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

Abstract

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.

Research Status and Development Trend of MEMS Switches: A Review

“…The inertial switch was fabricated by UV-LIGA, in which the method of width compensation was adopted to improve the fabrication accuracy. The result showed that the contact time can reach 260 μs when the designed switch is triggered by 32 g. At the same time, Xu et al [87] proposed a vertically driven MEMS inertial switch with a flexible structure. The designed switch can achieve 125 μs contact time at 288 g acceleration.…”

“…The result showed that the contact time can reach 260 μs when the designed switch is triggered by 32 g . At the same time, Xu et al [ 87 ] proposed a vertically driven MEMS inertial switch with a flexible structure. The designed switch can achieve 125 μs contact time at 288 g acceleration.…”

Multi-Threshold Inertial Switch With Acceleration Direction Detection Capability

“…The majority of the reported inertial switches have a single acceleration threshold, so that they only provide ON-OFF information [16][17][18][19][20][21][22]. They produce ON signal if the acceleration is higher than the predesignated threshold level and OFF signal otherwise.…”

Multi-Threshold Inertial Switch for Quantitative Acceleration Measurements

“…MEMS inertial switches are widely applied in many fields, such as military, automobiles, industrial transportation, handled devices, safety, and geriatric healthcare systems due to the advantages of miniaturization, low cost, large volume production, zero power consumption at a normal state, and resistivity to electromagnetic noise [7][8][9][10][11][12][13][14][15][16]. When the inertial switch is accelerated above the threshold value along the sensing direction, the movable electrode moves toward the stationary electrode touching it, which closes an external circuit [17][18][19][20][21][22][23][24].…”

“…A two bits accelerometer has been successfully fabricated and demonstrated in the 0-1g range. Most of the reported inertial switches are inertial switches with one threshold level [9,[11][12][13] and many of these devices are not resettable [32][33][34].…”