Non-Linear Imprint Behavior of PZT Thin Films

Abstract

Ferroelectric thin film capacitors are promising candidates for non-volatile ferroelectric Random Access Memories (FeRAM's) as they exhibit a switchable polarization. There are three important failure-mechanisms influencing the performance of these capacitors and disturbing the long-term stability and reliability under operation conditions fatigue, retention, and imprint. The imprint effect of lead zirconate titanate (PZT) thin films was investigated in this paper. Establishing and maintaining a polarization state leads to a shift of the hysteresis loop on the voltage axis and also to a loss of polarization. The voltage shift as well as the loss of polarization can cause a failure of the ferroelectric memory cell (read and write failure). The experimental results obtained on PZT films are discussed in view of the predictions of imprint models proposed in the literature.

Quantifying electronic charge trap states and the effect of imprint on ferroelectric poly(vinylidene fluoride-trifluoroethylene) thin films

“…Once polarized, ferroelectric materials become stabilized in the existing poling orientation and resist reversal up to a critical coercive field. [15][16][17] This logarithmic time dependence of the imprint voltage has also been observed in P͑VDF-TrFE͒ films 18 and is shown in Fig. Experimentally, imprint is observed as a shift in the polarization hysteresis curve to higher fields with increasing wait time in a given polarization state, or as an increase in the electric field required to achieve a given polarization switching rate.…”

Interface-induced phenomena in polarization response of ferroelectric thin films

“…22, where the voltage shift of the P-E loop as a function of oxygen pressure is shown for a PZT capacitor with oxide electrodes. For an empirical fit of this dependence, different single functions and combination of functions have been used-for instance, a single logarithm function, 80 two logarithm functions with different parameters at small and large times, 90 and a stretched exponential function. Experimental data that can also indicate the role of oxygen vacancies in the formation of built-in field in PZT thin films have been reported on imprint in donor-doped ͑Nb, Ta, and W substitutions for Ti͒ films.…”

Monte Carlo simulations of imprint behavior in ferroelectrics

“…In earlier publication, it could be clearly shown that the imprint behavior is not a linear function of the elapsed time ͑on a logarithmic scale͒ as commonly assumed. 8 To achieve a sufficient fit approach, several dependencies were performed and compared by their minima values of nonlinear least squares. So qualitatively, this behavior has to be approximated by a slight exponential growth fit.…”