Mechanically tri-stable SPDT metal-contact MEMS switch embedded in 3D transmission line

This paper presents an electrostatically actuated MEMS switch mechanism for a mechanically tri-stable single- pole-double-throw (SPDT) metal-contact switch, which is fully embedded in the signal line of a low-loss 3D-micromachined coplanar-waveguide T-junction. The switch features mechanical tri-stability, i.e. all three stable states of the switch are maintained by an interlocking mechanism without applying external actuation energy. The actuation voltage is only necessary for triggering the transition between the three stable states. In contrast to conventional MEMS switch designs where the switch actuator is built around the transmission line and thus creates a discontinuity in the waveguide, the switch mechanism of the presented design is completely embedded in the signal line of the coplanar waveguide. This, together with a 3D micromachined transmission line design confining the major part of the field lines in the air and not in the substrate, results in very low insertion loss and low reflections. Furthermore, the switches feature active opening which results in very reliable operation of the switches. Single-pole-double-throw metal-contact switches have been fabricated in a very simple, single photolithography mask process, and successfully evaluated from DC to 15 GHz.