Method of making magnetoresistive memory cell over a selector pillar
A spin-orbit-torque (SOT) magnetoresistive random access memory (MRAM) device includes a SOT MRAM cell containing a first two terminal selector element, a nonmagnetic metallic assist plate, and a magnetic tunnel junction located between the first two terminal selector element and the nonmagnetic metallic assist plate, and a circuit selection element selected from a transistor or a second two terminal selector element electrically connected to the nonmagnetic metallic assist plate of the SOT MRAM cell.
1. A method of forming a magnetoresistive memory device, comprising:
forming first electrically conductive lines over a substrate;
forming a two-dimensional array of pillars each comprising a selector element over the first electrically conductive lines;
forming a layer stack over the two-dimensional array of pillars, the layer stack comprising an unpatterned magnetic free layer, an unpatterned magnetic reference layer and an unpatterned tunneling dielectric layer located between the unpatterned magnetic free layer and the unpatterned magnetic reference layer; and
patterning the layer stack to form a two-dimensional array of vertical stacks over the two-dimensional array of pillars, wherein each of the vertical stacks comprises a magnetic free layer, a magnetic reference layer and a tunneling dielectric layer located between magnetic free layer and the magnetic reference layer; and
forming second electrically conductive lines over the two-dimensional array of vertical stacks;
wherein the selector element comprises an ovonic threshold switch material portion.
2. The method of claim 1 , wherein the ovonic threshold switch material portion comprises a chalcogenide material.
3. The method of claim 1 , wherein the pillars comprise rectangular pillars.
4. The method of claim 3 , wherein each of the rectangular pillars includes a stack of the ovonic threshold switch material portion and a metal pillar structure.
5. The method of claim 3 , further comprising forming an insulating liner in line trenches located between the rectangular pillars prior to forming the layer stack.
6. The method of claim 5 , wherein the layer stack is formed over the two-dimensional array of rectangular pillars and over the insulating liner.
7. The method of claim 1 , wherein:
the layer stack further comprises a synthetic antiferromagnetic material layer stack; and
the unpatterned magnetic reference layer comprises a portion of the synthetic antiferromagnetic material layer stack.
8. The method of claim 7 , wherein:
each of the vertical stacks further comprises a synthetic antiferromagnetic structure; and
each magnetic reference layer comprises a portion of the synthetic antiferromagnetic structure.
9. The method of claim 1 , wherein the magnetic free layer comprises CoFe or CoFeB.
10. The method of claim 9 , wherein the magnetic reference layer comprises CoFe or CoFeB.
11. The method of claim 10 , wherein the tunneling dielectric layer comprises MgO.
12. The method of claim 10 , wherein the magnetic free layer, the magnetic reference layer and the tunneling dielectric layer form a magnetic tunnel junction.
13. The method of claim 1 , wherein the step of patterning the layer stack comprises:
forming a patterned photoresist layer over the layer stack; and
etching the layer stack using the patterned photoresist layer as a mask.
14. The method of claim 1 , wherein each of the vertical stacks comprises a magnetoresistive random access memory (MRAM) cell.
15. The method of claim 14 , wherein the two-dimensional array of vertical stacks comprises a two-dimensional array of MRAM cells.
16. The method of claim 15 , wherein the two-dimensional array of MRAM cells has a same two-dimensional periodicity as the two-dimensional array of pillars.
17. The method of claim 16 , wherein the two-dimensional array of pillars comprises a two-dimensional array of rectangular pillars.
18. The method of claim 17 , wherein the MRAM cells are not rectangular.
19. The method of claim 17 , wherein at least one sidewall of the MRAM cells is laterally offset from a corresponding sidewall of the underlying rectangular pillar.