MEMS (Micro Electro Mechanical System) three-state inertia switch and preparation method thereof

Abstract

The invention provides an MEMS (Micro Electro Mechanical System) three-state inertia switch and a preparation method thereof. In the inertia switch, a first glass cover plate is provided with a first closed electrode and a pull-in polar plate, and the upper and lower surfaces of a mass block with an interlayer silicon structure are respectively provided with a first closed electrode and a second closed electrode; the second glass cover plate is provided with a second closed electrode; in an initial state, the first closing electrode is closed, and the pull-in polar plate is not in contact with the mass block and is locked by static electricity; when inertia force borne by the three-state inertia switch reaches inertia overload force, the mass block is separated from electrostatic adsorption and moves towards the second glass cover plate to enter an intermediate state, and the processing circuit outputs second voltage; when the inertia force is increased, the second closed electrode contacts and enters a closed state, and the processing circuit outputs a third voltage. The structure of the three-state inertia switch can be manufactured by adopting an MEMS (Micro Electro Mechanical System) process, and the sensor is small in size; the three-state jump is not limited by the compression of the spring and can occur instantaneously, so that more requirements for detecting external overload are met.

Description

Technical Field

[0001] The present invention relates to the technical field of inertial switch design, and particularly relates to a MEMS three-state inertial switch and a preparation method thereof. Background Art

[0002] An inertial switch is a precision inertial device that senses inertial acceleration and performs a mechanical switching action. It is generally divided into two states: closed and open, and is widely used in inertial control systems such as aerospace, automotive electronics, and ammunition.

[0003] Generally speaking, an inertial switch mainly consists of a spring-mass-damping system. The spring is directly connected to the mass block, and the rigidity of the spring is used to meet the requirement of closing or opening when the overload reaches the threshold. When there is no static overload, the spring is at a pre-set length, and at this time, the inertial switch can be closed or open depending on the designed structure; when the overload arrives, the entire system senses the inertial acceleration and starts to perform the mechanical switching action, and the compression of the spring corresponds to the disconnection or connection.

[0004] The MEMS (Micro-Electro-Mechanical System) process can be classified into silicon micromachining technology, LIGA processing technology, and other processing technologies according to the processed materials. The more commonly used one is silicon micromachining technology. Among them, silicon micromachining technology can be divided into bulk silicon processing technology and surface silicon processing technology: the bulk silicon process mainly grows and etches on silicon materials through various process means to achieve the desired mechanical structure, and these process means include: photolithography, etching, doping, etc.; the surface silicon process forms various microstructures through the sequential deposition and selective etching of different materials on the silicon plane, involving processes such as deposition and bonding.

[0005] In the prior art, inertial switches usually have only two states: closed and open. For example, in Document 1 (see Xiong Zhuang, Zhang Fengtian, Yuan Mingquan. Design and Process Optimization of Low-g MEMS Inertial Switches [J]. Chinese Journal of Inertial Technology, 2016, 24(3): 404–408.), an inertial switch with a glass-silicon-glass structure is provided. As Figure 1 shown, metal electrodes are distributed at the lower end of the mass block in the silicon structure and the upper end of the glass substrate. When this structure is impacted in the sensitive direction, the mass block moves a distance Z0, the metal electrodes come into contact, and the entire circuit is closed, thus realizing the function of the inertial switch.

[0006] It can be seen that an inertial switch generally has only two states without an intermediate state transition, and may be accidentally triggered in some special situations, such as maintenance processing, etc. The applicant has proposed a three-state inertial switch (see Patent Publication No. CN116007455A), but the sensor structure has disadvantages such as many parts, complex assembly, and large volume, and it is difficult to ensure the reliability and safety in the application of complex environments. Moreover, during the transition from the intermediate state to the closed state, not only a greater overload is required, but also an increase in the spring compression stroke is needed, which takes a certain amount of time and cannot occur instantaneously together with the transition from the initial state to the intermediate state, and cannot meet the requirements for detecting more external overloads. Summary of the Invention

[0007] In view of this, the present invention provides a MEMS three-state inertial switch and a manufacturing method thereof. The structure of the three-state inertial switch can be manufactured by MEMS technology, and the sensor has a small volume; the three-state transition is not restricted by spring compression and can occur instantaneously, meeting the requirements for detecting more external overloads.

[0008] In order to solve the above technical problems, the present invention is implemented as follows.

[0009] A MEMS three-state inertial switch includes a first glass cover plate, an intermediate silicon structure, a second glass cover plate, and a processing circuit, which are manufactured by MEMS technology;

[0010] The intermediate silicon structure includes a peripheral support structure and a mass block. The mass block is located within the support structure and is connected to the support structure through a flexible connection structure; the first glass cover plate and the second glass cover plate are bonded and connected to the upper and lower sides of the support structure;

[0011] On the relative surface of the first glass cover plate and the mass block, there are mutually cooperating first closing electrodes; the first glass cover plate is provided with a suction plate to provide electrostatic force and is electrostatically attracted and locked with the surface of the mass block; the height of the suction plate is lower than the height of the first closing electrodes on the first glass cover plate. When the first closing electrodes come into contact, the suction plate and the mass block do not come into contact, and the distance between them is d, which is designed according to the inertial overload force F1 of the inertial switch; on the relative surface of the second glass cover plate and the mass block, there are mutually cooperating second closing electrodes; all the closing electrodes are electrically connected to the processing circuit;

[0012] In the initial state, the first closing electrodes are closed, and the suction plate and the mass block are electrostatically locked, and the processing circuit outputs a first voltage; when the inertial force received by the three-state inertial switch reaches the inertial overload force F1, the mass block moves away from the electrostatic adsorption and moves towards the second glass cover plate, entering the intermediate state, and the processing circuit outputs a second voltage; when the inertial force increases and the second closing electrodes come into contact, it enters the closed state, and the processing circuit outputs a third voltage.

[0013] Preferably, the first closed electrode disposed on the first glass cover plate is a non-closed annular structure, the attracting electrode plate is installed inside the annular structure, and the connecting wire of the attracting electrode plate is led out through the opening of the non-closed annular structure;

[0014] The first closed electrode disposed on the surface of the mass block is an annular structure that cooperates with the non-closed annular structure, and the plane of the mass block inside the annular structure serves as another attracting electrode plate that cooperates with the attracting electrode plate.

[0015] Preferably, the flexible connection structure is an island-beam structure.

[0016] Preferably, in the island-beam structure, the cross-sectional area of the beam gradually thickens from the mass block to the support structure.

[0017] Preferably, the processing circuit includes resistor R0, resistor R L , electrostatic power supply voltage V in and power supply voltage V cc ;

[0018] Resistor R0 and resistor R L are connected in series between the positive and negative poles of the power supply voltage V cc ;

[0019] The first end of resistor R0 is connected to the second closed electrode on the second glass cover plate, and the second end is connected to the second closed electrode on the mass block;

[0020] The closed electrodes on the upper and lower sides of the middle-layer silicon structure are electrically connected to two points with equal potential, and are connected between resistor R L and resistor R0. At the same time, the potential value of this point is also the output voltage V out of this structure.

[0021] Preferably, the processing circuit is fabricated on a PCB packaging substrate; the sandwich structure of the MEMS three-state inertial switch is laterally installed in the installation groove provided by the PCB packaging substrate;

[0022] At the position of the PCB packaging substrate corresponding to the first glass cover plate, a connecting wire to the electrostatic power supply voltage V in pad is arranged on the left side of the first glass cover plate; a connecting wire from the first closed electrode to resistor R L , ground GND pad is arranged on the right side of the first glass cover plate;

[0023] At the position of the PCB packaging substrate corresponding to the second glass cover plate, a connecting wire from the second closed electrode to resistor R0 and the power supply voltage V cc pad is arranged on the right side of the second glass cover plate;

[0024] At the position on the PCB packaging substrate corresponding to the intermediate silicon structure, a first closed electrode is arranged on the right side of the intermediate silicon structure to the resistor R0, resistor R L , voltage output terminal V out connection lines of the pads.

[0025] Preferably, the electrostatic force supply voltage V in pad, ground GND pad, supply voltage V cc pad, voltage output terminal V out pads are arranged on one side of the PCB packaging substrate and arranged in rows;

[0026] Resistor R0, resistor R L are vertically arranged up and down and arranged between the sandwich structure of the MEMS three-state inertial switch and the four pads.

[0027] The present invention also provides a preparation method of the above-mentioned MEMS three-state inertial switch, and the method includes: a first glass cover plate preparation process, a second glass cover plate preparation process, an intermediate silicon structure preparation process, and a bonding process;

[0028] The first glass cover plate preparation process and the second glass cover plate preparation process are the same, and both include:

[0029] Step A1: Sputter a layer of Cr / Cu seed layer on the surface of the glass cover plate;

[0030] Step A2: Spin-coat photoresist on the seed layer, and after drying, photolithograph the patterns of the electrodes and layout leads on the glass cover plate;

[0031] Step A3: Electroplate a layer of metal Ni as the electrodes and layout leads on the glass cover plate;

[0032] Step A4: Remove all photoresist and remove the seed layer;

[0033] The intermediate silicon structure preparation process includes:

[0034] Step B1: Define the two sides of the silicon structure as side A and side B; perform anisotropic etching from side B of the silicon structure to complete the construction of the support structure, mass block, and lead groove on side A of the intermediate silicon structure;

[0035] Step B2: Perform deep reactive ion etching from side A of the silicon structure to complete the construction of the connection structure;

[0036] Step B3: Sputter a Cr / Cu seed layer on side B of the silicon structure, spin-coat photoresist, and after drying, photolithograph the patterns of the closed electrodes and layout leads on side B of the silicon structure;

[0037] Step B4: First, electroplate a layer of metal Ni on the B surface of the silicon structure, and then electroplate a layer of metal Au as the closed electrode at the bottom of the silicon structure. After electroplating, remove all photoresist and the seed layer.

[0038] Step B5: Thermally oxidize a layer of SiO2 on the A surface of the silicon structure as the insulating layer, and spin-coat photoresist on the oxidized surface to expose the etching window of SiO2. The photoresist covers the position where the support structure on the B surface in the middle-layer silicon structure is to be formed.

[0039] Step B6: Etch the SiO2 not covered by photoresist, and then remove all photoresist.

[0040] Step B7: Sputter a Cr / Cu seed layer on the A surface of the silicon structure. Then, spin-coat photoresist on the seed layer. After drying, photolithograph the patterns of the closed electrode and the layout leads on the A surface of the silicon structure.

[0041] Step B8: First, electroplate the first layer of metal Ni on the A surface of the silicon structure, and then electroplate the second layer of metal Au on the metal Ni as the closed electrode at the top of the silicon structure. Then, remove all photoresist and the seed layer to form a complete middle-layer silicon structure.

[0042] The bonding process: Bond two glass cover plates and the middle-layer silicon structure together to obtain a complete MEMS three-state inertial switch.

[0043] Preferably, the bonding of the two glass cover plates and the middle-layer silicon structure adopts an anodic bonding process.

[0044] Advantages:

[0045] (1) The inertial switch of traditional machining is relatively mature in application. However, due to its disadvantages such as many parts, complex assembly, and large volume, it is difficult to ensure the reliability and safety in applications in complex environments. The structure of the present invention can be manufactured by MEMS technology, with small size, light weight, no need for assembly, and can be mass-produced, and the reliability and safety in applications in complex environments can be ensured.

[0046] (2) The present invention designs three states - the initial state, the intermediate state, and the closed state. Since spring compression is not adopted, the three-state transition is not restricted by spring compression and can occur instantaneously, which can meet more requirements for detecting external overloads.

[0047] (3) At present, the research on MEMS low-g inertial switches is relatively rich, and the general trigger threshold is about several tens of g. This design can achieve a higher trigger threshold and can meet the requirements for a larger threshold.

[0048] (4) In a preferred embodiment, through the COB packaging method based on the PCB substrate, the equipotential of the upper and lower closing electrodes of the silicon structure is realized on the PCB substrate. Compared with other methods that may achieve equipotential, such as the through-silicon via technology - digging a through-hole in the island of the island-beam structure of the silicon structure, this method does not add additional MEMS manufacturing processes, making the complexity of the MEMS manufacturing process lower and improving the success rate of the MEMS manufacturing process to a certain extent.

[0049] (5) The design of the three states enables this switch to have a higher detection accuracy for overload. On the one hand, the output signal of the traditional inertial switch has only two states, and it is difficult to completely distinguish the overload interference existing in the ballistic environment from the penetration overload. On the other hand, the jump of the output signal of the traditional inertial switch requires the moving element to move in place, so it is difficult to accurately judge the moments when the projectile enters and exits the target. For this structure, during the penetration process, the overload initially received by the three-state inertial switch is small, less than the electrostatic force provided by the attracting plate, and the upper closing electrode in the silicon structure is electrically connected to the closing electrode in the first glass cover plate, and the circuit output signal is in the initial state; as the penetration overload gradually increases, the inertial force exceeds the electrostatic force, and the island-beam structure in the silicon structure begins to move towards the second glass cover plate, and the upper closing electrode in the silicon structure is disconnected from the closing electrode in the first glass cover plate, and the circuit output signal is in the intermediate state; when the penetration overload continues to increase, the island-beam structure continues to move downward, and the lower closing electrode in the silicon structure is electrically connected to the closing electrode in the second glass cover plate, and the circuit output signal is in the final state. The output signal of this structure has three states. Compared with the traditional inertial switch whose output signal has only two states, it can effectively reduce the overload interference in the service state and the flight trajectory and improve the safety of the fuse. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 is a schematic diagram of the prior art.

[0051] Figure 2 is a schematic diagram of the MEMS three-state inertial switch of the present invention.

[0052] Figure 3 is a top view of the intermediate layer silicon structure of the present invention.

[0053] Figure 4 is a structural diagram of the first glass cover plate. (a) is a top view, (b) is a side view, and (c) is a three-dimensional view.

[0054] Figure 5 is a structural diagram of the intermediate layer silicon structure. (a) is a three-dimensional view, and (b) is a top view.

[0055] Figure 6 is a schematic diagram of the connection of the processing circuit.

[0056] Figure 7It is a schematic diagram of the PCB board layout.

[0057] Figure 8 It is a schematic diagram of the effect of the three - state switch sandwich structure mounted on the PCB board. (a) Top view, (b) Side view.

[0058] Figure 9 It is a schematic diagram of the preparation of the MEMS three - state switch of the present invention. Specific implementation manners

[0059] The following combines the accompanying drawings and gives examples to describe the present invention in detail.

[0060] The present invention designs a MEMS three - state inertial switch, and its structure can be manufactured by MEMS technology. As Figure 2 shown, the three - state inertial switch includes a first glass cover plate 1, an intermediate silicon structure 2, and a second glass cover plate 3. The intermediate silicon structure 2 is made of silicon (Si) material.

[0061] The intermediate silicon structure 2, as Figure 3 shown, includes a peripheral support structure 21 and a mass block 22. The mass block is located within the support structure and is connected to the support structure through a flexible connection structure 23. The first glass cover plate and the second glass cover plate are connected to the upper and lower sides of the support structure through anodic bonding.

[0062] On the opposite surface of the first glass cover plate 1 and the mass block 22, there are mutually - matching first closing electrodes 4, 5. The closing electrodes can contact each other to achieve electrical connection. The first glass cover plate is provided with an attracting electrode plate 8 to provide an electrostatic force. On the upper side of the intermediate silicon structure, there is only a closing electrode because at this end, the silicon mass block will simultaneously serve as another attracting electrode, and the attracting electrode plate 8 and the surface of the mass block are locked by electrostatic attraction. In addition, the height of the attracting electrode plate 8 is lower than the height of the first closing electrode 4 on the first glass cover plate, ensuring that during the entire working process of the MEMS three - state inertial switch, even when the two first closing electrodes 4, 5 contact, the attracting electrode plate 8 and the mass block 22 will not adsorb together. When the first closing electrodes 4, 5 contact, the distance between the attracting electrode plate and the upper surface of the mass block is d, and d affects the electrostatic force and needs to be designed according to the inertial overload force F1 of the inertial switch. On the opposite surface of the second glass cover plate 3 and the mass block 22, there are mutually - matching second closing electrodes 6, 7. All the closing electrodes 4, 5, 6, 7 are electrically connected to the processing circuit.

[0063] In the initial state, the first closing electrodes are closed, the attracting electrode plate and the mass block are locked by electrostatic force, and the processing circuit outputs a first voltage. When the inertial force received by the three - state inertial switch reaches the inertial overload force F1, the mass block breaks away from the electrostatic adsorption and moves towards the second glass cover plate, entering the intermediate state, and the processing circuit outputs a second voltage. When the inertial force increases and the second closing electrodes contact, it enters the closed state, and the processing circuit outputs a third voltage.

[0064] Figure 4 shows the preferred structure of the first glass cover plate. As Figure 4 shown, the first closed electrode 4 provided on the first glass cover plate 1 is a non-closed annular structure, the attracting plate 8 is located inside the annular structure, and the connecting wire of the attracting plate 8 is led out through the opening of the non-closed annular structure. The annular structure can also be in the shape of a circular ring or a square ring, etc. In practice, the first closed electrode 4 may not be an annular structure, but a strip structure, a square structure, etc. In order to ensure smooth force application, it is preferably arranged symmetrically with respect to the center of the first glass cover plate. The attracting plate 8 is arranged at the center position of the first glass cover plate.

[0065] The first closed electrode 5 provided on the surface of the mass block is an annular structure that cooperates with the non-closed annular structure. This annular structure can be closed, as Figure 3 shown by the square frame in the center. The plane of the mass block inside this annular structure serves as another attracting electrode that cooperates with the attracting plate 8.

[0066] Figure 5 shows the preferred structure of the intermediate layer silicon structure 2. As shown in the figure, the support structure 21 in the intermediate layer silicon structure 2 is a rectangular frame, the mass block 22 is located at the center position inside the rectangular frame, and the first closed electrode 5 and the second closed electrode 6 are respectively installed on the upper surface and the lower surface of the mass block 22. The flexible connection structure 23 between the support structure 21 and the mass block 22 adopts an island-beam structure. The "island" is the mass block 22, and the four "beams" are the connection structures 23. In practice, the connection structure 23 can also adopt the spiral mechanism mentioned in Background Art Document 1.

[0067] The anti-overload performance generally refers to the ability of the inertial switch to still maintain a sound structure and stable performance under the action of an overload acceleration. For this structure, the anti-overload performance is particularly important because in the application scenario of this structure, there is often an overload of tens of thousands of g in the axial direction of the switch, far exceeding the threshold of the switch itself. Therefore, the improvement of the anti-overload performance can reduce the damage rate of the switch in extreme working environments and greatly improve the durable use ability of the switch. When this structure is subjected to axial overload, due to the island-beam structure, a relatively large stress will act on the outermost periphery of the beam, which is also the place that needs the most attention when this structure is subjected to overload. Therefore, this structure selects to thicken at the place where the stress is most concentrated to improve the anti-overload performance. As Figure 5 shown, in a preferred embodiment, the cross-sectional area of the beam in the island-beam structure gradually thickens from the mass block to the support structure.

[0068] A small hole 24 and two small grooves 25 are also opened on the two side walls of the intermediate layer silicon structure 2, both of which are holes for metal electrode wiring, corresponding to the above four closed electrodes and one attracting electrode.

[0069] In this embodiment, the states of the switch are divided into three states: the initial state, the intermediate state, and the closed state, corresponding to three cases of the switch output: zero, low voltage, and high voltage, and its processing circuit is as Figure 6 shown. The processing circuit includes resistor R0, resistor R L , the electrostatic power supply voltage V in , and the power supply voltage V cc ; Resistor R0 and resistor R L are connected in series between the positive and negative poles of the power supply voltage V cc ; The first end of resistor R0 is connected to the second closed electrode on the second glass cover plate, and the second end is connected to the second closed electrode on the mass block; The closed electrodes on the upper and lower sides of the intermediate silicon structure are electrically connected to two points with equal potential, and are connected between resistor R L and resistor R0. At the same time, the potential value of this point is also the output voltage V out of this structure.

[0070] In the initial state, due to the action of the electrostatic force between the suction electrodes in the upper cavity of the silicon structure, the two upper closed electrodes are attached together, and R L is short-circuited, and the output voltage is 0 at this time; When the inertial force received by the switch is greater than the electrostatic force between the suction electrodes (assuming that the inertial force and the electrostatic force are in opposite directions at this time), the two upper closed electrodes are separated, and the switch enters the intermediate state. At this time, the output voltage is low voltage (voltage division of two resistors); When the inertial force received by the switch continues to increase, the island-beam structure continues to move downward. After moving a certain stroke, the two closed electrodes in the lower cavity of the silicon structure are attached, and R0 is short-circuited. The switch enters the closed state, and the output voltage is high voltage.

[0071] Among them, the electrostatic force formula is shown in Equation (1).

[0072]

[0073] In the formula, ε is the permittivity, S represents the relative area of the parallel plates, V is the bias voltage value between the two suction electrodes, that is, V in , x0 is the initial distance between the plates, x represents the displacement of the two plates relative to the approaching direction, and x0 - x represents the distance d between the suction electrodes. In this structure, the minimum inertial force required for the transition from the initial state to the intermediate state is the first threshold of this switch, and the inertial force required for the transition from the intermediate state to the closed state is the second threshold of this switch. Generally, it can be considered that reaching the closed state during the impact process of the structure meets the impact conditions we need to detect. The intermediate state provides a good effect in anti-interference and greatly improves the detection accuracy.

[0074] During the impact on this structure, the attracted plates in the silicon structure are generally affected by these three forces: electrostatic force, inertial impact force, and elastic restoring force of the island-beam structure that wants to return to the normal state. At this time, the distance between the upper and lower attracted plates in the normal state of the island-beam structure can be minimized as much as possible, and the threshold can be increased from two aspects: 1. At the initial state, the distance between the two plates is further reduced, and the electrostatic force increases, which can increase the threshold; 2. At the initial state, the strain of the beam in the island-beam structure is small, and the elastic restoring force is reduced, which can increase the threshold (the elastic restoring force and the inertial impact force are in the same direction, and both are doing work to change the structure from the initial state to the intermediate state).

[0075] Ignoring the elastic restoring force, the attracted plates are affected by the electrostatic force and the inertial impact force: when the structure is about to enter the intermediate state, the electrostatic force is equal to the inertial impact force, as shown in Equation (2).

[0076]

[0077] The estimated value of the threshold can be calculated through this equation. In the formula, the determined parameters are shown in Table 1.

[0078] Table 1 Parameter Table

[0079]

[0080] In addition, in this structure, the magnitude of the electrostatic force can be controlled by designing some structural parameters such as S, V, x0, etc., so as to regulate the threshold for the transition from the initial state to the intermediate state, and achieve the function of high threshold and controllability. Now assume that the required threshold is 500g and the given voltage is 12V. Substituting the above parameters into the formula for calculation, it can be obtained that when the structure size is designed in the micron order, this threshold can be achieved, and the micron order can also be achieved in today's MEMS process.

[0081] In terms of packaging, in a preferred solution, this structure selects the COB packaging method based on the PCB substrate. The processing circuit is prepared on the PCB packaging substrate (as Figure 7 shown), and the sandwich structure of the three-state switch can be laterally mounted in the groove provided by the PCB packaging substrate through epoxy adhesive, as Figure 8 shown, and then the electrodes in the structure are led to the packaging substrate through the process of wire bonding. At the same time, this packaging method can also solve the problem of electrical interconnection between the upper and lower electrodes of the silicon structure, because this problem can be solved by connecting the two circuits together on the packaging substrate. Among them, the types of packaging substrates include phenolic paper substrates, glass fiber substrates, and composite substrates, etc. This structure selects the PCB glass fiber substrate as the packaging substrate.

[0082] See Figure 7 and Figure 8, at the position on the PCB packaging substrate corresponding to the first glass cover plate, the electrostatic power supply voltage V is arranged on the left side of the first glass cover plate in connecting wire of the pad; the first closing electrode is arranged on the right side of the first glass cover plate to the resistor R L , connecting wire of the ground GND pad; at the position on the PCB packaging substrate corresponding to the second glass cover plate, the second closing electrode is arranged on the right side of the second glass cover plate to the resistor R0, power supply voltage V cc connecting wire of the pad; at the position on the PCB packaging substrate corresponding to the intermediate layer silicon structure, the first closing electrode is arranged on the right side of the intermediate layer silicon structure to the resistor R0, resistor R L , voltage output terminal V out connecting wire of the pad.

[0083] For the convenience of connection, the electrostatic power supply voltage V in pad, ground GND pad, power supply voltage V cc pad, voltage output terminal V out pads are arranged on one side of the PCB packaging substrate and arranged in rows; resistor R0, resistor R L are vertically arranged up and down and arranged between the sandwich structure of the MEMS three-state inertial switch and the four pads.

[0084] Figure 9 shows the main process flow chart of the MEMS three-state inertial switch of the present invention, as Figure 9 shown, the method includes the preparation process of the first glass cover plate in steps ① to ④, the preparation process of the second glass cover plate in steps ⑤ to ⑧, ⑨ to the preparation process of the intermediate layer silicon structure, and step the bonding process.

[0085] Specifically:

[0086] ① Sputter a layer of Cr / Cu seed layer on the surface of the glass substrate;

[0087] ② Spin-coat a layer of photoresist on the seed layer, and after drying, lithograph the patterns of the closing electrodes and layout leads on the glass substrate;

[0088] ③ Electroplate a layer of metal Ni as the closing electrodes and layout leads on the glass substrate;

[0089] ④ Remove all the photoresist, (and configure a mixed solution of hydrogen peroxide and ammonia water and potassium permanganate solution) to remove the seed layer.

[0090] ⑤ Sputter a layer of Cr / Cu seed layer on the surface of the glass cover plate;

[0091] ⑥ Spin-coat a layer of photoresist on the seed layer, and after drying, lithograph the patterns of the attracting plates, closing electrodes and layout leads on the glass cover plate;

[0092] ⑦ Electroplate two parts of metal Ni in total. The metal Ni near the center serves as the attracting electrode, and the outer metal Ni serves as the closing electrode on the glass cover plate and the layout lead wire.

[0093] ⑧ Remove all photoresist, and (prepare a mixed solution of hydrogen peroxide and ammonia water and a potassium permanganate solution) to remove the seed layer.

[0094] (Hereinafter, it is default that side A is the top of the silicon structure, and the other side of side A is the bottom of the silicon structure)

[0095] ⑨ Anisotropically etch from the bottom of the silicon structure with potassium hydroxide to complete the construction of the mass island structure and the lead groove.

[0096] ⑩ Perform deep reactive ion etching (ICP etching) from side A to complete the construction of the beam structure around the mass.

[0097] Sputter a layer of Cr / Cu seed layer on the bottom of the silicon structure, spin-coat a layer of photoresist, and after drying, photolithograph the pattern of the closing electrode and the layout lead wire at the bottom of the silicon structure.

[0098] First, electroplate a layer of metal Ni, then electroplate a layer of metal Au as the closing electrode at the bottom of the silicon structure. After electroplating, remove all photoresist and the seed layer. Metal Ni has three functions: one is to reduce the undercutting phenomenon during electroplating of gold, the second is to conduct signals as a lead wire, and the third is to reduce part of the cost.

[0099] Thermally oxidize a layer of SiO2 on the top of the silicon structure as an insulating layer to prevent the electrostatic force from disappearing due to the contact between the glass cover plate and the silicon structure after bonding. And spin-coat a layer of photoresist on the oxidized surface to expose the etching window of SiO2.

[0100] (Use an oxide etching solution) Etch the SiO2 without photoresist coverage, and then remove all photoresist.

[0101] Sputter a layer of Cr / Cu seed layer on the top of the silicon structure, then spin-coat a layer of photoresist on the seed layer, and after drying, photolithograph the pattern of the closing electrode and the layout lead wire at the top of the silicon structure.

[0102] Electroplate a layer of metal Ni. The function of Ni is the same as that in step Then electroplate a second layer of metal Au on the metal Ni as the closing electrode at the top of the silicon structure. Then remove all photoresist, and prepare a mixed solution of hydrogen peroxide and ammonia water and a potassium permanganate solution to remove the seed layer.

[0103] Finally, bond the glass cover plate, silicon structure, and glass substrate together (an anodic bonding process can be used) to obtain a complete MEMS three-state inertial switch.

[0104] The above specific embodiments only describe the design principle of the present invention. The shapes and names of the components in this description can be different and are not limited. Therefore, those skilled in the art of the present invention can modify or equivalently replace the technical solutions recorded in the foregoing embodiments; and these modifications and replacements do not depart from the purpose and technical solutions of the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A MEMS three-state inertial switch, characterized in that: It includes a first glass cover plate, an intermediate silicon structure, a second glass cover plate and a processing circuit manufactured by MEMS process; The intermediate layer silicon structure comprises a peripheral support structure and a mass block, wherein the mass block is located inside the support structure and connected to the support structure via a flexible connection structure; the first glass cover plate and the second glass cover plate are bonded to the upper and lower sides of the support structure; The first glass cover plate and the mass block are provided with mutually matching first closed electrodes on the opposite surfaces thereof; the first glass cover plate is provided with a pull-in electrode plate to provide electrostatic force, and is locked with the surface of the mass block by electrostatic pull-in; the height of the pull-in electrode plate is lower than the height of the first closed electrode on the first glass cover plate, and when the first closed electrode is in contact, the pull-in electrode plate (1) and the mass block are not in contact, and the distance between the two is d, which is designed according to the inertial overload force F1 of the inertial switch; the second glass cover plate and the mass block are provided with mutually matching second closed electrodes on the opposite surfaces thereof; All closed electrodes are electrically connected to the processing circuit; In the initial state, the first closed electrode is closed, the attraction plate and the mass block are locked by electrostatics, and the processing circuit outputs a first voltage; when the inertial force exerted on the three-state inertial switch reaches the inertial overload force F1, the mass block breaks away from the electrostatic adsorption and moves toward the second glass cover plate, entering the intermediate state, and the processing circuit outputs a second voltage; when the inertial force increases, the second closed electrode contacts and enters the closed state, and the processing circuit outputs a third voltage.

2. The MEMS three-state inertial switch according to claim 1, characterized in that: The first closed electrode arranged on the first glass cover plate is a non-closed annular structure, the pull-in electrode plate (1) is installed in the annular structure, and the connection line of the pull-in electrode plate is led out through the opening of the non-closed annular structure; The first closed electrode arranged on the surface of the mass block is an annular structure matched with the non-closed annular structure, and the plane of the mass block in the annular structure serves as another attraction electrode matched with the attraction electrode plate (1).

3. The MEMS three-state inertial switch according to claim 1, characterized in that: The flexible connection structure is an island-beam structure.

4. The MEMS three-state inertial switch according to claim 1, characterized in that: The cross-sectional area of ​​the beam in the island-beam structure gradually increases from the mass block to the support structure.

5. The MEMS three-state inertial switch according to claim 1, characterized in that: The processing circuit includes a resistor R0, a resistor R L , electrostatic force supply voltage V in and the supply voltage V cc ; Resistor R0, resistor R L After connecting in series to the supply voltage V cc Between positive and negative electrodes; A first end of the resistor R0 is connected to a second closed electrode on the second glass cover plate, and a second end of the resistor R0 is connected to a second closed electrode on the mass block; The closed electrodes on the upper and lower sides of the middle layer silicon structure are electrically connected to two points with equal potential and connected to the resistor R L The potential value of this point is also the output voltage V of this structure. out .

6. The MEMS three-state inertial switch according to claim 5, characterized in that: The processing circuit is prepared on a PCB packaging substrate; the sandwich structure of the MEMS three-state inertia switch is laterally installed in a mounting groove provided by the PCB packaging substrate; The position corresponding to the first glass cover on the PCB packaging substrate is arranged on the left side of the first glass cover to the electrostatic force power supply voltage V in The connection line of the pad; the first closed electrode is arranged on the right side of the first glass cover to the resistor R L , the connection wire of the ground GND pad; The position corresponding to the second glass cover on the PCB package substrate is arranged on the right side of the second glass cover to the resistor R0 and the power supply voltage V cc The connection wires of the pads; The position of the middle layer silicon structure on the PCB package substrate corresponds to the position of the middle layer silicon structure. The first closed electrode is arranged on the right side of the middle layer silicon structure to the resistor R0 and the resistor R L , voltage output terminal V out The connection wires of the pads.

7. The MEMS three-state inertial switch according to claim 6, characterized in that: Electrostatic force supply voltage V in Pad, ground GND pad, power supply voltage V cc Pad, voltage output terminal V out The pads are arranged on one side of the PCB package substrate and arranged in rows; Resistor R0, resistor R L It is arranged vertically from top to bottom and is placed between the sandwich structure of the MEMS three-state inertial switch and the four pads.

8. A method for preparing a MEMS three-state inertial switch according to any one of claims 1 to 7, characterized in that: The method comprises: a first glass cover plate preparation process, a second glass cover plate preparation process, an intermediate layer silicon structure preparation process and a bonding process; The preparation process of the first glass cover plate and the preparation process of the second glass cover plate are the same, and both include: Step A1: sputtering a Cr / Cu seed layer on the surface of the glass cover plate; Step A2: Spin-coating photoresist on the seed layer, and after drying, photolithography to form patterns of electrodes and layout leads on the glass cover plate; Step A3: electroplating a layer of metal Ni as electrodes and layout leads on the glass cover; Step A4: removing all photoresists and removing the seed layer; The intermediate layer silicon structure preparation process comprises: Step B1: define the two sides of the silicon structure as side A and side B; perform anisotropic etching on side B of the silicon structure to complete the construction of the support structure, mass block and lead groove on side A of the intermediate silicon structure; Step B2: performing deep reactive ion etching from the A surface of the silicon structure to complete the construction of the connection structure; Step B3: sputtering a Cr / Cu seed layer on the B surface of the silicon structure, and spin-coating a photoresist, and after drying, photolithography is performed to form a closed electrode and layout lead pattern on the B surface of the silicon structure; Step B4: electroplating a layer of metal Ni on the B surface of the silicon structure, and then electroplating a layer of metal Au as a closed electrode at the bottom of the silicon structure, and removing all photoresist and seed layers after electroplating; Step B5: thermally oxidize the A surface of the silicon structure to form a layer of SiO2 as an insulating layer, and spin-coat a photoresist on the oxidized surface to expose the SiO2 corrosion window, and the photoresist covers the position where the B surface support structure in the intermediate layer silicon structure is to be formed; Step B6: etching SiO2 not covered by photoresist, and then removing all photoresist; Step B7: sputtering a Cr / Cu seed layer on the A surface of the silicon structure, then spin-coating a photoresist on the seed layer, and after drying, photolithography is performed to form the pattern of the closed electrode and layout leads on the A surface of the silicon structure; Step B8: electroplating a first layer of metal Ni on the A surface of the silicon structure, and then electroplating a second layer of metal Au on the metal Ni as a closed electrode at the top of the silicon structure, and then removing all photoresists and seed layers to form a complete middle layer silicon structure; The bonding process is as follows: two glass cover plates and an intermediate silicon structure are bonded together to obtain a complete MEMS three-state inertial switch.

9. The method according to claim 8, characterized in that The two glass cover plates and the intermediate silicon structure are bonded by an anodic bonding process.

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