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This paper reports on novel electrostatically actuated dc-to-RF metal-contact microelectromechanical systems (MEMS) switches, featuring a minimum transmission line discontinuity since the whole switch mechanism is completely embedded inside the signal line of a low-loss 3-D micromachined coplanar waveguide. Furthermore, the switches are based on a multistable interlocking mechanism resulting in static zero-power consumption, i.e., both the onstate and the offstate are maintained without applying external actuation energy. Additionally, the switches provide with active opening capability, potentially improving the switch reliability, and enabling the usage of soft low-resistivity contact materials. Both two-port single-pole-single-throw (SPST) switches featuring mechanical bistability and three-port single-pole-double-throw (SPDT) T-junction switches with four mechanically stable states are presented. The switches, together with the transmission lines, are fabricated in a single photolithography process. The loss created by the discontinuity of the switch mechanism alone is 0.08 dB at 20 GHz. Including a 500 m long transmission line with less than 0.4 dB/mm loss up to 20 GHz, the total insertion loss of the two-port devices is 0.15 and 0.3 dB at 2 and 20 GHz, and the isolation is 45 and 25 dB at 2 and 20 GHz. The three-port switches, including their T-junction transmission line, have an insertion loss of 0.31 and 0.68 dB, and an isolation of 43 and 22 dB, at 1 and 10 GHz, respectively. Actuation voltages are 23-39 V for the two-port switches and 39-89 V for the three-port switches. The microwave propagation in the micromachined transmission line and the influence of the different switch designs were analyzed by finite-element method (FEM) simulations of electromagnetic energy and volume current distributions, proving the design advantages of the proposed concept.
Date of Publication: July 2010