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극단치 분포의 모수 추정방법 비교 연구(회귀 분석법을 기준으로)
우지용,김명석,Woo, Ji-Yong,Kim, Myung-Suk 한국통계학회 2009 Communications for statistical applications and me Vol.16 No.3
극단치 분포의 모수 추정방법으로 최우추정법, 확률가중적률법, 회귀분석법은 기존 연구에서 활발하게 적용되어져 왔다. 그러나 이들 세 가지 추정방법 가운데, 회귀분석법의 우수성은 엄격하게 평가되어진 적이 없다. 본 논문에서는 몬테칼로 시뮬레이션을 통하여 Generalized Extreme Value(GEV) 분포와 Generalized Pareto(GP) 분포의 모수 추정에 회귀분석법 및 다른 추정방법을 적용하여 비교 연구한다. 시뮬레이션 결과, 표본의 크기가 작은 경우 회귀분석 법은 GEV 분포의 위치모수 추정시 편의 측면과 효율성 측면에서 다른 방법보다 우수한 경향을 나타내었다. GP 분포의 규모모수 추정시에는 표본의 크기 가 작을 경우 회귀분석법이 다른 방법보다 작은 편의를 나타내었다. 회귀분석법은 표본의 크기 가 작거나 적당히 큰 경우에도 GEV 분포나 GP 분포의 형태모수 추정시에 형태모수의 값이 -0.4일 경우, 다른 방법보다 우수한 경향을 나타내었다. Parameter estimation methods such as maximum likelihood estimation method, probability weighted moments method, regression method have been popularly applied to various extreme value models in numerous literature. Among three methods above, the performance of regression method has not been rigorously investigated yet. In this paper the regression method is compared with the other methods via Monte Carlo simulation studies for estimation of parameters of the Generalized Extreme Value(GEV) distribution and the Generalized Pareto(GP) distribution. Our simulation results indicate that the regression method tends to outperform other methods under small samples by providing smaller biases and root mean square errors for estimation of location parameter of the GEV model. For the scale parameter estimation of the GP model under small samples, the regression method tends to report smaller biases than the other methods. The regression method tends to be superior to other methods for the shape parameter estimation of the GEV model and GP model when the shape parameter is -0.4 under small and moderately large samples.
Kim Yeriaron,우지용,임솔이,이예슬,김종훈,임종필,서동우,양상모,윤성민,문성은 한국물리학회 2020 Current Applied Physics Vol.20 No.12
In this paper, we report stable polarization switching in metal-HfZrOx (HZO)-metal capacitors when pulses are repeatedly applied from the initial state. By examining various process parameters including annealing method, annealing temperature, and annealing time, we investigated the optimal conditions for realizing ferroelectricity in HZO layers deposited by sputtering systems. More specifically, we examined how polarization behaviors evolved as a function of annealing temperatures. Our results showed that annealing HZO capped by a top electrode, when annealing temperature was higher than 850 ◦C, drives the transformation to large quantities of orthorhombic phases, and enables constant remnant polarization without the fluctuations caused by wake-up and fatigue. We continued to observe stable polarization up to 108 cycles with a pulse width of 5 μs.
높은 수율의 임계값 스위칭 특성을 위한 CMOS 호환 전극을 갖는 NbO<SUB>x</SUB> 층에서 산화물 장벽의 역할
최현식(Hyeonsik Choi),김윤서(Yunsur Kim),박형진(Hyoungjin Park),정지애(Jiae Jeong),우지용(Jiyong Woo) 대한전자공학회 2023 대한전자공학회 학술대회 Vol.2023 No.11
This study shows how the threshold switching (TS) characteristics of a NbOx layer with noninert W electrodes can be improved by introducing an oxide barrier. The ~10-nm-thick NbOx layer exhibits TS, which is known to originate from NbO₂, after electroforming. However, through X-ray photoelectron spectroscopy, a Nb₂O<SUB>5</SUB> layer, which is known to cause resistive memory switching, is formed mainly at the top interface as well. This results in a worsening TS yield. Therefore, thin oxides were introduced to improve the TS behavior and systematically investigate the role of the oxide barrier by considering their location and material properties. The barrier inserted at the bottom interface makes the formation of NbO₂ difficult, preventing TS. When the barrier was introduced at the top interface, the unwanted Nb₂O<SUB>5</SUB> created through reaction with the W electrode can be mitigated, promoting the occurrence of TS. Note that when an AL₂O₃ (or HfO₂) barrier is used, which prefers to scavenge (or provide) oxygen from (or to) the NbOx, a dielectric (or weak TS) behavior is shown. As a result, excellent cell-to-cell uniformity of the TS is achieved in the ZrO₂/NbOx stack, which not only prevents the formation of Nb₂O<SUB>5</SUB> but also stabilizes the NbO₂ in the NbOx layer. Through examining the temperature dependence of the TS obtained from the W/NbOx/W and W/ZrO₂/NbOx/W stacks, it was found that the suppression of the Nb₂O<SUB>5</SUB> at the top interface is indirectly shown as a strengthened Schottky barrier from an electrical measurement perspective.