Suppressing Undesired Channel Length-Dependent Electrical Characteristics of Fully Integrated InGaZnO Thin-Film Transistors via Defect Control Layer

Demand for increased scalability of oxide thin-film transistors (TFTs) continues to rise, along with the need for ever-higher integration densities and driving currents. However, the undesirable channel length (L_CH)-dependency renders short channels difficult. To overcome such behavior in back-channel etched devices, back-channel interface engineering using commercially favorable silicon oxide (SiO_x) and the effects thereof on the electrical characteristics of fully integrated TFTs are investigated. Process-dependent investigation reveals that a sequential formation of double-layered SiO_x with a defect control layer (DCL) effectively alleviates back-channel damage. The proposed method imparts advanced functionality to conventional materials of SiO_x. The DCL promotes oxygen inter-diffusion to the oxygen-deficient back-channel, suppresses excess hydrogen inflow, and boosts out-diffusion of residual copper from the back-channel. This afforded excellent device uniformity and electrical characteristics with the proposed device, including field effect mobility of ≈14.0 ± 1.0 cm² V⁻¹ s⁻¹, threshold voltage (V_th) of ≈1.22 ± 0.39 V, and subthreshold gate swing of ≈0.46 ± 0.09 V dec⁻¹ at W/L = 4/7 µm. Furthermore, V_th variation when L_CH decreased from 20 to 4 µm is dramatically suppressed from >11.39 V with the pristine device to 0.78 V with the proposed device, because of controlled back-channel properties providing sufficient effective L_CH.