研究生: |
林志名 Jhih-ming Lin |
---|---|
論文名稱: |
以磁控濺鍍法製備氧化鈰及摻雜釓與銀薄膜之電阻式氧氣感測器與性能比較 The Study of Sputter-Deposited CeO2,GDC and Ag-CeO2 Thin Films for Resistive Oxygen Sensors |
指導教授: |
周賢鎧
Shyan-kay Jou |
口試委員: |
周振嘉
Chen-Chia Chou 胡毅 Yi Hu |
學位類別: |
碩士 Master |
系所名稱: |
工程學院 - 材料科學與工程系 Department of Materials Science and Engineering |
論文出版年: | 2008 |
畢業學年度: | 96 |
語文別: | 中文 |
論文頁數: | 106 |
中文關鍵詞: | 電阻式氧氣感測器,氧化鈰,薄膜,濺鍍 |
外文關鍵詞: | Resistive oxygen sensor, Cerium oxide, Sputter, Thin film |
相關次數: | 點閱:718 下載:12 |
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本論文使用磁控式濺鍍沉積氧化鈰(CeO2)及摻雜釓與銀[(Gd2O3)x-(CeO2)1-x、Ag- CeO2]之氧化鈰固態薄膜電解質在氧化鋁基材上,後藉由熱處理後再濺鍍白金電極製備成電阻式氧氣感測器。本論文改變氧化鈰薄膜的微結構,並於改變溫度環境中進行電性分析與獲得活化能,以及測試與比較其對氧氣感測之靈敏度。本研究最後做出在高溫與低溫操作溫度下,應答時間快,靈敏性佳的氧氣感測器。
初濺鍍的氧化鈰薄膜能連續且緻密的沉積在氧化鋁基材上,且經XRD可確認其結構已形成結晶相,經過750℃、1000℃、1250℃的熱處理溫度後能穩定薄膜的結構與控制氧化鈰粒徑大小;相同結果也適用於GDC薄膜上。利用鑲嵌靶材濺鍍方式可濺鍍出重量含量為所需之複合銀-氧化鈰薄膜,利用TEM與Auger電子分析銀顆粒之分散性,證明銀確實可均勻分散在氧化鈰薄膜內,於750℃熱處理一小時與五小時後,以EDS分析在CeO2中的銀含量為3.7%與2.9%,而未熱處理的銀含量為5.9%。
本研究於穩定的氧濃度下進行氧化鈰氧氣感測器電阻值在改變氧濃度後對應之靜態量測關係,進一步以瞬間改變氧濃度的動態測試量測感測器電阻改變時的應答時間。本研究發現純氧化鈰薄膜感測器應答時間與熱處理溫度有關,熱處理溫度越高,應答時間越慢,對應氧化鈰微結構為晶粒越大,晶界越少,故傳導路徑變少。
以750℃、1000℃、1250℃熱處理之氧化鈰於750℃量測溫度下,氧分壓由0 Torr改變至152 Torr的應答時間分別為350毫秒、1.5秒、3秒;而摻雜釓之氧化鈰薄膜與摻雜銀之氧化鈰薄膜在低溫450℃下量測所得應答時間為350毫秒與500毫秒。
感測器靈敏性方面,純氧化鈰在高溫下靈敏度比低溫高,但相差不大;GDC感測器在低溫下反應靈敏性較高,越高溫靈敏性越差;銀-氧化鈰感測器也是在低溫下靈敏性較佳,但在高溫因為銀析出問題會影響整體穩定度,未摻雜的純氧化鈰薄膜靈敏性比摻雜過後的薄膜靈敏性好。
本研究分析薄膜之導電性獲得活化能部份,純氧化鈰的活化能在高低溫因傳導機制改變會有兩區段的活化能,而經過熱處理後,活化能會隨著熱處理溫度越高而升高。在未熱處理、750℃、1000℃和1250℃溫度五小時熱處理下,活化能分別為1.23 ev、1.55 ev、1.69 ev與、1.81ev,攙雜釓和銀的氧化鈰只有一區段的活化能,分別為1.1 ev與0.73 ev。
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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