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 N2, NH3, or O2 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 NH3 at 400°C showing the highest carrier mobility of 0.45 cm2/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.