<title>Reflectively tuned x-band capacitive switch</title>

Abstract

This Paper presents the design, simulation and fabrication of a single-bridge capacitive switch and a double-bridge reflectively tuned capacitive switch for X-band applications. These switches possess low loss, high isolation and low pull-down voltage. The switching element consists of a thin metallic membrane suspended over the center conductor and fixed at both ends to the ground conductors of a Coplanar Waveguide (CPW) line. The switches have two states, actuated and unactuated, depending on the applied bias voltage between the metallic membrane and the bottom electrode. The serpentine folded hinges are used to get higher inductance so as to make the resonant frequency to be at X-band. The single-bridge switch achieves over 27 dB isolation with an insertion loss of 0.2 ± 0.1 dB at X-band. The largest isolation, 37 dB is obtained at 10.5 GHz. The double-bridge reflectively tuned switch contains two single metal membrane separated by a short length of high-impedance transmission line. The reflectively tuned switch provides an isolation of 51 dB at 10 GHz with an insertion loss of 0.5 dB. At X-band frequency range, its isolation exceeds 42 dB with an insertion loss of 0.5 ± 0.1 dB. Besides, the serpentine folded hinges provide a very low spring constant resulting in 3.6-volt pull-in voltage. The static mechanical model predicts the effective stiffness constant and the pull-in voltage. Deformation of the bridge and its contact behaviour with the dielectric layer are also precisely analysed using Finite Element Method. Finally this paper discusses the fabrication of the RF capacitive switches, which combines bulk- micromachining and surface-micromachining techniques. The thermal oxide layer (buffer layer) is patterned to be discontinuous so as to decrease the attenuation loss.