DEPOSITION AND CHARACTERIZATION OF ZnO THIN FILMS FOR THIN-FILM TRANSISTOR APPLICATIONS

Abstract

Zinc oxide (ZnO) is an attractive semiconductor for thin-film transistor (TFT) applications because of its wide direct band gap, relatively high electron mobility, optical transparency, chemical stability and compatibility with low-temperature thin-film processing. The performance of ZnO-based TFTs is strongly dependent on the structural quality, surface morphology, film thickness, carrier concentration, optical properties and defect chemistry of the semiconductor layer. This study investigated the deposition and characterization of ZnO thin films intended for thin-film transistor applications. ZnO thin films were deposited as channel layers using a sol-gel spin coating technique to ensure uniformity and scalability, while the AAO dielectric layers were formed by controlled electrochemical anodization of aluminium substrates. The physical and structural characteristics of the films were examined using profilometry to determine thickness uniformity, scanning electron microscopy (SEM) to observe surface morphology, and Hall effect measurements to evaluate carrier mobility and electron concentration. Electrical performance of the fabricated TFTs was evaluated using standard current–voltage (I–V) testing in a field-effect transistor configuration. Profilometry confirmed uniform film thicknesses across both the ZnO and AAO layers, a prerequisite for stable device performance. SEM imaging showed that ZnO formed a dense, compact morphology beneficial for charge transport, whereas AAO displayed a nanoporous structure that contributes to its high surface area but can influence dielectric strength. Hall measurements indicated that ZnO exhibited a high carrier mobility of 114.6 cm²/Vs and moderate electron concentration, confirming its suitability for TFT channels. However, electrical characterization of the AAO layer revealed unintended conductivity, suggesting possible residual conductive pathways or incomplete anodization, which highlights the need for further process optimization. Nonetheless, further refinement of the AAO anodization process is needed to minimize leakage and enhance dielectric reliability.