Hyung-Ki Hong

Thick-film zinc-oxide gas sensor for the control of lean air-to-fuel ratio in domestic combustion systems

Abstract We have investigated the sensing properties of Al2O3-doped ZnO for combustion control in lean-burn conditions. Planar-type sensing elements made of heater, electrode and sensing layer were formed on an alumina substrate using a screen-printing technique. Our exhaust-gas sensor exhibits significant resistance changes even under lean conditions, apparently due to the simultaneous functioning of bulk and surface conduction mechanisms. Utilizing the sensor for the feedback control of a domestic boiler, we have demonstrated that the system can be successfully operated at the best combustion conditions.

Portable electronic nose system with gas sensor array and artificial neural network

Abstract A portable electronic nose system has been fabricated and characterized using an oxide semiconductor gas sensor array and artificial neural network. The sensor array consists of such thick-film oxide semiconductor sensing materials as Pd-doped WO3, Pt-doped SnO2, TiO2–Sb2O5–Pd-doped SnO2, TiO2–Sb2O5–Pd-doped SnO2+Pd-coated layer, Al2O3-doped ZnO and PdCl2-doped SnO2. The portable electronic nose system consists of an Intel 80c196kc as CPU, an EEPROM and an LCD for displaying gas concentrations, etc. As an application, the system has been used to identify 26 CO/HC car exhausting gases and the identification has been successfully demonstrated.

Ozone sensing properties of In2O3-based semiconductor thick films

Ozone sensing properties of In2O3-based semiconductor thick films have been investigated. The In2O3 sensing layer is quite sensitive to ozone, but the rapid saturation in sensitivity cannot be obtained. The addition of Fe2O3 (3 wt.%) into In2O3 and the high temperature firing of the mixed powder give rise to a remarkable improvement in response and recovery, although the sensitivity decreases. The sensing layer fired at 1300°C and operated at 550°C shows excellent properties such as fast response, stable sensitivity, and rapid recovery. In addition to it, the sensor shows a good linearity with ozone concentration and a good reproducibility. The preliminary results clearly demonstrated that the sensor was successfully applied for the ozone detection of parts per billion range.

Multi-layered thick-film gas sensor array for selective sensing by catalytic filtering technology

Abstract A C3H8 gas sensor array with high sensitivity and good selectivity by the combination of the catalytic filtering and the gas diffusion control has been achieved. The gas sensor array consists of a couple of catalytic filter layers, one with a Pd and the other with a Pt, a SiO2 insulating layer and two sensing layers on an alumina substrate. The sensor array shows high sensitivity to 500 ppm of C3H8 at temperature above 400°C and good selectivity for the interfering gases such as CO and C2H5OH by using a simple signal processing technique.

Gas identification using micro gas sensor array and neural-network pattern recognition

Abstract In order to identify CH3SH, (CH3)3H, C2H5OH and CO gases in the concentration range of 0.1 to 100 ppm, a gas recognition system using a gas sensor array and neural-network pattern recognition has been fabricated. The sensor array consists of such thin film oxide semiconductor sensing materials as 1 wt% Pd-doped SnO2, 6 wt% Al2O3-doped ZnO, WO3 and ZnO. The principal component analysis and the neural-network pattern recognition analysis were used for the discrimination of gas species and concentrations. Good separation among gases and concentrations was obtained using the principal component analysis. The recognition probability of the neural-network was 100% for each 5 trials of 12 gas samples.

Electronic nose system with micro gas sensor array

Abstract We have fabricated an electronic nose system using a thin film oxide semiconductor micro gas sensor array which shows only 65 mW of power consumption at an operating temperature of 300°C. Principal component analysis and neural network pattern recognition analysis were used to identify 12 gas samples (CH3SH, (CH3)3N, C2H5OH and CO gases in the concentration range of 0.1–100 ppm) or six flavor samples (carrot, green onion, womans perfume (eau de cologne), mans perfume (eau de toilette), 25% liquor (Korean soju) and 40% liquor (whisky)). Good separation among the gases with different concentrations or flavor samples was obtained using the principal component analysis. The recognition probability of the neural network was 100% for each of the 5 trials of 12 gas samples and 93% for each of 10 trials of 6 flavor samples.

Highly sensitive and selective ammonia gas sensor

We have fabricated and examined an ammonia gas sensor with high sensitivity using thick-film technology. The sensing material of the gas sensor is FeO/sub x/-WO/sub 3/-SnO/sub 2/ oxide semiconductor. 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. We have proposed and investigated a novel method for detecting ammonia gas quite selectively by using a sensor array with two sensing elements which contains an ammonia gas sensor and a compensation element. The compensation element is a Pt-doped WO/sub 3/-SnO/sub 2/ gas sensor which shows an opposite direction of resistance change in comparison with the ammonia gas sensor upon exposure to ammonia gas. Excellent selectivity has been achieved using the sensor array with two sensing elements.

Abnormal current-voltage characteristics of WO3-doped SnO2 oxide semiconductors and their applications to gas sensors

Abstract We have investigated abnormal current-voltage characteristics of an oxide semiconductor and have developed a novel method of detecting reducing gases utilizing the self-heating mechanism of the sensing layer without an additional heater. Planar-type sensors based on WO 3 -doped SnO 2 were fabricated using a screen-printing technique. The applied voltage across the sensing layer caused heating of the sensing layer and the current abruptly varied upon exposure to a gas, mainly as a result of surface reactions. A fascinating aspect of the gas sensing scheme is that no additional heater is necessary for detection. The new sensing method has been applied to C 2 H 5 OH gas in this preliminary work.