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Detailed Program
Paper Number : SE-I02
Time Frame : 11:10~11:35
Presentation Date : Thurse day, 27, November
Session Name : Sensor Materials
Session Chair 1# : Jong-heun Lee
Session Chair 2# : Kengo Shimanoe
Development of Oxide Semiconductor Gas Sensors for High Sensitivity under Humid Condition
Kengo SHIMANOE
Kyushu University
Semiconductor gas sensors using metal oxides are widely used for various purposes such as alarms of gas leakage and toxic gas, alcohol checker and so on. Recently the strict requirements to gas sensors is increasing, for example lower detection limit in humid atmosphere. So far, we have reported important three factors, receptor and transducer functions and utility factor, for material design of semiconductor gas sensor. Especially the former function is related with the water vapor poisoning deeply. In this presentation, I would like to show the properties of Pd-loaded and Sb-doped SnO2 as a receptor function.
Neat SnO2 and antimony-doped tin dioxide powders were prepared by co-precipitation and hydrothermal method. In addition, Pd was loaded on neat SnO2 by impregnation method using Pd(NH3)2(NO2)2 aqueous solution. The obtained powders were screen-printed on an alumina substrate (9 mm ¡¿ 13 mm¡¿ 0.38 mm) attached with Au electrodes. The resulting devices were heat-treated at 580 ¡ÆC for 3 h in air to stabilize the sensing layer. The sensor measurements were carried out in a conventional gas flow apparatus equipped with an electric furnace. The sensor response was defined as the ratio of electric resistance in synthetic air (Ra) and hydrogen gas (Rg).
Figure 1 shows the sensor responses to H2 in different humidity for Pd-loaded and Sb-doped SnO2. The sensor responses of both devices under humid condition were fairly constant although that of neat SnO2 was decreased with increasing water vapor concentration. Such a stability to humidity change seems to be due to oxygen adsorption species. From the dependence of electric resistance on oxygen partial pressure under humid condition, O2- was found to be main adsorption species for the Pd-loaded and Sb-doped SnO2 although neat SnO2 was related with O-. Such a difference in adsorption species is known to give a great influence on sensor response1). In addition, it seems that both p-n junction of PdO-SnO2 and property of Sb on SnO2 surface are related with suppression of water vapor poisoning. The detail will be explained in the presentation.















Figure 1 Sensor response to hydrogen under humid condition for Pd-loaded SnO2 (a)
and Sb-doped SnO2 (b).

Reference:
[1] N. Yamazoe, K. Suematsu, K. Shimanoe, Sens. Actuators B, 163, 128-135 (2012).
Acknowledgements :