摘要
1988年，巨磁阻(giant magnetoresistance，以下簡稱GMR)由Baibich等人在Fe/Cr超晶格(super lattice)中發現後，GMR開始受到普遍的注意與發展。對於自旋閥結構之讀取頭感應器(sensor)表現的好壞與否，熱穩定性(thermal stability)是一重要關鍵，而且在長期的高電流密度操作下會導致電性熱衰退(thermal degradation)，其主要原因是在多層模界面上的互相擴散(interdiffusion)，因為，非磁性層(nonmagnetic layer)和磁性層之間的界面結構，對GMR效應而言扮演著一重要角色。

本論文先是利用實際巨式磁阻自旋閥讀取磁頭超薄膜結構，去發展適用的TEM分析技術，然後再針對各多層膜之間的互相擴散對磁性質所造成的影響改變做深入的探討。再者，利用一巨磁阻自旋閥結構，直接探討磁阻性質與溫度及組成元素擴散之互相關係，並利用過去曾發展出之理論實驗模型與實驗的結果相比較。

Cap/NiFe/CoFe/Cu/CoFe/Ru/CoFe/NiFe/NiMn/seed layer巨磁阻讀取磁頭感應區在熱應力測試200oC，1000小時之後，利用高分辨穿透式電子顯微鏡結合奈米電子束X光能譜及能量損失譜儀研究多層膜之間奈米尺度的相互擴散。利用一個累積積分法用來做高分辨影像的處理以分析晶格常數的變化，而為改善所測得成分分佈之空間解析度，運用一Wiener過濾器來移除從奈米電子束X光能譜量測中所產生的電子束延展效應。此外，利用能量損失譜儀，從元素分佈萃取去求界面之粗糙度。結合這些分析技術能更清楚顯現在自旋閥元件超薄多層膜間之相互擴散的訊息。成分分佈的分析顯示Ni已擴散至 Cu層。分析的結果亦揭示在自旋結構，Ru層不只是作為合成反鐵磁層之間隔層而且似乎亦能當作Ni和Mn元素之擴散阻礙層。為研究自旋閥元件□組成元素之擴散機制，簡易地利用Boltzmann-Matano方法來探究組成元素之擴散係數。結果發現對於Cu在Co層、Co在Cu層以及Ni在Co層的擴散，晶界擴散是主要的支配機制。

seed layer/NiFe/CoFe/Cu/CoFe/Ru/CoFe/PtMn/Cap自旋閥結構在平行磁場下針對數個溫度(220、250、280、300、320、350及400 oC)，退火，結果發現，雖然巨磁阻性質隨溫度上升而衰減，然而對CoFe/Cu/CoFe結構之合成反鐵磁層自旋閥，於在250 oC、20小時退火後，由於Co與Cu界面混合區之產生分解，界面變較鮮明(sharper)及成份純度高，使巨磁阻變化率上升(約10%)與矯頑場變小(約減少2.5 Oe)，界面混合區約減少了約1個原子層。此外，對於其他組成元素的擴散，Ni在300 oC，20小時後已擴散至CoFe/Cu界面混合區。對於Ru作為反鐵磁層元素Pt與Mn之擴散阻礙層之觀察，由nanobeam EDX分析，直至350 oC，Ru仍可作為Pt與Mn之擴散阻礙層。溫度升至400oC，Ru仍能作為Mn之擴散阻礙層，然而，Pt已穿過Ru往Cu層擴散。

Abstract
Since the discovery of giant magnetoresistance (GMR) in Fe/Cr super lattices by Baibich et al. [1], the GMR has received great interest over the last few years for applications in high-density magnetic recording heads. Spin-valve with multilayers is one of the promising magnetic devices and has been applied in the advanced magnetoresistive read head. However, it is not easy to deposit homogeneous ultra thin films to fabricate a multiplayer spin valve. In addition, long-term operations under a high current density also enhance the interlayer diffusion of the constituent atoms, which can significantly degrade the GMR performance. In our study, we first collect and develop the proper HRTEM technique for the analysis utilizing the spin valve structure of GMR read head device. Then study the interdiffusion in detail among the multiplayer. Moreover, we probe into the dependence between interdiffusion and GMR properties. Furthermore, another spin valve sample was used to directly discuss the relation among the GMR properties, anneal temperatures, and interdiffusion. Finally, the analytical results was fitted and compared by Dieny model.

Cap/NiFe/CoFe/Cu/CoFe/Ru/CoFe/NiFe/NiMn/seed layer after the life stress test of the spin-valves read head at 200 o C for 1000 hr is investigated by using high resolution transmission electron microscopy (HRTEM) coupling with nanobeam energy dispersive spectrometer x-ray (EDX) and electron energy loss spectrometer (EELS). Investigation was focused on the interdiffusion among interlayers in the nanometer scale. Accumulated sum technique was applied to analyze the lattice-spacing variation across the ultra-thin film from HRTEM micrographs. A Wiener filter was used to remove the electron beam broadening effect from nanobeam EDX data so that the spatial resolution of composition profile is improved. Furthermore, interface roughness was extracted by utilizing EELS map. Combination of these techniques (lattice variation measurement, the deconvolution of nanobeam EDX, and EELS maps) allows the insight of interdiffusion among ultra-thin films in the spin-valve device to be revealed. The compositional analysis demonstrated that Ni diffused into the Cu/Co bilayer. The analytical result also suggests that the Ru layer may not only act as the spacer of the synthetic antiferromagnet but also behave as a good diffusion barrier for Ni and Mn element in the spin valve structure. To further study the diffusion mechanism of constituent elements in the spin valve device, the diffusion coefficients of constituent elements are simply investigated using the Boltzmann-Matano method. The diffusion mechanisms of Cu in Co layer, Co in Cu layer, and Ni in Co layer were primarily dominated by the grain boundary.

The spin valves, seed layer/NiFe/CoFe/Cu/CoFe/Ru/CoFe/PtMn/cap, were annealing at several temperatures (220~400 oC) for 20 hr in the parallel magnetic field. Accordingly, it is shown that the magnetoresistance ratio (MR ratio) was degraded with increasing annealing temperature. Surprisingly, there was a demixing phenomenon in the intermixing region of CoFe/Cu bilayer during the annealing at 250 oC for 20 hr. It is consequently shown that the GMR was enhanced due to the sharper and more pure interface of CoFe/Cu and Cu/CoFe. Besides, regarding to the interdiffusion of another constituent elements, Ni diffused into the CoFe/Cu bilayer after 300 oC annealing. Moreover, the analytical result also suggests that the Ru layer may not only act as the spacer of the synthetic antiferromagnet but also behave as a good diffusion barrier for Pt and Mn element in the spin valve structure up to 350 oC annealing. The annealing temperature raised sequentially to 400 oC, Ru layer could also behave as the diffusion barrier for Mn.

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