Method and structure to reset multi-element MTJ
The process margin for the manufacture of devices formed from multi-element MTJ or GMR devices has been widened by providing a method and structure to reset the magnetization directions of all pinned layers simultaneously so that their directions of magnetization become evenly distributed. This has the effect of minimizing non-linearity and hysteresis in these devices during their subsequent operation.
1. A method to improve process yield by reducing non-linearity and hysteresis during operation of a multi-element magnetic sensor, comprising:
fabricating each of said elements as a multilayer stack whose aspect ratio, in plan view, exceeds 1.2, whereby each element has an anisotropy axis and an associated anisotropy field that determines a preferred direction for magnetization of the element, all such anisotropy axes being parallel to each other;
providing a common top electrode for the elements and connecting said common top electrode to a common bottom electrode through said elements;
exposing said sensor to a magnetic pulse whose direction is perpendicular to said anisotropy axes and whose magnitude exceeds said anisotropy field; and
thereby causing each element to be magnetized along its anisotropy axis in a direction that is parallel to about half that of said elements and antiparallel to that of all remaining elements in said magnetic sensor.
2. The method of claim 1 wherein each of said multilayer stacks is selected from the group consisting of MTJ and GMR devices.
3. The method of claim 1 wherein said magnetic pulse is delivered by passing a current through said common top electrode.
4. The method of claim 1 wherein said magnetic pulse is delivered by passing a current through said common bottom electrode.
5. The method of claim 1 wherein said magnetic pulse is delivered by passing a current through a wire disposed to lie above said magnetic sensor and separated therefrom by an insulating layer.
6. The method of claim 1 wherein said magnetic pulse is delivered by passing a current through a wire disposed to lie below said magnetic sensor and separated therefrom by an insulating layer.
7. The method of claim 1 wherein each multi-element magnetic structure comprises at least 50 of said elements.
8. The method of claim 1 wherein each of said multilayer stacks has an elliptical shape.
9. The method of claim 1 wherein the aspect ratio of each of said stacks is at least 2.
10. A structure that reduces non-linearity and hysteresis during operation of a multi-element magnetic sensor, comprising:
each of said elements being a multilayer stack whose aspect ratio, in plan view, exceeds 1.2, whereby each element has an anisotropy axis and an associated anisotropy field that determines a preferred direction for magnetization of the element, all such anisotropy axes being parallel to each other;
a common top electrode for the elements that connects said common top electrode to a common bottom electrode through said elements;
a reset line which, when energized, will expose said sensor to a magnetic pulse whose direction is perpendicular to said anisotropy axes and whose magnitude exceeds said anisotropy field; and
each element having a preferred direction of magnetization along its anisotropy axis that is parallel to that of about half of said elements and antiparallel to that of all remaining elements in said magnetic sensor.
11. The structure described in claim 10 wherein each of said multilayer stacks is selected from the group consisting of MTJ and GMR devices.
12. The structure described in claim 10 wherein said structure is said common top electrode.
13. The structure described in claim 10 wherein said structure is said common bottom electrode.
14. The structure described in claim 10 wherein said structure is a wire disposed to lie above said magnetic sensor, separated therefrom by an insulating layer.
15. The structure described in claim 10 wherein said structure is a wire disposed to lie below said magnetic sensor, separated therefrom by an insulating layer.
16. The structure described in claim 10 wherein each multi-element magnetic structure comprises at least 50 of said elements.
17. The structure described in claim 10 wherein each of said multilayer stacks has an elliptical shape.
18. The structure described in claim 10 wherein each stack has an aspect ratio of at least 2.