Spin Based Biosensor with Hard Axis Assist for Enhanced Sensitivity

Abstract: We demonstrate the influence of hard axis assist on an in-plane polarized nanomagnet layer to greatly enhance the sensitivity of a magnetic nano particle (MNP) based MTJ biosensor. The hard axis assist has been provided to the sensing layer in the forms of spin Hall Effect (SHE) induced spin injected torque and stress based effective magnetic field induced torque separately. Present work mainly focuses on the efficient and qualitative detection of a single magnetic bead with the aim of detecting a single bimolecular recognition event at an extremely low analyte concentration. Interfacial spin current arising from spin orbit metal is expected to impose a torque on the free layer along sensitive direction improving the signal strength by a factor of ~ 6.5 for a 100 nm bead at a height of 500 nm above the sensor surface. Furthermore, the potentiality of a multiferroic composite consisting of a piezoelectric layer coupled with magnetostrictive CoFeB based MTJ has been investigated in the Biosensing applications. An external stress voltage of 500 mV has been observed to be sufficient to enhance the sensitivity (~ 6 times). The use of nanoscaled spin devices and the absence of external magnetic field operated magnetization rotation facilitates in achieving highly compact and extremely low power designs. This establishes the possibility of utilizing the present schemes for advanced, highly sensitive, miniaturized and low power bioassaying system-on-chip applications. Numerical results were compared with some earlier reported experimental results to validate our proposed model.