Micrometer-scaled OFET channel patterns fabricated by using PEDOT/PSS microfibers

We have easily fabricated channel patterns of organic field-effect transistors (OFETs), in which channel lengths were 5 μm, by using wet-spun poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) microfibers with diameters of ca. 5 μm. Pentacene-based FETs with a top-contacted configuration, showed a hole mobility of 0.13 cm2 V−1 s−1 and on/off current ratio of 9.4 × 104. The device also showed large current of ca. 160 μA (VD = −50 V; VG = −50 V), reflecting shorter channel length of the devices. We have evaluated self-assembled monolayer (SAM) through measurements of water contact angle and by Zisman plot. As a result, critical surface tension of the octadecyltrichlorosilane (OTS)-treated SiO2 surface is 17 mN m−1 which is consistent with that of well-known SAM. We also well analyzed the cross-sections of the device by a scanning transmission electron microscopic (STEM) technique. The results indicated that the thicknesses of the pentacene layer in the channel part and Au layer in the source/drain part were ca. 30 and 30 nm, respectively. Furthermore, it is also indicated that the 100-nm grains of the pentacene were well adhered on the surface of the SAM-formed SiO2 layer.