Transmission Lines on Low Resistivity Silicon Substrate for MMICs Applications

In this paper, transmission lines structures (Thin Film Microstrip -TFMS- and coplanar waveguide -CPW-) on low resistivity (¿ = 10 ¿-cm) silicon substrate are investigated, for millimeter wave applications. From the designer point of view, useful parameters such as losses versus characteristic impedance are calculated. The results obtained on TFMS fabricated with CMOS 15 ¿-cm process from ST Microelectronics (five metal levels) and an alternative solution using BCB layer are shown. Moreover, low loss CPW structures on silicon substrate are designed and optimized using a thick dielectric layer (10 ¿m of BCB). Finally, to obtain low value of characteristic impedance with this configuration, a fully embedded CPW transmission line is used. Attenuation coefficient of these structures is less than 0.6 dB/mm @ 50GHz.