• Journal of Electrical Engineering and Technology
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• v.5 no.3
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• pp.493-496
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• 2010

At present, Metal Oxide gas Sensors (MOXs) are widely used in gas detection because of its advantages, including high sensitivity and low cost. However, MOX presents well-known problems, including lack of selectivity and environment effect, which has motivated studies on different measurement strategies and signal-processing algorithms. In this paper, we present an artificial neural network (ANN) that models an MOX sensor (TGS822) used in a dynamic environment. This model takes into account dependence in relative humidity and in gas nature. Using MATLAB interface in the design phase and optimization, the proposed model is implemented as a component in an electronic simulator library and accurately expressed the nonlinear character of the response and that its dependence on temperature and relative humidity were higher than gas nature.

• Korean Journal of Materials Research
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• v.23 no.9
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• pp.477-482
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• 2013

We investigated the detection properties of nitrogen monoxide (NO) gas using transparent p-type $CuAlO_2$ thin film gas sensors. The $CuAlO_2$ film was fabricated on an indium tin oxide (ITO)/glass substrate by pulsed laser deposition (PLD), and then the transparent p-type $CuAlO_2$ active layer was formed by annealing. Structural and optical characterizations revealed that the transparent p-type $CuAlO_2$ layer with a thickness of around 200 nm had a non-crystalline structure, showing a quite flat surface and a high transparency above 65 % in the range of visible light. From the NO gas sensing measurements, it was found that the transparent p-type $CuAlO_2$ thin film gas sensors exhibited the maximum sensitivity to NO gas in dry air at an operating temperature of $180^{\circ}C$. We also found that these $CuAlO_2$ thin film gas sensors showed reversible and reliable electrical resistance-response to NO gas in the operating temperature range. These results indicate that the transparent p-type semiconductor $CuAlO_2$ thin films are very promising for application as sensing materials for gas sensors, in particular, various types of transparent p-n junction gas sensors. Also, these transparent p-type semiconductor $CuAlO_2$ thin films could be combined with an n-type oxide semiconductor to fabricate p-n heterojunction oxide semiconductor gas sensors.

• The Korean Journal of Ceramics
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• v.4 no.2
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• pp.103-113
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• 1998

By using a gas-tight electrochemical cell, we can perform high-temperature coulometric titration and measure electronic transport properties to determine the elecronic defect structure of metal oxides. This technique reduces the time and expense required for conventional thermogravimetric measurements. The components of the gas-tight coulometric titration cell are an oxygen sensor, Pt/yttria stabilitized zirconia(YSZ)/Pt, and an encapsulated metal oxide sample. Based on cell design, both transport and thermodynamic measurements can be performed over a wide range of oxygen partial pressure ($pO_2=10^{-35}$ to 1 atm). This paper describes the high-temperature gas-tight electrochemical cells used to determine electronic defect structures and transport properties for pure and doped-oxide systems, such as YSZ, doped and pure ceria $(Ca-CeO_2 \;and\; CeO_2)$, copper oxides and copper-oxide-based ceramic superconductors, transition metal oxides, $SrFeCo_{0.5}O_x,\; and \;BaTiO_2$.

• Journal of Industrial and Engineering Chemistry
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• v.67
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• pp.417-428
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• 2018

In this study, we fabricated hierarchically self-assembled thin films composed of graphene oxide (GO) sheets and gold nanoparticles (Au NPs) using the Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) techniques and investigated their gas-sensing performance. First, a thermally oxidized silicon wafer ($Si/SiO_2$) was hydrophobized by depositing the LB films of cadmium arachidate. Thin films of ligand-capped Au NPs and GO sheets of the appropriate size were then sequentially transferred onto the hydrophobic silicon wafer using the LB and the LS techniques, respectively. Several different films were prepared by varying the ligand type, film composition, and surface pressure of the spread monolayer at the air/water interface. Their structures were observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and their gas-sensing performance for $NH_3$ and $CO_2$ was assessed. The thin films of dodecanethiol-capped Au NPs and medium-sized GO sheets had a better hierarchical structure with higher uniformity and exhibited better gas-sensing performance.

• Korean Journal of Materials Research
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• v.22 no.11
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• pp.609-614
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• 2012

We report on the NO gas sensing properties of non-directional ZnO nanofibers synthesized using a typical electrospinning technique. These non-directional ZnO nanofibers were electrospun on an $SiO_2$/Si substrate from a solution containing poly vinyl alcohol (PVA) and zinc nitrate hexahydrate dissolved in distilled water. Calcination processing of the ZnO/PVA composite nanofibers resulted in a random network of polycrystalline ZnO nanofibers of 50 nm to 100 nm in diameter. The diameter of the nanofibers was found to depend primarily on the solution viscosity; a proper viscosity was maintained by adding PVA to fabricate uniform ZnO nanofibers. Microstructural measurements using scanning electron microscopy revealed that our synthesized ZnO nanofibers after calcination had coarser surface morphology than those before calcination, indicating that the calcination processing was sufficient to remove organic contents. From the gas sensing response measurements for various NO gas concentrations in dry air at several working temperatures, it was found that gas sensors based on electrospun ZnO nanofibers showed quite good responses, exhibiting a maximum sensitivity to NO gas in dry air at an operating temperature of $200^{\circ}C$. In particular, the non-directional electrospun ZnO nanofiber gas sensors were found to have a good NO gas detection limit of sub-ppm levels in dry air. These results illustrate that non-directional electrospun ZnO nanofibers are promising for use in low-cost, high-performance practical NO gas sensors.

• Journal of Sensor Science and Technology
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• v.6 no.6
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• pp.445-450
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• 1997

An ammonia gas sensor with high sensitivity using thick-film technology were fabricated and examined. The material for sensing the ammonia gas was the mixture of oxide semiconductor, $FeO_{x}-WO_{3}-SnO_{2}$. The sensor exhibits resistance increase upon exposure to low concentration of ammonia gas. The resistance of the sensor is decreased, on the other hand, for exposure to reducing gases such as ethyl alcohol, methane, propane and carbon monoxide. A novel method for detecting ammonia gas quite selectively utilizing a sensor array consisting of an ammonia gas sensor and a compensation element were proposed and developed. The compensation element is a Pt-doped $WO_{3}-SnO_{2}$ gas sensor which shows opposite direction of resistance change in comparison with that of the ammonia gas sensor upon exposure to ammonia gas. Excellent selectivity has been achieved using the sensor array having two sensing elements.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.609-611
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• 1997

Pt thin films flow sensors were fabricated by using aluminum oxide films as medium layer and their characteristics were investigated after annealing at $600^{\circ}C$ for 60min. Aluminum oxide improved adhesion of Pt thin films to $SiO_2$ layer without any chemical reactions to Pt thin films under high annealing temperatures. Output voltages increased as gas flow rate and gas conductivity increased because heat loss of heater, which was integrated with a sensing resistor in the flow sensor, increased. Output voltage of flow sensor fabricated on membrane structure was 101mV at $O_2$ flow rate of 2000sccm, heating power of 0.8W while flow sensor fabricated on Si substrate without membrane had output voltage of 78mV under the same conditions.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.12
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• pp.17-23
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• 2003

A sensor array (3${\times}$5$\textrm{mm}^2$ in diaphragm dimension) of 12 sensing clements with different operating temperatures was optimized with respect to thermal operation. This sensor array with single heater on a glass diaphragm over back-etched silicon bulk realizes a novel concept of a sensor array: an array of sensor clements operated at different temperatures can yield more information than single measurement. The proposed micro sensor array could provide well-integrated array structure because it had only single heater at the center of the diaphragm and used the various sensing properties of two kinds of metal oxide layers with various operating temperatures.

• Journal of Sensor Science and Technology
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• v.31 no.5
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• pp.348-352
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• 2022

Hydrogen gas (H₂) which is odorless, colorless is attracting attention as a renewable energy source in varions applications but its leakage can lead to disastrous disasters, such as inflammable, explosive, and narcotic disasters at high concentrations. Therefore, it is necessary to develop H₂ gas sensor with high performance. In this paper, we confirmed that H₂ gas detection ability of SnO₂ based H₂ gas sensor along with thermal treatment effect of SnO₂. Proposed SnO₂ based H₂ gas sensor is fabricated by MEMS technologies such as photolithgraphy, sputtering and lift-off process, etc. Deposited SnO₂ thin films are thermally treated in various thermal treatement temperature in range of 500-900 ℃ and their H₂ gas detection ability is estimatied by measuring output current of H₂ gas sensor. Based on experimental results, fabricated H₂ gas sensor with SnO₂ thin film which is thermally treated at 700 ℃ has a superior H₂ gas detection ability, and it can be expected to utilize at the practical applications.

• Journal of Sensor Science and Technology
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• v.17 no.1
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• pp.35-40
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• 2008

Low power bridge type micro gas sensors were fabricated by micro machining technology with TMAH (Tetra Methyl Ammonium Hydroxide) solution. The sensing devices with different heater materials such as metal and poly-silicon were obtained using CMOS (Complementary Metal Oxide Semiconductor) compatible process. The tellurium films as a sensing layer were deposited on the micro machined substrate using shadow silicon mask. The low power micro gas sensors showed high sensitivity to NO with high speed. The pure tellurium film used micro gas sensor showed good sensitivity than transition metal (Pt, Ti) used tellurium film.