Development of Microsensors for NOx Gas Detection Based on Porous Silicon and Nano Structures

• Main Authors: Guan-pei Li, 李冠霈
• Other Authors: Hsing-Cheng Chang
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/32929131471077364547

碩士 === 逢甲大學 === 產業研發碩士班 === 97 === This study presents the design of metal-oxide micro gas sensors based on MEMS technology with porous silicon and nano-properties for NOx gas sensing in low concentration(5ppm) at relative low temperature(25℃∼60℃). Sensitivity is defined by measuring the variation of resistance for sensing layers caused by Schottky contact when gas specimens adsorb on the surface of sensing films. It is proposed that sensing films deposited onto the porous silicon surface fabricated by electrochemical etching are mixed with WO3 and MWCNTs by a sol-gel technique in order to increase effective area and chemical reactions on which gas molecules can be adsorbed. Interdigitated Ni catalytic electrodes are deposited onto the sensing films with a shadow mask by evaporating to improve gas adsorption on the surface of sensing films and increasing sensitivity. The gas micro sensor is also integrated with a heater made via lithography and deep etching processes for enhancing the properties of operation and response time. Experiments reveal the highest sensitivity of WO3 films is occured in the 5ppm of NOx at 60℃ and it is possible to detect 5ppm of NOx in room temperature. The response and recovery time of gas micro sensors are decreased with rising temperature that are 25s and 32s at lowest respectively. The results investigate the variation of sensitivities for sensing layers at various operating temperatures and different concentrations of NOx. The influence of dimensions for porous silicon and catalytic electrode on sensing response is also discussed.