors. Summary of the invention

[0020] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a mass-discrete MEMS device impact-resistant structure and design method.

[0021] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0022] A mass discretized MEMS device anti-shock structure, in which a mass block in a sensitive structure of the MEMS device is discretized into a plurality of sub-mass blocks, each of which is supported on a substrate by an independent beam;

[0023] Each sub-mass block is respectively provided with a sub-detection electrode for detecting its motion signal; and each sub-detection electrode located at the same deflection direction side of each sub-mass block is connected in series.

[0024] Further, each sub-mass block is arranged in a horizontal direction or / and in a vertical direction.

[0025] Furthermore, a plurality of sub-mass blocks are arranged in a vertical direction by wafer stacking.

[0026] Furthermore, the corresponding sub-detection electrodes on the same side of the stack are connected in series by TSV.

[0027] Further, each sub-mass block, a sub-detection electrode corresponding to detecting a motion signal of the sub-mass block, and a beam corresponding to supporting the sub-mass block constitute a sub-structure;

[0028] The substructures located in the horizontal direction are arranged in an axisymmetric manner, an anti-symmetric manner, an array arrangement or a staggered array arrangement.

[0029] Furthermore, the total mass of the plurality of discrete sub-mass blocks is not less than the mass of the original overall mass block.

[0030] A method for designing the impact resistance of a MEMS device with mass discretization is characterized in that the original overall mass block in the sensitive structure of the MEMS device is discretized into N sub-mass blocks, and the mass of each sub-mass block is Where m0 is the mass of the original overall mass block, M is the ratio of the mass of the overall mass block to the mass of a single sub-mass block; each sub-mass block is supported on the substrate by an independent beam; the elastic coefficient of the beam of each sub-mass block is Where k0 is the elastic coefficient of the elastic beam supporting the original overall mass block, K is the ratio of the elastic coefficient of the elastic beam supporting the original overall mass block to the elastic coefficient of the beam supporting a single sub-mass block; the detection capacitor area of ​​each sub-mass block is Where A0 is the detection capacitor area of ​​the original overall mass block, A is the ratio of the detection capacitor area of ​​the original overall mass block to that of a single sub-mass block; the ratio of the deflection angle of each sub-mass block around the beam caused by the impact to the deflection angle of the original overall mass block around the elastic beam is By designing the values ​​of coefficients K and M, The deflection angle is reduced and the overload resistance is improved.

[0031] Furthermore, under the same acceleration a0 input, the capacitance change ΔC detected after discrete design is a1 Compared with the original overall design, the capacitance change ΔC a0 The ratio is

[0032] To ensure that the sensitivity of the MEMS device does not decrease after the discretization design, that is, ΔC a1 ≥ΔC a0 , then you need

[0033] Combined with design requirements You need Therefore, it is designed that N>A.

[0034] The present invention reduces the mass and area of ​​each sub-mass block by discretizing the mass block into sub-mass blocks, and the inertial force generated by the corresponding impact acceleration on the sub-mass block is also reduced accordingly. Through reasonable design, the impact resistance of a single sub-mass block is greatly improved compared with the original overall mass block. This method can not only improve the impact resistance of MEMS devices, but also be used to suppress the g sensitivity generated by the sensitive structure of the MEMS device affected by acceleration.

[0035] The beneficial effects achieved by the present invention are:

[0036] The mass discretization MEMS device anti-shock structure and design method of the present invention discretizes the mass block into sub-mass blocks, so that the mass and area of ​​each sub-mass block are reduced, and the inertial force generated by the corresponding impact acceleration on the sub-mass block is also reduced accordingly. By reasonably designing the values ​​of coefficients K and M, The impact resistance of a single mass block can be greatly improved compared to the original overall mass block. After the mass block is discrete, the area of ​​the corresponding detection electrode is also reduced accordingly. By reasonably designing the values ​​of coefficients N and A, so that N>A, the detection sensitivity can be increased instead of decreased after the mass block discrete optimization design.

[0037] For the MEMS gyroscope, this method can not only improve the impact resistance of the MEMS gyroscope, but also suppress the influence of gravity acceleration on the MEMS gyroscope.

[0038] The method proposed in this patent is not only applicable to Z-axis torsion-pendulum MEMS capacitive accelerometers, but also to various MEMS sensors such as sandwich MEMS accelerometers, comb-tooth MEMS accelerometers, MEMS gyroscopes, MEMS pressure sensors, MEMS microphones, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the sensitive structure of the Z-axis torsion pendulum MEMS capacitive accelerometer.

[0040] Figure 2 This is a top view schematic diagram of the sensitive structure of the Z-axis torsion pendulum MEMS capacitive accelerometer.

[0041] Figure 3 Schematic diagram of the top view of the sensitive structure of the Z-axis torsion-type MEMS accelerometer designed for mass discreteness.

[0042] Figure 4 Schematic diagram of the sensitive structure of a Z-axis torsion-type MEMS accelerometer designed for mass discreteness.

[0043] Figure 5 Schematic diagram of the electrode leads of a Z-axis yaw MEMS accelerometer designed for mass dispersion.

[0044] Figure 6 Schematic diagram of the distribution of submodules of the Z-axis torsion accelerometer designed for mass discreteness.

[0045] Figure 7 Schematic diagram of the cross-distribution of the submodules of the Z-axis yaw accelerometer designed for mass discreteness.

[0046] Figure 8 This is a top view schematic diagram of the comb-tooth MEMS capacitive accelerometer sensitive structure.

[0047] Fig. 9 Schematic top view of the comb-tooth accelerometer sensitive structure designed for mass discretization.

[0048] Fig.10 Schematic diagram of the leads of a wafer-stacked MEMS accelerometer designed for mass dispersion. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0050] This patent proposes a method for designing the shock resistance of MEMS devices with discretized mass.

[0051] The following uses the Z-axis torsion pendulum MEMS capacitive accelerometer as an example to illustrate the shock resistance method of MEMS devices with discretized mass. However, this method is not limited to the shock resistance design of Z-axis torsion pendulum MEMS accelerometers. This method can be widely applied to MEMS accelerometers of other structural forms, and is also applicable to the shock resistance design of MEMS sensors such as MEMS gyroscopes and MEMS pressure sensors.

[0052] Traditional MEMS capacitive accelerometers are composed of a mass block, an elastic beam, an anchor point, a detection electrode, and a silicon substrate. One end of the elastic beam is connected to the mass block, and the other end is connected to the anchor point. The anchor point is fixedly connected to the silicon substrate. The mass block is suspended on the silicon substrate through the elastic beam and the anchor point. The mass block of the traditional Z-axis torsion pendulum MEMS capacitive accelerometer is composed of a larger complete mass block.

[0053] The white noise formula for a MEMS accelerometer is:

[0054]

[0055] where k B is the Boltzmann constant, T is the temperature, ω is the angular frequency, BW is the bandwidth, m is the mass, and Q is the quality factor. From formula (1), it can be seen that increasing the mass of the MEMS accelerometer is an effective way to reduce the noise of the MEMS accelerometer. This is also the reason why MEMS sensors require larger mass blocks.

[0056] Assuming that the moment of inertia of the active mass block of the MEMS accelerometer around the beam is I0, the total elastic coefficient of the MEMS accelerometer mass block connecting the beam is k0, and f0 is the operating modal natural frequency of the MEMS accelerometer mass block, then the operating modal angular frequency of the mass block is

[0057]

[0058] When the MEMS accelerometer is working normally, when detecting the axial input acceleration a0, the deflection angle of the mass block of the Z-axis torsion pendulum MEMS capacitive accelerometer around the elastic beam can be expressed as

[0059]

[0060] Where M0 is the torque generated by the input acceleration on the mass block, Q is the quality factor, ω0 is the operating modal angular frequency of the accelerometer mass block, ω in is the angular frequency of the input acceleration, where M0 is proportional to the moment of inertia I0. Usually ω0>>ω in ,therefore

[0061] The detection electrode arranged under the mass block is used to measure the deflection angle of the mass block around the torsion beam. From the calculation formula of capacitance, it can be seen that the capacitance value is proportional to the area A0 of the capacitor plate. Assume that the conversion coefficient between the deflection angle and the capacitance change is k θ2c , then when the input acceleration a0, the capacitance change caused by the mass deflection angle θ0 of the Z-axis torsion pendulum MEMS capacitive accelerometer can be approximately expressed as

[0062] ΔC a0 ≈k θ2c A0θ0 (4)

[0063] With the help of the capacitance / voltage conversion circuit, the capacitance change can be detected, and then the input acceleration a0 can be calculated in reverse.

[0064] The above is the case when the MEMS accelerometer works normally. Assume that when an external Z-axis impact occurs, the impact acceleration is a shock =K a a0, where K a is the ratio of the impact acceleration to the normal working acceleration. Then the deflection angle of the mass block around the elastic beam caused by the impact acceleration is

[0065]

[0066] Among them, M 0_shock is the external input impact acceleration a shock The torque generated by the overall mass block.

[0067] Generally speaking, K a It is about 100 to 10000. Therefore, the deflection angle θ of the mass block around the elastic beam caused by the impact 0_shock It is much larger than the deflection angle θ0 when the accelerometer is working normally. In order to avoid the mass block from colliding with the electrode due to the excessive deflection angle of the mass block around the elastic beam, resulting in structural failure, the stiffness of the elastic beam can be increased to reduce the deflection angle of the mass block around the elastic beam caused by the impact. However, increasing the stiffness of the elastic beam of the structure will cause the sensitivity of the sensitive structure of the accelerometer to decrease, and the accelerometer will lose some performance. Therefore, a stop structure is usually designed to limit the deflection angle of the mass block to avoid the collision between the mass block and the electrode, thereby improving the impact resistance of the accelerometer. When the impact magnitude is low, this method can effectively improve the impact resistance of the original MEMS device structure, but when the impact magnitude is high, when the stop structure contacts the mass block to limit the further movement of the mass block, the contact surface between the stop structure and the mass block may be broken, fractured, and other failure phenomena.

[0068] This method proposes a new idea for the shock resistance design of MEMS devices: the mass block in the sensitive structure of the MEMS device is designed into multiple discrete small mass blocks. Each discrete small mass block is supported by an independent elastic beam structure. Since the mass of the mass block is reduced exponentially after being discrete, the torque M generated by each discrete small mass block under the same impact is 0_shock It is also reduced exponentially, and the deflection angle caused by the impact on each discrete small mass block is also reduced exponentially. Although the detection capacitance on each discrete small mass block is also reduced exponentially with the discretization of the mass block, by connecting the detection capacitance on these discrete small mass blocks in series accordingly, the sensitivity of the total detection capacitance after discreteness can be kept basically the same as the original design. It is even possible to increase the number of small mass blocks so that the total mass of all discrete mass blocks is greater than the mass of the original overall mass block. While improving the impact resistance of the MEMS device, it also increases the total mass of the sensitive structure and improves the mechanical sensitivity of the device. The specific design analysis is as follows:

[0069] The mass block of the MEMS device is designed to be discretized into N (N is a positive integer) independent sub-mass blocks, and the mass of each sub-mass block is Where m0 is the mass of the original overall mass block, and M is the mass ratio of the overall mass block to the mass of a single sub-mass block. Each sub-mass block is supported by a separate beam, and the elastic coefficient of the connecting beam of each sub-mass block is Where k0 is the elastic coefficient of the elastic beam of the original overall mass block structure, and K is the ratio of the elastic coefficient of the elastic beam of the original overall structure to the elastic beam of a single sub-mass block. Since the moment of inertia of the mass block rotating around the beam is proportional to the mass, the moment of inertia of each sub-mass block rotating around its beam structure is Where I0 is the moment of inertia of the original overall mass block structure. The operating modal angular frequency of each sub-mass block is The detection capacitance area of ​​each sub-mass block also decreases accordingly with the discretization: Wherein A0 is the detection capacitor area of ​​the original overall mass block structure, and A is the ratio of the detection capacitor area of ​​the original overall structure to that of the single sub-mass block structure.

[0070] When the MEMS accelerometer is working normally and detecting the axial input acceleration a0, the deflection angle of each sub-mass block of the discretely designed Z-axis torsion pendulum MEMS capacitive accelerometer around the elastic beam can be expressed as

[0071]

[0072] Where M1 is the torque generated by the input acceleration a0 on each sub-mass block, Q is the working modal quality factor, ω1 is the working modal angular frequency of each sub-mass block, ω in is the angular frequency of the input acceleration, where M1 is proportional to the moment of inertia I1. Design so that ω1>>ω in ,therefore

[0073] The capacitance change produced by each sub-mass block can be approximately expressed as

[0074] ΔC a1 ≈k θ2c A1θ1 (7)

[0075] When the external input impact acceleration a shock When each sub-mass block generates a torque of M 1_shock Since the mass of each sub-mass is reduced by M times, The deflection angle of each sub-mass block around the elastic beam is

[0076]

[0077] The ratio of the deflection angle of each sub-mass block around the elastic beam caused by the impact to the deflection angle of the overall designed mass block around the elastic beam is

[0078]

[0079] From the above formula, we can see that when That is to say, the elastic coefficient of the elastic beam of the sub-mass block is 1 / M times greater than the elastic coefficient of the elastic beam of the original overall mass block design, which means that the deflection angle of the new discretized structure under the same impact is K / M times smaller than that of the original overall structure, that is, the overload resistance is improved by M / K times. This can be achieved by reasonably designing the values ​​of the coefficients K and M.

[0080] The discrete mass block design reduces the mechanical sensitivity of the sub-mass block. The detection electrodes caused by the mass discretization are also discretized accordingly. Therefore, the discrete electrodes can be connected in series through leads so that the detected electrical signals are added to compensate for the signal reduction problem caused by the discrete design.

[0081] Before and after discrete design, under the same acceleration a0 input, the capacitance change Δc detected after discrete design a1 Compared with the original overall design, the capacitance change Δc a0 The ratio is

[0082]

[0083] From the above formula, we can know that in order to ensure that the sensitivity of the MEMS accelerometer does not decrease after the discretization design, that is, Δc a1 ≥ΔG a0 , then you need In order to improve the impact resistance of the structure, the design requires Therefore, it is necessary That is, N>A.

[0084] Usually, the thickness of the sensitive structure layer of the MEMS device is fixed due to the manufacturing process. Therefore, after the mass block is discretized, the mass of the sub-mass block is reduced by M times, and the area of ​​the mass block is also reduced by M times, and the area of ​​the corresponding detection electrode is also reduced by M times. Therefore, M = A in general. Therefore, by increasing the total number of discrete sub-mass blocks N, that is, N>M, the detection sensitivity can be increased instead of decreased after the mass block is discretely optimized, and the impact resistance of the MEMS device can also be improved.

[0085] The impact-resistant structure and design method of MEMS devices proposed in this patent are not limited to Z-axis torsion-pendulum MEMS capacitive accelerometers, but can also be applied to various MEMS sensors such as sandwich MEMS accelerometers, comb-tooth MEMS accelerometers, MEMS gyroscopes, MEMS pressure sensors, MEMS microphones, etc.

[0086] Since the g-sensitivity index of the MEMS gyroscope represents the sensitivity of the MEMS gyroscope to the linear accelerometer, this method can not only improve the impact resistance of the MEMS gyroscope, but also suppress the g-sensitivity of the MEMS gyroscope.

[0087] The mass block can be discretized not only in the plane, but also in the vertical direction by wafer stacking. After vertical discretization, the corresponding electrodes in the stacking structure can be connected in series by TSV to achieve signal addition.

[0088] Taking the Z-axis torsion pendulum MEMS capacitive accelerometer as an example, the conventional Z-axis torsion pendulum MEMS capacitive accelerometer is composed of a mass block 101, elastic beams 103a and 103b, anchor points 102a and 102b, detection electrodes 104a and 104b, a silicon substrate, etc. Figure 1 and Figure 2 As shown. One end of the elastic beam 103a is connected to the mass block 101, and the other end is connected to the anchor point 102a. One end of the elastic beam 103b is connected to the mass block 101, and the other end is connected to the anchor point 102b. The anchor points 102a and 102b are fixedly connected to the silicon substrate. The mass block 101 is suspended on the silicon substrate through the elastic beams 103a, 103b and the anchor points 102a, 102b. The detection electrodes 104a and 104b arranged at both ends below the mass block 101 form a group of differential capacitor pairs with the mass block 101. The mass block of the traditional Z-axis torsion pendulum MEMS capacitive accelerometer is composed of a larger complete mass block 101.

[0089] The design arranges the elastic beam 103 offset from the central symmetry axis of the mass block 101, so that the mass block 101 has different masses on both sides of the axis along the elastic beam 103. When the external Z-axis acceleration is input, the unequal masses on both sides generate a torsional moment around the axis where the beam 103 is located. The mass block 101 deflects around the beam 103 under the Z-axis acceleration. The detection electrodes 104a and 104b arranged at both ends below the mass block detect a pair of output signals in opposite directions. After differential amplification by the subsequent detection circuit, a deflection angle signal is output. Finally, the Z-axis input acceleration can be calculated based on the output deflection angle signal.

[0090] When there is a strong impact or strong vibration on the Z axis, the mass block 101 may collide strongly with the detection electrode 104 under the impact or vibration. The strong collision may cause the collision contact part to be broken or fractured. To avoid this situation, a common design method is to design and process a stopper bump structure higher than the detection electrode 104 under the mass block. However, since the stopper bump structure and the mass block 101 in contact with it are both rigid structures and are not easily deformed, the stopper structure under strong impact conditions collides with the bottom surface of the mass block, which is easy to cause structural damage or fracture.

[0091] In order to improve the device's ability to resist strong shock or vibration, this patent proposes a method for designing a MEMS device with discrete mass to resist shock. The original designed structure is divided and discretized into several substructures to achieve the discretization of the mass block. In this embodiment, the discretization into four substructures is taken as an example. Figure 3 The original design structure is divided into four identical substructures 201a, 201b, 201c and 201d, as shown in FIG. Figure 4 shown. Figure 3The neutron structures 201a and 201b are axially symmetrical, 201c and 201d are axially symmetrical, and the substructures 201a, 201b and 201c, 201d are axially symmetrical.

[0092] Substructure 201a is composed of a new mass block 301a, elastic beams 303a and 303b, anchor points 302a and 302b, and detection electrodes 304a and 304b; substructure 201b is composed of a new mass block 301c, elastic beams 303c and 303d, anchor points 302c and 302d, and detection electrodes 304c and 304d; substructure 201c is composed of a new mass block 301e, elastic beams 303e and 303f, anchor points 302e and 302f, and detection electrodes 304e and 304f; substructure 201d is composed of a new mass block 301g, elastic beams 303g and 303h, anchor points 302g and 302h, and detection electrodes 304g and 304h. Figure 4 As shown. The connection relationship within each substructure is the same as that of a conventional Z-axis torsion pendulum MEMS capacitive accelerometer. Taking substructure 201a as an example, one end of the elastic beam 303a is connected to the mass block 301a, and the other end is connected to the anchor point 302a; one end of the elastic beam 303b is connected to the mass block 301a, and the other end is connected to the anchor point 302b. Anchor points 302a and 302b are fixedly connected to the silicon substrate. The mass block 301a is suspended on the silicon substrate through the elastic beams 303a, 303b and the anchor points 302a, 302b. The detection electrodes 304a and 304b arranged at both ends below the mass block 301a form a set of differential capacitor pairs with the mass block 301a. The same applies to the remaining substructures 201b, 201c, and 201d.

[0093] When the positive acceleration of the Z axis is input, the mass block 301a deflects toward the direction close to the detection electrode 304a, the mass block 301c deflects toward the direction close to the detection electrode 304d, the mass block 301e deflects toward the direction close to the detection electrode 304e, and the mass block 301g deflects toward the direction close to the detection electrode 304h. At this time, the signal directions detected by the detection electrodes 304a, 304d, 304e and 304h are in the same direction, and the signal directions detected by the detection electrodes 304b, 304c, 304f, 304g are in the opposite direction. Figure 5As shown, by designing lead 402, the detection electrodes 304a, 304d, 304e and 304h of the same signal can be connected in series, that is, the signals detected by the detection electrodes 304a, 304d, 304e and 304h are added and connected to the bonding points 401a and 401c. The detection electrodes 304b, 304c, 304f and 304g of the same signal can be connected in series through lead 403, that is, the signals detected by the detection electrodes 304b, 304c, 304f and 304g are added and connected to the bonding point 401b. After the bonding points 401a, 401b, 401c are connected to the detection circuit, the electrical signal is output to the detection circuit, and the detection circuit realizes differential amplification of the signal, and finally outputs the mass block deflection angle signal.

[0094] In other embodiments, the plurality of discretized substructures may be in a repeated array, or may be designed symmetrically or antisymmetrically about a certain axis, or may be designed in a staggered array, such as Figure 6 and Figure 7 shown.

[0095] This method is also applicable to the overload resistance design of comb-tooth accelerometer. Figure 8 This is the original comb-tooth accelerometer design, in which the mass block is a one-piece structure. Fig. 9 Schematic diagram of the structure of an overload-resistant comb-tooth accelerometer designed using the mass block discretization method. The mass block in the figure is divided and discretized into four separate sub-mass blocks.

[0096] The mass block can be discreted not only in the plane, but also in the vertical direction by wafer stacking. After vertical discretization, the corresponding electrodes in the stacking structure can be connected in series by TSV to achieve signal addition, such as Fig.10 As shown. TSV electrodes 501a and 501b realize the series connection of signals of the upper and lower layers. Leads 504a and 504b realize the interconnection of electrodes 502a and 502b of the same polarity with TSV electrode 501a. Leads 505a and 505b realize the interconnection of electrodes 503a and 503b of the same polarity with TSV electrode 501b.

[0097] In the shock resistance design of discrete mass blocks, the mass blocks can be discretely designed into any number of sub-mass blocks according to the shock resistance requirements. Since the mass of each sub-mass block is reduced compared to the mass of the original mass block, the shock resistance of a single sub-mass block is greatly improved compared to the original overall mass block. The shock resistance design method of the discrete mass block can even increase the number of sub-mass blocks so that the total mass of all sub-mass blocks is greater than the mass of the original overall mass block.

[0098] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A mass-discrete MEMS device anti-shock structure, characterized in that: The mass block in the sensitive structure of the MEMS device is discretized into multiple sub-mass blocks, each of which is supported on the substrate by an independent beam; Each sub-mass block is respectively provided with a sub-detection electrode for detecting its motion signal; the sub-detection electrodes located on the same deflection direction side of each sub-mass block are connected in series; A plurality of sub-mass blocks are arranged in a vertical direction by wafer stacking.

2. The mass-discrete MEMS device anti-shock structure according to claim 1, characterized in that: The corresponding sub-detection electrodes on the same side of the stack are connected in series using TSV.

3. The mass-discrete MEMS device anti-shock structure according to claim 1, characterized in that: The total mass of the multiple discretized sub-mass blocks is not less than the mass of the original overall mass block.

4. A method for designing the impact resistance of a mass-discrete MEMS device, characterized in that: The original overall mass block in the sensitive structure of the MEMS device is discretized into N sub-mass blocks, and the mass of each sub-mass block is Where m0 is the mass of the original overall mass block, M is the ratio of the mass of the overall mass block to the mass of a single sub-mass block; each sub-mass block is supported on the substrate by an independent beam; the elastic coefficient of the beam of each sub-mass block is Where k0 is the elastic coefficient of the elastic beam supporting the original overall mass block, K is the ratio of the elastic coefficient of the elastic beam supporting the original overall mass block to the elastic coefficient of the beam supporting a single sub-mass block; the detection capacitor area of ​​each sub-mass block is Where A0 is the detection capacitor area of ​​the original overall mass block, A is the ratio of the detection capacitor area of ​​the original overall mass block to that of a single sub-mass block; the ratio of the deflection angle of each sub-mass block around the beam caused by the impact to the deflection angle of the original overall mass block around the elastic beam is By designing the values ​​of coefficients K and M, The deflection angle is reduced and the overload resistance is improved.

5. The method for designing the anti-shock performance of a MEMS device with mass discretization according to claim 4 is characterized in that: Under the same acceleration a0 input, the capacitance change ΔC detected after discrete design a1 Compared with the original overall design, the capacitance change ΔC a0 The ratio is To ensure that the sensitivity of the MEMS device does not decrease after the discretization design, that is, ΔC a1 ≥ΔC a0 , then you need Combined with design requirements You need Therefore, it is designed that N>A.

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