外延鈦酸鍶薄膜及介電調(diào)諧性能研究
發(fā)布時間：2019-03-20 19:14
【摘要】：鈦酸鍶(STO)薄膜在液氮溫區(qū)具有非常好的非線性介電性質(zhì),這種介電常數(shù)隨著外加電場變化的特性,使得它在電可調(diào)諧微波集成器件上有著廣闊的應用前景。雖然介電材料已經(jīng)得到了廣泛的研究,但如何在實現(xiàn)高調(diào)諧率的同時依然保持較低的介電損耗仍然是研究的難點。近年來,研究發(fā)現(xiàn)多層外延薄膜可以實現(xiàn)這種協(xié)調(diào)。鎳酸鑭(LNO)薄膜與STO同屬鈣鈦礦結(jié)構(gòu),具有良好的導電性且與STO晶格匹配性好,因而可以成為外延STO薄膜優(yōu)異的電極材料。本文從STO薄膜的熱處理溫度和上電極材料兩方面對其介電調(diào)諧性能的影響進行了研究,取得以下研究成果:(1)采用溶膠-凝膠法在(00l)LAO基板上制備了以LNO為底電極的外延STO薄膜,研究了異質(zhì)同構(gòu)薄膜取向特性的檢測方法,發(fā)現(xiàn)采用高指數(shù)晶面可以分析外延薄膜的面內(nèi)取向。進一步研究了熱處理溫度對STO/LNO復合薄膜介電調(diào)諧性能的影響,發(fā)現(xiàn)隨著熱處理溫度的提高,Pt/STO/LNO結(jié)構(gòu)的介電調(diào)諧率增加,介電損耗降低,最佳熱處理溫度下制備的Pt/STO/LNO復合結(jié)構(gòu)的調(diào)諧率為49.8%,介電損耗為0.0115,優(yōu)值因子為43.3。(2)采用感光溶膠-凝膠法制備出了具有良好導電性的LNO圖形化薄膜,將其應用于STO/LNO復合薄膜上電極的制備,形成上下電極對稱的LNO/STO/LNO電容結(jié)構(gòu),介電性能分析表明LNO/STO/LNO結(jié)構(gòu)比Pt/STO/LNO結(jié)構(gòu)介電性能更加優(yōu)異,其優(yōu)值因子可達到82.4。(3)通過J-V特性分析了 Pt、LNO上電極材料對STO/LNO結(jié)構(gòu)中STO介電性能的影響機理。研究發(fā)現(xiàn),隨著溫度的降低(80～300 K溫度范圍內(nèi)),Pt/STO/LNO和LNO/STO/LNO兩種異質(zhì)結(jié)構(gòu)中的漏電流密度均減小,進一步分析發(fā)現(xiàn)Pt/STO/LNO結(jié)構(gòu)中Pt/STO界面存在肖特基勢壘,LNO/STO/LNO結(jié)構(gòu)中并沒有觀察到明顯的勢壘,肖特基勢壘的存在影響了 STO的極化過程,導致Pt/STO/LNO異質(zhì)結(jié)構(gòu)中更高的介電損耗。
[Abstract]:Strontium titanate (STO) thin films have very good nonlinear dielectric properties in the liquid nitrogen temperature region. This dielectric constant changes with the applied electric field, which makes it have a broad application prospect in electrically tunable microwave integrated devices. Although dielectric materials have been extensively studied, how to achieve high tunability while maintaining low dielectric loss is still a difficult problem. In recent years, it has been found that multilayer epitaxial films can achieve this coordination. Lanthanum nickel (LNO) films belong to perovskite structure as well as STO, and have good electrical conductivity and good lattice matching with STO. Therefore, lanthanum nickel thin films can be used as excellent electrode materials for epitaxial STO films. In this paper, the effects of heat treatment temperature and upper electrode material on the dielectric tuning properties of STO thin films have been studied. The research results are as follows: (1) the epitaxial STO thin films with LNO as the base electrode were prepared by sol-gel method on (00l) LAO substrate, and the methods of measuring the orientation characteristics of heterogeneous and isomorphic thin films were studied. It is found that the in-plane orientation of epitaxial films can be analyzed by using high index crystal plane. The effect of heat treatment temperature on the dielectric tuning properties of STO/LNO composite films was further studied. It is found that the dielectric tunability of Pt/STO/LNO structure increases and the dielectric loss decreases with the increase of heat treatment temperature. The tunability and dielectric loss of the Pt/STO/LNO composite structure prepared at the optimum heat treatment temperature are 49.8% and 0.0115, respectively. The excellent value factor was 43. 3. (2) LNO patterned thin films with good conductivity were prepared by photosensitive sol-gel method and applied to the preparation of electrodes on STO/LNO composite films. The structure of LNO/STO/LNO capacitor with symmetrical upper and lower electrodes is formed. The dielectric properties of LNO/STO/LNO structure are better than that of Pt/STO/LNO structure, and the dielectric properties are better than that of Pt/STO/LNO structure. The excellent value factor can reach 82.4. (3) the mechanism of the effect of the electrode material on Pt,LNO on the dielectric properties of STO in STO/LNO structure is analyzed by J _ (?) V characteristics. It is found that the leakage current density in both Pt/STO/LNO and LNO/STO/LNO heterostructures decreases with the decrease of temperature (in the temperature range of 80? 300K). Further analysis shows that there is Schottky barrier at the interface of Pt/STO in Pt/STO/LNO structure, but no obvious barrier is observed in LNO/STO/LNO structure. The existence of Schottky barrier affects the polarization process of STO. It leads to higher dielectric loss in Pt/STO/LNO heterostructure.
【學位授予單位】：西安理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TB383.2
本文編號：2444539
[Abstract]:Strontium titanate (STO) thin films have very good nonlinear dielectric properties in the liquid nitrogen temperature region. This dielectric constant changes with the applied electric field, which makes it have a broad application prospect in electrically tunable microwave integrated devices. Although dielectric materials have been extensively studied, how to achieve high tunability while maintaining low dielectric loss is still a difficult problem. In recent years, it has been found that multilayer epitaxial films can achieve this coordination. Lanthanum nickel (LNO) films belong to perovskite structure as well as STO, and have good electrical conductivity and good lattice matching with STO. Therefore, lanthanum nickel thin films can be used as excellent electrode materials for epitaxial STO films. In this paper, the effects of heat treatment temperature and upper electrode material on the dielectric tuning properties of STO thin films have been studied. The research results are as follows: (1) the epitaxial STO thin films with LNO as the base electrode were prepared by sol-gel method on (00l) LAO substrate, and the methods of measuring the orientation characteristics of heterogeneous and isomorphic thin films were studied. It is found that the in-plane orientation of epitaxial films can be analyzed by using high index crystal plane. The effect of heat treatment temperature on the dielectric tuning properties of STO/LNO composite films was further studied. It is found that the dielectric tunability of Pt/STO/LNO structure increases and the dielectric loss decreases with the increase of heat treatment temperature. The tunability and dielectric loss of the Pt/STO/LNO composite structure prepared at the optimum heat treatment temperature are 49.8% and 0.0115, respectively. The excellent value factor was 43. 3. (2) LNO patterned thin films with good conductivity were prepared by photosensitive sol-gel method and applied to the preparation of electrodes on STO/LNO composite films. The structure of LNO/STO/LNO capacitor with symmetrical upper and lower electrodes is formed. The dielectric properties of LNO/STO/LNO structure are better than that of Pt/STO/LNO structure, and the dielectric properties are better than that of Pt/STO/LNO structure. The excellent value factor can reach 82.4. (3) the mechanism of the effect of the electrode material on Pt,LNO on the dielectric properties of STO in STO/LNO structure is analyzed by J _ (?) V characteristics. It is found that the leakage current density in both Pt/STO/LNO and LNO/STO/LNO heterostructures decreases with the decrease of temperature (in the temperature range of 80? 300K). Further analysis shows that there is Schottky barrier at the interface of Pt/STO in Pt/STO/LNO structure, but no obvious barrier is observed in LNO/STO/LNO structure. The existence of Schottky barrier affects the polarization process of STO. It leads to higher dielectric loss in Pt/STO/LNO heterostructure.
【學位授予單位】：西安理工大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TB383.2
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