• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.21 no.6
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• pp.499-502
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• 2008

In this work, Ga-doped ZnO (GZO) thin films for gas sensor application were deposited on low temperature co-fired ceramics (LTCC) substrates, by RF magnetron sputtering method. The LTCC substrate is one of promising materials for this application since it has many advantages (e.g., low cost production, high manufacturing yields and easy realizing 3D structure etc.). The LTCC substrates with thickness of $400\;{\mu}m$ were fabricated by laminating 12 green tapes which consist of alumina and glass particle in an organic binder. The structural properties of the fabricated GZO thin film with thickness of 50 nm is analyzed by X-ray diffraction method (XRD) and field emission scanning electron microscope (FESEM). The film shows good adhesion to the substrate. The GZO gas sensors are tested by gas measurement system and show fast response and recovery characteristics to $NO_x$ gas that is 27.2 and 27.9 sec, recpectively.

• Transactions on Electrical and Electronic Materials
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• v.13 no.2
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• pp.106-109
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• 2012

A low power methane gas sensor with microheater was fabricated by silicon bulk micromachining technology. In order to heat up the sensing layer to operating temperature, a platinum (Pt) micro heater was embedded in the gas sensor. The line width and gap of the microheater was 20 ${\mu}m$ and 4.5 ${\mu}m$, respectively. Zinc oxide (ZnO) nanowhisker arrays were grown on a sensor from a ZnO seed layer using a hydrothermal method. A 200 ml aqueous solution of 0.1 mol zinc nitrate hexahydrate, 0.1 mol hexamethylenetetramine, and 0.02 mol polyethylenimine was used for growing ZnO nanowhiskers. Temperature distribution of the sensor was analyzed by infrared thermal camera. The optimum temperature for highest sensitivity was found to be $250^{\circ}C$ although relatively high (64%) sensitivity was obtained even at as low a temperature as $150^{\circ}C$. The power consumption was 72 mW at $250^{\circ}C$, and only 25 mW at $150^{\circ}C$.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.105-105
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• 2011

ZnO is a promising material since it could be applied to many fields such as solar cells, laser diodes, thin films transistors and gas sensors. ZnO has a wide and direct band gap for about 3.37 eV at room temperature and a high exciton binding energy of 60 meV. In particular, ZnO features high sensitivity to toxic and combustible gas such as CO, NOX, so on. The development of gas sensors to monitor the toxic and combustible gases is imperative due to the concerns for enviromental pollution and the safety requirements for the industry. In this study, we investigated the effect of substrate temperature and post-annealing on structural and electrical properties of ZnO thin films. ZnO thin films were deposited by pulsed laser deposition (PLD) at various temperatures at from room temperature to $600^{\circ}C$. After that, post-annealing were performed at $600^{\circ}C$. To inspect the structural properties of the deposited ZnO thin films, X-ray diffraction (XRD) was carried out. For gas sensors, the morphology of the films is dominant factor since it is deeply related with the film surface area. Therefore, the atomic force microscopy (AFM) and field emission scanning electron microscopy (FE-SEM) were used to observe the surface of the ZnO thin films. Furthermore, we analyzed the electrical properties by using a Hall measurement system.

• Journal of Sensor Science and Technology
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• v.21 no.3
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• pp.180-185
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• 2012

${\gamma}$-ray radiolysis was used to functionalize networked ZnO nanowires with Au nanoparticles. The networked ZnO nanowires were prepared through a vapor phase selective growth method. The sensing performances of the Au-functionalized ZnO nanowires were investigated in terms of $NO_2$, CO and benzene gases. The Au-funtionalized ZnO nanowire sensors showed an applicable, reliable capability to detect the gases, indicating their potential in chemical gas sensors.

• Journal of Sensor Science and Technology
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• v.8 no.1
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• pp.24-31
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• 1999

Ammonia gas sensors were fabricated with ZnO-based thin films grown by RF-magnetron sputtering method. The films which were doped with $MoO_3$ catalysts of various weight percents were grown in different sputtering gases to fabricate the sensors with a high sensitivity, low working temperature and rapid response time. To improve electrical stability, the films were aged in various conditions. The sensors doped with the catalysts and grown in oxygen sputtering gas showed the improvement of sensitivity. These exhibited the increase of surface carrier concentration and electron mobility. The sensor with 0.875wt.% $MoO_3$ catalysts showed the maximum sensitivity of 70 in ammonia gas concentration of 160 ppm at a working temperature of $300^{\circ}C$. The sensor which is aged at $330^{\circ}C$ for 72hrs in oxygen ambient exhibited tourer sensitivity of 57, but more stable properties, excellent linearity.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.29 no.4
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• pp.272-278
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• 1993

The trimethylamine-sensing characteristics of ZnO based thin film semiconductors and the sensitivity enhancement by squttering conditions have been investigated to develop a new type sensor for detecting fish freshness. The sensor fabricated with a 300nm of ZnO thin film with 4 wt% Al sub(2) O sub(3) and 1 wt% TiO sub(2) exhibited the highest sensitivity of 155 at 30$0^{\circ}C$ of working temperature and to the 240 ppm TMA gas. Deposition of ZnO thin film using a RF magnetron sputter was carried out at a pressure of 10 super(-2) Torr in pure oxygen gas with an RF power of 100W. The sensor exhibited a large response to the actual gases produced by a mackerel at an early stage of decomposition.

• Journal of Sensor Science and Technology
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• v.30 no.6
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• pp.369-375
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• 2021

In this study, heterogeneous ZnO/CNTF composites were developed to improve the NO₂-sensing response, facilitated by the self-heating property. Highly conductive and mechanically stable CNTFs were prepared by a wet-spinning process assisted by the liquid crystal (LC) behavior of CNTs. Metal-organic frameworks (MOFs) of ZIF-8 were precipitated on the surface of the CNTF (ZIF-8/CNTF) via one-pot synthesis in solution. The subsequent calcination process resulted in the formation of the ZnO/CNTF composites. The calcination temperatures were controlled at 400, 500, and 600 ℃ in an N₂ atmosphere to confirm the evolution of the microstructures and NO₂-sensing properties. Gas sensor characterization was performed at 100 ℃ by applying a DC voltage to induce Joule heating through the CNTF. The results revealed that the ZnO/CNTF composite after calcination at 500 ℃ (ZnO/CNTF-500) exhibited an improved response (R_air/R_gas = 1.086) toward 20 ppm NO₂ as compared to the pristine CNTF (R_air/R_gas = 1.063). Selective NO₂-sensing properties were demonstrated with negligible responses toward interfering gas species such as H₂S, NH₃, CO, and toluene. Our approach for the synthesis of MOF-driven ZnO/CNTF composites can provide a new strategy for the fabrication of wearable gas sensors integrated with textile materials.

• Korean Journal of Materials Research
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• v.23 no.4
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• pp.211-214
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• 2013

The effects of a Ni coating on the sensing properties of nano ZnO:Ni based gas sensors were studied for $CH_4$ and $CH_3CH_2CH_3$ gases. Nano ZnO sensing materials were prepared by the hydrothermal reaction method. The Ni coatings on the nano ZnO surface were deposited by the hydrolysis of zinc chloride with $NH_4OH$. The weight % of Ni coating on the ZnO surface ranged from 0 to 10 %. The nano ZnO:Ni gas sensors were fabricated by a screen printing method on alumina substrates. The structural and morphological properties of the nano ZnO : Ni sensing materials were investigated by XRD, EDS, and SEM. The XRD patterns showed that nano ZnO : Ni powders with a wurtzite structure were grown with (1 0 0), (0 0 2), and (1 0 1) dominant peaks. The particle size of nano ZnO powders was about 250 nm. The sensitivity of nano ZnO:Ni based sensors for 5 ppm $CH_4$ gas and $CH_3CH_2CH_3$ gas was measured at room temperature by comparing the resistance in air with that in target gases. The highest sensitivity of the ZnO:Ni sensor to $CH_4$ gas and $CH_3CH_2CH_3$ gas was observed at Ni 4 wt%. The response and recovery times of 4 wt% Ni coated ZnO:Ni gas sensors were 14 s and 15 s, respectively.

• Korean Journal of Materials Research
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• v.21 no.9
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• pp.486-490
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• 2011

Nano-indium-coated ZnO:In thick films were prepared by a hydrothermal method. ZnO:In gas sensors were fabricated by a screen printing method on alumina substrates. The gas sensing properties of the gas sensors were investigated for hydrocarbon gas. The effects of the indium concentration of the ZnO:In gas sensors on the structural and morphological properties were investigated by X-ray diffraction and scanning electron microscopy. XRD patterns revealed that the ZnO:In with wurtzite structure was grown with (1 0 0), (0 0 2), and (1 0 1) peaks. The quantity of In coating on the ZnO surface increased with increasing In concentration. The sensitivity of the ZnO:In sensors was measured for 5 ppm $CH_4$ gas and $CH_3CH_2CH_3$ gas at room temperature by comparing the resistance in air with that in target gases. The highest sensitivity to $CH_4$ gas and $CH_3CH_2CH_3$ gas of the ZnO:In sensors was observed at the In 6 wt%. The response and recovery times of the 6 wt% indiumcoated ZnO:In gas sensors were 19 s and 12 s, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.06a
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• pp.247-247
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• 2009

In this work, Ga-doped ZnO (GZO) thin films for toxic gas sensor application were deposited on low temperature co-fired ceramic (LTCC) substrates, by RF magnetron sputtering method. LTCC is one of promising materials for integration with heater, low cost production and high manufacturing yields than silicon substrate. The LTCC substrates with thickness of $400\;{\mu}m$ were fabricated by laminating 12 greentapes which consist of alumina and glass particle in an organic binder. The GZO thin films deposited on the substrates and were analyzed by X-ray diffraction method (XRD) and field emission scanning electron microscope (FESEM). The films are well crystallized in the hexagonal (wurzite) structure with increasing thickness. The fabricated sensors showed good sensitivity and fast response time to common types of toxic gases (NOx, COx).