Dielectric properties of PZT thin films derived by a chemical solution-deposition process on steel substrates

PZT (53/47) thin films with a lead excess of up to 30 mol% were prepared by a chemical solution-deposition process on steel substrates, the steel acting both as substrate and electrode. The films were deposited using the doctor blade method and rapid furnace-annealed at 600°C. Single layer film thickness was up to 1 μm; with repeated deposition procedures overall film thicknesses of about 4 μm were obtained. XRD measurements show a perovskite phase formation; no phases due to chemical interactions with the substrate were found. By TEM investigations grain sizes up to 1 μm were found, pores of about 50 nm in diameter were detected within the grains. Small signal dielectric measurements showed permittivity values of about 400, independent on film thickness. After postannealing the samples at 700°C the permittivity slightly increases. Hysteresis measurements show decreasing coercive field values with increasing film thickness; typical coercivity values are in the range of 10 V/μm. Polarization values were found to be about 35 μC/cm², for postannealed samples a somewhat higher polarization was obtained. A frequency dependence was found by large signal dielectric measurements, resulting in a broadening of the hysteresis loops with decreasing frequency due to conductivity. Fatigue measurements show a decay of the ferroelectric properties after 10⁴ poling cycles