BEOL-Compatible High-Performance Indium-Tin-Oxide Transistors Enabled by Quantum Confinement-Engineered Properties

In this work, several key contributions have been made. First, based on the observation of quantum confinement-induced properties transition in indium-tin-oxide (ITO) films with a sub-10-nm thickness, the de-doping phenomenon in ITO has been utilized to satisfy demands from different device modules, e.g., relatively thick ITO for the source/drain (S/D) and thin ITO for the channel. Second, through precise engineering of the ITO film thickness by depositing channel and S/D regions separately, a thickness-dependent hetero design has been applied to further boost the device performance by suppressing the S/D series resistance (RSD)while maintaining the integrity of the channel. Finally, a comprehensive investigation into the impact of extremely thin ITO channel thickness (TCH)at sub-4-nm regime on device characteristics has been carried out, which reveals a tradeoff between achieving high field-effect mobility (μ eff)and maintaining an appropriate threshold voltage (Vₜₕ). By integrating all the aforementioned innovations, the device with 3.5-nmTCHand 50-nm channel length (LCH)achieves one of the highest peak transconductance (Gm, max)of617~μS/μm among ITO thin-film transistors (TFTs), along with an extremely lowRSDof140~Ω · μm. In addition, by further scalingTCHdown to 2 nm, the device with 50-nmLCHdemonstrates a desired enhancement-mode operation, together with a highG_ m, maxof508~μS/μm, and a respectable subthreshold swing (SS) of 85 mV/decade.