Electrical optical and gas sensing properties of barium titanate/strontium titanate thin films

Abstract

Polycrystalline SrTiO3/BaTiO3 multlayer flms (STO/BTO) were prepared by a sol-gel spin coating technique on diffierent types of substrates suitable to the desired applications. ITO oated on glass was used as a substrate to investigate the optial properties of the films. The value of energy gap gradually decreased from 4.19 to 4.03 eV as the films were annealed at lower temperature (300-550C) while that of the films annealed at higher temperature of 600 and 650 C was in the 3.64-3.74 eV range. The refractive index of the films was in the range of 1.69-2.10 depending on annealing temperature and the extinction coefficient of the films was in the order of 10-2. Al2O3 was used as a substrate to characterze ethanol sensing and dieletric properties of the films. The senstivity of the films can be improved with increasing Fe-doping oncentration and operating temperature. The sensitivity obtained at 350C to ethanol vapor concentraton in the 100-1000 ppm of the films doped with Fe 8 wt% in the 3-10 range whch was about two times higher than that of the Fe 2 wt% doped flms. The dielectric constant of the films can be improved by constructing multilayer films and by irradiating gamma ray on the film devices. The room temperature dielectric constant of STO/BTO, uniform BTO and uniform STO films was approximately 522, 280 and 188, repectively measuring at 100 kHz whereas the dielectric constant of STO/BTO films increased up to 830 after irradiated to gamma ray at dose of 30 kGy. The loss tangent of all films was in the order of 10-2 at 100 kHz.