Wan-Young Chung

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.

Low-power micro gas sensor

The stable and low-power heating characteristics of a microheater are very important for the micro gas sensor. Membrane-type gas sensors have been fabricated by silicon IC technology. Steady-state thermal analysis by the finite-element method is performed to optimize the thermal properties of the gas sensor. From the analysis, the desirable size of the microheater for low power consumption is determined. The heating properties of fabricated poly-Si and Pt microheaters have been tested. The sensing characteristics of the packaged microsensor are also examined.

Spin-coated indium oxide thin film on alumina and silicon substrates and their gas sensing properties

Abstract Thin films of indium oxide were prepared on alumina and silicon substrates by spin-coating from an aqueous acetic acid solution dissolving In(OH) 3 and ammonium carboxymethyl cellulose. The films could cover well the large grains of rough alumina as well as the flat surface of silicon. By changing the number of spin-coating, the film thickness was well controlled between 70nm and 210nm on alumina or between 65 nm and 220 nm on silicon, as observed by cross-sectional FE-SEM. Gas sensing properties including sensitivity, selectivity and the rates of response and recovery were strongly dependent on the kind of substrate, film thickness and operating temperature.

SO2 sensing characteristics of Nasicon electrolytes

Abstract The SO 2 sensing characteristics of the Nasicon electrolyte cells Pt,SO 2 ,O 2 (I) I Na 2 SO 4 I Nasicon I O 2 (II) in air, Pt and Pt,SO 2 ,O 2 (I) l Na 2 SO 4 (BaSO 4 ) I Nasicon I Na 2 SiO 3 ,Pt have been studied in 5–98 ppm SO 2 concentration range at 300–550°C. The cell with the O 2 reference electrode was very unstable. However, good agreement between the measured and calculated slopes in the Nernst equation was obtained for the cell with the Na 2 SiO 3 solid reference electrode. The addition of 40 mol% BaSO 4 to the Na 2 SO 4 auxiliary electrolyte could eliminate the water vapor effect under the wet SO 2 atmosphere.

Characterization of porous tin oxide thin films and their application to microsensor fabrication

Abstract A porous tin oxide thin film has been prepared by thermal evaporation of metallic tin granules onto a silicon wafer and subsequent thermal oxidation. The temperature profile in the thermal oxidation greatly affects the microstructure and gas-sensitivity characteristics of the tin oxide film. The thin sensitive film is applied to microsensor fabrication. An SDB (silicon direct bonding) wafer is used as a substrate. In this wafer, the membrane thickness is exactly controlled without any stresses from the epitaxial layer or other membrane oxide material used for the etch-stop layer. The contact properties of Pt-SnO 2 and the sensing characteristics of the microsensor have also been investigated.

Low Power Micro Gas Sensor

The stable and low power heating characteristics of a microheater are very important for the micro gas sensor. The membrane type gas sensors were fabricated by silicon IC technology. The steady-state thermal analysis by finite-element method was performed to optimize the thermal properties of gas sensor and to reduce operating power and heat transfer to peripheral IC circuit. The heating characteristics of fabricated poli-Si and Pt heaters were examined.

Real Time Drowsiness Detection by a WSN based Wearable ECG Measurement System

Whether a person is feeling sleepy or reasonably awake is important safety information in many areas, such as humans operating in traffic or in heavy industry. The changes of body signals have been mostly researched by looking at electroencephalogram(EEG) signals but more and more other medical signals are being examined. In our study, an electrocardiogram(ECG) signal is measured at a sampling rate of 100 Hz and used to try to distinguish the possible differences in signal between the two states: awake and drowsy. Practical tests are conducted using a wireless sensor node connected to a wearable ECG sensor, and an ECG signal is transmitted wirelessly to a base station connected to a server PC. Through the QRS complex in the ECG analysis it is possible to obtain much information that is helpful for diagnosing different types of cardiovascular disease. A program is made with MATLAB for digital signal filtering and graphing as well as recognizing the parts of the QRS complex within the signal. Drowsiness detection is performed by evaluating the R peaks, R-R interval, interval between R and S peaks and the duration of the QRS complex..

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.