Charge carrier transport in Ta2O5 oxide nanolayers

The paper will present the modeling of charge transport in Ta2O5 nanolayers together with experimental verification of the model. MIS structure model for tantalum capacitors with conducting polymer cathode will be described on the base of the leakage current analysis. Ta205 films show good electrical and dielectric properties for considered applications and low leakage current density value 10-4A/m2 for the electric field 100 MV/m. It is assumed that electrons tunnel from the localized states in the impurity band into the conduction band of the insulating Ta2O5 layer and, at low temperatures, from conducting polymer cathode to the conduction band of Ta2O5. The decreasing the thickness of the insulating Ta2O5 layer below 100 nm, the classical physical models are not able to give satisfactory descriptions of charge transport mechanism, and voltage and temperature dependences of electrical current. Dominant mechanism of charge carrier transport is ohmic conduction for the low electric field, while Poole-Frenkel mechanism becomes dominant for electric fields is the range 100 to 200 MV/m. Tunneling current becomes dominant for the electric field higher than 200 MV/m. Ohmic current component and Poole-Frenkel current component are thermally activated, while the tunnelling current component is temperature independent. We have observed that for temperatures above 250 K the leakage current is given predominantly by the ohmic and Poole-Frenkel mechanism. For temperatures below 250 K the tunneling is dominant charge carrier transport mechanism. VA characteristics measured for tantalum capacitor in the temperature range 10 to 300 K were analyzed.