Structural and chemical composition investigation of thin lead zirconate titanate films

Abstract

Thin lead zirconate titanate (PZT) ferroelectric films are currently being used in a variety of applications. One of the more novel uses is in nonvolatile random access memory devices. As part of such a memory device, these PZT films undergo a significant amount of thermal cycling during standard semiconductor processing. Therefore, it is of considerable importance to understand the evolution of the PZT film morphology and composition as a function of temperature. The ferroelectric domain and PZT grain boundary evolution in sputtered and sol-gel deposited PZT films has been recorded. Hot stage transmission electron microscopy has been used for this investigation between room temperature and 600 °C. The ferroelectric domains in all the samples are very distinct. The transition from the tetragonal to the cubic paraelectric phase was observed at Curie temperatures (TC) close to those expected for the various compositions analyzed. Zr/Ti ratios in these films ranged from 48/52 to 30/70. Since the films are polycrystalline and some compositional inhomogeneity exists from crystallite to crystallite, a distribution of transition temperatures has been observed throughout a single PZT film. This result fits very well with electrically measured values of TC, which exhibit very broad maxima. Nanoprobe analysis of the composition of these films was performed before and after heating to see if there are any significant changes. Line scans were used to analyze grain and grain boundary composition in both plan view and cross section. The difficulties of obtaining reliable analytical results are explored in detail.