Pushing Roll-to-Roll Nanoimprint Lithography towards Commercial Applications: Challenges, Opportunities and Findings
Professor Kenneth R. Carter
Department of Polymer Science and Engineering
University of Massachusetts Amherst
With the shift from the development of processes for silicon wafer platforms to the development of manufacturing platforms for fabrication of low-cost, large-area nano-materials and devices using roll-to-roll processing technology, new opportunities and challenges are presented. We have built a roll-to-roll nanoimprint (R2RNIL) facility to address the challenge of fabricating nanostructured thin films on a high-speed, high-reliability platform. The goal of our work is to enable commercialization of R2RNIL by any number of entities for a wide variety of end-applications ranging from sensors, water purification, batteries and thin film organic electronic devices. Fast R2R processes have several stringent requirements in terms of the selection of materials for imprint. First, liquid resists having good coating properties are preferred because they can be continuously and uniformly coated onto plastic substrates and be easily imprinted with low pressure - imprinting will be done under web tension only. Second, such liquid resists should have low viscosity before curing for fast imprinting. Third, resists used in R2RNIL need to be quickly cured and with minimum shrinkage after curing. We initially pursued UV-curable compositions as thermoplastic materials used in NIL processes require very high pressures and relatively long processing times to complete the imprinting. We note that UV curing can be accomplished in seconds. The proper choice of mold material and surface chemistry is a critical component of the successful implementation of this R2RNIL. We report the use of a range of different silicones and fluoropolymers in the NIL process. Our initial focus has been to generate molds of optical gratings of periodicities and aspect ratios. We will report our results, including the fabrication of 70nm grating arrays and demonstration of applications of R2R-fabricated sensors and detectors. Key challenges and findings will be outlined in the selection of mold-materials, resists and amelioration of defects.