A dual function metal oxide interlayer as an oxygen-defect inhibitor and a gate-leakage suppressor for a hysteresis-free, solution-processed top-gated IGZO TFT

Abstract

Amorphous oxide thin-film transistors (TFTs), including a-InGaZnO (IGZO) in particular, are promising devices for display and other applications. For commercial fabrication, IGZO is typically fabricated using vacuum-based methods, involving high costs and complex equipment. These drawbacks are overcome by cost-effective, solution-based processes, which, however, do not deliver the IGZO layer of the same quality as vacuum-based methods. This results in a trade-off between mobility and stability of the respective devices, diminishing their overall performance. The compromise between mobility and stability in these devices arises from defects, notably oxygen vacancies, during solution-based fabrication. Here, we suggest a solution to this problem by the introduction of a MgO or AlO_x interlayer between the IGZO semiconductor and polymer insulator in a top-gate, bottom-contact TFT. The Mg and Al ions, originating from such an interlayer, suppress the appearance of the interfacial oxygen vacancies, serving as the major source of device instability, preserving at the same time bulk oxygen vacancies, promoting the mobility. In addition to this favorable function, the MgO/AlO_x interlayer, characterized by a wide band gap, improves the performance of the joint dielectric layer by reducing the leakage current. As the result of both these favorable properties within the proposed strategy, a stable, hysteresis-free, and considerably performing device with a mobility of 4.6 cm² V⁻¹ s⁻¹, an ON/OFF ratio exceeding >10^6.5, and a shift of the threshold voltage of 0.6 V could be fabricated, with all these parameters being superior as compared to the standard TFTs.