The Optimization and Development of Additive Manufacturing Strategies for High Performance Printed Electronics and Metal Interconnects

Abstract

Additive manufacturing strategies, including printing, provide tremendous potential to manufacture low-cost, high-performance electronic devices. While printed electronics have been prepared by a variety of traditional printing strategies including gravure and inkjet printing, these techniques face limitations including low lateral resolution and aspect ratio (feature height/feature width) and difficulty aligning multiple layers of functional materials to build complex electronic devices including diodes and transistors. Previous research in the Francis and Frisbie research groups at the University of Minnesota led to the development of the SCALE (Self-aligned Capillarity-Assisted Lithography for Electronics) process to address these limitations. This process combines high resolution UV micro imprinting of capillary channels and connected ink receiving reservoirs with inkjet printing of electrically functional inks into the reservoirs and spontaneous capillary flow which fills the connected capillary channels with the inks. By creating networks of carefully positioned capillary channels, the complex structures of electronic devices are deposited with higher resolution and layer-to-layer positioning accuracy than achieved with conventional printing methods. These strategies are fully compatible with roll-to-roll production, but this capability hadn’t been demonstrated prior to this work. In this dissertation, a process for roll-to-roll production of the plastic substrates patterned with SCALE capillary channels and reservoirs was developed using low-cost, roll-based imprinting stamps and common sources of air entrapment defects were identified and addressed. Low resistance, high precision metal interconnects were developed and optimized using these patterned plastic substrates. Variables affecting the conductor uniformity, flexibility, and reproducibility were identified and optimized to maximize the useful length and electrical performance of the conductors. This resulted in a fully roll-to-roll compatible manufacturing process for low resistance, flexible metal interconnects. A new, two level capillary channel geometry was developed for conductor fabrication to allow the production of solid metal conductors with flat tops, aspect ratios near 2, and precise feature edges, embedded in the plastic substrates. Finally, a roll-to-roll inkjet printing process was developed for full continuous manufacturing of SCALE devices, and silver SCALE conductors were prepared using this continuous process. This work develops strategies for full roll-to-roll production of SCALE devices and high-performance metal interconnects on patterned plastic substrates.