Aqueous-solution-driven HfGdOx gate dielectrics for low-voltage-operated α-InGaZnO transistors and inverter circuits

Abstract In this work, a non-toxic and environmentally friendly aqueous-solution-based method has been adopted to prepare gadolinium-doped hafnium oxide (HfO2) gate dielectric thin films. By adjusting the gadolinium (Gd) doping concentration, the oxygen vacancy content, band offset, interface trap density, and dielectric constant of HfGdOx (HGO) thin films have been optimized. Results have confirmed that HGO thin films with Gd doping ratio of 15 at.% have demonstrated appropriate dielectric constant of 27.1 and lower leakage current density of 5.8 × 10−9 A cm-2. Amorphous indium-gallium-zinc oxide (α-IGZO) thin film transistors (TFTs) based on HGO thin film (Gd: 15 at.%) as gate dielectric layer have exhibited excellent electrical performance, such as larger saturated carrier mobility (μsat) of 20.1 cm2 V-1 S-1, high on/off current ratio (Ion/Ioff) of ∼108, smaller sub-threshold swing (SS) of 0.07 V decade-1, and a negligible threshold voltage shift (△VTH) of 0.08 V under positive bias stress (PBS) for 7200 s. To confirm its potential application in logic circuit, a resistor-loaded inverter based on HGO/α-IGZO TFTs has been constructed. A high voltage gain of 19.8 and stable full swing characteristics have been detected. As a result, it can be concluded that aqueous-solution-driven HGO dielectrics have potential application in high resolution flat panel displays and ultra-large-scale integrated logic circuits.