Electrical Characterization of Anodically Oxidized Ta₂O₅ Films

Abstract

The basic electrical properties of Ta₂O₅ thin films, anodically oxidized in H₃PO₄ solution, were investigated with the aim of analyzing the electronic behavior of metal/Ta₂O₅/Ta capacitors. The investigation was done from the perspective of the work functions of the devices. The current-voltage (I-V) characteristics of Au, Cu and Ag/Ta₂O₅/Ta capacitors demonstrated that a Schottky-barrier might be formed at the Au, Cu or Ag/Ta₂O₅ interface. The capacitance at low frequency (1 kHz) increased with increasing forward bias, corresponding to the I-V behavior. This could be correlated with the lifetime of carriers (electrons or holes, or both) injected into the Ta₂O₅ film. When A1 was used as a counter electrode, the I-V and C-V characteristics (1 kHz) were nearly symmetrical for both bias polarities, although the work function is almost the same as that of Ag. This is because the barrier height for Al/Ta₂O₅ is lower than that of Ag/Ta₂O₅ due to the difference in the reactivity of the metals with oxygen at metal/Ta₂O₅ interfaces. An energy band diagram is proposed to explain the experimental results.