• Journal of Mechanical Science and Technology
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• v.20 no.12
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• pp.2094-2104
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• 2006

As demands for complex microstructures with high aspect ratios have increased, the existing methods, MEMS and LIGA, have had difficulties coping with the number of masks and fabricable heights. A microstereolithography technology can meet these demands because it has no need of masks and is capable of fabricating high aspect ratio microstructures. In this technology, 3D part is fabricated by stacking layers, 2D sections, which are sliced from STL file, and the Dynamic Image Projection process enables the resin surface to be cured by a dynamic image generated with $DMD^{TM}$ (Digital Micromirror Device) and one irradiation. In this paper, we address optical design process for implementing this microstereolithography system that takes the light path based on DMD operation and image-formation on the resin surface using an optical design program into consideration. To verify the performance of this implemented microstereolithography system, complex 3D microstructures with high aspect ratios were fabricated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1175-1178
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• 2005

Brittle materials, especially single-crystal silicon wafer, are widely used for sensors, IC industry, and MEMS applications. e general machining process of crack easy materials is by chemical agents, but it is hazardous and time consuming. Also, it is difficult to get high aspect ratio micro structure. As an alternative tool, an AJM(Abrasive jet machining) is promising method in terms of high aspect ratio and production cost. In this study, to get more precise detail compared to general AJM, photo polymer mask, SU-8, used in photolithography was applied in AJM. Process parameters such as abrasive diameter, air pressure, nozzle diameter, flow rate of abrasive in AJM and a variety of conditions in spin coating were decided. Finally, micro channel and mixer was fabricated to see the efficiency of the AJM with photo polymer mask.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1704-1705
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• 2011

MEMS(Micro Electro Mechanical Systems) 기술과 니켈 전기도금공정을 이용하여 수십 내지 수백개의 탐침을 갖는 일체형 탐침 패드(Probe Pad)를 제작하였다. PI(Polyimide) Film은 일본 UBE사의 $50{\mu}m$ 두께를 갖는 유피렉스를 사용하였다. 일체형 탐침 패드는 Polyimide Film에 Cu를 증착 후 사진식각공정을 통하여 PR Mold 형성한 후 전류가 흐르는 Cu 라인(line) 배선을 형성하기 위해 Cu를 식각하였으며 형성된 Cu Line 위에 니켈 전해도금공정을 실시하여 니켈 배선을 형성하였다. Ni 배선 위에 니켈 범프를 형성하기 위하여 PR Strip을 실시한 후 다시 PR Mold를 형성하였다. PR Mold 형성 후 다시 니켈 전해도 금을 실시하여 니켈 범프(bump)를 형성하였다. 제작된 탐침패드의 니켈배선의 폭은 $18.0{\mu}m$이고 피치(Pitch)는 $35{\mu}m$이며, 니켈 범프의 두께(Thickness)는 $10.0{\mu}m$로 제작되었다. 본 연구에서 제작된 탐침패드를 더욱 더 고집적화(Fine Pitch)하여 일체형 탐침 패드를 제작하게 되면 이를 사용하는 프로브유니트의 제작에 있어서 비용 절감 및 생산성(Throughput)을 크게 향상 시킬 수 있을 것이다.

• Journal of Electrical Engineering and Technology
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• v.7 no.5
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• pp.784-788
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• 2012

In this paper, a high-performance optical gating in a junction device based on a vanadium dioxide dioxide ($VO_2$) thin film grown by a sol-gel method was experimentally demonstrated by directly illuminating the $VO_2$ film of the device with an infrared light at ~1554.6 nm. The threshold voltage of the fabricated device could be tuned by ~76.8 % at an illumination power of ~39.8 mW resulting in a tuning efficiency of ~1.930 %/mW, which was ~4.9 times as large as that obtained in the previous device fabricated using the $VO_2$ thin film deposited by a pulsed laser deposition method. The rising and falling times of the optical gating operation were measured as ~50 ms and ~200 ms, respectively, which were ~20 times as rapid as those obtained in the previous device.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.25 no.1
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• pp.62-67
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• 2016

This paper presents a silicon nanostructure array embedded in a polymer film. The silicon nanostructure array was fabricated by using basic microelectromechanical systems (MEMS) processes such as photolithography, reactive ion etching, and anisotropic KOH wet etching. The fabricated silicon nanostructure array was transferred into polymer substrates such as polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polycarbonate (PC) through the hot-embossing process. In order to determine the transfer conditions under which the silicon nanostructures do not fracture, hot-embossing experiments were performed at various temperatures, pressures, and pressing times. Transfer was successfully achieved with a pressure of 1 MPa and a temperature higher than the transition temperature for the three types of polymer substrates. The transferred silicon nanostructure array was electrically evaluated through measurements with a semiconductor parameter analyzer (SPA).

• Journal of Sensor Science and Technology
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• v.17 no.4
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• pp.250-255
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• 2008

A vanadium pentoxide ($V_2O_5$)-based bolometric infrared (IR) sensor has been designed and fabricated using micro electro mechanical systems (MEMS) technology for glucose detection and its resistive characteristics has been illustrated. The proposed bolometric infrared sensor is composed of the vanadium pentoxide array that shows superior temperature coefficient of resistance (TCR) and standard silicon micromachining compatibility. In order to achieve the best performance, deposited $V_2O_5$ thin film is optimized by adequate rapid thermal annealing (RTA) process. Annealed vanadium oxide thin film has demonstrated a linear characteristic and relatively high TCR value (${-4}%/^{\circ}C$). The resistance of vanadium oxide is changed by IR intensity based on glucose concentration.

• Journal of Biomedical Engineering Research
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• v.31 no.2
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• pp.87-93
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• 2010

Researches for stem cells have been focused on scientists in biomedical sciences as well as clinical application for its great therapeutic potentials. Stem cells have two distinct characteristics: self-renewal and differentiation. In this short review, the links between stem cell research and biomedical engineering is discussed based on the basic characteristics of stem cells. This concept can be extended to the fundamental questions of biological sciences for cells such as proliferation, apoptosis, differentiation, and migration. For understanding proliferation and apoptosis of stem cells, techniques from biomedical engineering such as surface patterning, MEMS, nanotechnologies have been used. The advanced technologies such as microfluidic technologies, three dimensional scaffold fabrication, and mechanical/electrical stimulation have also been used in cell differentiation and migration. Basic and unsolved questions in the stem cell research field have limitations by studying conventional technologies. Therefore, the strategic fusion between stem cell biology and novel biomedical engineering field will break the barriers for understanding fundamental questions of stem cells, which can open the window for the clinical applications of stem cell based therapeutics as well as regeneration of damaged tissues.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.9
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• pp.1733-1740
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• 2011

In this research, a MEMS vibratory gyroscope with dual-mass system in the sensing mode has been proposed to increase the stability of the device using wide bandwidth. A wide flat region between the two resonance peaks of the dual-mass system removes the need for a frequency matching typically required for single mass vibratory gyroscopes. Bandwidth, mass ratio, spring constant, and frequency response of the dual-mass system have been analyzed with MATLAB and ANSYS simulation. Designed first and second peaks of sensing mode are 5,917 and 8,210Hz, respectively. Driving mode resonance frequency of 7,180Hz was located in the flat region between the two resonance peaks of the sensing mode. The device is fabricated with anodically bonded silicon-on-glass substrate. The chip size is 6mm x 6mm and the thickness of the silicon device layer is $50{\mu}m$. Despite the driving mode resonance frequency decrease of 2.8kHz and frequency shift of 176Hz from the sensing mode due to fabrication imperfections, measured driving frequency was located within the bandwidth of sensing part, which validates the utilized dual-mass concept. Measured bandwidth was 768Hz. Sensitivity calculated with measured displacement of driving and sensing parts was 22.4aF/deg/sec. Measured slope of the sensing point was 0.008dB/Hz.

• Journal of the Korean Vacuum Society
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• v.8 no.4A
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• pp.425-431
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• 1999

$Pb(Zr_{0.52}, Ti_{0.48})O_3$ (PZT) thick films as an actuating material with conducting oxides, $(La_{0.5}Sr_{0.5}) CoO_3$ (LSCO), have been fabricated by sol-gel method for Optical Micro-Electro-Mechanical System (MEMS) devices, in which PZT/LSCO/SiO2 structures were used. In order to improve the adhesion to LSCO solution in order to enhance the wetting behavior of a water-based LSCO precursor solution and further to improve the adhesion between LSCO and $SiO_2$ layers. PZT films were made using 1-3 propanediol based precursor solution which has a high viscosity and a boiling point appropriate for thick film fabrication. In the precursor solution, Ti-propoxied and Zr-propoxied are partially substituted with acetylacetone to achieve the solution stability while maintaining reactivity. Crack free PZT films (0.8~1$\mu\textrm{m}$) have been successfully fabricated at crystallization temperatures above $700^{\circ}C$. Dielectric constants and dielectric losses of the PZT films were 900~1200and 2~5%, respectively. Piezoelectric constant $d_{33}$ of the PZT films constrained by a substrate were 200pm/V at 100kV/cm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07b
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• pp.892-895
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• 2003

This paper describes on RIE(Reactive Ion Etching) characteristics of 3C-SiC(Silicon Carbide) grown on Si(100) wafers. During RIE of 3C-SiC films in this work, $CHF_3$ gas is used to form of polymer as a side wall for excellent anisotropy etching. From this process, etch rates are obtained a $60{\sim}980{\AA}/min$ by various conditions such as $CHF_3$ gas flux, $O_2$ addition ratio, RF power and electrode distance. Also, approximately $40^{\circ}$ mesa structures are successfully formed at 100 mTorr $CHF_3$ gas flow ratio, 200 W RF power and 30 mm electrode distance. Moreover, vertical side wall is fabricated by anisotropy etching with 50% $O_2$ addition ratio and 25 mm electrode distance. Therefore, RIE of 3C-SiC films using $CHF_3$ could be applicable as fabrication process technology for high-temperature 3C-SiC MEMS applications.