SOT MRAM cell with perpendicular free layer and its cross-point array realization
The present disclosure generally relates to a SOT-MRAM cell that has a spin Hall effect layer and a magnetic tunnel junction. The magnetic tunnel junction is disposed at an edge of the spin Hall effect layer. In order to write the cell, current is applied through the spin Hall effect layer to create spin accumulation of z-polarized spins under the free layer due to the spin Hall effect. The spins exert a spin torque on the free layer via spin diffusion. Based upon the design, the SOT-MRAM cell has deterministic switching of the perpendicular free layer with the spin Hall effect layer without application of an external magnetic field.
1. A memory array, comprising:
a plurality of rows of spin Hall effect lines, wherein each row of spin Hall effect lines has two transistors coupled thereto;
a plurality of columns of bitlines, wherein each column of bitlines has a transistor coupled thereto; and
a spin Hall effect layer having a first end, a second end, a first edge, and a second edge, wherein the first end of the spin Hall effect layer is parallel to the second end of the spin Hall effect layer, wherein both the first end and the second end are perpendicularly coupled to the first edge and the second edge, wherein a magnetic tunnel junction is disposed at an intersection of a spin Hall effect line and a bitline, and wherein at least one magnetic tunnel junction is disposed adjacent the first edge of the spin Hall effect layer and spaced from the second edge, the first end, and second end of the spin Hall effect layer, wherein the first edge, the second edge, the first end, and the second end are on a common plane, wherein a ratio of a spin diffusion length of the spin Hall effect layer to a diameter of the at least one magnetic tunnel junction is between ⅙ to ½, wherein the ratio of the thickness of the spin Hall effect layer to the diameter of the magnetic tunnel junction is between 0.1 to 0.2, and wherein the ratio width of the spin Hall effect layer to the diameter of the magnetic tunnel junction is 1 to 2.5, wherein the memory array is a spin orbit torque magnetoresistive random-access memory.
2. The memory array of claim 1 , wherein the array does not have an external magnetic field coupled thereto.
3. The memory array of claim 1 , wherein the spin Hall effect lines are formed from Pt, Ta, W, or copper doped with either bismuth or iridium, or combinations thereof.
4. The memory array of claim 1 , further comprising a spacer layer coupled to each magnetic tunnel junction.
5. The memory array of claim 4 , wherein each magnetic tunnel junction comprises:
a free layer having primarily two bi-stable magnetization directions, wherein the free layer is disposed on the spacer layer;
a reference layer having a fixed magnetization direction; and
an insulating tunnel barrier layer positioned between the free layer and the reference layer.
6. The memory array of claim 1 , wherein the edge comprises a bump-out portion.
7. The memory array of claim 6 , wherein the at least one magnetic tunnel junction is coupled to the bump-out portion.