The comparison of organic field effect transistor (OFET) structures

Basically, structures of pentacene OFETs are divided into top contact transistors and bottom contact transistors. The top contact OFET is an OFET where firstly the pentacene layer is formed on the SiO
2
and after that, Au electrodes are formed. Because it is difficult to apply the micro fabrication technology on pentacene layer, generally, Au electrodes are formed by the thermal evaporation method using metal masks. Therefore, it is difficult to fabricate top contact transistors with small channel length. The top contact structure has lower contact resistance and higher mobility than the bottom contact structure has. Meanwhile, the bottom contact OFET is an OFET where firstly, Au electrodes are formed on SiO
2
and then pentacene are formed on the electrodes. Since the microfabrication technology can be applied when forming electrodes on SiO
2
, the bottom contact structure can have small channel length. However, because there are steps between the electrodes and the gate insulator, the bottom contact structures have poor continuity between the electrodes and the semiconductor layers. This leads to high contact resistance, low mobility and high variance. The organic thin film semiconductor can be formed by the wet process like spin coating or dry process like thermal evaporation. The top contact and bottom contact OFETs fabricated in this research have mobility of 0.2 cm
²
/(Vs) and 0.02 cm
²
/(Vs) respectively.