Microstructural effects on leakage current behavior of (Ba,Sr)TiO ₃ thin films for dram applications

We have investigated the effects of microstructure on the leakage current behavior of Pt/(Ba,Sr)TiO3/Pt film capacitors. To single out the microstructural effects only, (Ba,Sr)TiO3 films of three different microstructures (granular, columnar, possibly epitaxial), but having an identical interfacial state density, were prepared using a seed layer by sputtering. The leakage behavior depends strongly on the film microstructure. Schottky emission dominates in the film composed of granular grains, while the epi-like film shows the higher leakage current and Fowler-Nordheim tunneling mechanism. Interestingly, the film of columnar grains shows tunneling at low temperatures and Schottky emission at high temperatures. We propose a model based on energy band diagrams explaining the results.