Characterization of Al₂O₃ and ZnO multilayer thin films deposited by low temperature thermal atomic layer deposition on transparent polyimide

Recently, flexible and stretchable displays with organic light emitting diodes are one of hottest technical issues in electronic industries. Therefore, the application of polymer substrates is required because current glass-based materials cannot meet the required properties of flexible and stretchable displays. But there are some limitations for using polymers in display substrate such as inferior surface characteristics such as low scratch resistance, low hardness, and so on. Polymers have many additional technical issues like low stiffness, low heat resistance, low barrier properties, and high sensitivity to degradation compared with glass material. The low temperature atomic layer deposition (ALD) can be a good solution as a functional coating on the polymer substrate to resolve such surface characteristic issues. In this study, two oxide thin films, i.e., Al₂O₃ and ZnO, are deposited on a transparent polyimide (TPI) film substrate using a low temperature thermal ALD technique. To fabricate a reliable and high quality thin film, the pretreatment using O₂ plasma was conducted on the surface of TPI. Two oxide thin films are deposited as multilayer thin films by layer-by-layer process to investigate the effect of multilayer deposition of oxide thin films on mechanical properties. Surface morphologies of the deposited thin films are observed using optical microscopy and scanning electron microscope. Chemical characteristics of the deposited thin film are analyzed using x-ray photoelectron spectroscopy. The physical and mechanical characteristics of the Al₂O₃ and ZnO multilayer thin film are investigated using nanoindentation and microtensile tests.