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We have investigated the nonanal sensing properties of Pt-, Pd-, and Au-loaded SnO2 (Pt, Pd, Au/SnO2) thick films. These films show a higher response to nonanal than a non-loaded SnO2 film, can detect several tens of ppb of nonanal and exhibit fast response and recovery times. Their nonanal sensing ability is improved by pretreatments, such as annealing temperature and aging. The resistance of these films in pure air depends on the working temperature, but the resistance in nonanal gas depends mainly on the film thickness. We suggest nonanal detection models for Pt, Pd, Au/SnO2 films with different film thicknesses, and determine the optimum film thickness for nonanal detection.

Thermoelectric gas sensors (TGS) for microcalorimeters with a CO combustion catalyst were fabricated and tested for the detection of ppm level CO. Two types of CO combustion catalysts containing 3 wt% Au, Pd, and Pt loaded on CoO and Co 3 O 4 were prepared through a colloidal mixing process and integrated on the TGS. The 3 wt% AuPdPt loaded on the CoO and Co 3 O 4 catalysts exhibited stable CO combustion performance at temperatures as low as 200 °C, which is a much lower temperature than that of a previous study using a Au/Co 3 O 4 catalyst. The TGS of 3 wt%(AuPdPt)/CoO catalyst showed better CO selectivity than that of Co 3 O 4 , and could detect CO over a wide concentration range from 1 ppm to 1% (v/v) CO in air, with a gas concentration resolution of 1 ppm CO, signal to noise ratio of 6.8, and CO selectivity against H 2 of 1.75.

Thin-film couples of BiSbTe and Pt were deposited by RF sputtering and patterned by lift-off technique to form thermopile structures. To fabricate a planar micro-TE-generator, 11 thermopiles are connected in series as an array and Pt-loaded alumina ceramic catalyst was deposited on the thermopile as a combustor layer. The combustion and TE performance of the generator was investigated flowing 3 v/v% hydrogen in air into the test chamber; the average temperature gradient of eleven thermopiles developed between the hot and cold junctions of thermopiles was 50.6 K, and 1.9 μW of power was generated.

The performance of a microcombustor thermoelectric generator device based on a thermopile using p-type Bi0.3Sb1.7Te3 (BST) and n-type Pt films has been investigated. The BST films were prepared by two different methods—pulsed laser deposition (PLD) and sputter deposition—on Si3N4/SiO2 multilayers on Si substrate. The ceramic catalyst combustor was patterned on the thermopile end on a thin membrane fabricated by back-side bulk etching of the silicon substrate. At 138°C the thermoelectric power factors of the PLD and sputter-deposited films were 3.6 × 10−3 W/mK2 and 0.22 × 10−3 W/mK2, respectively. The power from the generator with the sputter-deposited film was 0.343 μW, which was superior to that of the device with the PLD film, which provided 0.1 μW, for combustion of a 200 sccm flow of 3 v/v% hydrogen in air.

The CO gas, which is several ppm level in the human breath, is used for medical examination. In this study, CO combustion catalysts of Au, Pt and Pd loaded on CoO on the thermoelectric gas sensor (TGS) were developed and the combustion performance of these catalysts was evaluated. We have demonstrated that the micro-THS detected the CO concentration in air from low as 1 ppm to high as 1 vol%. The noise voltage level of the sensor was 0.13V, and the signal to noise ratio, S/N was 2.09V/0.13V = 16.1 for 1ppm CO/air.

We have investigated the VOCs-sensing properties of Pt, Pd, Au-loaded SnO2 thick film for exhaled breath air. It has been reported that breaths of lung cancer patients include long methylene chain-aldehydes, such as nonanal. The Pt, Pd, Au-loading for SnO2 type gas sensors is advantage for detect to low concentration VOCs. The Pt,Pd,Au/SnO2 element shows higher response to nonanal than a non-loaded SnO2 element. The combustion of nonanal molecules on the surface of SnO2 grains is assisted by added noble metals. A nonanal-sensing property of the The Pt,Pd,Au/SnO2 depend on an annealing temperature. We installed the sensor element to a prototype of breath monitor with gas-chromatograph system, and analyzed mixed gas including three long methylene chain-aldehyde gases.