Functional Design of Semiconductor Gas Sensors for Development of Odor Sensors

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The present project was focused on functional design of semiconductorgas sensors for development of odor sensors capable of detecting of odor components, such as trimethylamine (TMA), dimethylamine (DMA) and ammonia, with high sensitivity and selectivity.Thickness dependence of TMA gas sensistvity of sensors equipped with interior electrodes have been investigated by employing semiconductor metal oxides loades with and without different amounts of noble metals. It has revealed that optimum design of both the thickness and the catalytic activity for TMA oxidation of sensor materials is of primary importance for the development of TMA gas sensors.It was found that In_2O_3-MgO (5mol%) loaded with 3.0 wt% Pt (3.0Pt/In_2O_3-MgO (5mol%)) was the only sensor which exhibited higher sensitivity to DMA than TMA at 300ﾟC,among the sensors tested. The DMA sensitivity was further enhanced by coating the surface of 3.0Pt/In_2O_3-MgO (5mol%) sensor with a TiO_2 or 0.5Pt/TiO_2 layr. The high DMA sensitivity of the single layr sensor was found to be attributed to its high activity for producing ethylenimine and less activity for producing NO_X. Ethylenimine produced during the oxidation of TMA is more reactive with chemisorbed oxygen on the sensor material, while NO_X are oxidation products of TMA and act as interference gases.High NH_3 sensitivity could be realized with the doible layr sensor consisting of an In_2O_3-MgO (5mol%) sensing layr, a 0.5Ir/TiO_2 coating layr atop the sensing layr and electrodes between these two layrs. It was found that selection of both the sensor materials having moderate NH_3 oxidation without producing large amounts of NO_X and the coating layr exhibiting high activity for reduction of NO_X into N_2 by NH_3 is of primary importance for developing an NH_3 sensor having high sensitivity.