Fabrication of High-Performance Organic Thin-Film Transistor Arrays and Application to 5-inch Flexible Displays
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1196-C05-02
Fabrication of High-Performance Organic Thin-Film Transistor Arrays and Application to 5-inch Flexible Displays Y. Fujisaki, T. Takei, Y. Nakajima, H. Sato, M. Suzuki, H. Fukagawa, G. Motomura, D. Kumaki, T. Yamamoto, H. Fujikake, T. Kurita, and S. Tokito 1
NHK Science and Technology Research Laboratories, Kinuta, Setagaya-ku, Tokyo 157-8510, Japan. ABSTRACT We have demonstrated a 5-inch flexible color liquid crystal display (LCD) and organic light emitting display (OLED) driven by low-voltage-operation organic thin-film transistors (OTFTs). To achieve high-quality and high-resolution moving images, OTFTs with high performance, for example, high mobility, high ON/OFF ratio, low sub-threshold slope (SS), and low operating voltage, have been developed. We fabricated pentacene-based low-voltage OTFTs with a Ta2O5 gate dielectric prepared in a low-temperature process. The resulting OTFT array showed a high mobility of 0.3-0.4 cm2/Vs, an ON/OFF ratio over 107, VT of 2.7 V, and low SS at 0.3 V/decade. OTFTs with solution-processable materials such as fluoropolymer gate dielectric and liquid-crystalline semiconducting polymers, PBTTT, were also investigated. The electrical characteristics and stabilities of these devices, as well as a demonstration of OTFT-driven flexible displays, are discussed. Both the flexible LC device and the OLED device were successfully fabricated on the pentacene-based OTFT arrays. Printing and lamination techniques were introduced to assemble the flexible LC device. Phosphorescent polymer materials, which can be patterned by ink-jet printing, were used for the emitting layer of the OLED. Color moving images were successively shown on the resulting 5-inch displays using an active-matrix driving technique of the OTFT at a low driving voltage of 15 V. INTRODUCTION Organic thin-film transistors (OTFTs), which can be fabricated directly on plastic film at low temperature, have attracted considerable attention for their application to low-cost and largearea electron devices. In recent years, the performance of OTFTs has improved considerably, and a number of vacuum-deposited or solution-processed organic semiconductors have been reported that equal or even surpass the performance of a-Si TFTs [1,2]. With this rapid progress, many studies aimed at developing a wide range of plastic electronics have been reported. Among these applications, flexible displays are attracting considerable attention due to their low weight, robustness, large area, portability, and lower processing cost. These displays are sought after as a new-generation technology, following the maturation of large flat panel display technology. Many research institutes are developing various types of flexible displays aimed at practical applications [3-5]. However, to realize such applications, the performance of the OTFTs requires further improvement in carrier mobility, subthreshold slope, and current on/off ratio. A reduction in operating voltage and improvement of stability and reliability are still concerns. Moreover, the
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