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Article http://pubs.acs.org/journal/acsodf
Proving Scalability of an Organic Semiconductor To Print a TFTActive Matrix Using a Roll-to-Roll Gravure Junfeng Sun,† Hyejin Park,† Younsu Jung,† Grishmi Rajbhandari,† Bijendra Bishow Maskey,† Ashish Sapkota,† Yasuo Azuma,‡ Yutaka Majima,‡ and Gyoujin Cho*,† †
Department of Printed Electronics Engineering of Sunchon National University, National University, Sunchon 540-742, Korea Materials and Structure Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
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S Supporting Information *
ABSTRACT: Organic semiconductor-based thin-film transistors’ (TFTs) chargecarrier mobility has been enhanced up to 25 cm2/V s through the improvement of fabrication methods and greater understanding of the microstructure chargetransport mechanism. To expand the practical feasibility of organic semiconductor-based TFTs, their electrical properties should be easily accessed from the fully printed devices through a scalable printing method, such as a roll-to-roll (R2R) gravure. In this study, four commercially available organic semiconductors were separately formulated into gravure inks. They were then employed in the R2R gravure system (silver ink for printing gate and drain−source electrodes and BaTiO3 ink for printing dielectric layers) for printing 20 × 20 TFT-active matrix with the resolution of 10 pixels per inch on poly(ethylene terephthalate) (PET) foils to attain electrical properties of organic semiconductors a practical printing method. Electrical characteristics (mobility, on−off current ratio, threshold voltage, and transconductance) of the R2R gravure-printed 20 × 20 TFT-active matrices fabricated with organic semiconducting ink were analyzed statistically, and the results showed more than 98% device yield and 50 % electrical variations in the R2R gravure TFT-active matrices along the PET web.
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INTRODUCTION During the past two decades, printed electronics has been developed for manufacturing novel flexible and large electronic devices with low functionality, such as passive radio frequency identification tags, digital signage, e-papers, and wireless sensors.1−3 However, to date, there are no commercial products in the category of fully printed thin-film transistor (TFT)-based electronic devices because Si-based devices prevail in the competition to commercialize TFT-based devices. To have competitiveness over Si-based devices, printed TFT-based electronic devices should prove their superior scalability to mass-produce flexible large-area devices through a roll-to-roll (R2R) printing method as a typical advanced manufacturing system4−7 because the flexible large-area TFT-based devices are difficult to manufacture using current photolithography and vacuum deposition technologies, which are generally used in Si technology. An R2R gravure has been recently demonstrated as a potential advanced manufacturing technology to fabricate TFT-active matrix (TFT-AM)-based tactile sensors on poly(ethylene terephthalate) (PET) roll using silver-nanoparticle-based conducting ink, BaTiO3-nanoparticle-based dielectric ink, and carbon-nanotube-based semiconducting ink.8,9 Those inks were all formulated to meet the continuous R2R gravure printing with a printing speed of 6 m/min using a thermal curing chamber with length of 1 m under 150 °C, and R2R-printed TFTs were operated under a reasonable direct current (DC) voltage (
