The Korea Institute of Materials Science (KIMS) has announced an advancement in semiconductor technology. Researchers from KIMS, in collaboration with Professor Hyun-Sang Hwang’s team at POSTECH, have developed a new heterojunction technology that combines tungsten disulfide (WS₂), a two-dimensional (2D) material with hafnium zirconium oxide (HZO), a ferroelectric material. The breakthrough addresses interfacial stability and crystallinity challenges, which are critical factors in enhancing the performance and reliability of ferroelectric devices.

The research results have been accepted by the International Electron Devices Meeting 2024 (IEDM 2024), one of the world’s leading semiconductor conferences, often described as the “Olympics of Semiconductors.” The presentation will take place on December 11 in San Francisco.

Credit: Korea Institute of Materials Science (KIMS)
– [Left] The schematic shows the multi-functions of the 2D-WS2 bottom interfacial layer for interface stability and the vertically well-ordered domain structures of HZO, which leads to excellent ferroelectric properties. [Right] P-V hysteresis loops of ferroelectric capacitors without (red) and with (blue) 2D-WS2 bottom interfacial layer at pristine state. A significant increase in 2Pr is observed in the bottom interface engineering.

Materials and challenges addressed
Tungsten disulfide (WS₂) is a 2D material with an ultrathin atomic-layer structure. Its properties are suitable for semiconductors and energy storage devices. HZO, a ferroelectric material, exhibits spontaneous polarization, essential for non-volatile memory devices capable of retaining data without power.

The study tackled two significant challenges in HZO-based ferroelectric device technology. First, it ensured interfacial stability, critical for maintaining material properties and device performance over time. Second, it improved the crystallinity of HZO to enhance device reliability by addressing issues with disordered domain alignment.

Traditional methods for HZO deposition face limitations, including high-temperature annealing and oxygen migration, which lead to chemical reactions and defects at the interface. These issues degrade ferroelectric properties and contribute to variability in device performance.

Key innovations
The research team introduced a tungsten disulfide (WS₂) layer between the electrode and HZO to overcome these challenges. This addition improved interfacial stability by minimizing chemical reactions and controlling oxygen migration during high-temperature processes. The approach also preserved the intrinsic properties of the materials and maximized the ferroelectric performance of HZO.

The researchers used the lattice compatibility between WS₂ and HZO to achieve superior crystallinity. By aligning material domains, the team significantly improved the uniformity and reliability of device performance. These advancements are seen as a critical step toward commercializing HZO-based ferroelectric devices.

Applications and future work
The new heterojunction technology is expected to play a key role in developing next-generation non-volatile memory devices, particularly those required for advanced semiconductor applications. The researchers aim to optimize the technology for low-temperature processes (below 400° C), making it suitable for integration in back-end-of-line (BEOL) manufacturing in the semiconductor industry.

“We have resolved the critical challenge of controlling disordered domains, which was the biggest obstacle to commercializing HZO-based non-volatile memory devices, thereby achieving non-volatile memory characteristics with high reliability and durability,” said Dr. Yong-Hun Kim, lead researcher at KIMS.

Funding and presentation
The research received support from the Ministry of Science and ICT, the fundamental research program of KIMS, the Global TOP Strategy Research Group Program, and the National Research Foundation of Korea. Seung-Kwon Hwang, a doctoral researcher at KIMS and first author of the study, will present the findings at IEDM 2024.