Effect of temperature on capacitive RF MEMS switch performance—a coupled-field analysis

Three-dimensional multiphysics finite element analysis (FEA) was performed to investigate the reliability of RF MEMS switches at various operational temperatures. The investigated MEMS capacitive switch consists of a freestanding metal membrane actuated by a bottom electrode coated by a dielectric film. Coupled-field simulations between thermal, structural and electrostatic domains were performed. The simulations show that temperature significantly changes both the membrane stress state and out-of-plane geometry. In particular, the membrane buckles when temperature increase, from room temperature, takes place. The buckling temperature, i.e. the upper bound to the operational temperature, is a function of manufacturing residual stress state, membrane initial out-of-plane profile and a mismatch in materials coefficient of thermal expansion. The analysis also shows that temperature reduction, from room temperature to −40 °C, causes an increase in pull-in voltage to values that could compromise the switch reliability as a result of charge build-up in the dielectric layer. Our analyses illustrate that by proper designing of the membrane out-of-plane profile, it is possible to keep the pull-in voltage, at all operational temperatures, within allowable values. This design feature of RF MEMS switches offers an effective way to achieve reliable pull-in voltages in applications where large temperature variations are expected such as in satellites and airplane condition monitoring based on wireless communication.