Fabrication and characterization of large figure-of-merit epitaxial PMnN-PZT/Si transducer for piezoelectric MEMS sensors

This paper reports a highly c-axis oriented 0.06Pb(Mn1/3,Nb2/3)O3-0.94Pb(Zr0.5,Ti0.5)O3 (PMnN-PZT) epitaxial thin film sputter-deposited on a Si substrate for MEMS (MicroElectro Mechanical Systems) sensor applications. High c-axis orientation ratio more than 75% was obtained for the PMnN-PZT epitaxial thin film with thicknesses up to 4 μm by fast cooling after sputter deposition. The films exhibited a relatively large piezoelectric coefficient, e31,f ≃ −14C/m2, and a quite small dielectric constant, εr33 ≃ 200. As a result, a figure of merit defined as (e31,f)2/ε0εr33 reached ∼110 GPa, which is the highest value ever reported for piezoelectric thin films on Si. Neither significant degradation nor damage of the PMnN-PZT thin film was observed during MEMS fabrication processes. The dependency of the piezoelectric and dielectric properties on temperature was small compared with conventional PZT polycrystalline thin film on Si. This epitaxial PMnN-PZT/Si transducer has a great potential for application to piezoelectric MEMS sensors.