• Journal of the Microelectronics and Packaging Society
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• v.29 no.2
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• pp.121-127
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• 2022

Micro-LED is a light-emitting diode smaller than 100 ㎛ in size. It attracts much attention due to its superior performance, such as resolution, brightness, etc., and is considered for various applications like flexible display and VR/AR. Micro-LED display requires a mass transfer process to move micro-LED chips from a LED wafer to a target substrate. In this study, we proposed a vacuum chuck method as a mass transfer technique. The vacuum chuck was fabricated with MEMS technology and PDMS micro-mold process. The spin-coating approach using a dam structure successfully controlled the PDMS mold's thickness. The vacuum test using solder balls instead of micro-LED confirmed the vacuum chuck method as a mass transfer technique.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.46 no.4
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• pp.15-20
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• 2009

In a detection system based on laser light scattering, focusing an excitation laser beam into a focal point of a channel in a microfluidic chip is important for obtaining the highest excitation intensity, and consequently for obtaining a laser light scattering signal using a photodetector with a high efficiency. In this paper, we present a polydimethylsiloxane (PDMS) microfluidic chip consisting of an integrated PDMS microlens for cell detection based on laser light scattering. We fabricated PDMS microlens for optical detection system by simply putting down on PDMS chips. The PDMS microlens was fabricated by photoresist reflow and replica molding. This fabrication technique is simple and has an excellent property in terms of the microlens and a high-dimensional accuracy. The PDMS microlens integrated on the PDMS microfluidic chip has been verified to improve the laser intensity, and accordingly, the signal-to-noise ratio and sensitivity of laser light scattering detection for red blood cells(RBCs)

• Transactions of the Korean Society of Mechanical Engineers A
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• v.41 no.6
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• pp.553-560
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• 2017

3D printing technology has been a great interest in human bio-interfaces and human-like robotics since they require arbitrary and adaptive manufacturing. This research mainly concerns the 3D fabrication of a packed biosensor using elastomeric sheets made of PDMS. It is essential to design the PDMS molding with 3D printing since, in the case of biosensors, it should not only produce a conformal shape depending on an arbitrary skin surface but also guarantee a uniform thickness distribution during solidification in the PDMS prepolymer solution. To satisfy the characteristics of the PDMS molding, such as flexibility in the de-molding and stiffness in the solidification processes, multi-materials have been selectively applied to the PDMS molding design, which has been validated with finite element analyses and compared with the 3D printed molding.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.6
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• pp.35-41
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• 2006

In this paper, we focus on improving the performance of the piezoelectric diaphragms of valveless micropumps. A circular lightweight piezoelectric composite actuator (LIPCA) with a high level of displacement and output force has been developed for piezoelectrically actuated micropumps. We used numerical and experimental methods to analyze the characteristics of the actuator to select optimal design. With the developed circular LIPCA, we fabricated a valveless micropump by photo-lithography and PDMS molding techniques. The displacement of the diaphragm, the flow rate and the back pressure of the micropump were evaluated and discussed. With a semi-empirical method, the flow rate with respect to driving frequency was predicted and compared with experimental one. The test results confirm that the circular LIPCA is a promising candidate for micropump application and can be used as a substitute for a conventional piezoelectric actuator diaphragm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.351-354
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• 2004

This work presents a simple and cost-effective approach for maskless fabrication of positive-tone silicon master for the replica molding of hyperfine elastomeric channel. Positive-tone silicon masters were fabricated by a maskless fabrication technique using the combination of nanoscratch by Nanoindenter ⓡ XP and XOH wet etching. Grooves were machined on a silicon surface coated with native oxide by ductile-regime nanoscratch, and they were etched in a 20 wt％ KOH solution. After the KOH etching process, positive-tone structures resulted because of the etch-mask effect of the amorphous oxide layer generated by nanoscratch. The size and shape of the positive-tone structures were controlled by varying the etching time (5, 15, 18, 20, 25, 30 min) and the normal loads (1, 5 mN) during nanoscratch. Moreover, the effects of the Berkovich tip alignment (0, 45$^{\circ}$) on the deformation behavior and etching characteristic of silicon material were investigated.

• Clean Technology
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• v.18 no.3
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• pp.295-300
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• 2012

Synthesis of well-defined particle with tunable size, shape, and functionalities is strongly emphasized for various applications such as chemistry, biology, material science, chemical engineering, medicine, and biotechnology. This study presents micromolding method for the fabrication of anisotropic particles with elegant control of curvature of covex roof. For the demostration of rapid fabrication of the particles, we have applied polydimethylsiloxane (PDMS) micromold as structure guiding template and wetting fluid to control curvature of roof of the particles. Based on this approach, we can control the radius of curvature from $20{\mu}m$ to $70{\mu}m$ with different aspect ratio of mold. In addition, wetting fluids with different wetting properties can also modulate the height and radius of curvature of the particles. We envision that this methodology is promising tool for precise control of particle shape in 3-dimensional space and new synthetic route for anisotropic particles with cost effective, simple, easy, and fast procedure.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.426-428
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• 2007

A simple method is presented for fabricating micro/nanoscale combined hierarchical structures using a two-step UV-assisted capillary molding technique. This lithographic method consists of two steps: (i) fabrication of partially cured polymer microstructures using a PDMS mold and (ii) subsequent nanofabrication using a high-resolution polyurethane acrylate (PUA) mold on top of the pre-formed microstructures. Using this technique, various micro/nano hierarchical structures were fabricated with minimum resolution down to 70 nm over a large area with very good reproducibility.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2016.11a
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• pp.150-150
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• 2016

디스플레이, 센서 등 전자소자는 소형화 단계를 지나 인체 부착형 소자로의 발전을 요구하고 있다. 부착형 소자에서는 접착력과 큰 마찰력이 필요하지만 마찰특성이 더 중요하므로 인체 및 물체의 마찰을 위해서는 다양한 표면에 대항하는 마찰 특성과 내구성이 요구되며 이를 위해 개코도마뱀 또는 딱정벌레, 말벌날개와 같은 자연모사형 건식 마찰 방식에 대한 연구가 활발히 진행되고 있다. 그러나 기존 폴리머를 이용하여 자연모사형 마이크로/나노 구조 형성은 기계적으로 가공된 금형 몰딩을 통한 매무 복잡한 공정을 요구된다. 본 연구에서는 이러한 복잡한 공정을 통한 마찰재 제작을 단순화하기 위해서 플라즈마 표면처리를 활용하여 나노구조 형성하는 방법을 소개하고자 하며, 건식 접착 및 마찰용 폴리머 소재(PDMS(Poly dimethyl siloxane))에 따른 표면구조 변화와 표면에너지 및 화학결합 변화에 대한 연구를 수행하였다. 플라즈마 표면처리를 위해서 자체 개발한 선형이온소스를 활용하였으며 입사에너지에 따라 표면형상 변화를 주사전자현미경을 활용하여 관찰하였다. 표면에너지 변화는 접촉각측정기를 활용하였으며, Tribology tester(Ball on disk)를 활용하여 마찰특성을 평가하였다. PDMS(Poly dimethyl siloxane)는 입사에너지가 증가함에 따라 주름형태 구조 크기가 증가하는 것을 관찰하였고, 플라즈마 처리를 통해 표면에너지 및 마찰력 증가를 관찰하였다. 그리고 플라즈마 처리 후 표면에너지 변화인 FOTS(Trichloro-(1H,1H,2H,2H- perfluorooctyl) silane) 처리를 통하여 표면에너지 감소와 마찰력이 절반으로 감소하였다. 본 연구 결과는 나노구조에 따라 표면형상 및 표면에너지 변화에 따른 PDMS의 마찰력 변화를 확인하였고, 이러한 특성을 활용하여 마찰재와 피부 부착형 접착 패치에 응용이 가능할 것으로 기대된다.

• Korean Chemical Engineering Research
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• v.58 no.1
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• pp.122-126
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• 2020

In this study, we produced the micropatterned channel system using polydimethylsiloxane (PDMS) and micromolding in capillaries (MIMIC) technology and evaluated cellular polarity signals through high-resolved imaging at the single-cell level. In cells treated with platelet-derived growth factor (PDGF), three types of key signals in cell migration; phosphoinositide 3-kinase (PI3 K), Rac, and Actin, were strongly activated in the front area compared to the rear region, whereas myosin light chain (MLC) showed no notable activity in the front and rear areas. Our results will, therefore, provide important information and methodology for studying the correlation between cell polarity signals and cell migration under the newly defined microenvironment.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.141.2-141.2
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• 2016

디스플레이, 센서 등 전자소자는 소형화 단계를 지나 인체 부착형 소자로의 발전을 요구하고 있다. 인체 부착을 위해서는 민감한 피부에 장시간 부착시 무해성과 탈부착의 자유로움이 요구되기에 기존의 화학물질을 활용한 접착 방식에서 개코도마뱀 또는 딱정벌레 발바닥에서 영감을 얻은 자연모사형 건식 접착 방식에 대한 연구가 활발하게 진행되고 있다. 폴리머를 이용하여 자연모사형 마이크로/나노구조 형성은 기계적으로 가공된 금형 몰딩과 후처리를 통한 매우 복잡한 공정이 요구된다. 본 연구에서는 이러한 복잡한 공정을 단순화하기 위해서 폴리머 소재에 플라즈마를 활용한 나노구조를 형성하는 방법을 소개하고자 하며, 건식 접착용 폴리머 소재(PMMA, PDMS)에 따른 표면구조 변화와 표면에너지 변화에 대한 연구를 수행하였다. 플라즈마 표면처리를 위해서 본 연구실에서 자체 개발한 선형이온소스를 활용하였으며 입사에너지, 노출시간, 사용가스에 따른 표면형상 변화를 주사전자현미경을 활용하여 관찰하였다. 또한 처리조건에 따른 표면에너지 변화를 확인하기 위해 물접촉각 변화를 측정하였다. PMMA는 입사에너지, 노출시간이 증가함에 따라 쉽게 나노기둥구조가 형성되었으나, 과도한 입사에너지 또는 노출시간에서는 표면구조가 에칭되면서 무너지는 것이 관찰되었다. 또한 PDMS는 동일한 조건에서 주름구조 형태를 보였으며 노출시간이 증가할수록 주름구조의 간격이 늘어남을 확인하였다. 본 연구 결과를 통해 나노 구조를 쉽게 제어할 수 있는 PMMA가 피부 부착형 접착 패치에 응용이 가능할 것으로 기대된다.