Method for modifying switching field characteristics of magnetic tunnel junctions

DETAILED DESCRIPTION Reference is now made to FIG.
1, which illustrates an MRAM device 10 including a resistive cross point array 12 of SDT junctions 14.
The SDT junctions 14 are arranged in rows and columns, with the rows extending along an x-direction and the columns extending along a y-direction.
Only a relatively small number of the SDT junctions 14 is shown to simplify the illustration of the MRAM device 10.
In practice, arrays of any size may be used.
Traces functioning as word lines 16 extend along the x-direction in a plane on one side of the array 12.
Traces functioning as bit lines 18 extend along the y-direction in a plane on an adjacent side of the array 12.
There may be one word line 16 for each row of the array 12 and one bit line 18 for each column of the array 12.
Each SDT junction 14 is located at a cross point of a word line 16 and a bit line 18.
The MRAM device 10 includes a read/write circuit (not shown) for sensing the resistance states of selected SDT junctions 14 during read operations and for supplying write currents to selected word and bit lines 16 and 18 during write operations.
Reference is made to FIG.
2, which shows an SDT junction 14 in greater detail.
The SDT junction 14 includes a pinned ferromagnetic (FM) layer 52, an insulating tunnel barrier 56 on the pinned FM layer 52, and a sense FM layer 54 on the tunnel barrier 56.
The pinned FM layer 52 has a magnetization vector M0 that is oriented in the plane of the pinned layer 52.
The pinned FM layer 52 may be made of a ferromagnetic material such as NiFe, iron oxide (Fe.
sub.
3 O.
sub.
4), chromium oxide (CrO.
sub.
2), cobalt, or cobalt alloys (e.
g.
, CoFe, NiFeCo).
The magnetization vector M0 of the pinned layer 52 may be pinned by a structure including first and second seed layers 46 and 48, and an AF pinning layer 50.
The first seed layer 46 allows the second layer 48 to be grown with a (111) crystal structure orientation, and the second seed layer 48 establishes a (111) crystal structure orientation for the AF pinning layer 50