(1)雙鈣鈦氧化物製程與電性研究和(2)一維垂直注入式自旋傳輸磁矩系統

Abstract

高介電常數和低損耗介電材料對於節省能源和使用效率是非常重要的。本論文目的在探討雙蓋鈦礦系統的高介電常數對外加場頻率響應之間的基本物理關係。我們觀察到對於不同氧化學計量比的雙蓋鈦礦系統對於介電極化的影響。這能使我們進一步了解不同製程環境和介電常數機制的關係。 論文的第一個部份，我們利用阻抗分析技術研究雙蓋鈦礦系統Ba2LnRuO6樣品再不同冷卻速度燒解下，樣品的異質成分對介電性質的影響。我們分別觀察到在高溫和低溫時，微結構晶界和晶粒對於材料介電極化的影響。 第二部份我們探討Ba2LnMoO6樣品在 Ar/H2 和 O2 的不同環境燒解下表現的介電行為。我們觀察到在Ar/H2 燒解下的樣品介電常數會較O2燒解的樣品介電常數來的大。這可以讓我們利用調控氧的化學計量來達到操縱Ba2LnMoO6樣品的介電常數。 論文最後的部分，我們利用非平衡格林函數計算分別探討二個和四個電極的自旋轉矩系統。對於相干性情況，在一個給定的參數空間範圍，我們發現四個電極的抗阻尼轉矩比二個電極的抗阻尼轉矩大。對於退相干情況，我們發現在去相干的環境下，抗阻尼轉矩會被增強。結果顯示，當系統的散射長度越長，抗阻尼轉矩增強效應會變小。對於四個電極的抗阻尼轉矩在散射長度越長時，我們發現去相干會促進抗阻尼轉矩強度。

High dielectric constant and low dielectric loss are of great importance for the energy saving and efficient power delivery. This thesis aims to investigate fundamental frequency dependent dielectric properties and high-k dielectric constant in the double perovskites related oxides. Throughout this thesis, we have observed the role of the oxygen stoichiometry and polarization on the dielectric properties of the double perovskites oxides, allowing a great understanding of the synthesis condition and polarization mechanisms. In the first section of the thesis, we explore the dielectric properties of the double perovskites Ba2LnRuO6 samples sintered at different cooling rates, using the impedance techniques in order to resolve the electrical heterogeneities components contributing to the dielectric constant. We observe a significant polarization dependence on the microstructure due to the grain/grain boundary effect at high and low temperatures.. The second section of this thesis investigates the dielectric materials Ba2LnMoO6 sintered at different atmospheres, one is in the Ar/H2 and the other is in the O2. We observe that Ba2LnMoO6 sintered in Ar/H2 shows a high dielectric constant while the Ba2LnMoO6 sintered in O2 exhibits a low dielectric constant. This allow us to tune the oxygen stoichiometry and obtain the more intrinsic dielectric properties for Ba2LnMoO6. The final part of the thesis is to investigate 2- and 4- terminal spin transfer torque systems using non-equilibrium Green function method. For coherent cases, We find that the lateral geometry (4-terminal) renders enhanced anti-damping torques compared with the conventional one (2-terminal) in a certain parameter region. For incoherent cases, we discover that the dephasing can enhance the anti-damping torque. The results show that enhancement of the anti-damping torques declines when the scattering region is longer. For the four-terminal MTJ of larger scattering length, the dephasing can expedite the anti-damping torque.