Quasi-TEM characteristic impedance of micromachined CMOS coplanar waveguides

Micromachined coplanar waveguides (CPW's) fabricated in CMOS technology con sist of glass-encapsulated metal conductor strips, fully suspended by selec tive etching of the silicon substrate. The minimum amount of etching necess ary for proper operation of the micromachined waveguides is determined by u sing an isolation criterion. In this paper, the quasi-TEM characteristic im pedance of a CPW is derived, including the finite conductor thickness and t he thicknesses of surrounding dielectric layers. The employed analytical ap proach is based on conformal mapping and the partial capacitance technique. The losses both in conductor and dielectric layers are neglected. The anal ytical results and proposed approximations are verified by integral-equatio n computation and by measurement of various sample structures.