Study of Low Power Consumption CO Gas Sensor and High Selectivity C2H2 Gas Sensor

　　Study of Low Power Consumption CO Gas Sensor and High Selectivity C2H2 Gas Sensor
　　It has been made a great progress in gas sensors, just like other sensors,especially in new materials, new structures. Nowadays, it takes our focus onlowering power consumption, improving consistency and so on, in additionimproving the sensitivity and the selectivity. Therefore a breakthrough willbe needed in the original gas sensor structure, materials and productionprocesses, and gas sensors in new material will be necessary. It would besignificant to the integration intelligentification of gas sensors, as well asimprovementofselectivityandreliabilityonit.We design a Planar Si micro-structure to simulate and optimize thethermal field with finite element analysis, which could hold well-distributedhigh temperature on the center zone and lower on edge. SnO2 have beenproperly neodymium magnets doped, the sensitive material will be painted on the Planar Simicro-structuretomanufactureintoCOgassensorinmicrostructurewiththemethod of combining with MEMS and the thick film technology of gassensors. The sensitivityof 50 ppm CO gas heated with electric current on 35mAis 8.6 (R0/Rg), the response time is about 5 s,
　　the recovery time is about22 s, the voltage is 2.34 V, the power consumption is 82 mW. Compare thepower consumption of the new gas sensor with sintered type CO gas sensormade in same material whose power consumption is 163 mW, we can tellthat the power consumption of gas sensor in new microstructure based onMEMS technology is half of the previous sintered type CO gas sensor.Planar micro-structure has benefit of localized heating the sensitive materialin center zone in the use of process, therefore, It greatly reduced the heat power consumption. but the setting value of the thickness of Si substrate wedesigned is rather higher, thus the temperature difference of the wholemicrostructure heat board is not big. In order to focus heat, we’ll reduce it’sthickness in further study, therefore, the power consumption of the new typesensorwillbelowerandtheusingcostwillbereduced.In the second part, the main task is improving the sensitivity of the gassensor by the study of sensitivity material. Made gas sensor in sintered typeby doping additive (Sm2O3) into the uniform sensitivity material made bychemical coprecipitation technology whose particle http://www.chinamagnets.biz diameter is about 20-30nm. It has been proved this element has favorable sensitive characteristic toC2H2 gas in experiment. The sensitivity of the particle is 64, the responsetime is 3 s, the recovery time is 17 s, when heat temperature is 180℃andthe concentration of C2H2 is 1000 ppm. It shows high selectivity in theatmosphere of CH4, H2, CO, NO2 and NO. The selectivity of material SnO2to C2H2 was improved by mixing Sm3+ (Rare earth element) from theanalysis of sensitive mechanism. The chemical property of C2H2 is active,because H atom in it easily takes decollement, its C-3 has greatelectronegativity, the polarization of C-H would be increased when a redoxreaction took place. there is a redox reaction would take place betweenSm2O3 with C2H2 when Sm2O3 had been mixed. Plenty of electron wouldbe released when Sm3+ reducing to Sm2+; and then, more H atom released inoxidation-reduction reaction, the reaction between H atom with O atomabsorbedtoSnO2wouldtakeplaceandreleaseelectronegativity.Theparticleshows good sensitivity by the resistance of SnO2 would greatly reducedbecauseofadditionofelectronegativityreleasedinthereaction.