Large Area Printing of Organic Transistors via a High Throughput Dry Process
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Large Area Printing of Organic Transistors via a High Throughput Dry Process Graciela B. Blanchet*, Yueh-Lin Loo†º, J. A. Rogers†, F. Gao*, C. R. Fincher* * DuPont, Central Research Wilmington, DE, 19880, USA † Bell Laboratories, Lucent Technologies, Murray Hill, NJ, 07974, USA º Current Address, University of Texas at Austin, Austin, Texas Organic electronic systems offer the advantage of low weight and flexibility at potentially lower cost. Although the fabrication of functioning plastic transistors using approaches such as ink jet, lithography and stamping has been described i1-3, chemically compatible materials that allow for the sequential application of liquid layers is a technical barrier. Material issues maybe the Achilles heel of ultimately printing organic electronic devices as newspapers today, at high speeds and in a reel to reel process. We introduce a novel process -- thermal transfer -- a nonlithographic technique that enables printing multiple, successive layers via a dry additive process. This method is capable of patterning a range of organic materials at high speed over large areas with micron size resolution and excellent electrical performance. Such a dry, potentially reel-to-reel printing method may provide a practical route to realizing the expected benefits of plastics for electronics. We illustrate the viability of thermal transfer and the ability to develop suitable printable organics conductors by fabricating a functioning 4000 cm2 transistor array. Having demonstrated the feasibility of organics as active electronic components 1-3 it is now important to identify viable material sets and fabrication methods. Since printing thin film transistors (TFT) from sequential liquid layers present serious compatibility issues, it is perhaps more practical today to consider fabricating organic electronic devices using techniques that circumvent the serious materials and process uncertainties presently associated with printing sequential layers from solution. Thermal imaging provides an attractive alternative path. With printing proceeding via the ablative transfer of solid layers the solvent compatibility issues that are encountered when printing sequential layers from solution are entirely avoided. Thermal imaging also offers high printing speed, micron resolution and adequate registration. This method involves the pixelized transfer of a thin solid layer, encompassing a digital image, from a donor film onto a flexible receiver. The sequential transfer of images from different solid layers builds multilayer devices. The structure of these films is illustrated in Figure 1. A 40 Watt 780 nm infrared diode laser, split into 250 2.7 _m x 5 _m individually addressable spots, is focused through the donor base onto a light sensitive layer . The efficient conversion of light to heat at this interface decomposes surrounding organics into gaseous products. Their expansion thus propels the thin conducting layer onto the receiver film. The desired conducting pattern is printed by selectively transferrin
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