Spin transfer torque MRAM with a spin torque oscillator stack and methods of making the same
A MRAM cell includes a magnetic tunnel junction containing a reference layer having a fixed magnetization direction, a free layer, and a nonmagnetic tunnel barrier layer located between the reference layer and the free layer, a spin torque oscillator stack, and a first nonmagnetic spacer layer located between the free layer and the a spin torque oscillator stack.
1. A MRAM cell, comprising:
a magnetic tunnel junction comprising a reference layer having a fixed magnetization direction, a free layer, and a nonmagnetic tunnel barrier layer located between the reference layer and the free layer;
a spin torque oscillator stack; and
a first nonmagnetic spacer layer located between the free layer and the spin torque oscillator stack;
wherein:
the spin torque oscillator stack comprises a spin torque layer, a spin polarization layer and a second nonmagnetic spacer located between the spin torque layer and the spin polarization layer;
the spin torque layer comprises a first magnetic material having a first conical magnetization with respect to a vertical axis that is parallel to the fixed vertical magnetization direction of the reference layer; and
the spin polarization layer comprises a second magnetic material having a second conical magnetization with respect to the vertical axis that is parallel to the fixed vertical magnetization direction of the reference layer.
2. The MRAM cell of claim 1 , wherein an in-plane component of the first conical magnetization and an in-plane component of the second conical magnetization are free to precess around the vertical axis upon application of current through the spin torque layer, the second nonmagnetic spacer layer, and the spin polarization layer.
3. The MRAM cell of claim 2 , wherein the fixed vertical magnetization direction of the reference layer maintains a same orientation upon application of electrical current through the reference layer.
4. The MRAM cell of claim 1 , wherein the spin polarization layer comprises a ferromagnetic material having the second conical magnetization with respect to the vertical axis.
5. The MRAM cell of claim 4 , wherein the ferromagnetic material has an axial magnetization component that is parallel or antiparallel to an axial magnetization component of the first conical magnetization of the spin torque layer.
6. The MRAM cell of claim 1 , wherein the spin polarization layer comprises:
a first spin polarization component layer having zero or negative magnetization; and
a second spin polarization component layer having an axial magnetization that is parallel or antiparallel to the vertical axis.
7. The MRAM cell of claim 6 , wherein the second spin polarization component is vertically spaced from the first spin polarization component layer by a third nonmagnetic spacer layer.
8. The MRAM cell of claim 6 , wherein the second spin polarization component comprises a multilayer stack of cobalt layers and at least one of platinum or palladium layers.
9. The MRAM cell of claim 8 , wherein the first spin polarization component comprises a cobalt-iridium alloy comprising 70 to 90 atomic percent cobalt and 10 to 30 atomic percent iridium.
10. The MRAM device of claim 8 , wherein the first spin polarization component comprises a cobalt-iron alloy comprising 90 to 99.5 atomic percent cobalt and 0.5 to 10 atomic percent iron.
11. The MRAM device of claim 8 , wherein the first spin polarization component comprises a cobalt-iron-boron alloy.
12. The MRAM device of claim 8 , wherein the first spin polarization component comprises a multilayer stack of cobalt layers and iron layers.
13. The MRAM cell of claim 8 , wherein a combined magnetization of the first spin polarization component layer and the second spin polarization component layer provides the second conical magnetization that is coupled to the first conical magnetization of the spin torque layer.
14. A MRAM cell, comprising:
a magnetic tunnel junction comprising a reference layer having a fixed magnetization direction, a free layer, and a nonmagnetic tunnel barrier layer located between the reference layer and the free layer;
a spin torque oscillator stack; and
a first nonmagnetic spacer layer located between the free layer and the spin torque oscillator stack;
wherein:
the spin torque oscillator stack comprises a spin torque layer, a spin polarization layer and a second nonmagnetic spacer located between the spin torque layer and the spin polarization layer;
the spin torque layer comprises a first magnetic material having a negative magnetization; and
the spin polarization layer comprises a second magnetic material having a second conical magnetization with respect to a vertical axis that is parallel to the fixed vertical magnetization direction of the reference layer.
15. The MRAM cell of claim 14 , wherein the first magnetic material comprises a cobalt-iridium alloy comprising 70 to 90 atomic percent cobalt and 10 to 30 atomic percent iridium, a cobalt-iron alloy comprising 90 to 99.5 atomic percent cobalt and 0.5 to 10 atomic percent iron, a cobalt-iron-boron alloy, or a multilayer stack of cobalt layers and iron layers.