Characterization of anodic aluminum oxide film and its application to amorphous silicon thin film transistors

AL(2)O(3)/SINx double-layered dielectric films suitable for large-size amorphous silicon thin film transistor liquid crystal displays (a-Si:H TFT LCD) have been prepared by anodization and plasma enhanced chemical vapor deposition (PECVD). Al2O3 films were formed at various pH values and volume ratio of water (H2O%) in the electrolyte. The optimal quality of Al2O3 film was achieved at pH = 6 and H2O% = 30. These high-quality Al2O3 films have denser structure, lower etching rate (90 Angstrom min(-1)) and smooth surface morphology after etching. The capacitors made of the anodization show a breakdown field as high as 7.8 MV cm(-1) and a low leakage current density of 10 nA cm(-2) at a dielectric field of 3 MV cm(-1). Furthermore, a-Si:H TFTs with Al gate and different gate dielectrics (Al2O3/SINx and SiNx) were also fabricated and evaluated. The TFTs with Al2O3/SiNx double-layered gate dielectric provide better performances, such as the smaller threshold voltage (1.76 V), improved subthreshold swing (1.0 V dec(-1)), and lower off-current (3.8 PA) than those of the device with single SiNx, film.