Impact of quantum confinement on source-to-drain tunneling and sub-threshold behavior of ultra-thin-body MOSFETs at cryogenic temperatures

Recently, an anomalous behavior of the sub-threshold swing (SS), not adhering to Boltzmann limits and saturating below a certain critical temperature, has been observed in MOSFETs. In this work, we consider ultra-thin channel double-gate Silicon-on-Insulator (SOI) MOSFETs, where particularly at low device temperatures (T < 50 K), we illustrate the impact of Quantum Confinement Effects (QCEs) in enhancing the Source-to-Drain Tunneling (SDT) currents, thus resulting in these SDT currents significantly degrading the sub-threshold swing behavior. With reducing SOI channel thickness, where QCEs become more significant, we first show a non-linear increase in SS (degradation of SS, with increasing device temperatures), at low device temperatures, for shorter channel lengths, which then results in the saturation of SS for intermediate channel lengths, until eventually attaining SS values closer to the Boltzmann limit for longer channels, when SDT has become comparable to, or reduced below, the thermionic currents. The simulation approach presented in this work makes it possible to estimate the impact of QCEs on SDT accurately, through which the SS behavior at varying device temperatures (T = 15–150 K) can be theoretically explained for nanoscale MOSFETs.