Nuclear Reaction Probe of Oxygen Vacancy Migration in Electrically Fatigued PZT Thin Film Capacitors

Abstract

ABSTRACTThe migration of oxygen vacancies and their entrapment near film-electrode interfaces has been proposed as a cause of fatigue (i.e., polarization weakening) in ferroelectric thin film capacitors. To test this idea, lead zirconate titanate (PZT) thin films were epitaxially deposited by laser ablation on LaAlO3 substrates with yttrium barium cuprate (YBCO) base electrodes. Thin film capacitors were formed by deposition of noble metal (Pt) cap electrodes; half of them were then electrically fatigued by repeated polarization reversals (108 cycles). The distributions of oxygen in the two halves were then compared by means of accelerator-based nuclear backscattering (using the narrow elastic resonance at 3.045 MeV in the scattering of 4He from 16O) throughout the bulk of the PZT films and especially right under the Pt electrodes. We were unable to detect any difference in the oxygen profiles to within the accuracy of measurement, which was about 1 % of the oxygen concentration. Compositional changes, at least involving oxygen, do not seem to be responsible for the striking electrical alterations seen in fatigued PZT.