Comparative Study of Device Performance and Reliability in Amorphous InGaZnO Thin-Film Transistors with Various High-$k$ Gate Dielectrics

A comparative study of the electrical characteristics and device instabilities in InGaZnO thin-film transistors (IGZO-TFTs) with four different high-$k$ gate dielectrics (Al 2 O 3 , HfO 2 , Ta 2 O 5 , and ZrO 2 ) has been conducted. High-$k$ gate dielectrics have a sufficiently low leakage current for the gate insulator of IGZO-TFTs and ZrO 2 has the highest dielectric constant, followed by Ta 2 O 5 , HfO 2 , and Al 2 O 3 . However, the charge trapping in high-$k$ gate dielectrics induced the bias stress instability and degradation of IGZO-TFTs over time. In particular, the positive bias stress (PBS) and positive bias temperature stress (PBTS) caused a large positive threshold voltage ($V_{\text{th}}$) variation due to electron trapping, while the negative bias stress (NBS) and negative bias temperature stress (NBTS) brought about a much smaller $V_{\text{th}}$ shift. In particular, the Al 2 O 3 and HfO 2 gate insulators have significant threshold voltage shifts for the PBS and PBTS measurements. Among the four different high-$k$ gate dielectrics, ZrO 2 is the most promising high-$k$ gate dielectric for the IGZO-TFTs because of its high dielectric constant, low subthreshold swing, high mobility, large drive current, small hysteresis, and high on/off current ratio.