• Korean Journal of Optics and Photonics
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• v.27 no.3
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• pp.106-113
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• 2016

In this paper, we deal with the wavefront compensation capability of a silicon carbide (SiC) deformable mirror (DM) with 37 actuators for adaptive optics. The wavefront compensation capability of the SiC DM is predicted by computer simulation and examined by actual experiments with a closed-loop adaptive optics system consistsing of a light source, a phase plate, a SiC DM, a high speed Shack-Hartmann sensor, and a control computer. Distortion of wavefront is caused by the phase plate in the closed-loop adaptive optics system. The distorted wavefront has a peak-to-valley (PV) wavefront error of $0.3{\mu}m{\sim}0.9{\mu}m$ and root-mean-square (RMS) error of $0.06{\mu}m{\sim}0.25{\mu}m$. The high-speed Shack-Hartmann sensor measures the wavefront error of the distortion caused by the phase plate, and the SiC DM compensates for the distorted wavefront. The compensated wavefront has residual errors lower than $0.1{\mu}m$ PV and $0.03{\mu}m$ RMS. Consequently, we conclude that we can compensate for the distorted wavefront using the SiC DM in the closed-loop adaptive optics system with an operating frequency speed of 500 Hz.

• Korean Journal of Materials Research
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• v.7 no.8
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• pp.654-659
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• 1997

HMDS[Si$_{2}$(CH$_{3}$)$_{6}$]단일 선구체를 이용하여 화학증착 방법으로 성장된 3C-SiC/Si(001) 이종접합박막의 특성을 XRD, 라만 스펙트럼 및 투과전자현미경(TEM)등을 이용하여 조사하였으며 시판되고 있는 상용 3C-SiC/Si 시편을 같은 방법으로 분석하여 특성을 비교검토하였다. $C_{3}$H$_{8}$-SiH$_{4}$-H$_{2}$혼합가스를 선구체로 이용하여 5$\mu\textrm{m}$두께로 성장된 상용 3C-SiC/Si 이종접합박막 시료의 XRD스펙트럼에서는 강한 3C-SiC(002)피크 만이 관찰되었으며, 라만 스펙트럼의 LO피크는 970nm$^{-1}$ 정도에서 강하게 나타났다. TEM 관찰 결과 다수의 전위, 쌍정, 적층결함 및 APB와 같은 결정결함들이 3C-SiC/Si 계면 근처에 집중적으로 분포되어 있었으며 성장된 박막은 단결정임을 확인할 수 있었다. 선구체로 HMDS를 사용하여 0.3$\mu\textrm{m}$ 및 2$\mu\textrm{m}$ 두께로 성장시킨 3C-SiC/Si 박막 시료의 XRD 스펙트럼은 다소 완만한 3C-SiC(002) 피크와 함께 3C-SiC(111)피크가 관찰되었으며, TEM으로 확인한 결과 소경각 결정립들이 약 5˚-10˚ 정도 방위차를 가지고 성장하여 기둥구조(columnar structure)를 이루고 있기 때문임을 알 수 있었다. 라만 스펙트럼 분석 결과 박막의 LO 피크가 967-969nm$^{-1}$정도로 다소 낮은 wavenumber쪽으로 이동되어 박막 내에 상당한 응력이 존재함을 확인할 수 있었다. 이와 같은 HMDS 3C-SiC박막의 특성은 성장 온도가 낮고 박막 성장용 가스로 사용한 HMDS 선구체에서 탄소가 과잉으로 공급되기 때문으로 제안되었다.다.

• Journal of the Korean Ceramic Society
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• v.30 no.12
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• pp.999-1006
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• 1993

Si3N4(p)-SiC(p) composites were prepared by gas pressure sintering at 190$0^{\circ}C$ for 1 hour. $\alpha$-SiC with average particle size of 0.48${\mu}{\textrm}{m}$ were dispersed from zero to 50vol% in $\alpha$-Si3N4 with average particle size of 0.5${\mu}{\textrm}{m}$. Y2O3-Al2O3 system was used as sintering aids. When 10vol% of SiC was added to Si3N4, optimum mechanical properties were observed; relative density of 98.8%, flextural strength of 930MPa, fracture toughness of 5.9MPa.m1/2 and hardness value of 1429kg/$\textrm{mm}^2$. Grain growth of $\beta$-Si3N4 was inhibited as the amount of added SiC was increased. SiC particles were found inside the $\beta$-Si3N4 intragrains in case of 10, 20 and 30vol%SiC added composites.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1593-1595
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• 2002

Single crystal 3C-SiC(cubic silicon carbide) thin-films were deposited on Si(100) wafers up to a thickness of 4.3 ${\mu}m$ by APCVD method using HMDS(hexamethyildisilane) at $1350^{\circ}C$. The HMDS flow rate was 0.5 sccm and the carrier gas flow rate was 2.5 slm. The HMDS flow rate was important to get a mirror-like crystal surface. The growth rate of the 3C-SiC films was 4.3 ${\mu}m/hr$. The 3C-SiC epitaxial films grown on Si(100) were characterized by XRD, AFM, RHEED, XPS and raman scattering, respectively. The 3C-SiC distinct phonons of TO(transverse optical) near 796 $cm^{-1}$ and LO(longitudinal optical) near $974{\pm}1cm^{-1}$ were recorded by raman scattering measurement. The hetero-epitaxially grown films were identified as the single crystal 3C-SiC phase by XRD spectra($2{\theta}=41.5^{\circ}$).

• 한국정보디스플레이학회:학술대회논문집
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• 2005.07b
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• pp.1025-1028
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• 2005

Microcrystalline Si (${\mu}c-Si$) TFTs were fabricated using a conventional bottom gate amorphous Si (a-Si) process. A unique ${\mu}c-Si$ deposition technique and TFT architecture was proposed to enhance the reliability of the TFTs. This three-mask TFT fabrication process is comparable with existing a-Si TFT procesess. In order to suppress nucleation at the bottom interface of Si, before deposition of the ${\mu}c-Si$ an $N_2$ plasma passivation was conducted. A typical transfer characteristic of the TFTs shows a low off-current with a value of less than 1 pA and a sub threshold slop of 0.7 V/dec. The DC stress was applied to verify the use of ${\mu}c-Si$ TFTs for AMOLED displays. After 10,000 s of application of the stress, the off-current was even lowered and sub-threshold slope variation was less than 5%. For AMOLED displays, OLED pixel simulation was performed. A pixel current of 13 ${\mu}A$ was achieved with $V_{data}$ of 10 V. After the simulation, a linear equation for the pixel current was suggested.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.03a
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• pp.81-84
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• 1997

The hot deformation behavior of SiCp/AA2024 composites reinforced with different sizes of SiCp reinforcements (1, 8, 15, 36, and 44${\mu}{\textrm}{m}$) was investigated by hot torsion tests. The hot restoration of the composites depending on the SiCp reinforcements particle size was studied from the effective stress - strain curves. Dynamic recrystallization (DRX) was occurred in the SiCp/AA2024 composites during the hot deformation at 320 - 43$0^{\circ}C$ under a strain rate of 1.0/sec. Also, the critical strain for DRX decreased with decreasing the reinforcement size of SiCp from 44 to 8${\mu}{\textrm}{m}$. The composite reinforced with SiCp of 8${\mu}{\textrm}{m}$ showed the highest flow stress (265 MPa) and the work hardening rate at 32$0^{\circ}C$ under a strain rate of 1.0/sec.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.589-592
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• 1999

This paper describes direct $\mu$C-Si/CaF$_2$/glass thin film growth by RPCVD system in a low temperature for thin film transistor (TFT), photovoltaic devices. and sensor applications. Experimental factors in a low temperature direct $\mu$ c-Si film growth are presented in terms of deposition parameters: SiH$_4$/H$_2$ ratio, chamber total pressure, substrate temperature, rf power, and CaF$_2$ buffer layer. The structural and electrical properties of the deposited films were studied by means of Raman spectroscopy, I-V, L-I-V, X-ray diffraction analysis and SEM. we obtain a crystalline volume fraction of 61%, preferential growth of (111) and (220) direction, and photosensitivity of 124. We achieved the improvement of crystallinity and electrical property by using the buffer layers of CaF$_2$ film.

• Journal of Sensor Science and Technology
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• v.18 no.3
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• pp.207-209
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• 2009

This paper describes the characteristics of poly 3C-SiC micro resonators with $3{\times}10^{17}{\sim}1{\times}10^{19}cm^{-3}$ doping concentrations. The 1.2 ${\mu}m$ thick cantilever and the 0.4 ${\mu}m$ thick doubly clamped beam resonators with different lengths were fabricated using poly 3C-SiC thin films. The characteristics of poly 3C-SiC micro resonators were evaluated by quartz and a laser vibrometer in vacuum at room temperature. The resonant frequencies of micro resonators decreased with doping concentrations owing to reduction in the Young's modulus of poly 3C-SiC thin films. It was confirmed that the resonant frequencies of poly 3C-SiC resonators are controllable by doping concentrations. Therefore, poly 3C-SiC resonators could be applied to MEMS devices and bio/chemical sensor applications.

• Journal of the Korean Ceramic Society
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• v.39 no.4
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• pp.413-419
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• 2002

Particulate composites of $Al_2O_3$/TiC/SiC, $Al_2O_3$/TiC and $Al_2O_3$/SiC have been fabricated by hot pressing and their R-curve behaviors and mechanical properties were investigated. $Al_2O_3$ containing 30 vol% TiC particles showed higher toughness by 8% than that for monolithic alumina and its fracture strength was increased significantly by approximately 30%. On the other hand, the addition of 30 vol% SiC of $3{\mu}m$ in $Al_2O_3$ decreased the fracture strength slightly but induced a rising R-curve behavior owing to the strong crack bridging of SiC particles. In case of $Al_2O_3$/TiC/SiC, arising R-curve behavior was also observed and the fracture toughness reached 6.6 MPa${\cdot}\sqrt{m}$ at the crack length of $1000{\mu}m$, which was lower than that of $Al_2O_3$/SiC, however, while the fracture strength was higher by about 20%. The fracture toughness seemed to be decreased as smaller TiC particles roughened the SiC interface and pullout of the SiC particles for crack bridging became less active.

• Korean Journal of Materials Research
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• v.12 no.1
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• pp.48-53
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• 2002

$Al_2O_3-SiC$ and $Al_2O_3-SiC$-TiC composite powders were prepared by SHS process using $SiO_2,\;TiO_2$, Al and C as raw materials. Aluminum powder was used as reducing agent of $SiO_2,\;TiO_2$ and activated charcoal was used as carbon source. In the preparations of $Al_2O_3-SiC$, the effect of the molar ratio in raw materials, compaction pressure, preheating temperature and atmosphere were investigated. The most important variable affecting the synthesis of $Al_2O_3-SiC$ was the molar ratio of carbon. Unreactants remained in the product among all conditions without compaction. The optimum condition in this reaction was $SiO_2$: Al: C=3: 5: 5.5, 80MPa compaction pressure under Preheating of $400^{\circ}C$ with Ar atmosphere. However there remains cabon in the optimum condition. The effect of $TiO_2$ as additive was investigated in the preparations of $Al_2O_3-SiC$. As a result of $TiO_2$ addition, $Al_2O_3-SiC$-TiC composite powder was prepared. The $Al_2O_3$ powder showed an angular type with 8 to $15{\mu}m$, and the particle size of SiC powder were 5~$10{\mu}m$ and TiC powder were 2 to $5{\mu}m$.