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

Yingchun Peng,Zhengguo Shang,Dongling Li,Zhiyu Wen

doi:10.3390/s17020387

Abstract

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.

Highlights

MEMS technology-based inertial switches have great potential for acceleration sensing applications [1,2] due to its miniaturization, high integration level, and low or even no power consumption [3,4]
Since the first inertial micro-switch was reported in 1972 [5], a great number of inertial micro-switches have been developed, and they can be grouped into two categories: persistent switches, wherein the switch was designed with a keep-close function that can keep it closed after the acceleration event is over, and intermittent switches, wherein the switch re-opens after the acceleration dissipates
The switch is designed to be vertically driven to employ the squeeze-film damping effect, since the slid-film damping effect involved by laterally driven switches is so weak that it is usually neglected

Summary

Introduction

MEMS (micro-electro-mechanical system) technology-based inertial switches have great potential for acceleration sensing applications [1,2] due to its miniaturization, high integration level, and low or even no power consumption [3,4]. Since the first inertial micro-switch was reported in 1972 [5], a great number of inertial micro-switches have been developed, and they can be grouped into two categories: persistent switches, wherein the switch was designed with a keep-close function that can keep it closed after the acceleration event is over, and intermittent switches, wherein the switch re-opens after the acceleration dissipates Persistent switches such as the latching switch [6,7,8], the bi-stable switch [9,10], and the micro-fluidic switch [11,12] has an excellent contact effect but usually requires an additional

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