Low aspect ratio micron size tunnel magnetoresistance sensors with permanent magnet biasing integrated in the top lead

Optimized single magnetic bead detection requires magnetic sensors with an improved field detection limit and a sensor area matching the bead cross section (micron size spatial resolution). This work shows that square micron sized tunnel magnetoresistance sensors can be fabricated with integrated longitudinal permanent magnet (PM) biasing that show a linearized field response and low noise. PMs (Co66Cr16Pt18) were integrated in the top lead of an AlOx based magnetic tunnel junction sensor for transfer curve linearization. Sensors patterned with dimensions down to 3 x 3 mu m(2) present field detection limits of 6 nT/Hz(0.5) and 3 nT/Hz(0.5) at 10 kHz and 500 kHz, respectively, corresponding to a field sensitivity of 1.8% per mT (linear field detection range Delta B = -8 mT+8 mT) and alpha(H) 3.9 +/- 0.3 x 10(-10) mu m(2) (RxA = 1.9 k Omega mu m(2)). (C) 2011 American Institute of Physics. [doi:10.1063/1.3537926]