Multi-resistance MRAM
Apparatuses, systems, and methods are disclosed for magnetoresistive random access memory. A magnetic tunnel junction (MTJ) for storing data may include a reference layer. A free layer of an MTJ may be separated from a reference layer by a barrier layer. A free layer may be configured such that one or more resistance states for an MTJ correspond to one or more positions of a magnetic domain wall within the free layer. A domain stabilization layer may be coupled to a portion of a free layer, and may be configured to prevent migration of a domain wall into the portion of the free layer.
1. A system comprising:
a neuromorphic computing die, the neuromorphic computing die comprising a plurality of artificial neurons and a synapse array of multi-state magnetic memory cells coupling the artificial neurons, wherein a multi-state magnetic memory cell comprises:
a fixed layer;
a magnetic storage layer separated from the fixed layer by a barrier layer, the magnetic storage layer configured such that one or more states for the multi-state magnetic memory cell correspond to one or more positions of a magnetic domain wall within the magnetic storage layer; and
a domain stabilization layer coupled to a portion of the magnetic storage layer, the domain stabilization layer configured to provide a fixed magnetization for the portion of the magnetic storage layer.
2. The system of claim 1 , wherein the domain stabilization layer comprises an antiferromagnetic layer configured to induce a unidirectional magnetic anisotropy in the portion of the magnetic storage layer.
3. The system of claim 1 , wherein the domain stabilization layer comprises a multilayer configured to induce a coercivity increase in the portion of the magnetic storage layer.
4. The system of claim 1 , wherein the multilayer comprises one or more of: a cobalt/platinum multilayer and a cobalt/palladium multilayer.
5. The system of claim 1 , further comprising a controller configured to change a resistance state of the multi-state magnetic memory cell by applying a write current to move the domain wall, wherein changing the resistance state comprises one of: applying a first write current to move the domain wall in a first direction, and applying a second write current in a direction opposite to the first write current, to move the domain wall in a second direction opposite to the first direction.
6. The system of claim 1 , wherein the magnetic storage layer comprises a nucleation region configured to form the domain wall, and an arm extending from the nucleation region, the arm comprising a plurality of pinning sites for pinning the domain wall.
7. The system of claim 5 , wherein resistance state of the multi-state magnetic memory cell corresponds to a weight of an artificial neural network.
8. The system of claim 7 , wherein the controller is further configured to:
perform one or more reads for a plurality of weights corresponding, for each of the weights, to a product of the weight and an input value; and
perform a summation of the products of weight values and input values for the plurality of weights.
9. The system of claim 8 , wherein the controller includes an activation component further configured to produce an output based on the summation.
10. The system of claim 6 , wherein the plurality of pinning sites of the arm comprises one or more intermediate pinning sites of a first pinning strength and a terminal pinning site of a second pinning strength, the second pinning strength greater than the first pinning strength.
11. The system of claim 10 , wherein the magnetic storage layer further comprises a second arm extending from the nucleation region, the second arm comprising an initial arm selection pinning site of a third pinning strength, the third pinning strength greater than the second pinning strength.
12. The system of claim 11 , wherein the second arm further comprises one or more intermediate pinning sites of the first pinning strength and a terminal pinning site of the second pinning strength.
13. The system of claim 12 , wherein the magnetic storage layer further comprises one or more further arms extending from the nucleation region.
14. The system of claim 13 , wherein the one or more further arms comprise one or more intermediate pinning sites of the first pinning strength, one or more terminal pinning sites of the second pinning strength, and one or more initial arm selection pinning sites of increasing pinning strengths relative to the third pinning strength.
15. The system of claim 6 , wherein the domain wall forms at the nucleation region in response to a write current.
16. The system of claim 15 , wherein the domain wall migrates along the arm from one pinning site to a subsequent pinning site in response to an increased write current.
17. The system of claim 15 , wherein the write current controls a magnetic field applied to the magnetic storage layer.
18. The system of claim 15 , wherein the write current controls a spin current injected into the magnetic storage layer.
19. The system of claim 15 , wherein the write current controls a spin current injected into the magnetic storage layer.
20. The system of claim 15 , further comprising a controller configured to supply the write current.