Investigation of Ring-TFET for Better Electrostatics Control and Suppressed Ambipolarity

The inherent asymmetry in area and position of drain/source region in the ring field-effect transistor (Ring-FET) provides a unique channel electrostatic, different from symmetric double-gate FET, which renders it with immunity to short channel effects (SCEs). This electrostatics of ring-FET has the potential to mitigate ambipolarity in tunnel FET (TFET). In this article, using a well-calibrated TCAD simulation and analytical model, we investigate the electrostatics of all-silicon n-type Ring-TFET (R-TFET). The results are compared with conventional all-silicon n-type double gate TFET (DG-TFET). Two possible configurations of R-TFET obtained by interchanging the source and the drain positions are termed as source-inside TFET (SI-TFET) and drain-inside TFET (DI-TFET). We observed that DI-TFET mitigates the ambipolarity by $100 \times$ at $V_{DS}=\text{0.5 V}$ and $2000 \times$ at $V_{DS}=\text{1 V}$ compared to DG-TFET. Besides, the drain induced barrier thinning (DIBT) of DI-TFET is (89 mV/V) less than DG-TFET (108 mV/V), for a channel length of 32 nm, thus the proposed DI-TFET also offers better short channel immunity.