Schottky Tunneling Effects in a Tunnel FET.

Tunnel FETs (TFETs) have attracted a great deal of attention due to their steep subthreshold swing (SS) of less than 60 mV/dec, which overcomes the theoretical constraint imposed by the thermal limit in a conventional inversion-mode (IM) FET. Based on its advantages as a short-channel device with low stand-by power consumption, TFETs shows promise to replace IM-FETs. As the channel length is shortened to minimize the total gate pitch; however, the gate sidewall spacer is miniaturized as well. In this paper, the influence of junction extension length (Lext) on TFET behavior is discussed where the length of the gate spacer is assumed to be the gap between the source and drain (S/D) electrodes and the gate edge. It was found that, when Lext is aggressively scaled down, having S/D electrodes (silicide or metal) with identical work functions (WFs) leads to a severely high OFF-current (IOFF) and high SS. By adopting separate asymmetric WFs for the p-type and n-type S/D electrodes, the on/off characteristics were improved with suppressed IOFF and steeper slopes. It was also shown that the device performance of a TFET with higher source-side doping concentrations (~5 × 1020 cm-3) can be further improved even at the aggressively scaleddown Lext by boosting the on-current. [ABSTRACT FROM AUTHOR]