Reduction of the interfacial trap density of indium-oxide thin film transistors by incorporation of hafnium and annealing process

The stable operation of transistors under a positive bias stress (PBS) is achieved using Hf incorporated into InO_x-based thin films processed at relatively low temperatures (150 to 250 °C). The mobilities of the Hf-InO_x thin-film transistors (TFTs) are higher than 8 cm²/Vs. The TFTs not only have negligible degradation in the mobility and a small shift in the threshold voltage under PBS for 60 h, but they are also thermally stable at 85 °C in air, without the need for a passivation layer. The Hf-InO_x TFT can be stable even annealed at 150 °C for positive bias temperature stability (PBTS). A higher stability is achieved by annealing the TFTs at 250 °C, originating from a reduction in the trap density at the Hf-InO_x/gate insulator interface. The knowledge obtained here will aid in the realization of stable TFTs processed at low temperatures.