Tunneling magnetoresistance and current distribution effect in spin-dependent tunnel junctions

In this paper, spin-dependent tunnel junctions fabricated by shadow mask (junction area. 0.25 mm(2)) and by lithography (junction area down to 9X2 lI m'l were stuclled..l.he junctions have NiFe and CoFe electrodes and the insulating barrier Al2O3 is formed by depositing a 10-30 Angstrom thick Al layer, followed by a 1-3 min plasma oxidation in an O-2 atmosphere. The mm(2)-size junctions show tunneling magnetoresistances (TMR) of 10%-13.5% at room temperature (RT), with 50% decrease in TMR for a bias voltage of 220 mV. The junction resistances range from hundreds of Omega to tens of k Omega. The analysis of current distribution indicates that no geometrically enhanced magnetoresistance occurs in the cross-shaped mm2-size junctions when the measured junction resistance is five times larger than the electrode resistance over junction area. The mu m(2)-size junctions show TMR of 17%-24% at RT, independent of the junction area, and have a resistance between 90 k Omega and 1 M Omega for the 9 X 2 mu m(2) size (resistance-area products of similar to 3 M Omega X mu m(2)). The mu m(2)-size junctions show 50% decrease in TMR fur a bias voltage of 430 mV, and high sensitivity (>20%/Oe). (C) 1998 American Institute of Physics.