• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.31 no.4
• /
• pp.417-424
• /
• 2007

This paper reports fabrication and characterization of a pressure sensor using a pitch-based carbon fiber. Pitch-based carbon fibers have been shown to exhibit the piezoresistive effect, in which the electric resistance of the carbon fiber changes under mechanical deformation. The main structure of pressure sensors was built by performing backside etching on a SOI wafer and creating a suspended square membrane on the front side. An AC electric field which causes dielectrophoresis was used for the alignment and deposition of a carbon fiber across the microscale gap between two electrodes on the membrane. The fabricated pressure sensors were tested by applying static pressure to the membrane and measuring the resistance change of the carbon fiber. The resistance change of carbon fibers clearly shows linear response to the applied pressure and the calculated sensitivities of pressure sensors are $0.25{\sim}0.35 and 61.8 ${\Omega}/k{\Omega}{\cdot}bar$ for thicker and thinner membrane, respectively. All these observations demonstrated the possibilities of carbon fiber-based pressure sensors.

• Journal of Powder Materials
• /
• v.20 no.2
• /
• pp.120-124
• /
• 2013

This study is carried out to develop the new process for the fabrication of ultra-fine electrodes on the flexible substrates using superhydrophobic effect. A facile method was developed to form the ultra-fine trenches on the flexible substrates treated by plasma etching and to print the fine metal electrodes using conductive nano-ink. Various plasma etching conditions were investigated for the hydrophobic surface treatment of flexible polyimide (PI) films. The micro-trench on the hydrophobic PI film fabricated under optimized conditions was obtained by mechanical scratching, which gave the hydrophilic property only to the trench area. Finally, the patterning by selective deposition of ink materials was performed using the conductive silver nano-ink. The interface between the conductive nanoparticles and the flexible substrates were characterized by scanning electron microscope. The increase of the sintering temperature and metal concentration of ink caused the reduction of electrical resistance. The sintering temperature lower than $200^{\circ}C$ resulted in good interfacial bonding between Ag electrode and PI film substrate.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.24 no.5
• /
• pp.374-380
• /
• 2011

In this paper a printing process for patterning electrodes on large area substrate was developed by combining screen printing with reverse off-set printing. Ag ink was uniformly coated by screen printing. And then etching resist (ER) was patterned in the Ag film by reverse off-set printing, and then the non-desired Ag film was etched off by etchant. Finally, the ER was stripped-off to obtain the final Ag patterns. We extracted the suitable conditions of reverse Using the process we successfully fabricated gate electrodes and scan bus lines of OTFT-backplane used for e-paper, in which the diagonal size was 6 inch, the resolution $320{\times}240$, the minimum line width 30 um, and sheet resistance 1 ${\Omega}/{\Box}$.

• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.30A no.10
• /
• pp.33-40
• /
• 1993

A reflection type 16x8 S-SEED array from LP(Low Pressure)-MODVD-grown GaAs/AlGaAs extremely shallow quantum well(ESQW) structures, with 4% Al fraction, has been fabricated. Its intrinsic region consists of 50 pairs of alternating 100.angs. GaAs and 100.angs. $Al_{0.04}$Ga$_{0.96}$As layers. A multilayer reflector stack of $Al_{0.04}$/Ga$_{0.96}$ As(599$\AA$)/AlAs(723$\AA$) was incorporated for the reflection plane below the p-i-n structures. The device processing after the MOCVD growth includes the mesa etching, isolation etching, insulator deposition, p & n metallization, and AR(Anti-Reflection) coating. For switching characteristics of the S-SEED in the form of p-i-n ESQW diode, the maximum optical negative resistance was observed at 856nm. Reflectance measurements showed a change from 15.6% to 43.3% for +0.9V to -6V bias. The maximum contrast ration of the S-SEED array was 2.0 and all the 128 devices showed optical bistability with contrast ratios over 2.4 at 5V reverse bias.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.232.2-232.2
• /
• 2014

Since its discovery in 2004, graphene, a sp2-hybridized 2-Dimension carbon material, has drawn enormous attention. A variety of approaches have been attempted, such as epitaxial growth from silicon carbide, chemical reduction of graphene oxide and CVD. Among these approaches, the CVD process takes great attention due to its guarantee of high quality and large scale with high yield on various transition metals. After synthesis of graphene on metal substrate, the subsequent transfer process is needed to transfer graphene onto various target substrates, such as bubbling transfer, renewable epoxy transfer and wet etching transfer. However, those transfer processes are hard to control and inevitably induce defects to graphene film. Especially for wet etching transfer, the metal substrate is totally etched away, which is horrendous resources wasting, time consuming, and unsuitable for industry production. Thus, our group develops one-step process to directly grow graphene on glass substrate in plasma enhanced chemical vapor deposition (PECVD). Copper foil is used as catalyst to enhance the growth of graphene, as well as a temperature shield to provide relatively low temperature to glass substrate. The effect of growth time is reported that longer growth time will provide lower sheet resistance and higher VSG flakes. The VSG with conductivity of $800{\Omega}/sq$ and thickness of 270 nm grown on glass substrate can be obtained under 12 min growing time. The morphology is clearly showed by SEM image and Raman spectra that VSG film is composed of base layer of amorphous carbon and vertically arranged graphene flakes.

• Korean Journal of Materials Research
• /
• v.23 no.6
• /
• pp.322-328
• /
• 2013

The relationship the between electrical properties and surface roughness (Ra) of a wet-etched silicon wafer were studied. Ra was measured by an alpha-step process and atomic force microscopy (AFM) while varying the measuring range $10{\times}10$, $40{\times}40$, and $1000{\times}1000{\mu}m$. The resistivity was measured by assessing the surface resistance using a four-point probe method. The relationship between the resistivity and Ra was explained in terms of the surface roughness. The minimum error value between the experimental and theoretical resistivities was 4.23% when the Ra was in a range of $10{\times}10{\mu}m$ according to AFM measurement. The maximum error value was 14.09% when the Ra was in a range of $40{\times}40{\mu}m$ according to AFM measurement. Thus, the resistivity could be estimated when the Ra was in a narrow range.

• Proceedings of the KIEE Conference
• /
• 1994.07b
• /
• pp.1268-1270
• /
• 1994

Fine lithographic technology in a submicron design regime is necessary for the fabrication of VLSI circuits. In such lithography, fine pattern delineation is performed by electron beam, ion beam and X-ray lithography instead of photolithography. Therefore, the new resist materials and development method have been required. So, we are investigating another positive E-beam resists which have high sensitivity and dry etching resistance, Plasma co-polymerized resist was prepared using an interelectrode gas-flow-type reacter. Methymethacrylate, tetramethyltin and styrene were chosen as the monomer to be used. The delineated pattern in the resist was developed with gas-flow-type reactor using an argon and 02 as etching gas. We studied about the effects of discharge power and mixing rate of the co-polymerized thin :film. The molecular structure of thin film was investigated by ESCA and IR, and then was discussed in relation to its quality as a resist.

• Journal of the Korean Ceramic Society
• /
• v.46 no.5
• /
• pp.441-446
• /
• 2009

Dense crack-free yttria film with 10 $\mu m$ thickness was prepared on aluminum by aerosol deposition. X-ray diffraction pattern on the film showed that it contained the same crystalline phase as the raw powder. Transmission electron microscopy revealed a nanostructured yttria film with grains smaller than 100 nm. Tensile adhesion strength between the film and aluminum substrate was 57.8 $\pm$ 6.3MPa. According to the etching test with $CF_4-O_2$ plasma, the etching rate of the yttria film was 1/100 that of quartz, 1/10 that of sintered alumina and comparable to that of sintered yttria.

• Journal of Magnetics
• /
• v.6 no.3
• /
• pp.90-93
• /
• 2001

Co/$Al_O_3$/NiFe and CO/$Al_O_3$/Co tunnel junctions were fabricated by a radio frequency magnetron sputtering at room temperature with hard mask on glass and $4^{\circ}$ tilt cut Si (111) substrates. The barrier layer was formed through two steps. After the Al layer was deposited, it was oxidized in the chamber of a reactive ion etching system (RIE) with $O_2$plasma at various conditions. The dependence of the TMR value and junction resistance on the thickness of Al layer (before oxidation) and oxidation parameters were investigated. Magnetoresistance value of 7% at room temperature was obtained by optimizing the Al layer thickness and oxidation conditions. Circular shape junctions on $4^{\circ}$tilt cut Si (111) substrate showed 4% magnetoresistance. Photovoltaic energy conversion effect was observed with the cross-strip geometry junctions on Si substrate.

• Proceedings of the Korean Magnestics Society Conference
• /
• 2011.12a
• /
• pp.29-30
• /
• 2011

We have demonstrated the fabrication of sub 30 nm MTJ pillars with PMA characteristics. The multi-step IBE process performed at $45^{\circ}$ and $30^{\circ}$, using NER resulted in almost vertical side profiles. There deposition on the sidewalls of the NER prevented lateral etching of the resist hard mask allowing vertical MTJ side profile formation without any reduction in the lithographically defined resist lateral dimensions. For the 28nm STT-MTJ pillars, the measured TMR ratio was 13 % with resistance of 1 $k{\Omega}$, which was due to remaining redeposition layers less than 0.1 nm thick. With further optimization in multi-step IBE conditions, it will be possible to fabricate fully operating sub 30 nm perpendicular STT-MTJ structures for application to future non-volatile memories.