We report on measurements of the time dependent capacitance of a RF MEMS shunt switch. A high time resolution detection setup is used to determine switching time and motion of the device. From the equation of motion the damping force is extracted. The measured damping force is found to be approximately proportional to the speed over the gap distance to the third power (F D ∝ v/z 3 ), in good agreement with squeeze film damping theory. Measurements at low pressure show underdamped harmonic oscillations in the opening motion and contact bounce effects in the closing motion. Effects of dielectric charging on the C-V curves are discussed. Experimental results are compared with electromechanical and damping simulations.
MEMS tunable capacitors have been fabricated in a thin-film technology for passive integration. Using a dual-gap relaytype design, continuous and reversible capacitance tuning with a tuning ratio up to 17 has been demonstrated, while requiring an actuation voltage of only 20 V. A quality factor of 150 to 500 has been measured in the frequency range of 1 to 6 GHz, making these devices very suitable as building blocks in many RF applications. These are the highest tuning ratio and quality factor reported to date for parallel-plate tunable capacitors.
A closed-form relationship between the insertion loss, the externally applied mechanical shock and the RF signal voltage of a capacitive RF-MEMS shunt switch is derived. It is shown that, based on this relationship, the minimum required mechanical stiffness of the suspended structure can be calculated. This allows determination of the minimum electrostatic switching voltage in a given process flow. The results are illustrated for specifications regarding shock resistance of electronic equipment as set out in MIL-STD-883. Even under the least severe test conditions, the shocks can affect the insertion loss of RF-MEMS switches, and can provoke self-biasing. This paper gives guidelines to avoid such false operation modes. The method can also be extended to yield the sensitivity of RF-MEMS devices to harmonic vibrations.
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