MEMS Switches Technique For Acceleration Detection

Acceleration switches are inertial sensors triggered and closed by an acceleration exceeding the threshold value. Due to their merits of low power consumption, low cost and high shock resistance, switches have a wide application in inertial monitoring system such as munition fusing, airbag system, etc.A novel acceleration switch with threshold adjusting and 'on'-state latching functions is developed. By using electrostatic force combined with the dynamic inertial force, the threshold acceleration level of the switch can be adjusted by the switch voltage. This function can also compensate for the threshold inaccuracy from fabrication tolerance. Besides, a new self-latching function is introduced by the pull-in effect, to hold the switch at 'ON' state even the acceleration signal vanished. Theoretical analysis is carried out for step shocking response, with the response frequency bandwidth and response time taken into consideration.A shock-acceleration switch with threshold levels of 1 000-5 000g is designed, simulated with CoventorWare. Theoretical results of response time and acceleration tolerance are less than 80us and 10g respectively.An array of the threshold switch is fabricated using a substrate transfered technology. During the process, an electrical equivalent model of SOI-glass bonding physics and a modified bonding technique to increase the yield are developed.The threshold adjusting and 'on' state latching function of the shocking switch are verified in a dropping hammer experiment test. The test date generally has an agreement with the simulated results.Moreover a mechanical switch of low threshold value and cost is designed using a simplified process.