臺灣博碩士論文加值系統

本論文描述表面聲波(surface acoustic wave, SAW)感測器之感測機制，以及SAW濕度感測器之製作與量測。並以聚乙烯醇(polyvinyl-alcohol , PVA)薄膜材料塗佈於在表面聲波共振器之壓電基板，製作濕度感測器並研究其感測能力。
我們量測表面聲波濕度感測器之相對濕度對中心頻率和插入損失的影響，量測範圍從30 至90%的相對濕度，當聚乙烯醇薄膜厚度在3000Å，我們獲得中心頻率差有1517 KHz、插入損失差有-10.31dB的變化範圍。另外，我們也研究該感測器之水氣吸收與去吸附的短期再現性、磁滯(hysteresis)性與老化(aging)速率之特性。
實驗結果顯示聚乙烯醇薄膜具有一個良好濕度感測性質，能提供表面聲波濕度感測元件應用在較高的相對濕度環境之感測。

The thesis describes the sensing mechanism, the fabrication and the measurements of the SAW humidity sensors. Highly sensitive SAW humidity sensors were fabricated by spin-coating polyvinyl-alcohol (PVA) thin film onto piezoelectric substrate of the SAW resonators.
The transmission properties of the SAW sensor, including center frequency and insertion loss were studied at a relativity humidity ranging from 30 to 90%. Frequency deviation of 1517 KHz and insertion loss deviation of –10.31 dB were obtained when the PVA thin film thickness was increased to about 3000 Å in the variation of relative humidity.
In the other hand, the short-term repeatability, the hysteresis properties and aging rate of water absorption and desorption cycle have been examined. The results have justified the suitability for the PVA film coated SAW resonators in the application of sensing humidity at a higher relative humidity.

目錄
中文摘要……………………………………………………………Ⅰ
英文摘要……………………………………………………………Ⅱ
誌謝…………………………………………………………………Ⅲ
符號說明……………………………………………………………Ⅳ
目錄…………………………………………………………………Ⅴ
表目錄………………………………………………………………Ⅷ
圖目錄………………………………………………………………Ⅸ

第一章 緒論……………………………………………………1
1-1 研究背景………………………………………………1
1-2 研究動機………………………………………………5
1-3 論文架構………………………………………………5
第二章 壓電理論與感測機制
2-1 壓電理論背景……………………………………………… 7
2-1-1 壓電等效電路……………………………………………10
2-1-2 機電耦合係數……………………………………………16
2-2 SAW元件理論與特徵…………………………………… …17
2-2-1 SAW元件交叉指狀轉換器…………………………… …17
2-3濕度感測機制理論背景…………………………………… 19
2-3-1表面聲波之擾動……………………………………… …21
2-3-2表面聲波之質量負載效應……………………………… 22
2-4相對濕度之定義…………………………………………… 23
第三章 實驗架構與方法
3-1 SAW 濕度感測器之元件規格………………………………24
3-2 塗佈材料……………………………………………………25
3-3 聚乙烯醇薄膜製作方法……………………………………25
3-4 量測設備規劃與設計………………………………………26
3-4-1量測設備……………………………………………… …26
3-4-2量測資料之擷取……………………………………… …27
3-5 振盪電路之設計……………………………………………27
第四章 結果與討論
4-1 薄膜塗佈之均勻度…………………………………………29
4-2 薄膜厚度對傳輸性質之影響………………………………29
4-3中心頻率及插入損失對相對濕度之影響……………… …31
4-4 SAW濕度感測器之溫度特性…………………………… …32
4-5 SAW濕度感測器之再現性……………………………… …33
4-6 SAW濕度感測器之磁滯特性…………………………… …33
4-7 SAW濕度感測器之老化情形…………………………… …33
4-8 SAW振盪器之輸出測特………………………………… …34
第五章 結論與未來研究方向
5-1 結論…………………………………………………………35
5-2未來研究方向…………………………………………… …35
參考文獻…………………………………………………………62


表目錄
表1-1各種濕度感測器特性之比較………………………………36
表1-2濕度感測器之應用…………………………………………37
表1-3論文架構……………………………………………………38
表2-1石英材料之等效參…………………………………………39
表2-2壓電基板之參數……………………………………………39
表3-1SAW resonator 之電氣性質………………………………39
表4-1感測薄膜對表面聲波感測器之傳輸性質的影響…………40
表4-2表面聲波感測器特性比較…………………………………41


圖目錄
圖1-1表面聲波感測器之結構…………………………………42
圖2-1正壓電效應………………………………………………42
圖2-2逆壓電效應………………………………………………42
圖2-3壓電元件之等效電路……………………………………43
圖2-4壓電石英材料之阻抗對頻率的變化……………………43
圖2-5表面聲波傳播方式………………………………………44
圖2-6聲波能量與縱深能量之關係…………………………45
圖2-7 SAW元件基本結構………………………………………45
圖2-8 SAW元件之IDT基本結構………………………………46
圖2-9頻率響應曲線……………………………………………46
圖2-10單一之IDT的等效電路………………………………47
圖2-11 能量密度對入射功率與傳播速度之關係……………47
圖3-1 SAW諧振器之頻率響應曲線……………………………48
圖3-2 SAW諧振器之外觀結構…………………………………48
圖3-3 SAW諧振器之外觀尺寸…………………………………49
圖3-4 PVA分子結構……………………………………………49
圖3-5聚乙烯醇薄膜塗佈在氧化鋁基板之製作………………50
圖3-6聚乙烯醇薄膜電阻對相對之濕度之變化………………50
圖3-7聚乙烯醇薄膜全塗滿於壓電基板之製作………………51
圖3-8 Hp 4195A網路分析儀…………………………………51
圖3-9恆溫恆濕箱(ESPEC-240)………………………………52
圖3-10 SAW濕度感測器之量測治具…………………………52
圖3-11 SAW濕度感測器量測架構……………………………53
圖3-12 SAW振盪電路之工作原理……………………………53
圖3-13 SAW濕度感測器之振盪電路…………………………54
圖3-14 SAW濕度感測器之振盪電路的Layout圖……………54
圖3-15實作SAW濕度感測器之振盪電路……………………55
圖4-1(a)圖PVA薄膜厚度約為1000Å之樣品…………………55
圖4-1(b) PVA薄膜厚度約為3000Å之樣品…………………56
圖4-2諧振器元件之壓電基板的材料分析…………………56
圖4-3在不同PVA膜厚下之頻率對插入損失的變化…………57
圖4-4在不同PVA膜厚下相對濕度對插入損失的變化………57
圖4-5在不同PVA膜厚下相對濕度對中心頻率的變化………58
圖4-6不同溫度下之校正曲線………………………………58
圖4-7在室溫下之短期再現性(on/off)循環測試…………59
圖4-8相對濕度與插入損失的變化對磁滯的影響…………59
圖4-9相對濕度與中心頻率的變化對磁滯的影響……………60
圖4-10 PVA感測薄膜之老化特性………………………………60
圖4-11 SAW元件之433.92 MHz振盪頻率輸出…………………61

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