Effects of annealing temperature and gas on pentacene OTFTs with HfLaO as gate dielectric

Abstract

Pentacene organic thin-film transistors (OTFTs) with high-κ HfLaO as gate insulator were fabricated. HfLaO film was prepared by sputtering method. To improve the film quality, the dielectric was annealed in N 2, NH 3, or O 2 at two temperatures, i.e., 200 °C and 400 °C, respectively. The I-V characteristics of the OTFTs and C-V characteristics of corresponding organic capacitors were measured. The OTFTs could operate at a low operating voltage of below 5 V, and the dielectric constant of the HfLaO film could be above ten. For all the annealing gases, the OTFTs annealed at 400 °C achieved higher carrier mobility than their counterparts annealed at 200 °C (with the one annealed in NH 3 at 400 °C showing the highest carrier mobility of 0.45 cm 2/ V·s), which could be supported by SEM images which indicate that pentacene tended to form larger grains on HfLaO annealed at 400 °C than on that annealed at 200 °C. The C-V measurement of the organic capacitors indicated that the localized charge density in the organic semiconductor/oxide was lower for the 400 °C annealing than for the 200 °C annealing. Furthermore, through the characterization of gate current leakage, HfLaO film annealed at 400 °C achieved much smaller leakage than that annealed at 200 °C. Since the maximum processing temperature of ITO glass substrates is around 400 °C , this study shows that 400 °C is suitable for the annealing of HfLaO film in high-performance OTFTs on glass substrate. © 2011 IEEE.