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標題: | 鐵電薄膜低溫相變及厚度效應之電性分析 Electrical Analysis of Cryogenic Phase Transition and Thickness Effect in Ferroelectric Film |
作者: | 邢軼凡 Yifan Xing |
指導教授: | 劉致為 Chee Wee Liu |
關鍵字: | 鐵電,反鐵電,氧空缺,超晶格,低溫相變,鐵電隨機存取記憶體,鐵電穿隧結,鐵電場效電晶體, ferroelectric (FE),anti-ferroelectric (AFE),oxygen vacancy,superlattices,cryogenic phase transition,FeRAM,FTJ,FeFET, |
出版年 : | 2023 |
學位: | 碩士 |
摘要: | 本篇論文討論基於氧化鉿鋯之鐵電薄膜,用於新型非揮發性記憶體。我們採用電漿輔助原子層沉積方法沉積HfO2-ZrO2混合物,並沉積TiN上下電極形成金屬-鐵電氧化物-金屬電容結構。電漿輔助原子層薄膜沉積的優勢在本文中討論,包括沉積溫度,前驅物,反應氣體等,以達到低缺陷沉積Hf0.5Zr0.5O2的目的。通過透射電子顯微鏡和高角度暗場技術來支援材料分析,以區分超晶格和合金結構。通過電性分析,低氧空缺含量有利於鐵電正交晶系的生成以及高氧空缺含量有利於反鐵電四方晶系的生成,本文闡明了Hf0.5Zr0.5O2的氧空缺效應。實驗介電常數是通過非滯後電容-電壓測量來提取的,以分辨晶系的含量。
從亞穩的四方晶系向正交晶系的低溫相變在增強所需鐵電特性中起著關鍵作用。在此研究中,我們在Hf0.5Zr0.5O2合金中實驗性地研究了低溫相變,觀察到電特性中從反鐵電向鐵電的可逆相變。我們還分析了穩定的正交晶系的形成,在超晶格Hf0.5Zr0.5O2中,77K時具有顯著的23%剩餘極化增加。為了驗證關於低溫下相變現象的理論,我們採用了Landau-Ginzburg-Devonshire理論和第一原理計算的分析組合。詳細的計算揭示了隨著溫度降低,四方晶系相對自由能增加有助於降低能量屏障,促進從亞穩的四方晶系向正交晶系的相變。這項工作提出了一個綜合的低溫相變模型,涉及Hf0.5Zr0.5O2中的四方晶系和正交晶系,為基於氧化鉿的新型低溫原件中增強鐵電性能提供了新的方法。 此外,通過降低Hf0.5Zr0.5O2的厚度,改善了讀出電流較低的問題。4nm Hf0.5Zr0.5O2的電流數量級比6.7nm的大1000倍,直流開/關比超過10。在1E-2秒脈衝寬度下,4nm的Hf0.5Zr0.5O2的交流開/關比為2.1,並在1E-3秒脈衝寬度時達到飽和。 This dissertation investigates the HfO2-ZrO2-based ferroelectric thin film for novel non-volatile memory. The HfO2-ZrO2 mixture is deposited by plasma enhanced atomic layer deposition (PEALD) and sandwiched by in-situ TiN electrodes, forming the MFM capacitor structure. The advantages of PEALD thin film deposition are studied to optimize the quality of Hf0.5Zr0.5O2. The transmission electron microscope and high-angle annular dark-field support material analysis to distinguish the superlattices and alloys. The oxygen vacancy effect of Hf0.5Zr0.5O2 is clarified by electrical characteristics in low oxygen vacancy favoring ferroelectric orthorhombic phase and high oxygen vacancy favoring anti-ferroelectric tetragonal phase. The experimental dielectric constant is extracted from non-hysteretic capacitance-voltage measurement. The cryogenic transition from the metastable tetragonal phase to the orthorhombic phase is crucial in achieving desired ferroelectric characteristics. In this study, we experimentally investigate the cryogenic phase transition in Hf0.5Zr0.5O2 alloys, observing the reversible change from antiferroelectricity to ferroelectricity in electrical properties. We also analyze the formation of stabilized o-phase, which exhibits a significant 23% increase in remanent polarization at 77K in superlattice Hf0.5Zr0.5O2. To provide theoretical insights into the phase transition phenomenon at lower temperatures, we employ a combination of Landau-Ginzburg-Devonshire theory and first-principle calculations. The detailed calculations reveal that the increasing relative free energy of the t-phase contributes to lowering the energy barrier as the temperature decreases, facilitating the transition from the metastable tetragonal phase to the orthorhombic phase. This research presents a comprehensive cryogenic phase transition model involving tetragonal and orthorhombic phases in Hf0.5Zr0.5O2, offering a promising approach to enhance ferroelectricity in emerging cryo-devices based on HfO2. Moreover, the issue of low read-out current is ameliorated by reducing the thickness of Hf0.5Zr0.5O2. The current magnitude of 4nm Hf0.5Zr0.5O2 is 1000 times more than 6.7nm with a DC swept on/off ratio of more than 10. The AC on/off ratio of 4nm Hf0.5Zr0.5O2 is 2.1 at pulse width 1E-2 second and saturates at pulse width 1E-3 second. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/88131 |
DOI: | 10.6342/NTU202301680 |
全文授權: | 同意授權(全球公開) |
顯示於系所單位: | 電子工程學研究所 |
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