80% tunneling magnetoresistance at room temperature for thin Al-O barrier magnetic tunnel junction with CoFeB as free and reference layers

Magnetic tunnel junctions (MTJs) with structures of Ta(5)/Cu(10)/Ta(5)/Ir21Mn79(10)/Co75Fe25(2)/Ru(0.75)/Co40Fe40B20(3)/Al(0.6)-O/Co40Fe40B20(2.5)/Ta(3)/Ru(7) (units in nanometers) were deposited via ultrahigh vacuum magnetron sputtering (ULVAC). Microscale ring-type magnetic tunnel junctions (RMTJs) with an outer radius of 2 mu m and an inner radius of 1 mu m were patterned using standard UV lithography combined with ion milling. Both reference and free layers were Co40Fe40B20 and a very thin Al-O (0.6 nm) barrier layer was used. Tunneling magnetoresistances (TMRs) of up to 81% at room temperature and 107% at 4.2 K were observed. These RMTJs with high TMR and low coercivity, of about 26 Oe, combined with the ring-type geometry, which greatly reduces stray magnetic field, are ideal for certain magnetic field sensor applications.