Nanoscale Domain Dynamics in Ferroelectric Thin Films

Abstract

This paper reviews nanoscale phenomena in ferroelectric thin films. Specific focus is polarization relaxation dynamics and piezoelectric characterization in model thin films and nanostructures using voltage modulated scanning force microscopy coupled with nanofabrication techniques. We present results of studies on the time dependent relaxation of the remanent polarization in model epitaxial PZT ferroelectric thin films, containing a uniform 2-dimensional grid of 90° domains (c-axis in the plane of the film). Clear evidence of the role of 90° domain walls in the nucleation of the 180° reverse domains and on a very local scale, pinning and bowing of domain walls is shown. The kinetics of relaxation is modeled through a stretched exponential approach. The second part of this paper illustrates how a conventional AFM can be used as a “nano” probe for ferroelectric properties. The characterization of the longitudinal piezoelectric constant (d33) in nanoscale capacitors (or islands) of various PZT compositions is elucidated. We show that by altering the electromechanical interplay between the substrate and the ferroelectric thin film, in compositions closer to the morphotropic phase boundary, an unusual field dependence of the d33 exists. Due to this effect, the change in strain at saturation field is twice the theoretical prediction, opening new applications such as highly strain tunable devices. Secondly we discuss in highly tetragonal Pb(Zr0.2Ti0.8)O3, movement of elastic 90° domains with applied DC field, a phenomenon hitherto observed only in bulk single crystals or ceramics. This results in a d33 of ∼ 250 pm/V at remanence, which is approximately 3–4 times the predicted value of 87 pm/V for a single domain single crystal. We summarize this review with some possible directions for future work.