MEMS based digital variable capacitors with a high-k dielectric insulator

Luo, J.K., Lin, M., Fu, Y.Q., Wang, L., Flewitt, A.J., Spearing, S.M., Fleck, N.A. and Milne, W.I. (2006) MEMS based digital variable capacitors with a high-k dielectric insulator. Sensors and Actuators A: Physical, 132 (1), 139-146. (doi:10.1016/j.sna.2006.04.025). (Submitted)

Abstract

A novel MEMS based digital variable capacitor was designed and fabricated. The device consists of a multi-cantilever (or bridge) with variable length, suspended over a bottom electrode. By applying a voltage between the electrodes, the electrostatic force pulls the beams in one-by-one, realizing a digital increase in capacitance. A high-k dielectric HfO2 is also introduced to increase the capacitance value and tuning range. These devices were fabricated by a four-mask process, and electrical tests have confirmed the stepwise increase of the capacitance with bias. However it was found that it is difficult to pull-in more than 10 cantilevers and most of the cantilevers remained on the substrate when the bias is off. Charge injection from the pulled-in electrode into the insulator increases the pull-in voltage drastically, and prevents pulling-in more cantilevers. Trapped charges in the insulator produce an electrostatic force and keep the cantilever stuck on the substrate

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Contributors

Author: S.M. Spearing

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