The Design And Fabrication Of RF MEMS Switches

Advances in MEMS technology in the late twentieth century made possible the design and fabrication of micromechanical switches. MEMS switches have low resistive loss, negligible power consumption, good isolation and high power handling capability compared with semiconductor switches. The development of substrate-independent MEMS switches could introduce affordable microwave components and systems into the marketplace, with a dramatic improvement in both performance and cost.In this thesis, a torsion-type RF MEMS switch is proposed. The switch utilizes single crystal silicon as the movable parts to improve residual stress deformation of the film. The mechanical part of the switch uses a torsion seesaw to solve the problem of contact points' cohesive connection in traditional switch. The main achievements of this work are summarized as follows:1. In the first place, paper analyses the merit and shortage of several typical MEMS switches, and a novel seesaw type single crystal silicon based switch is proposed. The mechanical dynamics, mechanical shock and gravity of the seesaw type beam are discussed theoretically to analyze the mechanical characteristics of the seesaw type switch.2. Two different drive models of the seesaw type switches are proposed in this thesis; they are the electrostatic switch and the electromagnetic switch. The mechanical and electromagnetic characteristics of the two type switches are analyzed theoretically. The actuation voltage of electrostatic switch is about 5 volts; the actuation current is about 100mA for the electromagnetic switch and the driven force is lager than 25μN. Design and optimizes the structure of the switches and the CPW transmission line, the switches is then emulated by Ansoft HFSS, for the electrostatic switch the isolation is much better than -20dB at 40GHz, while for electromagnetic switch the isolation is much better than -40dB at 40GHz.3. The processes for the switches are designed and fabricated. Several key processes are developed and discussed, such as ICP etching, sacrificial layer releasing, interconnection process and bulk silicon etching. In order to apply the sacrificial layer releasing, a supercritical point carbon dioxide releasing equipment is fabricated.4. The problems in the fabrication of the switches are analyzed, the electrostatic switch are tested, the isolation is about -45dB at 20GHz; in the end this paper discuss the results of sacrificial layer releasing.