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 Al 2 O 3, single-layer SiO 2, and an Al 2 O 3 /SiO 2 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 Al 2 O 3 -only device exhibited the best intrinsic TFT performance, hydrogen diffused into the Al 2 O 3 /SiO 2 bilayer during the plasma-enhanced chemical vapor deposition of SiO 2, 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 cm 2 V –1 s –1, a subthreshold swing of 0.09 V dec –1, and an on/off ratio of 8.78 × 10 9 . 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.