• 전기전자학회논문지
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• 제16권1호
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• pp.15-19
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• 2012

본 논문에서는 체스판 형태를 갖는 주파수 선택구조를 설계하였다. 주파수 선택구조의 주파수 응답 특성을 변화시키는 변수로서 단위셀을 구성하는 개구면 및 패치의 크기, 간격, 두께의 변화에 따른 주파수 응답 특성 변화를 관찰하였다. 변수의 변화에 따라서 대역 저지 및 대역 통과 특성을 얻을 수 있었으며, 공진 주파수 및 대역폭을 제어할 수 있는 설계 변수를 얻을 수 있었다. 설계 결과를 바탕으로 X-band 공진특성을 갖는 패치 타입의 주파수 선택구조를 두께 1mm의 FR4 기판으로 제작 및 측정하여 설계 결과를 검증하였다. 본 논문에서 제안하는 체스판 형태를 갖는 주파수 선택구조를 사용하게 되면, 원하는 주파수 대역에 따라 주파수를 선택적으로 제어할 수 있는 레이돔과 같은 전자기구조 설계에 유용하게 사용될 것으로 예상된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.185.2-185.2
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• 2014

We have studied the atomic and electronic structure of graphene nanoribbons (GNRs) on a hexagonal boron nitride (h-BN) sheet with intercalated atoms using first-principles calculations. The h-BN sheet is an insulator with the band gap about 6 eV and then it may a good candidate as a supporting dielectric substrate for graphene-based nanodevices. Especially, the h-BN sheet has the similar bond structure as graphene with a slightly longer lattice constant. For the computation, we use the Vienna ab initio simulation package (VASP). The generalized gradient approximation (GGA) in the form of the PBE-type parameterization is employed. The ions are described via the projector augmented wave potentials, and the cutoff energy for the plane-wave basis is set to 400 eV. To include weak van der Waals (vdW) interactions, we adopt the Grimme's DFT-D2 vdW correction based on a semi-empirical GGA-type theory. Our calculations reveal that the localized states appear at the zigzag edge of the GNR on the h-BN sheet due to the flat band of the zigzag edge at the Fermi level and the localized states rapidly decay into the bulk. The open-edged graphene with a large corrugation allows some space between graphene and h-BN sheet. Therefore, atoms or molecules can be intercalated between them. We have considered various types of atoms for intercalation. The atoms are initially placed at the edge of the GNR or inserted in between GNR and h-BN sheet to find the effect of intercalated atoms on the atomic and electronic structure of graphene. We find that the impurity atoms at the edge of GNR are more stable than in between GNR and h-BN sheet for all cases considered. The nickel atom has the lowest energy difference of ~0.2 eV, which means that it is relatively easy to intercalate the Ni atom in this structure. Finally, the magnetic properties of intercalated atoms between GNR and h-BN sheet are investigated.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.409-409
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• 2014

Recently hexagonal boron nitride (h-BN), III-V compound of boron and nitrogen with strong covalent $sp^2$ bond, is a 2 dimensional insulating material with a large direct band gap up to 6 eV. Its outstanding properties such as strong mechanical strength, high thermal conductivity, and chemical stability have been reported to be similar or superior to graphene. Because of these excellent properties, h-BN can potentially be used for variety of applications such as dielectric layer, deep UV optoelectronic device, and protective transparent substrate. Ultra flat and charge impurity-free surface of h-BN is also an ideal substrate to maintain electrical properties of 2 dimensional materials such as graphene. To synthesize a single or a few layered h-BN, chemical vapor deposition method (CVD) has been widely used by using an ammonia borane as a precursor. Ammonia borane decomposes into hydrogen (gas), monomeric aminoborane (solid), and borazine (gas) that is used for growing h-BN layer. However, very active monomeric aminoborane forms polymeric aminoborane nanoparticles that are white non-crystalline BN nanoparticles of 50~100 nm in diameter. The presence of these BN nanoparticles following the synthesis has been hampering the implementation of h-BN to various applications. Therefore, it is quite important to grow a clean and high quality h-BN layer free of BN particles without having to introduce complicated process steps. We have demonstrated a synthesis of a high quality h-BN monolayer free of BN nanoparticles in wafer-scale size of $7{\times}7cm^2$ by using CVD method incorporating a simple filter system. The measured results have shown that the filter can effectively remove BN nanoparticles by restricting them from reaching to Cu substrate. Layer thickness of about 0.48 nm measured by AFM, a Raman shift of $1,371{\sim}1,372cm^{-1}$ measured by micro Raman spectroscopy along with optical band gap of 6.06 eV estimated from UV-Vis Spectrophotometer confirm the formation of monolayer h-BN. Quantitative XPS analysis for the ratio of boron and nitrogen and CS-corrected HRTEM image of atomic resolution hexagonal lattices indicate a high quality stoichiometric h-BN. The method presented here provides a promising technique for the synthesis of high quality monolayer h-BN free of BN nanoparticles.

• 대한전자공학회논문지SD
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• 제48권6호
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• pp.1-6
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• 2011

투명 산화물 반도체 (Transparent Oxide-TFT)를 활성층과 소스/드레인, 게이트 전극층으로 동시에 사용한 비결정 indium zinc oxide (a-IZO), 절연층으로 co-sputtered $HfO_2-Al_2O_3$ (HfAIO)을 적용하여 실온에서 RF-magnetron 스퍼터 공정에 의해 제작하였다. TFT의 게이트 절연막으로써 $HfO_2$ 는 그 높은 유전상수( > 20)에도 불구하고 미세결정구조와 작은 에너지 밴드갭 (5.31eV) 으로 부터 기인한 거친계면특성, 높은 누설전류의 단점을 가지고 있다. 본 연구에서는, 어떠한 추가적인 열처리 공정 없이 co-sputtering에 의해 $HfO_2$와 $Al_2O_3$를 동시에 증착함으로써 구조적, 전기적 특성이 TFT 의 절연막으로 더욱 적합하게 향상되어진 $HfO_2$ 박막의 변화를 x-ray diffraction (XRD), atomic force microscopy (AFM) and spectroscopic ellipsometer (SE)를 통해 분석하였다. XRD 분석은 기존 $HfO_2$ 의 미세결정 구조가 $Al_2O_3$와의 co-sputter에 의해 비결정 구조로 변한 것을 확인 시켜 주었고, AFM 분석을 통해 $HfO_2$ 의 표면 거칠기를 비교할 수 있는 RMS 값이 2.979 nm 인 것에 반해 HfAIO의 경우 0.490 nm로 향상된 것을 확인하였다. 또한 SE 분석을 통해 $HfO_2$ 의 에너지 밴드 갭 5.17 eV 이 HfAIO 의 에너지 밴드 갭 5.42 eV 로 향상 되어진 것을 알 수 있었다. 자유 전자 농도와 그에 따른 비저항도를 적절하게 조절한 활성층/전극층 으로써의 IZO 물질과 게이트 절연층으로써 co-sputtered HfAIO를 적용하여 제작한 Oxide-TFT 의 전기적 특성은 이동도 $10cm^2/V{\cdot}s$이상, 문턱전압 2 V 이하, 전류점멸비 $10^5$ 이상, 최대 전류량 2 mA 이상을 보여주었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2009년도 하계학술대회 논문집
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• pp.105-105
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• 2009

$ZrO_2$ is one of the most attractive high dielectric constant (high-k) materials. As integrated circuit device dimensions continue to be scaled down, high-k materials have been studied more to resolve the problems for replacing the EY31conventional $SiO_2$. $ZrO_2$ has many favorable properties as a high dielectric constant (k= 20~25), wide band gap (5~7 eV) as well as a close thermal expansion coefficient with Si that results in good thermal stability of the $ZrO_2/Si$ structure. In order to get fine-line patterns, plasma etching has been studied more in the fabrication of ultra large-scale integrated circuits. The relation between the etch characteristics of high-k dielectric materials and plasma properties is required to be studied more to match standard processing procedure with low damaged removal process. Due to the easy control of ion energy and flux, low ownership and simple structure of the inductively coupled plasma (ICP), we chose it for high-density plasma in our study. And the $BCl_3$ included in the gas due to the effective extraction of oxygen in the form of $BCl_xO_y$ compound In this study, the surface kinetic properties of $ZrO_2$ thin film was investigated in function of Ch addition to $BCl_3/Ar$ gas mixture ratio, RF power and DC-bias power based on substrate temperature. The figure 1 showed the etch rate of $ZrO_2$ thin film as function of gas mixing ratio of $Cl_2/BCl_3/Ar$ dependent on temperature. The chemical state of film was investigated using x-ray photoelectron spectroscopy (XPS). The characteristics of the plasma were estimated using optical emission spectroscopy (OES). Auger electron spectroscopy (AES) was used for elemental analysis of etched surface.

• 한국전자파학회논문지
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• 제16권7호
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• pp.760-767
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• 2005

본 논문에서 우리는 DAML(Dielectric Air-gapped supported Microstrip Line) 구조를 이용하여 새로운 구조의 SIR대역 통과 여파기를 설계 제작하였다. 제작된 SIR대역 통과 여파기는 MIM capacitor를 커플링 포트로써 사용함으로 DAML구조를 이용하여 쉽게 제작될 수 있다. 더욱이 이러한 구조는 CPW interfaces를 가지고 있고 DAML구조의 링 공진기는 기판으로부터 $10{\mu}m$높이로 분리되어 있기 때문에 일반적인 평면 구조의 MMICs와 집적하기 유리하다. 제작된 필터의 측정 결과, 60 GHz에서 $10\%$의 대역폭, 60.7 GHz에서 2.84 dB의 삽입 손실, 56 GHz에서 18.4 dB의 감쇠 특성, 60 GHz에서 23 dB의 반사 특성을 얻었다.

• 한국전기전자재료학회논문지
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• 제26권11호
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• pp.816-820
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• 2013

We investigated the characteristics of the silicon oxy-nitride and nitride films grown by plasma-enhanced chemical vapor deposition (PECVD) at the low temperature with a varying $NH_3/N_2O$ mixing ratio and a fixed $SiH_4$ flow rate. The deposition temperature was held at $150^{\circ}C$ which was the temperature compatible with the plastic substrate. The composition and bonding structure of the nitride films were investigated using Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Nitrogen richness was confirmed with increasing optical band gap and increasing dielectric constant with the higher $NH_3$ fraction. The leakage current density of the nitride films with a high NH3 fraction decreased from $8{\times}10^{-9}$ to $9{\times}10^{-11}(A/cm^2$ at 1.5 MV/cm). This results showed that the films had improved electrical properties and could be acceptable as a gate insulator for thin film transistors by deposited with variable $NH_3/N_2O$ mixing ratio.

• Transactions on Electrical and Electronic Materials
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• 제18권4호
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• pp.199-202
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• 2017

Silicon carbide (SiC) is being spotlighted as a next-generation power semiconductor material owing to the characteristic limitations of the existing silicon materials. SiC has a wider band gap, higher breakdown voltage, higher thermal conductivity, and higher saturation electron mobility than those of Si. When using this material to implement Schottky barrier diode (SBD) devices, SBD-state operation loss and switching loss can be greatly reduced as compared to that of traditional Si. However, actual SiC SBDs exhibit a lower dielectric breakdown voltage than the theoretical breakdown voltage that causes the electric field concentration, a phenomenon that occurs on the edge of the contact surface as in conventional power semiconductor devices. Therefore in order to obtain a high breakdown voltage, it is necessary to distribute the electric field concentration using the edge termination structure. In this paper, we designed an edge termination structure using a field plate structure through oxide etch angle control, and optimized the structure to obtain a high breakdown voltage. We designed the edge termination structure for a 650 V breakdown voltage using Sentaurus Workbench provided by IDEC. We conducted field plate experiments. under the following conditions: $15^{\circ}$, $30^{\circ}$, $45^{\circ}$, $60^{\circ}$, and $75^{\circ}$. The experimental results indicated that the oxide etch angle was $45^{\circ}$ when the breakdown voltage characteristics of the SiC SBD were optimized and a breakdown voltage of 681 V was obtained.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2013년도 제45회 하계 정기학술대회 초록집
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• pp.285-285
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• 2013

Recently, hexagonal boron nitride (h-BN), which is III-V compound of boron and nitride by strong covalent sp2 bonds has gained great interests as a 2 dimensional insulating material since it has honeycomb structure with like graphene with very small lattice mismatch (1.7%). Unlike graphene that is semi-metallic, h-BN has large band gap up to 6 eV while providing outstanding properties such as high thermal conductivity, mechanical strength, and good chemical stability. Because of these excellent properties, hBN can potentially be used for variety of applications such as dielectric layer, deep UV optoelectronic device, and protective transparent substrate. Low pressure and atmospheric pressure chemical vapor deposition (LPCVD and APCVD) methods have been investigated to synthesize h-BN by using ammonia borane as a precursor. Ammonia borane decomposes to polyiminoborane (BHNH), hydrogen, and borazine. The produced borazine gas is a key material that is a used for the synthesis of h-BN, therefore controlling the condition of decomposed products from ammonia borane is very important. In this paper, we optimize the decomposition of ammonia borane by investigating temperature, amount of precursor, and other parameters to fabricate high quality monolayer h-BN. Synthesized h-BN is characterized by Raman spectroscopy and its absorbance is measured with UV spectrophotometer. Topological variations of the samples are analyzed by atomic force microscopy. Scanning electron microscopy and Scanning transmission Electron microscopy are used for imaging and analysis of structures and surface morphologies.

• 한국융합학회논문지
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• 제12권2호
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• pp.29-34
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• 2021

본 논문에서는 중심에 동공을 갖는 원통형태 광결정 도파로가 제안되어지고, 이 전송로의 도파 특성에 대한 분석이 수행되어진다. 여기서 동공은 일반적인 공기이거나 임의의 액체나 고체 물질들에 의한 저지수 유전체로써 형성되게 된다. 베셀 함수를 이용한 분석적 방법으로 전자장에 대한 엄밀한 해를 구하기 위하여, 행렬 기법이 고유치 방정식의 유도에 사용되고, 실효 굴절률, 분산, 전자장 분포 등의 기본 모드의 중요한 전송 성질들이 조사된다. 또한 분석 결과 정확도의 검증을 위하여 엄밀한 완전 벡터 유한 차분법을 적용해보고, 광결정 도파로의 설계와 제조 상의 문제를 해결하는데 용이하게 활용하고자 한다. 설계된 중심-동공 광도파관의 실효 모드 면적이 2.6056 ㎛2에서 5.9673 ㎛2까지 동작 파장에 따라 다양하게 변하며, 일반적으로 광도파로의 중심으로부터 바깥쪽으로 원통형의 층수가 적을수록 그리고 굴절률 n1이 약간 큰 저지수일수록 실효 면적은 작아지므로, 비선형 소자 응용의 관점에서 훨씬 더 최적화된 결과를 나타낸다.