High thermal stability tunnel junctions

Abstract

The thermal stability of CoFe/Al2O3/CoFe/MnIr spin-tunnel junctions fabricated by ion beam, using two oxidation methods is studied for annealing temperatures up to 450 °C. Tunnel magnetoresistance (TMR) is 40% after annealing at 300 °C, and a TMR of 15% is still achieved after annealing at 380 °C. The TMR decay with anneal depends on the oxidation process (O2 beam or remote plasma) and on the thickness of the MnIr exchange layer. Overoxidation of the Al, or higher kinetic energy of the O2 ions, during oxidation, lead to faster thermal degradation of the TMR. Thinner MnIr retards thermal degradation. Rutherford backscattering shows a strong interdiffusion of Mn into the CoFe electrode above 300 °C, but no significant changes are detected at the CoFe/Al2O3/CoFe interfaces, even after annealing at 435 °C (the junction resistance remains high confirming barrier stability). The pinned layer moment decreases upon annealing as expected from Mn incorporation. Also, the strong TMR decrease may indicate polarization loss when Mn reaches the Al2O3/CoFe interface. At 410 °C, the TMR is still 5%, with the fast switching characteristics of the free layer unchanged.

Failure of exchange-biased low resistance magnetic tunneling junctions upon thermal treatment

“…1,4,6,7 The loss of spin polarization at the insulator interfaces, shortcircuiting of the electrodes due to the structural change of FM electrodes, and interdiffusion at ferromagnetic-antiferromagnetic interfaces are believed to be responsible for the eventual failure of the MTJ upon thermal treatment. 8 In spite of the importance of the thermal stability of the tunnel junctions, a single mechanism to completely explain the annealing characteristics of MTJ has yet to be proposed and little reported transmission electron microscope ͑TEM͒ experimental work 9,10 exists that provides direct observation of the corresponding changes in microstructure accompanying thermal treatment.…”

Fabrication and properties of spin dependent tunneling junctions with CoFeHfO as free layers

“…This V 1/2 value is among the highest values for different SDT materials. 8,9 Typical breakdown voltage is about 1.5 V for these junctions, resulting in a dielectric strength of about 10 MV/cm, assuming a tunnel barrier thickness of 1.5 nm oxidized from a 1.2 nm Al layer.…”

“…7 The thermal stability has been found to be adequate for on-chip integration with integrated circuit ͑IC͒ electronics and for high temperature operations. 8,9 These attributes make SDT materials especially attractive for lowfield/low-power device applications. Furthermore, as desired by many applications, high speed can be achieved using these SDT junctions, which can be further integrated with high-speed IC electronics.…”

Influence of Ta antidiffusion barriers on the thermal stability of tunnel junctions

“…[1][2][3] Above this temperature the TMR decreases. In our previous work, 4,5 tunnel junctions based on NiFe/CoFe/Al 2 O 3 /CoFe/MnIr 2 were annealed up to 450°C, and two different mechanisms were proposed for the loss of TMR above 320°C. First, structural and magnetic changes in the CoFe/MnIr layers due to Mn diffusion into the CoFe pinned layer were observed above 320°C, with the Mn diffusing into the CoFe, and reducing its magnetic moment.…”