Sputter-Deposited copper iodide thin film transistors with low Operating voltage

This paper reports on a back-gated p-type thin film transistor (TFT) with copper iodide (CuI) as the channel material, a HfO₂ gate dielectric layer, and Al₂O₃ passivation. The γ-CuI channel was deposited from a CuI target using DC magnetron sputtering at room temperature. Our TFT can be fully shut off by V_G = 4 V, with a field-effect channel hole mobility μ_h ∼ 1.5–2 cm² V⁻¹ s⁻¹. An anneal in forming gas was performed twice, once at 200 °C, then at 250 °C to improve gate control, yielding a final I_on/I_off current ratio of ∼ 250. The anneal served two purposes: to reduce the oxygen acceptor density in the CuI channel and reduce the concentration of interface states between the CuI, Al₂O₃ passivation, and HfO₂. A model of the device was built in an industrial TCAD simulator, which reproduces the measured characteristics and allows an estimation of interface state densities and channel doping.