• 한국전자파학회논문지
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• 제25권1호
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• pp.92-98
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• 2014

본 논문에서는 패치 배열과 그리드 구조를 응용하여 C-밴드인 7 GHz 대역에서 동작하는 재구성 주파수 선택 구조를 설계하였다. 본 논문에서 제안한 구조는 바랙터 다이오드를 이용하여 슬롯에서 발생하는 커패시턴스 변화로부터 주파수 재구성 특성을 얻었으며, 커패시턴스의 변화에 따른 투과 주파수의 변화를 구현하였다. 설계한 결과를 바탕으로 유연성을 갖는 FPCB(Flexible Printed Circuit Board)와 상용 바랙터 다이오드를 이용하여 재구성 주파수 선택 구조를 제작하고, 바이어스 전압의 변화에 따른 주파수 재구성 특성을 측정하였다. 제작된 재구성 주파수 선택 구조는 약 6.6~7.6 GHz의 광대역 주파수 재구성 특성(투과 주파수의 가변 범위)을 가지며, 본 논문에서 제안한 구조는 제한된 곡률에 대하여 유연성을 갖기 때문에, 항공기 또는 군함의 레이돔과 같은 곡면 형상 구조 중 완만한 곡면 구조에 적용이 용이하다.

• 한국주조공학회지
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• 제36권1호
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• pp.10-17
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• 2016

Numerical analysis has been performed to evaluate effect of the shape variables such as core length, slot width and slot length on misrun in aluminum die casting process for motor rotor. The predictive method for misrun in diecasting process was established by comparing the result of numerical analysis and an actual motor rotor. Solidification modulus was introduced to predict quantitatively the castability of aluminum diecasting process for motor rotor. It was found that there are minimum critical solidification modulus and slot width to prevent misrun according to core length through diecasting limit diagram proposed using the predictive method. The critical solidification modulus and slot width increase as core length increases to prevent misrun of aluminum motor rotor in diecasting process. Based on the results, the design criteria of slot shape to prevent misrun of aluminum motor rotor with various core length were established.

• 반도체디스플레이기술학회지
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• 제19권3호
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• pp.30-35
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• 2020

A microlens has been fabricated by various methods such as a thermal reflow, hot embossing, diamond milling, etc. However, these methods require a relatively complex process to control the microlens shape. In this work, we report on a simple and cost-effective method to fabricate a cylindrical microlens (CML), which can diffuse light widely. We have employed a slot-die head with the dual plate (a meniscus guide with a protruded μ-tip and a shim with a slit channel) for coating of a narrow stripe using poly(methyl methacrylate) (PMMA). We have shown that the higher the coating gap, the lower the maximum coating speed, which causes an increase in the stripe width and thickness. The coated PMMA stripe has the concave shape. To make it in the shape of a convex microlens, we have applied the thermal reflow method. When the stripe thickness is small, however, its effect is negligible. To increase the stripe thickness, we have increased the number of repeated coating. With this scheme, we have fabricated the CML with the width of 223 ㎛ and the thickness of 7.3 ㎛. Finally, we have demonstrated experimentally that the CML can diffuse light widely, a feature demanded for light extraction efficiency of organic light-emitting diodes (OLEDs) and suppression of moiré patterns in displays.

• 한국초전도ㆍ저온공학회논문지
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• 제9권1호
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• pp.14-17
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• 2007

The slot-die coating & calcination process was adopted to fabricate the long YBCO precursor films on the buffered metal tape for the $2^{nd}$ generation coated conductors. To obtain the smooth and crack-free surface of long YBCO precursor films, the parameters of slot-die coating and the process variables of calcination step must be optimized simultaneously in reel-to-reel method. Among the parameter of slot-die coating process, the viscosities of the precursor solution was controlled from 60cP to 200cP to obtain the thicker films from on single coating. The slot-die gap, the injection rate of precursor solution, the moving speed of buffered metal tape etc. are controlled lot the full coverage and smooth surface of YBCO precursor films. The slot-die coated films are moved through the tube furnace with predetermined heating profiles in humid oxygen ambient The YBCO precursor films was identifed with $Y_2O_3,\;BaF_2$, and CuO phase by XRD and consisted of fine grains of about 20nm size observed by FE-SEM. The YBCO films show the critical current density over $MA/cm^2$ using the precursor films formed by the continuous slot-die coating & calcination process.

• 반도체디스플레이기술학회지
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• 제21권4호
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• pp.39-44
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• 2022

Using a CFD (computational fluid dynamics) simulation tool, we have offered a design guideline of a slot-die head having a simple T-shaped cavity through an analysis of the fluid dynamics in terms of cavity pressure and outlet velocity, which affect the uniformity of coated thin films. We have visualized the fluid flow with a transparent slot-die head where poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) is injected. We have shown that the fluid dynamics inside the slot-die head depends sensitively on the cavity depth, cavity length, land length, and channel gap (i.e., shim thickness). Of those, the channel gap is the most critical parameter that determines the uniformity of the pressure and velocity distributions. A pressure drop inside the cavity is shown to be reduced with decreasing shim thickness. To quantify it, we have also calculated the coefficient of variation (CV). In accordance with Hagen-Poiseuille's laws and electron-hydraulic analogy, the CV value is decreased with increasing cavity depth, cavity length, and land length.

• 반도체디스플레이기술학회지
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• 제23권2호
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• pp.65-70
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• 2024

Using a computational fluid dynamics(CFD) simulation tool, we have provided a coating guideline for slot-die coating with a double layer slot die head. We have analyzed the fluid dynamics in terms of the coating speed, flow rate ratio, and viscosity ratio, which are critical for the stability of coating meniscus. We have identified the common coating defects such as break-up, air entrainment, and leakage by varying the coating speeds. The flow rate ratio is the critical parameter determining the wet film thickness of the top and bottom layers. It is shown that when the flow rate ratio exceeds or equals 1.8, air entrainment occurs due to insufficient hydraulic pressure in the bottom layer, even though the total flow rate remains constant. Furthermore, we have found that the flow of the bottom layer is significantly affected by the viscosity of top layer. The viscosity ratio of 4 or higher obstructs the flow of the bottom layer due to the increased hydraulic resistance, resulting in leakage. Finally, we have demonstrated that as the viscosity ratio increases from 0.1 to 10, the maximum coating speed rises from 0.4 mm/s to 1.6 mm/s, and the minimum wet film thickness decreases from 800 ㎛ to 200 ㎛.

• 대한전자공학회논문지TE
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• 제39권3호
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• pp.59-64
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• 2002

ISM 대역을 사용하는 RFID 시스템에서 대상물에 장착되는 태그는 내장된 컨트롤러와 메모리를 동작시키기 위해서 소형 안테나로부터 들어온 전파 신호를 쇼트키 다이오드로 정류하여 전원으로 사용하게 된다. 반도체 소자의 비선형성에 의한 고조파 성분과 안테나의 고차 모드의 공진으로 여기되는 불요파는 태그의 성능 저하를 가져온다. 본 논문에서는 2차 고조파 성분을 제거함으로써 시스템 효율을 개선하기 위하여 "스터브 I 형 DGS 슬롯 구조"를 이용한 새로운 형태의 저역통과 필터를 구현하였다. 스터브 폭과 I 형 슬롯의 연결 폭을 조정하여 최적의 통과대역 및 저지대역 주파수 특성을 갖도록 설계하고 제작하였다. 제작된 저역통과 필터의 측정결과는 차단 주파수는 3.25 GHz 이고 2.4 GHz~2.5 GHz 의 대역에서 삽입손실은 -0.29~-0.3 dB 이고 반사손실은 -27.688~-33.665 dB 로 비교적 양호한 특성을 보여주고 있으며, 2배 고조파의 대역인 4.9 GHz 에서의 저지특성은 약 -19.367 dB를 보여준다. 이 구조의 필터를 이용하여 RFID, WLAN 등의 응용에 적용되어 고조파와 불요파를 제거함으로서 시스템 효율의 개선에 사용할 수 있을 것이다.

• 반도체디스플레이기술학회지
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• 제14권1호
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• pp.61-65
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• 2015

We have fabricated poly(3,4-ethylenedioxythiophene) : poly(4-styrenesulfonate) (PEDOT : PSS) thin films using a slotdie coater for the applications of OLED lightings. It is demonstrated that the properties of slot-die coated PEDOT : PSS films are comparable with those of spin-coated ones. Namely, the average and peak-to-peak roughness of the slot-die coated 50-nm-thick PEDOT : PSS film are measured to be as low as 0.247 nm and 1.3 nm, respectively. Moreover, we have obtained excellent thickness uniformity (~1.91%). With the slot-die coated PEDOT : PSS films, we have fabricated green phosphorescent OLED devices. For comparison, we have also fabricated OLED devices with spin-coated PEDOT : PSS films. Both show almost no discrepancy in device performance. The power efficiency (25.4 lm/W) and emission uniformity (77%) of OLEDs with slot-die coated PEDOT : PSS films are shown to be slightly lower than those (27.3 lm/W, 80%) of OLEDs with spin-coated PEDOT : PSS films at the luminance of 1,000nit, increasing the feasibility of using a slot-die coating process for the fabrication of large-area OLED lighting sources at a competitive price.

• 반도체디스플레이기술학회지
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• 제18권4호
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• pp.69-74
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• 2019

The aim of this work is to investigate the effect of the microtip length in a slot-die head on coating of a fine poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) stripe. To this end, we have employed a meniscus guide with a 150-㎛-wide microtip and performed roll-to-roll slot-die coatings by varying its length between 500 ㎛ and 50 ㎛. When the microtip length is 150 ㎛ or shorter, we have observed three unexpected phenomena; 1) though the solution spreads much wider than the microtip width, yet the coated stripe width is almost the same as the microtip width, 2) the stripe width decreases, but the stripe thickness is rather increased with increasing coating speed at a fixed flow rate, 3) we obtain stripes much narrower than the microtip width at high coating speeds. It is due to the fact that 1) the meniscus is not well controlled by a short microtip, 2) the main stream of solution from the outlet is very close to the substrate and thus the distributed solution along the head lip merges with the main stream, and 3) the solution is not spread over the entire microtip end at high coating speeds, causing a tiny wobble in the meniscus. Using the 150-㎛-wide and 250-㎛-long microtip, we have fabricated 153-㎛-wide and 94-nm-thick PEDOT:PSS stripe at the maximum coating speed of 13 mm/s. To demonstrate its applicability in solution-processable organic light-emitting diodes (OLEDs), we have also fabricated an OLED device with the fine PEDOT:PSS stripe and obtained strong light emission from it.

• 반도체디스플레이기술학회지
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• 제18권2호
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• pp.6-10
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• 2019

In the presence of $\mu-tip$ for narrow stripe coating, there appears lateral capillary flow along the hydrophilic head lip because the $\mu-tip$ has some resistance to flow. It was known to be suppressed by increasing the contact angle of the head lip. In this paper, we have demonstrated by computational fluid dynamics(CFD) simulations that it can also be suppressed by the formation of micro-patterns on the shim and meniscus guide embedded into the slot-die head. To optimize the micro-patterned structure, we have performed simulations by varying the groove width, depth, and clearance. In the absence of micro-patterns, it is shown by experiment and simulation that the solution spreads to a distance of $1,300{\mu}m$ from the ${\mu}-tip$. In the presence of micro-patterns with the groove width and clearance of $50{\mu}m$, the distance the solution spreads is reduced to $260{\mu}m$. However, no further suppression in the capillary flow is observed with micro-patterns with the groove width of $40{\mu}m$ or less. It is also observed that the capillary flow is not affected by the groove depth if it is larger than $10{\mu}m$. We have shown that the distance the solution spreads can be reduced further to $204{\mu}m$ by coating a hydrophobic material (contact angle of $104^{\circ}$) on the surface of micro-patterns having the groove width and clearance of $50{\mu}m$.