Improved Performance of Pentacene OTFTs With HfLaO Gate Dielectric by Using Fluorination and Nitridation

Pentacene organic thin-film transistors (OTFTs) with fluorinated high-κ HfLaO as gate insulator were fabricated. The dielectrics were prepared by sputtering method and then annealed in N₂ or NH₃ at 400°C. Subsequently, the dielectrics were treated by fluorine plasma for different durations (100, 300, and 900 s). The N₂ and NH₃-annealed OTFTs with a 100-s plasma treatment achieve a carrier mobility of 0.62 and 0.66 cm²/V·s, respectively, which are higher than those of the OTFTs without plasma treatment (0.22 and 0.41 cm²/V·s). Moreover, the plasma-treated OTFTs realize better 1/f noise characteristics than those without plasma treatment. The improved performance is due to passivation of the dielectric surface by plasma-induced fluorine incorporation. However, for longer time (300 and 900 s) of plasma treatment, the performance of the OTFTs deteriorates in terms of carrier mobility and 1/f noise characteristics due to increased plasma-induced damage of the dielectric surface. The morphology of the pentacene film grown on the HfLaO gate insulator was characterized by SEM. It reveals that the pentacene film has larger grain size and smoother surface on the HfLaO dielectric (for both annealing gases) with 100-s plasma treatment than the others (0, 300, and 900 s). Finally, AFM characterization of the HfLaO film also confirms the damaging effect of excessive plasma treatment on the dielectric.