Initialization method of a perpendicular magnetic random access memory (MRAM) device

摘要

Methods using a sequence of externally generated magnetic fields to initialize the magnetization directions of each of the layers in perpendicular MTJ MRAM elements for data and reference bits when the required magnetization directions are anti-parallel are described. The coercivity of the fixed pinned and reference layers can be made unequal so that one of them can be switched by a magnetic field that will reliably leave the other one unswitched. Embodiments of the invention utilize the different effective coercivity fields of the pinned, reference and free layers to selectively switch the magnetization directions using a sequence of magnetic fields of decreasing strength. Optionally the chip or wafer can be heated to reduce the required field magnitude. It is possible that the first magnetic field in the sequence can be applied during an annealing step in the MRAM manufacture process.

主权项

1. A method for initializing perpendicular magnetization directions of magnetic layers in a set of MRAM elements with each element having at least one free layer and at least first and second fixed layers, the method comprising the steps of:
applying a first externally generated magnetic field to the set of MRAM elements, the first externally generated magnetic field having a first field direction and having a first field magnitude sufficient to switch magnetization directions of the fixed layers of each element into a first perpendicular magnetization direction; and applying a second externally generated magnetic field to the set of MRAM elements, the second externally generated magnetic field having a second field direction opposite to the first magnetic field and having a second field magnitude sufficient to switch the magnetization direction of the first fixed layer into a second perpendicular magnetization direction while leaving the second fixed layer in the first perpendicular magnetization direction.