Flexible oxide epitaxial thin films for wearable electronics: Fabrication, physical properties, and applications

Formation and physical properties of the self-assembled BFO–CFO vertically aligned nanocomposite on a CFO-buffered two-dimensional flexible mica substrate

“…With the exponentially increasing demands in speed and functionalities for meeting the rapidly moving technologies, integrating materials with vastly different structures and properties onto the same substrate, preferably exible in many cases, to make the desired devices not only has become mainstream research but a necessity. [1][2][3][4] Indeed, ubiquitous applications of exible electronics have been forecasted or even realized in various industry sectors, such as wearable healthcare and environmental monitoring, human-machine interactivity, displays and storage devices, energy conversion and harvesting, communication, and wireless networks. [5][6][7][8] Numerous functional materials which were originally delivered in thin lms deposited on rigid substrates have been transformed into exible thin lms to meet the demands of exibility while keeping the functionality required for device applications.…”

“…2,3,9 Perhaps, the most stringent requirement is the temperature that the exible substrate has to withstand in order to obtain exible thin lms with the required morphology and architecture designs without degrading their physical properties. [1][2][3][4] For instance, the widely used polymer substrates for growing exible thin lms mostly would result in amorphous or polycrystalline thin lms because they usually cannot withstand the high-temperature deposition process. Alternatively, exible metal substrates might appear to be a viable choice for obtaining thin lms with good crystallinity due to their better endurance to higher temperatures.…”

“…However, it turns out that most metal substrates with high melting point are high density, mostly polycrystalline with a rough surface, containing metallic impurities, and very reactive with intermediary gas during the thin lm growth. 2,9 Very recently, catalytically mediated epitaxy has been successfully demonstrated for growing highly crystalline Si and Ge nanocrystals on van der Waals substrates, such as graphene and hexagonal boron nitride (hBN), by using solid catalysts composed of Ag + Au. 10 Although this approach may be able to grow 3D metals and semiconductor nanostructures on 2D van der Waals substrates and expand the horizons for electronic and photonic applications, it is yet to be veried whether or not it would work for growing more complex oxides with specic functionalities.…”

“…In this respect, some exible ceramics substrates have been considered as viable candidates for growing high-quality crystalline thin lms owing to having at surfaces up to atomic scale. 2,7 Especially for thin-lm heterostructures, the choice of heterostructure design such as bilayer (2-2 system), particulates (0-3 system), and vertically aligned nanocomposite (VAN) (1-3 system) had been achieved with highly crystalline constituent phases. For instance, recently, exible mica substrate has attracted tremendous attention since it can be easily exfoliated along the (001)-plane to obtain dangling bond-free atomic level at surface suitable for growing VAN complex oxide with epitaxial quality.…”

High Yield Transfer of Clean Large-Area Epitaxial Oxide Thin Films

“…The key issue for a good transfer is to prevent the crack formation and minimize contamination. We note that while free-standing thin films of metals and some oxides have been shown to be relatively flexible [ 33 , 35 ] compared to their bulk counterparts, it is clear that ceramic films are still brittle in thin film form and if crack initiation sites are present, the films will behave in a brittle manner [ 36 , 37 ].…”