Effects of annealing on high-magnetoresistance tunnel junctions using Co75Fe25 ferromagnetic electrodes

Tunnel junctions, Ta (5 nm)/Ni79Fe21 (3 nm)/Cu (20 nm)/Ni79Fe21 (3 nm)/lr(2 2)Mn(78) (10 nm)/Co75Fe25 (4 nm)/Al (d nm)-oxide/Co75Fe25 (4 nm)/Ni79Fe21 ( 20 nm)/Ta(5 nm) wherein d=1.3 and 0.8 nm, with small active area from 100x1 00 down to 3x3 mum(2) were fabricated using a micro-fabrication technique. The optical lithography combined with Ar ion-beam etching and CF4 active et ching was used to pattern the junction area. A thin barrier layer and a sho rt plasma-oxidation time for At-oxide layer were used in order to reduce th e junction resistance and increase the TMR ratio. The optimum annealing tem perature and time for the highest TMR obtained were investigated to be arou nd 300 degreesC for an hour in this work. TMR ratio, effective barrier heig ht and width, and breakdown voltage of the junctions can be remarkably enha nced upon annealing. High TMR ratio of 49.7% at room temperature and 69.1% at 4.2 K were achieved. TMR ratio and resistances decrease with increasing de bias voltage from 0 to 1000 mV or with increasing temperature from 4.2 K to room temperature.