Planar flux concentrator for MRAM devices
View Patent ↗The present invention provides an MRAM that includes a conductive line for generating a magnetic field. The latter is enhanced by the addition of a flux concentrator made from a single plane of soft ferromagnetic material, magnetically stabilized by means of an antiferromagnetic layer. This structure, in addition to being very easy to fabricate, facilitates close control over its magnetic properties, including uniformity and domain structure.
1. A low cost flux concentrator, comprising:
an MTJ stack, including a capping layer having a top surface, a bottom electrode, and a dielectric layer, having a top surface, that encapsulates said MTJ stack and extends above said capping layer;
in said dielectric layer, a trench, having vertical sidewalls, that is longer and wider than said capping layer and that extends downwards as far as said capping layer top surface;
said trench being filled with a conductive material that serves as a bit line that passes over said MTJ stack and that has a top surface coplanar with said dielectric top surface;
an insulating layer on said coplanar surfaces;
a ferromagnetic layer on said insulating layer; and
on said ferromagnetic layer, an antiferromagnetic layer that serves to keep said ferromagnetic layer magnetized in a direction parallel to said bit line, thereby providing a domain stabilizing field.
2. The flux concentrator described in claim 1 further comprising a layer selected from the group consisting of super-paramagnetic materials and ferromagnetic materials, on said vertical sidewalls.
3. The flux concentrator described in claim 1 further comprising, between said insulating and ferromagnetic layers, a seed layer, selected from the group consisting of NiCr and NiFeCr, having a thickness of between about 30 and 50 Angstroms.
4. The flux concentrator described in claim 1 wherein said ferromagnetic layer has a permeability normal to said bit line direction of between about 10 and 300 by virtue of containing one or more dopants selected from the group consisting of Ta, Cr, Pt, Ti, B, W, and Cu and by having an adjusted thickness.
5. The flux concentrator described in claim 1 wherein said insulating layer has a thickness of between about 100 and 500 Angstroms.
6. The flux concentrator described in claim 1 wherein said ferromagnetic layer is selected from the group consisting of NiFe, NiFeCo, and NiFeX, where X is a non-magnetic metal known to be a magnetic moment dilution agent.
7. The flux concentrator described in claim 1 wherein said ferromagnetic layer has a thickness of between about 50 and 500 Angstroms.
8. The flux concentrator described in claim 1 wherein said insulating layer is also ferromagnetic or super paramagnetic.
9. The flux concentrator described in claim 1 wherein said flux concentrator and said MTJ stack are part of a magnetic random access memory.