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

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 $$I_{\mathrm{ON}}$$ , $$I_{\mathrm{OFF}}$$ , subthreshold swing (SS), $$C_{\mathrm{gs}}$$ , $$C_{\mathrm{gd}}$$ , and $$f_\mathrm{t}$$ . It is found that the ambipolar behavior and Miller capacitance $$C_{\mathrm{gd}}$$ 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 $$I_{\mathrm{OFF}}$$ . 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.