Scaling the vertical tunnel FET with tunnel bandgap modulation and gate workfunction engineering

In this paper, we look into the scaling issues of a vertical tunnel field-effect transistor (FET). The device, a gated p-i-n diode based on silicon, showed gate-controlled band-to-band tunneling from the heavily doped source to the intrinsic channel. An exponentially increasing input characteristics, perfect saturation in the output characteristics, and off-currents of the order of 1 fA/μm for sub-100-nm channel lengths were observed. Further, with a δp⁺ SiGe layer at the p-source end, improvements in the device performance in terms of on-current, threshold voltage and subthreshold swing were shown, albeit trading off the off-currents which increase with Ge content x. We show here that the tunnel FET performance is nearly independent of channel length scaling L and with δp⁺ SiGe layer, scaling t_ox is not critical to tunnel FET scaling. Further, with gate workfunction engineering, the tunnel FET can be tuned to achieve a high on-current as well as very low off-currents. Due to the perfect saturation in the output characteristics, the device looks good for sub-100-nm low-power analog devices.