Record-Low Metal to Semiconductor Contact Resistance in Atomic-Layer-Deposited In2O3 TFTs Reaching the Quantum Limit

In this work, we demonstrate the record-low metal- to-semiconductor contact resistance R
c
= 23.4Ω μm at n
2D
= 5.0 × 10
¹³
cm
⁻²
(reaching the quantum limit) in atomic-layer-deposited (ALD) In
2
O
3
thin-film transistors (TFTs) with back-end-of-line (BEOL) compatibility. Our long-channel devices (L
ch
= 1 μm) exhibit excellent drain current saturation, while our short-channel devices (L
ch
= 50 nm) achieve high on-current performance (2.6 mA/μm. at 295 K, and 5.4 mA/μm at 10 K). The superior ohmic contact is made possible by the charge neutrality level (CNL) deeply aligned inside the conduction band of In
2
O
3
, which can also be understood as an interfacial donor-like trap-induced negative Schottky barrier. Notably, we investigate the contact resistance at various temperatures, O
2
annealing conditions, and channel thicknesses, providing a comprehensive understanding of this material system. Furthermore, we demonstrate an ultra-low contact resistivity of ρ
c
≈ 1.3 × 10
⁻⁹
Ω cm
²
and current transfer length of L
T
≈ 2 nm in 1 nm thin films. These findings position In
2
O
3
as a highly promising candidate for ultra-scaled, high-performance BEOL transistors from the contact engineering point of view.