Micromachined variable capacitors with wide tuning range

In this paper, ultra-thin silicon wafers, SU-8 bonding and deep reactive ion etching (DRIE) technology have been combined for the fabrication of folded spring, dual electrostatic drive, vertical plate variable capacitor devices with displacement limiting bumpers. The SU-8 bonding replaces the use of expensive SOI wafers and enables a more flexible design. The thick SU-8 also decreases the parasitic substrate capacitance. Due to the presence of the bumpers, our variable capacitor with parallel plate drive electrodes has two tuning voltage regimes: first a parabolic region that achieves roughly a 290% tuning range, then a linear region that achieves an additional 310%, making the total tuning range about 600%. Our variable capacitor with comb drive electrodes has a parabolic region that achieves roughly a 205% tuning range, then a linear region that achieves an additional 37%, making its total tuning range about 242%. The variable capacitors have Q factors around 100 at 1 MHz owing to the use of silicon electrodes other than lower resistivity metal. (C) 2003 Elsevier Science B.V. All rights reserved.