Progress of a GMR element by the simulation of film formation process and microfabrication

HDD的记录密度以每年80%至100%的速度上升。Co/Cu多层膜的巨磁电阻效应是实现高灵敏度磁头的重要课题之一。众所周知，电流垂直于平面（CPP）GMR比电流平面（CIP）GMR显示出更高的MR比。众所周知，巨磁电阻效应取决于超晶格中界面处的纳米结构。(1)为了阐明薄膜形成过程中表面的纳米结构，我们对Cu在aCu（111）单晶衬底上的沉积行为进行了分子动力学（MD）模拟。在单晶衬底上沉积0.6个Cu原子单层后，在表面观察到[ABC]和[AB/A]结构。随着沉积层厚度的增加，[ABC]和[AB/A]结构相互接触，并且在第三沉积层内部出现堆垛层错。然后，在第四沉积层内仅在第三沉积层内观察到堆垛层错的区域上出现晶粒结构。然后，由模拟得到的界面结构与入射原子动能的关系与核磁共振谱的实验结果吻合得很好。(2)我们利用聚焦离子束（FIB）刻蚀机对Co/Cu多层膜进行了微加工，通过改变电流路径来提高MR比，FIB刻蚀引起的样品Ga污染在3 nm以内。因此，MR比率从4.55%增加到8.90%。

The recording density of HDDs rises at an annual rate of 80 to 100 %. The giant magnetoresistance (GMR) effect in Co/Cu multilayers is one of the important issues for achieving high sensitive magnetic head. It is known that current-perpendicular-to-the-plane (CPP) GMR shows higher MR ratios than current-in-plane (CIP) GMR. It is commonly known that GMR effect depends on the nanostructure at the interface in the superlattice.(1) For the purpose of clarifying the nanostructure at the surface during the film formation process, we performed molecular dynamics (MD) simulations for the Cu deposition behavior on aCu (111) single crystal substrate. After the deposition of 0.6 Cu atoms monolayer on a single crystal substrate, [ABC] and [AB/A] structures were observed at the surface. With increasing thickness of the deposited layer, [ABC] and [AB/A] structures contacted each other, and stacking faults appeared inside the third deposited layer. Then the grain structure appeared inside the fourth deposited layer merely over the area where the stacking faults were observed inside the third deposited layer. Then, the dependence of the interface structure to the kinetic energies of incident atoms derived from simulations corresponds well to the experimental results of NMR spectram.(2) We performed micro fabrication of Co/Cu multilayers using a focused ion beam (FIB) etching machine to increase MR ratios by changing the current flow path. Ga contamination of the specimen caused by FIB processing was within 3 nm. As a result, the MR ratio increased from 4.55 % to 8.90%.