摘 要
近年來，對於應用在磁性隨機存取記憶體(MRAM)與磁性讀取頭的亞錳酸鹽鈣鈦礦磊晶薄膜之巨磁阻效應已受到廣泛的重視，許多研究指出磁阻的改變與材料的微觀結構有密切的關連，本實驗乃針對該巨磁阻材料的磁阻與微觀結構作一深入探討。
本實驗所研究的鑭鈣錳氧(La0.67Ca0.33MnO3, LCMO)薄膜乃是以射頻磁控濺鍍(RF Sputtering)法，在750℃的成長溫度下，於(001)氧化鎂和(001)鈦酸鍶基板上分別成長不同厚度的薄膜，這兩種基材提供了兩種晶格不匹配的程度，對於氧化鎂和鈦酸鍶分別為+9％和+1％。本研究，以X光繞射分析薄膜晶體結構，掃瞄式電子顯微鏡觀察薄膜的表面型態，穿透式電子顯微鏡觀察薄膜與基材界面的微結構，拉塞福回向散射則量測薄膜厚度與薄膜成份組成，最後利用四點量測在溫度範圍77K到300K之間，檢測薄膜的電阻與磁性轉換溫度。
實驗結果顯示成長於鈦酸鍶基材的LCMO薄膜為一具有超晶格結構之磊晶薄膜，而成長於氧化鎂基材的薄膜，因為受到晶格不匹配的影響，呈現多晶結構，此外當薄膜厚度超過2000Å時，受到晶格不匹配的影響逐漸減緩，因此薄膜的晶格常數和磁阻改變轉換溫度與LCMO塊材相近，所以薄膜與基材因晶格不匹配所產生的應變與薄膜的微結構及磁性有強烈的關係存在。

Abstract

Recently, the large magneto-resistance effects in epitaxial manganite thin films has interested in the doped manganite perovskite materials for magnetic random access memory (MRAM) and read-head application. The relation between the magneto-resistance and microstructure of the colossal magneto-resistance materials has been evaluated in this study.
Different thickness of La0.67Ca0.33Mn03 (LCMO) thin films were grown on (001) MgO and (001) SrTi03 (STO) substrates at growth temperature 750 degree C with RF magnetron sputtering technique, respectively. These substrates provide two different lattice-mismatch conditions for the LCMO films (+9% for MgO and +1% for STO). The crystal structure of LCMO films were characterized with X-ray diffraction (XRD), the surface morphology of LCMO films were observed by scanning electron microscope (SEM), the interface of microstructure between LCMO films and substrate were studied by transmission electron microscope (TEM), the thickness and chemical composition of LCMO films were determined by Rutherford backscattering spectrometer (RBS), and finally the resistance and I-M transition temperature were evaluated at temperature range from 77K to 300K.
The results show that the epitaxial LCMO films with a superlattice structure were obtained on STO substrate and polycrystal structure of LCMO films were on MgO substrate due to larger lattice mismatch.. The transition temperature of magneto-resistance of LCMO thin film is quite sensitive with film thickness. The transition temperature increases with film thickness increased. When the film with thickness excess of 2000A, the transition temperature is nearly same as that of LCMO bulk material.. The existed strain and the microstructure of LCMO films are two important factors related with magnetic resistance and electrical properties of LCMO films.

目 錄
中文摘要 Ⅰ
英文摘要 Ⅱ
誌謝 Ⅲ
目錄 Ⅳ
圖目錄 Ⅶ
表目錄 XI
第一章 前言 1
1-1 簡介 1
1-2 研究動機 2
第二章 基本理論 9
2-1 磁性理論 9
2-1-1 磁性起源 9
2-1-2 磁化率 9
2-1-3 磁性分類 10
2-2 磁阻特性 13
2-2-1 磁阻效應 13
2-2-2 磁阻分類 16
2-3 巨磁阻材料 19
2-3-1 巨磁阻理論 19
2-3-2 巨磁阻的種類 22
2-4 雙重交換理論與Jahn-Teller效應 26
2-5 鈣鈦礦結構 28
第三章 實驗方法 29
3-1 實驗流程 29
3-2 試片清洗 30
3-3 X光繞射儀 30
3-4 掃瞄式電子顯微鏡 31
3-5 穿透式電子顯微鏡試片製作 32
3-6 穿透式電子顯微鏡 32
3-7 拉塞福背向散射分析 34
3-8 磁性量測 35
第四章 結果與討論 36
4-1 X光繞射分析 36
4-1-1 θ-2θ掃瞄 36
4-1-2 Φ掃瞄 38
4-2 掃瞄式電子顯微鏡 46
4-3 穿透式電子顯微鏡 50
4-3-1 LCMO/MgO 50
4-3-2 LCMO/STO 58
4-4 拉塞福背向散射分析 62
4-5 磁性量測 64
第五章 結論 70
參考文獻 71

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