MEMS electrostatic switching technology for microwave systems

The development of MicroElectroMechanical Systems (MEMS) switch technology and integration of this technology into Radio Frequency (RF) electronics has created numerous applications. The incorporation of RF MEMS switches into microwave systems offers unprecedented reductions in insertion loss (on-resistance) with extremely low switching power levels as compared with active devices such as Field Effect Transistors (FETs) and Positive-Intrinsic-Negative (PIN) diodes. The objective of this research was to investigate the interactions of mechanical design, material properties, and processing conditions on the electrical performance of RF MEMS switches, as measured by RF device performance. The design goal included development of low actuation voltage electrostatic actuated switches fabricated on gallium arsenide substrates.; Two types of switch structures were investigated, cantilever beams and microbridges. These structures provided a controllable medium to allow for fundamental examination of the performance dependencies. The switches were designed for capacitive coupling and operated in a series configuration. The switches consisted of a suspended metal beam over a dielectric-isolated bottom metal. An applied direct current voltage was used to actuate the switch while the RF signal passed through the dielectric.; The electrical and structural integrity of the switches was investigated by evaporating bilayer films of titanium and gold, while maintaining a constant total thickness of 1.5 micrometers. Results demonstrated that a thick titanium layer of 0.5 micrometers gold on 1.0-micrometers titanium produced functional cantilevers with no discernible curling due to stress gradients within the film. Cantilevers 300 micrometers long exhibited an insertion loss of −0.5 dB with an isolation of −11.7 dB at 10 GHz, with an actuation voltage of 20 V. Other bilayer combinations resulted in a stress gradient that caused the cantilevers to curl excessively, but resulted in functional microbridges. The bilayer combination of 1.0 micrometers gold on 0.5 micrometers titanium produced an insertion loss of −0.7 dB with −4.9 dB isolation at 10 GHz, and 14 V actuation voltage for an 800 micrometers long beam. A gold dominated film of 1.5-micrometers gold on 200-angstrom titanium produced an insertion loss of −0.5 dB with −6.1 dB isolation and an actuation voltage of 42 V.