Simulation Research On Information Storage Mechanism Of STT-MRAM

STT-MRAM is a new type of memory that reversing the magnetic moment ofnano-magnet by spin-polarized current directly to realize data storage, a potentialrevolutionary general memory technology. It integrates many superior performances,such as high-density like DRAM, fast reading and writing like SRAM, non-volatilitylike Flash, low power consumption and high stability. Moreover, it has unlimitedendurance. By contrast with traditional MRAM, the scalability is better, theprogramming current needed is lower, and it is compatible with more advancedsemiconductor technology.Based on the connotation of STT-MRAM, the related free layer material andstructure of the memory unit’s magnetic tunnel junction, the correlative theories ofSpin-electronics are studied. The parts of the effective fields, spin transport, the spintorque effect to the magnetic moment in MTJ’s free layer caused by polarized currentare analyzed. The LLGS equation is established based on the macro-spin model and themodel is solved numerically with Newton iteration method. Then the STT-MRAMInformation Storage Mechanism Simulation System is developed. Finally, theprecession reversal of the magnetic moment in MTJ’s free layer is studied; the writingin of data “0” or “1” is demonstrated. The effect to the current density and time neededto write information and to the precession reversal trajectory of the free layer magneticmoment caused by the material or structure parameters, such as the thickness of thefree layer, the saturation magnetization, magnetocrystalline anisotropy constant,damping coefficient and demagnetizing factor is analyzed in detail. The informationstorage mechanism of STT-MRAM is investigated in-depth. Under the condition ofreasonable parameter values, the writing time can be controlled within5ns, while thecurrent density needed to reverse the free layer magnetic moment at the level of106A/cm2.Then, according to the simulation results, some specific methods to diminish theswitching current density are proposed from the aspects of optimizing ferromagneticlayer material and improving the structure of MTJ and free layer. The ways to improve working reliability and stability of STT-MRAM is discussed in this paper, too.