Flexible Polar Materials on Mica

Flexible electronic devices have been extensively investigated in recent years, in which polymeric substrates such as polyimide and polyethylene terephthalate have been widely employed. However, the relatively low thermal stability of these polymers has limited the direct epitaxial growth of high-quality functional oxides. To overcome this bottleneck, mica has been gradually adopted as a two-dimensional flexible platform, because of its atomically flat surface, excellent thermal stability, and the unique van der Waals interlayer interaction. In this review, recent progress on the use of mica as a flexible substrate for inorganic ferroelectric oxide thin films is systematically summarized. The van der Waals epitaxy mechanism and the release of the substrate clamping effect are first discussed, followed by recent developments of flexible ferroelectric memories and high-energy-storage dielectric capacitors, piezoelectric and electrocaloric coupling films, multiferroic and flexoelectric heterostructures, and pyroelectric thermal-electric conversion. The potential of such mica-based fully inorganic ferroelectric films for extreme-environment and space-electronics applications is also briefly addressed. This review aims to provide a structured overview of this emerging research field, known as "MICAtronics".