Magnetic memory array with paired asymmetric memory cells for improved write margin

摘要

A nonvolatile magnetic memory array uses magnetic memory cells that are formed in two types of shapes. The cells lie at the intersections of rows and columns of electrically conductive lines, which serve as the conductive paths for the write currents used to change the magnetization states of the magnetic cells. The two types of cells have shapes that are mirror images of each other, i.e, the shape of the second type of cell is arrived at by rotating the first type of cell 180 degrees about an axis through the cell. The two types of cells are thus a pair of asymmetric cells because they are asymmetric in regard to the predominant axis of magnetization. In the preferred pattern, each of the cells has a parallelogram shape with a length and a width with the predominant axis of magnetization lying substantially along a line between the acute corners of the parallelogram. The two types of cells are preferably arranged in the array in an alternating checkerboard pattern, which means that one type of cell is surrounded by neighboring cells of the other type. Because the predominant axis of magnetization of all neighboring cells is different from the predominant axis of magnetization of the cell selected for writing, there is substantially less likelihood that adjacent neighboring cells will also be written to. The memory array may be formed using either magnetic tunnel junction (MTJ) cells or giant magnetoresistance (GMR) cells.