Design of a MEMS Capacitive Comb-drive Micro-accelerometer with Sag Optimization

• Main Authors: B. D. PANT, Lokesh DHAKAR, P. J. GEORGE, S. AHMAD
• Format: Article
• Language: English
• Published: IFSA Publishing, S.L. 2009-09-01
• Series: Sensors & Transducers
• Subjects: Accelerometer; Comb-drive; Capacitive sensing; High aspect ratio; DRIE
• Online Access: http://www.sensorsportal.com/HTML/DIGEST/september_09/P_488.pdf

The current paper presents an optimization study for the designing of a highly sensitive inertial grade capacitive accelerometer based on comb-drive actuation and sensing. The proof mass, suspension system (beams or tethers), stators and rotors have to be realized through an HAR (high aspect ratio) DRIE (deep reactive ion etching) process for which process optimization has already been done at our laboratory. As the proof mass is a bulk micro-machined structure having a mass in milligram range, the optimum positioning of the tethers on the proof mass is important to have minimum sag, necessary to reduce the off-axis sensitivity. The optimization for the positioning of the tethers has been carried out using a commercial software tool ANSYSTM Multiphysics. The accelerometer has been modeled analytically to predict its characteristics. The dependency of sensitivity on the dimensions of the suspension beams (tethers) has also been verified using the above FEM software tool. The present device has been designed to deliver a high sensitivity of 13.6 mV/g/V for low-g applications.