Ultra-Thin Flexible Electronics with the Enhancement Inverter Based-on Pentacene Thin Film Transistor

Abstract

Thin film technology is advancing the research on fully flexible system for new applications in various fields, such as electronics, sensors and energy harvesting. In particular, thin film transistor (TFT) based flexible circuits have been studied for diagnostic devices, solar-cells, and flexible display. Although many companies and research groups have presented semi-flexible devices; a fully flexible system has not shown the sufficient result in terms of mechanical and electrical performance. Recently, inorganic-organic hybrid type TFTs have been developed and it shows the useful performance. However, the devices show limited performance at extremely small bending radius (< 1mm). In order to overcome the limitations, many researchers have suggested various solutions such as new materials of high mechanical strength, neutral strain position fabrication and ultra-thin substrates. Among these solutions, ultra-thin substrate is promising in the field of smart-skin, implantable device and patch-type biosensor. Depending on the decreasing substrate thickness, the strain strength also decreases dramatically. In this study, we demonstrate a nm-level ultra-thin device based on pentacene TFT, using de-bonding-technology. For de-bonding, a double layer of PVA and PAA based water soluble release layer was spin coated on the glass substrate. Subsequently, we coated the buffer layer on the release layer. The Al as gate electrode was deposited on the buffer layer by thermal evaporation. PMMA was then spin-coated and baked at 100 °C for 30 min. The pentacene and gold layer was deposited using thermal evaporation. CYTOP material was used for the passivation of the device. Finally, the device was de-bonded in double deionized water followed by curing at 75 °C for 30 min. Based on this process, we fabricated the nm-level thick TFT and enhancement inverter. After de-bonding process, the nm-level ultra-thin device showed good performance compared with the initial device before de-bonding.