Large Area and Low Aspect Ratio Linear Magnetic Tunnel Junctions With a Soft-Pinned Sensing Layer

Large area MTJs with linear response and very larger sensitivities are needed to fulfill the requirements for the detection of pT/Hz
$^{0.5}$
magnetic fields at low frequency and room temperature. MTJ stacks with soft-pinned sensing layers have been developed and the stack was optimized, providing a tunable soft-pinning field over a large range of values. Sensitivities corresponding to resistance changes of up to 7%/Oe are obtained in patterned MTJs with areas of 20
$\,\times\,$
20
$\mu$
m
$^{2}$
starting from films with high sensitivity soft-pinned layers made from 3.0 Co
$_{40}$
Fe
$_{40}$
B
$_{20}$
/0.21 Ta/8.0 Ni
$_{81}$
Fe
$_{19}$
/8.0 Ir
$_{20}$
Mn
$_{80}$
.