Magnetic random access memory with dual spin torque reference layers
A magnetic data storage cell, applicable to spin-torque random access memory (ST-RAM), is disclosed. A magnetic cell includes first and second fixed magnetic layers and a free magnetic layer positioned between the fixed magnetic layers. The magnetic cell also includes terminals configured for providing a spin-polarized current through the magnetic layers. The first fixed magnetic layer has a magnetization direction that is substantially parallel to the easy axis of the free magnetic layer, and the second fixed magnetic layer has a magnetization direction that is substantially orthogonal to the easy axis of the free magnetic layer. The dual fixed magnetic layers provide enhanced spin torque in writing to the free magnetic layer, thereby reducing the required current and reducing the feature size of magnetic data storage cells, and increasing the data storage density of magnetic spin torque data storage.
1. A magnetic cell comprising:
a first fixed magnetic layer;
a second fixed magnetic layer;
a free magnetic layer positioned between the first and second fixed magnetic layers; and
terminals configured for providing a spin-polarized current through the magnetic layers
wherein the magnetic cell defines a perpendicular orientation that is perpendicular to the layers and a diametrical orientation that is planar with the layers, and the magnetization direction of the first fixed magnetic layer and the easy axis of the free magnetic layer are oriented in the perpendicular orientation, and the magnetization direction of the second fixed magnetic layer is oriented in the diametrical orientation.
2. The magnetic cell of claim 1 , wherein the first fixed magnetic layer has a magnetization direction that is substantially parallel to an easy axis of the free magnetic layer, and the second fixed magnetic layer has a magnetization direction that is substantially orthogonal to the easy axis of the free magnetic layer.
3. The magnetic cell of claim 1 , wherein at least one of the magnetic layers are composed at least in part of a ferromagnetic material.
4. The magnetic cell of claim 3 , wherein the ferromagnetic material comprises at least one of iron, cobalt, nickel, boron, lanthanide, neodymium, samarium, a Permalloy, and a Heusler alloy.
5. The magnetic cell of claim 1 , further comprising interlayers between the first fixed magnetic layer and the free magnetic layer and between the free magnetic layer and the second fixed magnetic layer.
6. The magnetic cell of claim 5 , wherein the interlayers comprise a tunnel barrier comprising an electrically insulating material.
7. The magnetic cell of claim 6 , wherein the insulating material comprises an oxide of one or more of aluminum, tantalum, titanium, or magnesium.
8. The magnetic cell of claim 5 , wherein the interlayers comprise an electrically conducting material.
9. The magnetic cell of claim 8 , wherein the electrically conducting material comprises one or more of copper, gold, silver, or aluminum.
10. The magnetic cell of claim 5 , wherein the first fixed magnetic layer has a magnetization direction that is substantially parallel to an easy axis of the free magnetic layer, and the second fixed magnetic layer has a magnetization direction that is substantially orthogonal to the easy axis of the free magnetic layer, and wherein the interlayer between the first fixed magnetic layer and the free magnetic layer comprises an electrically insulating material, and the interlayer between the second fixed magnetic layer and the free magnetic layer comprises an electrically conducting material.
11. The magnetic cell of claim 1 , wherein the fixed magnetic layers each have a substantially greater magnetic volume than the free magnetic layer.
12. The magnetic cell of claim 1 , wherein the fixed magnetic layers are magnetically pinned.
13. A magnetic cell comprising:
a first fixed magnetic layer;
a second fixed magnetic layer;
a free magnetic layer positioned between the first and second fixed magnetic layers; and
terminals configured for providing a spin-polarized current through the magnetic layers,
wherein the magnetic cell defines a perpendicular orientation that is perpendicular to the layers and a diametrical orientation that is planar with the layers, and the magnetization direction of the first fixed magnetic layer is oriented in the perpendicular orientation, and the magnetization direction of the second fixed magnetic layer and the easy axis of the free magnetic layer are oriented in the diametrical orientation.
14. A magnetic cell comprising:
a first fixed magnetic layer;
a second fixed magnetic layer;
a free magnetic layer positioned between the first and second fixed magnetic layers; and
terminals configured for providing a spin-polarized current through the magnetic layers,
wherein the magnetic cell defines a first diametrical orientation that is planar with the layers and a second diametrical orientation that is planar with the layers and substantially orthogonal to the first diametrical orientation, and the magnetization direction of the first fixed magnetic layer is oriented in the first diametrical orientation, and the magnetization direction of the second fixed magnetic layer and the easy axis of the free magnetic layer are oriented in the second diametrical orientation.
15. A data storage system comprising:
a plurality of magnetic data storage cells; and
operative signal connections with one or more of the magnetic data storage cells;
wherein a representative one of the magnetic data storage cells comprises:
a stack of three or more magnetic layers, operably connected to a first terminal and a second terminal configured for providing a spin-polarized current through the magnetic data storage cell, the three or more magnetic layers comprising a first fixed magnetic layer proximate to the first terminal, a second fixed magnetic layer proximate to the second terminal, and a free magnetic layer positioned between the first and second fixed magnetic layers;
wherein the first fixed magnetic layer has a fixed magnetization direction, the second fixed magnetic layer has a fixed magnetization direction that is substantially orthogonal to the magnetization direction of the first fixed magnetic layer, and the free magnetic layer has an easy axis that is substantially parallel to a magnetization direction of a primary reference layer, the primary reference layer comprising either the first fixed magnetic layer or the second fixed magnetic layer, thereby predisposing the free magnetic layer to have a magnetization direction either parallel or antiparallel to the magnetization direction of the primary reference layer;
wherein the data storage system is configured to provide write signals and read signals via the signal connections, whereby the write signals cause spin-polarized currents having a current density above a critical value to be provided through the magnetic data storage cells to controllably set the magnetization direction of the free magnetic layers of the magnetic data storage cells, and the read signals cause spin-polarized currents having a current density below the critical value to be provided through the magnetic data storage cells to generate a read output signal that indicates the magnetization direction of the free magnetic layers of the magnetic data storage cells.
16. The data storage system of claim 15 , wherein the representative magnetic data storage cell defines a vertical axis that runs generally between the terminals and generally perpendicular to the magnetic layers, and the magnetization direction of the first fixed magnetic layer is oriented generally parallel to the vertical axis, the magnetization direction of the second fixed magnetic layer is oriented either generally parallel or generally orthogonal to the vertical axis, and the easy axis of the free magnetic layer is oriented generally parallel to the magnetization direction of either the first fixed magnetic layer or the second fixed magnetic layer.
17. The data storage system of claim 15 , wherein the representative magnetic data storage cell defines a vertical axis that runs generally between the terminals and generally perpendicular to the magnetic layers, the magnetization direction of the first fixed magnetic layer is oriented generally orthogonal to the vertical axis, the magnetization direction of the second fixed magnetic layer is oriented generally orthogonal to the vertical axis and generally orthogonal to the magnetization direction of the first fixed magnetic layer, and the easy axis of the free magnetic layer is oriented generally parallel to the magnetization direction of either the first fixed magnetic layer or the second fixed magnetic layer.