| Abstract Scope |
Printed electronics is an emerging technology for large area electronics such as display, RFID, and flexible electronics to reduce manufacturing cost and improve throughput [1]. This research is focused on high resolution offset roll printing method to replace the expensive photolithography process which requires several steps to pattern one layer. This printing technique can also be used to directly print the soluble conductors and soluble semiconductor layer for all printed thin-film transistors (TFTs). The technique, championed by LG Display, was successfully used to demonstrate a 15” display where all etch resists were printed [2]. However, the versatility of this printing process can be further demonstrated by direct printing of soluble metals and semiconductors on flexible platform. In this work, we study reverse offset printing process and propose new method to form a high resolution printing plate. Employing this process, our work will encompass printing of high resolution electrode and devices. At first, we have focused on reverse offset printing method with particular emphasis given to blanket materials, printing plates and ink modification for fine print features. Blankets of this type of printing system require low surface energy, high hardness, smooth surface roughness, and uniform thickness. Instead of soft PDMS, silicone elastomer (methyl vinyl silicone) with high hardness is applied as blanket material. Etching methods such as wet etch, laser ablation, and dry etch are evaluated to pattern glass and Si wafers for realizing high resolution printing plate. Among these techniques, deep RIE shows good results having etch-profiles with deep and steep angles. To increase surface energy of plate, molybdenum with high surface energy is deposited on the surface of Si plate to easily take ink off of blanket with low surface energy. To print etch mask for replacement of photolithography, instead of developing new ink, commercial resist with 25% Novolak resin is modified by mixing high boiling point solvent to retard fast drying rate of ink. Finally very well defined patterns and line spaces of around 6um are achieved using this process. Using this verified process, we are in process of building TFTs where etch-resist is printed and metal layers are substituted by silver nanoparticles to achieve the small printed channel length. [1] Vivek Subramanian et al, Proceedings of IEEE, VOL. 93, No. 7, July 2005. [2] Youn Gyoung Chang et al, Journal of the SID 17/4 (2009), 301-307 (2009). |