Low Damping Differential-Capacitive Sensing Comb
Soon Chang Yeon, Yong Hyup Kim
Department of Aerospace Engineering, College of Engineering, Seoul National University, KR
Keywords: squeezed damping, comb, quality factor, high aspect ratio
In the present study, a specially designed sensing comb is proposed for low damping and high capacitance. Many researchers have proposed high aspect ratio single crystal silicon structure to improve sensitivity in capacitive sensing and laterally oscillating MEMS devices. However, high aspect ratio structures usually result in high damping force.
Major factors of squeezed film damping between rectangular shape stator and rotor are distance, width(W) and length(L) of rotor and stator. Therefore, the dimensions of stator and rotor are very important in damping characteristics. The damping force is proportional to the longer dimension and the cube of the shorter dimensions of comb area. In general high aspect ratio sensing comb finger, the length is longer than the height. It means that the damping force is proportional to the cube of the height. Therefore, dimension of the height is restricted by the damping force.
To reduce the damping force in high aspect ratio structure, the stator is designed in a separate manner. If the length of stator is designed smaller than the height, the squeezed damping force is proportional to the cube of the length of the stator. Then, the height of structure is not restricted by the damping force with little decrease in the capacitance.
Numerical analysis has been performed as shown in Fig. 1, 2. and the 50m height specimens are fabricated using silicon-glass eutectic bonding and Deep RIE with three masks. Quality factor and capacitance of the sensing comb will be measured.
NSTI Nanotech 2003 Conference Technical Program Abstract