Highly reliable Si 3N 4–HfO 2 stacked heterostructure to fully flexible poly-(3-hexylthiophene) thin-film transistor

Abstract

A new and fully flexible Si 3N 4–HfO 2 stacked poly-(3-hexylthiophene) p-type thin film transistor (P3HT-TFT) was successfully fabricated on thin semi-transparent polyimide (PI) substrate. The success of the TFT manufacturing adopts: (a) very simple and cost-effective sol–gel spin-coating technique to obtain 10-nm high- k HfO 2 as dielectric layer over fully flexible PI substrate; (b) 50-nm silicon nitride (Si 3N 4) as the most efficient passivation layer on top of HfO 2 film; (c) bendable 30-nm P3HT channel film by spin-coating method. Current–electric field characteristics of HfO 2 layer in metal–insulator–metal (MIM) and TFT configurations, with or without Si 3N 4 passivation layer, were carefully evaluated. The origin of unsatisfactory leakage current in MIM and TFT structures could be effectively suppressed by means of Si 3N 4 film as the efficient passivation layer. The bottom-gate TFT demonstrated the on-to-off ratio 2 × 10 4 for drain current, −1.9 V threshold voltage and good saturation mobility (0.041 cm 2 V −1 s −1). The proposed devices were examined in convex and concave types of various radii of curvature ( R c) in order to explore the manufacturing feasibility and electrical reliability of the fully flexible TFT for practical applications. In addition, various folding times and environmental stability on aforementioned devices with respective to electrical performances were also evaluated.