CMU MEMS Laboratory Publication Abstract


in Sensors and Actuators A: Physical, Volume 95, Issue 2-3, pp. 212-221, January 2002.
Vertical Comb-Finger Capacitive Actuation and Sensing for CMOS-MEMS
H. Xie and G. Fedder
A new method for out-of-plane (vertical) electrostatic actuation and capacitive displacement-sensing that utilizes sidewall capacitance change of multiconductor comb fingers is analyzed and experimentally verified. Combining the inherited in-plane (lateral) actuation and sensing capacities of comb fingers, three-dimensional actuation/sensing can be realized. A maskless post-CMOS micromachining process is employed and the fabrication is compatible with standard CMOS processes. Applications include an three-axis microstage, a z-axis accelerometer and a lateral-axis gyroscope that use the proposed vertical comb-finger actuation/sensing method. The measured maximum vertical displacement of the microstage is 3.5µm with a resonant frequency of 6.17 kHz. Measured sensitivity of the z-axis accelerometer is 0.5 mV/g with less than 40 dB cross-axis sensitivity, noise floor 6mg/Hz, and linear range from -27 to 27 g. The lateral-axis gyroscope design uses integrated comb drives for out-of-plane actuation, and is motivated by the desire to integrate three-axis gyroscopes on a single chip. The packaged gyroscope operates at atmospheric pressure with a sensitivity of 0.12 mV/º/s and the resonant frequency of the drive mode is thermomechanically tuned between 4.2-5.1 kHz. Resonant frequency matching between the drive and sense modes is realized by integrating a polysilicon heater inside the spring beams.
© 2002 Elsevier. All rights reserved.
Full paper not available from outside CMU

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