MICROMACHINED MICROWAVE TRANSMISSION-LINES IN CMOS TECHNOLOGY

Coplanar waveguides were designed and fabricated through a commercial CMOS process with post-processing micromachining. The transmission-lin e layouts were designed with commercial computer-aided design (CAD) to ols. Integrated circuits (IC's) were fabricated through the MOSIS serv ice; and subsequently suspended by top-side etching. The absence of th e lossy silicon substrate after etching results in significantly impro ved insertion-loss characteristics, dispersion characteristics, and ph ase velocity. Two types of layout sire presented for different ranges of characteristic impedance. Measurements of the waveguides both befor e and after micromachining were performed at frequencies from 1 to 40 GHz using a vector network analyzer and de-embedding techniques, showi ng improvement Of loss characteristics of orders of magnitude. For the entire range of frequencies, for the 50-Omega layout, losses do not e xceed 4 dB/cm. These losses are mainly due to the small width and thic kness of the metal strips. Before etching, losses are as high as 38 dB /cm due to currents in the underlying substrate. Phase velocity in the micromachined transmission lines is close to that in free spare.