Interdielectric Layer Engineering for Reliable Monolithic Integration of ITZO TFT Backplanes and InP QLEDs

The electrical performance and driving capability of monolithically integrated oxide thin-film transistor (TFT)-quantum-dot light-emitting diode (QLED) pixels are strongly affected by the dielectric environment formed during backplane-emitter integration. In this study, three interdielectric configurations─single-layer Al₂O₃, single-layer SiO₂, and an Al₂O₃/SiO₂ bilayer─were systematically investigated to elucidate the influence of dielectric composition and interfacial chemistry on the stability of indium-tin-zinc oxide (ITZO) TFTs and QLED driving behavior. Although the Al₂O₃-only device exhibited the best intrinsic TFT performance, hydrogen diffused into the Al₂O₃/SiO₂ bilayer during the plasma-enhanced chemical vapor deposition of SiO₂, which generated donor-like defects in the ITZO channel and negatively shifted the threshold voltage. Nevertheless, the bilayer simultaneously provided superior current leakage suppression and compatibility with the subsequent solution-processed QLED fabrication, enabling stable pixel operation. The bilayer-based TFT achieved a mobility of 24.82 cm² V^-1 s^-1, a subthreshold swing of 0.09 V dec^-1, and an on/off ratio of 8.78 × 10⁹. When used to drive InP QLEDs, the integrated pixel reached a peak luminance of 9,488.8 cd m^-2, a maximum current density of 285.3 mA cm^-2, and an external quantum efficiency of 7.15%, while maintaining an unchanged electroluminescence spectrum when driven by TFTs. These results demonstrate that interdielectric layer engineering, particularly the balance between hydrogen-induced voltage threshold shifts and process robustness, is critical for achieving reliable monolithic TFT-QLED operation for next-generation active-matrix display technologies.