Revealing the role of defects in ferroelectric switching with atomic resolution

Abstract

Ferroelectric materials are characterized by a spontaneous polarization, which can be reoriented with an applied electric field. The switching between polarized domains is mediated by nanoscale defects. understanding the role of defects in ferroelectric switching is critical for practical applications such as non-volatile memories. This is especially the case for ferroelectric nanostructures and thin films in which the entire switching volume is proximate to a defective surface. Here we report the nanoscale ferroelectric switching of a tetragonal PbZr 0.2 Ti 0.8 o 3 thin film under an applied electric field using in situ transmission electron microscopy. We found that the intrinsic electric fields formed at ferroelectric/electrode interfaces determine the nucleation sites and growth rates of ferroelectric domains and the orientation and mobility of domain walls, whereas dislocations exert a weak pinning force on domain wall motion.

Atomic-scale mechanisms of ferroelastic domain-wall-mediated ferroelectric switching

“…2b, a new À c-domain (where the negative sign indicates downward polarization) nucleates and grows at the top interface at a bias of 8.2 V, leading to the contrast change from bright to dark. Although previous studies proposed that the nucleation of c-domains preferentially begins from 90°domain walls 3,8,15 , our in situ TEM observations revealed that nucleation occurs only at the top interface with a negative bias 5,10 . The switched À c-domain grew with increasing voltage (Fig.…”

“…2c). As a single needle-like domain was observed in dislocation-free PZT thin films grown on more closely lattice matched DyScO 3 substrates 10 , local pinning causes non-uniform growth of the switched domain front. Once the created À c-domain reached the edge of the a-domain (Fig.…”

“…Under a constant voltage ( Fig. 2c-g), the domain grew slowly, which may result from a relatively high density of dislocations acting as weak pinning centres in the film 10 . Dislocations also account for the sawtooth shape of the domain (Fig.…”

“…In comparison with general measurement techniques, in situ TEM can be used to directly observe atomicscale domain interactions in real time during switching through the thickness of the film, enabling switching dynamics to be correlated with local defect microstructures in real time 13,18,19 . Employing spherical aberration-corrected TEM with sub-angstrom resolution 20,21 , we are able to directly map the local polarization at the atomic scale [9][10] . We combine this with mesoscale phase-field modelling of the dynamic polarization-switching processes to corroborate our observations with current models of ferroelectric thin films.…”

“…An understanding of the local response and underlying dynamic behaviour of individual domain walls and defects throughout the thickness of the film during the switching process is necessary, however, to engineer reliable ferroelectric devices [6][7][8][9][10][11][12][13][14] . This is especially important in ferroelectric memory devices scaled down to the nanometre scale to achieve a high data storage density where a single defect may dominate the total switching process.…”