Technical Papers and Presentations

In this paper, the effects of roughness in the surfaces of the plates caused due to nonuniform etching during their release and/or due to defects in the original wafer on the capacitance in RF-MEMS parallel plate varactors are analyzed. Capacitance extraction due to surface roughness has been carried out by mixed mode analysis in three steps: 3D modeling of rough surface in COMSOL, linking of the displacement results with MATLAB for generation of best fit polynomials and evaluation of capacitance by closed form integral expressions. This mixed mode of analysis enables fast computation of capacitances for rough surfaces with different boundary conditions in a flexible manner. The analysis has been carried out on different two plate varactor structures reported by others. It has been found that incorporation of small asperities of 80nm heights in these structures reduces the percentage error in the simulated capacitance from the experimental values by more than 10% which is quite significant.