| Summary: | 碩士 === 國立雲林科技大學 === 機械工程系 === 104 === This study is mainly to fabricate and study the resistive type micro CO2 gas sensors by using the La2O2CO3/SnO2 as the gas sensing material. In this thesis, the present work has many advantages such as micro-scale chip, low power consumption, high sensitivity, low cost and well batch mass production capability and so on. All the device processes needed were successfully completed by using the standard integrated circuits (ICs) and micro-electro-mechanical-system (MEMS) processes. And then, the characteristics of structure and material of gas sensors were measured and analyzed by SEM, EDS and XRD, respectively. Finally, the characteristics of developed resistive type micro CO2 gas sensors were also calibrated and verified. The research topics of this thesis mainly include with (1) the synthesis and analysis of La2O2CO3 catalytic materials, (2) the study of fabrication process of CO2 gas sensors especially focused on the coating and annealing conditions of La2O2CO3 catalytic materials or other fabrication conditions of sensors, and (3) the characterization of developed CO2 gas sensors.
In this result, first, a 500 nm/200 nm thick LPCVD SiO2/Si3N4 layer was deposited on the 6 inch p-type (100) silicon substrate as the insulation layer. Then, a 150 nm/300 nm/40 nm thick Ta/Pt/Au layer and a 800 nm thick SnO2 layer were deposited by using PVD and patterned as the electrodes, micro-heater and gas sensing resistor on the substrate, respectively. Next, the La(OH)3 uniform mixture containing with a mixing weight ratio of La(OH)3:IPA:Flux=1:1:2 was prepared by using an ultrasonicator for 60 minutes and then spin-coated at a spin speed of 2500 rpm on the substrate with a thin film thickness of 2 µm. Then, the heat insulation cavity underneath the micro-heater was etched and made by ICP DRIE. Finally, the La(OH)3 thin film was annealed at 450 oC for 60 minutes in the ambient air, and then transferred to be the La2O2CO3 catalytic crystals. The CO2 gas sensors were completed. Before the packaging and calibration of fabricated CO2 gas sensors, the sensors were annealed again at 450 oC for 24 hours to reduce the noise of output signal and the micro-heater was powered under an applied power of 154 mW with an operating temperature of 300 oC for two hours to stabilize the electrical signal level, respectively. In this study, in the best result under an applied power of 154 mW, the sensitivities of resistive type micro CO2 gas sensor are 6.53, 12.63, 17.32, 21.47, 24.68 and 26.58 % under the CO2 gas concentrations of 400, 800, 1200, 1600, 2000 and 2400 ppm, respectively. The more detailed study information will be discussed in this thesis.
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