Development of W-Band Low-Loss MEMS Switches

We have developed low-loss MEMS switches for 70-120 GHz applications. The MEMS switches are integrated on a high-resistivity silicon substrate, and are built in a coplanar-waveguide configuration. The MEMS switches are fabricated using a thin gold bridge, suspended 1.5-2.5 um above the center conductor of the cpw line. The MEMS bridge is 250 um long with a width of 2540 um, depending in the height of the bridge. The inductance of the bridge is around 10 pH, and the MEMS switch is designed to resonate in the down-state position at 70-80 GHz by choosing the down-state capacitance to be only 500 fF. This results in a high isolation at W-band frequencies since, at resonance, the isolation is given by the series resistance of the switch and not by the down-state capacitance. Typical performance, to be shown at the conference, is an isolation better than 20 dB with an insertion loss of less than 0.1 dB at 80-100 GHz. We have also developed two MEMS switches configured in a Pi-match circuit. In this case, the up-state reflection coefficient is less than —20 dB over the entire W-band frequency range, and the down-state isolation is better than —30 dB over 80-100 GHz. The Pi-match circuit is quite small (less than 100 um) and therefore, the insertion loss in the up-state position is only 0.2 dB. This represents state-of-the-art performance at W-band frequencies for MEMS switches, and is much better than PIN diode or FET switches. The application areas of MEMS switches is in low-loss phase shifters, low-loss tunable matching networks at the input and output of multipliers, and low loss tunable filters for receiver applications.