Optimum channel thickness of rubrene thin-film transistors

We report the influence of channel thickness on the field effect mobility of rubrene-based thin-film transistors (TFTs). Prior to crystallization annealing, amorphous (α) rubrene film was deposited under thickness conditions of 40, 50, 80, 120, and 160 nm by thermal evaporation on self-assembled-monolayer treated SiO2 / p+ -Si. Field effect mobility of the TFTs increased from almost 0 to 0.01 cm2 /V s with the rubrene channel thickness until it reaches to 120 nm because the rubrene crystallization on our substrate would not be perfect below 120 nm. The mobility decreased with the thickness over 120 nm due to parasitic resistance. We thus conclude that there exists an optimum channel thickness for rubrene TFTs.