Structural and electrical characteristics of (Pb1−xLax)(Zr0.5Ti0.5)O3 thin film capacitors

Electrical characteristics associated with crystal structure changes as a function of La content for (Pb1−xLax)(Zr0.5Ti0.5)O3 (PLZT) thin films were investigated for applications in DRAM capacitors. Tetragonality of the PLZT films dramatically decreased with increasing La content. Films with La ≥ 20 at% were found to be cubic. Films with La ≥ 10 at% exhibited broader dielectric peaks, compared with those of bulk ceramics, and behaved as relaxor ferroelectrics. Tetragonal PLZT film with 10 at% La had a dielectric constant maximum of 1330 at room temperature and a charge storage density of ∼18 μC/cm2 at 5 V. A decrease in the coercive field and remnant polarization with increasing La amount was due to the reduced dipolar response caused by the decreased crystal anisotropy. The effective permittivity values were nearly identical to the measured values for films with La ≥ 14 at%, as a result of minimized remnant polarization with increasing La content. Leakage current densities < 10−8 A/cm2 were observed for films with La ≥ 14 at%.