Subcritical switching dynamics and humidity effects in nanoscale studies of domain growth in ferroelectric thin film

New J. Phys. 17 013002 (2015).

Cédric Blaser and Patrycja Paruch.

Department of Quantum Matter Physics, University of Geneva, 24 Quai Ernest-Ansermet, 1211 Geneva 4, Switzerland.

ABSTRACT

Ferroelectric domain switching in c-axis-oriented epitaxial Pb(Zr0.2Ti0.8)O3 thin films was studied using biased scanning probe microscopy tips. While linear and logarithmic dependence of domain size on tip bias and writing time, respectively, are well known, we report an additional linear dependence on relative humidity in the 28–65% range. We map out the switched domain size as a function of both the tip bias and the applied pulse time and describe a growth-limited regime for very short pulses and a nucleation-limited regime for very low tip bias. Using ‘interrupted-switching’ measurements, we probe the nucleation regime with subcritical pulses and identify a surprisingly long relaxation time on the order of 100 ms, which we relate to ionic redistribution both on the surface and within the thin film itself.

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Significance Statement

A detailed understanding of polarization switching is both fundamentally interesting, and crucial for potential applications in information storage and nonlinear optics. The important role of surface water, which determines the electrostatic boundary conditions and thus the size, shape and growth rate of the domain, has long been recognized. Recently observed quasiperiodic switching controlled by these electrostatic boundary conditions has even been proposed for encoding information in memcomputing operations. In contrast, the subcritical regime, where the voltage pulses are too short to fully stabilize domains of inverted polarization, is much less well understood experimentally.

Main results. In this article, we present a complete scanning probe microscopy mapping of domain formation as a function of probe bias, writing time, and relative humidity (RH). We differentiate between a low-bias nucleation-limited regime, where successful switching of large domains depends on the local activation threshold, and a high-bias, short-write-time, growth-limited regime, where successful switching depends on the stabilization of the critical nucleus under the probe tip, leading to the formation of very small domains. Using very short repeated pulses well below switching limits, we specifically explore the subcritical regime, and demonstrate the unexpectedly long term metastability of the initial polarization softening and critical nucleus formation.

Wider implications. Since both fundamental and applied polarization switching studies are generally carried out in ambient conditions, recognizing the precise influence of RH is crucial, especially for potential memory or nonlinear optics devices based on nanoscale ferroelectric domain patterning. We show here that the annual humidity variation of a standard laboratory can lead to difference of a factor of two in the sizes of domains written under otherwise identical conditions.

Figure legend

(a) Schematic of the electric field induced nucleation and subsequent growth of a domain in a ferroelectric thin film. Representative images of (b) topography, (c) PFM phase and (d) PFM amplitude signals on our Pb(Zr0.2Ti0.8)O3 (PZT) sample.

Subcritical switching dynamics and humidity effects in nanoscale studies of domain growth in ferroelectric thin films. Advances In Engineering

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