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Ferroelectric thin films compatible with oxide electrodes

(a) FCD domains in the PTO layer with symmetric oxide electrodes. (b) Alternating current domains in the PTO layer with asymmetric oxide electrodes. Credit: Shuang Li and Yinlian Zhu

The theory that oxide electrodes destabilise ferroelectric phenomena called flux-closure domains (FCDs) in ferroelectric thin films has been disproved by researchers at the Chinese Academy of Sciences.

FCD structures are said to be microscopic topological phenomena that feature distinct electric polarisation properties. In the development of thin films for ferroelectric devices, researchers have thought that contact with commonly used oxide electrodes limits FCD formation.

"The general thinking has been that oxide electrodes would destabilise flux-closure domains. However, our work has shown that this is no longer true when the top and bottom electrodes are symmetric, which physically makes sense," said Professor Yinlian Zhu.

The researchers used two types of oxide electrodes: one based on strontium ruthenate, the other based on lanthanum strontium manganite, chosen as oxide electrodes because of their similar perovskite structures, which they claim work well in layer-by-layer film growth.

They studied how these electrodes influenced FCD formation in PbTiO3 (PTO) perovskite-oxide-based thin films deposited on gadolinium scandium oxide substrates.

They found that periodic FCD arrays can be stabilised in PTO films when the top and bottom electrodes are symmetric, while alternating current domains appear when they apply asymmetric electrodes.

"We successfully grew ferroelectric thin films with symmetric oxide electrodes in which flux-closure domains and their periodic arrays clearly do exist," Zhu said. "Our work sheds light on understanding the nature of flux-closure domains in ferroelectrics. We expect that it will open research possibilities in the evolution of these structures under external electric fields."

The researchers believe FCD formation could benefit next-generation electronic devices, including data storage components and spintronic tunnel junctions to ultra-thin capacitors.

Peggy Lee

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