• Journal of Sensor Science and Technology
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• v.13 no.3
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• pp.218-223
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• 2004

Thin film gas sensor based on tin oxide was fabricated and its characteristics were examined. Target gas is acetonitrile ($CH_{3}CN$) that is simulant gas of blood agent gas. Sensing materials are $SnO_{2}$, $SnO_{2}$/Pt, and (Sn/Pt)oxidation with thickness from $1000{\AA}$ to $3000{\AA}$. Sensor was consisted of sensing electrode with interdigit (IDT) type in front side and a heater in back side. Its dimension was $7{\times}10{\times}0.6mm^{3}$. Fabricated sensor was measured as flow type and monitored real time using PC. The optimal sensing material for $CH_{3}CN$ was {Sn($3000{\AA}$)/Pt($30{\AA}$)}oxidation and its sensitivity and operating temperature were 30%, $300^{\circ}C$ in $CH_{3}CN$ 3 ppm.

• Korean Journal of Materials Research
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• v.23 no.12
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• pp.667-671
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• 2013

We present an easy method of preparing two-dimensional (2D) periodic hollow tin oxide ($SnO_2$) hemisphere array gas sensors using polystyrene (PS) spheres as a template. The structures were fabricated by the sputter deposition of thin tin (Sn) metal over an array of PS spheres on a planar substrate followed by calcination at an elevated temperature to oxidize Sn to $SnO_2$ while removing the PS template cores. The $SnO_2$ hemisphere array structures were examined by scanning electron microscopy and X-ray diffraction. The structures were calcined at various temperatures and their sensing properties were examined with varying operation temperatures and concentrations of nitric oxide (NO) gas. Their gas-sensing properties were investigated by measuring the electrical resistances in air and the target gases. The measurements were conducted at different NO concentrations and substrate temperatures. A minimum detection limit of 30 ppb, showing a sensitivity of S = 1.6, was observed for NO gas at an operation temperature of $150^{\circ}C$ for a sample having an Sn metal layer thickness corresponding to 30 sec sputtering time and calcined at $600^{\circ}C$ for 2 hr in air. We proved that high porosity in a hollow $SnO_2$ hemisphere structure allows easy diffusion of the target gas molecules. The results confirm that a 2D hollow $SnO_2$ hemisphere array structure of micronmeter sizes can be a good structural morphology for high sensitivity gas sensors.

• Korean Journal of Materials Research
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• v.13 no.2
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• pp.111-114
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• 2003

Effects of substrate materials on the microstructure and the sensitivity of $SnO_2$thin film gas sensors have been studied. Various substrates were studied, such as oxidized silicon, sapphire, polished alumina, and unpolished alumina. It was observed that strong correlation exists between the electrical resistance and the CO gas sensitivity of the manufactured sensors and the surface roughness of $SnO_2$thin films, which in turn was related to the surface roughness of the original substrates. X$SnO_2$thin film gas sensor on unpolished alumina with the highest surface roughness showed the highest initial resistance and CO gas sensitivity. The transmission electron microscopy observation indicated that shape and size of the columnar microstructure of the thin films were not critically affected by the type of substrates.

• Journal of the Korean Ceramic Society
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• v.40 no.10
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• pp.973-980
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• 2003

The effects of additives in n-type semiconducting SnO$_2$-based gas sensors on oxidizing gases were investigated. The resistivity of SnO$_2$ sensors decreased when exposed to reducing gases, which act as electronic donors. However, the resistivities of the SnO$_2$ sensors increased when exposed to oxidizing gases, which act as electronic accepters. The products formed from the reaction of oxidizing gases ever SnO$_2$-based powders were analyzed by gas chromatography as compared with those formed from the reaction of reducing gases of alcohols. The SnO$_2$ sensors doped with PdCl$_2$ or A1$_2$O$_3$ showed unique dual response patterns toward oxidizing gases of $CH_3$CN and $CH_3$NO$_2$ depending on the operating temperature. The combination of these two sensors along with proper pattern recognition technique could enhance the selectivity for the gases with electron-accepting groups.

• Journal of the Korea Institute of Military Science and Technology
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• v.7 no.2 s.17
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• pp.81-87
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• 2004

Semiconductor thick film gas sensors based on tin oxide are fabricated and their gas response characteristics are examined for four simulant gases of chemical warfare agent (CWA)s. The sensing materials are prepared in three different sets. 1) The Pt or Pd $(1,\;2,\;3\;wt.\%)$ as catalyst is impregnated in the base material of $SnO_2$ by impregnation method.2) $Al_2O_3\;(0,\;4,\;12,\;20\;wt.\%),\;In_2O_3\;(1,\;2,\;3\;wt.\%),\;WO_3\;(1,\;2,\;3\;wt.\%),\;TiO_2\;(3,\;5,\;10\;wt.\%)$ or $SiO_2\;(3,\;5,\;10\;wt.\%)$ is added to $SnO_2$ by physical ball milling process. 3) ZnO $(1,\;2,\;3,\;4,\;5\;wt.\%)$ or $ZrO_2\;(1,\;3,\;5\;wt.\%)$ is added to $SnO_2$ by co-precipitation method. Surface morphology, particle size, and specific surface area of fabricated sensing films are performed by the SEM, XRD and BET respectively. Response characteristics are examined for simulant gases with temperature in the range 200 to $400^{\circ}C$, with different gas concentrations. These sensors have high sensitivities more than $50\%$ at 500ppb concentration for test gases and also have shown good repetition tests. Four sensing materials are selected with good sensitivity and stability and are fabricated as a sensor array A sensor array Identities among the four simulant gases through the principal component analysis (PCA). High sensitivity is acquired by using the semiconductor thick film gas sensors and four CWA gases are classified by using a sensor array through PCA.

• Proceedings of the Korean Ceranic Society Conference
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• 2003.10a
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• pp.190.2-190
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• 2003

• Journal of Sensor Science and Technology
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• v.17 no.4
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• pp.295-302
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• 2008

$TiO_2,\;ZrO_2$, and $SiO_2$ were added in the concentration of 1 - 3 wt.% to improve long-term stability for the $SnO2$ thick film gas sensor. Short-term sensor resistances up to 90 h were measured to investigate the stabilization time of initial resistance in air. Long-term resistance drifts in air and in gas to 5000 ppm methane for the sensors annealed at $750^{\circ}C$ for 1 h and continuously heated at an operating temperature of $400^{\circ}C$ were also measured up to 90 days at an interval of 1 day. The long-term drifts in methane sensitivity for the three metal oxide-doped $SnO2$ sensors are closely related to methane sensitivity level, catalytic activity, and long-term drift in sensor resistance in air. Those stabilities are mainly discussed in terms of oxidation state and catalytic activity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.267-268
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• 2006

전력소모를 감소시키기 위해 MEMS 기술을 이용하여 마이크로 히터를 제작하고 그 위에 감지물질을 도포하여 마이크로 센서를 제작하였다. 마이크로 가스센서는 $SnO_2$를 모물질로 하였으며 가스 감도를 향상시키기 위해 Pd와 Rh, ${\alpha}-Fe_2O_5$, $V_2O_5$를 첨가하여, CO 가스 강도를 조사하였다. $SnO_2$에 촉매로서 Pd만을 첨가하였을 때보다 Rh, ${\alpha}-Fe_2O_5$. $V_2O_5$등을 첨가하였을 때 CO가스에 대한 감도 반응이 우수하였다. 마이크로 가스센서의 소비전력은 42mW이었다.

• Journal of the Microelectronics and Packaging Society
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• v.15 no.4
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• pp.101-106
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• 2008

The $SnO_2$ thin films doped with Pd and CNT as $NO_2$ gas sensor were prepared by spin coating and then the $NO_2$ gas response of these films were evaluated under $1ppm{\sim}5ppm\;NO_2$ concentration and operating temperature of $200^{\circ}C$. It was found that the sensor resistance was increased with $NO_2$ exposure and $NO_2$ concentration. The 3wt% Pd doped sample showed a sensitivity of 26.5 which was 10 times higher than that of pure $SnO_2$. And also the sensitivity of CNT doped sample increased with CNT content and it had 72 when 0.225 wt% of CNT was added under 5ppm $NO_2$ concentration.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.5
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• pp.239-243
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• 2012

$SnO_2$ thin films were prepared on the Si substrate by radio frequency (RF) magnetron sputtering and then post deposition vacuum annealed to investigate the effect of annealing temperature on the structural properties and hydrogen gas sensitivity of the films. The films that annealed at $300^{\circ}C$ show the higher sensitivity than the other films annealed at $150^{\circ}C$. From atomic force microscope observation, it is supposed that post deposition annealing promotes the rough surface and also, increase gas sensitivity of $SnO_2$ films for hydrogen gas. These results suggest that the vacuum annealed $SnO_2$ thin films at optimized temperatures are promising for practical high-performance hydrogen gas sensors.