Integration of ZnO nanoparticle transistors on freestanding flexible substrates

Nowadays, thin-film transistors (TFTs) are being actively researched not only by the scientific community but also by the industry. They are the crucial elements for the driving currents in flexible displays, radio frequency identification tags and wearable electronic skins. In this study, we present a low-cost integration process of ZnO nanoparticle TFTs on flexible substrates with a maximum process temperature limited to 115 °C. As gate dielectric a high-k resin filled with TiO2 nanoparticle was used. This nanocomposite combines the mechanical flexibility of organic compounds with the high dielectric permittivity of inorganic materials. For the stabilization of the nanoparticulated ZnO film, a high humidity treatment was performed subsequent to an ultra-violet irradiation step in order to prevent the adsorption of oxygen molecules by the nanoparticles. The transistor integration process was performed on a freestanding polyethylene terephthalate (PET) substrate. This technique enables a more realistic scenario for a later large-scale production and avails adequate photolithographic resolution and accurate alignment between different mask levels. Additionally, in order to improve the electrical properties of the nanoparticulated semiconducting film, the nanoparticles were deposited using either spin-coating or spray-coating techniques; furthermore, different surface pretreatments were executed