Electrical characterization of anodically oxidized Ta2O5 films

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 Al 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.