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>

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>

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.

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

Influence of Structural Defects in Solution-Processed InZnO Semiconductors on the Electrical Stability of Thin-Film Transistors

Hyeonju Lee,Chintalapalli Jyothi,Sungkeun Baang,Jin-Hyuk Kwon,Jin-Hyuk Bae 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.11

In this study, we investigate the morphological effect of solution-processed indium-zinc-oxide (InZnO) active layers on the electrical stability of InZnO thin-film transistors (TFTs). We first observe that in the spin-coating method, precursor agglomerates and aggregates remain on the substrates after spin coating an InZnO solution at a low spin speed, thereby causing particle-type morphological defects in the InZnO films. The morphological defects are proven to degrade the basic performance parameters of the InZnO TFTs, including the electrical current level, field-effect mobility, and threshold voltage. In addition, devices having morphological defects show a relatively large hysteresis in transfer characteristics compared to those without defects. In a test of the electrical stability over time, we determine that particle-type morphological defects cause a rapid increase in the conductivity of the InZnO films, which affects the variations in the saturation drain current and the threshold voltage.

무선 MAN에서 Best Effort 서비스를 위한 충돌 중재 방식 : 설계 및 성능 분석

박진경(Jin Kyung Park),방성근(Sungkeun Baang),최천원(Cheon Won Choi) 대한전자공학회 2009 電子工學會論文誌-TC (Telecommunications) Vol.46 No.5

IEEE 802.16 무선 MAN 표준안에서 best effort 서비스는 가장 낮은 우선 순위이며 예약 ALOHA 기반의 MAC 방식의 지원을 받는다. 이러한 MAC 방식에서 요청 간의 충돌은 피할 수 없으므로 표준안은 충돌 중재를 위해 이진 지수형 back-off 규칙을 채택하였다. 본 논문에서는 throughput 성능의 향상을 위해 pristine 규칙과 metamorphosed 규칙으로 명명된 p-persistence 규칙에 기반한 두 가지 충돌 중재 규칙을 대안으로 제시한다. 또한 각 규칙에서 포화 throughput의 근사값을 계산하는 해석적 방법을 개발한다. 모의 실험 결과와의 비교를 통해 이러한 해석적 방법의 높은 정확성을 확인하고 이진 지수형 back-off 규칙과의 비교하여 pristine 규칙 및 metamorphosed 규칙은 높은 포화 throughput을 가져올 수 있음을 관찰한다. In the IEEE 802.16 Wireless MAN standard, the best effort service class is ranked on the lowest position in priority and is assisted by a MAC scheme based on reservation ALOHA. In such a MAC scheme, a collision among the requests is unavoidable so that the standard adopted a binary exponential back-off rule to arbitrate a collision. Aiming at improving throughput performance, we present two generic collision arbitration rules based on p-persistence rule, (identified as pristine and metamorphosed rules), as alternatives in a wireless MAN. For each of these rules, we then develop an analytical method to calculate an approximate value of saturated throughput. In comparison with simulation results, we confirm the high accuracy of the analytical method. Also, the pristine and metamorphosed rules are observed to exhibit higher saturated throughput compared with the binary exponential back-off rule.

Poly(4-vinylphenol-co-methyl methacrylate)/Titanium Dioxide Nanocomposite Gate Insulators for 6,13-Bis(triisopropylsilylethynyl)-Pentacene Thin-film Transistors

Xue Zhang,Ji-Ho Park,Sungkeun Baang,박재훈,Shang Hao Piao,김소희,최형진 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.11

Poly(4-vinylphenol-co-methyl methacrylate)/titanium dioxide (TiO2) nanocomposite insulatorswere fabricated for application in 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS-Pn) thin-filmtransistors (TFTs). The capacitance of the fabricated capacitors with this nanocomposite insulatorincreased with increasing content of the high-dielectric-constant TiO2 nanoparticles. Nonetheless,particle aggregates, which were invariably produced in the insulator at higher TiO2 contents,augmented gate-leakage currents during device operation while the rough surface of the insulatorobstructed charge transport in the conducting channel of the TIPS-Pn TFTs. These results suggesta significant effect of the morphological characteristics of nanocomposite insulators on TFTperformance, as well as on their dielectric properties. Herein, the optimal particle composition wasdetermined to be approximately 1.5 wt%, which contributed to characteristic improvements in thedrain current, field-effect mobility, and threshold voltage of TIPS-Pn TFTs.

Influence of thickness of poly(3-hexylthiophene-2,5-diyl) hole transport layer on electrical characteristics of lead sulfide quantum dot-based shortwave infrared photodiodes

Seo Kyeong-Ho,Zhang Xue,Baang Sungkeun,Park Jaehoon,Bae Jin-Hyuk 한국물리학회 2021 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.79 No.5

Lead sulfide quantum dots (PbS QDs) have emerged as one of the promising photoactive materials for shortwave infrared (SWIR) photodiodes because of their uncooled processability, cost efficiency, and broadband tunability. In this study, PbS QD-based SWIR photodiodes were fabricated by using poly(3-hexylthiophene-2,5-diyl) (P3HT) and zinc oxide nanoparticles as hole and electron transporting materials, respectively. The P3HT films with different thicknesses of approximately 32, 71, and 141 nm were fabricated by using the solutions with the P3HT/chlorobenzene composition conditions of 5, 10, and 20 mg/mL, respectively. Herein, the PbS QD-based SWIR photodiodes showed an increase in current by SWIR light irradiation, and in particular, the device with a 71-nm-thick P3HT hole transport layer (HTL) exhibited the most superior photo-induced current, i.e., current amplification upon SWIR light. Since the difference (approximately 0.13 − 0.41 nm) in surface roughness among P3HT films with different thicknesses was much less than the size (4.5 − 5.0 nm) of PbS QDs, the results could be understood through the influence of the P3HT HTL thickness on the electrical characteristics of PbS QDbased SWIR photodiodes. Further analysis of the photodiode performance according to the P3HT HTL’s thickness reveals that the transport properties of photogenerated charge carriers through the hole transport layer have a crucial role in the photo-induced current and therefore decisively influence the photoresponsivity. These results suggest that P3HT HTLs affect the transport and extraction processes of photogenerated holes so that proper optimization of their thickness can contribute to enhancing the photoresponse efficiency of PbS QD-based SWIR photodiodes.

LED IT 기반의 간편한 비캐리어 가시광 통신 시스템 구현

임경순(Kyeong Sun Lim),방성근(Sungkeun Baang),이용업(Yong Up Lee) 한국통신학회 2011 韓國通信學會論文誌 Vol.36 No.9

옥내와 옥외간 무선 통신에서 다중 안테나 알고리즘 적용을 통한 통신 성능 향상

이준호,이용업,서영준,방성근,김종대,Lee Junho,Lee Yong Up,Seo Youngjun,Baang Sungkeun,Kim Jong Dae 한국통신학회 2005 韓國通信學會論文誌 Vol.30 No.5C

This paper is discussed about the technology of the performance enhancement in the wireless communication between indoor and outdoor environments. In the outdoor wireless communication, the signal has mainly a severe degradation by the fading effect of channel, but that problem may be overcome by using ordinary multiple antenna technology and array signal processing algorithm. Hence, since the channel has the characteristics of both fading and angle spread in the wireless communication between indoor and outdoor, the ordinary technology cannot solve the signal degradation due to the angle spread. In order to solve the problem, in this paper, the characteristic of the wireless channel between indoor and outdoor is first analyzed and considered the channel models fit to that case. We propose the new multiple antenna algorithm by use of mean steering vector concept, and obtained the results of the performance enhancement. With the results of the performance analyses through of the numerical study and computer simulation, we show that the proposed algorithm has more enhanced signal to noise ratio than the previous algorithm. 이 논문은 옥내와 옥외에 걸친 무선 통신 환경에서 통신 성능을 향상시키는 기술에 관한 것이다. 옥외 무선 통신에서 신호 감쇠는 주로 채널의 페이딩 특성으로 발생되는데, 기존의 다중 안테나 방식과 배열 신호처리 알고리즘을 적용하면 이 문제를 해결할 수 있다. 그러나, 옥내 및 옥외 무선 채널을 가진 통신인 경우, 채널 특성은 페이딩과 각도 퍼짐 특성 모두에 영향을 받으므로, 일반적인 방식으로 채널의 각도 퍼짐 특성을 극복할 수 없다. 이를 해결하기 위해 이 논문에서는 옥내와 옥외에 걸친 채널 특성을 분석하고, 각각에 적합한 채널 모형을 생각한다. 또한, 옥내외 채널의 각도 퍼짐 특성을 극복하고 옥내외 통신 성능을 향상하기 위해, 새로운 평균주사 벡터 개념을 사용한 배열 안테나 처리 알고리즘을 제안하고 성능 분석을 수행한다. 컴퓨터 모의 실험을 통한 성능 분석으로 옥내 전송 신호를 옥외 환경에서 다중 안테나로 수신하는 경우, 기존 방식보다 제안된 방식이 좋은 신호대 간섭 잡음비 특성을 가짐을 보인다.