Thin film ceramic Au/BaxSr(1−x)TiO3/YBCO/MgO planar capacitors with x ranging from 1 to 0.4 were fabricated using pulsed laser deposition (PLD). Structural and chemical characterisation showed the ferroelectric layers to be of perovskite crystallography, with cation stoichiometry close to that of the target. Auger depth profiling showed the interface between ferroelectric and lower electrode to be reasonably chemically sharp.
Capacitance versus temperature measurements performed in air showed a pronounced difference in behaviour between bulk and thin film devices. Bulk samples exhibited the expected capacitance anomaly at the Curie temperature. In contrast, thin film capacitors showed a prominent peak in capacitance at temperatures between 7 and 25°C on heating, irrespective of composition and did not show any evidence of expected Curie anomalies.
Further characterisation under vacuum and with deliberate additions of water vapour to the vacuum chamber indicated that the peaks observed in thin film devices described above could be attributed to the presence of atmospheric water vapour. This demonstrates that water vapour in the air can have a significant effect on the dielectric response of thin film capacitors around room temperature.
Studies on higher quality films showed a reduced response to water vapour.