Vibration sensors with a high bandwidth and low SNR, enhanced with post processing gap reduction

Vibration sensors require a high sensitivity; however the fabrication process is limited by minimum gap size due to design rules. FhG ENAS and X-FAB MEMS Foundry GmbH report on a capacitive MEMS sensor element design, characterization and finally fabrication with the Open Platform technology XMB10 with additional electrostatic actuators for the post process gap adjustment. For the first time, the post process gap reduction process developed at FhG ENAS was performed on capped chips and with an industrial fabrication technology. The fabricated electrode gaps of 4 µm are reduced to 0.7 µm. Thereby, the aspect ratio is increased from 19 to 107. Moreover, the sensitivity of the sensor increases through this post processing gap reduction process by a factor of more than 30 without changing the size of the sensor chip itself.