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研究生:李思毅
研究生(外文):Lee Seu Yi
論文名稱:以脈衝雷射沉積法在具有鈦酸鍶緩衝層之矽晶片上成長鈮酸鉀薄膜及其表面聲波應用
論文名稱(外文):PLD PROCESSING OF KNbO3 FILMS ON Si WITH STO BUFFER LAYERS AND ITS SAW APPLICATION
指導教授:吳慕鄉
指導教授(外文):Wu Mu Shiang
學位類別:碩士
校院名稱:大同工學院
系所名稱:電機工程研究所
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:1998
畢業學年度:86
語文別:中文
中文關鍵詞:鈮酸鉀鈦酸鍶脈衝雷射沉積法表面聲波機電耦合係數
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鈮酸鉀薄膜由於晶格常數與矽晶片基板差異很大以及兩者間存在有內部擴散的問題所以很難直接在矽晶片基板成長高品質的鈮酸鉀薄膜。鈦酸鍶單晶基板因為其晶格常數與鈮酸鉀薄膜相近,故常被用來作為基板,成長高方向性的鈮酸鉀薄膜。但是其單價相當高昂,且多來自國外,所以大大增加了製作成本。為了解決此一問題,並整合現有半導體技術,我們利用脈衝雷射沉積法先在矽晶片基板成長一層鈦酸鍶薄膜,以利鈮酸鉀薄膜的成長。首先,我們先找到鈦酸鍶薄膜的成長條件。我們發現在760 oC、氧壓為180mTorr時,可成長(002)方向的鈦酸鍶薄膜;在溫度為720 oC、壓力維持在0.05 mTorr不通氧的情況下,則可以成長出(110)方向的鈦酸鍶薄膜。接著,在(002)方向的鈦酸鍶緩衝層上,當溫度為680 oC、氧壓保持在10 mTor時,可以成長出(002)優選方向的鈮酸鉀薄膜;而在(110)方向的鈦酸鍶緩衝層上,維持溫度為760 oC、氧壓為200 mTor,則可以成長(200方向的高品質鈮酸鉀薄膜。我們分別量度鈮酸鉀薄膜的電容電壓曲線(C-V)與電流-電壓曲線(I-V),發現(002)方向的鈮酸鉀薄膜有效電容值為7.0×10-11 F(200)方向的鈮酸鉀薄膜的有效電容值則為2.8×10-11 。在我們對其外加一負直流電源一段時間後,可以發現電容值變大,且曲線變窄,這是因為產生電荷注入所致。另外當在2.58 V時,鈮酸鉀薄膜的漏電流大小為8.4×10-10 A/cm。最後,藉由表面聲波的理論分析結果,我們可以知道,當鈮酸鉀薄膜方向為(100)的時後,FFF+SF的結構下所產生的機電耦合係數要較其他型式來得高,並且會隨著緩衝層的厚度增加而降低。另外所能得到的最佳機電耦合係數值是當鈮酸鉀薄膜hk=0.時,此時機電耦合係數值為4.456%。

It is very difficult to prepare high-quality KNbO3 thin films on Si substrates directly because of mismatch and interdiffusion problem between KNbO3 thin film and Si substrate. Strantium titanate (SrTiO3, STO) single-crystal substrate is widely used to grow epitaxial KNbO3 thin films owing to the small difference of lattice constants between them. However, the fabrication cost increased expensively because the price of the substrate is very high and they are mostly supplied from the oversea. To solve these problems, we deposited STO buffer layer on Si by pulse laser deposition(PLD) to grow highly oriented KNbO3 thin films. First of all, the deposition conditions of STO buffer layer was explored. We can deposit STO buffer layer for (002) orientation in the 180 mTorr oxygen pressure at 760 oC; (110) orientation in the 0.05mTorr without oxygen at 720 oC. Then, we discuss KNbO3thin film on STO buffer layer by PLD method. We can grow (002) preferred KNbO3thin film which was in-situ annealed at 680 oC, 10 mTorr on STO buffer layer for (002) orientation, and also can grow (200) preferred KNbO3 thin film whichwas in-situ annealed at 760 oC, 200 mTorr on STO buffer layer for (110) orientation. The electrical properties of KNbO3 thin film, which was measured, were C-V curve and I-V curve. The effective capacitance of KNbO3 (002) thin film 0×10-11 F and the capacitance of KNbO3 (200) thin film is ×10-11.F; We added a minus DC bias voltage on KNbO3 thin film for a whileand the effective capacitance became larger and C-V curve varied narrower. Theleakage current density was 8×10-10A/cm2 when the applied field is 2.58V.Finally, according to the theoretical surface acoustic wave (SAW) analysis, it revealed that the structure of FFF+SFF structure has higher electro-mechanical coupling coefficient than others at (100) orientation of KNbO3. The thicker buffer layer, the lower electro-mechanical coupling coefficient. Besides, the K2 of FFF+SFF structure of KNbO3 thin films (hk=0.4) on STO/Si is 4.456%.

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