A snapshot review of double magnetic junctions for STT-MRAM

The development of double magnetic junctions for spin-transfer torque magnetoresistive random access memory (STT-MRAM) is reviewed, with an emphasis on work from IBM. A brief overview of the theory of spin-transfer torque in double magnetic tunnel junctions is given, showing that for high spin-polarization, up to a factor of 10 improvement in switching efficiency is theoretically possible. Experimental results on double magnetic tunnel junctions, using two tunnel barriers, show a factor of two improvement in switching efficiency. Experimental results on double spin-torque magnetic tunnel junctions, using one tunnel barrier and one low resistance spacer, show close to a factor of two improvement in switching efficiency, and enable reliable switching down to 250 ps. Graphical Abstract