Hyunsoo Song

Inkjet-printed stretchable silver electrode on wave structured elastomeric substrate

We report high performance and stable inkjet-printed stretchable silver electrodes on wave structured elastomeric substrates. Highly conductive silver electrodes were deposited directly on a ultraviolet ozone treated polydimethylsiloxane (PDMS) substrates having vertical wavy structures. Adhesion between printed silver lines and PDMS surface has been enhanced by intentionally roughened PDMS surface with wire-electro discharge machined aluminum mold. During slow (16.7 μm/s) stretching test, resistance of the printed silver electrode was increased only by three times at 30% tensile strain. Inkjet-printed silver electrodes also showed good mechanical stability during 1000-time fast (1 mm/s) cycling test with 10% tensile strain, showing maximum resistance change of less than three times.

Correlation between clinical diagnosis based on RDC/TMD and MRI findings of TMJ internal derangement

This study was conducted to investigate the value of magnetic resonance imaging (MRI) in the diagnostic process based on the Research Diagnostic Criteria for Temporomandibular Disorder (RDC/TMD) by evaluating agreement between RDC/TMD and MRI diagnosis of disc displacement (DD) and correlation amongst MRI findings such as DD, joint effusion (JE), degenerative change and superior lateral pterygoid muscle (SLPM) attachment. Randomly selected MRIs of 200 joints from 100 TMD patients differentiated into RDC/TMD group II representing DD by clinical examination were reviewed retrospectively. The results show that Cohens kappa value was 0.336 showing overall disagreement between RDC/TMD group II and MRI diagnoses (P<0.001). The Cohens kappa value for group IIa, DD with reduction (DDWR), was -0.223 (P<0.01) showing disagreement, whilst the value was 0.546 for group IIb, DD without reduction (DDWOR) with limited opening, and 0.490 for group IIc, DDWOR without limited opening, showing moderate agreement (P<0.001). JE was detected with a higher probability as the state of DD advanced (P<0.001) and when degenerative joint changes were present (P<0.05). The difference of DD according to SLPM attachment was insignificant. MRI could be used when clinical examination cannot predict the true position of the disc.

Lateral-crack-free, buckled, inkjet-printed silver electrodes on highly pre-stretched elastomeric substrates

We report the formation of lateral-crack-free silver electrodes on highly pre-stretched poly(dimethylsiloxane) (PDMS) substrates using the inkjet-printing method followed by an annealing process under the pre-stretched state. Due to Poissons effect, cracks are easily obtained in the direction lateral to the pre-stretching and releasing directions when the highly pre-stretched substrate is released after the electrode formation. In our method, however, Poissons effect is suppressed significantly from the PDMS thermal expansion perpendicular to the pre-stretched direction during the annealing process. In order to prevent the formation of a lateral crack, the annealing temperature needs to be optimized for each pre-stretching condition. We modelled their relationship using Poissons ratios and thermal expansion coefficients of the substrate and silver materials. Our measurement results showed consistent result with the simulation. The resistance of the fabricated silver electrodes negligibly changes under up to 17% strain and even after 1000 time stretching cycle tests.

Inkjet-printed stretchable single-walled carbon nanotube electrodes with excellent mechanical properties

Inkjet-printed single-walled carbon nanotube (SWCNT) thin films on stretchable substrates were developed, and their electrical properties were investigated. The 1- and 5-layer printed SWCNT thin films had sheet resistances of 169.76 and 19.08 Ω/sq, respectively, and maintained conductive properties under 100% tensile strain. A nitric acid treatment significantly improved the conductivity of the SWCNT electrodes, and after an initial increase, the 5-layer printed SWCNT electrodes showed a normalized resistance of less than 1.2 after 1000 cycles under 100% tensile strain. The potential of the inkjet-printed SWCNT thin films for stretchable electrode applications was demonstrated via integration with a light-emitting diode.

Effects of defect creation on bidirectional behavior with hump characteristics of InGaZnO TFTs under bias and thermal stress

We investigated the hump characteristics of amorphous indium–gallium–zinc oxide thin-film transistors. The device showed a field effect mobility of 24.3 cm2 V−1 s−1, a threshold voltage (Vth) of 4.8 V, and a subthreshold swing of 120 mV/dec. Under positive gate bias stress, Vth showed bidirectional shift with a hump. Vth was positively and negatively shifted in the above-threshold and subthreshold regions, respectively. At high temperatures, Vth was more positively shifted without bidirectional shift. Under simultaneous drain bias stress (VDS,stress), the hump was maintained. However, the bidirectional shift was not observed with an increasing VDS,stress. The hump and positive shift are related to the defect creation of the shallow donor-like and deep-level acceptor-like states, respectively. We performed a two-dimensional device simulation to further investigate this phenomenon. By varying the peak values of the Gaussian shallow donor-like and deep acceptor-like states, we qualitatively confirmed the relationship between the two states and transfer curve changes.

Effects of the defect creation on the bidirectional shift of threshold voltage with hump characteristics of InGaZnO TFTs under bias and thermal stress

We have investigated the hump characteristics of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs). Under positive gate bias stress, the threshold voltage (Vth) of a-IGZO TFTs showed bidirectional shift with hump; the positive shift in above Vth region and negative shift in subthreshold region. The amount of bidirectional shift depended on the temperature or drain voltage of stress condition. It was concluded that the origins of the bidirectional shift with hump were the shallow donor-like states and deep-level states creation in the semiconductor bulk or at the semiconductor/dielectric interface. Two-dimensional device simulation was also performed to further investigate this phenomenon.

Accurate Defect Density-of-State Extraction Based on Back-Channel Surface Potential Measurement for Solution-Processed Metal-Oxide Thin-Film Transistors

We report more accurate extraction method of the defect density of states for solution-processed indium-gallium-zinc-oxide (IGZO) thin-film transistors (TFTs). Since the solution-processed IGZO TFTs have a very thin (~8 nm) active semiconductor layer, their back-channel surface potential should be considered in the field-effect method. If the back-channel surface potential is ignored, deviation between theoretically derived and experimentally measured activation energy data becomes more significant as the thickness of the semiconductor layer decreases in comparison with its Debye length. Dependence of the back-channel surface potential on the applied gate voltages was verified by scanning Kelvin probe microscopy and found to be proportional to the gate voltages. The modified field-effect method provided a more accurate model of the activation energy over the subthreshold region and correspondingly more accurate defect density of states of the IGZO TFTs.

Development of Fast-Response CO2Analyzer and Analysis of Engine-out Emission during Cold Start of SI Engine

Abstract A fast-response CO 2 analyzer has been developed for measuring the CO 2 concentration during transient condition of a SI engine. The analyzer consists of the non-dispersive infrared absorption method, electrical chopping system and water cooling system. The analyzer has good repeatability, linearity and permissible drift characteristic. Besides, it showed 18ms of a response to measure the CO 2 concentration. The fast-response CO 2 analyzer was applied to a single cylinder SI engine and the CO 2 emission was examined during engine start. Simultaneously, the standard exhaust gas analyzer, which has slow response time, was used for confirming the accuracy of the exhaust gas analysis using the fast-response CO 2 analyzer. The developed analyzer showed much faster responsive characteristic than that of a standard analyzer and made cycle by cycle exhaust gas analysis possible. The transient engine operating characteristics will be estimated from the CO 2 concentration of engine-out emissions and engine operating variables. 기호설명 DPF : 디젤 입자상 물질 필터 (diesel particulate filter) SCR : selective catalytic reduction EGR : 배기가스 재순환(exhaust gas recirculation) HC : 미연탄화수소(unburned hydrocarbon) CO : 일산화탄소(carbon monoxide) CO

Sessile Drop Evaporation on Surfaces of Various Wettability

This work experimentally investigates the evaporation rates of water drops on surfaces of various wettability. By measuring the temporal evolutions of the drop radius and contact angle, we find the qualitative difference between the evaporation behavior on hydrophilic surfaces where the contact radius remains constant initially and that on the superhydrophobic surfaces where the contact angle remains constant. Also, the evaporation rate is observed to depend on the surface material although the currently available models assume that the rate is solely determined by the drop geometry. Although the theory to explain this dependence on the surface remains to be pursued by the future work, we give the empirical relations that can be used to predict the drop volume evolution for each surface.Copyright