• Journal of Biomedical Engineering Research
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• v.36 no.6
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• pp.283-290
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• 2015

We proposed blink based online speller for the locked-in syndrome (LIS) patients, paralyzed in nearly all voluntary muscles expect for the eyes, with a simple and easy-to-use eye blink detection glasses. Electrooculogram (EOG) is the golden standard method of eye movement or blink measurement with Ag/AgCl electrodes. However, this method has several drawbacks such as skin irritation and dehydration of conductive gel. To resolve the shortcomings, we used a blink detection system based on a transparent capacitively coupled electrode, which is conductive indium tin oxide (ITO) films. The films make it possible to measure eye blink without direct skin contact and obstruction of field of view. We finally developed user-friendly blink based online speller with the blink detection system. To classify voluntary and non-voluntary blink, we used the double blink for command of the speller. The online speller experiment result with six healthy subjects shows that mean accuracy is 98.96% and letter per minute (LPM) is 4.73, which are better result by comparison with conventional P300 or auditory brain-computer interface (BCI) paradigm. The result of the experiment demonstrates the possibility of applying the proposed system as a communication method for the LIS patients.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.235.2-235.2
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• 2015

The front transparent conductive oxide (TCO) films must exhibit good transparency, low resistivity and excellent light scattering properties for high efficiency amorphous silicon (a-Si) thin film solar cells. The light trapping phenomenon is limited due to non-uniform and low aspect ratio of the textured glass [1]. We present the low cost electrochemically deposited uniform zinc oxide (ZnO) nanorods with various aspect ratios for a-Si thin film solar cells. Since the major drawback of the electrochemically deposited ZnO nanorods was the high sheet resistance and low transmittance that was overcome by depositing the RF magnetron sputtered AZO films as a seed layer with various thicknesses [2]. The length and diameters of the ZnO nanorods was controlled by varying the deposition conditions. The length of ZnO nanorods were varied from 400 nm to $2{\mu}m$ while diameter was kept higher than 200 nm to obtain different aspect ratios. The uniform ZnO nanorods showed higher haze ratio as compared to the commercially available FTO films. We also observed that the scattering in the longer wavelength region was favored for the high aspect ratio of ZnO nanorods and much higher aspect ratios degraded the light scattering phenomenon. Therefore, we proposed our low cost and uniform ZnO nanorods for the high efficiency of thin film solar cells.

• Journal of Sensor Science and Technology
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• v.30 no.4
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• pp.229-235
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• 2021

This study presents a simple approach for the assembly of a free-standing conductive electronic nanofilm of single-walled carbon nanotubes (SWNTs) suitable for enzymatic electrochemical biosensors. A large-scale SWNT electronic film was successfully produced by the dialysis of p-Terphenyl-4,4''-dithiol (TPDT)-treated SWNTs. Furthermore, Horseradish peroxidase (HRP) was immobilized on the TPDT-SWNT electronic film, and the enzymatic detection of hydrogen peroxide (H₂O₂) was demonstrated without mediators. The detection of H₂O₂ in the negative potential range (-0.4 V vs. Ag/AgCl) was achieved by direct electron transfer of heme-based enzymes that were immobilized on the TPDT-SWNT electronic film. The SWNT-based biosensor exhibited a wide detection range of H₂O₂ from 10 µM to 10 mM. The HRP-doped SWNT electronic film achieved a high sensitivity of 342 ㎛A/mM·cm² and excellent selectivity against a variety of redox-active interfering substances, such as ascorbic acid, uric acid, and acetaminophen.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.03b
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• pp.20-20
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• 2010

We present a simple process for the fabrication of high performance transparent conducting films that contain single-walled carbon nanotubes (SWCNTs) noncovalently coated with an ultrathin titania layer. The hydrophobic interactions between nanotube surfaces and the acetylacetone (acac) ligands used to stabilize the $TiO_2$ precursor provide an interesting alternative method for noncovalently coating the SWCNTs with a titania layer. The ultrathin titania layer on SWCNTs prevented the oxidation of functionalized SWCNTs at high temperatures, and protected against water molecule absorption.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.279-279
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• 2010

We present a simple process for the fabrication of high performance transparent conducting films that contain single-walled carbon nanotubes (SWCNTs) noncovalently coated with an ultrathin titania layer. The hydrophobic interactions between nanotube surfaces and the acetylacetone (acac) ligands used to stabilize the $TiO_2$ precursor provide an interesting alternative method for noncovalently coating the SWCNTs with a titania layer. The ultrathin titania layer on SWCNTs prevented the oxidation of functionalized SWCNTs at high temperatures, and protected against water molecule absorption.

• Analytical Science and Technology
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• v.15 no.3
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• pp.236-242
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• 2002

A method was investigated to determine the thickness of coating on steel sheet using rf glow discharge atomic emission spectrometer. The RF gas-jet boosted glow discharge has such salient feature as good pleasure stability and high sputtering efficiency that it was possible to determine the thickness of silicon resin film on zinc electroplated steel. The erosion speed variation is dependent on discharge power, gas flow rate and discharge pressure. therefore determine discharge condition to measure the thickness of coating on steels. The fundamental studies have been carried out to investigate an optimum condition for in-depth analysis and composition of zinc coating on steel. In this study, the calibration curve for thickness determination of silicon resin film was found to be linear in the range of $1000{\sim}3500mg/m^2$ film thickness. The developed rf gas-jet boosted glow discharge was applied to the analysis of zinc coating and silicon resin film on steel made by RIST.

• Korean Chemical Engineering Research
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• v.54 no.1
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• pp.114-119
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• 2016

In this study, we tried to add the conductivity to natural polymer like bacterial cellulose (BC) coated with the conductive polymer PEDOT:PEG, graphene and silver nano-wire (AgNW). Sulfuric acid of 10 to 20% was previously mixed with PEDOT:PEG and then the solution was electron spin-coated on the BC membrane. And then, additive coating with graphene and AgNW were done to improve conductivity, which was examined by hall effect. As the result, we confirmed a considerable improvement of conductivity compared to BC-coated film without sulfuric acid treatment as $2.487{\times}10^{10}$ vs $8.093{\times}10^{15}$ ($1/cm^3$), showing higher electron density with $3.25{\times}10^5$ times. Also, we identified that changed particle type to the polymer type by sulfuric acid using SEM analysis. For FT-IR analysis, it was confirmed that S-O radical ($1200cm^{-1}$) increased in the sulfuric acid treatment than non-treated sulfuric acid. As the method used very small amount of PEDOT:PEG, its transparency could be kept, and pre-treatment process of sulfuric acid will be able to simplify the production process.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.96-97
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• 2012

In nitride and oxide film deposition, sputtered metals react with nitrogen or oxygen gas in a vacuum chamber to form metal nitride or oxide films on a substrate. The physical properties of sputtered films (metals, oxides, and nitrides) are strongly influenced by magnetron plasma density during the deposition process. Typical target power densities on the magnetron during the deposition process are ~ (5-30) W/cm2, which gives a relatively low plasma density. The main challenge in reactive sputtering is the ability to generate a stable, arc free discharge at high plasma densities. Arcs occur due to formation of an insulating layer on the target surface caused by the re-deposition effect. One current method of generating an arc free discharge is to use the commercially available Pinnacle Plus+ Pulsed DC plasma generator manufactured by Advanced Energy Inc. This plasma generator uses a positive voltage pulse between negative pulses to attract electrons and discharge the target surface, thus preventing arc formation. However, this method can only generate low density plasma and therefore cannot allow full control of film properties. Also, after long runs ~ (1-3) hours, depends on duty cycle the stability of the reactive process is reduced due to increased probability of arc formation. Between 1995 and 1999, a new way of magnetron sputtering called HIPIMS (highly ionized pulse impulse magnetron sputtering) was developed. The main idea of this approach is to apply short ${\sim}(50-100){\mu}s$ high power pulses with a target power densities during the pulse between ~ (1-3) kW/cm2. These high power pulses generate high-density magnetron plasma that can significantly improve and control film properties. From the beginning, HIPIMS method has been applied to reactive sputtering processes for deposition of conductive and nonconductive films. However, commercially available HIPIMS plasma generators have not been able to create a stable, arc-free discharge in most reactive magnetron sputtering processes. HIPIMS plasma generators have been successfully used in reactive sputtering of nitrides for hard coating applications and for Al2O3 films. But until now there has been no HIPIMS data presented on reactive sputtering in cluster tools for semiconductors and MEMs applications. In this presentation, a new method of generating an arc free discharge for reactive HIPIMS using the new Cyprium plasma generator from Zpulser LLC will be introduced. Data (or evidence) will be presented showing that arc formation in reactive HIPIMS can be controlled without applying a positive voltage pulse between high power pulses. Arc-free reactive HIPIMS processes for sputtering AlN, TiO2, TiN and Si3N4 on the Applied Materials ENDURA 200 mm cluster tool will be presented. A direct comparison of the properties of films sputtered with the Advanced Energy Pinnacle Plus + plasma generator and the Zpulser Cyprium plasma generator will be presented.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.19.2-19.2
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• 2010

Printed electronics using printing process has broadened in all respects such as electrics (lighting, batteries, solar cells etc) as well as electronics (OLED, LCD, E-paper, transistor etc). Copper is considered to be a promising alternative to silver for printed electronics, due to very high conductivity at a low price. However, Copper is easily oxidized, and its oxide is non-conductive. This is the highest hurdle for making copper inks, since the heat and humidity that occurs during ink making and printing simply accelerates the oxidation process. A variety of chemical treatments including organic capping agents and metallic coating have been used to slow this oxidation. We have established synthetic conditions of copper nanoparticles (CuNPs) which are resistant to oxidation and average diameter of 20 to 50nm. Specific resistivity should be less than $4\;{\mu}{\Omega}{\cdot}cm$ when sintered at lower temperature than $250^{\circ}C$ to be able to apply to conductive patterns of FPCBs using ink-jet printing. Through this study, the parameters to control average diameter of CuNPs were found to be the introduction of additive agent, the feeding rate of reducing agent, and reaction temperature. The CuNPs with various average diameters (58, 40, 26, 20nm) could be synthesized by controlling these parameters. The dispersed solution of CuNPs with an average size of 20 nm was made with nonpolar solvent containing 3 wt% of binder, and then coated onto glass substrate. After sintering the coated substrates at $250^{\circ}C$ for 30 minutes in nitrogen atmosphere, metallic copper film resulted in a specific resistivity of $4.2\;{\mu}{\Omega}{\cdot}cm$.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.6
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• pp.297-301
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• 2006

In the present work, we investigate the characteristics of new composition material, chalcogenide $Ge_1Se_1Te_2$ material in order to overcome the problems of conventional PRAM devices. The Tc of $Ge_1Se_1Te_2$ bulk was measured $231.503^{\circ}C$ with DSC analysis. For static DC test mode, at low voltage, two different resistances are observed. depending on the crystalline state of the phase-change resistor. In the first sweep, the as-deposited amorphous $Ge_1Se_1Te_2$ showed very high resistance. However when it reached the threshold voltage(about 11.8 V), the electrical resistance of device was drastically reduced through the formation of an electrically conducting path. The phase transition between the low conductive amorphous state and the high conductive crystal]me state was caused by the set and reset pulses respectively which fed through electrical signal. Set pulse has 4.3 V. 200 ns. then sample resistance is $80\sim100{\Omega}$. Reset pulse has 8.6 V 80 ns, then the sample resistance is $50{\sim}100K{\Omega}$. For such high resistance ratio of $R_{reset}/R_{set}$, we can expect high sensing margin reading the recorded data. We have confirmed that phase change properties of $Ge_1Se_1Te_2$ materials are closely related with the structure through the experiment of self-heating layers.