Large Area Microcontact Printing Presses for Plastic Electronics
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Large Area Microcontact Printing Presses for Plastic Electronics Hee Hyun Lee1,2, Etienne Menard1, Nancy G. Tassi2, John A. Rogers1 and Graciela B. Blanchet 2 University of Illinois at Urbana-Champaign, Department of Materials Science and Engineering, Urbana, IL 61801, U.S.A. 2 DuPont, Central Research, Wilmington, DE 19880, U.S.A. 1
ABSTRACT Low cost fabrication is key to the successful introduction of organic electronics and roll to roll manufacturing processes. We propose here that extending flexography into the micron size resolution regime may provide an economical commercialization path for plastic devices. Flexography is a high-speed technique commonly used for printing onto very large area flexible substrates.[1] Although low resolution and poor registration are characteristics of today’s flexographic process, it has many similarities with soft lithographic techniques. This work shows that large, (12”x12”) high-resolution printing plates appropriate for use on small tag and label flexographic presses can be prepared using simple and inexpensive flexographic compatible processes. We illustrate the use of these plates for three representative soft lithographic processes: microcontact printing, replica molding, and phase shift lithography.
INTRODUCTION Microcontact printing (µCP) [2,3], a representative soft lithographic technique, has a demonstrated ability to print sub-micron features of Au and other metals, typically over small areas. It is well suited for the fabrication of conducting layers in high performance electronic devices such as backplanes for electrophoretic displays.[4] Numerous groups around the world have demonstrated that several techniques are viable for printing electronic devices[5-7]. Source/drain levels of thin film transistors (TFT) with small channel lengths have been printed using µCP [4], thermal [5], ink jet printing [6] and photolithography [7]. However, commercializing high performance flexible displays manufactured in a roll to roll process, would perhaps entail fabricating large area µCP plates and adopting a flexography-like process.[1] A starting point in such ambitious path, and the heart of this work, is learning how to produce flexible plastic printing plates that offer high resolution over large areas at a reasonable cost. In this work, we demonstrate that 12” x 12” polydimethylsiloxane (PDMS) stamps with micron size features can be fabricated via a simple procedure. The size was chosen to fit the plate size requirements of small commercial tags and labels flexographic presses. Stamps were used to print micron-size Au lines onto 12” x 12” Mylar substrates using standard thiol chemistry. We show also that these same stamps can be used as molds for replica molding of photopolymers and as phase masks for exposing photoresist layers.[8]
EXPERIMENTAL DETAILS
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The large PDMS stamps were constructed via a straightforward and inexpensive process. A standard photoresist (PR) coating on 12” x 14” kapton sheet (thickness = 125µm) was used to create relief structu
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