Ferroelectric Domain Wall Motion in Freestanding Single‐Crystal Complex Oxide Thin Film

Abstract

Ferroelectric domain walls in single-crystal complex oxide thin films are found to be orders of magnitude slower when the interfacial bonds with the heteroepitaxial substrate are broken to create a freestanding film. This drastic change in domain wall kinetics does not originate from the alteration of epitaxial strain; rather, it is correlated with the structural ripples at mesoscopic length scale and associated flexoelectric effects induced in the freestanding films. In contrast, the effects of the bondbreaking on the local static ferroelectric properties of both top and bottom layers of the freestanding films, such as domain wall width and spontaneous polarization, are modest and governed by the change in epitaxy-induced compressive strain. Single-crystal complex oxide ferroelectric (FE) thin films exhibit high spontaneous polarization, coherent switching, and low coercive field-a unique set of properties ideal for the manufacture of energy-efficient, beyond-CMOS logic and memory components, [1] as well as future quantum computing devices. [2] One of the primary bottlenecks in this field stems from the great difficulty in producing high-quality interfaces between these single-crystal oxides and the singlecrystal silicon-the prevalent substrate in microelectronics, hindering their widespread use. Recent developments in complex oxide layer transfer techniques (LTTs), however, may make the monolithic integration of not only FE materials possible [3,4] but also other single-crystal functional oxides such as half-metals, high T c superconductors, and multiferroic materials-even down to monolayer Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))

Beyond Substrates: Strain Engineering of Ferroelectric Membranes

“…[46] Structural inhomogeneities emerging in unclamped membranes, however, can mask the impact of the substrate release on the switching kinetics. [47] Therefore, preserving high crystal quality in the ferroelectric membranes after the release is important to identify intrinsic changes in switching mechanisms and domain-wall mobilities with the aim of lowering switching times, as is sought after for ultra-high-speed, non-volatile memories, [48] memristors, [49] and neuromorphic networks. [50] Here, we demonstrate that high-quality nanoscale epitaxial films of the ferroelectric Ba 1-x Sr x TiO 3 can be transferred from single-crystal oxide substrates to silicon and polymer substrates without structural degradation.…”

Freestanding Ferroelectric Bubble Domains

“…For example, it has been found that in the freestanding state PbZr x Ti 1‐x O 3 and BiFeO 3 thin films attain superelasticity, [ 19 ] sustain extreme strain without being fractured, [ 20 ] deviate from the flat phase of atomic planes and create structural ripples. [ 21,22 ] However, properties of freestanding heterostructures have remained largely unknown. Two intriguing questions in this regard are: First, how does the freestanding state affect the energy landscape of low dimensional ferroelectrics?…”

Simple Method to Obtain Large‐Size Single‐Crystalline Oxide Sheets

“…Then the film is lifted off from the substrate by etching, laser lift‐off, or a sacrificial layer. [ 14–19 ] Particularly, a lift‐off and transfer technique utilizing a water‐soluble oxide Sr 3 Al 2 O 6 (SAO) as a sacrificial layer is applicable to various perovskite‐based oxides [ 20–26 ] because SAO has a matched lattice constant. For example, a /4 of SAO with a cubic structure (3.964 Å) is close to a of SrTiO 3 (STO) (3.905 Å).…”