Sungkyunkwan University announced that Professor Tae-sung Kim’s research group at the school of mechanical engineering (first author: Jin-Hyoung Lee, Gun-Hoo Woo) has developed a "Free-standing ferro-ionic memristor" that selectively controls ion migration using only a tip-induced shear strain. Memristor devices, which are attracting attention as the next generation of devices that can be used in next-generation non-Von Neumann structures, have various strengths compared to conventional semiconductor devices such as in-memory computing and weight storage at low power, but it is essential to secure the reliability of each memristor device to realize practical large-scale neural computing. However, the biggest limitation of memristor devices is the "randomness" of ion movement, and this stochastic ion behavior has traditionally prevented them from being commercially valuable due to the critical limitation that it reversibly affects the reliability and reproducibility of memristor devices.

To address this stochastic limitation, this research team has focused at the flexoelectric effect, which occurs at the nanometer (nm) scale. In 2011, it was reported in the previous research that the flexoelectric field can be maximized when the lattice structure of a material is bended by an external force, generating the internal polarization and electric fields. However, in order to selectively activate phase change and ion migration at the desired location within flexoelectricity, much larger lattice bending is required than those in previous studies. Therefore, to spatially maximize the flexoelectric field beyond previous studies, they applied vertical shear stresses to free-standing 2D materials with an atomic force microscope (AFM) tip to selectively maximize the flexoelectric field and its corresponding downward polarization at the specific regions. Consequently, the research team successfully observed the selective growth of conductive filaments via localized flexoelectric field. Furthermore, they succeeded to reversibly control the phase transition threshold voltage by modulating the bottom ferroelectric polarization, enabling active spatial control of conductive filaments at the nanometer scale.

Professor Tae-Sung Kim remarked, “This research overcomes the stochastic limitations of conventional ferro-ionic materials and offers a new perspective on ion movement based on the flexoelectric effect from a structural standpoint. It is expected to significantly enhance the performance and reliability of semiconductor devices in future studies by enabling precise spatial control of ions.” This research was supported by the National Research Foundation of Korea and the Korea Basic Science Institute. The research were published in the prestigious international journal “Nature Communications” on June 18.

※Title: Free-standing two-dimensional ferro-ionic memristor

※Author: Taesung Kim (corresponding author), Jinhyoung Lee, Gunhoo Woo (first author), Jinill Cho, Sihoon Son, Hyelim Shin, Hyunho Seok, Min-Jae Kim, Eungchul Kim, Ziyang Wang, Boseok Kang, Won-Jun Jang (co-author)

※Journal Link: https://www.nature.com/articles/s41467-024-48810-3

Next-generation freestanding memristor device platform implemented based on probe-guided substation