次臨界擺幅（Subthreshold Swing，S.S.）是衡量元件開關特性的重要參數。因此，在現如今的半導體領域，如何減小電晶體的S.S.是一個很重要的議題。傳統的金屬氧化物半導體場效電晶體（Metal-Oxide-Semiconductor Field Effect Transistor , MOSFET）其S.S.被限制在60mV/dec。然而，使用鐵電材料作為閘極氧化層的電晶體，由於鐵電材料內部存在極化的現象，會使得電晶體的S.S.<60mV/dec，即出現所謂的“負電容”現象。除此之外，由於鐵電材料的極化在閘極電壓撤銷後仍然存在，故鐵電材料電晶體還具有非揮發性記憶體（Non-Volatile Memory, NVM）特性。
本文主要以鋁摻雜二氧化鉿(Al-doped HfO2, Al-HfO2)為鐵電材料，SiO2作為介面層，通過實驗製作不同厚度鐵電材料、不同厚度介面層的金屬－鐵電層－絕緣層－半導體（Metal-Ferroelectric-Insulator-Semiconductor, MFIS）結構鐵電材料電晶體，探究鐵電材料電晶體／記憶體的特性以及不同介面層厚度、不同鐵電層厚度對電晶體特性的影響。通過引入鐵電材料，元件的S.S.甚至可以達到27mV/dec。另外，本文也驗證了當Al-HfO2厚度減小到8nm仍具備鐵電特性。

Subthreshold swing (S.S.) plays an important role in the characteristics of MOSFET’s, so how to achieve a lower S.S. is a big issue in today’s semiconductor industry. The value of S.S. has been restricted by transistor physics to 60 mV/dec in traditional MOSFET’s. However, due to the polarization characteristic of ferroelectric materials, S.S.<60 mV/dec can be obtained while using ferroelectric materials as gate oxide, which is called "Negative Capacitance." Besides, since the polarization of dipoles still exists when gate voltage is off, ferroelectric transistors can be used as non-volatile memories.
MOSFET’s with Al-doped HfO2-based ferroelectric material was studied in this thesis. Metal-Ferroelectric-Insulator-Semiconductor (MFIS) transistors with various ferroelectric-layer thicknesses and various interface-layer thicknesses were fabricated to figure out how thickness can affect the characteristics of ferroelectric transistors or memories. In this thesis, S.S.=27mV/dec was achieved while ferroelectric material was introduced into MOSFET. Besides, ferroelectric characteristic can still be observed in 8 nm thick Al-HfO2 layer.

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