Effects of contact roughness and trapped free space on characteristics of RF-MEMS capacitive shunt switches

Dielectric surface roughness and top electrode metal asperities tend to affect both the life-time reliability and frequency response of RF MEMS capacitive shunt switches. Down-state (off) capacitance of these switches is considerably affected by interface irregularities and trapped free space. There exists two very contradictory concepts regarding theoretically completely conformal Metal-Insulator-Metal contacts and commercially available RF MEMS capacitive switches. We explained the sole source of this contradiction, and offered a new model that is more accurate to describe RF MEMS switches. With this model we consider the effects of both contact roughness and free space trapped in down-state capacitance. Using the proposed model, different switch characteristics like frequency response and capacitance ratio is evaluated.