Magnetic tunnel junction field sensors with hard-axis bias field

摘要

We have fabricated and studied the magnetic properties of the Ni_(81)Fe_(19)/Al_(2)O_(3)/Ni_(81)Fe_(19) based magnetic tunnel junction sensors. Magnetoresistance (MR) of 35 is achieved with a small applied field (<10 Oe). The introduction of a hard axis bias field linearizes the MR response. The hysteresis disappears in hard-axis fields greater than 3 Oe, which corresponds to the effective anisotropy field along the easy axis. A sensitivity of 3.5/Oe has been demonstrated in this linear region. Low-frequency noise measurements indicate that sensor noise is dominated by field-dependent 1/f noise caused by magnetization fluctuations. Finally, a noise level as low as 1 nT/Hz~(1/2) has been obtained.