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.