Solution-processed high-k HfO2 gate dielectric processed under softening temperature of polymer substrates

Abstract

A low-temperature, solution-processed high-k HfO₂ gate dielectric was demonstrated. To decompose a hafnium precursor at a temperature lower than 200 °C, an aqueous solution of HfCl₄ was used because the strongly hydrated hafnium precursor was decomposed at a much lower temperature than anhydrous or partially hydrated hafnium chloride. No hazardous organic material was required in the low-temperature HfO₂ coating process. Thus this precursor solution is environmentally safe and it is preferable to use this solution for gate dielectric coating on flexible substrates. The fabricated HfO₂ gate dielectric shows reliable breakdown characteristics and high dielectric constant. We fabricated a thin film transistor (TFT) device with this gate dielectric and a maximum processing temperature of 150 °C for all the components of the TFT. The ZnO TFT on the HfO₂ gate dielectric shows field-effect mobility of 1.17 cm² V⁻¹ s⁻¹ and threshold voltage of 5.87 V. These results demonstrate the potential of our HfO₂ thin film for flexible electronic device fabrication.