The influence of surface roughness on the electric conduction process in amorphous Ta2O5 thin films

Amorphous Ta2O5 thin films were deposited by radio-frequency magnetron sputtering at the substrate temperatures of 100, 200, and 300 degrees C, respectively. The electrical properties of Ta2O5 thin films were investigated as a function of substrate temperature and film thickness. The leakage current of the Ta2O5 films was in the order of 10(-5) to 10(-6) A/cm(2) for an applied field of 1 MV/cm. The charge storage capacitances (epsilon E-breakdown) were 7.7 (100 degrees C), 7.9 (200 degrees C), and 3.7 (300 degrees C) mu C/cm(2). Most of the electrical analyses were performed with the data obtained for the Ta2O5 thin films deposited at 200 degrees C substrate temperature because they showed optimum electrical properties. The dominant conduction mechanism changed from Schottky emission current at low field to PooleFrenkel current at the high field. With increasing film thickness, the surface roughness increased, whereas the transition fields from the electrode-limited current to the bulk-limited current process decreased. To verify the effect of this surface roughness on the electrical conduction mechanism, a two-dimensional numerical simulator, MEDICI, was used to simulate the electric field distribution at the bulk region of the thin film and the interface region between the thin film and electrode. (C) 1999 The Electrochemical Society. S0013-4651(98)11-090-X. All rights reserved.