Improvement on performance and reliability of TaN/HfO₂ LTPS-TFTs with fluorine implantation

In this paper, we demonstrate the low-temperature polycrystalline silicon thin-film transistors (LTPS-TFTs) with TaN metal-gate and HfO₂ gate dielectric to achieve high performance characteristics. A high performance LTPS-TFT with low threshold voltage 0.9 V, excellent subthreshold swing 0.15 V/decade and high I_on/I_min current ratio 1.9 × 10⁶ are derived without any hydrogen treatment. In addition, we also introduce the fluorine implantation prior to the Si thin-film crystallization to passivate the defects in grain-boundaries of the channel film and HfO₂/polysilicon interface. Significant improvements on subthreshold swing and I_min are observed. In addition, the transconductance degradation and threshold voltage instability due to hot carrier stress is also investigated, respectively. Finally, we derive a high reliability and performance LTPS-TFT with low threshold voltage ∼1.38 V, ultra-low subthreshold swing 0.132 V/decade and high I_on/I_min current ratio 1.21 × 10⁷, which is suitable for the application of system-on panel (SOP).