• Journal of Korean Society on Water Environment
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• v.38 no.2
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• pp.103-112
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• 2022

A gold amalgam voltammetric microelectrode (GAVM) system was developed for the quantification of dissolved biogeochemical species, such as O₂, Fe²⁺, Mn²⁺, and HS^- in sediment porewater. Commercially available Ag/AgCl and platinum electrodes were used as the reference and counter electrode, respectively, and a gold amalgam microelectrode was fabricated in the laboratory using 150-um diameter gold wire and a borosilicate capillary tube with a 1.6-mm diameter. A portable potentiostat (Metrohm, DropSens) was used for the application of voltage sweeping and to acquire the electric current. For sediment profiling, a commercially available actuator was customized and modified. The analysis method used in the system used the most widely used analysis method among the electrochemical analysis currently used The GAVM system was successively calibrated with the species and applied to estuarine sediments. The porewater analysis showed that the oxygen concentration was decreased to zero at a depth of 0.6 mm, and maximum Mn²⁺ and Fe²⁺ concentrations of 50 uM and 20 uM were detected at 2 and 3-cm depths, respectively. Maximum HS^- concentrations of 10 uM were detected at 4 cm in the deeper sediments. The GAVM system was successfully developed and applied to the sediment and can be used to better understand biogeochemical reactions.

• The Korean Journal of Physiology
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• v.24 no.1
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• pp.39-49
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• 1990

It has been reported that bombesin induces contraction of the smooth muscle of the gastrointestinal tract. Thus, the present investigation was undertaken to see an influence of bombesin on electrical activity of the gastric smooth muscle, since electrical activity is associated with contractile activity in the smooth muscle of the stomach. Smooth muscle strips $(5\;{\times}\;1.5\;cm)$ that included the corpus and antrum were prepared from the ventral and dorsal portion of the feline stomach along the greater curvature. Circular muscle strips $(1\;{\times}\;0.3\;cm)$ of the corpus were also obtained. Electrical activity of the corpus and antrum of the muscle strip was monophasically recorded by using Ag-AgCl capillary electrodes placed on the circular muscle layer. Contractile activity of the circular muscle strip was also recorded. The recordings were performed in Krebs-Ringer solution that was continuously aerated with $O_{2}$ containing 5% $Co_{2}$, and kept at $36^{\circ}C$. Dose-related responses of electrical activity and contractility to bombesin was studied after frequency of slow waves and contraction of each strip reached to a steady state. An action of $D-leu^{13}-{\psi}\;(CH_{2}NH)-D-leu^{14}-bombesin,\;D-pro^{2}-D-trp^{7,9}-substance\;P$, tetrodotoxin, hexamethonium, atropine, phentolamine or propranolol on the effect of bombesin was also observed. 1) Bombesin increased frequency of slow waves and contractions dose-dependently at concentrations from $10^{-9}\;M\;to\;3\;{\times}\;10^{-8}\;M$. 2) The bombesin analogue at a concentration of $3\;{\times}\;10^{-7}\;M$ antagonized the effect of bombesin on frequency of slow waves. 3) The effect of bombesin on frequency of slow waves was inhibited by tetrodotoxin $(10^{-6}\;M)$ and hexamethonium $(10^{-3}\;M)$ but unaffected by atropine $(10^{-6}\;M)$, phentolamine $(10^{-5}\;M)$ and propranolol $(10^{-5}\;M)$. 4) The effect of bombesin on frequency of slow waves was blocked by the substance P analogue at a concentration of $10^{-5}\;M$. 5) Substance P at a concentration of $10^{-5}\;M$ failed to change frequency of slow waves. It is concluded from the above results that bombesin increases the frequency of slow waves as well as contractions of the smooth muscle strip from the feline stomach, and the effect of bombesin might be mediated by non-cholinergic or non-adrenergic mechanism at neuromuscular junction. However, enteric nerves that have substance P as a neurotransmitter do not appear to participate in the action of bombesin on frequency of slow waves.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.245-245
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• 2012

차세대 디스플레이로 각광받고 있는 AMOLED에 대한 관심이 높아짐에 따라 구동 소자의 연구가 활발히 이루어지고 있다. 산화물 반도체 박막 트랜지스터는 비정질 실리콘 박막 트랜지스터에 비해 100 $cm^2$/Vs 이하의 높은 이동도와 우수한 전기적 특성으로 AMOLED 구동 소자로서 학계에서 입증되어왔고, 현재 여러 기업에서 산화물 반도체를 이용한 박막 트랜지스터 제작 연구가 활발히 이루어지고 있다. 본 연구는 열처리 조건을 가변하여 제작한 산화물 반도체 박막 트랜지스터의 전기적 특성 분석을 목적으로 한다. 실리콘 기판에 oxidation 공정을 이용하여 SiO2 100 nm, DC스퍼터링을 이용하여 ITZO (Indium-Tin-Zinc Oxide) 산화물 반도체 박막 50 nm, 증착된 산화물 반도체 박막의 열처리 후, evaporation을 이용하여 source/drain 전극 Ag 150 nm 증착하여 박막 트랜지스터를 제작하였다. 12 sccm의 산소유량, 1시간의 열처리 시간에서 열처리 온도 $400^{\circ}C$, $200^{\circ}C$의 샘플은 각각 이동도 $29.52cm^2/V{\cdot}s$, $16.15cm^2/V{\cdot}s$, 문턱전압 2.61 V, 6.14 V, $S{\cdot}S$ 0.37 V/decade, 0.85 V/decade, on-off ratio 5.21 E+07, 1.10 E+07이었다. 30 sccm의 산소유량, 열처리 온도 $200^{\circ}C$에서 열처리 시간 1시간, 1시간 30분 샘플은 각각 이동도 $12.27cm^2/V{\cdot}s$, $10.15cm^2/V{\cdot}s$, 문턱전압 8.07 V, 4.21 V, $S{\cdot}S$ 0.89 V/decade, 0.71 V/decade, on-off ratio 4.31 E+06, 1.05 E+07이었다. 산화물 반도체의 열처리 효과 분석을 통하여 높은 열처리 온도, 적은 산소의 유량, 열처리 시간이 길수록 이동도, 문턱전압, $S{\cdot}S$의 산화물 박막 트랜지스터 소자의 전기적 특성이 개선되었다.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.25 no.12
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• pp.1015-1020
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• 2012

Resistance of the front electrode is the highest proportion of the ingredients of the series resistance in crystalline silicon solar cell. While resistance of the front electrode is decreased with larger area, it induces the optical loss, causing the conversion efficiency drop. Therefore the front electrode with high aspect ratio increasing its height and decreasing is necessary for high-efficiency solar cell in considering shadowing loss and resistance of front electrode. In this paper, we used the screen printing method to form high aspect ratio electrode by multiple printing. Screen printing is the straightforward technology to establish the electrodes in silicon solar cell fabrication. The several printed front electrodes with Ag paste on silicon wafer showed the significantly increased height and slightly widen finger. As a result, the resistance of the front electrode was decreased with multiple printing even if it slightly increased the shadowing loss. We showed the improved electrical characteristics for c-Si solar cell with repeatedly printed front electrode by 0.5%. It lays a foundation for high efficiency solar cell with high aspect ratio electrode using screen printing.

• Current Photovoltaic Research
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• v.2 no.4
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• pp.173-176
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• 2014

We have investigated the seed layer formation of front side contact using the inkjet printing process. Conductive silver ink was printed on textured Si wafers with 80 nm thick $SiN_x$ anti reflection coating (ARC) layers and thickened by light induced plating (LIP). The inkjet printable sliver inks were specifically formulated for inkjet printing on these substrates. Also, a novel method to prepare nano-sized glass frits by the sol-gel process with particle sizes around 5 nm is presented. Furthermore, dispersion stability of the formulated ink was measured using a Turbiscan. By implementing these glass frits, it was found that a continuous and uniform seed layer with a line width of $40{\mu}m$ could be formed by a inkjet printing process. We also investigated the contact resistance between the front contact and emitter using the transfer length model (TLM). On an emitter with the sheet resistance of $60{\Omega}/sq$, a specific contact resistance (${\rho}_c$) below $10m{\Omega}{\cdot}cm^2$ could be achieved at a peak firing temperature around $700^{\circ}C$. In addition, the correlation between the contact resistance and interface microstructures were studied using scanning electron microscopy (SEM). We found that the added glass particles act as a very effective fire through agent, and Ag crystallites are formed along the interface glass layer.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.6
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• pp.410-415
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• 1999

$Ba_{1-x}Sr_xTiO_3$ thin films with various ratio of Sr (X = 0.4, 0.5, 0.6) were grown $Pt/TiN/SiO_2/Si$ subastrate by RF magnetron sputtering deposition. As, Ag, and Cu films were deposited on $Ba_{1-x}Sr_xTiO_3$ thin films as top electrodes by using a thermal evaporator. The electrical properties of $Ba_{1-x}Sr_xTiO_3$ thin films for various compositions were characterized and the physical properties at interface between $Ba_{1-x}Sr_xTiO_3$ thin films and top electrodes were evaluated in terms of the work function difference. At x =0.5, the degradation of capacitance is lower to the other compositions. As negative biasapplied, the specimen with Cu top electrode has board saturation region and low leakage current since work function of Cu is bigger than other electrodes.$ Ba_{0.5}Sr_{0.5}TiO_3$ thin films with Cu top electrode, the dielectric constant was measured to the value of 354 at 1 kHz and the leakage current was obtained to the value of $5.26\times10^{-6}A/cm2$ at the forward bias of 2 V.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.373-375
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• 2011

최근 태양전지 연구에서 저가격화를 실현하는 방법 중 하나로 폐 실리콘 웨이퍼를 재생하는 방법에 관하여 많은 연구가 진행되고 있다. 그러나 기존 웨이퍼 재생공정은 높은 재처리 비용과 복잡한 공정등의 많은 단점을 가지고 있다. 결정형 태양전지에서 저가격화 및 고효율은 태양전지를 제작하는데 있어 필수 요소 이다. 그 중 결정질 태양전지 고효율을 위한 여러 연구 방법 중 표면 텍스쳐링(texturing)에 관한 연구가 활발하다. 텍스쳐링은 표면반사에 의한 광 손실을 최소화 하여 효율을 증가시키기 위한 방법으로 습식 식각과 건식 식각을 사용하여 태양전지 표면 위에 요철 및 피라미드구조를 형성하여 반사율을 최소화 시킨다. 건식식각은 습식식각과 다른 환경적 오염이 적은 것과 소량의 가스만으로 표면 텍스쳐링이 가능하여 많은 연구가 진행중이다. 건식 식각 중 하나인 RIE(reactive ion etching)는 고주파를 이용하여 플라즈마의 이온과 silicon을 반응 시킨다. 실험은 RIE를 이용하여 SF6/02가스를 혼합하여 비등방성 에칭 및 피라미드 구조를 구현하였다. RIE 공정 중 SF6/02가스는 높은 식각 율을 갖으며 self-masking mechanism을 통해 표면이 검게 변화되고 반사율이 감소하게 된다. 이 과정을 통해 블랙 실리콘을 형성하게 된다. 블랙 실리콘은 반사율 10% 이하로 self-masking mechanism으로 바늘모양의 구조를 형성되는 게 특징이며 표면이 검은색으로 반사율이 낮아 효율증가로 예상되지만 실제 바늘 모양의 블랙 실리콘은 태양전지 제작에 있어 후속 공정 인 전극 형성 시 Ag Paste의 사이즈와 표면 구조를 감안할 때 태양 전지 제작 시 Series resistance를 증가로 효율 저하를 가져온다. 본 연구는 SF6/02가스를 혼합하여 기존 RIE로 형성된 바늘모양의 구조의 블랙 실리콘이 아닌 RIE 내부에 metal-mesh를 장착하여 단결정(100)실리콘 웨이퍼 표면을 텍스쳐링 하였고 SF6/02 가스 1:1 비율로 공정을 진행 하였다. metal-mesh 홀의 크기는 100um로 RIE 내부에 장착하여 공정 시간 및 Pressure를 변경하여 실험을 진행하였다. 공정 시간이 변경됨에 따라 단결정(100) 실리콘 웨이퍼 표면에 피라미드 구조의 균일한 1um 크기의 블랙 실리콘을 구현하였다. 바늘모양의 블랙 실리콘을 피라미드 구조로 구현함으로써 바늘 모양의 단점을 보완하여 태양전지 전기적 특성을 분석하여 태양전지 제작시 변환 효율을 증가시킬 것으로 예상된다.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2018.06a
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• pp.81-81
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• 2018

Bi-Te계 열전소자는 상온에서의 열전 효율이 우수하기 때문에 항공, 컴퓨터 등의 열전발전 또는 열전냉각 모듈에 널리 사용된다. 이 열전소자를 활용한 열전모듈은 다수의 n형 및 p형 열전소자가 세라믹 위에 형성된 Cu 전극에 전기적으로 직렬이 되도록 서로 솔더링 접합이 되어 있는 구조를 가지고 있다. 이처럼 직렬 연결된 방식에서는 높은 접합강도를 필요로 한다. 열전모듈 제작 시 Bi-Te 계 소자를 바로 Cu 기판에 접합시키면 솔더에 들어있는 Sn과 기판의 Cu가 접합하는 과정에서 소재 내로 확산하여 접합강도를 저하시킨다. 이러한 열전모듈의 접합강도 저하를 막기 위해 무전해 Ni-W-P 도금층을 확산 방지층으로 적용하였다. 본 연구에서는 Ni-W-P 도금이 Bi-Te 계 열전 모듈의 접합강도에 미치는 영향을 조사하였다. 본 연구에서는 Bi-Te계 열전소자에 양호한 밀착성을 가지는 Ni-W-P 도금층을 형성시키기 위해서 알루미나 분말을 이용한 sand-blasting 방법을 사용하여 Bi-Te 소재 표면에 분사하는 방법으로 표면을 거칠게 하였다. 그 후 무전해 Ni-W-P 도금을 $85^{\circ}C$에서 20분간 실시하여 약 4um의 Ni-W-P 도금층을 형성시켰다. 열전 모듈은 Sn-Ag-Cu 솔더를 사용하여 제작하였으며 접합강도는 Bonding tester를 사용하여 측정하였다. 제작한 열전 모듈의 단면 및 파단면 관찰을 통하여 접합강도가 변하는 요인을 조사하였다. 제작한 열전 모듈의 단면을 FE-EPMA로 관찰한 결과 Ni-W-P 도금층이 Bi-Te 소자와 Sn과 Cu사이의 확산을 방지하는 확산방지층 역할을 하는 것을 관찰할 수 있었다. 또한 열처리 전 열전모듈과 200도, 150시간 열처리 후 접합강도를 각각 측정해 본 결과, 열처리 후의 접합강도가 상승하는 것을 확인 할 수 있었다. 따라서 Bi-Te계 열전모듈 제작에 무전해 Ni-W-P 도금층을 형성시키므로 인해 확산방지층의 생성과 접합강도의 상승에 도움을 주었다.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.49 no.2
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• pp.107-112
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• 2000

$(Sr_{0.85}Ca_{0.15})TiO_3$(SCT) thin films were deposited on Pt-coated $TiO_2/SiO_2/Si$ wafer by the rf sputtering method. Experiments were conducted to investigate the electrical properties of SCT thin films with various top electrodes. Various top electrodes as Pt, Al, Ag, Cu were deposited on SCT thin films by sputter and thermal evaporator. The characteristics of C-F and C-V of SCT thin films were not obviously varied with various top electrodes, SCT thin films annealed at $600^{\circ}C$ represents as favorable capacitance characteristics than SCT thin films not annealed, and Pt top electrode have the most high capacitance. The characteristic of I-V of SCT thin films showed that Pt top electrode revealed more less leakage current density than other electrodes, had a leakage current density below 10-8$[A/cm^2]$ until 25[V] applied voltage.

• Korean Journal of Materials Research
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• v.20 no.8
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• pp.401-407
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• 2010

We studied the influence of different types of metal electrodes on the performance of solution-processed zinc tin oxide (ZTO) thin-film transistors. The ZTO thin-film was obtained by spin-coating the sol-gel solution made from zinc acetate and tin acetate dissolved in 2-methoxyethanol. Various metals, Al, Au, Ag and Cu, were used to make contacts with the solution-deposited ZTO layers by selective deposition through a metal shadow mask. Contact resistance between the metal electrode and the semiconductor was obtained by a transmission line method (TLM). The device based on an Al electrode exhibited superior performance as compared to those based on other metals. Kelvin probe force microscopy (KPFM) allowed us to measure the work function of the oxide semiconductor to understand the variation of the device performance as a function of the types metal electrode. The solution-processed ZTO contained nanopores that resulted from the burnout of the organic species during the annealing. This different surface structure associated with the solution-processed ZTO gave a rise to a different work function value as compared to the vacuum-deposited counterpart. More oxygen could be adsorbed on the nanoporous solution-processed ZTO with large accessible surface areas, which increased its work function. This observation explained why the solution-processed ZTO makes an ohmic contact with the Al electrode.