Materials suitable for use as monolithic substrates are summarized. A study of the properties of silicon substrates as transmission line media shows that serious consideration should be given to them for use at mm-wave frequencies. It is concluded that for silicon resistivities of 2000 ohm-cm or greater, microstrip loss in silicon at mm-wave frequencies is only slightly higher than that in GaAs or alumina. The cross section width of a transmission line represents an appreciable part of a wavelength when microstrip is used as an impedance transformer at mm-wave frequencies. Therefore, substrate thickness (using the latest dispersion characteristics) is especially considered in circuit design. These effects on the design of 3-dB interdigitated and branch-line couplers are demonstrated. Fabrication of silicon IMPATT diodes operating up to 200 GHz has been accomplished by novel techniques that maintain the silicon's high resistivity. We report on diodes yielding 25 mW cw at 102 GHz, 16 mW cw at 132 GHz, and 1 mW at 195 GHz. The techniques described are ion implantation, laser annealing, unique secondary-ion mass spectrometry (SIMS) profile diagnostics, and novel wafer thinning. The utilization of these technologies paves the way for the processing of silicon monolithic mm-wave integrated circuits.
Rosen, A., Caulton, M., Gombar, A.M. et al. (1981) Silicon as a Millimeter-Wave Monolithically Integrated Substrate - A New Look. RCA Review 43: 633-660.