Inkjet Printing of Polymer Thin-Film Transistor Circuits
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Inkjet Printing of
Polymer Thin-Film Transistor Circuits
Seamus E. Burns, Paul Cain, John Mills, Jizheng Wang, and Henning Sirringhaus Abstract We present a process for manufacturing printable thin-film transistors (TFTs) that is based on solution processing and direct inkjet printing of polymer semiconductors, dielectrics, and conductors, as well as inorganic nanoparticle conductors. We show that the high device yield, uniformity, and resolution required for thin-film electronic applications can be achieved by using a substrate that contains a surface energy pattern to control the flow and spreading of inkjet droplets. This technique overcomes many of the limitations of current inkjet printing technology related to its limited droplet placement accuracy. We demonstrate the potential of this printing-based TFT manufacturing process with the fabrication of 50 dpi active-matrix, polymer dispersed liquid-crystal and Gyricon Smartpaper electronic paper displays. Keywords: displays, inkjet printing, polymer electronics, thin-film transistors (TFTs).
Introduction Inorganic semiconductors and the technology of manufacturing integrated circuits based on photolithographic patterning and vacuum deposition have experienced phenomenal development over the last 50 years and penetrated virtually every area of today’s life. In the field of thin-film electronics, thin-film transistor (TFT) technology based on amorphous silicon (a-Si) or polycrystalline silicon (poly-Si) has become the dominant technology for largearea electronic circuits on noncrystalline substrates such as active-matrix liquidcrystal displays on glass. However, there is a range of interesting potential applications that inorganic TFT technologies have found difficult to address: to date, no active-matrix displays on flexible substrates exist, in spite of long-standing research efforts. Generally, there is no established thin-film electronics technology that can place electronic functionalities directly onto flexible substrates such as plastic or paper. Manufacturing of very large-area electronic circuits, such as poster-sized displays, is challenging, and applications that require low-cost transistor circuits, such as very inexpensive (less
MRS BULLETIN/NOVEMBER 2003
than 10 cents each) intelligent labels as replacements for optical bar codes, have not been realized using conventional silicon technology. To develop such large-area or low-cost applications on flexible substrates, there is currently a strong interest in thin-film electronics technologies that, unlike conventional a-Si or poly-Si, are not based on vacuum or plasma deposition techniques and photolithographic patterning, but on materials deposition and patterning by solution processing and direct-write printing using both organic1–8 and inorganic materials.9 Some recent work in the field has been reviewed, for example, in the July 2001 issue of MRS Bulletin on “Emerging Methods for Micro- and Nanofabrication.” Manufacturing by solution-based printing offers attractive potential advantages: A so
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