Stacked inductors and 1-to-2 transformers in CMOS technology

A modification of stacked spiral inductors increases the self-resonance frequency by 100% with no additional processing steps, yielding values of 5 nH to 266 nH and self-resonance frequencies of 11.2 GHz to 0.5 GHz. Closed-form expressions predicting the self-resonance frequency with less than 5% error have also been developed. A 1-to-2 transformer consisting of 3 stacked spirals achieves a voltage gain of 1.8 at 2.5 GHz. The structures have been fabricated in standard CMOS technologies with four and five metal layers.