Nature-inspired breakthrough enables subatomic ferroelectric memory

Ferroelectric domain switching at the sub-unit cell level in Brownmillerite oxides. @ POSTECH

A research team led by Prof. Si-Young Choi from the Department of Materials Science and Engineering and the Department of Semiconductor Engineering at POSTECH (Pohang University of Science and Technology) has discovered ferroelectric phenomena occurring at a subatomic scale in the natural mineral Brownmillerite, in collaboration with Prof. Jae-Kwang Lee’s team from Pusan National University as well as Prof. Woo-Seok Choi's team from Sungkyunkwan University. The research was published on May 20 in Nature Materials.

Electronic devices store data in memory units called 'domains,' whose minimum size limits the density of stored information. However, ferroelectric-based memory has been facing challenges in minimizing domain size due to the collective nature of atomic vibrations. The research team found inspiration to overcome these limitations in nature. They focused on Brownmillerite, a naturally occurring mineral characterized by its unique alternating layers of tetrahedral (FeO4) and octahedral (FeO6) iron-oxygen structures, resembling a sandwich with alternating layers of bread and ham.

Strikingly, Brownmillerite exhibits a special phenomenon known as 'phonon decoupling.' Phonons represent atomic vibrations; normally, when atoms vibrate, nearby atoms are also influenced, due to collective vibrations. However, in Brownmillerite, when the tetrahedral layers vibrate, the adjacent octahedral layers remain mostly unaffected. This unique property enables the selective formation of domains within the tetrahedral layers when an electric field is applied.

This phenomenon was confirmed in various types of Brownmillerite, such as thin films of SrFeO2.5 and CaFeO2.5. and a single crystalline CaFeO2.5. Their experiments demonstrated that the electric field influenced only the tetrahedral layers, altering the atomic positions while leaving the octahedral layers unchanged. The team further demonstrated the practicality of this phenomenon by successfully developing ferroelectric capacitors and thin-film transistor devices based on this structure.

If commercialized, this technology is expected to enable the development of memory devices that are tens of times smaller and faster than current models. Consequently, the storage capacity and processing speed of smartphones and computers could be significantly improved, accelerating advancements in high-speed data processing technologies such as artificial intelligence (AI) and autonomous vehicles. Prof. Si-Young Choi of POSTECH remarked, “This study exemplifies how wisdom derived from nature can provide critical solutions to technological limitations. Unlocking the secrets of still-unexplained natural phenomena could further enhance the applicability of various advanced technologies.” Reference Sub-unit-cell-segmented ferroelectricity in brownmillerite oxides by phonon decoupling

Jinhyuk Jang, Yeongrok Jin, Yeon-Seo Nam, Heung-Sik Park, Jaegyu Kim, Kyeong Tae Kang, Yerin So, Jiwoung Choi, Youngchang Choi, Jaechan Shim, Panithan Sriboriboon, Dong Kyu Lee, Kyoung-June Go, Gi-Yeop Kim, Seungbum Hong, Jun Hee Lee, Daesu Lee, Myung-Geun Han, Junwoo Son, Yunseok Kim, Hiroki Taniguchi, Seokhyeong Kang, Jang-Sik Lee, He Tian, Chan-Ho Yang, Yimei Zhu, Sang-Wook Cheong, Woo Seok Choi, Jaekwang Lee & Si-Young Choi https://www.nature.com/articles/s41563-025-02233-7 POSTECH