Dependence of Pentacene Crystal Growth on Dielectric Roughness for Fabrication of Flexible Field-Effect Transistors

Abstract

The dependence of pentacene nanostructures on gate dielectric surfaces were investigated for flexible organic field-effect transistor (OFET) applications. Two bilayer types of polymer/aluminum oxide (Al2O3) gate dielectrics were fabricated on commercial Al foils laminated onto a polymer back plate. Some Al foils were directly used as gate electrodes, and others were smoothly polished by an electrolytic etching. These At surfaces were then anodized and coated with poly(alpha-methyl styrene) (PAMS). For PAMS/Al2O3 dielectrics onto etched Al foils, surface roughness up to similar to 1 nm could be reached, although isolated dimples with a lateral diameter of several micrometers were still present. On PAMS/Al2O3 dielectrics (surface roughness >40 nm) containing mechanical grooves of Al foil, average hole mobility (mu(FET)) of 50 nm thick pentacene-FETs under the low operating voltages (vertical bar V vertical bar < 6 V) was similar to 0.15 cm(2) V-1 s(-1), in contrast, pentacene-FETs employing the etched Al gates exhibited mu(FET) of similar to 0.39 cm(2) V-1 s(-1), which was comparable to that of reference samples with PAMS/Al2O3 dielectrics onto flat sputtered Al gates. Conducting-probe atomic force microscopy and two-dimensional X-ray diffraction of pentacene films with various thicknesses revealed different out-of-plane and in-plane crystal orderings of pentacene, depending on the surface roughness of the gate dielectrics.