Why In₂O₃ Can Make 0.7 nm Atomic Layer Thin Transistors

In this work, we demonstrate enhancement-mode field-effect transistors by an atomic-layer-deposited (ALD) amorphous In₂O₃ channel with thickness down to 0.7 nm. Thickness is found to be critical on the materials and electron transport of In₂O₃. Controllable thickness of In₂O₃ at atomic scale enables the design of sufficient 2D carrier density in the In₂O₃ channel integrated with the conventional dielectric. The threshold voltage and channel carrier density are found to be considerably tuned by channel thickness. Such a phenomenon is understood by the trap neutral level (TNL) model, where the Fermi-level tends to align deeply inside the conduction band of In₂O₃ and can be modulated to the bandgap in atomic layer thin In₂O₃ due to the quantum confinement effect, which is confirmed by density function theory (DFT) calculation. The demonstration of enhancement-mode amorphous In₂O₃ transistors suggests In₂O₃ is a competitive channel material for back-end-of-line (BEOL) compatible transistors and monolithic 3D integration applications.