Control of electrical properties and gate bias stress stability in solution-processed a-IZO TFTs by Zr doping

• Improved subthreshold swing and ON/OFF ratio in a-IZO TFTs by Zr doping.
• Role of Zr in a-IZO TFTs as a carrier suppressor.
• Control of the turn on point at zero gate voltage.
• Evaluation of the gate bias stability of Zr doped IZO TFTs.
• Enhanced stability under negative gate bias stress (NBS).

Zr-doped indium zinc oxide (IZO) thin film transistors (TFTs) are fabricated via a solution process with different Zr doping ratios. The addition of Zr suppressed the carrier concentration in the IZO films, which was confirmed by Hall Effect measurements. As the amount of Zr was increased in the oxide active layer of TFTs, the subthreshold swing (S.S) reduced, the ON/OFF ratio improved, and the threshold voltage (Vth) shifted positively. Moreover, the starting points of the ON state for TFTs near the point zero gate voltage could be controlled by the addition of Zr. The 0.3% Zr-doped IZO TFT exhibited a high saturation mobility of 7.0 cm2 V−1 s−1, ON/OFF ratio of 2.6 × 106 and S.S of 0.57 V/decade compared the IZO TFT with 10.1 cm2 V−1 s−1, 1.7 × 106 and 0.75 V/decade. The Zr effect of the gate bias stability was examined. Zr-doped IZO TFTs were relatively unstable under a positive bias stress (PBS), whereas they showed good stability at a negative bias stress (NBS). The gate bias stability of the oxide TFTs were compared with the extracted parameters through a stretched-exponential equation. The characteristic trapping time under NBS of 0.3% Zr-doped IZO TFTs was improved from 8.3 × 104 s for the IZO TFT to 3.1 × 105 s.