Ferromagnetic RF inductors and transformers for standard CMOS/BiCMOS

Integrated solenoidal radio-frequency (RF) inductors and transformers with a ferromagnetic core are demonstrated by using a fully IC-compatible fabrication process. For a 500-nm-thick Ni/sub 80/Fe/sub 20/ film, a cut-off frequency of over 7.5 GHz for a 2.5-nH inductor is realized. Optimum inductor design based on tailored inductance, quality factor, and cut-off frequency is discussed. RF transformers realized have a coupling factor of /spl sim/70% up to 200 MHz.