The effect of surface treatment of bottom contact organic thin film transistor

A bottom contact organic thin film transistor (OTFT) is fabricated with an organic double-layered gate insulator (GI) and pentacene. Poly(methyl methacrylate) (PMMA) and 2-mercapto 5-nitrobenzimidazole (MNB) layers are deposited on the gate insulator and source/drain gold (S/D, Au) electrode before depositing pentacene to investigate the device properties. The sequence of surface treatment significantly affects the device performance. The ultra-thin PMMA (less than 5 nm) was deposited on the organic gate insulator and S/D metal by the spin coating method, which caused no deterioration of the on-state current (Ion), although a bottom contact structure was exploited. The lack of increase in the contact resistance (Rc) may be due to the difference in wettability between PMMA/Au and PMMA/organic GI. As a result, the devices treated with PMMA → MNB showed much better Ion behavior than those fabricated with MNB → PMMA. We report on the difference in the physical and electrical performances associated with the surface treatment sequence.