Influence of Atmospheric Conditions on Electrical Characteristics of Solution-Processed IZO Thin-Film Transistors

Baang, Sungkeun,Lee, Hyeonju,Ham, Youngjin,Park, Jaehoon American Scientific Publishers 2017 Journal of nanoscience and nanotechnology Vol.17 No.6

<P>The electrical characteristics of indium zinc oxide (IZO) thin-film transistors (TFTs) fabricated by solution process are analyzed under different atmospheric conditions. Compared to the electrical properties measured in atmospheric air, a positive shift in the threshold voltage and a decrease in the off-state current invariably are observed under vacuum. During consecutive operations of the IZO TFTs, the threshold voltage shifts towards a negative direction in atmospheric air but a positive direction under vacuum. In addition, the characteristic variations in the linear operation region are more pronounced when the TFTs are operated under vacuum environment. However, the effects of O-2 and N-2 gaseous ambient on the electrical characteristics of IZO TFTs are found to be negligible. These results suggest that the environmental influence on the performance of solution-processed IZO TFTs, which is observed in atmospheric air and under vacuum, is originated mainly from the interplay between polar H2O molecules and majority carrier electrons in the IZO film.</P>

Deadbeat Control for Linear Systems with State Constraints

BAANG, Dane,CHWA, Dongkyoung The Institute of Electronics, Information and Comm 2009 IEICE transactions on fundamentals of electronics, Vol.92 No.4

<P>This paper presents a deadbeat control scheme for linear systems with state constraints. The proposed controller increases the number of steps on-line for the deadbeat tracking performance, satisfying given admissible state constraints. LMI conditions are given to minimize the unavoidable step delay. The proposed schemes can be easily developed by using LMI approach, and are validated by numerical simulation.</P>

Operational stability of solution-processed indium-oxide thin-film transistors: Environmental condition and electrical stress

Baang, Sungkeun,Lee, Hyeonju,Zhang, Xue,Park, Jaehoon,Kim, Won-Pyo,Ko, Young-Woong,Piao, Shang Hao,Choi, Hyoung Jin,Kwon, Jin-Hyuk,Bae, Jin-Hyuk 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol. No.

<P>We investigate the operational stability of bottom-gate/top-contact-structured indium-oxide (In2O3) thin-film transistors (TFTs) in atmospheric air and under vacuum. Based on the thermogravimetric analysis of the In2O3 precursor solution, we utilize a thermal annealing process at 400 A degrees C for 40 min to prepare the In2O3 films. The results of X-ray photoemission spectroscopy and field-emission scanning electron microscopy show that the electron is the majority carrier in the In2O3 semiconductor film prepared by a spin-coating method and that the film has a polycrystalline morphology with grain boundaries. The fabricated In2O3 TFTs operate in an n-type enhancement mode. When constant drain and gate voltages are applied, these TFTs in atmospheric air exhibit a more acute decay in the drain currents with time compared to that observed under vacuum. In the positive gate-bias stress experiments, a decrease in the field-effect mobility and a positive shift in the threshold voltage are invariably observed both in atmospheric air and under vacuum, but such characteristic variations are also found to be more pronounced for the atmospheric-air case. These results are explained in terms of the electron-trapping phenomenon at the grain boundaries in the In2O3 semiconductor, as well as the electrostatic interactions between electrons and polar water molecules.</P>

Development of Effective Analytical Signal Models for Functional Microwave Imaging

Baang, Sung-Keun,Kim, Jong-Dae,Lee, Yong-Up,Park, Chan-Young The Korean Society of Medical and Biological Engin 2007 의공학회지 Vol.28 No.4

Various active microwave imaging techniques have been developed for cancer detection for past several decades. Both the microwave tomography and the UWB radar techniques, constituting functional microwave imaging systems, use the electrical property contrast between normal tissues and malignancies to detect the latter in an early development stage. Even though promising simulation results have been reported, the understanding of the functional microwave imaging diagnostics has been relied heavily on the complicated numerical results. We present a computationally efficient and physically instructive analytical electromagnetic wave channel models developed for functional microwave imaging system in order to detect especially the breast tumors as early as possible. The channel model covers the propagation factors that have been examined in the previous 2-D models, such as the radial spreading, path loss, partial reflection and transmission of the backscattered electromagnetic waves from the tumor cell. The effects of the system noise and the noise from the inhomogeneity of the tissue to the reconstruction algorithm are modeled as well. The characteristics of the reconstructed images of the tumor using the proposed model are compared with those from the confocal microwave imaging.

Perfect Tracking Control for Linear Systems with State Constraint

Dane Baang,Jin Young Choi,Hyungbo Shim 대한전기학회 2007 International Journal of Control, Automation, and Vol.5 No.2

This paper presents a new Perfect Tracking Control (PTC) scheme for linear systems with state constraint. The proposed controller increases the number of the steps on-line for perfect tracking to satisfy the given ellipsoid-type state constraint. The unavoidable step delay that we impose is minimized by solving LMI feasibility problems and the possible feedback information loss is avoided. The proposed schemes are easy to develop, theoretically simple and clear, and include the conventional PTC as its special case.

Adaptive Observer using Auto-generating B-splines

Dane Baang,Julian Stoev,Jin Young Choi 대한전기학회 2007 International Journal of Control, Automation, and Vol.5 No.5

This paper presents a new adaptive observer design method for a class of uncertain nonlinear systems by using spline approximation. This scheme leads to a simplified observer structure which requires only fixed number of integrations, regardless of the number of parameters to be estimated. This benefit can reduce the number of integrations of the observer filter dramatically. Moreover, the proposed adaptive observer automatically generates the required spline elements according to the varying output value and, as a result, does not requires the pre-knowledge of upper and lower bounds of the output. This is another benefit of our approach since the requirement for known output bounds have been one of the main drawbacks of practical universal approximation problems. Both of the benefits stem from the local support property, which is specific to splines.

IEEE 802.15.3a 기반의 무선 위치인식을 위한 평균가중 신호 도착방향 매개변수 추정 기법

방성근(Sungkeun Baang),이용업(Yong Up Lee) 한국통신학회 2010 韓國通信學會論文誌 Vol.35 No.5

마이크로파 reflectometry의 산란 신호 응답 특성

방성근(Sungkeun Baang) 한국전자파학회 2008 한국전자파학회논문지 Vol.19 No.5

시간 지연이나 위상 지연과 같은 레이다 기법을 기반으로 하는 마이크로파 reflectometry를 비균질 매질의 밀도 특성을 조사하기 위한 비파괴 검사 장치로 응용하기 위한 시스템 특성을 연구하였다. 특히 마이크로파 reflectometry를 플라즈마 연구 분야에 응용하기 시작한 것은 비교적 최근의 일로서 그 활용도가 점차 증가하고 있는데, 마이크로파 reflectometry로 비균질 매질을 조사하기 위해서는 대상에 따른 시스템의 하드웨어 구성이 최적화되어야 하며, 시스템에서의 신호 응답 특성이 이해되어야만 전체적인 시스템 해법을 제공하는 것이 된다. 마이크로파 reflectometry를 이용하여 진단하는 대상인 플라즈마의 특성에 따른 시스템의 구성을 설명하고, 파동수 및 밀도 섭동에 관한 시스템의 특성을 실험적으로 조사하기 위한 장치를 설명하였다. 마이크로파 reflectometry의 신호는 대부분의 전자기파 에너지가 반사되는 지역에서 기인하는 cutoff 신호와 교란 신호와의 상호 작용으로 발생하는 산란 신호로 구성된다. 이 논문에서는 마이크로파 reflectometry의 산란 신호 특성을 실험적 방법으로 조사한 결과를 제시하며, 1차원 파동방정식을 이용한 수치 해석적 결과와 비교 분석하였고, cutoff 신호 특성과도 비교하였다. The characteristics of microwave reflectometry, which is based on the technologies of FM radar and is applied as a non-invasive method to examine the properties including density distribution of inhomogeneous media, is investigated. The microwave reflectometry system requires not only an optimized system hardware but as well as the understanding of system response from the media under test in order to provide the system solution describing the object under test quantitatively. The introduction of microwave reflectometry especially in the area of applied plasma physics has been relatively new and the number of usage is found to be increasing gradually. The experimental method to characterize the microwave system as a device to examine the properties of plasma is explained. The microwave reflectometry signals consist of the cutoff signals which originate from the region where most of the reflected power comes from and the scattered signals which result as an interaction of the microwave and the density perturbations. This paper describes the experimental results of the scattered signal from the microwave reflectometry, such as the wavenumber dependence and the sensitivity on density perturbation, and the comparison of the characteristics with those from the numerical simulations and those from the cutoff signals.

연구용 원자로의 출력제어기법 설계 및 적용사례

방대인(Dane Baang),이종복(Jongbok Lee),서용석(Yongsuk Suh) 대한전자공학회 2014 전자공학회논문지 Vol.51 No.9

본 논문에서는 연구용 원자로의 출력제어기법 설계와 이를 실제 원자로에 적용하여 성능을 검증한 사례를 소개한다. 연구용 원자로의 출력제어를 위해 제안된 설계 원리는 오버슈트(overshoot)의 억제, 출력 증가율의 억제, 그리고 안전해석에 기반한 최대 출력치의 제한이라는 세 가지이며, 이를 만족키 위해 한국원자력연구원 내의 연구용 원자로인 하나로의 설계개념에 기반을 두어 제어 로직의 개념설계, 상세설계, 구현, 시운전을 통해 해외의 원자로에 적용하여 실제 제어 성능을 검증하였다. Study and application result of power controller to research reactor is presented. Considering safety-oriented design concept and other control environment, we developed a simple closed-loop controller that provides limiting function of power-change-rate as well as low-overshoot and fine tracking performance. The design result has been well-proven via simulation and actual application to a research reactor.

Adaptive Feedback Linearization Control Based on Airgap Flux Model for Induction Motors

Seok Ho Jeon,Dane Baang,Jin Young Choi 대한전기학회 2006 International Journal of Control, Automation, and Vol.4 No.4

This paper presents an adaptive feedback linearization control scheme for induction motors with simultaneous variation of rotor and stator resistances. Two typical modeling techniques, rotor flux model and stator flux model, have been developed and successfully applied to the controller design and adaptive observer design, respectively. By using stator fluxes as states, over-parametrization in adaptive control can be prevented and control strategy can be developed without the need of nonlinear transformation. It also decrease the relative degree for the flux modulus by one, thereby, yielding a simple control algorithm. However, when this method is used for flux observer, it cannot guarantee the convergence offlux. Similarly, the rotor flux model may be appropriate for observers, but it is not so for adaptive controllers. In addition, if these two existing methods are merged into overall adaptive control system, it brings about structural complexies. In this paper, we did not use these two medeling methods, and opted for the airgap flux model which takes on only the positive aspects of the existing rotor flux model and stator flux model and prevents structural complexity from occuring. Through theoretical analysis by using Lyapunov's direct method, simulations, and actual experiments, it is shown that stator and rotor resistances converge to their actual values, flux is well estimated, and torque and flux are controlled independently with the measurements of rotor speed, stator currents, and stator voltages. These results were achieved under the persistent excitation condition, which is shown to hold in the simulation.