Description
In order for low-cost printed electronics to become ubiquitous, a suitable printing technique must be found. Gravure is a high-speed roll-to-roll printing technique which has many of the characteristics necessary for an industrially viable process for printed electronics. In gravure printing, an engraved cylinder is submerged in an ink fountain and then rolled over a flexible substrate such as plastic or paper. A tightly pressed blade, called the doctor blade, wipes off excess ink from the non-image areas of the cylinder surface before contact with the substrate. Gravure has the advantages of high throughput, long print runs, uniformity, and versatility.
We explore the construction of a gravure printing system, including the design of a laboratory size printer and cylinder making techniques. Industrial best practices are presented along with techniques discovered in the laboratory. We discuss the choice of cylinder material, as well as different metrics for determining acceptable cylinders. Next, we compare four methods of patterning cylinders and discuss challenges in scaling to an industrial printing system.
Next, we consider the theoretical considerations necessary to develop a printing process to deposit conductive lines less than 20 microns wide, suitable for bottom-gate thin film transistors (TFTs). We discuss the physical principles governing the gravure printing process, which can be separated into the two actions of cell emptying and drop spreading. We demonstrate gravure-printed nanoparticle lines and present techniques for optimizing the printed line quality by varying print parameters such as cell spacing and viscosity. Finally, we discuss possible routes to printed TFTs and future work.