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 (Al₂O₃, HfO₂, Ta2O5, and ZrO₂) has been conducted. High-k gate dielectrics have a sufficiently low leakage current for the gate insulator of IGZO-TFTs and ZrO₂ has the highest dielectric constant, followed by Ta2O5, HfO ₂, and Al₂O₃. 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 (Vth) variation due to electron trapping, while the negative bias stress (NBS) and negative bias temperature stress (NBTS) brought about a much smaller Vth shift. In particular, the Al₂O₃ and HfO₂ gate insulators have significant threshold voltage shifts for the PBS and PBTS measurements. Among the four different high-k gate dielectrics, ZrO₂ 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.