• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.912-915
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• 2004

A vacuum environment is very important for NGL(Next Generation Lithography) apparatuses such as EUVL(Extreme Ultra Violet Lithography) or EPL(Electron Projection Lithography) and so on. The performance of these systems is dominated by vacuum level of processing and positioning accuracy of a stage. So, ultra-precision stage usable in a high vacuum level is needed for the improved performance of these devices. In contrast to atmospheric condition, a special attention must be paid to guide bearing, actuator and other elements. In this paper, air bearing is adopted because of its very high motional accuracy. So, air bearing is designed to be vacuum compatible using differential exhaust method, which prevents air from entering into vacuum chamber. For this, leakage analysis is performed theoretically and verified from experiment.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.10
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• pp.103-112
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• 2006

This paper describes a theoretical analysis and experimental verification on the performances of a vacuum-compatible air bearing, which is designed with a cascaded exhaust scheme to minimize the air leakage in a vacuum environment. The design of the vacuum-compatible air bearing equipped with the differential exhaust system requires great care because several design parameters, such as the number of exhaust stages, diameter of exhaust tube, pumping speed of a vacuum pump, and bearing clearance greatly influence the air leakage and thus degree of vacuum. In this study, a performance analysis method was proposed to estimate the performances of the air bearing, such as load capacity, stiffness, and air leakage. Results indicate that the load capacity and stiffness of the air bearing was improved as its boundary pressure, which was determined by the $1^{st}$ exhaust method, was lowered, and the dominant factors on the chamber's degree of vacuum were the number of exhaust stages, exhaust tube diameter and bearing clearance. A vacuum chamber and air bearing stage using porous pad were fabricated to verify the theoretical analysis. The results demonstrate that chamber pressure up to an order of $10^{-3}$ Pa was achieved with the air bearing stage operating inside the chamber, and this analysis method was valid by comparing predicted values with experimental data, for the mass flow rates from the porous pad, and pressures at each exhaust port and chamber, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.371-372
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• 2008

In this paper, we experimentally investigated discharge phenomena inside vacuum interrupter at 1 to 20 Torr to simulate the vacuum leakage. We used glass type of vacuum interrupter where the internal pressure and the type of gasses can be varied according to requirement. The experiment is conducted under ac applied voltage and the experimental circuit is constructed to simulate the actual circuit used in cubical type insulated switchgear. We used two types of gases such as air and $SF_6$. The use of glass type vacuum interrupter allowed us to measure discharges occurring in vacuum interrupter optically. We measured and discussed the discharge occurring in both gases with a current transformer and ICCD camera. We also revealed that electromagnetic wave spectra emitted by the discharge have same frequency range for both gasses.

• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.1-8
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• 2008

We analyzed the characteristics of water leakage from cooling components of the storage ring in the Pohang Light Source. The water leaks led localized pressure bumps and abnormal pressure changes. The leakage also changed the residual gas compositions depending not only on the position between leakage place to gas analyzer but also on on/off switching of ion pump and electron beam. We found that the residual gas analysis of $CH_4$, CO, NO was useful in determining water leaks.

• Journal of the Korean Society for Precision Engineering
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• v.24 no.6
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• pp.86-95
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• 2007

This paper presents the optimal design of an exhaust system of a vacuum-compatible air bearing using a genetic algorithm. To use the air bearings in vacuum conditions, the differential exhaust method is adopted to minimize the air leakage, which prevents air from leaking into a vacuum chamber by recovering air through several successive seal stages in advance. Therefore, the design of the differential exhaust system is very important because several design parameters such as the number of seals, diameter and length of an exhaust tube, pumping speed and ultimate pressure of a vacuum pump, seal length and gap(bearing clearance) influence on the air leakage, that is, chamber's degree of vacuum. In this paper, we used a genetic algorithm to optimize the design parameters of the exhaust system of a vacuum-compatible air bearing under the several constraint conditions. The results indicate that chamber's degree of vacuum after optimization improved dramatically compared to the initial design, and that the distribution of the spatial design parameters, such as exhaust tube diameter and seal length, was well achieved, and that technical limit of the pumping speed was well determined.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.350-350
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• 2012

본 연구에서는 Oxide 두께가 각각 4, 6 nm인 Symmetric NMOSFET의 전기적 특성 분석에 관한 연구를 진행하였다. 게이트 전압에 따른 Drain saturation current (IDSAT), Threshold Voltage(VT) 및 드레인 전압에 따른 Off-states 특성 변화를 분석하였다. 소자 측정 결과 oxide 두께가 4 nm인 경우 Vt는 0.3 V, IDSAT은 73 ${\mu}A$ (@VD=0.05)로, oxide 두께가 6 nm인 경우 Vt는 0.65 V, IDSAT은 66 ${\mu}A$ (@VD=0.05)로 각각 측정되었다. 이는 oxide 두께가 얇은 경우 게이트 전압 인가 시 Electric field 증가에 따른 것으로 판단된다. 또한 드레인 전압 인가에 따른 소자 특성 분석 결과 oxide 두께가 4nm인 경우 급격한 Gate leakage 증가를 보였으며, 이에 따라 Off-state에서의 leakage current가 증가함을 확인하였다. 본 연구는 Oxide 두께에 따른 MOSFET 소자의 전기적 특성 분석을 위해 진행되었으며, 상기 결과와 같이 oxide 두께 가변은 Idsat, Vt, leakage current 등의 주요 파라미터에 영향을 주어 NMOSFET 소자의 전기적 특성을 변화시킴을 확인하였다.

• Journal of Chest Surgery
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• v.51 no.1
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• pp.76-80
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• 2018

Early diagnosis followed by primary repair is the best treatment for spontaneous esophageal perforation. However, the appropriate management of esophageal leakage after surgical repair is still controversial. Recently, the successful adaptation of vacuum-assisted closure therapy, which is well established for the treatment of chronic surface wounds, has been demonstrated for esophageal perforation or leakage. Conservative treatment methods require long-term fasting with total parenteral nutrition or enteral feeding through invasive procedures, such as percutaneous endoscopic gastrostomy or a feeding jejunostomy. We report 2 cases of esophageal leakage after primary repair treated by endoscopic vacuum therapy with continuous enteral feeding using a Sengstaken-Blakemore tube.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.388.1-388.1
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• 2014

The performance of PVA(polyvinyl alchol) is better than another organic dielectric material. Therefore, PVA has been researched for organic and in-organic dielectric material. But research of changing PVA's dielectric constant and leakage current by increasing temperature and concentration was insigificant. We try to find pure PVA and cross-linked PVA's characteristic of dielectric by changing temperature and concentration. 5/10/15wt% PVA concentration (5% interval) was in progress, PVA at $100/150/200/250^{\circ}C$ ($50^{\circ}C$ interval) of experiments was conducted in relation to temperature. The higher the concentration, leakage currents decrease, and dielectric constant is increased. With regard to temperature, we could not see a big change of leakage current and dielectric constant of pure PVA until $200^{\circ}C$. However, we could see a tendency to increase significantly at $250^{\circ}C$. Also, leakage current and dielectric constant of cross-linked PVA gradually increased from at $100^{\circ}C$ to $200^{\circ}C$ and then sharply increased from at $250^{\circ}C$. We tried to find that PVA's inner bonds(hydroxyl group (OH-) lead to the results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.243-244
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• 2008

We experimentally investigated discharge phenomena inside vacuum interrupter at 1 to 20 Torr to simulate the vacuum leakage. We used glass type of vacuum interrupter where the internal pressure and the type of gasses can be varied according to requirement. The experiment is conducted under ac applied voltage and the experimental circuit is constructed to simulate the actual circuit used in cubical type insulated switchgear. We used two types of gases such as air and $SF_6$. The use of glass type vacuum interrupter allowed us to measure discharges occurring in vacuum interrupter optically. We measured and discussed the discharge occurring in both gases with a current transformer and ICCD camera. We a1so revealed that electromagnetic wave spectra emitted by the discharge have same frequency range for both gasses.

• Proceedings of the Korean Vacuum Society Conference
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• 2009.08a
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• pp.230-230
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• 2009