  In this work, we demonstrate enhancement-mode field-effect transistors by
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 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 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.
