Improvement of reliability and dielectric breakdown strength of Nb-doped lead zirconate titanate films via microstructure control of seed

A Pb(Zr,Ti)O₃ (PZT) seed layer without Pb-deficient defective areas was developed to improve the dielectric breakdown strength and lifetime of thin film piezoelectric actuators. The proportion of defective area in the seed layers was reduced by adjusting the amount of Pb excess in the solution, combined with implementation of a dense, large-grained (>200 nm) Pt bottom electrode. The optimal Pb excess amount in the solution was about 20 at%; seeding was improved when a slightly Ti-rich composition (relative to the morphotropic phase boundary) was utilized. It was found that the dielectric breakdown strength and lifetime of PZT films improved as the proportion of visible defective area on the PZT seed layer decreased. Dielectric breakdown strength increased from approximately 300 kV/cm to about 1 MV/cm. The lifetime, characterized by highly accelerated lifetime testing, was increased 60 times by reducing the fraction of defective area. The activation energy (E_a) and voltage acceleration factor (N) for failure of devices (eg, patterned PZT films) were 1.12 ± 0.03 eV and 4.24 ± 0.07 respectively.