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

Abstract

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 2μm and an inner radius of 1μm were patterned using standard UV lithography combined with ion milling. Both reference and free layers were Co40Fe40B20 and a very thin Al–O (0.6nm) barrier layer was used. Tunneling magnetoresistances (TMRs) of up to 81% at room temperature and 107% at 4.2K were observed. These RMTJs with high TMR and low coercivity, of about 26Oe, combined with the ring-type geometry, which greatly reduces stray magnetic field, are ideal for certain magnetic field sensor applications.