High Performance 3-D Helical RF Transformers

We have designed, fabricated, and tested 3-dimensional helical RF transformers on high-resistivity Si substrate using stressed metal technology. The technology for these transformers is based on one step Cr/Au metal deposition and electroplating. These transformers exhibit high coupling coefficient and high power efficiency over an extended frequency range. A 4:4 turn ratio transformer in this work achieves a coupling coefficient k of 0.84 at 5 GHz, with k over 0.7 for frequencies from 1.6 to 6.6 GHz and with P_out/P_in over 75% up to 20 GHz.