Phase change and electrical properties of thin films BaTiO₃ system made by RF/DC magnetron sputtering

Thin films of the BaTiO₃ system were prepared by radio frequency (RF)/DC magnetron sputtering method. We have investigated crystal structure, surface morphology and PTCR (positive-temperature coefficient of resistance) characteristics of the specimen depending on second heat-treatment temperatures. Second heat treatments of the specimen were performed in the temperature range of 400 to 1350°C. X-ray diffraction patterns of BaTiO₃ thin films show that the specimen heat treated below 600°C is an amorphous phase and the one heat treated above 1100°C forms a crystal. In the specimen heat-treated at 1300°C, the lattice constant ratio c/a is 1.188. A scanning electron microscope (SEM) image of BaTiO₃ thin films shows that the specimen heat treated in between 900 and 1100°C shows grain growth. At 1100°C, the specimen stops grain-growing and becomes a crystal. The resistivity-temperature characteristic of the specimen depends on the doping concentrations of Mn. A resistivity ratio between the value at room temperature and the one above Curie temperature is 10⁴ for pure BaTiO₃ thin films and 10⁵ for BaTiO₃:0.127 mol% MnO