Effect of microgeometry on switching and transport in lead zirconate titanate capacitors: Implications for etching of nano-ferroelectrics

摘要

We evaluate different switching behaviors of lead zirconate titanate (PZT) thin film capacitors with two different geometries: one, a square 100×100 μm; the second, a ribbon (1.6 μm width but with approximately the same total area), as a function of temperature T, and applied electric field E. The ribbon capacitor shows a stronger dependence (by ca. 70) of activation field on T and E. This is interpreted as a chemical reduction of edge material in the long-perimeter ribbons due to plasma etching. In order to understand and model the different domain switching of these two types of PZT capacitor, we also investigate impedance spectra at various temperatures from 27 to 470℃. From ac conductance spectra, both square- and ribbon-type capacitors have similar trap levels, 0.38±0.02 eV. From analysis of conductivity spectra, we find that the ribbon capacitor contains an additional 0.19±0.02 eV trap level attributed to H-O dipoles due to hydrogen reduction; the latter trap results in domain pinning, which is interpreted as the origin of the relatively strong dependence of the activation field on T and E in the ribbons compared to the square capacitors. The additional loss peak in the ribbon capacitors is also observed in real cell-type capacitors, but only. when their edge/area ratio becomes large, as in submicron cells for megabit scale.