Low voltage, high-Q SOI MEMS varactors for RF applications

A micro electromechanical tunable capacitor with a low control voltage, a wide tuning range and high electrical quality factor is presented with detailed characterizations. A 50/spl mu/m thick single-crystalline silicon layer was etched using deep reactive ion etching (DRIE) for obtaining high-aspect ratio (>20) parallel comb-drive structures with vertical sidewalls. Consisting of only one lithographic mask step, the process sequence can be completed in a short time. Having 1 pF of nominal capacitance, the device offers an electrical quality factor of 100 at 100MHz and a self resonance at 4.08 GHz, enabling the usage as a passive component in the RF band. The mechanical settling time of the varactor is measured to be 200 /spl mu/s in ambient air. For control voltages ranging from 1.5V to 5V, tuning ratios of 2:1, 1.7:1 and 1.5:1 are obtained from different capacitor designs. It was found that the device is a suitable passive component to be used in band-pass filtering, voltage controlled oscillator or impedance matching applications on the very high frequency(VHF) and ultra high frequency (UHF) bands.