Cryogenic performance of gold-based and niobium-based RF MEMS devices

This paper presents the results of a comprehensive study on the performance of RF MEMS devices at cryogenic temperatures. More than 50 shunt capacitive RF MEMS switches are tested at room temperature (294 K) and liquid nitrogen temperature (77 K). The switches have various supports. The variation of the actuation voltage of each switch at room and cryogenic temperatures is investigated by mechanical simulation. The results show that the type of supports significantly affects the switch actuation voltage. In fact, depending on the shape of the supports the actuation voltage can decrease or increase at cryogenic temperatures. The hypothesis obtained from the analysis of the gold-based RF MEMS devices is confirmed by testing superconducting niobium-based RF MEMS devices, at liquid helium temperature (4 K). The RF performance of a capacitive shunt niobium-based RF MEMS switch and a niobium-based RF MEMS varactor show significant improvement of the insertion loss of the switch and an enormous enhancement of the quality factor of the varactor.