1,721,043 research outputs found
고유전 절연막을 이용한 기반의 박막 트랜지스터의 저전압 구동 특성 연구
No full text학위논문(박사) - 한국과학기술원 : 신소재공학과, 2009.2, [ xv, 133 p. ]Mechanically flexible, optically transparent, light, and low cost thin film transistors (TFTs) on polymer substrate are intensively interested for flexible and transparent display at future ubiquitous era. Until now organic thin film transistors (OTFTs) satisfied the requirements and they were studied for applications like active matrix OLED or LCD display, sensor devices, and radio frequency identification (RFID) tags. However, the operation voltage of OTFTs is large because of low capacitance of organic dielectrics. For low voltage operation devices suitable at portable and battery-powered electronic devices, high capacitance gate dielectrics are necessary. They can be obtained by using very thin film or using high-k dielectrics. Very thin gate dielectrics can lead to significant manufacturing problems such as poor leakage characteristics and pinholes come from rough surface of polymer thin film. I had an effort to use high-k oxides (BST) to reduce the operation voltage of TFTs. However, because BST films had poor leakage characteristics despite high dielectric constant, I added excess MgO having good leakage characteristics. In Chap. 3, four kinds of dielectrics BST, , , and thin films were fabricated at room temperature using pulsed laser deposition (PLD) at room temperature for feasibility test. As increasing MgO contents the leakage characteristics got better while the dielectric constants were decreased. After confirmed the possibility of MgO-BST to gate insulator of TFTs, I used sputtering method for large area application. I demonstrated the reason of reducing dielectric constant of the MgO-mixed BST thin film can be explained as the sum of each individual thin film (MgO and BST) using a series connection capacitance model, and the MgO plays a significant role in reducing the leakage current density of the thin film forming potential barrier.
Another problem of OTF...한국과학기술원 : 신소재공학과
Preparation and characterization of Ag added thin film by RF magnetron sputtering
No full text학위논문(석사) - 한국과학기술원 : 신소재공학과, 2005.2, [ iv, 83 p. ]본 연구에서는 단일 타겟을 이용하여 RF magnetron sputtering법으로 증착하였으며, 균일하고 밀도 높은 박막을 얻기 위한 조건을 잡기위해 다양한 RF Power 와 Ar 압력 조건을 변수로 하여 실험을 하였다. 이렇게 증착된 박막의 미세구조와 전기적 특성을 비교하였다. 비정질로 증착 된 박막의 결정화를 조사하기 위하여 여러 온도에서 RTA 로 열처리를 한 뒤 XRD 분석을 하였다. Four point probe 로 각 어닐링 온도에 따른 비저항을 비교하였고, SEM 분석을 통해 미세구조 관찰과 두께를 측정하였으며 열처리 전ㆍ후의 두께 변화 및 밀도 변화를 측정하기 위해 XRR을 이용하였다. 위의 방법으로 최적의 박막의 증착 조건을 잡은 뒤, co-sputtering 법으로 에 소량의 Ag을 도핑하여 증착된 박막의 결정성과 전기적 특성을 평가하였다.한국과학기술원 : 신소재공학과
Study on RDT and Computational models of pressure strain correlation in turbulent homogeneous shear flows
No full text학위논문(석사) - 한국과학기술원 : 기계공학전공, 2010.2, [ 76 p. ]Rapid distortion 이론은 큰 평균 속도 구배장에서 어떻게 난류 에디가 발전하는지, 레이놀즈 응력, 에너지 스펙트럼이 어떻게 변하는 지를 해석할 수 있는 선형해석방식이다. 본 연구의 목표는 크게 두 가지로 나뉠 수 있다. 우선 다양한 난류전단 유동장에 대해 WKB형 RDT를 수치 해석하여 이전의 연구결과와 비교하는 것이 일차 목표이며, RDT이론을 자세하게 언급한 책의 부재로 RDT이론을 최대한 자세하게 풀어쓰는 것을 일차의 부수적 목표로 하였다. 그리고 다른 하나는 레이놀즈응력방정식 모델에서 압력-변형률 상관관계 모형에서 저율항 모델과 고율항 모델을 동시에 사용하였을 때 어떠한 결과가 나타나는 가를 알아보고, 이 복합 모델을 사용하였을 때 Rapid distortion limit에서 앞서 언급된 수치해석 결과와 비교하는 것이 목표하다. 저율항 모델은 다양한 유동에서 가장 성능이 좋은 Chung & Kim 모델을 사용하였으며 고율항 모델은 Launder등에 의한 준 등방 모델 (LRR-QI)과 Jones & Musonge에 의한 JM모델, Speziale, Sarkar, Gatski에 의한 SSG 모델, 그리고 FLT모델과, HP모델이 사용하였다.한국과학기술원 : 기계공학전공
Design Optimisation of Electromagnetic Devices Using Continuum Design Sensitivity Analysis Combined with Commercial EM Software
No full textThis paper deals with two kinds of optimisation problems, relevant to the optimised source distribution and the shape optimum design, using Continuum Design Sensitivity Analysis (CDSA) in combination with standard electromagnetic (EM) software. Fast convergence and compatibility with existing EM software are the distinctive features of the proposed implementation. In order to verify the advantages and also to facilitate understanding of the method itself, two design optimisation problems have been tested: one is an MRI design problem related to finding an optimal permanent magnet distribution and the other is a pole shape design problem of a BLDC motor for reducing cogging torque, using both 2D and 3D models
Minimization of the sample temperature deviation and the effect of current during high-temperature compressive creep testing by the spark plasma sintering apparatus
No full textRecently, spark plasma sintering (SPS) systems have been used as high-temperature compressive creep testing devices. However, SPS systems can have complex temperature distributions within the experimental configuration that might lead to inaccuracies in the creep test results. For example, sample temperature profiles have been found to deviate from the initial temperature distribution as the sample is deformed during the creep test. Therefore, finite element analysis has been carried out on the SPS creep test mold configuration to evaluate the temperature distribution within an electrically conducing sample in three cases. Then, a multi-step thermal-electrical analysis was conducted to confirm the existence of and quantify a temperature deviation present during sample deformation. Thereafter, a systematic parametric investigation was performed to assess the effect of several geometrical parameters on the deviation in the sample temperature during deformation. Based on its results, recommendations for an optimal mold design that minimizes the sample temperature deviation during creep testing are provided. Finally, it is proposed that the thickness of the graphite felt used on the upper part of the die should be modified to further minimize the sample temperature deviation. The results of this study contribute to the overall understanding of the temperature distribution evolution and the effect of current during creep testing with an SPS apparatus and also provide practical geometrical recommendations for the use of SPS creep testing to achieve minimal sample temperature deviation.
Applying Continuum Design Sensitivity Analysis combined with standard EM software to shape optimisation in magnetostatic problems
No full textGeneralized Continuum Sensitivity Formula for Optimum Design of Electrode and Dielectric Contours
No full textNumerical investigation of the electric field distribution induced in the brain by transcranial magnetic stimulation (TMS)
No full textIntroduction.There has been considerable interest over the years in the treatment of serious physiological and clinical conditions, such as depression and pain relief, byutilising electromagnetic fields through Transcranial Magnetic Stimulation (TMS) of the human brain [1].Most of the effort has recently focused on the attempt to stimulate neurons deep inside the brain mass and to limit any hazards posed by this treatment. As a result, there is a need for new TMS coil configurations to generate sufficient and localized electric fields to achieve deep stimulation.The advent of more powerful computers and the emergence of more accurate models for the electric properties and shape of the human brain have enablednumerical modelling to become a significant and reliable tool for the design and optimisation of such new TMS devices in order to achieve the above requirements. The experimental prediction of the electric field distribution is still a formidable task so simulation of the fields induced inside the brain, is crucial in the optimisation and design of the stimulus coils.This paper presents results on the simulation ofTMS by using the Finite Element Method (FEM) in three dimensions and looks at the effects of the stimulation coils and geometrical model of the head on the distribution and penetration of the electric field induced in the brain during TMS. It is revealed that the incorporation of an accurate brain model in terms of shape as well as conductivity values is crucial for an improved estimation of field distribution and threshold fields inside the brain
Robust Optimization Utilizing the Second-order Design Sensitivity Information
No full textThis paper presents an effective methodology for robust optimization of electromagnetic devices. To achieve the goal, the method improves the robustness of the objective function by minimizing the second-order sensitivity information, called a gradient index and defined by a function of gradients of performance functions with respect to uncertain variables. The constraint feasibility is also enhanced by adding a gradient index corresponding to the constraint value. The validity of the proposed method is tested with the TEAM Workshop Problem 22
Further advances in applying continuum design sensitivity analysis in combination with commercial electromagnetic software to aid design optimization
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