RF-ICP sputtered AlN film was used as the gate insulator in pentacene-based organic thin-film transistors (TFTs). With the dielectric breakdown field larger than 5 MV/cm and the relative electrical permittivity as 7 in the AlN film, the proposed TFTs exhibit low operation voltage, low subthreshold swing (similar to 0.4 V/decade) and high on/off current ratio (> 10(6)). By adjusting the AlN sputtering process, it was found that smooth morphology of AlN film (surface roughness < 2 angstrom) can be obtained by lowering down the process temperature. This atomically smooth dielectric surface leads to the growth of large pentacene grains and improves the leakage current and also the field effect mobility. (c) 2006 The Electrochemical Society.