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Open Access Publications from the University of California

Robust metal contact and capacitive mini-MEMS switches

  • Author(s): Sedaghat Pisheh, Hojr
  • et al.
Abstract

This thesis presents the design, fabrication and measurements of a new metal-contact RF MEMS switch with low sensitivity to stress gradients and temperature variations. The switch is based on a circular geometry with arc type springs, and results in high contact force, fast switching time, and excellent microwave performance of up to > 40 GHz. This thesis also presents the design, fabrication and measurements of a new metal-contact RF MEMS single-pole double-throw (SPDT) switch with low sensitivity to stress gradients. The switch is based on a circular geometry with arc type springs, and results in high contact force, fast switching time, and excellent microwave performance of up to > 30 GHz. To our knowledge, this is the smallest high-performance SPDT switch to-date (0.04 mm²). Furthermore, the design, fabrication and measurements of a novel metal-contact RF MEMS switch with variable spring constant and high contact and release forces are demonstrated. The spring constant of the switch dramatically increases when the applied voltage is larger than the threshold voltage (Vt), defined as the voltage obtained when the tip touches a dielectric block. This design shows a total contact force and restoring force of 0.6 - 1.1 mN and a 0.5 mN, respectively, for an actuation voltage of 75-90 V. The measured switching time is < 10 [mu]s. The switch is an excellent candidate for high performance microwave applications requiring high power handling and a large contact force. Two generations of miniature RF MEMS switched capacitors with pull-down and pull-up electrodes for increased capacitance ratio and power handling are also presented. In the first generation, a 2x2 switch array is designed with three operation states : free-state, down-state and up state (switch attached to the pull-up electrode), with capacitances of 115 fF, 370 fF and 64 fF, respectively. The pull-up electrode increases the capacitance ratio from 3.2 (standard operation with no pull-up electrode) to 5.8. The pull-up electrode also solves the problem of RF self actuation and the 2x2 switch was tested up to 4 W at 5 GHz (pull-up electrode engaged) with no change in the measured S- parameters. In the second generation, a 2x2 switch array is designed also with three operation states : free-state, down-state and up state (switch attached to the pull-up electrode), with capacitances of 130 fF, 520 fF and 70 fF, respectively. The pull-up electrode increases the capacitance ratio from 4 (standard operation with no pull- up electrode) to 7.5. The pull-up electrode also solves the problem of RF self actuation and the 2x2 switch was tested up to 17 W at 10 GHz (pull-up electrode engaged) with no change in the measured S-parameters. The measured switching time from free-state to up-state is less than 1 μs and from free-state to down-state is less than 1.5 [mu]s. The switch is very stable in different temperature conditions between 25 to 85°C

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