Ternary cold source transistors for multivalue logic applications

A ternary cold source field effect transistor (T-CSFET) is proposed based on source density-of-state engineering, using a narrow-band-gap semiconductor at the source region. A current plateau at the subthreshold region is obtained in the transfer characteristics of T-CSFETs, namely an intermediate state with a constant current between on and off states. We meticulously study a two-dimensional T-CSFET based on a graphene-${\mathrm{Mo}\mathrm{S}}_{2}$ heterojunction by quantum transport simulations. It is shown that ternary states can be well distinguished with a current ratio between two adjacent states of over ${10}^{3}$ at a low overall supply voltage of 0.6 V. The intermediate state is stable with a constant current in a gate voltage region over 0.2 V and can be modulated by varying the doping density. We also obtain ternary transfer curves for T-CSFETs based on one-, two-, and three-dimensional materials. Based on T-CSFETs, a two-bit ternary adder with hybrid logic is implemented and verified by circuit simulations. The proposed T-CSFETs exhibit excellent properties for multivalue logic, including high drive current, tunable multivalue states, stable and reliable operation, energy and area efficiency, and a variety of material systems.