Ultra-High-Sensitive Detection Using Pulse-Heating of MEMS-Type Oxide Semiconductor Gas Sensor: (1) Detection of Toluene in Ppt Level

摘要

Ultra-High-Sensitive gas detection in ppt level has been proposed by using pulse-heating of MEMS-device based on SnO_2. My group reported three important factors, receptor, transducer functions and utility factor, for gas sensor material designs and their integration in 2003 (1) and 2006 (2), respectively. In 2014, based on the integration of the above factors, the gas sensor using Pd-SnO_2 clusters prepared by hydrothermal treatment could successfully detect toluene in ppb level (3). To enhance the sensor response more, we investigated the combination of utility factor and pulse-heating of MEMS. In 2018, we reported that such sensor responded to toluene in 0.1 ppb (4). To enhance the sensor response, we paid attention to oxygen adsorption species and the amounts. In the case of Pd-SnO_2, oxygen adsorbed as mainly O~(2-) on the surface, but the amounts become smaller with decreasing in temperature. To overcome such oxygen adsorption state, we investigated the preheating and waiting-time before pulse-heating for measurement. Finally, the gas response was found to increase as shown in Fig. 1. It is found that the sensor response depends on the waiting-time between pre-heating and measure-heating. In the presentation, I will show the details of UHS (Ultra-High Sensitive) gas sensor.