Ferroelectric properties of ultra-thin epitaxial Pb(Zr_0.2Ti _0.8)O₃ thin films grown on SrRuO₃/SrTiO ₃ substrates

Epitaxial PZT films with different thicknesses below 56 nm were prepared on an epitaxial SRO bottom electrode grown on STO with atomically flat surface. The PZT films of 56 to 22 nm thickness exhibit a typical square-shaped P-E hysteresis loop, which has the P_r of approximately 80 μ C/cm ². The P-E hysteresis loops of the PZT films shift toward a positive voltage corresponding to an imprint characteristics. The leakage current density of the films increases with decreasing the film thickness and the 56 nm thick-PZT films have a leakage current density of approximately 9 × 10^-8 A/cm² at 1 V. The films of an ultra-thin thickness from 56 nm to 6 nm exhibit a very clear domain switching by 180° domains. On the other hand, a voltage dependence of the piezoresponse signal in the films of 37 nm and 22 nm thickness shows typical ferroelectric hysteresis behavior.