High-Performance Compact 3-D Solenoids for RF Applications

A cost-effective technology is proposed for the integration of very compact and high-performance 3-D solenoid inductors. Based on a two metal level process, it involves a 3-D copper electroplating step for simultaneous integration of vertical and upper sections of coils. Several solenoids fabricated on a glass substrate and ranging from 2.3 to 9.5 nH are presented. The best performance is experimentally achieved by a three-turn 3-nH inductor showing a maximum Q-factor of 58 at 5.6 GHz and a self-resonant frequency of 19 GHz. The best inductance density of 63 nH/mm² is reached by an eight-turn 9.5-nH solenoid.