Magnetic tunnel junction based magnetoresistive random access memory

Publisher Summary This chapter presents the salient features of state-of-the-art magnetic tunnel junctions (MTJ)-based magnetoresistive random access memory (MRAM). The chapter provides a description of 0.18 um MRAM technology and its implementation in a 1 Mb memory array. MRAM bit size scaling and challenges associated with continued miniaturization are discussed. A novel switching approach with significantly improved scaling properties is also presented. The ability to scale the MRAM bit cell to smaller dimensions is essential for MRAM to be a competitive memory technology. As the bit size is reduced, write performance could be affected by several parameters—switching field, write line field generation, bit-to-bit variation of the switching field within an array, hard-axis field response, susceptibility to thermal fluctuations, and magnetostatic interactions between neighboring bits. Magnetostatic interactions between neighboring bits must also be considered as the size of the bit cell is reduced and the density of the array is increased. A given bit experiences different values and configurations of stray fields depending on the details of the magnetization directions of surrounding bits. Savtchenko switching relies on the unique behavior of a synthetic antiferromagnet (SAF) free layer that is formed from two ferromagnetic layers separated by a nonmagnetic coupling spacer layer. The moments of the balanced SAF free-layer are antiparallel in zero-field and the coupled system therefore responds to an applied magnetic field in a manner that is different from the single ferromagnetic layer of conventional MRAM.