HAIT Journal of Science and Engineering Volume x, Issue x, pp. xxx-xxx © 2006 Holon Institute of Technology |
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Radio-frequency micro electro mechanical system based digital variable capacitorsAnuj Kumar |
Advanced Instrumentation Lab., Instrumentation Design
Development Centre, Indian Institute of Technology Delhi, New Delhi, India e-mail: anuj_chauhan97@yahoo.co.in Received 2 June 2006, accepted 3 August 2006 |
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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. Wide bands 1GHz to 100GHz power system due to self pull-in due to RF signal line. |
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