https://scholar.dgist.ac.kr/handle/20.500.11750/820 2026-04-04T13:36:24Z https://scholar.dgist.ac.kr/handle/20.500.11750/60031 Title: Achieving wide-range steep slopes in SnS2 negative capacitance transistors through an isolated band structure and thermionic emission enhancement via Bi contacts Author(s): Song, Chong-Myeong; Park, Jaewoo; Lee, Shinbuhm; Kwon, Hyuk-Jun Abstract: Negative capacitance FETs aim for sub-60 mV dec-1 switching to curb power consumption, but often encounter instability and narrow steep-slope windows. We present a hysteresis-free NCFET that strategically utilizes a 2D SnS2 channel. The inherent isolated conduction band of SnS2, yielding a step-like density of states, is pivotal for sharp turn-on characteristics when effectively coupled with the negative capacitance effect. The SnS2 channel is integrated with an La:HfO2/HfO2 ferroelectric-dielectric gate stack and Bi contacts. This architecture shows an average subthreshold swing of 34 mV dec-1 across four current decades, maintaining sub-60 mV dec-1 operation over this wide range, and enabling sub-0.4 V operation. Bi contact is key, minimizing Fermi-level pinning at the SnS2/metal interface. This expands the thermionic emission region, allowing the negative capacitance to fully leverage the distinct properties of SnS2 for sustained wide-range steep-slope performance. This work demonstrates a novel approach to ultralow-power transistors by integrating an isolated-band semiconductor, optimized ferroelectric, and contact engineering. 2025-11-30T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59910 Title: Tunable Hydrogen Dynamics Under Electrical Bias for Neuromorphic Memory Applications Author(s): Noh, Hee Yeon; Lee, Chan-Kang; Haripriya, Gopalakrishnan Nair Ramani; Lee, Shinbuhm; Lee, Myoung-Jae; Wee, Jiyong; Lee, Hyeon-Jun Abstract: A wide variety of materials and device architectures have been explored for memristor applications targeting neural network simulations, most of which rely on oxide-based structures that exhibit resistive switching driven by oxygen-vacancy-mediated memory effects. In this study, we present a novel approach for modulating resistive and nonvolatile memory behavior in oxide semiconductors through the controlled injection and extraction of hydrogen. The proposed two-terminal device incorporates a hydrogen source layer that facilitates the diffusion of hydrogen ions into the active oxide matrix, where they form hydroxide (OH) bonds and locally modulate the electron concentration. This process induces a stable and reversible memory effect under an applied electric field. Hydrogen exchange predominantly occurs at the interface between the active and insulating layers, with the latter serving as a buffer to maintain an optimal hydrogen concentration. Furthermore, neural network simulations were performed by utilizing the synaptic characteristics controlled via hydrogen modulation, achieving a recognition accuracy of 97.2% on the MNIST data set. The effects of input data resolution and weight quantization on recognition performance were also systematically investigated and discussed. 2026-01-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59348 Title: High Oxygen Ion Conductivity in Hexagonal Perovskite Ba7Nb4MoO20 via Epitaxy-Assisted Orienting of Two-Dimensional Diffusion Pathways Author(s): Kim, Yunyeong; Kim, Dongha; Park, Jiseok; Chen, Aiping; MacManus-Driscoll, Judith L.; Lee, Shinbuhm Abstract: Oxygen ion conductors are a key component in solid-state ionic devices such as fuel cells, catalysts, sensors, and artificial intelligent devices. The recent discovery of undoped Ba7Nb4MoO20 hexagonal perovskites has attracted great attention due to the existence of two-dimensional oxygen diffusion pathways between NbO4 and MoO4 tetrahedra. However, there have been rare studies on the control parameters for hexagonal perovskites to further boost oxygen ion transport at lower temperatures. Here, we find significantly higher oxygen ion conductivity (5.6 x 10(-4) S cm(-1) at 340 degrees C, 3.2 x 10(-1) S cm(-1) at 600 degrees C) of (001)-oriented Ba7Nb4MoO20 epitaxial films by several orders of magnitude than that of sintered pellets. Our report is comparable to the oxygen ion conductivities of conventional doped conductors. X-ray diffraction and atomic-scale characterization with energy-dispersive X-ray spectroscopy reveal that this epitaxy-driven enhancement is attributed to the good alignment of two-dimensional pathways in an ion current direction. Our design principle of hexagonal perovskites will trigger an advanced understanding of the correlation between the crystal structure and ultrahigh oxygen ion conductivity 2025-08-31T15:00:00Z https://scholar.dgist.ac.kr/handle/20.500.11750/59233 Title: Exploring the Impact of Deposition Conditions on the Functionality of a-IGZO/AlOx-Based Sandwich Structures with Memory Effects Author(s): Haripriya, Gopalakrishnan Nair Ramani; Noh, Hee Yeon; Kim, June-Seo; Lee, Myoung-Jae; Lee, Shinbuhm; Lee, Hyeon-Jun Abstract: Memristors, inspired by the synaptic functions of the human brain, are crucial components for implementing synaptic weights in neuromorphic computing. Among them, semiconductor-oxide-based memristors have attracted significant attention owing to their material versatility and electrical tunability. However, their switching and conduction behaviors remain highly sensitive to fabrication conditions, often resulting in variability and poor reliability. While earlier studies have focused on oxygen vacancy control in either the active or reservoir layers, the combined influence of the plasma deposition environment exposed to the oxide layer, reservoir layer, and their interface for subtle processing variations has not been systematically examined. Here, we investigate amorphous InGaZnO (a-IGZO)-based memristors with an adjacent aluminum oxide (AlO x ) interfacial layer and demonstrate how minute changes in oxygen plasma conditions for the AlO x layer, along with the oxygen partial pressure during a-IGZO deposition, modulate interfacial oxygen distribution and vacancy stability. These interfacial modifications activate distinct conduction pathways-thermionic emission, thermionic field emission, and trap-assisted tunneling-that govern both steady-state conduction and current relaxation dynamics. Our results reveal that even slight variations in plasma and deposition conditions can induce pronounced shifts in the dominant conduction mechanisms, directly impacting device stability and performance. By establishing the interfacial origin of conduction mechanism transitions and current relaxation, this work advances the understanding of process-property relationships in oxide-based memristors and provides design guidelines for developing more stable and reproducible devices for neuromorphic applications. 2025-09-30T15:00:00Z