ALD W-doped SnO2 TFTs for indium-free BEOL electronics

This work reports back-end-of-line (BEOL) compatible, thin-film transistors (TFTs) with sub-10 nm tungsten-doped tin oxide (TWO) channels deposited by atomic layer deposition (ALD) at 150 °C. TFTs with undoped SnOx, undoped WOx, and W-doped SnOx channels with variable W concentrations were investigated. TFT with 10% W doping exhibited the best electrostatic control and overall device performance. Post-fabrication O2 annealing at 300 °C for 5 min significantly enhanced device characteristics, reducing the subthreshold swing (SS) by nearly 2×, increasing the Ion/Ioff ratio from 107 to 109, and decreasing hysteresis by nearly 3× and positive bias stress-induced threshold shift by over 2× to a low value of 93 mV at a stress field of 4 MV/cm. Kinetic Monte Carlo simulations using GinestraTM support the experimental observations and attribute the bias instability to charge trapping in the gate dielectric and at the interface. This work demonstrates low-temperature ALD-grown TWO TFTs as a promising indium-free platform for BEOL and monolithic 3D integration.