Conductive-atomic force microscopy study of local electron transport in nanostructured titanium nitride thin films

Simultaneous local current and topography measurements were made on the surface of titanium nitride thin films by conductive-atomic force microscopy (C-AFM). Two compositions, stoichiometric TiN and sub-stoichiometric TiN _0.76 were investigated. Local variation of current at grain and grain boundaries was examined. The current flow is filamentary in nature, with the number of percolation paths being smaller for sub-stoichiometric titanium nitride. Current-voltage characteristics of stoichiometric TiN reveal that the grain interiors are electrically conductive, while in sub-stoichiometric TiN_0.76 thin film, grains are electrically resistive, i.e., a potential barrier to electron transport exists at the junction between the grain and the grain boundary in sub-stoichiometric TiN_0.76. Therefore, electron transport in this film is due to tunneling through the junction, which leads to increased resistivity. The total resistance of the samples measured using the four probe technique is 1 and 400 kΩ for TiN and TiN _0.76 respectively. In both type of compounds the grain and grain boundary resistances are of the order of MΩ. The grain and grain boundaries are connected in a manner that causes the total resistivity to be lower than the local resistivity.