Effect of copper-oxide segregation on the dielectric properties of CaCu3Ti4O12 thin films fabricated by pulsed-laser deposition

Abstract

We investigated the effects of post-deposition cooling conditions on the surface morphologies and dielectric properties of CaCu3Ti4O12 (CCTO) thin films grown by pulsed-laser deposition on Pt/TiO2/SiO2/Si substrates. CCTO thin films cooled under the typical cooling parameters, i.e., slow cooling (3 degrees C/min) at high oxygen pressure (66 kPa) showed a severe segregation of nanoparticles near the grain boundaries, which was identified to be copper oxide from electron probe micro analyzer mapping. On the other hand, we could not observe any segregation on the film surface when the samples were cooled fast (similar to 20 degrees C/min) at relatively low oxygen pressure (100 Pa). The dielectric constant, epsilon(r). of CCTO thin films deposited at 750 degrees C with severe surface segregation (epsilon(r) similar to 750 at 10 kHz) was found to be much lower than that (epsilon(r) similar to 2000 at 10 kHz) of CCTO thin films with smooth surface. As the copper-oxide segregation becomes more serious, which preferentially occurs at relatively high ambient oxygen pressure and temperature, the degradation in the dielectric properties of CCTO films becomes larger. The variation of dielectric constant of CCTO films with no copper-oxide segregation could be related to the presence of an impurity phase at grain boundaries. (C) 2010 Elsevier B.V. All rights reserved.