Scaling Effects in Perovskite Ferroelectrics: Fundamental Limits and Process‐Structure‐Property Relations

Abstract

Ferroelectric materials are well‐suited for a variety of applications because they can offer a combination of high performance and scaled integration. Examples of note include piezoelectrics to transform between electrical and mechanical energies, capacitors used to store charge, electro‐optic devices, and nonvolatile memory storage. Accordingly, they are widely used as sensors, actuators, energy storage, and memory components, ultrasonic devices, and in consumer electronics products. Because these functional properties arise from a noncentrosymmetric crystal structure with spontaneous strain and a permanent electric dipole, the properties depend upon physical and electrical boundary conditions, and consequently, physical dimension. The change in properties with decreasing physical dimension is commonly referred to as a size effect. In thin films, size effects are widely observed, whereas in bulk ceramics, changes in properties from the values of large‐grained specimens is most notable in samples with grain sizes below several micrometers. It is important to note that ferroelectricity typically persists to length scales of about 10 nm, but below this point is often absent. Despite the stability of ferroelectricity for dimensions greater than ~10 nm, the dielectric and piezoelectric coefficients of scaled ferroelectrics are suppressed relative to their bulk counterparts, in some cases by changes up to 80%. The loss of extrinsic contributions (domain and phase boundary motion) to the electromechanical response accounts for much of this suppression. In this article, the current understanding of the underlying mechanisms for this behavior in perovskite ferroelectrics is reviewed. We focus on the intrinsic limits of ferroelectric response, the roles of electrical and mechanical boundary conditions, grain size and thickness effects, and extraneous effects related to processing. In many cases, multiple mechanisms combine to produce the observed scaling effects.

Formation of BiFeO3 from a Binary Oxide Superlattice Grown by Atomic Layer Deposition

“…However, there is little understanding of how the as‐grown amorphous films crystallize during post‐deposition heat treatment, which is required for ALD‐grown BFO films. In particular, for polycrystalline films both, composition and microstructure, have tremendous effects on the resulting properties …”

“…In particular, for polycrystalline films both, composition [26] and microstructure, have tremendous effects on the resulting properties. [27] In this report, we provideadetailed investigation of the crystallization of Bi-Fe-Of ilms grown via as uperlattice approach.H erein, semi-amorphous Fe 2 O 3 -Bi 2 O 3 superlattices were studied by in situ X-ray diffraction (XRD) and X-ray reflectivity (XRR), in situ X-ray photoelectron spectroscopy (XPS), scanning transmission electronm icroscopy( STEM) and transmission electron microscopy (TEM) after annealing at selected temperatures (T). In addition, we present piezoresponse force microscopy (PFM) results obtained on ap olycrystalline BFO film.…”

Thickness‐dependent domain wall reorientation in 70/30 lead magnesium niobate‐ lead titanate thin films

“…These design goals are, in principle, achievable via thickness reduction in the ferroelectric. However, it is widely reported that the functional properties of ferroelectric films are strongly thickness dependent, reducing concomitantly with film thickness …”

Functional and structural effects of layer periodicity in chemical solution‐deposited Pb(Zr,Ti)O3 thin films

“…Discontinuity at the crystallization interfaces, both in the grain/domain structure and crystallite orientation are readily visible in the TEM analyses ( Figure 4B,C,E). 36,37 In smaller grains where smaller domains are expected, domain walls are bound to exhibit reduced mobility, due to greater chances of interaction with other defects, including grain boundaries and domain walls-potentially resulting in diminished extrinsic contributions to the dielectric response. This observation is important since these discontinuities in the MLA film suggest that the density of such interfaces and the number of anneals can have a substantial impact on the crystallography throughout the film thickness, and hence the overall functional properties of the film.…”