在元件縮小的同時，有許多的挑戰必須要被克服。近年來，許多新結構的電晶體以及新的製程技術因此而被廣泛地研究。為了解決源極/汲極延伸區域高濃度與淺接面的不易達成，跨立閘結構金氧半場校電晶體因而被發展出來。跨立閘電晶體移除了傳統元件中源極/汲極延伸區域，而以反轉區來取代之，藉此避免源極/汲極延伸區域在製程上的困難。論文中將闡述此跨立閘電晶體的發展緣由、基本操作特性，並一一地討論各項元件操作之表現，期使能夠從中探討出跨立閘電晶體之最佳化設計，促使跨立閘電晶體日後能夠真正成為元件縮小的另一個有效的、可行的途徑。
近年來，半導體產業蓬勃發展，積體電路如今已發展到超大型積體電路﹙Ultra Large Scale Integrated Circuit，ULSI﹚的領域。為了追求更高密度、高速度以及低功率消耗的積體電路，金屬氧化物半導體﹙Metal-Oxide- Semiconductor，MOS﹚元件必須不斷的縮小。依照莫爾定律﹙Moore's Law﹚

，金氧半元件的大小每一個世代會比前一個世代縮小0.7倍，每隔三年就會進入下一個世代[1]。由早期到現在，金氧半元件各項參數的發展趨勢都完全受到這個定律所支配，諸如通道長度、閘極介電層厚度、源極/汲極接面深度、閘極延遲時間等等。

然而，儘管製程技術不斷地進步，當金氧半元件發展到一百奈米以下的世代時，仍有幾項重大的瓶頸有待克服[2]。這些問題當中，包括有閘氧化層穿透電流增加使得靜態功率增加與可靠性降低、源極/汲極延伸區域(Source/Drain Extension Region)的高濃度與淺接面在製程上的不易達成、通道中不規則的參雜導致臨界電壓產生很大的變化等等。為了解決以上幾項問題，S. Tiwari 等人在1998年發表了新結構的跨立閘電晶體 (Straddle-Gate Transistor)，藉此提供今後元件繼續縮小的另一個有效可行的途徑[3][4]。

跨立閘結構電晶體與傳統金氧半元件不同之處，在於其側壁下方通道的臨界電壓較電晶體控制區域的臨界電壓為低，這個區域會在電晶體導通之前先打開，並在電晶體完全導通後，提供電晶體正常的電流傳導。在跨立閘電晶體的設計概念提出之後，相關的研究並不多，它的各項元件特性以及類似結構尚未受到較為完整的討論。因此，在本篇論文中，除了針對跨立閘電晶體的各項元件特性做深入探討之外，同時也會將與跨立閘電晶體具有相同設計概念的未蝕刻閘電晶體 (Unetched-Gate Transistor)、雙材料閘電晶體 (Dual-Material Gate Transistor, DMG) 提出來做討論。

在本篇論文中，第二章將介紹元件縮小所遭遇的挑戰、跨立閘電晶體之發展過程與未來的發展趨勢。第三章將簡單介紹本文中所採用之模擬軟體，並說明跨立閘電晶體的元件結構與操作原理。第四章則對研究結果加以整理討論，除了比較跨立閘電晶體與傳統控制元件的基本元件特性之外，同時並討論改變元件結構參數後，元件特性所受的影響，最後則探討結合SOI之跨立閘電晶體元件特性。第五章則是本論文的結論。

As device scales down, some constraints must be overcome. Straddle-gate transistor is not limited by the source/drain extension region and leads another path to smaller devices. A comprehensive investigation of the transistor characteristics of Straddle-gate structure is presented in this work, which allows a better understanding and optimization of the straddle-gate transistors. Using the careful analysis of these characteristics, sub-100nm length straddle-gate transistors can be optimized with various structure variables, such as spacer width and side dielectric thickness. The straddle-gate transistor is shown to exert much better control on the channel than the control device with the same effective channel length, which leads to a significant improvement in off current characteristics.

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