On-chip vertically coiled solenoid inductors and transformers for RF SoC using 90nm CMOS interconnect technology

This paper presents very small on-chip vertically coiled solenoid inductors (V-solenoid) using 90 nm CMOS multilevel interconnect technology. In addition, a variety of areas-saving (10 um × 20 um) transformers without any additional processing steps are demonstrated: a V-solenoid surrounded by another different inside-diameter V-solenoid (dual-tube transformer), a V-solenoid coiled around another one with same dimensions (a double-helix or DNA-like transformer), and face-to-face V-solenoids (face-to-face transformer). Radio-frequency characteristics were evaluated on the basis of 2-port S-parameter measurements. Measured self-resonance frequencies resulted in higher than 40 GHz, and coupling coefficients were larger than 0.6.