Fabrication of organic field effect transistors and determination of their electricall characteristics

In this thesis study, pentacene and its derivative, 6,13-Bis(triisopropylsilylethynyl) pentacene (TIPS) organic semiconductors were used as the active layers in the preparation of organic field-effect transistors (OFETs). By investigating of the optical properties of pentacene and pentacene derivative TIPS films coated on the glass using thermal evaporation method, the optical parameters such as absorption band edge and band gap were calculated.Pentacene based OFETs were prepared by coating various gate insulator layers such as SiO2, Al2O3 SiO2/Al2O3 and BaTiO3 on different Si wafers with various widths of channel. Also, pentacene derivative TIPS based OFETs were fabricated using SiO2 gate insulator layer with various thicknesses TIPS film. The performance (output and transfer) characteristics of organic field effect transistors (OFETs) prepared using different widths of channel, oxide types, oxide thicknesses, organic semiconductors, coating-methods and the active layer (pentacene and TIPS) thicknesses were investigated under dark and illumination conditions. The electrical parameters of transistors such as mobilitiy, threshold voltage, Ion/Ioff ratio, sub-threshold swing value, photosensitivity, interface trap density and number of charge carriers per surface unit of prepared OFETs were calculated for dark and illumination conditions. The n-Si/BaTiO3/pentacene OFET exhibited the highest mobility of 41.171 cm2/Vs. While illumination intensity is increased, the number of charge carriers per surface unit Ntrap and sub-threshold swing S values of OFETs are decreased.The fabricated pentacene and its derivative TIPS based OFETs indicate a p-type OFET characteristics with good gate controllability due to increase in drain current with negative voltages, that is, the fabricated OFETs work in a p-channel operational mode. It is evaluated that the electrical performance of pentacene and its derivative TIPS based OFETs can be improved by depending on preparation conditions such as different widths of channel, oxide types, oxide thicknesses, coating-methods and the active layer (pentacene and TIPS) thicknesses.