新型高性能3D奈米柱狀結構PIN二極體甲烷(CH4)感測器研製

Abstract

The Pd/MOX/HfO2 p-i-n diodes on Si substrate were developed for methane gas (CH4) sensing applications. Firstly, the p(100) Si substrates were etched by AgNO3 mixed HF solution to form nanorod structure. Then the intrinsic layer HfO2 film was deposited on the Si nanorods with radio frequency sputtering system, and followed by deposition of various metal oxide such as WO3、SnO2、ZnO as sensing elements. The sensing element was examined using XRD、AFM and SEM, respectively for crystallinity, surface roughness and morphology. Finally, Pd metal was deposited thermally on the top as the catalyst and electrode contact to complete the device. We optimized the CH4 gas sensor performances through the following studies :(1) using different intrinsic layer materials such as p/n、HfO2、SiO2、TiO2 , (2) to deposit HfO2 film with varying O2/Ar flow ratio, (3) comparing the 3D nanorod structure to the conventional 2D thin film p/n diode one , and(4) use of different metal oxides such as WO3、SnO2、ZnO as sensing element. Experimental results show the intrinsic layer of hafnium oxide with oxygen atomic ratio of 5/1 is best dielectric for reduction of off leakage current. Besides, the 3D p-i-n nanostructure enhances the sensitivity of the sensor, from 498.5% of the conventional 2D thin film type to 1652%. In addition, under 200 oC, 3V reverse bias and 100ppm methane ambient, the WO3 sensing element can attain the highest sensitivity of 152.9%, which is more than 85.5% and 21.9% for SnO2 and ZnO, respectively. Furthermore, the WO3 has the fast response time of 20 sec and the highest selectivity compared with hydrogen and carbon dioxide gases. In this work, under 200 oC and 100ppm ambient, the developed 3D nanorod p-i-n CH4 sensor has the best performance of 152.9% and 20 sec, respectively for sensitivity and response time. The performances are better than that of 18% and 52.2 sec for the reported Pt/ZnO/Zn MSM Schottky diode under same conditions.