• Bulletin of the Korean Chemical Society
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• v.32 no.6
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• pp.1865-1872
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• 2011

This study investigates the sensitivity of a gas sensor to volatile organic compounds (VOCs) at various operating temperatures and catalysts. Nano-sized powdered $WO_3$ prepared by sol-gel and chemical precipitation methods was mixed with various metal oxides. Next, transition metals (Pt, Ru, Pd, and In) were doped on the surface of the mixture. Metal-$WO_3$ thick films were prepared using the screen-printing method. The physical and chemical properties of the films were studied by SEM/EDS, XRD, and BET techniques. The measured sensitivity to VOCs is defined as the ratio ($R_a/R_g$) of resistance ($R_{air}$) of $WO_3$ film in the air to resistance ($R_{gas}$) of $WO_3$ film in a VOCs test gas. The sensitivity and selectivity of the films were tested with various VOCs such as acetaldehyde, formaldehyde, methyl alcohol, and BTEX. The thick $WO_3$ film containing 1 wt % of Ru and 5 wt % of $SnO_2$ showed the best sensitivity and selectivity to acetaldehyde gas at an operating temperature of 300 $^{\circ}C$.

• Journal of Sensor Science and Technology
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• v.17 no.4
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• pp.250-255
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• 2008

A vanadium pentoxide ($V_2O_5$)-based bolometric infrared (IR) sensor has been designed and fabricated using micro electro mechanical systems (MEMS) technology for glucose detection and its resistive characteristics has been illustrated. The proposed bolometric infrared sensor is composed of the vanadium pentoxide array that shows superior temperature coefficient of resistance (TCR) and standard silicon micromachining compatibility. In order to achieve the best performance, deposited $V_2O_5$ thin film is optimized by adequate rapid thermal annealing (RTA) process. Annealed vanadium oxide thin film has demonstrated a linear characteristic and relatively high TCR value (${-4}%/^{\circ}C$). The resistance of vanadium oxide is changed by IR intensity based on glucose concentration.

• Journal of the Korean Vacuum Society
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• v.8 no.4B
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• pp.507-513
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• 1999

8mol%-yttria-stabilized zirconia(YSZ) thin films as oxygen ion conductor were deposited by rf-magnetron sputtering, and the oxygen gas sensors with the structure of $SiO_2$ substrate/Ni-NiO mixed reference layer/Pt/YSZ/Pt were fabricated and their oxygen sensing properties were investigated. The steady-state electro-motive force (EMF) values were measured as a function of oxygen partial pressure ($PO_2;form 1.013\times10^3 \textrm{Pa \;to}\; 1.013\times10^5$Pa) and operating temperature ($300^{\circ}C$ to $700^{\circ}C$). The fabricated YSZ oxygen sensor showed the best oxygen sensing properties at 50$0^{\circ}C$. However, oxygen sensing properties were very low at the temperature lower than 30$0^{\circ}C$ due to the lack of oxygen ion mobility and at the temperature higher than $700^{\circ}C$ due 새 intermixing of materials between the layers. Especially, the YSZ sensor operating at $500^{\circ}C$ and oxygen partial pressure above $1.565\times10^4$Pa showed the oxygen sensing properties close to the values predicted by ideal Nernst equation.

• Journal of Sensor Science and Technology
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• v.18 no.3
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• pp.202-206
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• 2009

Flat type catalytic combustible hydrogen sensors were fabricated using platinum micro-heaters and sensing material pastes. The platinum micro-heater was formed on an alumina substrate by sputtering method. The paste for the sensing materials was prepared using ${\gamma}-Al_2O_3$ 30 wt%, $SnO_2$ 35 wt%, and Pd/Pt 30 wt% and coated on the platinum micro-heater. The sensing performances were tested for the prepared sensors with different substrate sizes. The micro catalytic combustible hydrogen sensors showed quick response time, high reliability, and good selectivity against various gases(CO, $C_3H_8,\;CH_4$) at low operating temperature of $156^{\circ}\C$.

• Journal of Sensor Science and Technology
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• v.31 no.1
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• pp.41-44
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• 2022

In this study, we have fabricated and characterized vertical double-gate (DG) InGaAs tunnel field-effect-transistors (TFETs) with Al₂O₃/HfO₂ = 1/5 nm bi-layer gate dielectric by employing a top-down approach. The device exhibited excellent characteristics including a minimum subthreshold swing of 60 mV/decade, a maximum transconductance of 141 µS/㎛, and an on/off current ratio of over 10³ at 20℃. Although the TFETs were fabricated using a dry etch-based top-down approach, the values of DIBL and hysteresis were as low as 40 mV/V and below 10 mV, respectively. By evaluating the effects of constant voltage and hot carrier injection stress on the vertical DG InGaAs TFET, we have identified the dominant charge trapping mechanism in TFETs.

• Journal of Sensor Science and Technology
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• v.2 no.1
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• pp.101-108
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• 1993

$TiO_{2}$/Se : Te heterojunction for color sensor has been fabricated by RF reactive sputtering and thermal evaporation methods onto glass substrate. The optimum deposition condition of $TiO_{2}$ films was such that RF power was 120 W, substrate temperature was $100^{\circ}C$, oxygen concentration was 50%, working pressure was 50 mTorr for the $TiO_{2}$ film thickness of $1000{\AA}$. In this case, the optical transmittance of $TiO_{2}$ film at 550 nm-wavelength was 85%, resistivity was $2{\times}10^9{\Omega}{\cdot}cm$, refractive index was 2.3, and optical bandgap was 3.58 eV. The composition ratio of 0 to Ti by AES analysis was 1.7. When $TiO_{2}$ films were annealed at $400^{\circ}C$ for 30 min. in $O_{2}$ ambient, the optical transmittance of $TiO_{2}$ films at the wavelength range of $300{\sim}580$ nm was improved from 0 to 25%. When Se : Te films were annealed at $190^{\circ}C$ for 1 min., photosensitivity under illumination of 1000 lux was 0.75. The optical bandgap of Se : Te films was 1.7 eV. The structures of Se : Te films were the hexagonal with (100) and (110) orientation. The spectral response of a-Se was improved by the addition of Te, especially in the long wavelength region. The $TiO_{2}$/Se : Te heterojunction showed wide spectral response, and more improved one than that of a-Si film in the blue light region.

• Bulletin of the Korean Chemical Society
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• v.34 no.6
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• pp.1632-1636
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• 2013

$Ga_2O_3$ one-dimensional (1D) nanostructures were synthesized by using a thermal evaporation technique. The morphology, crystal structure, and sensing properties of the $Ga_2O_3$ nanostructures functionalized with Pt to $NO_2$ gas at room temperature under UV irradiation were examined. The diameters of the 1D nanostructures ranged from a few tens to a few hundreds of nanometers and the lengths ranged up to a few hundreds of micrometers. Pt nanoparticles with diameters of a few tens of nanometers were distributed around a $Ga_2O_3$ nanorod. The responses of the nanorods gas sensors fabricated from multiple networked $Ga_2O_3$ nanorods were improved 3-4 fold at $NO_2$ concentrations ranging from 1 to 5 ppm by Pt functionalization. The Pt-functionalized $Ga_2O_3$ nanorod gas sensors showed a remarkably enhanced response at room temperature under ultraviolet (UV) light illumination. In addition, the mechanisms via which the gas sensing properties of $Ga_2O_3$ nanorods are enhanced by Pt functionalization and UV irradiation are discussed.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.11 no.6
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• pp.193-199
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• 2001

Active control of forced vibration of the cantilevered laminated composite plates using collocated piezoceramic sensor/actuator is analyzed numerically and verified experimentally for various fiber orientations. Impact on the stiffness and the damping properties is studied by varying stacking sequence of [$\theta$$_{4}$O$_{2}$90$_{2}$]s for the laminated composite plate. For the forced vibration control, the plate is excited by one pair of collocated PZT exciters in resonance and its vibrational response is suppressed by the other collocated PZT sensor/actuator using direct negative velocity feedback. It is shown that the active control of forced vibration is more effective for the smart laminated plate with higher modal damped stiffness(2ζ$\omega$/aup 2/) .

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2369-2371
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• 2005

MEMS 기술을 이용하여 마이크로 $H_2$ 가스센서를 제작하고 마이크로 히터의 열적 특성과 $H_2$ 가스 농도 변화에 따를 마이크로 가스센서에 대한 감도를 분석하였다. 마이크로 가스센서의 전압 인가에 따른 히터의 온도는 1.0V에서 $250-280^{\circ}C$의 고온 특성을 보였으며, 동작온도 $250^{\circ}C$에서 $H_2$ 가스는 $SnO_2/V_2O_5/Pd$의 감응물질을 도포한 센서의 반응이 우수한 특성을 확인하였다. 동작 온도 $250^{\circ}C$ $H_2$ 농도 5000ppm의 조건에서 $SnO_2/V_2O_5/Pd$의 감응물질을 도포한 가스센서에서 $H_2$ 흡착 반응 시간은 3sec이 탈착 반응 시간은 8-10sec의 결과를 보였다.

• Journal of Sensor Science and Technology
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• v.9 no.5
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• pp.389-395
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• 2000

In this paper, we propose the formation of an $Al_2O_3$ pre-layer using a protective Si-oxide layer and Al layer. Deposition of a thin film layer of aluminum onto a Si surface covered with a thin Si-oxide layer and annealing at $800^{\circ}C$ led to the growth of epitaxial $Al_2O_3$ layer on Si(111). And ${\gamma}-Al_2O_3$ layer was grown on the $Al_2O_3$ per-layer. Etching of the Si substrate by $N_2O$ gas could be avoided in the initial growth stage by the $Al_2O_3$ pre-layer. It was confirmed that the $Al_2O_3$ pre-layer was effective in improving the surface morphology of the very thin ${\gamma}-Al_2O_3$ films.