Experimental study and analytical modeling of the channel length influence on the electrical characteristics of small-molecule thin-film transistors

Abstract Bottom-contact p-type small-molecule copper phthalocyanine (CuPc) thin film transistors (TFTs) with different channel lengths have been fabricated by thermal evaporation. The influence of the channel length on the current–voltage characteristics of the fabricated transistors were investigated in the linear and saturation regimes. The devices exhibit excellent p-type operation characteristics. Results show that devices with smaller channel length ( L  = 2.5 μm and 5 μm) present the best electrical performance, in terms of drain current value, field effect mobility and subthreshold slope. Saturation field-effect mobilities of 1.7 × 10 −3  cm 2  V −1  s −1 and 1 × 10 −3  cm 2  V −1  s −1 were obtained for TFTs with channel lengths of L  = 2.5 μm and L  = 5 μm, respectively. Transmission line method was used to study the dependence of the contact resistance with the channel length. Contact resistance becomes dominant with respect to the channel resistance only in the case of short channel devices ( L  = 2.5 μm and 5 μm). It was also found that the field effect mobility is extremely dependent on the channel length dimension. Finally, an analytical model has been developed to reproduce the dependence of the transfer characteristics with the channel length and the obtained data are in good agreement with the experimental results for all fabricated devices.