Organic Field Effect Transistors Having Hundreds of Nanometers Long Channels
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Organic Field Effect Transistors Having Hundreds of Nanometers Long Channels Liwei Shang, Ming Liu, Deyu Tu, Lijuan Zhen, Ge Liu, and Xinghua Liu Key Laboratory of Nanofabrication and Novel Devices Integration Technology, Institute of Microelectronics, Chinese Academy of Sciences, No.3, West road of Beitucheng, Chaoyang Disctrict, Beijing, 100029, China, People's Republic of ABSTRACT This work studied systemically the device characteristics when the OFETs' channels turn into hundreds of nm. Standard planar OFETs have been fabricated using electronic beam lithography. Copper phthalocyanine is used as the semiconductor materials. When reduce the L to about 300 nm will lead an abrupt degradation of device performance. The ratio of Ion/Ioff turns from several hundreds into couple of tens. And when change the L to about 100 nm, the mobility turns from 10-2 cm2/Vs into 10-5 cm2/Vs, and the threshold voltage turns from about 12 V into 36 V. These abrupt changes are due to the changes of interface between active layer and insulator layer caused by the reducing the L to close to the grain size. INTRODUCTION Recently, organic field-effect transistors (OFETs) have attracted much attention due to their potential applications of a variety of large-area electronic applications, such as displays, sensors and electronic barcodes etc [1]. Most of the reported devices focus on the channel length (L) range of several micrometers. Only a few of reports demonstrated the situation of OFET having L of submicrometer [2-15]. Y. Zhang et al has indicated that some sub-100 nm OFET had been fabricated in 1987 [2] and 1993 [3], but their characteristics were poor [8], exhibiting only minor gating effect. They also summarized the development of submicrometer channel long OFET during 1993 and 2003. In these work, the characteristics of the devices have degraded when the channel length was decreased to a certain minimum value [8]. The reason was analyzed to be ballistic transporting [6] or punch-through effect [7]. Using a 3 steps EBL process, Zhang et al have successfully made an OFET with only 27 nm long channel in 2003. Although this device show an obviously saturation section, the performance is still not good as single grain transistor [8]. Meanwhile, J. Zaumseil et al have made a series of OFETs with channel length from 250 µm to 150 nm using high resolution rubber stamps supported source and drain metal electrodes [9]. Their result showed that there is degradation when the channel length decreased to 150 nm like the previous results [4-7]. In the same year, N. Stutzmann et al reported that the embossed vertical-channel polymer field-effect transistors on flexible poly (ethylene terephthalate) substrates, in which the critical channel length of 700 nm to 900 nm micrometers was defined by the thickness of a spin-coated insulator layer, did not show a saturation section, and the gate control effect is weak and the off leakage current is high comparing with operating current [10]. In 2004, A. P. Kam et al have investigated the inf
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