• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.332-332
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• 2010

We have successfully demonstrated the inkjet printing method to create $Al_2O_3$ films withouWe have successfully demonstrated the inkjet printing method to create $Al_2O_3$ films without a high temperature sintering process. In order to remove the coffee ring effect in the ink drop, we have introduced a co-solvent system in order to create Marangoni flow in the ink drop, which leads to the dense packing of ceramic powders on the substrate during inkjet process. The packing density of the Inkjet-printed $Al_2O_3$ films is around 60% (max. 70%) which is very high compared to the value obtained from the same material films by other conventional methods such as film casting, dip coating process, etc. The voids inside the films (which are around 40% of the entire film volume) are filled with the polymer resin (Cyanate ester) by the infiltration process. This resin infiltration is also implemented by the inkjet printing process right after the Ah03 film ink-jetting process. The microstructures of the printed $Al_2O_3$ films are investigated by Scanning Electron Microscope (SEM) to understand the degree of packing density in the printed films. The inkjet-printed $Al_2O_3$ films have been characterized to investigate its thickness and roughness. Quality factor of the printed $Al_2O_3$ film is also measured to be over 300 at 1MHz.

• 한국지반공학회논문집
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• 제28권10호
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• pp.69-77
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• 2012

최근 국내 터널들이 노후화됨에 따라 배수공 막힘현상이 가장 큰 문제점 중 하나로 보수대책 공법이 필요한 실정이다. 현재는 유지 관리용 Robot이나 Water Jet Cleaning공법 등으로 배수공 내 생성된 스케일을 제거하고 있지만 비용이 비싸고 주기적인 관리를 필요로 하는 단점을 가지고 있다. 본 연구에서는 터널 배수공 내의 스케일을 SEM-EDS와 XRD로 분석하였고, 침전물은 탄산칼슘($CaCO_3$)성분의 스케일로 calcite로 확인되었다. 침전물 생성 억제 및 제거를 위해 퀀텀스틱 신기술을 사용하여 개방형 배수시험, 순환식 폐쇄수조시험을 실시하였다. 무게측정분석, 육안분석, 경도변화분석을 통하여 요소기술로 인한 스케일 생성량이 확연히 줄었음을 확인하였다. 결과적으로 퀀텀스틱이 배수공 내 침전물 생성을 방지하는데 효과가 있음을 확인할 수 있었다.

• 한국기계가공학회지
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• 제16권1호
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• pp.118-123
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• 2017

It is well known that water jetting is now widely used in the advanced cutting processes of polymers, metals, glass, ceramics, and composite materials because of some advantages, such as heatless and non-contacting cutting different from the laser beam machining. In this paper, we proposed the simulation model of waterjet by lengths and the inner spiral structure of the nozzle. The simulation results show that the outlet velocity of the nozzle is faster than the inlet. Furthermore, we found rapid velocity reduction after passing through the outlet. The nozzle of diameter ${\phi}500$ and length 70mm, shows the optimal fluid width and velocity distribution. Also, the nozzle with inner spiral structure shows a Gaussian distribution of velocity and this model is almost twice as fast as the model without spiral structure, within the effective standoff distance (2.5 mm). In the future, when inserting abrasive material into the waterjet, we plan to analyze the fluid flow and the particle behavior through a simulation model.

• 대한기계학회논문집B
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• 제37권9호
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• pp.873-877
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• 2013

잉크젯 기술은 가정용 프린터에서부터 제조 도구로 확대 되었다. 최근 인쇄전자 분야에서 고해상도 인쇄가 요구되고 있다. 기존의 잉크젯 인쇄 패터닝 방식을 향상 시키기 위해 전기수력학잉크젯 기술이 최근 주목을 받고 있는데 노즐 직경보다 작은 방울을 토출할 수 있고 넓은 점도 범위와 재료를 사용할 수 있기 때문이다. 본 논문에서는 미세 패터닝을 위한 EHD 프린팅 시스템이다. 요구 적출형 프린팅에 의해 다양한 패턴을 인쇄하고 벡터와 레스터 프린팅 알고리즘을 개발하였다. 내경이 $8{\mu}m$ 인 노즐을 이용하여 $7{\mu}m$ 이하의 미세 전도성 선폭을 EHD 방식을 통해 만들 수 있다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2014년도 제46회 동계 정기학술대회 초록집
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• pp.162-162
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• 2014

최근 들어 wearable computing에 대한 수요가 증가하면서 flexible device에 대한 연구가 활발히 진행되고 있다. 하지만, flexible device를 구현하기 위해서는 기판의 damage를 줄이기 위한 저온공정, device life-time 향상을 위한 passivation, 와이어 본딩 등 다양한 문제들이 해결 되어야 한다. 이러한 문제들 중, polymer 기판과 금속간의 접착력을 향상시키기 위해서 많은 연구자들은 기판의 표면에 adhesive layer를 도포하거나 금속잉크의 solvent를 변화시키는 등의 연구를 진행해왔다. 종래의 연구는 기존 device를 대체 할 수 있을 정도의 생산성과 polymer 기판에 대한 열 적인 손상 이 문제가 되었다. 종래의 문제를 해결하기 위하여 저온공정, in-line system이 가능한 준 준 대기압 플라즈마를 사용하였다. 본 연구에서는 금속잉크를 Ink-jet으로 jetting하여 와이어 본딩 하는 과정에서 전도성 ink의 선폭을 유지시키고 접착력을 향상하기 위하여 준 대기압 플라즈마 공정을 이용하여 이러한 문제점을 해결하고자 하였다. Polymer 기판 표면에 roughness를 만들기 위해 대략 수백 nm 크기를 갖는 graphene flake를 spray coating하여 마스크로 사용하고 준 대기압 플라즈마를 이용하여 표면을 식각 함으로써 roughness를 형성시켰다. 준 대기압 플라즈마를 발생시키기 위해 double discharge system에서 6 slm/1.5 slm (He/O2) gas composition을 하부 전극에 흘려보내고 60 kHz, 5 kV 파워를 인가하였다. 동시에 상부 전극에는 30 kHz, 5 kV 파워를 인가하여 110초 동안 표면 식각 공정을 진행하였다. Graphene flake mask가 coating되어 있는 유연기판을 산소 플라즈마 처리 한 후 물에 3초 동안 세척하여 표면에 남아있는 graphene flake를 제거하고 6 slm/0.3 slm (He/SF6)의 유량으로 주파수와 파워 모두 동일 조건으로 110초 동안 표면 처리를 하였다. Figure 1은 표면 개질 과정과 graphene flake를 mask로 사용하여 얻은 roughness 결과를 SEM을 이용하여 관찰한 결과이다. 이와 같이 실험한 결과 ink와 기판간의 접촉면적을 늘려주고 접촉 각을 조절하여 Wenzel model 을 형성 할 수 있는 표면 roughness를 생성하였고 표면의 화학적 결합을 C-F group으로 치환하여 표면의 물과 접촉각 이 $47^{\circ}$에서 $130^{\circ}$로 증가하는 것을 확인하였다.

• 대한기계학회논문집A
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• 제41권6호
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• pp.525-532
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• 2017

차세대 주력 디스플레이인 유기 및 양자점 발광 다이오드를 잉크젯을 이용하여 저렴한 비용으로 생산하기 위한 연구개발이 진행되어 왔으며, 잉크 액적의 토출 신뢰성을 고속으로 검사하기 위한 모니터링 장비의 개발이 요구된다. 본 연구에서는 기존 직선 운동 방식의 잉크젯 모니터링 장비 대신에 로터리 및 리니어 초음파 모터를 이용하여 미러를 회전시킴으로써 노즐들에서 토출되는 잉크 액적들을 모니터링할 수 있는 장비를 개발하여 측정 능력을 시험하였다. $10{\mu}m$, $30{\mu}m$ 및 $50{\mu}m$ 직경 원형의 측정 오차는 각각 $0.5{\pm}1.0{\mu}m$, $-1.2{\pm}0.3{\mu}m$ 및 $0.2{\pm}0.5{\mu}m$였다. 모니터링 시간은 17초가 소요되었으며, 제어 프로그램의 최적화를 통해 8.6초까지 모니터링 시간을 단축할 수 있는 가능성을 확인하였다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.470-470
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• 2012

Organic thin film transistors (OTFTs) backplane constitute the active elements in new generations of plastic electronic devices for flexible display. The overall OTFTs performance is largely depended on the properties and quality of each layers of device material. In solution based process of organic semiconductors (OSCs), the interface state is most impediments to preferable performance. Generally, a threshold voltage (Vth) shift is usually exhibited when organic gate insulators (OGIs) are exposed in an ambient air condition. This phenomenon was caused by the absorbed polar components (i.e. oxygen and moisture) on the interface between OGIs and Soluble OSCs during the jetting process. For eliminating the polar component at the interface of OGI, the role of high vacuum seasoning on an OGI for all solution processable OTFTs were studied. Poly 4-vinly phenols (PVPs) were the material chosen as the organic gate dielectric, with a weakness in ambient air. The high vacuum seasoning of PVP's surface showed improved performance from non-seasoning TFT; a $V_{th}$, a ${\mu}_{fe}$ and a interface charge trap density from -8V, $0.018cm^2V^{-1}s^{-1}$, $1.12{\times}10^{-12}(cm^2eV)^{-1}$ to -4.02 V, $0.021cm^2V^{-1}s^{-1}$, $6.62{\times}10^{-11}(cm^2eV)^{-1}$. These results of OTFT device show that polar components were well eliminated by the high vacuum seasoning processes.

• 자원환경지질
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• 제26권1호
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• pp.55-65
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• 1993

Udo Island, some 3 km off the coast of Sungsan Peninsula at the eastern promontory of Cheju Island, occurs in such a regular pattern on the sequences which reprent an excellent example of an eruptive cycle. The island comprises a horseshoe-shaped tuff cone, a nested cinder cone on the crater floor, and a lava delta which extends over northwest from the moat between two cones. The volcanic sequences suggest volcanic processes that start with emergent Surtseyan eruption, progress through Strombolian eruption and end with lava effusion followed by reworking of smooth tephra on the tuff cone. Eruptive environment and hydrology of vent area in the Udo tuff cone are poorly constrained because the stratigraphic units under the tuff cone are unknown. It is thoughl, however, that the tuff cone could be mainly emergent because the present cone deposits show no evidence of marine reworking, and standing body of sea water could play a great role. The emergent volcano is characterized by distinctive steam-explosivity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry. The sea water gets into the vent by flooding accross or through the top or breach of tephra cone. Udo tuff cone was constructed from Surtseyan eruption which went into with tephra finger jetting activities in the early stage, late interspersed with continuous uprush activities and proceeded to only continuous uprush activities in the last. When the enclosure of the vent by a long-lived tephra barrier would prevent the flooding and thus allow the vent to dry out, the Surtseyan eruption ceased to transmit into Strombolian activities, which constructed a cinder cone on the crater floor of the tuff cone. The Strombolian eruption ceased when magma in the conduit gradually became depleted in gas. In the case of Udo, the last magmatic activity was Hawaiian-type (and/or fountain) which accumulated basalt lava delta. And then the loose tephra of the tuff cone reworked over the moat lava and the northeastern flank.

• 한국재료학회지
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• 제30권1호
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• pp.38-43
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• 2020

Sand casting 3D printing uses a binder jetting method to produce a mold having complicated shape by spraying a binder on sand coated with activator. Appropriate heat treatment process in sand mold fabrication can increase the degree of polymerization to improve flexural strength. However, long heat treatment of over 24 hours decreases flexural strength and reliability due to chemical bond decomposition through thermal degradation. The main role of the activator is to control the reaction rate between the polymer chains. As a result, when the activator composition is increased from 0.15 wt% to 0.25 wt%, the flexural strength is increased by 218 N/㎠. However, excess activator (0.40 wt%) has been shown to decrease reliability without increasing flexural strength. The main role of the binder is to control the flexural strength of the specimen. As the binder composition is increased from 2.00 wt% to 4.00 wt%, the flexural strength increases to about 255 N/㎠, indicating the maximum flexural strength increase. Finally, the reliability of the flexural strength of the fabricated specimens is evaluated by a Weibull plot. Weibull modulus calculations are used to evaluate the flexural strength reliability of the specimens, and maximum reliability value of 11.7 is obtained at 0.20 wt% activator composition. Therefore, it is confirmed that this composition has maximum flexural strength reliability.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 C
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• pp.1621-1622
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• 2006

This paper presents the effect of driving waveform for piezoelectric bend mode inkjet printhead with optimized mechanical design. Experimental and theoretical studies on the applied driving waveform versus jetting characteristic s were performed. The inkjet head has been designed to maximize the droplet velocity, minimize voltage response of the actuator and optimize the firing frequency to eject ink droplet. The head design was carried out by using mechanical simulation. The printhead has been fabricated with Si(100) and SOI wafers by MEMS process and silicon direct bonding method. To investigate how performance of the piezoelectric ceramic actuator influences on droplet diameter and droplet velocity, the method of stroboscopy was used. Also we observed the movement characteristics of PZT actuator with LDV(Laser Doppler Vibrometer) system, oscilloscope and dynamic signal analyzer. Missing nozzles caused by bubbles in chamber were monitored by their resonance frequency. Using the water based ink of viscosity of 4.8 cps and surface tension of 0.025N/m, it is possible to eject stable droplets up to 20kHz, 4.4m/s and above 8pL at the different applied driving waveforms.