채승철 교수

The random circuit breaker network model is proposed for unipolar resistance switching behavior. This model describes reversible dynamic processes involving two quasi-metastable states. The formation and rupture of conducting channels (see figure) in the polycrystalline TiO2 thin films may be analyzed by the self organized avalanche process in the random circuit breaker network model. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2089/2

We discovered stripe patterns of trimerization-ferroelectric domains in hexagonal REMnO(3) (RE=Ho,···,Lu) crystals (grown below ferroelectric transition temperatures (T(c)), reaching up to 1435 °C), in contrast with the vortex patterns in YMnO(3). These stripe patterns roughen with the appearance of numerous loop domains through thermal annealing just below T(c), but the stripe domain patterns turn to vortex-antivortex domain patterns through a freezing process when crystals cross T(c) even thou

The ferroelectricity in ultrathin HfO₂ offers a viable alternative to ferroelectric memory. A reliable switching behavior is required for commercial applications; however, many intriguing features of this material have not been resolved. Herein, we report an increase in the remnant polarization after electric field cycling, known as the "wake-up" effect, in terms of the change in the polarization-switching dynamics of a Si-doped HfO₂ thin film. Compared with a pristine spec

The interaction among topological defects can induce novel phenomena such as disclination pairs in liquid crystals and superconducting vortex lattices. Nanoscale topological vortices with swirling ferroelectric, magnetic, and structural antiphase relationships were found in multiferroic h-YMnO(3). Herein, we report the discovery of intriguing, but seemingly irregular configurations of a zoo of topological vortices and antivortices. These configurations can be neatly analyzed in terms of graph th

The recent demand for analogue devices for neuromorphic applications requires modulation of multiple nonvolatile states. Ferroelectricity with multiple polarization states enables neuromorphic applications with various architectures. However, deterministic control of ferroelectric polarization states with conventional ferroelectric materials has been met with accessibility issues. Here, we report unprecedented stable accessibility with robust stability of multiple polarization states in ferroele

Abstract Investigations concerning oxygen deficiency will increase our understanding of those factors that govern the overall material properties. Various studies have examined the relationship between oxygen deficiency and the phase transformation from a nonpolar phase to a polar phase in HfO 2 thin films. However, there are few reports on the effects of oxygen deficiencies on the switching dynamics of the ferroelectric phase itself. Herein, we report the oxygen- deficiency induced enhancement

Abstract Hafnium oxides‐based ferroelectric materials are promising for applications in nonvolatile memory devices. To control the ferroelectricity of such materials, it is necessary to tune their polymorphism, interfacial features, and defect (oxygen vacancy) distribution. A strategy is described for enhancing the ferroelectric properties of polycrystalline hafnium zirconium oxide (HZO) ultrathin films by modifying the oxygen pressure during the device preparation stage, which involves thermal

Topological materials, including topological insulators, magnets with Skyrmions and ferroelectrics with topological vortices, have recently attracted phenomenal attention in the materials science community. Complex patterns of ferroelectric domains in hexagonal REMnO(3) (RE: rare earths) turn out to be associated with the macroscopic emergence of Z(2)×Z(3) symmetry. The results of our depth profiling of crystals with a self-poling tendency near surfaces reveal that the partial dislocation (i.e.,

We report on multilevel switching behavior in the unipolar resistance switching of TiO2 thin films. Multiple metastable states were observed during the reset process by measuring I-V curves. As observed using a conducting atomic force microscope, the multilevel resistance switching was accompanied by decreases in area and in the conductance of the top surface conducting regions. These experimental observations at both the macroscopic and microscopic levels could be explained by using the “random

Abstract The groundbreaking discovery of unconventional ferroelectricity in HfO 2 opens exciting prospects for next‐generation memory devices. However, the practical implementation, particularly its epitaxial stabilization and a clearer understanding of its intrinsic ferroelectricity has been a significant challenge. The study arouses the potential importance of atomic layer deposition (ALD) for mass production in modern industries, demonstrating its proficiency in achieving epitaxial growth of

We report variations in the characteristic ferroelectric switching time and interface free carrier concentration associated with wake-up and split-up behaviors of a 4.2 mol. % Si-doped HfO2 thin film. Prior to the development of the split-up behavior, the thin films exhibited the wake-up behavior; the remanent polarization increased on repeated electric field cycling. After the wake-up behavior, Si-doped HfO2 films exhibited degradation of the remanent polarization values and splitting of the fe

인공지능(AI)에 기반한 자동화 시대를 대비하여 과학‧수학‧정보 교육과정의 재구조화와 융합교육의 필요성이 대두되고 있다. 그러나 교사들이 학교 과학 수업에 접목할 수 있는 데이터 기반의 교육자료가 아직은 부족한 실정이다. 이 연구에서는 과학 수업에 접목할 수 있도록 감쇠진동을 중심으로 AI 융합교육을 위한 데이터 기반의 교육자료를 개발하였다. 개발된 교육자료는 최근 기계학습 분야에서 많이 사용되고 있는 딥러닝 지도학습 방법을 이용하였으며, 온라인으로 배포 가능하도록 구글 Colaboratory를 사용하여 작성하였다. 교수학습과정에서 쉽게 사용할 수 있도록 학습 과정과 코드에 대해 자세히 설명하였으며, 직관적인 이해를 돕기 위해 결과를 시각화하였다.

We report on an oxygen partial pressure dependence of the unipolar resistance switching behavior of a Pt/NiO/Pt structure. By varying the oxygen partial pressure from 1 to 50 mTorr during film growth, we observed the reliable resistance switching behaviors in the films grown at high oxygen partial pressure, whereas we observed a failure of resistance switching behavior for the film grown at low pressure. In situ x-ray photoemission spectroscopy revealed that the unipolar resistance switching beh