Effect of scaling on tunnel magnetoresistance and thermal stability in magnetic tunnel junction (MS)

Abstract

The emerging non-volatile spin based memories, especially spin transfer torque random access memory (STT-RAM), are promising alternatives to memory devices, both in stand-alone configuration and embedding with CMOS for Non-Von Neumann computing. Magnetic tunnel junction (MTJ) as the basic storage cell of STT-RAM, promises low power consumption, high endurance, fast switching performance and compatibility with CMOS due to non-volatility and efficient switching mechanisms such as spin transfer torque and spin orbit torque. This thesis presents the comprehensive study of quantum transport, micromagnetics and interlayer exchange coupling in the MTJ. The effective mass tight binding (EMTB) and mode space approach is used to evaluate and study the role of transverse sub-bands in tunnel magneto-resistance (TMR) of the MTJ. The object oriented micromagnetics framework (OOMMF) based simulations are used to study the area dependence of important MTJ critical current density and thermal stability. The effect of the non-idealities in tunnel barrier on TMR is studied by including the dephasing in device Hamiltonian. Further various interlayer exchange coupling terms present in MTJ are first evaluated using spin dependent quantum well theory then the effect of interlayer exchange coupling on spin transfer torque and switching probability is studied. Finally, the thesis concludes with the proposal of optimized diameter range for different MTJ device applications and future prospects.