http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
Local Variation of Magnetic Parameters of the Free Layer in TMR Junctions
CheolGi Kim,Toshihiro Shoyama,Masakiyo Tsunoda,Migaku Takahashi,Tae Hyo Lee,Chong-Oh Kim 한국자기학회 2002 Journal of Magnetics Vol.7 No.3
Local M-H loops have been measured on the free layer of a tunneling magnetoresistance (TMR) junction using the magneto-optical Kerr effect (MOKE) system, with an optical beam size of about 2 ㎛ diameter. Tunnel junctions were deposited using the DC magnetron sputtering method in a chamber with a base pressure of 3 × 10^(-9) Torr. The relatively irregular variations of coercive force Hc (~17.5 Oe) and unidirectional anisotropy field Hua (~7.5 Oe) in the as-deposited sample are revealed. After 200 ℃ annealing, Hc decreases to 15 Oe but Hua increases to 20 Oe with smooth local variations. Two-dimensional plots of Hc and Hua show the symmetric saddle shapes with their axes aligned with the pinned layer, irrespective of the annealing field angle. This is thought to be caused by geometric effects during deposition, together with a minor annealing effect. In addition, the variation of root mean square (RMS) surface roughness reveals it to be symmetric with respect to the center of the pinned-layer axis, with the roughness of 2.5 Å near the edge and 5.8 Å at the junction center. Comparison of surface roughness with the variation of Hua suggests that the Hua variation of the free layer is well described by dipole interactions related to surface roughness. As a whole, the reversal magnetization is not uniform over the entire junction area and the macroscopic properties are governed by the average sum of local distributions.
Kazuhiro Nishikawa,Satoshi Ogata,Toshihiro Shoyama,Wan-Sick Cho,Tae-Sick Yoon,Masakiyo Tsunoda,Migaku Takahashi 한국자기학회 2002 Journal of Magnetics Vol.7 No.3
Three fabrication techniques for forming thin barrier layer with uniform thickness and large barrier height in magnetic tunnel junction (MTJ) are discussed. First, the effect of immiscible element addition to Cu layer, a high conducting layer generally placed under the MTJ, is investigated in order to reduce the surface roughness of the bottom ferromagnetic layer, on which the barrier is formed. The Ag addition to the Cu layer successfully realizes the smooth surface of the ferromagnetic layer because of the suppression of the grain growth of Cu. Second, a new plasma source, characterized as low electron energy of 1 eV and high density of 10¹² ㎝-³, is introduced to the Al oxidation process in MTJ fabrication in order to reduce damages to the barrier layer by the ion-bombardment. The magnetotransport properties of the MTJs are investigated as a function of the annealing temperature. As a peculiar feature, the monotonous decrease of resistance area product (RA) is observed with increasing the annealing temperature. The decrease of the RA is due to the decrease of the effective barrier width. Third, the influence of the mixed inert gas species for plasma oxidization process of metallic Al layer on the tunnel magnetoresistance (TMR) was investigated. By the use of Kr-O₂ plasma for Al oxidation process, a 58.8% of MR ratio was obtained at room temperature after annealing the junction at 300℃, while the achieved TMR ratio of the MTJ fabricated with usual Ar-O₂ plasma remained 48.4%. A faster oxidization rate of the Al layer by using Kr-O₂ plasma is a possible cause to prevent the over oxidization of Al layer and to realize a large magnetoresistance.