A novel low switching current MRAM design

Summary form only given. Present MRAM designs require switching current in the order of several mini-amperes, significantly higher than that in conventional semiconductor memory. In this paper, we present a novel MRAM design with switching current over one order of magnitude lower than conventional designs. The memory element is based on magnetic tunnel junction. Different from the conventional tunnel-junction memory design, the key feature here is that the memory layer consists of two magnetic layers, whose magnetizations orient naturally antiparallel to each other, sandwiching a non-magnetic conductive layer. The relative magnetization directions between the bottom layer in the memory layer sandwich and the SAF top layer determines the magnetoresistance state. A magnetic anisotropy is induced during fabrication to force the magnetization at the center of the element in the transverse direction. The ends of the memory layer sandwich are tapered. During a write operation, the write current, directed by the write-control transistor, flows in the plane of memory sandwich layer, generating opposite fields in the two magnetic layers. The center portion of the memory layer sandwich switches their moment directions while the magnetization at both ends remains unchanged. Further more, the magnetization at all the edges in the memory sandwich layers never reverses its direction during a writing process and the switching process is very robust and repeatable. A simulated magnetization configuration of the two magnetic layers in the memory layer sandwich during a switching is presented. It is shown that the antiparallel magnetization configuration between the two magnetic layers always maintained and the magnetostatic flux coupling between the two layers yields a very low switching current of 500 microA for the write operation. A scheme enhancing thermal stability at small memory cell dimensions is also discussed.