Magnetic memory cell with asymmetrical geometry programmable by application of current in the absence of a magnetic field
A memory slot including a pad formed of a stack of regions made of thin layers, including a first region made of a nonmagnetic conducting material; a second region made of a magnetic material exhibiting a magnetization in a direction perpendicular to the principal plane of the pad; a third region made of a nonmagnetic conducting material of different characteristics to those of the first region; the pad resting on a conducting track adapted to cause the flow of a programming current of chosen sense, in which the pad has an asymmetric shape with respect to any plane perpendicular to the plane of the layers and parallel to the central axis of the track, and with respect to its barycenter.
1. A memory cell comprising a pad formed of a stack of regions in thin layers, comprising:
a first region made of a conductive material;
a second region made of a magnetic material having a magnetization in a direction perpendicular to the main plane of the pad;
a third region of a non-magnetic material having characteristics different from those of the first region;
said pad integrally resting on a conductive track capable of circulating a programming current of selected direction,
wherein said pad has an asymmetrical shape, on the one hand with respect to any plane perpendicular to the plane of the layers and parallel to the central axis of the track, and on the other hand with respect to its barycenter,
whereby the direction of the magnetization in the second region is programmable by the circulation direction of said programming current, in the absence of an external magnetic field, and
wherein the pad has a triangular shape with a first side parallel to the direction of the programming current and two other sides, each forming an angle from ±20° to ±70° relative to the first side.
2. The memory cell of claim 1 , wherein the first region corresponds to a portion of the track underlying the pad or to an overthickness of this underlying portion.
3. The memory cell of claim 1 , wherein the pad has the triangular shape with rounded corners.
4. The memory cell of claim 1 , wherein the pad only extends across a portion of the width of the track.
5. The memory cell of claim 1 , wherein the second region comprises an alloy having a specific perpendicular magnetic anisotropy, that is FePt, FePd, CoPt, or a rare earth/transition metal alloy.
6. The memory cell of claim 1 , wherein the second region comprises a metal or an alloy having in the stack a perpendicular magnetic anisotropy induced by the interfaces, particularly Co, Fe, CoFe, Ni, CoNi.
7. The memory cell of claim 1 , wherein at least the first region or the third region is conductive and is made of a non-magnetic material selected among Pt, W, Ir, Ru, Pd, Cu, Au, Bi, Hf, or of an alloy of these metals, or is formed of a stack of a plurality of layers of each of these metals.
8. The memory cell of claim 1 , wherein the third region is made of a dielectric oxide, selected among SiOx, AlOx, MgOx, TiOx, TaOx, HfOx, or of a dielectric nitride selected among SiNx, and BNx.
9. The memory cell of claim 1 , wherein the thickness of the first and third regions is in the range from 0.5 to 200 nm.
10. The memory cell of claim 1 , wherein the third region is covered with a readout layer made of a magnetic material and with a readout electrode.
11. The memory cell of claim 1 , wherein the thickness of the second region is smaller than 3 nm.
12. The memory cell of claim 1 , wherein the first region is made of a conductive antiferromagnetic material.
13. The memory cell of claim 12 , wherein the thickness of the first region made of an antiferromagnetic material is in the range from 1 to 200 nm.
14. A method of programming the memory cell of claim 12 , comprising the step of conducting in the track, and accordingly in the first region of antiferromagnetic material, a current having an intensity capable of heating the material to disorganize its magnetization, the direction of the current being selected to program the magnetization of the magnetic material of the second region.