Micromagnetic Analysis of Statistical Switching in Perpendicular Magnetic Tunnel Junctions With Double Reference Layers

The recent technological realization of perpendicular magnetic tunnel junctions (MTJs) with two reference layers has opened a new route for scaling the overall size of spin-transfer torque magnetic random-access memory. This is because, for an antiparallel configuration of the magnetization of the reference layers, the two spin-transfer torques add constructively, giving rise to more efficient switching processes of the free layer magnetization as compared to a single MTJ. We use full micromagnetic simulations to study the magnetization switching of a double MTJ. The probability distribution function (PDF) of the switching time is the same for both switching processes (parallel to antiparallel and vice versa), and the PDF approaches a Gaussian shape for switching time smaller than 1 ns. The dynamical performance (achieved for switching time below 1 ns) of double MTJs with circular shape and diameter ranging from 30 to 14 nm is comparable. Compared to full micromagnetic data, computations of the PDF within the macrospin approximation show an overestimation of the skewness for MTJ with circular shape and diameter of 30 and 20 nm, whereas they are very close for 14 nm diameter, as expected. The proper micromagnetic model and a PDF comparison can drive the design of hybrid magnetic-CMOS systems.