Post-processed Cu inductors with application to a completely integrated 2-GHz VCO

A simple post-processing technique allowing Cu inductors to be added to integrated circuits fabricated in technologies providing only Al metallization is presented. The inductors use a 4-/spl mu/m thick electroless plated Cu layer to minimize resistance, and are formed over a 9-/spl mu/m thick polyimide dielectric to reduce substrate losses. Inductors optimized for 2.5-GHz had Q as high as 17. The effectiveness of the post-processing technique is demonstrated by application to a voltage-controlled oscillator (VCO) fabricated in a commercial bipolar technology with Al metallization. Circuits with post-processed Cu inductors gave a phase noise of -106 dBf/Hz at 100 kHz offset from a 2-GHz carrier, while control circuits with Al inductors gave a phase noise of only -101 dBc/Hz at 100 kHz offset from a 1.8-GHz carrier and had higher power consumption.