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전기화학적 임피던스 Fitting 개선을 위한 전극/전해질 계면의 전기회로 모델 연구
張鍾賢(Jong-hyeon Chang),朴政浩(Jungho Pak) 대한전기학회 2007 전기학회논문지 Vol.56 No.6
Exact impedance modeling of the electrode/electrolyte interface is important in bio-signal sensing electrode development. Therefore, the investigation of the equivalent circuit models for the interface has been pursued for a long time by several researchers. Previous circuit models fit the experimental results in limited conditions such as frequency range, type of electrode, or electrolyte. This paper describes a new electrical circuit model and its capability of fitting the experimental results. The proposed model consists of three resistors and two constant phase elements. Electrochemical impedance spectroscopy was used to characterize the interface for Au, Pt, and stainless steel electrode in 0.9% NaC1 solution. Both the proposed model and the previous model were applied to fit the measured impedance results for comparison. The proposed model fits the experimental data more accurately than other models especially at the low frequency range, and it enables us to predict the impedance at very low frequency range, including DC, using the proposed model.
반도체 미세공정 기술을 이용한 Hollow형 실리콘 미세바늘 어레이의 제작
金承國(Seung Kook Kim),張鍾賢(Jong-hyeon Chang),金秉玟(Byoungmin Kim),梁翔植(Sang Sik Yang),黃仁式(In Sik Hwang),朴政浩(Jungho Pak) 대한전기학회 2007 전기학회논문지 Vol.56 No.12
Hollow-type microneedle array can be used for painless, continuous and stable drug delivery through a human skin. The needles must be sharp and have sufficient length in order to penetrate the epidermis. An array of hollow-type silicon microneedles was fabricated by using deep reactive ion etching and HNA wet etching with two oxide masks. Isotropic etching was used to create tapered tips of the needles, and anisotropic etching of Bosch process was used to make the extended length and holes of microneedles. The microneedles were formed by three steps of isotropic, anisotropic, and isotropic etching in order. The holes were made by one anisotropic etching step. The fabricated microneedles have 170 ㎛ width, 40 ㎛ hole diameter and 230 ㎛ length.
표면에너지 차이를 이용한 패키징용 솔더볼 자가정렬 및 솔더링 방법
홍장원(Jangwon Hong),장종현(Jong-hyeon Chang),박정호(Jungho Pak) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.7
This paper presents a method of self-arranging solderballs by using surface energy difference. After evaporating Au which has high surface energy on Si substrates, Teflon passivation layer which has low surface energy was patterned by lift-off process. Droplets formed only on the hydrophilic Au solderball lands by the surface energy difference, not the hydrophobic Teflon surface. Scattered solderballs sticked by themselves to the wetted solderball lands on the tilted substrate. After setting preheating of 200℃ and soldering of 245℃ hot plates, the solderballs were soldered on the solderball lands and two substrates were soldered together completely. After measuring the mechanical shear strength of the soldered substrates with solderballs of 3×3, 4×4 and 5×5 arrays. the calculated shear strength per one solderball was 1.1~2.4kgf as high as the previous report.
용존 산소 측정용 초소형 Clark-type 센서에 대한 연구
朴正鎰(Jungil Park),張鍾賢(Jong-hyeon Chang),崔溟琦(Myungki Choi),李東永(Dong-young lee),金永美(Youngmi Kim),朴政浩(Jungho Pak) 대한전기학회 2007 전기학회논문지 Vol.56 No.8
This paper presents a microfabricated Clark-type sensor which exactly can measure dissolved oxygen in the cell containing solution. We designed, fabricated, and characterized a microfabircated Clark-type oxygen sensor for measuring dissolved oxygen. The microfabricated oxygen sensor consists of 3-electrodes on a glass substrate, a FEP (Fluorinated ethylene propylene) oxygen-permeable membrane, and PDMS (Polydimethylsiloxane) reservoir for storing sample solution. Thin-film Ag/AgCI was employed as a reference electrode and its durability was verified by obtaining a stable open circuit potential for 2 hours against a commercial Ag/AgCI electrode and a stable cyclic voltammetry curve. Selectivity, response time, and linearity of the fabricated oxygen sensor were also verified well by cyclic voltammetry and amperometry depending. The fabricated oxygen sensor showed a 90% response time of 40sec and an excellent linearity with a correlation coefficient of 0.994.
효율적인 소수성 표면 처리를 위한 Teflon 스핀코팅 특성 분석
최대영(Dae Young Choi),장종현(Jong-hyeon Chang),박정호(Jungho Pak) 대한전기학회 2010 대한전기학회 학술대회 논문집 Vol.2010 No.7
This paper presents Teflon spin-coating conditions and their characteristics for efficient hydrophobic surface treatment. In order to deposit Teflon thin films on each Si substrate, Teflon-AF was diluted in a fluorocarbon solvent of FC-40 to 0.1, 0.2, 0.3, and 0.6 wt% concentration, and each diluted Teflon solution was spin-coated for 30 sec with various spin speeds of 1000, 2000, and 4000 rpm. Then the samples were baked at 200℃ for 30 min. The Teflon thickness and water contact angle on each Teflon surface were measured. As the result, 0.2 wt% Teflon was appropriate and the thickness should be higher than 9 nm for efficient hydrophobic surface treatment. These results may be applicable to electrowetting devices as the hydrophobic surface treatment for improving the electrowetting efficiency.