| Summary: | 碩士 === 國立臺灣科技大學 === 材料科技研究所 === 96 === In this thesis, we deposit CeO2,(Gd2O3)x-(CeO2)1-x and Ag- CeO2 thin films on Al2O3 substrate by using magnetron sputtering process, anneal the films, then deposit Pt as electrode to fabricate resistive-type oxygen sensor, analyze its electronal properties, activation energy, and sensors sensitivity of CeO2 thin film, and correlate to their microstruture. Finally, we measure the oxygen sensor’s response time at high temperature(750℃) and low temperature(450℃) and fabricate the resistive oxygen sensors which have good sensitivity and fast response time.
The CeO2 thin film deposited on Al2O3 substrate were continuous and dense. Their structure and crystallinity were verified by XRD. The structure and particle sizes of CeO2 films were stablilized by annealing at 750℃,1000℃, and 1250℃ for 5 hours. This approach was also applicable to GDC thin films. Ag-CeO2 composite thin films were deposited by sputtering Ag-CeO2 inlaid targets. Ag particles were dispersed in CeO2 , verified by TEM and Auger. After annealing, the Ag-CeO2 films at 600℃ for 1 hour and 5 hours. Different Ag weight fractions of 5.9%, 3.7% and 2.9% were obtained by EDX analysis.
In this study, we measure the sensor’s resistance by changing the oxygen concentration in steady condition, and do the dynamic measurement by changing the oxygen concentration rapidly and recording its response time in osciscope and keithley 2410. We discover that the CeO2 thin film oxygen sensor’s response time is related to it’s heat treatment. The higher heat treatment, temperature the slower response time. With high temperature treatment, CeO2 grain become bigger, the grain boundary become less, so transmitting path become less.
In high temperature, GDC sensor has the shortesrresponse time. In low temperature, Ag-CeO2 and GDC sensors have shortresponse time. The CeO2 Oxygen sensors annealed at 750℃, 1000℃ and 1250℃ have response times of 350 ms, 1.5s and 3s tested in 750℃ by changing oxygen partial pressure from 0 Torr to 152 Torr, GDC and Ag-CeO2 oxygen sensors (with 750℃ heat treatment) have response times of 350 ms and 500 ms, tested at 450℃.
CeO2 thin films have good sensitivity then GDC and Ag-CeO2 thin films. GDC sensor has better sensitivity in low test temperature than high test temperature. Ag- CeO2 sensors also behave the same, but become unstable in high test temperature because of Ag diffusion and separation.
Finally, we calculated the activation energies of CeO2 thin films for different annealing temperature, The higher annealing temperature, the higher activation energy. The activation energy of CeO2 sensor with no heat treatment is 1.23 ev, and the activation energies of CeO2 sensor with 750℃, 1000℃ and 1250℃ heat treatment are 1.55 ev, 1.69 ev and 1.81ev. The activation energy of GDC and Ag-CeO2 thin films are 1.1 ev and 0.73 ev which are lower than those of CeO2 thin film.
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