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압전 액추에이터를 이용한 저전압 구동 MEMS 가변 캐패시터
황현석(Hyun-Suk Hwang) 대한전기학회 2022 전기학회논문지 P Vol.71 No.2
In this work, low voltage MEMS variable capacitor was presented. Compare with other RF MEMS technologies, piezoelectric MEMS devices offer certain benefits such as low actuation voltage and fast moving, etc. The proposed structure consists of dual piezoelectric actuation bridges of in-plane polarized lead zirconate titanate (PZT) film to improve actuation voltage and reliability of devices. The PZT thin film, deposited on Au structural layer using RF magnetron sputtering method, was poled and driven with interdigitated electrodes(IDEs) to exploit d<SUB>33</SUB> mode actuation. The in-plane polarized PZT films make it possible to develope d<SUB>33</SUB> mode bending devices which lead to about two times improvement in strain performance. The fabricated variable capacitor shows that the tuning range is varied 100.9 to 111.2 nF with control voltage ranging from 0 to 1 V.
증례 : 만성 신부전으로 발현된 Erdheim-Chester disease 1예
황현석 ( Hyun Suk Hwang ),지병수 ( Byoung Su Ji ),이진국 ( Chin Kook Lee ),김진영 ( Jin Young Kim ),최범순 ( Bum Soon Choi ),양철우 ( Chul Woo Yang ),김용수 ( Yong Soo Kim ) 대한내과학회 2007 대한내과학회지 Vol.73 No.2
Erdheim-Chester disease는 포말 대식세포에 의한 전신 염증 반응을 일으키는 드문 질환이다. 본 증례는 만성신부전으로 발현하여 원인을 찾는 과정에서 Erdheim-Chester disease를 진단하게 되었다. 만성신부전의 원인으로 Erdheim-Chester disease는 드문 질환이나 원인미상의 후복막섬유화증이 있는 경우 Erdheim-Chester disease에 대한 가능성을 고려하는 것이 중요하다고 판단된다. Erdheim-Chester disease is a rare non-langerhans cell histiocytic disorder of an unknown cause that may associate with multisystem, rapidly fatal, infiltrative disease. We report here on a case of Erdheim-Chester disease in a 45-year-old man who presented with chronic renal failure. The patient visited a local clinic due to renal failure that was accidentally diagnosed on a routine health examination. At that time, abdominal computed tomography revealed retroperitoneal fibrosis and bilateral hydronephrosis. However, he did not visit hospital for further evaluation. After 1 year, he visited our clinic due to exertional dyspnea that had developed several months previously. The chest and abdominal CT showed interstitial pneumonitis and pleural effusion and there was progressed hydronephrosis and perirenal fibrosis. He was diagnosed with Erdheim-Chester disease based on the characteristic findings of pleural biopsy (interstitial fibrosis, infiltration of macrophge, CD68-positive but S-100 negative). The patient was treated with insertion of a double J catheter and immunesuppression with prednisolone and azathioprine. Erdheim-Chester disease is a rare disease, but it should be considered in those patients displaying chronic renal failure with retroperitoneal fibrosis.(Korean J Med 73:216-222, 2007)
루테늄 전극위에 증착된 PZT 박막의 전기적 및 강유전 특성
황현석(Hyun Suk Hwang),유영식(Yougn Sik Yu),임윤식(Yun-Sik Lim),강현일(Hyun-il Kang) 대한전기학회 2014 전기학회논문지 P Vol.63 No.1
Pb(Zr0.52Ti0.48)O₃(PZT) thin films deposited on Ru/RuO₂ bottom electrode that grown for in-situ progress used rf magnetron sputtering method. We investigated the dependence of the crystalline and electrical properties in the way of capacitors PZT thin films. Our results show that all PZT films indicated polycrystalline perovskite structure with preferred orientation (110) and no pyrochlore phase is observed. The electric properties of the Ru improved with increasing Ru thin films thickness. A well-fabricated Ru/PZT/Ru (100 nm) /RuO₂ capacitor showed a leakage current density in the order of 2.03×10<SUP>-7</SUP> A/cm<SUP>2</SUP> as a 50 kV/cm, a remnant polarization (Pr) of 9.22 μC/cm², and a coercive field (-EC) of -32.22 kV/cm. The results show that Ru/Ru/RuO₂ bottom electrodes are expected to reduce the degradation ferroelectric fatigue and excellent ferroelectric properties.
LTCC 기판상에 증착한 GZO 가스 센싱 박막의 두께 의존 특성 연구
황현석,Hwang, Hyun Suk 한국전기전자재료학회 2011 전기전자재료학회논문지 Vol.24 No.3
A novel design of gas sensor using Ga-doped ZnO (GZO) thin films which are deposited on low temperature co-fired ceramic (LTCC) substrates is presented. The LTCC substrates with thickness of 400 ${\mu}m$ are fabricated by laminating 12 green tapes which consist of alumina and glass particle in an organic binder. The GZO thin films with different thickness are deposited on LTCC substrates, by RF magnetron sputtering method. The microstructure and sensing properties of GZO gas sensing films are analyzed as a function of the film thickness. The films are well crystallized in the hexagonal (wurzite) structure with increasing thickness. The maximum sensitivity of 3.49 is obtained at 100 nm film thickness and the fastest 90% response time of 27.2 sec is obtained at 50 nm film thickness for the operating temperature of $400^{\circ}C$ to the $NO_2$ gas.
심현석(Hyun-Suk Sim),황원준(Won-Jun Hwang),이우송(Woo-Song Lee) 한국산업융합학회 2015 한국산업융합학회 논문집 Vol.18 No.1
For high-accuracy position control of a linear motor, it has been proposed a nonlinear controller including a synchronization algorithm. Linear motors are easily affected by force ripple, friction, and parameter variations because there is no mechanical transmission to reduce the effects of model uncertainties and external disturbances. Synchronization error is also caused by skew motion, model uncertainties, and force disturbance on each axis. Nonlinear effects such as friction and ripple force are estimated and compensated for. The synchronization algorithm is used to reduce the synchronous error of the two side pillars. The performance of the controller is evaluated by computer simulations.
Investigation of Liquid Crystal Alignment on ion beam exposed polystyrene surface
황현석,이종덕,노정규,한정민,Hwang, Hyun Suk,Lee, Jong-Deok,Rho, Jungkyu,Han, Jeong-Min Korea Society of Satellite Technology 2014 한국위성정보통신학회논문지 Vol.10 No.3
본 연구에서는 이온빔을 조사한 폴리스타일렌 기판에 일정강도의 이온빔을 조사한 경우에 발생되는 액정배향의 특성에 대해서 연구하였다. 폴리스타일렌은 기계적강도 및 절연성에서 액정표시소자의 배향막으로 사용되는 폴리이미드 계열의 대체 물질로서 주목받고 있으며, 특히 비접촉 배향에서의 가능성이 새롭게 평가되고 있는 소재이다. 이온빔을 조사하여 이방성을 발생시킨 박막의 표면에서의 액정배향상태를 편광현미경으로 관찰하고, 액정배향에 기여한 메커니즘의 규명을 위해서 XPS(X-ray photoelectron spetroscopy) 분석을 사용하였다. 분석한 결과 15초까지의 이온빔 조사는 액정의 배향을 유발하는 중요한 원인으로 작용함을 알 수 있었으며, 이온빔조사에 의한 액정의 배향방법은 고온안정성도 겸비하고 있는 것을 실험을 통해서 알 수 있었다. This paper introduces homogeneous liquid crystal (LC) orientations on chemically modulated polystyrene (PS) surfaces using various ion beam (IB) exposure time. Transparent PS was replaced with conventional polyimide material. As a non-contact process, IB bombardment process induced LC orientation in the direction parallel to the IB process. Through x-ray photoelectron spectroscopy, it was shown that the chemical compositional changes of the IB-irradiated PS surfaces were determined as a function of IB exposure time.Using this analysis, the optimal IB bombardment condition was determined at IB exposure time of up to 15 s. Moreover, thermal stability on IB-irradiated PS surfaces were carried out which showed that a relatively high IB exposure time induced a thermally stable LC alignment property.