Horizontally aligned ALD-SnO films grown on SiO₂-passivated high-k HfO₂ dielectrics for high-mobility and low-power P-channel thin-film transistor

The fabrication of SiO₂-passivated HfO₂ (HfO₂/SiO₂) as a high-k dielectric stack for high-mobility, low-power p-channel SnO thin-film transistors (TFTs) is reported herein. To achieve superior TFT performance, a high-k HfO₂ film was introduced by replacing the thermally-grown SiO₂. However, the atomic layer deposited (ALD)-SnO films grown on the HfO₂ substrate exhibited a very rough surface and out-of-plane tilted SnO (001), resulting in a significantly degraded field-effect mobility (μ_FE) compared with that of SnO TFTs based on an SiO₂ gate dielectric. Therefore, 1–10 nm-thick ALD-SiO₂ passivation layers were deposited on high-k HfO₂ to effectively improve the surface morphology of the ALD SnO. Furthermore, SiO₂ passivation enabled the control of the crystallographic orientation of the ALD SnO. Through SiO₂ passivation, the horizontally aligned SnO (00l) planes parallel to the substrate demonstrated significantly improved μ_FE characteristics. The optimized SnO TFTs fabricated with HfO₂/SiO₂ stacks exhibited excellent carrier transport and low-voltage operation characteristics, with μ_FE of 2.3 cm²/V·s, subthreshold swing of 0.5 V/dec, on-to-off drain current ratio of 1.4 × 10⁴, and V_th of −1.2 V.