Gyo Kitahara1 2 Keisuke Aoshima1 Jun'ya Tsutsumi2 Hiromi Minemawari2 Shunto Arai1 Tatsuo Hasegawa1 2

1, The University of Tokyo, Tokyo, , Japan
2, National Institute of Advanced Industrial Science and Technology, Tsukuba, , Japan

The printing-based patterned-layer formation of electrode metal layers are one of the key printed electronics technologies. Recently, we developed a groundbreaking electrode printing technique, called as “surface photoreactive nanometal printing (SuPR-NaP)”, which allows easy manufacture of ultrafine conductive silver patterns with a high submicron resolution [1]. This technique is based on the unique chemisorption effect of silver nanoparticles (AgNPs) on a photo-activated patterned polymer surface that is manufactured by masked ultraviolet irradiation of a perfluoropolymer, Cytop (Asahi Glass Co., Ltd.), layers. The SuPR-NaP technique allows us to produce ultrafine electrode patterns with minimum line width of 0.8 micron, by which the mass production of transparent conductive electrodes is now undertaken for the use as touch screen sensors. The next important target of the printing technique is to use and accommodate the printed ultrafine electrode patterns for the production of organic thin-film transistor (OTFT) arrays on flexible plastic substrates.
In this presentation, we will present and discuss low-voltage operation of OTFTs composed of ultrafine printed source/drain electrodes produced by the SuPR-NaP technique [2]. For this purpose, we utilized the highly-insulating Cytop layer, not only for producing the photo-activated patterned surface for the SuPR-NaP technique, but also as the gate dielectric layer for producing bottom-gate, bottom contact OTFTs [3]. To realize the low-voltage operation of OTFTs, we systematically examined the thickness, voltage-durability and capacitance of the thin Cytop layers. We found that the ultrathin thickness as thin as 26 nm is useful to obtain high-voltage durability up to 2.4 MV/cm and large-capacitance of 97 nF/cm2, even after the top printed silver electrodes are deposited by the SuPR-NaP technique. Based on the examination, we successfully operated polycrystalline pentacene OTFTs using the ultrathin Cytop layer, at low voltage less than 2 V with negligible hysteresis characteristics. Additionally, we found that the surface modification of the printed silver electrodes with pentafluorobenzenethiol is effective to suppress the contact resistance and to enhance the drain current. We will discuss the stable low-voltage operation of the OTFTs in terms of the formation of high-quality semiconductor/gate insulator interface with use of the ultra-hydrophobic nature of the surfaces of ultrathin Cytop layers.
[1] T. Yamada et al., Nat. Commun. 7, 11402 (2016). [2] G. Kitahara et al., Organic Electron. 50, 426 (2017). [3] K. Aoshima et al., Organic Electron. 41, 137 (2017).