IGZO-TFT with High-k HfO2 Dielectric Layer on Flexible Substrate Prepared by In-line HiPIMS System at Room Temperature

High-k hafnium oxide (HfO2) film was prepared by high power impulse magnetron sputtering (HiPIMS). The influences of oxygen supply on the plasma state, film properties and TFT performance were investigated. The films are near-stoichiometric and preferentially (−1 1 1)-orientated. When the oxygen supply increased from 1% to 3%, the excitation/ionization rate of the plasma species increased, leading to the higher crystallinity, higher density and lower oxygen vacancy defect concentration of the film, therefore improving the dielectric properties of the film. When the oxygen supply further increased to 5%, the excitation/ionization rate decreased thereby led to the lower crystallinity, lower density and higher oxygen vacancy defect concentration of the film, therefore deteriorated the dielectric properties of the film. The film deposited at 3% oxygen supply exhibited the best dielectric properties with the highest k value of 24 and the highest breakdown-electric-field (4.7 MV/cm), which should be attributed to high crystallinity, high density and low oxygen vacancy defect concentration of the film. Finally, transparent thin film transistors (TFTs) with ITO gate electrode, HfO2 gate dielectric layer and indium-gallium-zinc oxide channel were fabricated on flexible colorless polyimide substrate at full room temperature by all HiPIMS process. The fixed positive charges and k value of HfO2 film have significant effects on the TFT performance. The best TFT exhibited good electrical performance featured with a remarkable low subthreshold swing of 0.13 V/decade. it also exhibited fair stability against bending and gate bias stress.