Spin-dependent tunneling junctions with Ta2O5 barrier

Spin-dependent tunneling junctions with the NiFe/oxide/NiFe structure have been fabricated with oxide barriers of Ta2O5, Al2O3 and composite Ta2O5/Al2O3 films. The barriers were formed by plasma oxidation of sputter-deposited Ta/Al films. Room-temperature tunneling magnetoresistance (TMR) effects observed are up to 4% in junctions with Ta2O5 and composite Ta2O5/Al2O3 barriers, significantly lower than the typical 15% effects seen in junctions with comparable Al2O3 barriers and having similar electrodes. X-ray Photoelectron Spectroscopy (XPS) was used to study the oxidation profile of the barrier. Depth-profiles in the barrier regions show Al is fully oxidized while some unoxidized Ta remains. Increasing the oxidation time yields fully oxidized barriers, and increases junction resistance and TMR. At increased oxidation times, however, slight oxidation of the underlying electrode was observed, pointing towards a tradeoff between full oxidation of the barrier and likelihood of damage to the underlying electrode. Lower TMR ratios in Ta oxide junctions may be due to spin-hip scattering of electrons by residual unoxidized Ta and/or a lower tunneling probability in Ta2O5.