Why In₂O₃ Can Make 0.7 nm Atomic Layer Thin Transistors

Abstract

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

Top-Gate Short Channel Amorphous Indium-Gallium-Zinc-Oxide Thin Film Transistors With Sub-1.2 nm Equivalent Oxide Thickness

“…morphous oxide semiconductor TFTs, due to their moderate mobility, low cost, large size uniformity, high transparency, and excellent flexibility, have been widely used in applications from large-scale display to flexible portable devices [1][2][3][4][5][6][7][8][9][10][11][12][13]. In addition, because of a low process temperature and extremely low off-state current (I off ), they have tremendous promise in emerging applications, including internet of things (IoT), monolithic three-dimensional (3D) integrated nano-electronic, and photonic systems [14][15][16][17], where low power and high performance are highly desired.…”

Recent progress and perspectives on atomic‐layer‐deposited semiconducting oxides for transistor applications

“…However, for In 2 O 3 to be used as an effective semiconducting channel layer in TFTs, the N e value should be less than 10 18 cm −3 . Various approaches are available to reduce the N e value in In 2 O 3 thin films, such as control of growth temperature, 30–33 post‐annealing, 34,35 reduction of the non‐stoichiometric ratio, 36 plasma treatment, 37,38 and downscaling of film thickness 39,40 . Among them, downscaling of ALD‐derived In 2 O 3 thickness was shown to be promising.…”

“…Among them, downscaling of ALD‐derived In 2 O 3 thickness was shown to be promising. Si et al 39 investigated the dependence of the thickness of the electrical properties of ALD‐derived In 2 O 3 thin films. An In 2 O 3 thin film 0.7 nm thick was found to be in an amorphous phase due to geometrical hindrance, which is frequently reported in oxide materials 41 .…”

“…The relative position of the TNL from the conduction band minima depends on the T ch of In 2 O 3 due to quantum confinement. Reprinted with permission 39 . Copyright 2021, American Chemical Society…”

Doping limits in p-type oxide semiconductors

“…[1][2][3][4][5] This field has recently been extended to include back-end-of-line (BEOL) semiconductor devices. [6][7][8][9] A typical application of these electronic rather than optical devices is that they act as switches with a particularly low off-state leakage current for charge storage devices (down to 10 −20 A). 7 So far, the successful oxides were mainly n-type, such as ZnO, Ga 2 O 3 , or amorphous In-Ga-ZnO 4 , whereas p-type materials have been much less successful.…”