Magnetic random access memories based on the spin transfer torque phenomenon (STT-MRAMs) have become one of the leading candidates for next generation memory applications. Among the many attractive features of this technology are its potential for high speed and endurance, read signal margin, low power consumption, scalability, and non-volatility. In this paper, we discuss our recent results on perpendicular STT-MRAM stack designs that show STT efficiency higher than 5 kBT/μA, energy barriers higher than 100 kBT at room temperature for sub-40 nm diameter devices, and tunnel magnetoresistance higher than 150%. We use both single device data and results from 8 Mb array to demonstrate data retention sufficient for automotive applications. Moreover, we also demonstrate for the first time thermal stability up to 400 °C exceeding the requirement of Si CMOS back-end processing, thus opening the realm of non-volatile embedded memory to STT-MRAM technology.
Articles you may be interested inInelastic tunneling conductance and magnetoresistance investigations in dual ion-beam sputtered CoFeB(110)/MgO/CoFeB (110) magnetic tunnel junctions Fabrication of magnetic tunnel junctions with a bottom synthetic antiferro-coupled free layers for high sensitive magnetic field sensor devices J. Appl. Phys. 111, 07C710 (2012); 10.1063/1.3677266High field-sensitivity planar Hall sensor based on NiFe/Cu/IrMn trilayer structure A structure of Ta/MgO/NiFe/MgO/Ta was designed and synthesized, which combines the advantages of both tunnel magnetoresistance materials with high magnetic field sensitivity and anisotropic magnetoresistance materials with high directional sensitivity. The magnetoresistance ratio in the device with structure of Ta͑5͒/MgO͑4͒/NiFe͑10͒/MgO͑3͒/Ta͑3͒ ͑thicknesses in nanometers͒ increases with an increase in annealing temperature, reaching a maximum value of 3.5% at 450°C, and then decreases with a further increase in annealing temperature. Meanwhile, a high sensitivity of 2.1%/Oe is obtained. The higher magnetoresistance ratio and sensitivity come from the significant specular reflection of electrons at both interfaces due to the crystalline MgO layer together with the sharp interfaces with the NiFe layer.
In this letter, we report on measurements of current-induced magnetization switching (CIMS) in current-perpendicular-to-plane exchange-biased spin-valves (ESPVs). The structures of the ESPVs are all “antisymmetric,” but with different thickness of a ruthenium (Ru) layer. It is confirmed that the “antisymmetric” structures largely enhance the spin transfer effect and therefore reduce critical current densities for the CIMS. The effect of the Ru layer on the spin transfer in the ESPVs is also systematically studied. With a decrease of the Ru layer’s thickness, the critical current densities can be further reduced. The lowest critical current we achieved in an “antisymmetric” structure is 1×106A∕cm2, which realizes a reduction of more than one order of magnitude compared with all the reported works.
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