Modeling and FEM Verification of Surface-Roughness Effect on the Static Response of RF-MEMS Switches

Radio Frequency Microelectromechanical systems (RF MEMS) are being employed in various commercial and military applications. However, the reliability of the switches still remains a matter of concern. During design phase of the RF MEMS switches, the surfaces of switch are considered to be smooth at micro scale and the effect of surface roughness is neglected. The theme of the present paper is to quantify surface roughness effect on the static pull in voltage and gap of an electrostatically actuated RF MEMS switches by providing a simple analytical model along with the FEM (Finite Element Modeling) simulations. The surface roughness effect on the static pull in voltage of RF-MEMS capacitive switches becomes severe in case of small distance between the suspended top bridge and bottom dielectric. The results in the paper shows that the value of pull in voltage and gap decreases whereas value of capacitance increases as radius of spherical surface roughness increased. The pull in voltage value of the capacitive switch for an air gap thickness of 0.5 μ m and 2.5 μ m decreases by approximately 27% and 23% from its smooth surfaced value for a roughness scale of 0.1 μm respectively. The results are important for the search of an ideal switch and are in good agreement with the mathematical model.