High‐Q LIGA‐MEMS vertical cantilever variable capacitors for upper microwave frequencies

Abstract

Simulation results for four MEMS variable capacitors suitable for fabrication using the LIGA process are presented. A Q‐factor as high as 435.6 was obtained using a copper‐device layer. The capacitor with a nominal capacitance of 0.24 pF has a self‐resonant frequency of 33.7 GHz, making it suitable for operation up to frequencies of approximately 18 GHz. Using a “pull‐away” actuation design, a tuning ratio of 1.43:1 was obtained with tuning voltages as low as 6.1 V. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 42: 507–511, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20352

Fabrication of RF MEMS variable capacitors by deep X-ray lithography and electroplating

“…As the cantilever is the only structure that is not fixed to the substrate, it can electrostatically be deflected when applying a bias voltage between the actuator electrode and the grounded cantilever. The electrostatic force between the two deflects the cantilever towards the actuator electrode, thus increasing the gap d and inversely proportionally decreasing the capacitance C. Figure 2 depicts a cantilever beam and the simulated cantilever deflection (Haluzan 2004). The deflection has been magnified by a factor of 100 so it can be observed more easily.…”

“…If the cantilever is actuated towards the actuator electrode only, an increase in tuning range over a two-plate capacitor can be achieved only if the actuator gap is made larger than the capacitance gap (Haluzan 2004). This increase in tuning range comes with an increase in tuning voltage, but RF and control signals can remain separate.…”