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, HfO2, 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 (V th) variation due to electron trapping, while the negative bias stress (NBS) and negative bias temperature stress (NBTS) brought about a much smaller V th 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.

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