A new shift register employing bottom-gate In-Ga-Zn-O thin-film transistors (IGZO TFTs) was proposed and fabricated. Depletion-mode IGZO TFTs were successfully turned off by employing two low-voltage-level signals. The IGZO shift register exhibited a high-voltage output pulse without any distortion and a maximum clock frequency of 417 kHz. The proposed shift register would be an important building block for a depletion-mode oxide TFT display.

This study examined the performance and photo-bias stability of double-channel ZnSnO/InZnO (ZTO/IZO) thin-film transistors. The field-effect mobility (μFE) and photo-bias stability of the double-channel device were improved by increasing the thickness of the front IZO film (tint) compared to the single-ZTO-channel device. A high-mobility (approximately 32.3 cm2/Vs) ZTO/IZO transistor with excellent photo-bias stability was obtained from Sn doping of the front IZO layer. First-principles calculations revealed an increase in the formation energy of O vacancy defects in the Sn-doped IZO layer compared to the IZO layer. This observation suggests that the superior photo-bias stability of the double-channel device is due to the effect of Sn doping during thermal annealing. However, these improvements were observed only when tint was less than the critical thickness. The rationale for this observation is also discussed based on the oxygen vacancy defect model.

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We demonstrated the fabrication of flexible amorphous indium gallium zinc oxide thin-film transistors (TFTs) on high-temperature polyimide (PI) substrates, which were debonded from the carrier glass after TFT fabrication. The application of appropriate buffer layers on the PI substrates affected the TFT performance and stability. The adoption of the SiNx/AlOx buffer layers as water and hydrogen diffusion barriers significantly improved the device performance and stability against the thermal annealing and negative bias stress, compared to single SiNx or SiOx buffer layers. The substrates could be bent down to a radius of curvature of 15 mm and the devices remained normally functional.