Structural, ferroelectric, and pyroelectric properties of highly c-axis oriented Pb1−xCaxTiO3 thin film grown by radio-frequency magnetron sputtering

Abstract

Thin films of ferroelectric Pb1−xCaxTiO3 (x=0.0–0.4) were formed on MgO, Pt/MgO, SrTiO3, and Pt/SrTiO3 substrates by rf magnetron sputtering. Characterization of the films by x-ray diffraction, x-ray precession, scanning electron microscopy, and electron probe microanalysis showed them to be epitaxially grown with their c-axis oriented perpendicular to the substrate. The decrease in the Curie temperature Tc and the increase in the pyroelectric coefficient dPs/dT with an increase in Ca doping were successfully explained by assuming that the Ca ions occupied Pb ion sites. Pyroelectric infrared detectors using Pb0.7Ca0.3TiO3 thin-film elements gave better performance than the detectors using PbTiO3 ceramic elements. The internal bias field EB and fixed polarization PB were observed to be a function of both the Ca content and temperature in ferroelectric hysteresis curves as well as in hysteresis curves of the dielectric constant as a function of the applied electric field. These phenomena were explained by the difference in thermal behavior between the sputtered films and the substrates at temperatures below Tc.