Numerical study of MEMS capacitive switches using TLM

In this paper we investigate the RF behaviour of a microelectromechanical capacitive switch by the Transmission Line Matrix method (TLM). These microelectromechanical (MEMS) switches can be utilized for antenna and phased array applications for communication systems or automotive radar. The switch under study consists of a thin metallic membrane connected to the ground of a CPW line which - when actuated by a dc voltage - forms a virtual short with the center conductor of the CPW. It is demonstrated how the TLM algorithm can be applied for the calculation of the scattering parameters of both switching states. The crucial point for the analysis of those structures is the aspect ratio of the geometrical dimensions. Especially in the off-state, where the virtual short is realized by a 0.1 μm thin dielectric layer between the two electrodes, the discretization becomes problematically. Here the tune domain analysis can solve this problem very elegantly by modeling the thin layer as a thick anisotropic medium with a very much higher dielectric constant in vertical direction. However, due to highly dispersive structure, a post-processing of time domain signal is necessary to avoid long calculation times and to suppress unwanted reflections at the not ideal absorbing boundary at the output planes. The signal is truncated suitably and then prolonged analytically by estimating the truncated part by a least square parameter estimation using AR models. The calculated results of a metal membrane switch show very good agreement to results obtained by other numerical methods.