• 대한전자공학회논문지SD
• /
• 제44권12호
• /
• pp.1-6
• /
• 2007

본 논문에서 기존에 사용하고 있는 metamorphic high electron transistor (MHEMT)의 채널에 InP를 추가하여 제작 하였다. InP는 In0.53Ga0.47As와 비교하여 낮은 충돌 이온화 계수를 가지고 있다. 그런 특성을 MHEMT의 문제점 중의 하나인 낮은 항복전압의 개선에 이용하였다. 우리는 기존의 MHEMT와 InP 합성 채널 MHEMT의 항복 특성과 주파수 특성을 비교 하였다. 본 논문에서 InP 합성 채널 MHEMT의 on-state와 off-state 항복전압이 각각 2.4와 5.7 V가 측정 되었고 또한 cut-off 주파수와 maximum oscillation 주파수는 각각 160 GHz와 230 GHz가 측정 되었다. 위의 결과는 InP 합성 채널 MHEMT가 밀리미터파 대역의 전력용 소자에 이용되는데 큰 장점을 갖는 소자임을 알 수 있다.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2006년도 하계종합학술대회
• /
• pp.467-468
• /
• 2006

To perform the comparative study, we experimented on two differential epitaxial structures, the conventional Metamorphic High Electron Mobility Transistor (MHEMT) using the InAlAs/InGaAs structure and the InP-composite channel MHEMT adopting the InAlAs/InGaAs/InP/n-InP structure. Compared to the conventional MHEMT, the InP-composite channel MHEMT shows improved breakdown performance; over about 3.5 V. This increased breakdown voltage can be explained by the lower impact ionization coefficient of the InP-composite channel MHEMT than that of the conventional MHEMT.

• 반도체디스플레이기술학회지
• /
• 제12권4호
• /
• pp.21-25
• /
• 2013

This paper is for enhancing the breakdown voltage of MHEMTs with an InP-etchstop layer. The fully removed recess structure in the drain side of MHEMT shows that the breakdown voltage enhances from 2 V to 4 V in the previous work. This is because the surface effect at the drain side decreases the channel current and the impact ionization in the channel at high drain voltage. In order to increase the breakdown voltage at the same asymmetric gate-recess structure, the InGaAs channel structure is replaced with the InGaAs/InP composite channel in the simulation. The simulation results with InGaAs/InP channel show that the breakdown voltage increases to 6V in the MHEMT as the current decreases. In this paper, the simulation results for the InGaAs/InP channel are shown and analyzed for the InGaAs/InP composite channel in the MHEMT.

• 한국재료학회지
• /
• 제19권1호
• /
• pp.33-36
• /
• 2009

Inorganic-organic composite thin-film-transistors (TFTs) of ZnO nanowire/Poly(3-hexylthiophene) (P3HT) were investigated by changing the nanowire densities inside the composites. Crystalline ZnO nanowires were synthesized via an aqueous solution method at a low temperature, and the nanowire densities inside the composites were controlled by changing the ultrasonifiaction time. The channel layers were prepared with composites by spin-coating at 2000 rpm, which was followed by annealing in a vacuum at $100^{\circ}C$ for 10 hours. Au/inorganic-organic composite layer/$SiO_2$ structures were fabricated and the mobility, $I_{on}/I_{off}$ ratio, and threshold voltage were then measured to analyze the electrical characteristics of the channel layer. Compared with a P3HT TFT, the electrical properties of TFT were found to be improved after increasing the nanowire density inside the composites. The mobility of the P3HT TFT was approximately $10^{-4}cm^2/V{\cdot}s$. However, the mobility of the ZnO nanowire/P3HT composite TFT was increased by two orders compared to that of the P3HT TFT. In terms of the $I_{on}/I_{off}$ ratio, the composite device showed a two-fold increase compared to that of the P3HT TFT.

• 한국진공학회지
• /
• 제22권6호
• /
• pp.335-340
• /
• 2013

본 논문은 InP 식각정지층을 갖는 MHEMT 소자의 항복전압을 증가시키기 위한 시뮬레이션 설계 논문이다. MHEMT 소자의 게이트 리세스 구조 및 채널 구조를 변경하여 시뮬레이션을 수행하였고 비교 분석하였다. MHEMT 소자의 드레인 측만을 완전히 제거한 비대칭 게이트 리세스 구조인 경우 $I_{dss}$ 전류가 90 mA에서 60 mA로 줄어들지만 항복 전압은 2 V에서 4 V로 증가함을 확인하였다. 이는 $Si_3N_4$ 보호층과 InAlAs 장벽층 사이의 계면에서 형성되는 전자-포획 음의 고정전하로 인해 채널층에서의 전자 공핍이 심화되어 나타나는 현상으로 이는 채널층의 전류를 감소시켜 충돌이온화를 적게 형성시켜 항복전압을 증가시킨다. 또한, 동일한 구조의 비대칭 게이트 리세스 구조에서 채널층을 InGaAs/InP 복합 채널로 바꾸어 설계한 구조에서는 항복전압이 5 V로 증가하였다. 이는 높은 드레인 전압에서 InP 층의 적은 충돌이온화와 이동도로 인해 전류가 더 감소했기 때문이다.

• Steel and Composite Structures
• /
• 제28권2호
• /
• pp.233-250
• /
• 2018

Back-to-back built-up cold-formed steel un-lipped channel sections are used in cold-formed steel structures; such as trusses, wall frames and portal frames. In such built-up columns, intermediate fasteners resist the buckling of individual channel-sections. No experimental tests or finite element analyses have been reported in the literature for back-to-back built-up cold-formed steel un-lipped channel sections and specially investigated the effect of screw spacing on axial strength of such columns. The issue is addressed in this paper. The results of 95 finite element analyses are presented covering stub to slender columns. The finite element model is validated against the experimental tests recently conducted by authors for back-to-back built-up cold-formed steel lipped channel sections. The verified finite element model is then used for the purposes of a parametric study to investigate the effect of screw spacing on axial strength of back-to-back built-up cold-formed steel un-lipped channel sections. Results are compared against the built-up lipped channel sections and it is shown that the axial strength of un-lipped built-up sections are 31% lesser on average than the built-up lipped channel sections. It was also found that the American Iron and Steel Institute (AISI) and the Australian and New Zealand Standards were over-conservative by around 15% for built-up columns failed through overall buckling, however AISI and AS/NZS were un-conservative by around 8% for built-up columns mainly failed by local buckling.

• Steel and Composite Structures
• /
• 제21권3호
• /
• pp.629-659
• /
• 2016

In cold-formed stainless steel lipped channel-sections, web openings are becoming increasingly popular. Such openings, however, result in the sections becoming more susceptible to web crippling, especially under concentrated loads applied near the web opening. This paper presents the results of a finite element parametric study into the effect of circular web openings on the web crippling strength of cold-formed stainless steel lipped channel-sections for the interior-one-flange (IOF) loading condition. This involves a bearing load applied to the top flange of a length of member, away from the end supports. The cases of web openings located centred beneath the bearing load (i.e. beneath the bearing plate delivering the load) and offset to the bearing plate, are considered. Three grades of stainless steel are considered: duplex EN1.4462, austenitic EN1.4404 and ferretic EN1.4003. In total, 2218 finite element models were analyzed. From the results of the parametric study, strength reduction factors for load bearing capacity are determined, where these reduction factors are applied to the bearing capacity calculated for a web without openings, to take account the influence of the web openings. The strength reduction factors are first compared to equations recently proposed for cold-formed carbon steel lipped channel-sections. It is shown that for the case of the duplex grade, the strength reduction factor equations for cold-formed carbon steel are conservative but only by 2%. However, for the cases of the austentic and ferritic grades, the cold-formed carbon steel equations are around 9% conservative. New strength reduction factor equations are proposed for all three stainless steel grades.

• Steel and Composite Structures
• /
• 제23권3호
• /
• pp.363-383
• /
• 2017

In cold-formed stainless steel lipped channel-sections, use of web openings for service purposes are becoming increasingly popular. Web openings, however, result in the sections becoming more susceptible to web crippling. This paper presents a finite element investigation into the web crippling strength of cold-formed stainless steel lipped channel-sections with circular web openings under the interior-two-flange (ITF) loading condition. The cases of web openings located centred and offset to the bearing plates are considered in this study. In order to take into account the influence of the circular web openings, a parametric study involving 2,220 finite element analyses was performed, covering duplex EN1.4462, austenitic EN1.4404 and ferritic EN1.4003 stainless steel grades. From the results of the parametric study, strength reduction factor equations are proposed. The strengths obtained from reduction factor equations are first compared to the strengths calculated from the equations recently proposed for cold-formed carbon steel lipped channel-sections. It is demonstrated that the strength reduction factor equations proposed for cold-formed carbon steel are unconservative for the stainless steel grades by up to 17%. New coefficients for web crippling strength reduction factor equations are then proposed that can be applied to all three stainless steel grades.

• Current Applied Physics
• /
• 제18권12호
• /
• pp.1546-1552
• /
• 2018

The polymer nanocomposite as a gate dielectric film was prepared via sol-gel method. The formation of crosslinked structure among nanofillers and polymer matrix was proved by Fourier transform infrared spectroscopy (FT-IR). Differential thermal analysis (DTA) results showed significant increase in the thermal stability of the nanocomposite with respect to that of pure polymer. The nanocomposite films deposited on the p- and n-type Si substrates formed very smooth surface with rms roughness of 0.045 and 0.058 nm respectively. Deconvoluted $Si_{2s}$ spectra revealed the domination of the Si-OH hydrogen bonds and Si-O-Si covalence bonds in the structure of the nanocomposite film deposited on the p- and n-type Si semiconductor layers respectively. The fabricated n-channel field-effect-transistor (FET) showed the low threshold voltage and leakage currents because of the stronger connection between the nanocomposite and n-type Si substrate. Whereas, dominated hydroxyl groups in the nanocomposite dielectric film deposited on the p-type Si substrate increased trap states in the interface, led to the drop of FET operation.

• 지구물리
• /
• 제5권1호
• /
• pp.19-27
• /
• 2002

장풍 폐광산의 갱내수와 폐광석 적치장에서 발생되는 산성광산폐수에 의한 침출수의 유동경로와 지화학적 특성을 알아보기 위해 지구물리탐사(자연전위, 전자탐사, 전기비저항, 탄성파굴절법)를 수행하여 그 결과를 지화학 물시료분석(pH, EC, ${SO_4}^{-2}$, 중금속 함량) 자료와 상관·분석하였다. 갱구에 수직 방향의 2개 측선에서 실시한 전기비저항 쌍극자탐사 결과 갱구에서 북서 방향으로 저비저항대가 이어지는데 이것은 갱구에서 지하로 유입된 산성광산폐수에 의한 침출수가 폐석더미와 기반암의 경계를 따라 이동하여 하천 방향으로 유입되어 나타나는 현상으로 해석된다. 이와 같은 양상은 전기비저항 수직탐사, 자연전위, 전자탐사의 반응 결과들에서 보이는 북서방향의 이상대 및 북서쪽에서 상대적으로 높은 값을 보이는 EC, 중금속함량, ${SO_4}^{-2}$의 분포와도 잘 상관된다.