125. A STRESS-TOLERANT TEMPERATURE-STABLE RF MEMS SWITCHED CAPACITOR

Department: Electrical & Computer Engineering
Research Institute Affiliation: Center for Wireless Communications (CWC)
Faculty Advisor(s): Gabriel Rebeiz

Primary Student
Name: Isak C Reines
Email: ireines@ucsd.edu
Phone: 858-822-5940
Grad Year: 2010

Abstract
We present the design, fabrication, and measurement of an RF MEMS (Radio Frequency Micro-Electromechanical System) switched capacitor that exhibits reduced sensitivity to residual stress and temperature. Commonly used rectangular fixed-fixed beam RF MEMS switches are sensitive to residual bi-axial stress which limits the operating temperature, leads to excessively varying actuation voltage and up-state capacitance versus temperature, and reduces the power handling and device uniformity. The device performance varies with temperature because a large portion of the spring constant is dependent on the residual stress, which changes due to the coefficient of thermal expansion mismatch between the substrate and bridge. The device presented here is based on a circularly symmetric geometry with orthogonal arc-type springs placed between the anchors and suspended beam. This design compensates for the effects of the residual biaxial stress in the beam, resulting in a pull-in voltage slope versus temperature of only -50 mV/ ºC from -5 ºC to 95 ºC. Reducing the device sensitivity to residual stress improves the performance uniformity on a wafer-scale, and from wafer-to-wafer lots. This novel switch design can be used to create compact device arrays for high-value capacitances making it ideal for VHF and UHF tunable filters and reconfigurable matching networks.

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