Analog/RF characteristics of a 3D-Cyl underlap GAA-TFET based on a Ge source using fringing-field engineering for low-power applications

Abstract

As an alternative to conventional tunnel field-effect transistor (TFET) devices for low-power applications, drain-underlap (DU) cylindrical (Cyl) gate-all-around (GAA) TFETs based on a Ge source using fringing-field effects can show suppressed subthreshold leakage current. In this work, such a fringing field is implemented using a hetero-spacer dielectric placed over the Ge source, resulting in enhanced direct-current (DC) and analog/radiofrequency (RF) characteristics such as ION, IOFF, subthreshold swing (SS), Cgs, Cgd, and ft. It is found that the ambipolar behavior and Miller capacitance Cgd are minimized in combination with a high band-to-band tunneling (BTBT) rate compared with devices based on a homo-spacer dielectric placed over a Si source. At the same time, the drain-underlap design increases the series resistance across the drain–channel junction overlapped by the fringing field, reducing IOFF. Furthermore, the performance of the proposed device matches well with experimental data when including the effects of trap-assisted tunneling (TAT) for improved device reliability. Thus, the behavior of the RF figure of merit of the proposed device is different compared with conventional TFET designs. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.