Spin-transfer torque memory (STTM) devices having magnetic contacts
Techniques are disclosed for forming integrated circuit structures including a magnetic tunnel junction (MTJ), such as spin-transfer torque memory (STTM) devices, having magnetic contacts. The techniques include incorporating an additional magnetic layer (e.g., a layer that is similar or identical to that of the magnetic contact layer) such that the additional magnetic layer is coupled antiferromagnetically (or in a substantially antiparallel manner). The additional magnetic layer can help balance the magnetic field of the magnetic contact layer to limit parasitic fringing fields that would otherwise be caused by the magnetic contact layer. The additional magnetic layer may be antiferromagnetically coupled to the magnetic contact layer by, for example, including a nonmagnetic spacer layer between the two magnetic layers, thereby creating a synthetic antiferromagnet (SAF). The techniques can benefit, for example, magnetic contacts having magnetic directions that are substantially in-line or substantially in-plane with the layers of the MTJ stack.
1. A spin-transfer torque memory (STTM) device comprising:
a magnetic tunnel junction (MTJ) comprising:
a fixed magnetic layer;
a free magnetic layer; and
a tunneling barrier layer disposed between the fixed and free magnetic layers;
contacts on either side of the MTJ, wherein at least one contact is magnetic; and
an additional magnetic layer antiferromagnetically coupled to the at least one magnetic contact.
2. The device of claim 1 , wherein the at least one magnetic contact and/or corresponding additional magnetic layer includes at least one ferromagnetic material.
3. The device of claim 1 , wherein the at least one magnetic contact and/or corresponding additional magnetic layer includes CoFeB.
4. The device of claim 1 , wherein a nonmagnetic spacer layer is disposed between each magnetic contact and corresponding additional magnetic layer.
5. The device of claim 4 , wherein each nonmagnetic spacer layer has a thickness between 0.7 and 1.0 nm.
6. The device of claim 4 , wherein each nonmagnetic spacer layer includes ruthenium (Ru).
7. The device of claim 1 , wherein each magnetic contact and corresponding additional magnetic layer have in-line magnetic moments.
8. The device of claim 1 , wherein each magnetic contact and corresponding additional magnetic layer have in-plane magnetic moments.
9. The device of claim 1 , further comprising a nonmagnetic cladding layer on either side of the at least one magnetic contact and/or corresponding additional magnetic layer, wherein the nonmagnetic cladding layer helps prevent magnetic material from diffusing into surrounding material.
10. The device of claim 9 , wherein the nonmagnetic cladding layer includes titanium nitride (TiN) or tantalum (Ta).
11. The device of claim 9 , wherein the nonmagnetic cladding layer has a thickness ranging from 2-10 nm.
12. The device of claim 1 , wherein both contacts are magnetic and antiferromagnetically coupled to a corresponding additional magnetic layer.
13. The device of claim 1 , wherein each additional magnetic layer helps prevent fringing fields from the corresponding magnetic contact from encroaching on the MTJ.
14. A computing system including the STTM device of claim 1 .
15. An integrated circuit comprising:
a magnetic tunnel junction (MTJ) comprising:
a fixed magnetic layer;
a free magnetic layer; and
a tunneling barrier layer disposed between the fixed and free magnetic layers;
a magnetic contact layer electrically connected to at least one side of the MTJ; and
an additional magnetic layer separated from the magnetic contact layer by a spacer layer;
wherein the spacer layer has a thickness between 0.7 and 1.0 nanometers (nm), and
wherein the magnetic moments of the magnetic contact layer and the additional magnetic layer are substantially antiparallel.
16. The integrated circuit of claim 15 , wherein the magnetic contact layer and the additional magnetic layer create a synthetic antiferromagnet (SAF).
17. An embedded memory device comprising the integrated circuit of claim 15 .
18. The embedded memory device of claim 17 , wherein the embedded memory device is a spin-torque transfer memory (STTM) device.
19. A method of forming a spin-transfer torque memory (STTM) device, the method comprising:
providing a substrate including a magnetic lower via; and
forming a multilayer stack on the substrate, the stack comprising:
a spacer layer;
a magnetic contact layer;
magnetic tunnel junction (MTJ) layers; and
an upper via layer.
20. The method of claim 19 , wherein the MTJ layers comprise a fixed magnetic layer, a free magnetic layer, and a tunneling barrier layer.
21. The method of claim 19 , further comprising:
forming an additional magnetic contact layer on the MTJ layers; and
forming a spacer layer between the additional magnetic contact layer and the upper via layer.
22. The method of claim 21 , wherein the upper via material is ferromagnetic.
23. The method of claim 19 , wherein the multilayer stack is formed by:
depositing, on the substrate, all of the layers that comprise the stack; and
etching all of the layers that comprise the stack to a desired width.
24. The method of claim 19 , wherein the multilayer stack is formed by:
depositing the spacer layer, magnetic contact layer, and MTJ layers on the substrate;
etching the deposited spacer layer, magnetic contact layer, and MTJ layers to a desired width;
depositing interlayer dielectric (ILD) material;
etching the ILD to create space above the MTJ layers; and
forming the upper via layer in the space above the MTJ layers.