High Tc/high coupling perovskite thin films

Ferroelectric thin films with high Curie temperature T_c and high piezoelectric coupling factor k are fascinated for a better piezoelectric MEMS. Pb(Zr, Ti)O₃ (PZT)-based ferroelectric ceramics exhibit high piezoelectricity, but the T_c is not high, i.e. T_c <;400°C. PZT-based piezoelectric thin films with higher T_c will be much useful. Based on a strain engineering, it is commonly understood the in-plane biaxial strain enhances the T_c of PZT thin films in a laminated composite structure. However, thickness of the PZT thin films is limited below a critical thickness typically <; 50nm. Recently it has been found in-plane relaxed single crystal PZT-based thin films, i.e. PMnN-PZT(48/52) thin films, thickness above the critical thickness (typically 1μm), exhibited enhanced T_c The T_c is extraordinary high, T_c = ~600°C. Their ferroelectric performances are beyond bulk PZT. The high T_c phenomena are demonstrated and the possible mechanisms of the high T_c behavior are discussed.