Yeongsoo Choi

Micro-Thermoelectric Hydrogen Sensors with Pt Thin Film and Pt ∕ Alumina Thick Film Catalysts

Micro-thermoelectric hydrogen sensor (micro-THS) was fabricated to operate with its unique working principle of the combination of the thermoelectric effect of SiGe thin film and the Pt-catalyzed exothermic reaction of hydrogen oxidation. We focused on improving sensitivity and response speed of micro-THS using a new catalyst deposition method. Comparing with the two catalysts of thin and thick film technology, sensitivity of the micro-THS with Pt/alumina thick film catalyst was 5 times higher than that of the sensor with Pt thin film catalyst. The ΔT A-B of Pt/alumina thick film catalyst was large enough for a wide detection range of hydrogen concentration from 25 ppm to 3%, although its size was small, 35% of the Pt thin film one. At operating temperature of 100°C, for the low hydrogen concentration of 25 ppm, clear response of 0.03 mV the micro-THS with Pt/alumina thick film catalyst was observed.

Micromachined Thermoelectric Hydrogen Sensor of Double-Membrane Structure

We have prepared a noble micromachined gas sensor by combining two identical micro-hot plates on membranes fabricated by anisotropic wet etching of silicon substrate and a thermoelectric hydrogen sensor. The thermoelectric hydrogen sensor selectively detects the hydrogen gas working with the thermoelectric effect of SiGe thin film and the Pt-catalyzed exothermic reaction of hydrogen oxidation. The double-membrane structure thermally isolates two central and rectangular membranes from the rim of a room-temperature bulk substrate, minimizing offset voltage by keeping both membranes at the same temperature. The Pt catalyst as small as 1.5 ×1.5 mm2 builds up the temperature difference in the thermoelectric film by the oxidation of 1% hydrogen in air, producing an output voltage of 0.38 mV as a signal at an operating temperature of 100°C.

Micro thermoelectric device with ceramic combustor

A combustor of Pt/alumina catalyst was developed for the integration on micro-thermoelectric hydrogen sensor (/spl mu/-THS) with a dispenser method. The Pt/alumina catalyst was deposited on Si substrate and the hydrogen/air mixture gas was flowed to test the combustion performance. The temperature difference, developed by the heat generated from hydrogen oxidation on the catalyst, between catalyst surface and Si substrate showed its maximum at the Pt content of 40 wt% in the catalyst. The effect of the catalyst size on the thermoelectric voltage (/spl Delta/Vs) of /spl mu/-THS was investigated. The catalyst (/spl Phi/ = 0.8 mm) smaller than the membrane developed the highest /spl Delta/Vs because of its good thermal insulation and high combustion performance. For the gas mixture of hydrogen/air, the /spl mu/-THS showed wide range hydrogen detection, 5 ppm

SiGe Thermoelectric Film for Gas Sensor Micro-Devices

3%, with the /spl Delta/Vs of 0.007 mV-34 mV.

Planar catalytic combustor film for thermoelectric hydrogen sensor

A gas sensor micro-device using both thermoelectric film and catalyst film has been developed on the platform of micro-hotplate. Thermoelectric thin film of B-doped SiGe was deposited on the Si 3 N 4 /SiO 2 /Si substrate by helicon sputtering method and thermal annealing was carried out to crystallize the as-deposited amorphous-like film. With increasing the annealing temperature and time, the crystallization of the SiGe thin film progressed, resulting in high carrier mobility and large absolute value of Seebeck coefficient. The hydrogen sensitivity of the micro-thermoelectric gas sensors was investigated.