Design guidelines for nanoscale vacuum field emission transistors

Nanoscale vacuum channel field emissiontransistors (VFETs) with different gate-structures, channel lengths, and emitter tip radii are comprehensively studied using technical computer-aided design simulation. With a multigate configuration, the operating gate voltage decreases and the transfer characteristics improve due to excellent gate controllability. The gate-all-around (GAA) VFET with short channel length and thin channel to gate distance would be most suitable for low power consumption and less sensitivity to device fluctuation. In order to further understand the impact of physical gate length on the on-current (Ion) and the gate leakage current in VFETs, full- and half-gate devices are compared. With shorter channel length and thinner channel to gate distance, the tunneling energy band becomes sensitive to the gate field, resulting in a more severe Ion fluctuation. The half-gate structure can mitigate the gate leakage current without sacrificing the on-current because the leakage current near the collector tip can be reduced in comparison to the full-gate structure. The GAA VFET also shows superior cut-off frequency performance resulting from high transconductance, compared with the single- and double-gate VFETs.