Magnetic tunnel junction and spin-current in modern computing

Electronic tunneling is a fundamentally quantum mechanical phenomenon. In a magnetic tunnel junction (MTJ), the tunnel conductance is further dependent on the electron’s spin-state, adding another degree of freedom, and leading to spin-orientation dependent tunnel resistance – known as tunnel magnetoresistance, and a spin-polarized tunnel current carrying angular momentum flow in addition to charge current. These two uniquely quantum mechanical attributes, a spin-dependent magnetoresistance, and a spin-current flow, brought a nanomagnetic tunnel junction capable of performing both read- and write-operation in a charge-current controlled environment such as in an integrated CMOS technology for computing. In this article, I review some of the basic concepts involved in an MTJ, for its tunnel magnetoresistance, and for its spin-current related spin-transfer-torque switching, and some of the lessons learnt over the course of developing the STT-switched MTJ for CMOS-integrated memory as a commercial technology.