https://scholarworks.unist.ac.kr/handle/201301/98 2026-04-08T22:05:52Z 2026-04-08T22:05:52Z Lee, Jina Yun, Seok Joon Choi, Soo Ho Kim, Hyung-Jin Kim, Hang Sik Kim, Minhyuk Cha, Wujoon Cho, Byeong Wook Krishna, Swathi Kim, Soo Min Jeong, Hu Young Kim, Young-Min Han, Young-Kyu Lee, Young Hee Kim, Ki Kang https://scholarworks.unist.ac.kr/handle/201301/91310 2026-04-08T02:00:23Z 2026-02-28T15:00:00Z

Title: Vacancy Cluster-Mediated Epitaxial Layer-by-Layer Growth of van der Waals Heterostructures Author(s): Lee, Jina; Yun, Seok Joon; Choi, Soo Ho; Kim, Hyung-Jin; Kim, Hang Sik; Kim, Minhyuk; Cha, Wujoon; Cho, Byeong Wook; Krishna, Swathi; Kim, Soo Min; Jeong, Hu Young; Kim, Young-Min; Han, Young-Kyu; Lee, Young Hee; Kim, Ki Kang Abstract: Two-dimensional transition metal dichalcogenide heterostructures offer a versatile platform for tailoring quantum and optoelectronic properties, yet their scalable synthesis remains challenging due to the inert nature of van der Waals (vdW) basal planes, which lack nucleation sites for epitaxy. Here, we report a vacancy cluster-mediated epitaxial layer-by-layer growth strategy that enables the deterministic construction of vdW heterostructures with atomic precision. Hydrogen plasma treatment generates chalcogen vacancy clusters on template monolayers, providing localized nucleation sites for subsequent overlayer growth. This process yields highly crystalline heterostructures, as confirmed by atomic-resolution scanning transmission electron microscopy and density functional theory, while postgrowth annealing under chalcogen-rich conditions heals interface vacancies, restoring optical quality and enabling robust interlayer excitonic coupling. Using this approach, we demonstrate versatile MoS2/WS2, MoSe2/WSe2, bilayer MoS2, and MoS2/MoSSe heterostructures, all exhibiting atomically sharp interfaces and epitaxial alignment. Our results establish vacancy cluster-mediated epitaxy as a general platform for programmable stacking of two-dimensional materials, advancing the scalable design of functional vdW solids.

2026-02-28T15:00:00Z Kim, Yechan Hur, Namwook Kim, Hyesoo Jeong, Hongsik Suh, Joonki Kwon, Yongwoo https://scholarworks.unist.ac.kr/handle/201301/91307 2026-04-08T01:30:16Z 2026-03-31T15:00:00Z

Title: Analysis of Thermal Disturbance in Vertically Stacked Phase-Change Memory Using Multiphysics Simulation Author(s): Kim, Yechan; Hur, Namwook; Kim, Hyesoo; Jeong, Hongsik; Suh, Joonki; Kwon, Yongwoo Abstract: Vertically stacked phase-change memory (PCM) architectures represent a promising strategy for realizing high device density; however, they remain susceptible to thermal disturbance (TD), manifested as heat-induced crosstalk between neighboring cells during switching operations. In this study, thermal effects in 3-D PCM arrays are systematically investigated using a multiphysics simulation framework, where our electrothermal and phase-field models are implemented within a commercial finite element solver. By quantitatively analyzing the effects of intercell spacing and cell dimensions, we identify geometrical regimes where TD can be suppressed without sacrificing memory density. Furthermore, we demonstrate that engineering the cell architecture to enhance thermal boundary resistance (TBR), for example, by incorporating recessed heater structures, significantly mitigates heat transfer to adjacent cells and enables lower reset energy operation. Simulation results further reveal the tradeoffs among heater thickness, interlayer dielectric (ILD) thickness, and device endurance over repeated programming cycles. These insights guide the design of stackable PCM cells for robust, energy-efficient, and scalable memory integration.

2026-03-31T15:00:00Z Kim, Jeongha Mohapatra, Debananda Son, Yeseul Jang, Jae Min Kim, Sang Bok Hong, Tae Eun Cheon, Taehoon Shong, Bonggeun Kim, Soo-Hyun https://scholarworks.unist.ac.kr/handle/201301/91301 2026-04-08T00:00:08Z 2026-02-28T15:00:00Z

Title: Enhanced functional properties of ABC-type atomic layer deposited Ru thin films for advanced Cu alternative nanoscale interconnects Author(s): Kim, Jeongha; Mohapatra, Debananda; Son, Yeseul; Jang, Jae Min; Kim, Sang Bok; Hong, Tae Eun; Cheon, Taehoon; Shong, Bonggeun; Kim, Soo-Hyun Abstract: Atomic layer deposition (ALD) technology requires high-temperature processes to achieve low resistivity, large grain size, and fewer impurities in ultrathin interconnects; however, the thermal stability of the precursor often constrains this approach. This study presents a novel ABC-type ALD process, using [tricarbonyl(trimethylenemethane)ruthenium, [Ru(TMM)(CO)3]] as the Ru precursor and two counter-reactants (O2 and NH3) sequentially, to deposit highly conductive ruthenium (Ru) thin films at a high temperature of 310 degrees C. A key innovation of this work is that grain growth occurs without the need for annealing. Compared to the conventional AB-type Ru ALD process, the ABC-type process significantly reduces resistivity from 20.1 & micro;Omega cm to 13.4 & micro;Omega cm. In addition to resistivity reduction, the process also improves surface roughness and reduces impurities in the Ru film. Using the Fuchs-Sondheimer and Mayadas-Shatzkes' model, the study quantitatively identifies the contribution of various factors to achieving low resistivity, highlighting grain size as the critical factor for this achievement. Moreover, machine learning potential (MLP) analysis was used to explore the adsorption and decomposition mechanisms of NH3, providing valuable theoretical insights that support the chemical rationale behind the surface reactions. Finally, the Ru thin films deposited by the ABC-type Ru ALD process achieve excellent step coverage on high-aspect-ratio trench patterns (similar to 30, opening width: 140 nm), presenting a breakthrough approach for next-generation nanoscale interconnects.

2026-02-28T15:00:00Z Kim, Juheon Jang, Minki Choi, Won Hong Park, Junhyeok Kim, Byungjo Kim, Sunghyup Chung, Hayoung https://scholarworks.unist.ac.kr/handle/201301/91251 2026-04-07T02:40:50Z 2026-06-30T15:00:00Z

Title: Structural characterization and bonding energy analysis for plasma-activated bonding of SiCN films: A reactive molecular dynamics study Author(s): Kim, Juheon; Jang, Minki; Choi, Won Hong; Park, Junhyeok; Kim, Byungjo; Kim, Sunghyup; Chung, Hayoung Abstract: Plasma-activated bonding of SiCN films enables high interfacial bonding strength, which is essential for the mechanical reliability of hybrid bonding technologies. While experimental studies have shown that the interfacial bonding properties of SiCN films depend on both film composition and plasma treatment conditions, the underlying atomistic correlations have not yet been established. In this work, we present an atomistic investigation of SiCN-SiCN plasma-activated bonding using reactive molecular dynamics simulations, focusing on the effects of SiCN composition and plasma fluence. The simulation model includes O2 plasma surface activation, surface hydroxylation, direct bonding, post-bonding annealing, and interfacial debonding. Structural analysis of plasma-activated SiCN surfaces reveals composition- and plasma fluence-dependent chemical and morphological modifications, characterized by changes in specific covalent bond density and surface roughness. Bonding energy, evaluated from traction-separation responses during debonding simulations, exhibits a positive correlation with the density of interfacial Si-O-Si linkages. As the interfacial Si-O-Si density reflects the combined effects of chemical activation and surface morphology, the dependence of bonding energy on both composition and plasma fluence can be interpreted at the atomic scale. These findings establish an atomic-level material-process-property relationship and provide practical guidance for selecting SiCN composition and plasma treatment conditions to enhance plasma-activated SiCN-SiCN bonding.

2026-06-30T15:00:00Z