Spiral inductors on si p/p(+) substrates with resonant frequency of 20 GHz

Porous Si of up to 200 mum in thickness has been used to fabricate high-per formance spiral inductors on heavily doped Si substrates (0.007 Omega -cm). Spiral inductors with L similar to 5.7 nH are fabricated demonstrating Q(m ax) similar to 29 at 7 GHz and f(r) > 20 GHz. The resonant frequency (f(r)) increases with increasing porous Si thickness and saturates beyond 120 mum . A corresponding decrease in total capacitance is observed, Q(max) increas es monotonically with porous Si layer thickness to beyond 200 mum. For indu ctors with a smaller footprint, Q(max) begins to saturate at less than 100- mum thick porous Si.