Memory based on charge storage (such as flash memory and others) is gradually approaching the physical limits of scalability. The increasing demand for minimization of microelectronic devices (e.g., MP3 players and mobile phones) has significantly accelerated the exploration of new concepts for nonvolatile memory during the past few years. Apart from good scalability a new type of memory must also exhibit low operating voltages, low power consumption, high operation speed, long retention time, high endurance, and simple structure.
Several concepts as potential replacements of the charge memory were proposed and developed. Some of the technologies are already available as prototype (such as carbon nanotube Random Access Memory (RAM) and Copper Bridge RAM (CBRAM)), others as products (Phase Change RAM (PCRAM), magnetoresistive RAM, and ferroelectric RAM), while technologies based on spin-torque transfer RAM, racetrack memory, and Resistive RAM (RRAM) are under intensive research. The theoretical predictions and the experiments of spin transfer switching demonstrated that the Spin Transfer Torque Random Access Memory (STTRAM) is one of the promising candidates for future universal memory. STTRAM is characterized by small cell size (4F×4F), fast access time (less 10ns), high endurance, and a long retention time. The reduction of the current density required for switching and the increase of the switching speed are the most important challenges in this area.
Measurements showed a decrease in the critical current density for the penta-layer Magnetic Tunnel Junction (MTJ) compared with the tri-layer MTJ. We investigate the dynamics of the switching process in a MTJ composed of five layers (where the magnetizations of the two layers are fixed). We performed extensive micromagnetic modeling of the penta-layer structures by employing the Slonczewski model for the spin torque. Based on this model, we are working on optimization the penta-layer MTJ by investigating the influence of the thicknesses of the fixed layers on the magnetostatic exchange magnetic field in the plane of the free magnetic layer.