Abstract

We have made theoretical time-domain analyses of the dispersion and loss of both square-wave and exponential pulses on microstrip transmission line interconnections on silicon integrated-circuit substrates. Geometric dispersion and conductor linewidth, as well as losses from conductor resistance, conductor skin effect, and substrate conductance are considered over the frequency range from 100 MHz to 100 GHz. Results show the enormous significance of the substrate losses, and demonstrate the need for substrate resistivities >10 Ω-cm for high performance circuits. The results also show the effects of geometric dispersion for frequencies above 10 GHz (which increase with decreasing linewidth), the transition from the high-frequency quasi-TEM regime to the "slow-wave" regime, and the unimportance of conductor skin-effect losses for frequencies up to 100 GHz. Qualitatively similar phenomena are seen for Al, W, and WSi₂ lines. The differences in resistivity of these materials do not significantly alter their pulse propagation properties. Surprisingly, however, slow-wave velocity is increased for either increasing conductor resistivity, decreasing conductor linewidth, or both. Poly-Si, with its significantly greater loss, shows qualitatively different frequency-dependent behavior. High phase velocity and high loss can coexist in poly-Si lines.

© 1985 Optical Society of America