Inertial Micro-switch Research Articles

Highly Sensitive Inertial Micro-Switch for Achieving Adjustable Multi-Threshold Acceleration

An inertial micro-switch with multi-threshold acceleration detection capability has been proposed, taking advantage of electromechanical coupling behavior. A mathematical model of electromechanical coupling behavior was established to display the dependence of highly sensitivity on pull-in characteristic and show the ability to detect threshold acceleration by controlling the voltage applied to the inertial micro-switch. The capability of sensitivity and detection that was described in mathematical model was implemented to occur at the inertial switch and showed agreement with that of a simulation. Inertia switches that were comprised of various microstructures with dimensions ranging 3.5 µm from 180 µm were manufactured by means of the micro-electro-mechanical system (MEMS) manufacturing process, and their functions were evaluated by a dropping system. The control method related to the manufacturing of inertial switches was obtained by analyzing the effect of the structural parameters of the inertial switch on threshold voltage and threshold acceleration, resulting in a relatively small error between simulation and experiment. The inertial micro-switch showed high sensitivity to achieving the pull-in effect at 30 V, sense multi-threshold acceleration ranging from 500 g to 2000 g in 2.46 ms and provided enough time for outputting the acceleration signal. Furthermore, the multi-threshold acceleration can be adjusted by controlling the voltage applied to inertial micro-switches. In addition, other functions of inertial micro-switches, such as lower residual stress, high recoverability, and repeatability, have been displayed.

A MEMS Inertial Switch With Large Scale Bi-Directional Adjustable Threshold Function

An inertial switch with bi-directional adjustable threshold function is designed, and the adjustable threshold is achieved by electrostatic force. Based on Micro-Electro-Mechanical System (MEMS) technology, an all-metal structure inertial switch is fabricated, and the core structure is composed of three-layer parallel plates. Besides, an insulating layer of polyimide is utilized on the top and bottom plates so as to avoid electrostatic breakdown. Typically, the proof-mass as a movable structure also serves as an intermediate plate. Electrostatic forces in different directions are generated by applying voltage on the bottom or top parallel plate electrodes. Through theoretical model and finite element simulation, the force state of the proof-mass during the operating inertial micro-switch is surveyed, and the influence of electrostatic force on the threshold acceleration is also analyzed. The experimental results show that the initial acceleration of the inertial micro-switch is 79 g without bias voltage. When a bias voltage with the range of 0–100 V is applied to the bottom plate, the threshold acceleration varies within the range of 79 g-13 g, and the relationship between voltage and threshold acceleration is negatively correlated. Furthermore, when a bias voltage with the range of 65-100 V is applied to the top plate, the threshold acceleration varies within the range of 170 g-240 g, and threshold acceleration is positively correlated. The experiment is well matched with the theoretical analysis. [2021-0184]

A Novel Inertial Microswitch With Dynamic Acceleration Band-Pass Characteristics

This letter reports an inertial microswitch with an integrated filtering mechanism to realize acceleration band-pass characteristics. The switch is composed of a normal acceleration threshold switch (a high-pass mechanism) and a specially designed filtering mechanism. Only acceleration between the upper and lower cut-off thresholds can make the switch transition to its `on' state. Both dynamic finite element simulations and experiments were performed to study the dynamic behavior of the switch. The results indicate that the acceleration band-pass characteristics have been successfully achieved. The upper and lower cut-off thresholds and bandwidth varied with shock duration. The experimental data agreed well with the simulated results.

A Heterogeneous Integrated MEMS Inertial Switch With Compliant Cantilevers Fixed Electrode and Electrostatic Locking to Realize Stable On-State

A novel heterogeneous integrated inertial micro-switch has been designed with adjustable acceleration threshold and a stable ‘on’-state due to a predefined bias voltage. The bias voltage is applied onto the large-area parallel-plate electrodes, which endows the movable proof-mass with electrostatic forces. With an external excitation acceleration, the movable electrode moves to the fixed electrode and it can be locked by the electrostatic force onto the compliant electrical contacts, which are composed of micro-cantilever array to eliminate the contact rebound during electrostatic pull-in process. Both the dynamic response of the proof-mass and the relationship between the bias voltage and the inertial excitation acceleration were analyzed using theoretical model and finite element simulation. A unique heterogeneous integration process including both the silicon-based and non-silicon surface micromachining processes was adopted to fabricate the switch. The tests using a standard dropping hammer system demonstrated that the switch could keep a stable switch-on at the 57 g excitation acceleration and 38 V bias voltage. As wide as 52% adjustment range of the acceleration threshold was obtained when the applied bias voltage was from 38 V to 44 V. The tested relationship between the bias voltage and the external acceleration was very consistent with the simulated relationship. [2019-0038]

Recent Advancements in Inertial Micro-Switches

Inertial micro-switches have great potential in the applications of acceleration sensing, due to the integrated advantages of a small size, high integration level, and low or even no power consumption. This paper presents an overview of the recent advancements made in research on the sensitive direction, threshold acceleration, contact effect, and threshold accuracy of inertial micro-switches. The reviewed switches were categorized according to the performance parameters, including multi-directional switches, multi-threshold switches, persistent closed switches, flexible-electrode switches, and low-g high-threshold-accuracy switches. The current challenges and prospects are also discussed.

The Elastic Contact and Stability Analysis of an Inertial Micro-Switch with a Spring Stationary Electrode.

A mechanical trigger inertial micro-switch with spring stationary electrode is proposed and fabricated by surface micromachining. The elastic contact process and stability performance are evaluated through experimental tests performed using a drop hammer. The test results show that the contact time is about 110 μs and 100 μs when the threshold acceleration is 480 g and the overload acceleration is 602 g, respectively. The vibration process of the electrodes is explained through an established physical mode. The elastic contact process is analyzed and discussed by Finite Element Analysis (FEA) simulations, which indicated that the contact time is about 65 μs when the threshold acceleration is 600 g. At the same time, this result also proved that the contact time could be extended effectively by the designed spring stationary electrode. The overload acceleration (800 g) has been applied to the Finite-Element model in ANSYS, the contact process indicated that the proof mass contacted with stationary electrode three times, and there was no bounce phenomenon during contact process, which fully proved that the stable contact process can be realized at high acceleration owing to the designed elastic stationary electrode.

A 5 g Inertial Micro-Switch with Enhanced Threshold Accuracy Using Squeeze-Film Damping.

Our previous report based on a 10 g (gravity) silicon-based inertial micro-switch showed that the contact effect between the two electrodes can be improved by squeeze-film damping. As an extended study toward its potential applications, the switch with a large proof mass suspended by four flexible serpentine springs was redesigned to achieve 5 g threshold value and enhanced threshold accuracy. The impact of the squeeze-film damping on the threshold value was theoretically studied. The theoretical results show that the threshold variation from the designed value due to fabrication errors can be reduced by optimizing the device thickness (the thickness of the proof mass and springs) and then establishing a tradeoff between the damping and elastic forces, thus improving the threshold accuracy. The design strategy was verified by FEM (finite-element-method) simulation and an experimental test. The simulation results show that the maximum threshold deviation was only 0.15 g, when the device thickness variation range was 16–24 μm, which is an adequately wide latitude for the current bulk silicon micromachining technology. The measured threshold values were 4.9–5.8 g and the device thicknesses were 18.2–22.5 μm, agreeing well with the simulation results. The measured contact time was 50 μs which is also in good agreement with our previous work.

Design and characterization of an inertial microswitch with synchronous follow-up flexible compliant electrodes capable of extending contact duration

An inertial microswitch with synchronous follow-up compliant electrodes for extending the contact duration is proposed in this paper. A flexible movable electrode and a stationary electrode in the double-stair and spring-shape structures are used for not only extending contact duration but also reducing the impact bounces. The simulated contact time can reach 350 μs under 500 g applied acceleration, which indicates there is a better contact effect than that reported elsewhere. The fabricated inertial microswitch based on surface micromachining technology was characterized by the dropping hammer system. No contact bouncing behavior can be observed under the acceleration amplitude ∼466 g and the test contact duration can reach 390 μs, longer than the microwitch with only one flexible electrode. The testing comparison of the microswitches with and without constraint structure indicates that the contact-bouncing behavior is easier to happen if without constraint structure, which indicates that the designed constraint structure can restrain the vibration of the proof mass in z-off-axis sensitive direction and effectively improve the stability of the device. The test results have an agreement with the simulated ones.

Shock-Resistibility of MEMS-Based Inertial Microswitch under Reverse Directional Ultra-High g Acceleration for IoT Applications

This paper presents a novel MEMS-based inertial microswitch design with multi-directional compact constraint structures for improving the shock-resistibility. Its shock-resistibility in the reverse-sensitive direction to ultra-high g acceleration (~hunderds of thousands) is simulated and analyzed. The dynamic response process indicates that in the designed inertial microswitch the proof mass weight G, the whole system’s stiffness k and the gap x2 between the proof mass and reverse constraint blocks have significant effect on the shock-resistibility. The MEMS inertial microswitch micro-fabricated by surface micromachining has been evaluated using the drop hammer test. The maximum allowable reverse acceleration, which does not cause the spurious trigger, is defined as the reverse acceleration threshold (athr). Test results show that athr increases with the decrease of the gap x2, and the proposed microswitch tends to have a better shock-resistibility under smaller gap. The measured responses of the microswitches with and without constraint structure indicates that the device without constraint structure is prone to spurious trigger, while the designed constraint structures can effectively improve the shock-resistibility. In this paper, the method for improving the shock-resistibility and reducing the spurious trigger has been discussed.

Design and Optimization of a Stationary Electrode in a Vertically-Driven MEMS Inertial Switch for Extending Contact Duration.

A novel micro-electro-mechanical systems (MEMS) inertial microswitch with a flexible contact-enhanced structure to extend the contact duration has been proposed in the present work. In order to investigate the stiffness k of the stationary electrodes, the stationary electrodes with different shapes, thickness h, width b, and length l were designed, analyzed, and simulated using ANSYS software. Both the analytical and the simulated results indicate that the stiffness k increases with thickness h and width b, while decreasing with an increase of length l, and it is related to the shape. The inertial micro-switches with different kinds of stationary electrodes were simulated using ANSYS software and fabricated using surface micromachining technology. The dynamic simulation indicates that the contact time will decrease with the increase of thickness h and width b, but increase with the length l, and it is related to the shape. As a result, the contact time decreases with the stiffness k of the stationary electrode. Furthermore, the simulated results reveal that the stiffness k changes more rapidly with h and l compared to b. However, overlarge dimension of the whole microswitch is contradicted with small footprint area expectation in the structure design. Therefore, it is unreasonable to extend the contact duration by increasing the length l excessively. Thus, the best and most convenient way to prolong the contact time is to reduce the thickness h of the stationary electrode while keeping the plane geometric structure of the inertial micro-switch unchanged. Finally, the fabricated micro-switches with different shapes of stationary electrodes have been evaluated by a standard dropping hammer system. The test maximum contact time under 288 g acceleration can reach 125 µs. It is shown that the test results are in accordance with the simulated results. The conclusions obtained in this work can provide guidance for the future design and fabrication of inertial microswitches.

A Low-G Silicon Inertial Micro-Switch with Enhanced Contact Effect Using Squeeze-Film Damping

Contact time is one of the most important properties for inertial micro-switches. However, it is usually less than 20 μs for the switch with rigid electrode, which is difficult for the external circuit to recognize. This issue is traditionally addressed by designing the switch with a keep-close function or flexible electrode. However, the switch with keep-close function requires an additional operation to re-open itself, causing inconvenience for some applications wherein repeated monitoring is needed. The switch with a flexible electrode is usually fabricated by electroplating technology, and it is difficult to realize low-g switches (<50 g) due to inherent fabrication errors. This paper reports a contact enhancement using squeeze-film damping effect for low-g switches. A vertically driven switch with large proof mass and flexible springs was designed based on silicon micromachining, in order to achieve a damping ratio of 2 and a threshold value of 10 g. The proposed contact enhancement was investigated by theoretical and experimental studies. The results show that the damping effect can not only prolong the contact time for the dynamic acceleration load, but also reduce the contact bounce for the quasi-static acceleration load. The contact time under dynamic and quasi-static loads was 40 μs and 570 μs, respectively.

Simulation Study of Inertial Micro-Switch as Influenced by Squeeze-Film Damping and Applied Acceleration Load.

Squeeze-film damping and acceleration load are two major issues in the design of inertial micro-switches. In order to deeply and systematically study these two issues, this paper proposes a typical vertically-driven inertial micro-switch, wherein the air and electrode gaps were chosen to design the required damping ratio and threshold value, respectively. The switch was modeled by ANSYS Workbench, and the simulation program was optimized for computational accuracy and speed. Transient analysis was employed to investigate the relationship between the damping ratio, acceleration load, and the natural frequency, and the dynamic properties (including contact bounce, contact time, response time, and threshold acceleration) of the switch. The results can be used as a guide in the design of inertial micro-switches to meet various application requirements. For example, increasing the damping ratio can prolong the contact time of the switch activated by short acceleration duration or reduce the contact bounce of the switch activated by long acceleration duration; the threshold value is immune to variations in the damping effect and acceleration duration when the switch is quasi-statically operated; the anti-jamming capability of the switch can be improved by designing the sensing frequency of the switch to be higher than the acceleration duration but much lower than the other order frequencies of the switch.

A surface-micromachining-based inertial micro-switch with compliant cantilever beam as movable electrode for enduring high shock and prolonging contact time

A novel laterally-driven inertial micro-switch with two L-shaped elastic cantilever beams as the movable electrode, which is attached to the proof mass, is proposed in this paper. The advantage of this design is that the contact time of the inertial micro-switch can be prolonged. Meanwhile, the micro-switch can withstand a higher shock than the traditional designs whose cantilever beams are attached to the fixed electrode. The designed inertial micro-switch was simulated and optimized with ANSYS software and fabricated on a quartz substrate by surface micromachining technology. The simulated result demonstrates that the threshold acceleration (aths) under stable switch-on state is about 288g and the contact time is about 198μs when the pulse width of acceleration loads is 1ms. At the same time, it indicates that the threshold acceleration, the response time and the contact time of designed micro-switch all increase with the pulse width of acceleration loads. The simulation of impact process in non-sensitive direction shows that the introduced constraint sleeve structure in the novel inertial micro-switch can lower the off-axis sensitivity. The fabricated micro-switch prototype has been tested by a standard dropping hammer system under shock accelerations with various amplitudes and pulse widths. The experimental measurements show that the contact time is about 150μs when the threshold acceleration is about 288g. It also indicates that the response time and the contact time both increase with the pulse width, which is consistent with the simulation ones.

Fabrication of a silicon based vertical sensitive low-g inertial micro-switch for linear acceleration sensing

Most of the MEMS inertial switches developed in recent years are intended for shock and impact sensing with a threshold value above 40 g. These switches were designed as lateral sensitive and were fabricated using either electroplating or silicon micromachining technology. Considering on the other hand the low-g micro-switch (threshold value <10 g), usually consists of a high volume proof mass and a low stiffness spring, were rarely reported because these switches were less practical to be fabricated with lateral sensitive structure design. In this paper, we report on a silicon based vertical sensitive low-g inertial switch designed for linear acceleration sensing. The inertial switch consists of a cylinder shaped proof mass, suspended by circular shaped spiral spring. The fabrication process is based on a customized symmetrical double-buried layer SOI wafer with standard silicon micromachining. The centrifugal experiment results show that the threshold value is around 5.5 g which is close to the designed value.

Design and fabrication of a laterally-driven inertial micro-switch with multi-directional constraint structures for lowering off-axis sensitivity

This paper proposes a novel laterally-driven inertial micro-switch with multi-directional compact constraint structures for lowering off-axis sensitivity and improving shock-resistibility. The design utilizes constraint sleeve and reverse stop-block structures to limit too much displacement of proof mass in the micro-switch and avoid damage to the device under a high shock load. The dynamic contact simulation indicates that the designed inertial micro-switch can limit the movement of proof mass and lower the off-axis sensitivity by constraint sleeve and reverse block structures. The first collision response time between proof mass and constraint structures in the z-direction has been analyzed theoretically and simulated, which have indicated that the collision response time mainly depends on geometric parameters, applied shock acceleration amplitude and the inherent frequency of the mass-spring inertial system. Simulated dynamic response curves under applied reverse directional shock accelerations show the proposed inertial micro-switch also has a good shock-resistibility. The inertial micro-switch fabricated by surface micromachining technology has been evaluated using a drop hammer system. The test results indicate that spurious triggering is more likely to occur in the inertial micro-switch without constraint structures, and the designed constraint structures can effectively lower the off-axis sensitivity and improve the shock-resistibility.

Fabrication and Characterization of a Low-g Inertial Microswitch With Flexible Contact Point and Limit-Block Constraints

A novel contact-enhanced low-g inertial microswitch has been proposed and fabricated by surface micromachining technology in this paper. A novel segmental circle spring has been designed in the low-g inertial switch, which can decrease its stiffness compared with traditional semicircle spring. The dynamic response of the microswitch is simulated by ANSYS software, which has estimated its threshold acceleration and holding time. The vibrations of proof mass under the applied overload acceleration in the sensitive direction and the opposite direction are both simulated and analyzed, which demonstrates that the rebound of proof mass can be restrained effectively by the introduced limit blocks. The fabricated prototype has been tested by a dropping hammer system. The test results indicate that the threshold acceleration of fabricated inertial switch is ∼25g with holding time ∼650 μs. The overload acceleration of 80g, 120g have been applied on the fabricated prototype, and the test results indicate that the spurious trigger have been eliminated due to the limit blocks, which is in agreement with the simulation results. The acceleration of 100g is applied to the tested inertial microswitch with and without limit block in the opposite sensitive directions, respectively. The test result verifies the function of limit blocks.

Simulation and characterization of a laterally-driven inertial micro-switch

A laterally-driven inertial micro-switch was designed and fabricated using surface micromachining technology. The dynamic response process was simulated by ANSYS software, which revealed the vibration process of movable electrode when the proof mass is shocked by acceleration in sensitive direction. The test results of fabricated inertial micro-switches with and without anti-shock beams indicated that the contact process of micro-switch with anti-shock beams is more reliable than the one without anti-shock beams. The test results indicated that three contact signals had been observed in the contact process of the inertial switch without anti-shock beams, and only one contact signal in the inertial switch with anti-shock beams, which demonstrated that the anti-shock beams can effectively constrain the vibration in non-sensitive direction.

A Wireless MEMS Inertial Switch for Measuring Both Threshold Triggering Acceleration and Response Time

Response time is one of the core attributes for threshold acceleration switches for determining the impact severity. Different from single function inertial switches for only converting circuit states, a wireless inertial microswitch incorporating the bistable flexible mechanism was designed and fabricated using multilayered microelectroforming technology, which can be used for remote detection of both the threshold acceleration and the corresponding response time in severe environments. The threshold snap-through characteristic of the nonlinear bistable mechanism has been introduced to achieve the threshold acceleration sensing capability. The switch mainly consists of one wireless module, one proof mass supported by two pairs of ultralong V-shaped slender beams with the dimension of 28.0~μ m × 25.0 μm × 5150.0 μm, and two contact points for recording triggering times through the high speed sending and receiving wireless module. Then, an accurate design model for analyzing the threshold acceleration and the dynamic response time was established. The 20 repeated experimental results are in good agreement under the same triggering threshold acceleration of 32.38 g, in which, the response time with the traveling distance of 530.0~μm is 179.80 ± 0.20 ms.

Simulation, fabrication and characterization of an all-metal contact-enhanced triaxial inertial microswitch with low axial disturbance

An all-metal inertial microswitch that is sensitive to three axial accelerations (+x, +y and +z) is fabricated by low-temperature photoresist modeled metal-electroplating technology. The inertial switch consists of four main parts: a quartz wafer with anti-stiction strips as the substrate; a proof mass suspended by conjoined serpentine springs as the movable electrode; two L-shaped flexible cantilevers and a multi-hole crossbeam as horizontal and vertical fixed electrodes, respectively; two anchors located in the middle of proof mass as limit blocks. ANSYS software is used to simulate the dynamic contact process in the microswitch, and the simulation results reveal that the flexible fixed electrode can prolong the contact time and eliminate the rebound during the contact process. The axial disturbance among different sensitive directions has been discussed by dynamic simulation. The modal analysis, crosstalk between horizontal and vertical directions, cross-axis sensitivity, and the disturbance under overload shock along the reverse sensitive direction are also simulated and discussed. The suspension and gap in the device structure can be precisely controlled utilizing the photoresist modeled metal-electroplating technology to reduce the axial disturbance effectively. Finally, the prototype is fabricated successfully and tested by dropping hammer system. It is shown that the test threshold acceleration is 255–260g in horizontal directions (+x and +y), ∼75g in vertical direction. The contact time of the switch with elastic contact point is ∼60μs in horizontal direction and ∼80μs in vertical direction. The crosstalk between horizontal and vertical direction, cross-axis and overload disturbance have been also demonstrated by test results, which indicate the axial disturbance is low in the present inertial switch.

Tri‐axial all‐metal inertial microswitch with compliant stationary electrodes to prolong contact time

Published in Micro & Nano Letters; Received on 8th November 2013; Revised on 3rd June 2014; Accepted on 7th July 2014A tri-axial all-metal inertial microswitch with compliant stationary electrodes for prolonging the contact time is proposed and fabricated.A half-moon-shaped cantilever structure is designed and utilised as the compliant stationary electrode in the +x- and +y-directions. It cansufficiently deform and realise a flexible contact in horizontal directions. Similarly, the designed multi-hole crossbeam located in the +z-direction also decreases its own stiffness that can reduce the bounces and prolong the contact time in the vertical direction. These dynamiccontact processes of the microswitch are simulated and analysed by the finite element method. The contact time in the +x-,+y- and +z-directions of the fabricated inertial microswitch have been tested by a dropping shock experiment, which has good agreement with thesimulated ones. The crosstalk performance has been characterised by a shock test, which indicates that disturbance between the horizontaland vertical directions has been restrained.1. Introduction: The inertial microswitch is widely used in manyindustrial applications such as accessories, toys, healthmonitoring and automobiles [1–4]. Especially in recent years,internet of things has grown rapidly, so the inertial microswitchas a passive device has again attracted interest. It can be used todetect the vibratory shock level and then to send thecorresponding overload alarm signal in wireless sensor networksystems [5, 6]. Although many inertial microswitches have beenreported [7–10], most of them are still single-axis sensing andonly respond to unidirectional shock. To detect vibration shocksfrom different directions, several single-axis switches have to beassembled into an array, which inevitably leads to installationerror, centric deviation and expensive cost. In addition, the rigidcontact between the electrodes always leads to a very shortcontact time and the bouncing phenomenon, which leads to greatdifficulty in the following signal processing in practicalapplications. In the present work, an all-metal inertialmicroswitch with flexible compliant stationary electrodes wasdeveloped for prolonging the contact time. Compared withsilicon, the switch fabricated with metal (e.g. Ni) could suffer ahigher impact because of lower brittleness. Furthermore, thisinertial switch can detect the vibration shocks in the +x-,+y-and +z-directions using a single sensitive mass, which greatlyimproves the integration and lowers the cost.2. Design and simulation: When acceleration is applied to amass-spring inertial system in the sensing direction, themathematical model of the designed microswitch can bedescribed as follows:mx