Matrix-assisted pulsed-laser evaporated polymer films in all-organic field-effect transistors and metal-insulator-semiconductor diodes

The electrical properties of matrix-assisted pulsed-laser evaporated (MAPLE) 9,9-dioctylfluorene-co-bis-N-N-(4-butylphenyl)-bis-N, N-phenyl 1,4-phenylenediamine (PFB)-based bottom-gate organic field-effect transistors (FETs) and metal-insulator-semiconductor (MIS) diodes with poly (methyl methacrylate) (PMMA) as the dielectric layer have been investigated. The device characteristics were found to improve with an increase in the difference between the solubility parameters of PMMA and solvent. Shifts in flat band voltage of the MIS diodes were found to be due to the difference in the density of trapped holes located at the semiconductor-insulator interface. The threshold voltage of the FETs were correlated with differences in acceptor doping density and flat band voltage shifts of the MIS diodes, thereby demonstrating the role of interface traps in determining the electrical properties of organic devices. Electrical characterization of the FET shows the device to have a hysteresis-free operation in its transfer characteristics, a low threshold voltage of -0.2 V, and a field-effect mobility of 0.2 x 10 (4) cm(2) V (1) s (1). Interface trap states of the MIS diodes were found to be distributed in energy with their density decreasing non-linearly from approximately 2.8 x 10(12) to 1.2 x 10(12) eV (1) cm (2) over an energy range of 0.075-0.385 eV above the bulk Fermi level. Non-orthogonality of the semiconductor solvent had no deleterious effects on the underlying PMMA dielectric layer even without any high temperature baking, thus demonstrating that MAPLE is a viable technique for fabricating polymer dielectric-based devices and for improving the semiconductor-insulator interface. (C) 2011 Elsevier B.V. All rights reserved.