A Comparison of the Degradation in RF Performance Due to Device Interconnects in Advanced SiGe HBT and CMOS Technologies

This paper investigates the impact of the interconnect between the bottom and the top metal layers on the transistor RF performance of CMOS and silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) technologies. State-of-the-art 32-nm silicon-on-insulator (SOI) CMOS and 120-nm SiGe HBT technologies are analyzed in detail. Measured results indicate a significant reduction in the unity-gain frequency (f_T) from the bottom to the top metal layer for advanced CMOS technology nodes, but only a slight reduction for SiGe HBTs. The 32-nm SOI CMOS and SiGe HBT technologies have a reduction in the maximum oscillation frequency (f_max) from the bottom to the top metal layer of ~12% and 5%, respectively. By analyzing technology scaling trends, it is clear that SiGe HBTs can now achieve a similar peak f_T at the top metal layer in comparison with advanced CMOS technology nodes, and a significantly higher f_max. Furthermore, in CMOS technologies, the top metal layer f_max appears to have reached a peak around the 45-65-nm technology nodes, a result which has significant implications.