隨著半導體蓬勃的發展，元件已經與我們的生活息息相關，對於元件的研究也日益多元，其中，應用於薄膜電晶體上的透明金屬氧化物被給予莫大的關注，其在顯示技術上的優勢已使得其逐漸取代了氫化非晶矽(a-Si:H)。非晶金屬氧化物薄膜電晶體具有高載子遷移率(mobility)、高透明度、低製程溫度，高均勻性等優異特性，而在這之中尤以擁有優異的元件電流驅動能力、均勻性、及薄膜穩定性的非晶態氧化銦鎵鋅(Amorphous InGaZnO: a-IGZO)最具潛力。然而，在未來科技領域中，應用薄膜電晶體於大尺寸高解析度的顯示器、有機發光元件、量子點顯示器及軟性電子元件的相關研究快速發展，使得我們有更多針對薄膜電晶體的元件研究與開發的需要，本論文將著重於應用撓曲基板上的新穎低溫金屬氧化物高效能非晶態氧化銦鋅鎢半導體元件的開發，以及應用高介電絕緣層薄膜做為閘極絕緣層，特別是應用具有類鐵電特性薄膜做為低溫閘極絕緣層的相關研究。本論文特色為：(1) 摻雜鎢元素由與其和氧原子間的高鍵解離能(bond-dissociation energy)降低薄膜中氧空缺數量並且提升元件穩定性；(2) 由金屬的S軌域與氧原子形成導電帶，使得元件通道層在低溫環境載子濃度提高使得其可以應用與撓曲基板；(3) 特別使用低溫製程的高介電係數材料製做出具有類鐵電特性的閘極絕緣層以期望獲得更好的電性表現；(4) 特別應用超臨界流體製程低溫處理薄膜電晶體減少通道層及閘極氧化層中的缺陷，提升可撓曲基板上的元件性能表現。本文不僅通過降低製程熱預算(thermal budget)，在可撓曲的聚醯亞胺(Polyimide;PI)基板上完成元件，並且達成優秀的元件電性表現。
我們在元件的開發中，通過改變基本通道製程條件觀察應用複合閘極絕緣層的元件的電性變化，還探討閘極絕緣層實施沉積後退火的影響，以及對元件施予不同條件超臨界流體製程，其載子遷移率可大於70 cm2/V-s 、次臨界擺幅可小於60 mV/dec、開關比可大於106次方以上的可撓式元件.，以及通過應用高介電絕緣層將元件操作電壓降為2 V以內。此外，透過進行電容量測，可更精確的萃取出混合製程之複合閘極絕緣層的介電常數(dielectric constant)。另外還在可靠度測試方面，進行了閘極偏壓測試研究(gate bias stress)以及元件的撓曲測試。
最後，我們通過使用新穎的金屬氧化物半導體氧化銦鋅鎢薄膜做為通道層，結合低溫製程高介電常數的複合高介電系數材料設計製做出類鐵電閘極絕緣層以及透過特殊超臨界流體製程處理，克服低溫製程的困難，完成元件的開發，並且成功在透明的PI基板上，改善元件載子遷移率和次臨界擺幅，展現應用氧化銦鋅鎢電晶體與可撓曲電子的龐大市場潛力。

With the flourishing development of semiconductor science and technology, our lives are more and more relative to semiconductor. Therefore, the development of devices is more diversified. Transparent amorphous oxide semiconductors (TAOS) used on thin film transistors (TFTs) are given highly concerns, and also, TAOS have gradually taken the place of the material, a-Si:H in the technology of displays.
TAOS are equipped with superior characteristics, such as high mobility, high transmittance, low-temperature fabrication process, uniformity and so on. Among TAOS materials, amorphous InGaZnO: a-IGZO is the most potential material nowadays, because of its excellent drive current ability, uniformity, and film stability. However, in the future field of technology, the rapid evolution of the technology application like high-revolution large scale display, organic light-emitting diode, quantum-dot display, flexible electronics and etc. makes the high demand of further research, development and human needs of thin film transistors.
In this study, the development of the application of the innovative material, transparent amorphous indium tungsten zinc oxide (a-IWZO) in the thin film transistor on the flexible substrates fabrication and the development of the insulator layer of high dielectric constant, especially the film of ferroelectric characteristics used as the gate insulator of low temperature process have been both given a deep research. The characteristics separating into four points of this study are listed below: (1) The TAOS material doped with tungsten letting it have high bond-dissociation energy which can decrease the number of the oxygen vacancies in the film and upgrade the stability of the film; (2) The spherical isotropic ns (n>4) orbitals of the metallic cations overlap and form the conduction band minimum. This situation provides high concentration of carriers in the active layer using TAOS materials and makes the devices applied in the flexible electronics more easily; (3) Especially, the material of high dielectric constant with the low temperature process to be the gate insulator with ferroelectric characteristics is used to expect to have better electrical performance of the device; (4) The use of super fluid system is a low temperature process in that it provides a suitable process environment for the flexible substrate with rather low heat resistance, and the super fluid process treatment decreases the defects in the active layer and gate oxide insulator in order to upgrade the electrical performance of the device on the flexible substrate. This study shows that the thermal budget is decreased in that it leads to complete the development of the devices fabricated on the polyimide (PI) substrate and achieve excellent electrical characteristics.
In detail, during the development of the device, the thin film transistor, the difference of electrical performance of the devices with the multi-layer gate stack was investigated through changing the fabrication process parameters. Additionally, the device with the gate insulator stack of various post deposition annealing (PDA) conditions and the super fluid process treatment of various process parameters are investigated as well.
The optimized a-IWZO TFT on the flexible substrate obtained the outstanding electrical characteristics, μFE higher than 70 cm2/V-s , sub-threshold swing (S.S.) lower than 60 mV/dec., , Ion/Ioff ratio higher than 106, a small threshold voltage near 0V, and the operating voltage can be reduced in 2 V through using the gate insulator of high dielectric constant. Besides, by measuring the capacitor, the dielectric constant of the gate stack with hybrid process can be extracted correctly. Moreover, to test the reliability of the device, the gate bias stress measurement and the bending test are taken into investigation.
To summary, the flexible a-IWZO transistor with the innovative TAOS material, IWZO as the active layer in collocation with the low temperature process multi-layer high-dielectric-constant gate insulator acting ferroelectric phenomenon and in combination with low temperature process, super fluid system treatment in order to come through the difficulty while using low temperature process accomplished. In this research, the device fabricated on the colorless PI substrate achieved successfully and the mobility and S.S. of the device are improved showing the large potential in the application of the a-IWZO TFTs in the field of flexible electronics.

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