Effect of ALD- and PEALD- Grown Al2O3 Gate Insulators on Electrical and Stability Properties for a-IGZO Thin-Film Transistor

This study investigated the electrical and stability characteristics of Al2O3 as a gate insulator, which was deposited by various atomic layer deposition methods in top-gate staggered amorphous InGaZnO (a-IGZO) thin film transistors. A trimethylaluminum precursor was used as an Al source, and H2O gas (H2O device) and O-2 plasma with a long plasma time (O-2 LP device) and a short plasma time (O-2 SP device) were used as oxidants. The initial electrical characteristics, including the hysteresis, on-off current ratio, and subthreshold swing, were superior in the H2O device compared to the O-2 LP and O-2 SP devices. In the positive bias stress (PBS) results, the degradation characteristics showed a tendency similar to the transfer properties. However, under the negative bias illumination stress (NBIS), the stability of the H2O device was significantly reduced compared to the O-2 LP and O-2 SP devices. In this paper, the mechanism of instability, which has opposite results in terms of the PBS and NBIS for the three devices, was identified using capacitance-voltage, three-terminal charge pumping as electrical analysis techniques and secondary ion mass spectroscopy (SIMS) as a physical analysis technique. It was confirmed that the surface oxidation of a-IGZO deteriorates the interfacial properties, causing the transfer characteristics to degrade. The carbon of the Al2O3 film identified via SIMS analysis acts as a trap layer, causing deterioration in the PBS. Alternatively, in the NBIS, it was observed that the carbon acts as a capture site for photo-excited holes, thereby promoting device stability. [GRAPHICS] .Z

Automated summary

This study compared the electrical and stability characteristics of Al2O3 as a gate insulator deposited by various atomic layer deposition methods in a-IGZO thin film transistors. The H2O device exhibited superior initial electrical characteristics but reduced stability under negative bias illumination stress compared to the O-2 LP and O-2 SP devices.