Three-dimensional organic field-effect transistors on plastic substrates: flexible transistors with very high output cur
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1197-D09-05
Three-dimensional organic field-effect transistors on plastic substrates: flexible transistors with very high output current J. Takeya1, M. Uno1, 2, and K. Nakayama1 1 Graduate School of Science, Osaka University, Toyonaka 560-0043, Japan. 2 Technology Research Institute of Osaka Prefecture, Izumi 594-1157, Japan.
ABSTRACT Attractiveness of organic field-effect transistors are in their low-cost and easy fabrication processes as well as their mechanical flexibility, while a significant drawback has been their poorer transistor performances than those of silicon and oxide semiconductors because of lower carrier mobility in organic semiconductors. We have developed an easy MEMS-based process to fabricate three-dimensional organic transistors with metal-insulator-semiconductor structures of multiple vertical channels on plastic platforms. The design maximizes the space availability and the output current per area. The flexible three-dimensional organic transistors indeed present outstanding current of ~ 0.5 A/cm2, which is more than sufficient for driving pixels of typical organic light-emitting diodes. High on-off ratio up to 107 is also demonstrated. INTRODUCTION Development of organic semiconductor materials have been intensively driven by their attractiveness in low-cost and energy-saving fabrication processes for active electronic devices such as organic field-effect transistors (OFETs). Furthermore, the easy fabrication techniques at low temperature enable the use of plastic substrates, so that the organic transistors can form active-matrix elements in ultra-thin flexible displays, for example. So far, though much effort have been devoted to material development, even the best value of the carrier mobility ยต of organic semiconductor films remain in the order of 1 cm2/Vs [1-4], except for single-crystal devices [5-7]. Therefore, their performance in current amplification per pixel is not necessarily sufficient for practical use. Though decreasing the channel length L and increasing the width W can be another approach, this effect is limited as long as the channels and the electrodes are in the same plane as adopted in the conventional OFETs. Alternatively, we proposed a threedimensional organic field-effect transistor (3D-OFET) [8,9] to accumulate charge in its vertical semiconductor channels, so that space availability for the field-induced carriers is essentially improved. We already reported their very high output current per area and sufficient on-off ration with the structure using silicon substrates. Here in this presentation, we disclose a newly developed version with flexible substrates, which realized equally high performances; the flexible 3D-OFETs indeed present outstanding current exceeding 1 A/cm2, which is more than sufficient for driving pixels of typical organic light-emitting diodes (OLEDs), together with high on-off ratio of ~ 107.
EXPERIMENT Figures 1 illustrates schematic views of conventional planar-type and 3D-OFETs. In the 3D-OFET, the same metal-insulator-semiconductor (MIS)
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