Spontaneous pyro- and piezoelectricity of sol-gel La-modified lead titanate thin films

Polycrystalline La-modified lead titanate thin films have been processed, by a diol-based sol-gel route, on Si-based substrates. Multiple deposition and crystallization steps were carried out in order to promote heterogeneous nucleation and, as a consequence, a preferred crystallographic orientation and self polarization. Crystallization was achieved by rapid thermal processing at 650°C for 50s, at a heating rate of ∼30°C/s. The films developed either a <111> or a mixed <100>/<001> preferred orientation, which were determined by quantitative texture analysis of X-ray pole figures. Hysteresis cycles of the piezoelectric d33 coefficient versus electric field were obtained by a double-beam laser interferometric technique and found to strongly depend on the film texture. <111> oriented films present a thickness-dependent spontaneous pyroelectric coefficient and field endurance of the piezoelectric coefficient. These films are thus, appropriate to be used in non-switching applications, such as pyroelectric infra-red detectors and integrated piezoelectric sensors.