Magnetic Tunneling Junction based Sensors for Bio-detection Applications*

Magnetic tunneling junctions are capable of sensing very weak magnetic fields at room temperature. It is a suitable device to detect a biomolecule which is tagged with magnetic nanoparticles. We have designed and developed Al2O3- and MgO- based MTJ sensors using microfabrication techniques. The study reveals that in the case of Al2O3-based sensors the shape anisotropy in the free magnetic electrode results in a linear and hysteresis free magnetoresistance (MR) curve. Moreover, Al2O3 based sensor have 28{\%} TMR and sensitivity of up to 0.4 {\%}/Oe over a magnetic field range of $\pm $ 40 Oe. In the case of MgO-based sensors, there are two possible methods to achieve a linear and hysteresis free MR response. One can increase the aspect ratio in free magnetic electrode, alternatively, one can use superparamagnetic free layer. MgO-based sensor has about 90{\%} TMR and sensitivity of 1.1 {\%}/Oe over the field range of $\pm $ 40 Oe.