Development of design approaches using porous silicon that facilitate high frequency integration in silicon substrates

Oxide capped porous silicon has the potential to produce low loss designs for high-density RF passive and CMOS integrated circuits. The RF/Microwave properties of circuit designs on porous silicon samples are investigated. Effective dielectric constant results of porous silicon films are shown in the range of 3.1-2.1 at 50 GHz. Measured and simulated attenuation results of porous and bulk silicon samples are presented with the porous samples showing up to 64% lower loss than low resistivity (10-20 O-cm) bulk silicon designs. Use of a 20 mum polyimide film on the porous silicon film produces an additional decrease in attenuation of 11%. DC bias effects on RF response of interconnects on the porous silicon film shows negligible RF variation (less than +/- 0.005 dB/cm) under bias conditions of +/- 19V. Parameters contributing to slow-wave mode propagation (substrate resistivity, dielectric film thickness and dielectric constant) in MIS circuits on silicon substrates are modeled and compared to the porous silicon samples which are found to diminish slow-wave mode propagation. Passive circuit performance is also investigated using inductors, capacitors and filters. Fabricated inductors on porous silicon film show quality factors as high as 30 with a self resonance of >45 GHz for an inductance of 0.6 nH. Lumped element models are developed to understand the performance of MIM capacitors on various substrates under a shunt and series implementation with a CPW feedline. The analysis shows that the MIM capacitor performance is impacted by the presence of various parasitic effects. Loss reduction methods using porous silicon for filter design on lossy substrates is investigated Reduction in the thickness of the lossy underlying bulk silicon leads to a 30% decrease in the insertion loss in the passband (at 10 GHz) and as 35% improvement in the stopband performance (35 GHz). In addition a 15 GHz aperture coupled patch antenna with its feed line on porous silicon is demonstrated. The measured return loss results show a resonant frequency of 14.78 GHz and a bandwidth of 0.85 GHz. Measured radiation patterns show an antenna with a high front to back ratio.