Currently there is great interest in developing manufacturing methods for integrating electronic circuitry into flexible and stretchable substrates for a spectrum of applications including roll-up displays, wearable biosensors, smart labels, and electronic skins (‘e-skins’) for robotics, for example. One fabrication strategy that has captured imaginations involves the use of digital or analog printing techniques to pattern electronic inks onto paper, plastic, rubber, or metal foils. However, printed electronics has a number of significant challenges, including spatial resolution, pattern registration, and printed circuit performance. In this project, we are pursuing a multi-pronged approach to address these challenges in order to bring roll-to-roll (R2R) printed electronics closer to reality. First, we focus on innovations in materials that allow printing of low voltage thin film transistors (TFTs), the key building blocks of flexible circuits. Specifically, we are experts in a particular kind of TFT, known as the electrolyte gated transistors (EGT), which can be easily printed and operates at sub-2V supply voltages. Here the key enabling material is a gel electrolyte that provides ultrahigh capacitance necessary for low voltage transistor operation. Second, we are developing a University of Minnesota patented printing strategy that we term SCALE, or Self-Aligned Capillarity-Assisted Lithography for Electronics. SCALE offers both high spatial resolution and precision registration of multiple layers of electronic ink. Specifically, the SCALE process employs a combination of digital printing and in-substrate capillary flow to produce self-aligned devices with feature sizes that are currently as small as 1 µm. We have pilot R2R lines for implementing imprint lithography and ink jet printing in order to develop and improve the SCALE process. We are currently perfecting our approach to making all circuit building blocks including transistors, diodes, resistors, capacitors, and interconnects with the ultimate aim of printing full electronic systems on paper and plastic.
The SCALE process facilitates the fabrication of high performance printed electronic devices including resistors, capacitors, and transistor.
Current research is investigating roll-to-roll processing of imprinting and printing for electronics fabrication.