Magnetic shielding for MRAM devices

#The present invention generally relates to magnetic random access memory (MRAM) devices, and more particularly to a magnetic random access memory device having a shield member for shielding the magnetic memory cells from stray magnetic fields.

#An MRAM device includes an array of memory cells. The typical magnetic memory cell includes a layer of magnetic film in which the magnetization is alterable and a layer of magnetic film in which the magnetization is fixed or “pinned” in a particular direction. The magnetic film having alterable magnetization may be referred to as a data storage layer or sense layer and the magnetic film which is pinned may be referred to as a reference layer.

#Conductive traces (commonly referred to as word lines and bit lines) are routed across the array of memory cells. Word lines extend along rows of memory cells, and bit lines extend along columns of memory cells. Because the word lines and bit lines operate in combination to switch the orientation of magnetization of the selected memory cell (i.e., to write the memory cell) the word lines and bit lines can be collectively referred to as write lines. Additionally, the write lines can also be used to read the logic values stored in the memory cell.

#FIGS. 1a and 1b are top and perspective views of a simplified magnetic memory array as known in the prior art.

#FIGS. 2a through 2c illustrate the orientations of magnetization of active and reference magnetic films of a magnetic memory cell like that in FIGS. 1a and 1b.

#FIG. 3 is a perspective view of a memory cell like that in FIGS, 1a and 1b showing the magnetic fields generated by currents flowing through the write lines.

#In the following detailed description of the preferred embodiments, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

#A top plan view of an example of a simplified MRAM array 100 is presented in FIG. 1. In FIG. 1 and all that follow, it is to be understood that for the sake of clarity the various components of the illustrated devices are not necessarily shown to scale. The MRAM array 100 includes memory cells 120, word lines 130, and bit lines 132. The memory cells 120 are positioned at each intersection of a word line 130 with a bit line 132. Typically, the word lines 130 and bit lines 132 are arranged in orthogonal relation to one another and the memory cells 120 are positioned in between the write lines (130, 132), as illustrated in FIG. 1b. For example, the bit lines 132 can be positioned above the memory cells 120 and the word lines 130 can be positioned below.

#FIGS. 2a through 2c illustrate the storage of a bit of data in a single memory cell 120. In FIG. 2a, the memory cell 120 includes an active magnetic data film 122 (the sense layer) and a pinned magnetic film 124 (the reference layer) which are separated by a dielectric region 126 (the tunnel barrier). The orientation of magnetization in the sense layer 122 is not fixed and can assume two stable orientations is shown by arrow M1. On the other hand, the pinned reference layer 124 has a fixed orientation of magnetization shown by arrow M2. The sense layer 122 rotates its orientation of magnetization in response to electrical currents applied to the write lines (130, 132) during a write operation to the selected memory cell 120.