Solution-processed amorphous yttrium aluminium oxide YAlxOy and aluminum oxide AlxOy, and their functional dielectric properties and performance in thin-film transistors

Abstract

Fabrication of dielectric yttrium aluminium oxide YAl_xO_y thin films utilizing nitro functionalized malonato complexes of aluminium Al-DEM-NO₂1 and yttrium Y-DEM-NO₂2 is described. Their controlled thermal conversion under moderate conditions into amorphous ternary yttrium aluminium oxide dielectric thin films with a very low surface roughness (R_RMS < 0.2 nm) was accomplished. Capacitor devices composed of YAl_xO_y exhibit excellent dielectric properties at a processing temperature of 350 °C. It was possible to systematically modulate their significant performance parameters such as dielectric constant, leakage current density and breakdown voltage according to the amount of yttrium rare earth metal incorporation which showed an optimum at 30 mol% yttrium incorporation. The yttrium inclusion into the amorphous Al_xO_y lattice reduces the formation of carbonate species in comparison to yttrium free pristine Al_xO_y dielectric thin films. Finally, a solution-processed thin-film transistor (TFT) with YAl_xO_y (30 mol% – Y content) as the dielectric and indium zinc oxide (IZO) as the semiconductor exhibits good TFT characteristics with a saturation mobility (μ_sat) of 2.6 cm² V⁻¹ s⁻¹, an on-voltage (V_on) of −1.1 V, a threshold voltage (V_th) of 12.4 V and an on/off current ratio (I_on/off) of 1.8 × 10⁷. As an alternative to a necessary thermal annealing step deep UV irradiation at 160 nm allows the implementation of low-temperature (150 °C) solution processing of a yttrium free pure Al_xO_y dielectric, which exhibits excellent dielectric performance parameters. It displays an areal capacity of 153 nF cm⁻², a leakage current density of 1.7 × 10⁻⁹ A cm⁻² at 1 MV cm⁻¹ and a breakdown voltage of 4.1 MV cm⁻¹.