(Keynote) Design of Ultra-High-Sensitive Gas Sensors By Combination of Metal Oxides Semiconductor and MEMS

Abstract

Ultra-High-Sensitive (UHS) gas detection in ppt level has been proposed by using pulse-heating of MEMS-device based on SnO2. My group reported three important factors, receptor function, transducer function 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-loaded SnO2 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. The MEMS-type gas sensors are repeatedly heated and allowed to cool by the application of voltage to the micro-heater; the toluene gas penetrates into the interior of the sensing layer (Pd-loaded SnO2 clusters) during its unheated state. 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-loaded SnO2, oxygen adsorbed as mainly O2- 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 addition, to apply the UHS gas sensor using MEMS-type for aliphatic compounds such as alcohol, we have investigated a composite material that consists of the perovskite-type oxide (Ba0.9La0.1FeO3-σ) and SnO2 nanoparticles. The obtained results indicated that perovskite type oxide added SnO2 nanoparticles exhibits higher sensor response to C2H5OH than that of pure SnO2. Furthermore, the introducing of the pre-heating before measurement was effective for the sensor response as same as the case of toluene detection. Such sensor operation for composite material enabled the detection of ethanol in ppb level. It seems that the perovskite-type oxide plays a role of oxygen supplier to avoid the situation of oxygen absent or that the perovskite-type oxide works as a partial oxidation catalyst. In the presentation, I will show the design of UHS gas sensor in details.References(1) N. Yamazoe, G. Sakai, K. Shimanoe, Catalysis Surveys from Asia, 7(1), 63-75 (2003).(2) K. Shimanoe, N. Yamazoe, Proc. The 4th AIST International Workshop on Chemical Sensors, pp. 43-51 (2006).(3) K. Suematsu, Y. Shin, Z. Hua, K. Yoshida, M. Yuasa, T. Kida, K. Shimanoe, ACS Appl. Mater., 6, 5319−5326 (2014).(4) K. Suematsu, W. Harano, T. Oyama, Y. Shin, K. Watanabe, K. Shimanoe, Anal. Chem., 90(19), 11219-11223 (2018). Figure 1