Innovative micromachined microwave switch with very low insertion loss

This work fabricates a novel type of micromachined microwave switch on a semi-insulating GaAs substrate using a microactuator and a coplanar waveguide (CPW) using electrostatic actuation as the switching mechanism. The microactuator uses several continuously-bent cantilevers connected in series. A cantilever with two sections, a straight-beam section and a curved-beam section, forms the basic unit of the microactuator. The straight-beam section is made of an aluminum (Al) layer, 0.5 mu m thick. The curved-beam section is made of an Al layer of the same thickness, combined with a 0.1-mu m layer of chromium (Cr) film. This section is initially curled due to the different residual stress of Al and Cr. The low temperature (250 degrees C) process ensures that the switch is capable of monolithic integration with microwave and millimeter wave integrated circuits (MMIC). When no de potential is applied, the actuator is curled far from the signal line of the CPW, and therefore the insertion loss at this 'on' state is only 0.2 dB at 10 GHz. Because the metal microactuator is far from the signal line of the CPW at this 'on' state, the microwave propagation is hardly disturbed by the microactuator. When an applied electrostatic force pulls the actuator tip down into contact with the signal line of the CPW, it creates a large capacitance between the actuator and the CPW. The isolation at this 'off' state is -17 dB at 10 GHz. Maintaining the actuator in the 'off' state requires only a very low actuation voltage of 26 V. Once the de potential is removed, the residual stress of the actuator structure pulls it to the up position. The microactuator moving back and forth between these two switching states, acts like the movement of a frog's tongue. This switch has excellent performance at the wide-band RF frequencies used in transmit/receive modules of wireless communication. This study measured the critical corrupt (activating) voltage and recovery voltage of the microactuator. The 10-ms switching time of this switch is slower than the switching time of solid-state switches. (C) 2000 Elsevier Science S.A. All rights reserved.