Fatigue mechanisms in thin film PZT memory materials

Abstract

The recent evolution of high-quality thin films of the PZT family has brought closer the use of ferroelectrics in non-volatile memory applications. While the inherent properties of the films are more than acceptable for most memory applications, the reduction in switched charge under repeated ferroelectric switching remains a problem. This so-called fatigue leads to changes of phonon frequencies and Raman cross sections in PbZr_0.48Ti_0.52O₃ (PZT). Simultaneously, a characteristic IR absorption band near 4000 cm^-1 shifts towards higher energies. This absorption signal is discussed in terms of polaronic states related to carriers generated by oxygen loss from the samples. It will be shown that the fatigue in PZT can be related to an increase of the local lattice distortion and a formation of defects both caused by oxygen loss from the samples.