Organic Thin Film Transistors with Contacts Printed from Metal Nanoparticles
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Organic Thin-Film Transistors with Contacts Printed From Metal Nanoparticles Yiliang Wu, Yuning Li, Sandra Gardner, Beng S. Ong* New Materials Design and Synthesis Laboratory, Xerox Research Centre of Canada, Mississauga, Ontario, Canada L5K 2L1 ABSTRACT Metal nanoparticles were studied as solution printable precursors to highly conductive elements for electronic device applications. Dispersions of gold and silver nanoparticles stabilized respectively with butanethiol and hexadecylamine in organic solvents were used to prepare electrode features for organic thin film transistors (OTFTs) via stencil printing. The printed features, annealed at a relatively low temperature of 140-160 °C, yielded metal electrodes with conductivities resembling those of vacuum-evaporated pure metals. The OTFTs with the source and drain electrodes of this nature exhibited field effect transistor performance identical to those of devices having vacuum-evaporated metal electrodes.
INTRODUCTION Printed organic thin film transistors (OTFTs) are potentially low-cost alternatives to mainstream amorphous silicon-based technologies for electronic applications. They are particularly suited for the large-area devices (e.g., active-matrix displays) where high processing speeds and transistor density are not essential. They may also find applications in low-end electronics (e.g., radio frequency identification (RFID) tags) where high cost of silicon packaging becomes limiting. Most of the research efforts in this area has been devoted to the development of solution processable organic semiconductor materials [1-3], while relatively few studies have been conducted on the equally important conductive materials for use as electrodes, pixel pads, conductive lines, and interconnects for OTFT circuits [4-11]. The source and drain electrodes for OTFTs are particularly critical, as they need to meet specific physical and electrical requirements for long-term operational stability. First, they have to be energetically compatible with the organic semiconductor to form ohmic contact for efficient charge injection. Second, the electrodes must be chemically stable to the semiconductor and gate dielectric to prevent adverse chemical interactions at the interfaces. Third, they should be electrically stable over time to sustain a long operation life. Finally, it is highly desirable that the conductive materials are printable on flexible substrates to enable flexible electronic devices. Earlier work on printable conductors had focused on conductive polymers such as PEDOT/PSS [4], polyanilines [5], and polypyroles [6], which are essentially low-conductivity materials (200 °C) [10]. Conductive elements were recently inkjet printed from silver nanoparticles, but high conductivity was only obtained at high annealing temperatures (>300 °C) [11]. It appears that carefully designed metal nanoparticles can serve as solution processable precursors to highly conductive elements if the particle size is small enough and proper stabilizers are used. The melting temperatu
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