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 sput tering at the substrate temperatures of 100, 200, and 300 degrees C, respec tively. 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 app lied 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 obta ined for the Ta2O5 thin films deposited at 200 degrees C substrate temperat ure because they showed optimum electrical properties. The dominant conduct ion mechanism changed from Schottky emission current at low field to PooleF renkel current at the high field. With increasing film thickness, the surfa ce roughness increased, whereas the transition fields from the electrode-li mited 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 elect ric field distribution at the bulk region of the thin film and the interfac e region between the thin film and electrode. (C) 1999 The Electrochemical Society. S0013-4651(98)11-090-X. All rights reserved.