High Piezoelectric coefficientsin Ba(Zr0.2Ti0.8)O3-(Ba0.7Ca0.3)TiO3 Lead-free thin films

Danyang Wang and Bingcheng Luo

The industry is currently facing global restrictions on use of lead-based piezoelectrics because of the high toxicity of lead. Therefore, it is an urgent task to develop lead-free alternatives with piezoelectricity comparable to those of lead-based materials. Binary system (1-x)BaZr0.2Ti0.8O3-xBa0.7Ca0.3TiO3 (BZT-BCT) has been recently recognized as a promising lead-free piezoelectric material with a morphotropic phase boundary (MPB) near x=0.5. This finding shed a new light on the research of lead-free piezoelectrics and great efforts thereby have been made to study the microstructural, elastic, dielectric, pyroelectric and piezoelectric properties of BZT-BCT ceramics. However, studies on BZT-BCT thin films are still insufficient. In our work, high quality BZT-BCT thin films were fabricated on La0.7Sr0.3MnO3-coated SrTiO3 single-crystalline and semiconductor silicon substrates by off-axis RF magnetron sputtering. A strong dependence of ferroelectric and piezoelectric properties on the crystallographic orientations of the thin films was observed, attributing to the relative alignment of crystallites and spontaneous polarization vector. A large effective piezoelectric coefficients d33,eff of 100±5 pm/V was obtained in our BZT-BCT thin films. The d33,eff  values of our thin films are very much comparable to those of lead-based thin films, and are in the upper range of lead-free piezoelectric thin films reported in the literatures up to this date, suggesting that BZT-BCT is a promising candidate to replace the widely used lead-based piezoelectrics for the applications in high-performance microelectronic devices. In addition, the established orientation-property relationship in our epitaxial thin films may provide a valuable guidance on further development of textured BZT-BCT based materials.

Fig. 1 (a) Piezoresponse amplitude image (b) phase image and (c) local switching spectroscopy PFM amplitude voltage butterfly loop and phase voltage hysteresis loop for BZT-BCT thin films deposited on Si under optical conditions.