Effects of surface roughness on electromagnetic characteristics of capacitive switches

This paper studies the effect of surface roughness on up-state and down-state capacitances of microelectromechanical systems (MEMS) capacitive switches. When the root-mean-square (RMS) roughness is 10 nm, the up-state capacitance is approximately 9% higher than the theoretical value. When the metal bridge is driven down, the normalized contact area between the metal bridge and the surface of the dielectric layer is less than 1% if the RMS roughness is larger than 2 nm. Therefore, the down-state capacitance is actually determined by the non-contact part of the metal bridge. The normalized isolation is only 62% for RMS roughness of 10 nm when the hold-down voltage is 30 V. The analysis also shows that the down-state capacitance and the isolation increase with the hold-down voltage. The normalized isolation increases from 58% to 65% when the hold-down voltage increases from 10 V to 60 V for RMS roughness of 10 nm.