| Summary: | 碩士 === 國立雲林科技大學 === 材料科技研究所 === 104 === In this thesis, we focused on phase transformation of thin tungsten films.The spin current can be generated in nonmagnetic materials by the spin hall effect(SHE), which spin up and spin down currents could accumulate on the surface by charge current.We incooperated the perpendicular magnetic tunnel junctions (pMTJ) with SHE of structure CoFeB / MgO / CoFeB, which have the advantages of high magnetoresistance, small writing current and good thermal stability.
First,we use the TEM to calibrate the tungsten film thickness.The pMTJ structure is SiOx / W (X nm) / Co40Fe40B20 (1.1 nm) / MgO (2nm) / Co20Fe60B20 (2.2 nm) / Ta (5 nm) / Ru (5 nm),where Co40Fe40B20 served as free layer while Co20Fe60B20 served as fixed layer. In addition, we change the thickness of W bottom electrodes in pMTJ structure and observing how it influences on the magnetic properties of pMTJ. The experimental results show that with thin films thickness of tungsten increases, Co40Fe40B20 bias field declines.
The resistivity measurements showed that a sharp decline in the resistivity of tungsten when the thin film thickness ranging from 3 nm ~ 5 nm and 15 nm~17 nm, which is inferred to be the influences of W lattice structure changes. By using the XRD to characterize various thin film thickness analyses, they could be found that 3 nm is so thin that causes amorphous and 5nm is in β-phase. 10 nm is in the mix of α and β phases.While those thickness larger than 17 nm are all α-phase. The results described above indicate that it is the lattice structure influence the resistivity values.The study also finds out that the tungsten thickness for the β-phase about 5 nm.
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