近年來，二元金屬氧化物受到相當廣泛的討論與研究。良好的光穿透率與優良電性與機械性質表現使這些材料得以應用於透明電子電路上。相較於多晶薄膜，非晶氧化物薄膜更擁有製程溫度低、表面均勻性佳、低漏電流與優良的機械彈性等優點。另一方面，許多材料都被發現擁有穩定的電阻轉換現象，被認為下一世代非揮發性記憶體的選項之一。鈮酸基氧化物被廣泛應用在微波元件、光電元件與光激發元件上。在這些鈮酸基氧化物中，鈮酸鎂(MgNb2O6 , MNO)擁有高介電常數、優異微波特性、良好熱穩定性、光穿透率佳與寬光學能隙等優點。這些特性使鈮酸鎂薄膜有機會應用在透明電子電路以及多功能光電元件上。本論文將分為以下三個部分討論：

一、 以溶膠凝膠法製作鈮酸鎂薄膜與特性分析
第一部分討論在氧化銦錫/玻璃基板(ITO/glass)上以溶膠凝膠法製作透明非晶鈮酸鎂薄膜。此部分中，將介紹受到退火條件的影響鈮酸鎂薄膜化學態與光、電特性的改變。鈮酸鎂薄膜在經過攝氏六百度退火處理後仍為非晶狀態。根據X光光電子能譜儀的分析結果，薄膜中存在Mg2+、Nb5+、Nb4+與 O2-等化學組態。其中，Nb4+在經過高溫熱處理後可以被有效消除。在波長400–800奈米的範圍中，所有試片的平均光穿透率可達80%，且光學能隙約在5電子伏特左右。退火氣氛對薄膜特性的影響也將在此部分討論。當薄膜於缺乏氧氣的環境中進行退火處理時，由於Nb4+的比例增加，薄膜將呈現半導性。此外，MgNb2O6/ITO異質接面的電荷傳導機制也將在此進行討論。

二、鋅取代對鈮酸鎂薄膜電特性的影響
此部分將製作Al/Mg1-xZnxNb2O6 (MZNO)/ITO電容，並介紹鋅取代對鈮酸鎂薄膜電特性的影響。根據實驗結果，鈮酸鎂薄膜在鋅取代比例為20%時有最佳的電特性。經過攝氏四百度退火之後，薄膜的介電常數、光穿透率與光學能隙分別是21.2 (量測頻率1 MHz下), ~80% 與 4.86電子伏特。與純鈮酸鎂薄膜相比，不僅介電常數大幅增加，且製程溫度更可降低攝氏一百度。在電荷傳導機制方面，元件在外加電場由低到高時分別為歐姆傳導、空間電荷限制傳導與FN穿隧。其中，發生穿隧的臨界電場值也隨著鋅取代量而改變。

三、鈮酸鎂薄膜的電阻轉換現象
第三部分將介紹鈮酸鎂薄膜的電阻轉換現象。針對Al/MNO/ITO進行直流電壓掃描測試，在大氣下退火的試片呈現穩定雙極性電阻轉換現象；然而，當試片經過純氧氣退火後，薄膜電阻轉換現象將完全消失。此結果暗示鈮酸鎂薄膜的電阻轉換現象與薄膜內氧空缺有相當程度的關聯。此外，當薄膜經過氮氫氣氛退火處理後將呈現單極性電阻轉換且無需forming。為了瞭解退火氣氛對薄膜電阻轉換現象的影響，實驗中以高解析穿隧式電子顯微鏡針對元件剖面做進一步分析。

Binary metal oxides with high optical band gaps (Eg) have been researched and developed for several applications in recent years. The high optical transparencies and excellent electrical and mechanical properties lead these materials to have high potentials on transparent electronic devices. On the other hand, amorphous oxide films offer several advantages, such as lower processing temperatures, better surface uniformity, lower leakage current and superior mechanical flexibility compared to crystalline films. These excellent properties and advantages make amorphous transparent oxide films (a-TOFs) powerful candidates for dielectric layers to realize transparent electronics.
In addition, several materials systems have been found to possess stable resistive switching (RS) behavior, attracting great attention as candidates for next-generation non-volatile memory applications. Niobium-based oxides have been extensively studied for applications such as microwave dielectrics, optoelectronics, and photoactive materials. Among these materials, columbite MgNb2O6 (MNO) exhibits a high dielectric constant, excellent microwave properties, good thermal stability, high transparency, a wide bandgap, and optical activation. These excellent properties make MNO a promising material for transparent electronics or multi-functional optoelectronics. As mentioned above, the main study of this dissertation is divided by three parts:

1. Fabrication and Characteristic of Sol-Gel Derived MgNb2O6 Thin Films
Transparent amorphous-MgNb2O6 (MNO) thin films were fabricated on ITO/glass substrates using the sol-gel method. The change in the chemical states, as well as the optical and dielectric properties of MNO films at various annealing temperatures is investigated. The MNO films exhibited the amorphous phase when the annealing temperature was below 600°C. From X-ray photoelectron spectroscopy (XPS), the major parts of the films’ chemical states can be indexed as Mg2+, Nb5+, Nb4+ and O2-. Further, the Nb4+ element can be reduced at higher annealing temperatures. The average transmission percentage in the visible range (λ=400–800 nm) is over 80% for all MNO/ITO/glass samples, while the optical band gap (Eg) for all samples is estimated at ~5 eV. In addition, the dielectric constant was calculated to be higher than 20 under a 1 MHz AC electric field, with a leakage current density below 2×10-7 A/cm2 at 1 V. In addition, the effects of annealing atmosphere (N2, air and O2) on the electrical properties of sol-gel derived MNO/ITO heterostructures are discussed. All samples also exhibited the amorphous phase and were highly transparent. The percentage of Nb4+ content increased when the films were annealed in the oxygen deficient conditions, which could lead to semiconducting films. In addition, the results show that the electrical properties of sol-gel derived MNO thin films could be tuned based on the annealing atmosphere. Moreover, the conduction mechanisms of MNO /ITO heterostructures are also discussed. The results show that MNO thin films have potential for use in multifunctional optoelectronic applications, due to their flexible electrical properties and good transparency.

2. The Effects of Zinc Substitution on the Electrical Properties of MgNb2O6 Thin Films
For lowering the fabrication temperature, the Al/Mg1-xZnxNb2O6 (MZxNO)/ITO devices were investigated in this part. According to the experimental results, the great optical-electrical properties of the devices can be obtained at x=0.2. The dielectric constant, average transparency and optical band gap of the devices are 21.2 (@1 MHz), ~80% and 4.86 eV after 400°C annealing, respectively. Compared with 500°C-annealled MNO samples, the dielectric constant has highly enhancement. More important, the fabrication temperature of MZ0.2NO thin films is 100°C lower than that of MNO. From low to high applied electric field, the leakage conduction mechanisms of Al/MZxNO/ITO devices are ohmic conduction, space-charge-limited conduction (SCLC) and FN tunneling, respectively. Moreover, the critical electric field strength of the conduction mechanisms changed with zinc substitution proportions.

3. Resistive Switching Behaviors of MgNb2O6 Thin Films
The resistive switching (RS) behavior of the Al/MNO/ITO devices was investigated. From the DC voltage sweep test, the air-annealed MNO samples exhibited stable and reproducible bipolar resistive switching (BRS) behavior; however, the samples annealed in an O2-rich environment showed no RS property. These results suggest that the RS behavior of the MNO memory devices is highly related to the oxygen vacancy concentration and distribution within the MNO films. In addition, forming-free unipolar resistive switching (URS) behavior was observed when the MNO films were annealed under an N2H2 atmosphere. In order to determine the origin of the BRS and URS behaviors, cross-sectional high-resolution transmission electron microscopy images of the MNO samples were acquired. The RS behavior of the MNO films can be ascribed to the release and recombination of electrons and oxygen vacancies.

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