• Progress in Superconductivity
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• v.4 no.2
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• pp.109-113
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• 2003

We have developed a planar-type single layer second-order $high-T_{c}$ SQUID gradiometer, which can detect the $d^2$$B_{z/}$dxdy of the second-order field gradient. This SQUID gradiometer consists of four-way 'clover-leaf' pick-up loops and is coupled directly to a 4-junction dc SQUID in such a way that the coupling polarity of the two diagonal loops is opposite to that of the other two loops. The pickup loops are intrinsically balanced for both uniform field and the 1 st-order field gradient. The $YBa_2$$Cu_3$$O_{7}$ thin film was made by pulsed laser deposition method on $SrTiO_3$ single crystal substrate and patterned by photolithography with Ar ion milling technique. Response of this gradiometer was tested for both uniform field and the 2nd-order field gradient. Details of the design, fabrication, and results will be discussed.

• Proceedings of the KIEE Conference
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• 2004.11a
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• pp.20-22
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• 2004

유기 EL(Organic Light Emitting diode : OLED)은 자체발광 소자로서 액정 디스플레이(Liquid Crystal Display)에 비해 빠른 응답속도, 넓은 시야각 등의 뛰어난 화질 표현이 가능하다. 구동 박막 트랜지스터(TFT)의 전류가 OLED의 휘도를 결정하므로, 고품질의 영상을 위해 미세한 TFT 전류 조절 능력이 매우 중요하다. 비정질 실리콘(a-Si) TFT는 그레인 구조를 갖는 다결정 실리콘(poly-Si) TFT에 비해 균일한 전기적 특성을 나타내지만, 장시간 구동에 따른 문턱전압의 열화가 발생한다. 본 논문에서는 상기의 문제점을 최소화하기 위하여 positive bias에 의한 열화를 negative bias로 어닐링하는 구동방법을 제안하였다. 본 회로는 2개의 게이트 선택 신호와 6개의 a-Si TFT로 이루어져 있다. 실험 결과를 통해 추출된 소자 parameter를 바탕으로 제안된 회로의 simulation을 수행 및 검증하였다. 본 회로는 a-Si TFT에서 발생하는 문턱전압 열화 등의 신뢰성 문제를 감소시킨다.

• Journal of the Korean Society for Precision Engineering
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• v.25 no.6
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• pp.71-79
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• 2008

In the manufacture of flat panel display devices, there is a strong demand for contactless glass panel handling devices that can manipulate a glass panel without contaminating or damaging it. To fulfill this requirement, an electrostatic suspension device far glass panels where the glass panel is supported by electrostatic forces without any mechanical contact is proposed. To implement the system with low cost and compactness, switched-voltage control scheme that is based on the relay feedback control is utilized. Relay feedback control method deploys only a single high-voltage power supply that can deliver a DC voltage of positive and/or negative polarity and thus high voltage amplifiers that are costly and bulky are not needed any more. It is shown that despite the inherent limit cycle property of the relay feedback based control, an excellent performance in vibration suppression is attained due to the presence of a relatively large squeeze film damping originating from the electrodes and levitated object. Using this scheme, a $100{\times}100mm^2$ glass panel was levitated stably with airgap variation decreasing down to $1\;{\mu}m$ at an airgap of $100\;{\mu}m$.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.86-92
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• 2019

Polymers with various compositions of azobenzene and hexamethylene groups in the main chain were synthesized by a Schotten-Baumann reaction and their properties were investigated. The chemical structures and physical properties of the synthesized polymers were investigated by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, differential scanning calorimetry, thermogravimetric analysis, polarized optical microscopy, and x-ray diffraction. The polymers showed an inherent viscosity of 1.28-1.36 dl/g and were relatively insoluble in most organic solvents. The melt transition temperature increased rapidly with increasing number of azobenzene groups in the polymer. When the azobenzene monomer content was more than 50 mol%, no melting transition occurred below the decomposition temperature. Among the polymers with a melt transition temperature, the MP-A3C7 and MP-A5C5 polymers were liquid crystalline materials and exhibited a nematic phase with weak liquid crystallinity over a wide liquid crystal temperature range. This difference in the properties of the synthesized polymers is likely due to the changes in intermolecular forces resulting from the linearity and polarity of the trans-form of azobenzene.