Low–temperature fabrication of HfAlO alloy dielectric using atomic–layer deposition and its application in a low–power device

This paper presents a systematic study of HfAlO alloy films, which were prepared by doping HfO2 with different amounts of Al using atomic layer deposition at low growth temperature (150 °C). The chemical constituents of the various HfAlO films were determined by X–ray photoelectron spectroscopy. Carrier transport through the HfAlO layer presented a good fit with the Poole–Frenkel emission and Fowler–Nordheim tunnelling mechanisms in different voltage ranges. Barrier heights (conduction band offset) between the HfAlO films and Si substrate, which were derived from the Fowler–Nordheim fittings, increased with increasing Al content in the alloy films, and the leakage current was suppressed well owing to the higher barrier. The 10 nm HfAlO dielectric layer, which was grown by the repeated deposition of 1 cycle each of HfO2 and Al2O3 (defined as H1A1), showed a high gate capacitance of 723 nF/cm2, a high breakdown voltage of 8.0 V, a small leakage current, and a smooth surface. HfAlO films doped with different amounts of Al2O3 in HfO2 were employed to study their effects on the operation of amorphous indium–gallium–zinc oxide (a–IGZO) thin–film transistors (TFTs). The a–IGZO TFTs based on the H1A1 gate dielectric showed desirable properties including a high Ion/off ratio of 1.7 × 107, a small subthreshold swing of 176 mV/decade, and low operating voltage of 2.0 V.