CPM Seminar

CANCELLED

Nano-ring and nano-elliptic-ring shaped magnetic tunneling junctions and their applications in MRAM design with spin-polarized current switching

Xiufeng Han

Institute of Physics
Chinese Academy of Science

A series of nano-elliptic-ring (NER)-shaped magnetic tunnel junctions (MTJs) with the major axis of around 120 nm and minor axis of around 60 nm, and ring width of around 25 nm was fabricated successfully. Magnetic field and current-driven magnetization switching were observed in such NER-MTJs with key stack layers of both spin-valve-type antiferromagnetic (AFM)/ferromagnetic (FM)/insulator (I)/ ferromagnetic (FM) and sandwich-type hard-FM/ I /soft-FM structures. When the electric current density exceeds a critical value of the order of about 8x106A/cm2 (critical driven current is 0.40 mA), the magnetization of the free (soft-FM) and reference (hard-FM) layer nano-elliptic-rings can be switched back and forth between parallel and antiparallel onion states. Tunneling magneto-resistance (TMR) ratio between 10% and 40% with different thickness of thin Al-O barrier waere measured at room temperature as we apply a magnetic field or a pulsed current. The experiments and micromagnetic analysis show that the spin transfer torque (STT) plays a main switching role in the magnetization reversal and the pulse-current-induced elliptic magnetic field play an assisted-switching role in such NER-MTJs. Compared with our previous studies of nano-ring-shaped (NR) MTJs and Nanoring MRAM [1-3], the NER-MTJ has a relative symmetric current driven critical behavior, which is due to the shape anisotropy of elliptic-ring architecture. The NER-MTJs also show the comparative lower switching field or critical current value (or density) and can be as the memery bit cells. Therefore, the manipulation of anisotropy in NER-shaped MTJs open a new way to develop more reliable and easier operational NER-MRAM devices.

Fig.1 A typical NER-MTJ image with the major axis of 121 nm, minor axis of 68 nm and ring width of 21 nm.	Fig.2 Current-driven magnetization switching with TMR ratio of 16% at room temperature observed in the Al-O barrier based NER-MTJ.

References:
[1] Z. C. Wen, H. X. Wei, and X. F. Han, "Patterned nanoring magnetic tunnel junctions", Appl. Phys. Lett. 91 (2007) 122511. [2] X. F. Han, Z. C. Wen, and H. X. Wei , "Nanoring MTJ and its application in MRAM demo devices with spin-polarized current switching", J. Appl. Phys. 103 (2008) 07E933. [3] H. X. Wei, X. F. Han, S. Zhang and C. L. Chien et al., "Effects of the current on the nanoscale ring-shaped magnetic tunnel junctions", Phys. Rev. B 77 (2008) 134432 and 77 (2008) 224432.