ENHANCED FATIGUE AND RETENTION IN FERROELECTRIC THIN-FILM MEMORY CAPACITORS BY POST-TOP-ELECTRODE ANNEAL TREATMENT

Remanent polarization in thin ferroelectric films of lead zirconate titanate (PZT) is of considerable interest for rad-hard, nonvolatile memory applications. The fatigue and retention characteristics of PZT films, however, are influenced markedly by the processing and patterning techniques for the capacitor. A post-top-electrode anneal treatment of thin-film ferroelectric capacitor device structures, with the top electrode defined by conventional lift-off patterning, that clearly shows a significant enhancement in the retention and fatigue characteristics of ferroelectric memories is described. In addition to the remanent polarization characteristics of Ti-Pt/PZT/Pt sandwich structure, studied using conventional electronic probe techniques, an optical probe is employed to probe the probable influence of Schottky junction(s) and/or stress at the electrode/PZT interfaces in the device. The significant improvement in the fatigue/retention performance of the devices by the post-top-electrode anneal treatment is attributed primarily to the formation of stable interfaces, as shown by the voltage cycling studies. The effects of operational history on retention performance provide further insight into the role of time-dependent depolarization/polarization components in the functioning of the memory.