Piezoelectric properties of sputtered PbTiO3 films: Growth temperature and poling treatment effects

Abstract

Thin films of lead titanate (PbTiO3) were prepared on silicon substrates by sputtering. Two processes have been developed; (a) the in situ process (the growth temperature was 440 °C) and (b) the deposition at room temperature followed by a conventional annealing at 680 °C. The dielectric constant, the ferroelectric, and the piezoelectric properties were evaluated and compared. The dielectric constant of films deposited in situ was higher than those of postannealed films likely due to the dense microstructure with fine and homogeneous grains. The embedded beam method and the Berlincourt piezometer were used to measure the e31 and the d33 piezoelectric coefficients, respectively. The PbTiO3 films were naturally polarized, in particular the films grown in situ have large piezoelectric constants: e31=−0.49 C/m2 and d33=20 pC/N. These values agree broadly with data of bulk ceramics, however, with bulk material a poling treatment is necessary to attain these values. The poling of the postannealed films leads to a substantial increase of their piezoelectric properties; e31=−0.26 C/m2 and d33=8 pC/N for virgin film and e31=−0.41 C/m2−d33=18 pC/N for an applied electric field of 110 kV/cm (close to saturation) and a poling time of 30 min. The piezoelectric response was found to depend on the direction of the poling field. Note d33 and e31 decreased when the poling field was applied against the preferred polarization direction; the polar domains were oriented from the film surface to the substrate.