Characteristics of ultrathin CoFeB thin films with perpendicular magnetic anisotropy

• Main Authors: Shin-Hsueh Huang, 黃士學
• Other Authors: Te-Ho Wu
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/71170250642387891439

碩士 === 國立雲林科技大學 === 材料科技研究所 === 99 === In this study, we focused on the ultrathin CoFeB films with perpendicular magnetic anisotropy (PMA) which can be used for perpendicular magnetic tunnel junctions (pMTJs). The magnetic properties of the films were tuned by varying the CoFeB composition and the annealing temperatures. Two different compositions of CoFeB were studied: Co40Fe40B20 and Co20Fe60B20. At the first stage of the experiment, we fabricated both the bottom substructure Ta / CoFeB / MgO and the top structure MgO / CoFeB / Ta of pMTJs to look for conditions of PMA. The magnetic properties of the samples were measured by alternating gradient magnetometer (AGM). As for the annealing treatment, the samples were annealed at 300℃ and 350℃ with/without perpendicular applied magnetic field. The results show that the top structures Co40Fe40B20 of thickness 1.4 nm and 1.6 nm retained PMA for both as-deposition and post deposition annealing. The Co20Fe60B20 films of thickness from 1.2 nm to 1.6 nm had PMA from as-deposition condition to post annealing up to 300℃. In contrast with the bottom structures, no strong PMA was present for the top CoFeB structures. To overcome this problem, an ultrathin iron or magnesium layer was inserted between MgO and CoFeB layers. The results show that t adding Fe layer of thickness 0.2 nm together with the post annealing can enhance PMA of the top structures. In addition, we found that the bottom tantalum layer, served as the bottom electrode, becomes crystalline when sputtered on top of ruthenium layer. The crystallinity of tantalum can prevent intermix at Ta-CoFeB interface and reduce the thickness of magnetic dead layer of CoFeB after annealing treatment.