High-Field Transport and Statistical Variability of Nanosheet Oxide Semiconductor FETs With Channel Length Scaling

Abstract

We have investigated the scaling potential of nanosheet oxide semiconductor FETs (NS OS FETs) for monolithic 3-D (M3D) integration in terms of atomic layer deposition (ALD) material engineering, high-field transport, and statistical variability. We have developed and systematically compared InGaO (IGO), InZnO (IZO), and InGaZnO (IGZO) FETs by ALD. The effective mobility (µeff) characteristics of IGZO are higher than that of IGO and IZO at the same threshold voltage (Vth) in the normally-OFF region (Vth > 0). IGZO benefits from high µeff of IZO and low oxygen vacancy (Vo) of IGO and thus shows well-balanced characteristics. To study the carrier transport characteristics under a high electrical field, we have fabricated sub-100 nm gate length NS OS FETs and extracted transconductance (gm) as a metric. While bulk Si FETs show velocity saturation behavior even after parasitic correction, NS OS FETs show unsaturated velocity behavior. We also have obtained statistical variability data of NS OS FETs, which is comparable against bulk Si nFETs and Si SOI nFETs. This work provides evidence of the scalability of NS OS FETs for M3D integration.