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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.
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)
DLC Structure Layer for Piezoelectric MEMS Switch
황현석,이경근,유영식,임윤식,송우창,Hwang, Hyun-Suk,Lee, Kyong-Gun,Yu, Young-Sik,Lim, Yun-Sik,Song, Woo-Chang Korea Society of Satellite Technology 2011 한국위성정보통신학회논문지 Vol.9 No.1
본 논문에서는 d33 모드로 구동하여 우수한 성능을 가지는 RF-MEMS 스위치의 구현을 위한 희생층과 구조층의 조합으로서 DLC와 포토레지스트를 제안하였다. 포토레지스트의 경화현상을 방지하기 위하여 DLC 구조층은 상온에서 RF-PECVD 방법을 이용하여 증착하였다. 그리고 PZT 압전층은 RF 마그네트론 스퍼터링 방법을 이용하여 상온에서 구조층 위에 증착하였으며, 희생층의 제거 후 결정화를 위하여 급속 열처리 (RTA) 장비를 이용하여 후 열처리하였다. PZT의 결정화 과정과 DLC의 기계적 성질의 변화를 다양한 온도조건에 따라 분석한 결과 DLC는 PZT의 결정화 온도까지 영률과 강도면에서 우수한 특성을 나타냄을 확인하였다. 또한 포토레지스트를 사용함으로서 공정을 단순화하고 낮은 비용으로 제작이 가능하였다. In this paper, a new set of structural and sacrificial material that is diamond like carbon (DLC)/photoresist for high performance piezoelectric RF-MEMS switches which are actuated in d33 mode is suggested. To avoid curing problem of photoresist sacrificial layer, DLC structure layer is deposited at room temperature by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) method. And lead zirconate titanate (PZT) piezoelectric layer is deposited on structure layer directly at room temperature by rf magnetron sputtering system and crystallized by rapid thermal annealing (RTA) equipment. Particular attention is paid to the annealing of PZT film in order to crystallize into perovskite and the variation of mechanical properties of DLC layer as a function of annealing temperature. The DLC layer shows good performance for structure layer in aspect to Young's modulus and hardness. The fabrication becomes much simpler and cheaper with use of a photoresist.
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.
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.
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.
황현석,여동훈,김종희,송준태,Hwang, Hyun-Suk,Yeo, Dong-Hun,Kim, Jong-Hee,Song, Joon-Tae 한국전기전자재료학회 2008 전기전자재료학회논문지 Vol.21 No.6
In this work, Ga-doped ZnO (GZO) thin films for gas sensor application were deposited on low temperature co-fired ceramics (LTCC) substrates, by RF magnetron sputtering method. The LTCC substrate is one of promising materials for this application since it has many advantages (e.g., low cost production, high manufacturing yields and easy realizing 3D structure etc.). The LTCC substrates with thickness of $400\;{\mu}m$ were fabricated by laminating 12 green tapes which consist of alumina and glass particle in an organic binder. The structural properties of the fabricated GZO thin film with thickness of 50 nm is analyzed by X-ray diffraction method (XRD) and field emission scanning electron microscope (FESEM). The film shows good adhesion to the substrate. The GZO gas sensors are tested by gas measurement system and show fast response and recovery characteristics to $NO_x$ gas that is 27.2 and 27.9 sec, recpectively.