Stability of the unswitched polarization state of ultrathin epitaxial Pb (Zr,Ti) O3 in large electric fields

The initial stage of polarization switching in ferroelectric thin films depends on phenomena that occur at characteristic time scales of tens to hundreds of nanoseconds, including the nucleation polarization domains and the propagation of domain walls. These long intrinsic times allow short-duration electric fields with magnitudes far above the low-frequency coercive electric field to be applied across capacitor devices without inducing switching. Using time-resolved x-ray microdiffraction, we have found that a series of 50 ns duration electric field pulses switches the polarization of a 35-nm-thick ferroelectric Pb (Zr,Ti) O3 film only at electric fields greater than 1.5 MV/cm, a factor of three higher than the low-frequency coercive field. There is no switching in response to a large number of short pulses with amplitudes lower than 1.5 MV/cm, even when the total duration reaches several milliseconds. In comparison, a series of microsecond-duration pulses causes cumulative changes in the area of switched polarization and eventually switches the entire capacitor. The difference between long- and short-duration electric field pulses arises from effects linked to domain nucleation and charge transport in the ferroelectric film. A phase-field model shows that the shrinking of the switched domain in the interval between pulses is a less important effect. This opportunity to apply large fields for short times without inducing switching by domain-wall motion raises the possibility that future experiments could reach the intrinsic coercive field of ferroelectric layers and provides a way to study the properties of materials under high electric fields.