Effects of substrate temperature on the device properties of pentacene-based thin film transistors using Al2O3+x gate dielectric

We report on the electrical properties of pentacene-based organic thin film transistors (OTFTs), where the active pentacene channel layers have been deposited at fixed deposition rate of 1 Angstrom/s on a 250-nm-thick Al2O3+x gate dielectric film at various substrate temperatures: room temperature, 60 degreesC, and 90 degreesC. The grain size of the pentacene layer was found to increase with the substrate temperature, accompanied by a phase transition. The highest saturation current of 20 muA (under a gate bias of -40 V) was obtained with a high field-effect hole mobility of similar to0.21 cm(2)/V s from an OTFT prepared at 90 degreesC despite a relatively low on/off current ratio of 2x10(5). It is concluded that the pentacene channel deposited at a high substrate temperature contains not only large grains but also high density traps. (C) 2004 American Institute of Physics.