Comparative study of stack interwinding micro-transformers on silicon monolithic

Interwinding planar micro-transformers are developed using micro-machining technique. The transformers with a vertically stack coil structure on silicon monolithic substrate are designed to achieve high coupling and high inductance value in a relatively small coil area. In this work, various types of stack interwinding transformer are fabricated, measured and compared. The results show that the metal-to-metal effect of a multi-layer structure contributes to the significant increase of parasitic capacitances and hence limits the operating frequency. Moreover, the lumped element parameters are analyzed by extracting the measured S-parameter. This investigation can give important information for the future development of three-dimensional RF devices.