Investigation on the Band Tail States in FinFETs at Cryogenic Temperature

Accurate characterization and modeling is essential to develop the cryogenic CMOS technology for quantum computing and high-performance computing (HPC). However, instabilities introduced by band tail states at cryogenic temperature obstruct the accurate extraction of intrinsic cryogenic device properties. While the existing studies predominantly focus on empirical dc characteristic fitting, the physical origin of the band tail states, particularly in FinFETs, remains fundamentally unexplored. In this article, the band tail states at cryogenic temperature for FinFET technology are comprehensively studied. A significant deviation of subthreshold swing (SS) from Boltzmann limits at temperature as high as 150 K is observed, which differs greatly from that happens at 50 K in planar devices. Moreover, abnormal current relaxation, which is accompanied with ON-state current increase and subthreshold current reduction, is thoroughly studied. These new findings are well understood in the unified framework of band tail states induced by impurity and surface roughness. This work provides a deep understanding of cryogenic CMOS characterization and modeling.