High-Performance CMOS-Compatible Solenoidal Transformers With a Concave-Suspended Configuration

Reported are high-performance solenoid transformers concave suspended in standard (low resistivity) silicon wafers by using a post-CMOS microelectromechanical systems process. The concave-suspended structure of the transformers effectively depress the substrate effects including eddy current and capacitive coupling between the solenoids and substrate, thereby achieving both high-Q factor and broad usable frequency band. Maximum available gain Ga has been measured as high as 0.89 for the transformer. Within the wide usable frequency band of approximately 16 GHz, the measured Ga value is always higher than 0.75. An equivalent-circuit model has been established for optimal design of the high-performance transformers. By using the equivalent-circuit model and ADS software, the transformer parameters are calculated and simulated, resulting in a satisfactory agreement with the measured data. The CMOS-compatible concave-suspended solenoidal microtransformers are promising to be post-CMOS integrated with high-performance RF integrated circuits.