• Korean Journal of Materials Research
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• v.30 no.4
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• pp.204-210
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• 2020

ZnO thin films are of considerable interest because they can be customized by various coating technologies to have high electrical conductivity and high visible light transmittance. Therefore, ZnO thin films can be applied to various optoelectronic device applications such as transparent conducting thin films, solar cells and displays. In this study, ZnO rod and thin films are fabricated using aqueous chemical bath deposition (CBD), which is a low-cost method at low temperatures, and environmentally friendly. To investigate the structural, electrical and optical properties of ZnO for the presence of citrate ion, which can significantly affect crystal form of ZnO, various amounts of the citrate ion are added to the aqueous CBD ZnO reaction bath. As a result, ZnO crystals show a nanorod form without citrate, but a continuous thin film when citrate is above a certain concentration. In addition, as the citrate concentration increases, the electrical conductivity of the ZnO thin films increases, and is almost unchanged above a certain citrate concentration. Cu(In,Ga)Se₂ (CIGS) solar cell substrates are used to evaluate whether aqueous CBD ZnO thin films can be applicable to real devices. The performance of aqueous CBD ZnO thin films shows performance similar to that of a sputter-deposited ZnO:Al thin film as top transparent electrodes of CIGS solar cells.

• Journal of the Microelectronics and Packaging Society
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• v.27 no.3
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• pp.49-54
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• 2020

To attach a stretchable/flexible electrode to something or something to on electrode, conductive adhesives must be stretchable/flexible to suit the properties of the electrode. In particular, conductive adhesive require durability and heat resistance, and unlike conventional adhesives, they should also have conductivity. To this end, Epoxy, which has good strength and adhesion, was selected as an adhesive, and a plasticizer and a reinforcement were mixed instead of a two-liquid material consisting of a conventional theme and a hardener, and a four-liquid material was used to give stretchability/flexibility to high molecules. The conductive filler was selected as silver, a material with low resistance, and for high conductivity, three shapes of Ag particles were used to increase packing density. Conductivity was compared with these developed conductive adhesives and two epoxy-based conductive adhesives being sold in practice, and about 10 times better conductivity results were obtained than products being actually sold. In addition, conductivity, mechanical properties, adhesion and strength were evaluated according to the presence of plasticizers and reinforcement agent. There was also no problem with 60% tensile after 5 minutes of curing at 120℃, and pencil hardness was excellently measured at 6H. As a result of checking the adhesion of electrodes through 3M tape test, all of them showed excellent results regardless of the mixing ratio of binders. After attaching the Cu sheet on top of the electrode through conductive adhesive, the contact resistance was checked and showed excellent performance with 0.3 Ω.

• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.50-59
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• 2007

The advent of towed geo-electrical array surveying on water and land has resulted in datasets of magnitude approaching that of airborne electromagnetic surveying and most suited to 1D inversion. Robustness and complete automation is essential if processing and reliable interpretation of such data is to be viable. Sharp boundaries such as river beds and the top of saline aquifers must be resolved so use of smoothness constraints must be minimised. Suitable inversion algorithms must intelligently handle low signal-to-noise ratio data if conductive basement, that attenuates signal, is not to be misrepresented. A noise-level aware inversion algorithm that operates with one elastic thickness layer per electrode configuration has been coded. The noise-level aware inversion identifies if conductive basement has attenuated signal levels so that they are below noise level, and models conductive basement where appropriate. Layers in the initial models are distributed to span the effective depths of each of the geo-electric array quadrupoles. The algorithm works optimally on data collected using geo-electric arrays with an approximately exponential distribution of quadrupole effective depths. Inversion of data from arrays with linear electrodes, used to reduce contact resistance, and capacitive-line antennae is plausible. This paper demonstrates the effectiveness of the algorithm using theoretical examples and an example from a salt interception scheme on the Murray River, Australia.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.6
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• pp.65-71
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• 2019

Conventional methods of measuring ground resistance and ground resistance field measurement are used to measure voltage drop according to the resistance value of the site by applying current by installing a constant interval of measurement electrode. If the stratified structure of the site site is unique, errors in boundary conditions will occur in the event of back acid and the analysis of the critical ground resistance in the ground design will show much difference from simulation. This study utilizes the Arduino module and smart ground measurement technology in the convergent information and communication environment to develop a reliable smart land resistance measuring device even if the top layer of land is unique, to analyze the land resistance and accumulate data to predict the change in the age of the land. Considering the topographical characteristics of the site, we propose a ground resistance measuring device and its method of measuring ground resistance so that the auxiliary electrode can be installed by correctly positioning the angle and distance in measuring ground resistance. Not only is ground resistance value obtained through electrodes installed to allow accurate ground resistance values to be selected, but it can also be used as a useful material for installing electrical facilities in similar areas. Moreover, by utilizing reliable data and analyzing the large sections of the site, a precise analysis of the site, which is important in ground design as well as construction cost, is expected to be used much in ground facility design such as potential rise.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.348-348
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• 2011

Carbon nanotube (CNT) field effect transistors and sensors use CNT as a current channel, of which the resistance varies with the gate voltage or upon molecule adsorption. Since the performance of CNT devices depends very much on the CNT/metal contact resistance, the CNT/electrode contact must be stable and the contact resistance must be small. Depending on the geometry of CNT/electrode contact, it can be categorized into the end-contact, embedded-contact (top-contact), and side-contact (bottom-contact). Because of difficulties in the sample preparation, the end-contact CNT device is seldom practiced. The embedded-contact in which CNT is embedded inside the electrode is desirable due to its rigidness and the low contact resistance. Fabrication of this structure is complicated, however, because each CNT has to be located under a high-resolution microscope and then the electrode is patterned by electron beam lithography. The side-contact is done by depositing CNT electrophoretically or by precipitating on the patterned electrode. Although this contact is fragile and the contact resistance is relatively high, the side-contact by far has been widely practiced because of its simple fabrication process. Here we introduce a simple method to embed CNT inside the electrode while taking advantage of the bottom-contact process. The idea is to utilize a eutectic material as an electrode, which melts at low temperature so that CNT is not damaged while annealing to melt the electrode to embed CNT. The lowering of CNT/Au contact resistance upon annealing at mild temperature has been reported, but the electrode in these studies did not melt and CNT laid on the surface of electrode even after annealing. In our experiment, we used a eutectic Au/Al film that melts at 250$^{\circ}C$. After depositing CNT on the electrode made of an Au/Al thin film, we annealed the sample at 250$^{\circ}C$ in air to induce eutectic melting. As a result, Au-Al alloy grains formed, under which the CNT was embedded to produce a rigid and low resistance contact. The embedded CNT contact was as strong as to tolerate the ultrasonic agitation for 90 s and the current-voltage measurement indicated that the contact resistance was lowered by a factor of 4. By performing standard fabrication process on this CNT-deposited substrate to add another pair of electrodes bridged by CNT in perpendicular direction, we could fabricate a CNT cross junction. Finally, we could conclude that the eutectic alloy electrode is valid for CNT sensors by examine the detection of Au ion which is spontaneously reduced to CNT surface. The device sustatined strong washing process and maintained its detection ability.

• Journal of the Korean Magnetics Society
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• v.17 no.4
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• pp.156-161
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• 2007

To develop array magnetic sensors, specular-type giant magnetoresistive- spin valve (GMR-SV) film of Glass/Ta(5)MiFe(7)/IrMn(10)NiFe(5)/$O_2$/CoFe(5)/Cu(2.6)/CoFe(5)/$O_2$/NiFe(7)/Ta(5)(nm) was deposited by using a high-vacuum sputtering system. One of 15 way sensors in the area of $8{\times}8mm^2$ was Patterned a size of $20{\times}80{\mu}m^2$ in multilayer sample by Photo-lithography. All of 15 sensors with Cu electrodes were measured a uniform magnetic properties by 2-probe method. The highest magnetic sensitivity of MR and output voltage measured nearby an external magnetic field of 5 Oe were MS = 0.5%/Oe and ${\triangle}$V= 3.0 mV, respectively. An easy-axis of top-free layers of $CoFe/O_2/NiFe$ with shape anisotropy was perpendicular to one of bottom-pinned layers $IrMn/NiFe/O_2/CoFe$. When the sensing current increased from 1 mA to 10 mA, the output working voltage uniformly increased and the magnetic sensitivity was almost stable to use the nano-magnetic devices with good sensitive properties.

• Journal of the Korean Magnetics Society
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• v.10 no.4
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• pp.159-163
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• 2000

MR characteristics in magnetic tunnel junction using CoO as the oxide barrier were investigated. Spin-dependent tunnel junctions were fabricated on 4$\^$o/ tilt-cut (111)Si substrates in 3-gun magnetron sputtering system. The top and bottom ferromagnetic electrodes were Ni$\_$80/Fe$\_$20/(300 $\AA$) and Co(300 $\AA$), respectively. The oxide barriers (CoO) were formed by the thermal oxidation at room temperature in an O$_2$ atmosphere and the plasma oxidation. The increase of coercive field due to antiferromagnetic-ferromagnetic coupling has been observed in O$_2$plasma-oxidized CoO based junctions at room temperature. At a sensing current of 1 mA, MR ratios of O$_2$plasma-oxidized CoO based junction and thermal-oxidized CoO based junction at room temperature were 1% and 5%, respectively. Larger MR ratios are observed in magnetic tunnel juctions with thermal oxidized CoO when sensing current more than applied 1.5 mA. At a sensing current of 1.5 mA, we have observed MR value of 28 % and specific resistance (RA=R$\times$A) value of 10.9 ㏀$\times$㎛$^2$. When specific resistance values reached 2.28 ㏀$\times$㎛$^2$, we have observed that MR ratios become as high as 120%.

• Korean Journal of Materials Research
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• v.10 no.10
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• pp.684-690
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• 2000

In order to study effects of interfacial layers between $Pb(Zr,Til)Q_3(PZT)$ films and electrodes for Metal-Ferroelectric-MetaI(MFM) structure capacitors, we have fabricated the capacitors with the Pt/PZT/interfacial-layer/Pt/$TiO_2/SiO_2$/Si structure. $PbTiO_3(PT)$ interfacial layers were formed by sol-gel deposition and PbO, ZrO, and $TiO_2$ thin layers were deposited by reactive sputtering. $TiO_2$ interface layers result in the finest grains of PZT(crystalline Temp. $600^{\circ}C$) films compare to $PbO_2\;and\;ZrO_2$ layers. However, as the thickness of $TiO_2$ layer increases. PZT thin films become rough and electrical characteristics were deteriorated due to remained anatase phase. On the other hand. PT interface layers result in improved morphology of PZT films and do not significantly change ferroelectric properties. It is a also observed that seed layers at the middle and top of PZT films do not give significant effects on grain size but the PT seed layer at the interface between the bottom electrode and the PZT films results in the small grain size.

• Geophysics and Geophysical Exploration
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• v.11 no.1
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• pp.52-59
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• 2008

We have developed a new deep-towed marine DC resistivity survey system. It was designed to detect the top boundary of the methane hydrate zone, which is not imaged well by seismic reflection surveys. Our system, with a transmitter and a 160-m-long tail with eight source electrodes and a receiver dipole, is towed from a research vessel near the seafloor. Numerical calculations show that our marine DC resistivity survey system can effectively image the top surface of the methane hydrate layer. A survey was carried out off Joetsu, in the Japan Sea, where outcrops of methane hydrate are observed. We successfully obtained DC resistivity data along a profile ${\sim}3.5\;km$ long, and detected relatively high apparent resistivity values. Particularly in areas with methane hydrate exposure, anomalously high apparent resistivity was observed, and we interpret these high apparent resistivities to be due to the methane hydrate zone below the seafloor. Marine DC resistivity surveys will be a new tool to image sub-seafloor structures within methane hydrate zones.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.100-101
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• 2012

The plasma damage free and room temperature processedthin film deposition technology is essential for realization of various next generation organic microelectronic devices such as flexible AMOLED display, flexible OLED lighting, and organic photovoltaic cells because characteristics of fragile organic materials in the plasma process and low glass transition temperatures (Tg) of polymer substrate. In case of directly deposition of metal oxide thin films (including transparent conductive oxide (TCO) and amorphous oxide semiconductor (AOS)) on the organic layers, plasma damages against to the organic materials is fatal. This damage is believed to be originated mainly from high energy energetic particles during the sputtering process such as negative oxygen ions, reflected neutrals by reflection of plasma background gas at the target surface, sputtered atoms, bulk plasma ions, and secondary electrons. To solve this problem, we developed the NBAS (Neutral Beam Assisted Sputtering) process as a plasma damage free and room temperature processed sputtering technology. As a result, electro-optical properties of NBAS processed ITO thin film showed resistivity of $4.0{\times}10^{-4}{\Omega}{\cdot}m$ and high transmittance (>90% at 550 nm) with nano- crystalline structure at room temperature process. Furthermore, in the experiment result of directly deposition of TCO top anode on the inverted structure OLED cell, it is verified that NBAS TCO deposition process does not damages to the underlying organic layers. In case of deposition of transparent conductive oxide (TCO) thin film on the plastic polymer substrate, the room temperature processed sputtering coating of high quality TCO thin film is required. During the sputtering process with higher density plasma, the energetic particles contribute self supplying of activation & crystallization energy without any additional heating and post-annealing and forminga high quality TCO thin film. However, negative oxygen ions which generated from sputteringtarget surface by electron attachment are accelerated to high energy by induced cathode self-bias. Thus the high energy negative oxygen ions can lead to critical physical bombardment damages to forming oxide thin film and this effect does not recover in room temperature process without post thermal annealing. To salve the inherent limitation of plasma sputtering, we have been developed the Magnetic Field Shielded Sputtering (MFSS) process as the high quality oxide thin film deposition process at room temperature. The MFSS process is effectively eliminate or suppress the negative oxygen ions bombardment damage by the plasma limiter which composed permanent magnet array. As a result, electro-optical properties of MFSS processed ITO thin film (resistivity $3.9{\times}10^{-4}{\Omega}{\cdot}cm$, transmittance 95% at 550 nm) have approachedthose of a high temperature DC magnetron sputtering (DMS) ITO thin film were. Also, AOS (a-IGZO) TFTs fabricated by MFSS process without higher temperature post annealing showed very comparable electrical performance with those by DMS process with $400^{\circ}C$ post annealing. They are important to note that the bombardment of a negative oxygen ion which is accelerated by dc self-bias during rf sputtering could degrade the electrical performance of ITO electrodes and a-IGZO TFTs. Finally, we found that reduction of damage from the high energy negative oxygen ions bombardment drives improvement of crystalline structure in the ITO thin film and suppression of the sub-gab states in a-IGZO semiconductor thin film. For realization of organic flexible electronic devices based on plastic substrates, gas barrier coatings are required to prevent the permeation of water and oxygen because organic materials are highly susceptible to water and oxygen. In particular, high efficiency flexible AMOLEDs needs an extremely low water vapor transition rate (WVTR) of $1{\times}10^{-6}gm^{-2}day^{-1}$. The key factor in high quality inorganic gas barrier formation for achieving the very low WVTR required (under ${\sim}10^{-6}gm^{-2}day^{-1}$) is the suppression of nano-sized defect sites and gas diffusion pathways among the grain boundaries. For formation of high quality single inorganic gas barrier layer, we developed high density nano-structured Al2O3 single gas barrier layer usinga NBAS process. The NBAS process can continuously change crystalline structures from an amorphous phase to a nano- crystalline phase with various grain sizes in a single inorganic thin film. As a result, the water vapor transmission rates (WVTR) of the NBAS processed $Al_2O_3$ gas barrier film have improved order of magnitude compared with that of conventional $Al_2O_3$ layers made by the RF magnetron sputteringprocess under the same sputtering conditions; the WVTR of the NBAS processed $Al_2O_3$ gas barrier film was about $5{\times}10^{-6}g/m^2/day$ by just single layer.