CN111410168B - A shock-resistant structure and design method for a mass-discrete MEMS device - Google Patents
A shock-resistant structure and design method for a mass-discrete MEMS device Download PDFInfo
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Abstract
本发明公开了一种质量离散化的MEMS器件抗冲击结构和设计方法，将MEMS器件敏感结构中的质量块离散为多个子质量块，各子质量块分别由独立的弹性梁支撑在衬底上；各子质量块分别对应设置检测其运动信号的子检测电极；位于各子质量块同一偏转方向侧的各子检测电极串联连接。本发明通过将质量块离散成各子质量块，使各子质量块的质量、面积进行了减小，对应的冲击加速度在子质量块上产生的惯性力也相应的减小。通过合理设计，单个子质量块的抗冲击能力较原有整体质量块大幅提升。该方法不仅可以提高MEMS器件的抗冲击能力，也可用于抑制MEMS器件敏感结构受加速度影响而产生的g灵敏度。
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
The invention relates to the field of electronics, in particular to an impact-resistant structure of an MEMS device and a design method thereof.
Background
The MEMS sensor achieves the corresponding measurement to be measured by measuring some kind of change of the tiny sensitive structure. MEMS (Micro Electro MECHANICAL SYSTEM) sensor has advantages of small volume, light weight, low power consumption, low cost, etc. The MEMS sensor can be divided into MEMS mechanical sensor, MEMS chemical sensor, MEMS biological sensor, MEMS flow sensor, etc. according to the sensing quantity.
The MEMS inertial sensor is a MEMS mechanical sensor with extremely wide application. The MEMS inertial sensor comprises an MEMS acceleration sensor for detecting acceleration and an MEMS gyroscope for detecting angular velocity, and can be widely applied to the military and civil fields. In the field of industrial automation, it is mainly applied to advanced automatic safety systems, high-performance navigation systems, navigational stability, detection and prevention of roll, and airbag and brake systems. The method is mainly applied to digital products such as mobile phones, tablet computers and the like, image stabilization in photographic equipment, virtual reality products and computer games in the field of consumer electronics. In military application, the method is mainly applied to inertial guidance of ammunition, navigation and attitude control of an aircraft, platform stability, portable individual navigation and the like.
In some large-impact and strong-vibration application occasions, the MEMS sensor needs to have corresponding impact resistance to ensure that the device does not fail or degrade in performance, so that the measured measurement and perception in a severe environment are realized.
The prior art and the existing defects are that:
in order to solve the problem that the MEMS device is easy to fail or degrade in performance under the conditions of large impact and strong vibration, related researchers at home and abroad propose various solving approaches:
The invention patent application 'a capacitive acceleration sensor with an acoustic cavity' proposes to design and process a back plate with damping holes and limiting protruding points on the back surface of a sensitive structure of the acceleration sensor. The damping of the system is regulated by comprehensively utilizing the damping holes on the back polar plate, and meanwhile, the adhesion during overload is prevented by utilizing the limiting convex points, so that the strong impact resistance of the capacitive acceleration sensor is improved.
The invention discloses a high overload-resistant MEMS gyroscope, which is characterized in that fixed blocks with anti-collision convex points are symmetrically distributed on the periphery of a gyroscope mass block, and meanwhile, a central fixed block with the anti-collision convex points is arranged in a hollowed-out area of the center of the mass block, and the mass block adopts a grid cavity design, so that the overload-resistant capability of the gyroscope is improved.
The invention patent application of a device for preventing the transition movement of an MEMS component proposes a stopping device for preventing the damage of an MEMS device, wherein the stopping device is arranged above the MEMS device and is used for limiting the over-amplitude movement of a back plate of a MEMS microphone.
The invention patent application of micro-electromechanical system device, speed reducing stop, method for reducing impact and gyroscope, and European patent application EP2146182A1 Multistage Proof-mass movement deceleration WITHIN MEMS structure propose that at least one speed reducing beam extends from a mass block. The deceleration beams and the deceleration grooves are configured as deceleration structures so that the gyro comb tooth structure is decelerated or stopped before collision occurs under impact conditions.
U.S. Patent 8596123B2, MEMS DEVICE WITH IMPACTING Structure for ENHANCED RESISTANCE Stiction, proposes a "T" type vertical stop Structure to limit the displacement of the masses in the vertical direction.
U.S. Patent 5111693, motion Restraints for Micromechanical Devices, teaches to process a layer of a special material, such as gold, between the moving structure and the stop structure to prevent the moving structure from sticking to the stop structure after impact contact. The stop structure is a cantilever beam structure or a cap structure which is deposited and grown from the substrate.
Us patent US2009/0194397A1"Planar microelectromechanical device having a stopper structure for out-of-plane movements" proposes a stop structure coupled and fixed under the mass. The stop structure is configured to prevent movement of the mass in a vertical direction when the structure detects an incorrect rotation.
U.S. patent No. 2010/0223997A1, "Accelerometer with over-travel stop structure" proposes a stop structure that prevents the mass from exceeding a set range of motion. The stop structure is particularly designed to be fixedly connected to the connecting line of the anchor point of the mass block of the structural substrate and the sensitive axis.
U.S. Pat. No. 3, 5721377, angular velocity sensor with built-in limit stops, U.S. Pat. No. 6065341, semiconductor Physical Quantity Sensor With Stopper Portion, U.S. Pat. No. 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"、, U.S. Pat. No. US Patent 6865944B2"Methods and systems for decelerating proof mass movements within MEMS structures"、,2002/0046602A 1, micromachined DEVICES WITH stop members, U.S. Pat. No. 2013/0019678A1 LIMITING TRAVEL of proof MASS WITHIN FRAME of MEMS DEVICE, etc., all design various stop structures of different structural forms and different processing techniques from different design and manufacturing process angles, improving the overload resistance of MEMS devices.
The existing domestic and foreign patents almost all arrange a stop structure at the periphery of a movable mass block of an MEMS sensor to limit the movement displacement of the mass block, so that the protection of MEMS sensitive structures in a large-impact and strong-vibration environment is realized.
The stop structure needs to be designed according to different reliability requirements of the MEMS sensor in different application scenes. The distance between the stop structure and the mass block is larger than the maximum movement displacement of the mass block when the sensor works normally, and the mass block is prevented from moving after being contacted with the stop structure under the conditions of large impact and strong vibration, so that structural failure such as beam fracture or comb tooth structure collision fracture caused by large deviation of the mass block beyond the design range is avoided.
The potential of the stop structure also typically requires special design. Typically the active mass potential of the MEMS sensor is a non-zero value and the stop structures arranged around the active mass need to be designed to be insulating or equipotential with the mass. Because if an electric field is formed between the peripheral stop structure and the mass, the electric field will create an attractive electrostatic force between the mass and the stop structure. This electrostatic attraction force is detrimental to the separation and recovery of the initial position of the mass after the collision contact with the stop. The stop structure generally requires an equipotential connection design with the mass.
Under extremely strong impact environment, the fixed stop structure is not easy to deform due to high rigidity, and is unfavorable for buffering and absorbing inertial force generated by impact, so that the stress at the contact position of the movable structure and the fixed stop is high, and failures such as crushing, fracture and the like are easy to occur. Therefore, in an extremely strong impact environment, an elastic stop structure needs to be designed, which further increases the design difficulty of the MEMS sensor.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a mass discretization MEMS device impact-resistant structure and a design method thereof.
In order to solve the technical problems, the invention adopts the following technical scheme:
A mass block in a sensitive structure of a MEMS device is discretized into a plurality of sub-mass blocks, and each sub-mass block is respectively supported on a substrate by an independent beam;
The sub-mass blocks are respectively and correspondingly provided with sub-detection electrodes for detecting the motion signals of the sub-mass blocks, and the sub-detection electrodes positioned on the same deflection direction side of the sub-mass blocks are connected in series.
Further, the sub-masses are arranged in the horizontal direction or/and in the vertical direction.
Further, the plurality of sub-masses are vertically arranged in a wafer stack manner.
Further, the sub-detection electrodes on the same side of the stack are connected in series by means of TSVs.
Further, each sub-mass, a sub-detection electrode for detecting the motion signal of the sub-mass and a beam for supporting the sub-mass form a sub-structure;
the substructures in the horizontal direction are arranged in an axisymmetric way, an anti-symmetric way, an array way or a staggered way.
Further, the total mass of the discrete sub-masses is not less than the mass of the original whole mass.
A mass discretization MEMS device impact resistance design method is characterized in that an original integral mass block in a MEMS device sensitive structure is discretized into N sub-mass blocks, and the mass of each sub-mass block is thatWherein M 0 is the mass of the original whole mass block, M is the ratio of the whole mass block to the mass of a single sub-mass block, each sub-mass block is respectively supported on the substrate by an independent beam, and the elastic coefficient of the beam of each sub-mass block isWherein K 0 is the elastic coefficient of an elastic beam supporting the original whole mass, K is the ratio of the elastic coefficient of the elastic beam supporting the original whole mass to the elastic coefficient of a beam supporting a single sub-mass, and the detection capacitance area of each sub-mass isWherein A 0 is the detection capacitance area of the original whole mass block, A is the ratio of the detection capacitance area of the original whole mass block to the detection capacitance area of the single sub mass block, and the ratio of the deflection angle of each sub mass block around the beam generated by impact to the deflection angle of the original whole mass block around the elastic beam isBy designing the values of the coefficients K and M, the method can ensure thatThe deflection angle is reduced and the overload resistance is improved.
Further, under the same acceleration a 0 input condition, the ratio of the detected capacitance change delta C a1 after discrete design to the detected capacitance change delta C a0 of the original integrated design is
To ensure that the sensitivity of the MEMS device is not reduced after discretization, i.e., ΔC a1≥ΔCa0, then
Combining design requirementsThen need toThus, N > A is designed.
According to the invention, the mass blocks are scattered into the sub-mass blocks, so that the mass and the area of each sub-mass block are reduced, and the inertial force generated on the sub-mass blocks by the corresponding impact acceleration is correspondingly reduced. Through reasonable design, the impact resistance of the single sub-mass block is greatly improved compared with the original whole mass block. The method not only can improve the shock resistance of the MEMS device, but also can be used for inhibiting g sensitivity generated by the influence of acceleration on the sensitive structure of the MEMS device.
The invention has the beneficial effects that:
according to the mass discretization MEMS device impact-resistant structure and the design method, the mass blocks are discretized into the sub-mass blocks, so that the mass and the area of each sub-mass block are reduced, and the inertial force generated on the sub-mass blocks by the corresponding impact acceleration is correspondingly reduced. By reasonably designing the values of the coefficients K and M, the method leads to The impact resistance of the single mass block can be greatly improved compared with the original whole mass block. After the mass block is discrete, the area of the corresponding detection electrode is correspondingly reduced, and the detection sensitivity can be prevented from being reduced and raised after the mass block is discrete and optimally designed by reasonably designing the numerical values of the coefficients N and A to ensure that N is more than A.
For the MEMS gyroscope, the method not only can improve the shock resistance of the MEMS gyroscope, but also can restrain the influence of gravity acceleration on the MEMS gyroscope.
The method provided by the patent is not only suitable for the Z-axis torsion pendulum type MEMS capacitance accelerometer, but also suitable for various MEMS sensors such as sandwich type MEMS accelerometers, comb tooth type MEMS accelerometers, MEMS gyroscopes, MEMS pressure sensors, MEMS microphones and the like.
Drawings
Fig. 1 is a schematic diagram of a Z-axis torsion pendulum type MEMS capacitive accelerometer sensing structure.
Fig. 2 is a schematic top view of a Z-axis torsion pendulum type MEMS capacitive accelerometer sensitive structure.
Fig. 3 is a schematic top view of a Z-axis torsional MEMS accelerometer sensitive structure of a mass discrete design.
Fig. 4 is a schematic diagram of the structure of the Z-axis torsional pendulum MEMS accelerometer sensitive structure with a mass discrete design.
FIG. 5 is a schematic diagram of electrode leads of a Z-axis torsional MEMS accelerometer of discrete mass design.
FIG. 6 is a schematic diagram of the distribution of sub-modules of a Z-axis torsional pendulum accelerometer of discrete mass design.
FIG. 7 is a schematic diagram of the cross distribution of sub-modules of a Z-axis torsional pendulum accelerometer of discrete mass design.
Fig. 8 is a schematic top view of a comb-tooth MEMS capacitive accelerometer sensing structure.
Fig. 9 is a schematic top view of a comb accelerometer sensitive structure of a mass discrete design.
FIG. 10 is a schematic diagram of MEMS accelerometer leads for a wafer stack of mass discrete design.
Detailed Description
The invention is further described below with reference to the accompanying drawings. The following examples are only for more clearly illustrating the technical aspects of the present invention, and are not intended to limit the scope of the present invention.
The patent provides a mass discretization MEMS device impact resistance design method.
The impact resistance method of the mass discretization MEMS device is described by taking a Z-axis torsion pendulum type MEMS capacitance accelerometer as an example, but the method is not limited to the impact resistance design of the Z-axis torsion pendulum type MEMS accelerometer, and can be widely applied to the impact resistance design of MEMS accelerometers with other structural forms, and also applied to MEMS sensors such as MEMS gyroscopes, MEMS pressure sensors and the like.
The traditional MEMS capacitance accelerometer consists of a mass block, an elastic beam, an anchor point, a detection electrode, a silicon substrate and the like. Wherein one end of the elastic beam is connected with the mass block, the other end is connected with 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 of a traditional Z-axis torsional pendulum type MEMS capacitive accelerometer is composed of a larger complete mass.
The white noise formula of the MEMS accelerometer is
Where k B is the boltzmann constant, T is temperature, ω is angular frequency, BW is bandwidth, m is mass, and Q is quality factor. From equation (1), increasing the mass of the MEMS accelerometer is an effective means of reducing the MEMS accelerometer noise. This is also why a larger mass is required for the MEMS sensor.
Assuming that the moment of inertia of the movable mass block of the MEMS accelerometer around the beam is I 0, the total elastic coefficient of the connecting beam of the mass block of the MEMS accelerometer is k 0,f0, which is the natural frequency of the working mode of the mass block of the MEMS accelerometer, the angular frequency of the working mode of the mass block is
When the MEMS accelerometer works normally and detects the axial input acceleration a 0, the deflection angle of the mass block of the Z-axis torsion pendulum type MEMS capacitance accelerometer around the elastic beam can be expressed as
Where M 0 is the torque produced by the input acceleration on the proof mass, Q is the quality factor, ω 0 is the operational mode angular frequency of the accelerometer proof mass, ω in is the angular frequency of the input acceleration, where M 0 is proportional to the moment of inertia I 0. Omega 0＞＞ωin is usually designed so
The detection electrode arranged below the mass is used for measuring the movement deflection angle of the mass around the torsion beam. As can be seen from the calculation formula of the capacitance, the capacitance value is proportional to the area A 0 of the capacitance plate. Assuming that the conversion coefficient of the deflection angle and the capacitance variation is k θ2c, when the acceleration a 0 is input, the capacitance variation generated by the deflection angle θ 0 of the mass block of the Z-axis torsion pendulum type MEMS capacitance accelerometer can be approximately expressed as
ΔCa0≈kθ2cA0θ0 (4)
By means of the capacitance/voltage conversion circuit, the detection of the capacitance variation can be realized, and then the input acceleration a 0 can be calculated in a back-thrust manner.
The above is the case when the MEMS accelerometer is operating normally. Suppose that when a Z-axis shock occurs from the outside, the shock acceleration is a shock＝Kaa0, where K a is the ratio of the shock acceleration to the normal operating acceleration. The deflection angle of the mass block around the elastic beam caused by the impact acceleration is
Where M 0_shock is the torque produced by the integral mass when the impact acceleration a shock is externally input.
Generally, K a varies from about 100 to 10000. The deflection angle θ 0_shock of the mass around the spring beam due to the impact is much greater than the deflection angle θ 0 of the accelerometer when operating normally. In order to avoid collision between the mass block and the electrode caused by overlarge deflection angle of the mass block around the elastic beam, structural failure is generated, the rigidity of the elastic beam can be improved to reduce the deflection angle of the mass block around the elastic beam caused by impact, but the sensitivity of the sensitive structure of the accelerometer is reduced due to the improvement of the rigidity of the elastic beam of the structure, and part of performance of the accelerometer is lost. Therefore, a stop structure is generally designed to limit the deflection angle of the mass block, so that the collision between the mass block and the electrode is avoided, and the impact resistance of the accelerometer is improved. When the impact level is lower, the method can effectively improve the impact resistance of the original MEMS device structure, but when the impact level is higher, and the stop structure is contacted with the mass block to limit the further movement of the mass block, the contact surface of the stop structure and the mass block can possibly generate failure phenomena such as crushing, fracture and the like.
The method provides a new idea of the shock resistance design of the MEMS device, wherein the mass blocks in the sensitive structure of the MEMS device are designed into a plurality of discrete small mass blocks. Each discrete small mass is supported by a separate spring beam structure. Because the mass is reduced by times after the mass is scattered, the torque M 0_shock generated by each small scattered mass under the same impact effect is reduced by times, and the deflection angle generated by the impact on each small scattered mass is reduced by times. Although the detection capacitance on each small discrete mass is reduced by a factor accompanied by discretization of the mass, by correspondingly connecting the detection capacitances on the small discrete masses in series, the total detection capacitance sensitivity after discretization can be kept basically the same as that of the original design. Even the number of small mass blocks can be designed and increased, so that the total mass of all the discrete mass blocks is larger than that of the original whole mass blocks, the impact resistance of the MEMS device is improved, the total mass of a sensitive structure is increased, and the mechanical sensitivity of the device is improved. The specific design analysis is as follows:
Designing a mass block of the MEMS device to be discretized into N (N is a positive integer) independent sub-mass blocks, wherein the mass of each sub-mass block is Where M 0 is the mass of the original whole mass, and M is the mass ratio of the whole mass to the individual sub-masses. Individual beams of each sub-mass support, the spring rate of the connecting beams of each sub-mass beingWherein K 0 is the elastic coefficient of the elastic beam of the original whole mass block structure, and K is the ratio of the elastic coefficients of the elastic beam of the original whole structure and the elastic beam of the single sub mass block. Since the moment of inertia of the mass about the beam is proportional to the mass, the moment of inertia of each sub-mass about its beam structureWherein I 0 is the moment of inertia of the original whole mass structure. The working mode angular frequency of each sub-mass block isThe detection capacitance area of each sub-mass block is correspondingly reduced along with discretizationWherein A 0 is the detection capacitance area of the original whole mass block structure, and A is the ratio of the detection capacitance area of the original whole mass block structure to the detection capacitance area of the single sub mass block structure.
When the MEMS accelerometer works normally and detects the axial input acceleration a 0, the deflection angle of each sub-mass block of the Z-axis torsion pendulum type MEMS capacitance accelerometer with discrete design around the elastic beam can be expressed as
Where M 1 is the torque produced by the input acceleration a 0 on each sub-mass, Q is the operational mode quality factor, ω 1 is the operational mode angular frequency of each sub-mass, ω in is the angular frequency of the input acceleration, where M 1 is proportional to the moment of inertia being I 1. Designed such that omega 1＞＞ωin, therefore
The amount of capacitance change produced by each sub-mass can be approximately expressed as
ΔCa1≈kθ2cA1θ1 (7)
When the impact acceleration a shock is input from the outside, the torque generated by each sub-mass is M 1_shock. Since the mass of each sub-mass is reduced by a factor of M, thenThe deflection angle of each sub-mass block around the elastic beam is
The ratio of the deflection angle of each sub-mass around the spring beam generated by the impact to the deflection angle of the integrally designed mass around the spring beam is
As can be seen from the above, whenIn the process, the elastic coefficient of the elastic beam of the sub mass block is 1/M times larger than that of the elastic beam designed by the original integral mass block, so that the deflection angle of the discretized new structure under the same impact action condition is reduced by K/M times compared with that of the original integral structure, namely, the overload resistance is improved by M/K times. This can be achieved by rational design of the values of the coefficients K and M.
The discrete mass design causes a decrease in the mechanical sensitivity of the sub-masses. The detection electrode caused by the mass dispersion is correspondingly dispersed. The discrete electrodes can thus be connected in series by way of leads so that the detected electrical signals add up to compensate for the signal reduction problem caused by the discrete design.
Under the condition of the same acceleration a 0 input before and after the discrete design, the ratio of the detected capacitance change delta c a1 after the discrete design to the detected capacitance change delta c a0 of the original integrated design is
From the above, to ensure that the sensitivity of the MEMS accelerometer is not reduced after discretization, i.e., Δc a1≥ΔGa0, thenIn order to improve the impact resistance of the structure, the design requirement is thatThus need toI.e. N > a.
In general, the thickness of the sensitive structure layer of the MEMS device is limited and fixed by the manufacturing process, so that after the mass blocks are discrete, the mass of the sub-mass blocks is reduced by M times, the area of the mass blocks is also reduced by M times, and the area of the corresponding detection electrodes is also correspondingly reduced by M times. So typically m=a. Therefore, by increasing the total number N of the discrete sub-mass blocks, namely N > M, the detection sensitivity can be prevented from descending and ascending after the mass blocks are subjected to discrete optimization design, and the shock resistance of the MEMS device can be improved.
The shock-resistant structure and the design method of the MEMS device are not only limited to the Z-axis torsion pendulum type MEMS capacitance accelerometer, but also applicable to various MEMS sensors such as sandwich type MEMS accelerometers, comb tooth type MEMS accelerometers, MEMS gyroscopes, MEMS pressure sensors, MEMS microphones and the like.
The g sensitivity index of the MEMS gyroscope characterizes the sensitivity degree of the MEMS gyroscope to the linear accelerometer, so that the method not only can improve the shock resistance of the MEMS gyroscope, but also can inhibit the g sensitivity of the MEMS gyroscope.
The mass block can be scattered not only in the plane, but also in the vertical direction by adopting a wafer stacking mode. After the vertical direction is discrete, the corresponding electrodes in the stacked structure can be connected in series in a TSV mode, so that signal addition is realized.
Taking a Z-axis torsion pendulum type MEMS capacitive accelerometer as an example, a conventional Z-axis torsion pendulum type 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, and the like, as shown in fig. 1 and 2. Wherein the elastic beam 103a is connected to the mass 101 at one end and to the anchor point 102a at the other end. The elastic beam 103b has one end connected to the mass 101 and the other end connected to the anchor point 102 b. Anchor points 102a and 102b are fixedly attached to the silicon substrate. The mass 101 is suspended on the silicon substrate by means of spring beams 103a, 103b and anchor points 102a, 102 b. The detection electrodes 104a and 104b disposed at both ends below the mass 101 and the mass 101 constitute a set of differential capacitance pairs. The mass of a conventional Z-axis torsion pendulum MEMS capacitive accelerometer is made up of one large complete mass 101.
The spring beam 103 is designed to be arranged offset from the central symmetry axis of the mass 101 such that the mass 101 differs in mass along the axis on which the spring beam 103 lies. When the Z-axis acceleration is input from the outside, the masses with unequal sides generate torsion moment around the axis where the beam 103 is located, the mass block 101 deflects around the beam 103 under the action of the Z-axis acceleration, the detection electrodes 104a and 104b arranged at the two ends below the mass block detect a pair of opposite output signals, the deflection angle signals are output through differential amplification of a subsequent detection circuit, and finally the Z-axis input acceleration can be calculated according to the output deflection angle signals.
When there is a strong Z-axis impact or vibration, the mass 101 may collide strongly with the detection electrode 104 under the impact or vibration. A strong collision may cause breakage or breakage of the collision contact portion. To avoid this, a common design method is to design and process a stop bump structure under the mass block, which is higher than the detection electrode 104. However, since the stopper bump structure and the mass block 101 in contact with the stopper bump structure are both rigid structures and are not easily deformed, structural damage or breakage is easily caused after the stopper structure collides with the lower bottom surface of the mass block under a strong impact condition.
In order to improve the strong impact or vibration resistance of the device, the patent provides an impact resistance design method of a MEMS device with discrete mass. The structure of the original design is divided and discretized into a plurality of substructures, so that discretization of the mass block is realized. In this embodiment, discretization into 4 substructures is taken as an example, as shown in fig. 3. The original design structure is divided into 4 identical sub-structures 201a, 201b, 201c and 201d, as shown in fig. 4. In fig. 3, the substructures 201a and 201b are axisymmetric, the substructures 201c and 201d are axisymmetric, and the substructures 201a, 201b and 201c and 201d are axisymmetric.
The substructure 201a is composed of a new mass 301a, spring beams 303a and 303b, anchor points 302a and 302b, and sense electrodes 304a and 304b, the substructure 201b is composed of a new mass 301c, spring beams 303c and 303d, anchor points 302c and 302d, and sense electrodes 304c and 304d, the substructure 201c is composed of a new mass 301e, spring beams 303e and 303f, anchor points 302e and 302f, and sense electrodes 304e and 304f, and the substructure 201d is composed of a new mass 301g, spring beams 303g and 303h, anchor points 302g and 302h, and sense electrodes 304g and 304h, as shown in fig. 4. The connection relationship in each substructure is the same as that of a conventional Z-axis torsion pendulum MEMS capacitive accelerometer. Taking the substructure 201a as an example, an elastic beam 303a has one end connected to the mass 301a and the other end connected to the anchor point 302a, and an elastic beam 303b has one end connected to the mass 301a and the other end connected to the anchor point 302 b. Anchor points 302a and 302b are fixedly attached to the silicon substrate. The mass 301a is suspended on the silicon substrate by spring beams 303a, 303b and anchor points 302a, 302 b. The detection electrodes 304a and 304b disposed at both ends below the mass 301a and the mass 301a constitute a set of differential capacitance pairs. The remaining sub-structures 201b, 201c, 201d are the same.
When the Z-axis positive acceleration is input, the mass 301a deflects in a direction approaching the detection electrode 304a, the mass 301c deflects in a direction approaching the detection electrode 304d, the mass 301e deflects in a direction approaching the detection electrode 304e, and the mass 301g deflects in a direction approaching the detection electrode 304 h. At this time, the directions of the signals detected by the detection electrodes 304a, 304d, 304e, and 304h are the same, and the directions of the signals detected by the detection electrodes 304b, 304c, 304f, and 304g are opposite. As shown in fig. 5, the detection electrodes 304a, 304d, 304e, and 304h of the same signal can be connected in series by designing the lead 402, i.e., 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 the lead 403, that is, signals detected by the detection electrodes 304b, 304c, 304f, and 304g are added and connected to the bonding point 401b. The bonding points 401a, 401b, 401c are connected with a detection circuit, and then output an electric signal to the detection circuit, the detection circuit achieves differential amplification of the signal, and finally, a deflection angle signal of the mass block is output.
In other embodiments, the discrete sub-structures may be in a repeating array, or may be symmetrically or anti-symmetrically designed about a certain axis, or may be in a staggered array, as shown in fig. 6 and 7.
The method is also suitable for overload resistance design of the comb-tooth accelerometer. Fig. 8 is a design of an original comb-tooth accelerometer in which the mass is of one-piece construction. FIG. 9 is a schematic diagram of an overload resistant comb accelerometer designed using a mass discrete method, wherein the mass is divided and discrete into four individual sub-masses.
The mass may be not only in-plane but also in other embodiments in a vertical direction in a stacked wafer fashion. After the vertical direction is discrete, the corresponding electrodes in the stacked structure can be connected in series by adopting a TSV mode, so that signal addition is realized, as shown in fig. 10. The TSV electrodes 501a and 501b realize series connection of signals of upper and lower layers. Leads 504a, 504b interconnect the same polarity electrodes 502a and 502b with the TSV electrode 501 a. Leads 505a, 505b interconnect the same polarity electrodes 503a and 503b with the TSV electrode 501 b.
In the shock resistance design of the discrete mass blocks, the mass blocks can be designed to be discrete into any plurality of sub-mass blocks according to the shock resistance requirement. Because the mass of each sub-mass block is reduced compared with the mass of the original mass block, the shock resistance of the single sub-mass block is greatly improved compared with the original whole mass block. The shock resistance design method of the discrete mass blocks can even increase the number of the sub mass blocks, so that the total mass of all the sub mass blocks is larger than that of the original whole mass blocks.
The foregoing is merely a preferred embodiment of the present invention, and it should be noted that modifications and variations could be made by those skilled in the art without departing from the technical principles of the present invention, and such modifications and variations should also be regarded as being within the scope of the invention.
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| CN212198497U (en) * | 2020-04-26 | 2020-12-22 | 中国兵器工业集团第二一四研究所苏州研发中心 | An anti-shock structure of MEMS device with mass discretization |
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