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A number of reports have demonstrated the feasibility of oxide thin film transistors (TFTs) replacing silicon-based technology in active-matrix liquid-crystal displays (AMLCDs) and active-matrix organic light emitting diodes (AMOLEDs). Among oxide materials, zinc tin oxide (ZTO) is being tipped off as an appropriate alternative for amorphous-silicon. ZTO tops its adversaries because it has a robust amorphous phase compared to ZnO and has a more simple composition compared to InGaZnO. Although ZTO TFTs showed their good performance, the stability issues of these devices have not yet been addressed. Because TFTs are used in display technology, the effect of light on their electrical performance is a vital matter that should be considered. Therefore, in this work, the effect of light illumination on the negative bias temperature instability (NBTI) of ZTO TFTs is investigated.

Amorphous HfInZnO (HIZO) - thin film transistor (TFT) with the bottom gate structure were fabricated to investigate the effect of light illumination on the transfer curves and stability characteristics under negative bias stress. The TFTs with passivation layers showed promising characteristics when measured in the dark, with a saturation mobility (usat) of 9.0 cm2/Vs, a sub-threshold swing (SS) of 0.34 V/dec and an on/off ratio of ~108. However, when exposed to light of wavelengths below 500nm, the transfer curve changes remarkably, with an increase of SS and off-current (Ioff). The change in the transfer curves were also studied by examining them before and after negative bias-temperature-illumination stress. The increase of SS under light illumination can be due to the increase in the number of activated interfacial traps by photon energy.

Amorphous oxide semiconductor memory devices with HfInZnOx as the channel layer and high k dielectric stacks as the charge storage medium were fabricated. HfO2 and Al2O3 and HfAlOx films were examined as the charge trap layers. The drain current - gate voltage transfer curves of the fabricated charge trap memories show a large hysteresis due to the electron trapping and de-trapping at the interfaces between the high-k charge storage layer and the SiO2. The device structure and operational scheme for the amorphous oxide semiconductor charge trap memories were suggested based on these properties.

Amorphous HfInZnO (HIZO) - thin film transistor (TFT) with the bottom gate structure were fabricated to investigate the effect of light illumination on the transfer curves and stability characteristics under negative bias stress. The TFTs with passivation layers showed promising characteristics when measured in the dark, with a saturation mobility (µsat) of 9.0 cm2/Vs, a sub-threshold swing (SS) of 0.34 V/dec and an on/off ratio of ~108. However, when exposed to light of wavelengths below 500nm, the transfer curve changes remarkably, with an increase of SS and off-current (Ioff). The change in the transfer curves were also studied by examining them before and after negative bias-temperature-illumination stress. The increase of SS under light illumination can be due to the increase in the number of activated interfacial traps by photon energy.