Oxygen tracer studies of ferroelectric fatigue in Pb(Zr,Ti)O3 thin films

Abstract

Long-range oxygen motion has been observed in Pt/Pb(Zr,Ti)O3/Ir thin-film structures after electrical fatigue cycling at room temperature. Through an exchange anneal, isotopic O18 was incorporated as a tracer into bare Pb(Zr,Ti)O3 (PZT) films, allowing secondary ion mass spectrometry measurements of the tracer profile evolution as a function of the number of polarization reversals. Observation of O18 tracer redistribution during voltage cycling, which is presumably mediated by oxygen vacancy motion, was found to be strongly dependent upon the thermal history of the film. However, there was no strong correlation between the extent of O18 tracer redistribution and the extent of polarization suppression induced by voltage cycling. Our results suggest that oxygen vacancy motion plays, at most, a secondary role in ferroelectric fatigue of PZT thin films.

Oxygen Permeability of Ferroelectric Thin Film Top Electrodes and Its Effect on Detectable Fatigue Cycling-Induced Oxygen Isotope Motion

“…This is consistent with the overall findings of Ref. 15, in which no convincing correlation between the extent of fatigue and the tracer motion kinetics in the PZT films was found.…”

“…All exchange anneals were performed for 3 h at 400°C with the exception of the Pt/Ir top electrode comparison that utilized a 500°C, 10 h exchange anneal. Since the earlier report, 15 we have improved our exchange system. As before, oxygen exchange anneals are performed inside ampoules, but instead of placing unsupported PZT samples in the ampoule, we now place samples upon a thick nickel boat that rests upon a thin quartz plate.…”

“…In a previous paper 15 we presented our initial work, using 100 nm electron beam deposited Pt top electrodes, on isotopic oxygen tracer ( 18 O) drift in ferroelectric PZT thin films as a function of fatigue-inducing, bipolar electricfield cycling. In that work, we observed dramatically different results when we compared capacitors that underwent a post-electrode deposition, post-tracer exchange, 30 min, 650°C anneal in flowing nitrogen (labeled "Exchanged & Annealed," or E&A) to capacitors that did not undergo this final processing step (labeled "Exchanged," or E).…”

“…Figure 1 is a reproduction of a graph from Ref. 15 that shows plots of the measured oxygen tracer secondary ion mass spectroscopy (SIMS) depth profiles, in the PZT layer only, of the ratio of the tracer concentration ([ 18 O]) to the total oxygen concentration ([ 18 O] + [ 16 O]) for capacitors of both E&A and E samples. Whereas in the films that did not undergo the high temperature anneal (E) we observed significant oxygen tracer motion, samples that did experience the high temperature anneal (E&A) exhibited no oxygen tracer motion.…”

Fatigue effect in ferroelectric PbZr1−xTixO3 thin films

“…These kinds of defects are known to be the most dominant impurities in PZT films. 18 The trapped charges can clamp the domain wall and therefore hinder this seed to switch. 6 The fatigue process can be correlated as well to a number of occupied electronic states.…”