Tuning of MgO barrier magnetic tunnel junction bias current for picotesla magnetic field detection

Two sets of low resistance MgO junctions were patterned into junctions with areas from 1 to 24μm2. By properly choosing the operating conditions the background noise can be placed at the level of equivalent fields of ∼10−11 and ∼10−12T∕Hz0.5 calculated for 30 Oe linear range junctions of types 1 (150Ωμm2, tunnel magnetoresistance (TMR)=150%) and 2 (30Ωμm2, TMR=100%), respectively. Such room temperature sensitivities can only be achieved at frequencies where the 1∕f noise contribution is negligible. From the 1∕f noise Hooge constant (αH=2.66×10−9μm2 at R×A∼150Ωμm2 and αH=1.24×10−9μm2 at R×A∼30Ωμm2) the 1∕f noise corner in the optimum biasing conditions is predicted to be located between 10 and 70 MHz, depending on junction area and resistance.