Spiral inductors on Si p/p/sup +/ substrates with resonant frequency of 20 GHz

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