Development of Sputter Epitaxy Technique of Pure-Perovskite (001)/(100)-Oriented Sm-Doped Pb(Mg_1/3, Nb_2/3)O₃-PbTiO₃on Si

We have developed a unique sputter deposition technique for a pure-perovskite (001)/(100)-oriented samarium-doped Pb(Mg1/3, Nb2/3)O3-PbTiO3 (Sm-PMN-PT) epitaxial thin film on Si as a future piezoelectric transducer thin film in microelectromechanical systems (MEMSs). This technique bases on the use of a 'Pb(Zr,Ti)O3 (PZT)-based seed layer' and 'separate sputter deposition.' Undesired orientations and phases of such a relaxor-based ferroelectric are usually generated during the sputter deposition. This technique was demonstrated to provide preferential (001)/(100) orientation and pure-perovskite phase to the monocrystalline thin film. The fabricated film had excellent homogeneousness of the content distribution. Considering a practical thickness, a 2- μ m-thick monocrystalline thin film was grown on an Si substrate with this technique. Then, the piezoelectricity |e31,f| of the Sm-PMN-PT/PZT stacked film was evaluated through an actuation test of the unimorph cantilever. As a result, it measured 16-17 C/m2, which is almost comparable with intrinsic PZT polycrystalline thin films with high |e31,f| values. Considering that the actuation voltage was divided into Sm-PMN-PT and PZT layers, the inherent piezoelectricity of the Sm-PMN-PT thin film is expected to be higher. Optimization of the phase in the film by tuning the composition ratio also will further improve the piezoelectricity. We believe that this achievement is a great step to discover a giant piezoelectricity relaxor-based thin film beyond PZT for MEMS.