Chang-Hyun Shim

Tin oxide microsensor for LPG monitoring

Abstract A silicon-based SnO 2 gas sensor has been fabricated for monitoring liquified petroleum gas (LPG), commonly used as town gas. The gas sensor is made by silicon IC technology together with SnO f2 thin-film processing. The whole chip with a size of 9 mm x 9 mm consists of nine sensors (three by three array). each sensor is supported by a thin membrane of SiO 2 /Si 3 N 4 /SiO 2 layers that provides a low thermal mass and prevents heat conduction through the surrounding substrate material. Tin oxide thin film is prepared by thermal evaporation of metallic tin granules and subsequent thermal oxidation of the metallic film at 600 °C. To form the SnO 2 (Pt) thin film, a layer of Pt with a thickness of several tens of angstroms is sputtered onto the tin oxide film and heat treated at 500 °C in air for several hours in order to stabilize its electrical response. The fabricated SnO 2 (Pt) microsensors exhibit about 85 and 92% sensitivities to 5000 ppm C 3 H 8 and 5000 ppm C 4 H 10 (the main components of LPG) at 250 °C, respectively, and show a rapid response time of less than 5 s.

Gas sensing characteristics of SnO2 thin film fabricated by thermal oxidation of a Sn/Pt double layer

SnO2 thin film with homogeneously dispersed nano-crystallite Pt particles was reliably prepared via simple thermal oxidation of a Sn/Pt double layer on Si substrate oxidized. Its surface phase and morphology were probed using some surface sensitive tools such as X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM). The electrical response of SnO2 thin films to the i-C4H10 gas was systematically investigated at a wide range of temperatures and gas concentrations. In particular, a long-term stability test of the fabricated Pt/SnO2 thin films for the i-C4H10 gas proved its applicability as a reliable gas sensor because of its higher sensing stability than the conventional Pt/SnO2 films over a long period of run time.

Classification of workplace gases using temperature modulation of two SnO2 sensing films on substrate

Abstract Two SnO2-based sensing films (pure SnO2 and SnO2/Pt) and a Pt thin film as a temperature sensor were fabricated on an alumina substrate for classifying workplace environmental gases. By controlling the heating power in the shape of a trapezoid, a temperature profile of the SnO2 sensing films was created along with four unique sensing response curves to the tested gases. A principal component analysis (PCA) was performed using variables extracted from the sensing response curves. The results confirmed that the sensor array with the proposed operating mode was extremely effective in classifying workplace environmental gases, such as CO2, C3H8, and C4H10.

Three electrodes gas sensor based on ITO thin film

A three electrode type sensor was fabricated. This sensor consists of two parts. One is a tin doped indium oxide (or indium tin oxide: denoted ITO hereafter) film. It was fabricated by the metal thermal oxidation method. This produces a large surface area and low resistivity. So, this film has two functions, a gas sensitive film and an effective heater. The other part is a platinum resistor line covered with oxidized aluminum film. This part is located in the backside of the sensor. It plays three roles. The first is a load resistor for a measuring system. Secondly, it also acts as a heater. Most of the consumed power in the sensor is used as the thermal energy of gas sensing. The last role is catalytic combustible gas sensing in high gas concentrations. In this paper, the fabrication method of gas sensitive ITO film is researched. A complex sensor structure is fabricated. It acts as a hot wire semiconductor sensor at low gas concentration and a combustible catalytic sensor at high concentration.

Thermally oxidized tin black films for gas sensing

Abstract The tin dioxide (SnO2) films were been prepared by oxidization of tin black film which was deposited by thermal evaporation. This method can be used for a simple and economical fabrication of a SnO2 gas sensor. These films also have an ultra-porous structure and a grain size in the nanometer. The reduction of particle size to nanometers leads to a dramatic improvement in sensitivity. The particle size and structural properties of SnO2 film were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Through the addition of Pt sol as a catalyst, the SnO2/Pt films acquired an appropriate resistance and stable reaction, though sensitivity decreased. The gas sensing characteristics were also investigated using iso-C4H10, CH4, C3H8, and CO gases.

Development of High Sensitive Integrated Dual Sensor to Detect Harmful Exhaust Gas and Odor for the Automotive

A dual micro gas sensor array was fabricated using nano sized thin films which had good sensitivities to CO and combustible gases, or gas for air quality sensors in automobile. The already existed air quality sensor detects oxidizing gases and reducing gases, the air quality sensor(AQS), located near the fresh air inlet detected the harmful gases, the fresh air inlet door/ventilation flap was closed to reduce the amount of pollution entering the vehicle cabin through HVAC(heating, ventilating, and air conditioning) system. In this study, to make thin film AQS sensor, thin tin metal layer between 1000 and thick was oxidized between 600 and by thermal oxidation. The gas sensing layers such as , (pt) and (+CuO) were patterned by metal shadow mask for simple fabrication process on the silicon substrate. The micro gas sensors with (+Pt) and (CuO) showed good selectivity to CO gas among reducing gases and good sensitivity to that is main component of bad odor, separately.

Neural Network-Based Sensor Fault Diagnosis in the Gas Monitoring System

In this paper, we propose neural network-based fault diagnosis method to diagnose of sensor in the gas monitoring system. In the proposed method, using thermal modulation of operating temperature of sensor, the signal patterns are extracted from the voltage of load resistance. Also, ART2 neural network is used for fault isolation. The performance and effectiveness of the proposed ART2 neural network based fault diagnosis method are shown by simulation results using real data obtained from the gas monitoring system.

Classification of Indoor Environmental Gases Using Temperature Modulation

Two based sensing films(pure and /Pt) and a Pt thin film for temperature sensor on an alumina substrate were designed and fabricated for classifying the indoor environmental gases. By controlling the heating power in the shape of trapezoid, unique four sensing response curves created from both film and /Pt film. Then, various parameters were extracted from sensing response curves and carried out principal component analysis(PCA). The results confirm that a sensor array with the proposed operating mode was extremely effective in classifying indoor environmental gases such as , , .

Classification of Indoor Environmental Gases Using Temperature Modulation of Two SnO 2 Sensing Films on a Substrate

Two SnO2 based sensing fllms(pure SnO2 and SnO2/Pt) and a Pt thin film for temperature sensor on an alumina substrate were designed and fabricated for classifying the indoor environmental gases. By controlling the heating power in the shape of trapezoid, we made one temperature profile of SnO2 sensing films and the unique four sensing response curves to the tested gases from both SnO2 and SnO2/Pt film. We extracted variables from sensing response curves and carried out principal component analysis(PCA) with the variables and confirmed that the sensor array with this operating mode was very effective in classifying indoor environmental gases such as CO2, C3H8, C4H10.