Investigation of magnetic tunneling junctions with wedge-shaped barrier

Abstract

By oxidizing wedge-shaped Al films we were able to simultaneously fabricate Ni80Fe20/AlOx/Ni80Fe20 tunnel junctions with over, completely, and underoxidized barriers. We have systematically investigated TMR ratio, resistance, barrier height and thickness, and bias dependence along the wedge. The bias dependence of MR ratio is asymmetric in overoxidized regions and symmetric in underoxidized regions. The interesting bias dependences of resistance at parallel and antiparallel configurations will also be presented.

Aluminum oxide layers as possible components for layered tunnel barriers

“…40.Rw, 85.30.Kk, 85. 30.Mn Calculations 1,2,3 indicate that tunnel conductance of layered barriers, in particular those with "crested" potential profile peaking in the middle, may be much more sensitive to the applied voltage than that of the uniform layers. 4 This sensitivity, if combined with high endurance to electric stress, may be used in advanced floatinggate memories, including fast and scalable random access memories 5 and fast single-and few-electron memories, 6,7 and ultradense data storage systems, 1 as well as for improvement of the usual nonvolatile (e.g., "flash") memories.…”

Transport property studies on magnetic tunnel junctions with wedge-shaped barrier

“…To our knowledge, DC bias dependence is able to probe the oxidation level of the FM/I interface in MTJs, provided that both of the electrodes are made of the same material. It is clear that the plot of TMR versus DC bias is quite asymmetric for over-oxidized MTJ and symmetric for almost completely or under-oxidized MTJ [10,11]. In order to demonstrate the asymmetry quantitatively, same as that in Ref.…”

“…In order to demonstrate the asymmetry quantitatively, same as that in Ref. [10], we define V 0.7 and V À0.7 as the voltages at which the TMR ratio decreases to 70% of the maximum value. The bias dependence along the wedge for sample T1 is shown in Fig.…”

Probing tunnel barrier shape and its effects on inversed tunneling magnetoresistance at high bias

“…Inversed TMR refers to the phenomenon of conductance in a parallel magnetization configuration (σ ↑↑ in MTJs is lower than that in an antiparallel magnetization configuration σ ↑↓ ). [5][6][7] The inversed TMR phenomenon is very rare and is only observed in Co/SrTiO/Co, 8 TiO/CrO, 9 and Co/AlO/TaO/Co 10 systems. It should also be noted that the first two material systems show inversed TMR in all bias voltages, and the last type of MTJs show inversed TMR at high bias.…”