氧化鎂穿隧式磁阻的製備及研究

Fabrication and investigation of MgO-based magnetic tunneling junction

陳家庠(Chia-Hsiang Chen)

指導教授 ： 賴志煌

國立清華大學/工學院/材料科學工程學系/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00681

摘要

本論文探討以氧化鎂作為穿隧阻絕層，搭配兩層CoFeB鐵磁層的磁阻結構，將探討穿隧磁阻結構的磁性質，進一步研究氧化鎂結構的特性及其退火效應，同時建立磁阻結構微小化的製程平台。

在磁性質方面，製備出準自旋閥結構跟自旋閥結構的穿隧磁阻結構，並討論退火效應對於磁性質的影響。在初鍍膜及退火處後的試片皆可觀察到明顯的平行態及反平行態的磁矩翻轉行為。我們也探討氧化鎂厚度對於兩鐵磁層的交互作用力關係，在下固定層結構中可以看到隨厚度遞減伴隨些微震盪的曲線，而上固定層結構則為單調遞減的趨勢。

氧化鎂的結構方面，藉由調變鍍膜功率及工作氣壓觀察其結構的性質，同時也發現不同材料的緩衝層對氧化鎂結構的影響，並測試不同退火方式對於氧化鎂結構的影響。目前已經能夠製備出MgO(111)方向結晶的結構，而在MgO/CoFeB多層薄膜的結構中也發現CoFeB的鍍膜條件會影響到MgO的結構。

在微小化製程方面，利用光學微影搭配蝕刻的方式，製備出微小化的磁阻元件，在氧化鎂的穿隧磁阻結構中已量測到非線性的I-V曲線，但尚未量測到磁阻變化的圖形。

關鍵字

氧化鎂 ； 穿隧磁阻

並列摘要

MgO-based magnetic tunneling junctions (MTJs) with CoFeB ferromagnetic layers were fabricated in this study. The structural, magnetic and electrotransport properties of both as-deposited and annealed samples were well discussed. The pattern process was also set up to fabricate small size MTJs, which can avoid the geometric effect and improve the reliability of measured MR ratio, especially for low RA samples.
Both pseudo spin-valve and spin-valve type samples were prepared. The magnetic properties of these samples were well examined. The parallel and antiparallel states can also be well distinguished. We also investigated the dependence of MgO thickness on interlayer coupling between free layer and pinned layer. In the top pinned spin-valve structure, we observed a monotonic decay with increasing MgO thickness. However, some oscillation of interlayer coupling strength with the MgO thickness was observed in the bottom pinned structure.
The structural properties of MgO prepared with various sputtering powers and working pressures during deposition process were studied by using the XRD measurement. We found that different buffer layer can induce different MgO structure. The crystalline MgO with (111) preferred orientation was successfully fabricated in this study.
Photolithography and dry etching were both used in our pattern process, which worked well for our previous AlOx-based MTJs. But there were some problems in the MgO-based MTJs. Only nonlinear I-V curve can be observed, which means the existence of the tunneling effect.

並列關鍵字

MgO ； CoFeB ； tunneling junction

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