Spin torque oscillator with an antiferromagnetically coupled assist layer and methods of operating the same

Patent metadata

Field	Value
Publication number	US-11239016-B2
Application number	US-202016887715-A
Country	US
Kind code	B2
Filing date	May 29, 2020
Priority date	May 29, 2020
Publication date	Feb 1, 2022
Grant date	Feb 1, 2022

Abstract

A spin torque oscillator includes a first electrode, a second electrode and a device layer stack located between the first electrode and the second electrode. The device layer stack includes a spin polarization layer including a first ferromagnetic material, an assist layer including a third ferromagnetic material, a ferromagnetic oscillation layer including a second ferromagnetic material located between the spin polarization layer and the assist layer, a nonmagnetic spacer layer located between the spin polarization layer and the ferromagnetic oscillation, and a nonmagnetic coupling layer located between the ferromagnetic oscillation layer and the assist layer. The assist layer is antiferromagnetically coupled to the ferromagnetic oscillation layer through the non-magnetic coupling layer, and the assist layer has a magnetization that is coupled to a magnetization of the ferromagnetic oscillation layer.

First claim

What is claimed is:

1. A spin torque oscillator comprising:
a first electrode;
a second electrode;
a device layer stack located between the first electrode and the second electrode, wherein the device layer stack comprises:
a spin polarization layer including a first ferromagnetic material;
an assist layer including a third ferromagnetic material;
a ferromagnetic oscillation layer including a second ferromagnetic material located between the spin polarization layer and the assist layer;
a nonmagnetic spacer layer located between the spin polarization layer and the ferromagnetic oscillation layer; and
a nonmagnetic coupling layer located between the ferromagnetic oscillation layer and the assist layer, wherein the assist layer is antiferromagnetically coupled to the ferromagnetic oscillation layer through the non-magnetic coupling layer, and the assist layer has a magnetization that is coupled to a magnetization of the ferromagnetic oscillation layer,
wherein:
at least one of the first or second electrode comprises a ferromagnetic material having a fixed magnetization and comprising a ferromagnetic electrode layer and a ferromagnetic pillar that protrudes from the ferromagnetic electrode layer toward the device layer stack;
the ferromagnetic pillar has substantially a same lateral width as a lateral width of the device layer stack; and
a lateral width of the ferromagnetic electrode layer is larger than the lateral width of the ferromagnetic pillar, such that a ring shaped horizontal surface of the ferromagnetic electrode layer surrounds a base of the ferromagnetic pillar to provide a notch at a junction of the ferromagnetic electrode layer and the ferromagnetic pillar.

2. The spin torque oscillator of claim 1 , wherein the ferromagnetic oscillation layer has a greater magnetic moment-thickness product than the spin polarization layer.

3. The spin torque oscillator of claim 2 , wherein a ratio of a magnetic moment-thickness product of the ferromagnetic oscillation layer to a magnetic moment-thickness product of the spin polarization layer is in a range from 1.2 to 5.

4. The spin torque oscillator of claim 2 , wherein the antiferromagnetically coupled assist layer has a greater magnetic moment-thickness product than the ferromagnetic oscillation layer.

5. The spin torque oscillator of claim 4 , wherein a ratio of a magnetic moment-thickness product of the antiferromagnetically coupled assist layer to a magnetic moment-thickness product of the ferromagnetic oscillation layer is in a range from 2 to 10.

6. The spin torque oscillator of claim 1 , further comprising a control circuit configured to apply a bias voltage between the first and the second electrodes to induce flow of a spin current through the device layer stack between the first and the second electrodes.

7. The spin torque oscillator of claim 6 , wherein:
a magnetization of the ferromagnetic oscillation layer is ferromagnetically coupled to a magnetization of the spin polarization layer while the spin current does not flow through the device layer stack; and
the magnetization of the ferromagnetic oscillation layer and the magnetization of the spin polarization layer are in-plane magnetizations that are parallel to an interface between the spin polarization layer and the nonmagnetic spacer layer while the spin current does not flow through the device layer stack.

8. The spin torque oscillator of claim 7 , wherein while the spin current flows through the device layer stack:
the ring shaped horizontal surface generates a stray magnetic field along a side surface of the ferromagnetic pillar such that a vertical component of the stray magnetic field is applied to the layers of the device layer stack as a bias magnetic field; and
the magnetization of the spin polarization layer follows the magnetization of the ferromagnetic oscillation layer in an antiparallel direction, while an azimuthal angle of an in-plane component of the magnetization of the ferromagnetic oscillation layer is the same as an azimuthal angle of the in-plane component of the magnetization of the spin polarization layer.

9. The spin torque oscillator of claim 8 , wherein the magnetization of the ferromagnetic oscillation layer and the magnetization of the assist layer are in-plane magnetizations that are antiparallel to each other and are parallel to an interface between the ferromagnetic oscillation layer and the nonmagnetic spacer layer while the spin current does not flow through the device layer stack.

10. The spin torque oscillator of claim 9 , wherein:
the magnetization of the assist layer is coupled to the magnetization of the ferromagnetic oscillation layer, and precesses around a vertical axis with a same precession frequency as the magnetization of the spin polarization layer while the spin current flows through the device layer stack; and
the azimuthal angle of the in-plane component of the magnetization of the ferromagnetic oscillation layer is offset by 180 degrees from an azimuthal angle of an in-plane component of the magnetization of the assist layer while the spin current flows through the device layer stack.

11. The spin torque oscillator of claim 1 , wherein:
the first ferromagnetic material of the spin polarization layer comprises Fe, Co, Ni, a ferromagnetic alloy including at least one of Fe, Co or Ni, or a magnetic Heusler alloy;
the nonmagnetic spacer layer comprises a nonmagnetic metal, a semiconductor material, magnesium oxide or aluminum oxide;
the second ferromagnetic material of the ferromagnetic oscillation layer comprises Fe, Co, Ni, a ferromagnetic alloy including at least one of Fe, Co or Ni, or a magnetic Heusler alloy;
the nonmagnetic coupling layer comprises ruthenium, rhodium or iridium; and
the third ferromagnetic material of the assist layer comprises Fe, Co, Ni, a ferromagnetic alloy including at least one of Fe, Co or Ni, or a magnetic Heusler alloy.

12. The spin torque oscillator of claim 11 , wherein:
the spin polarization layer has a thickness in a range from 1 nm to 3 nm;
the nonmagnetic spacer has a thickness in a range from 0.8 nm to 3 nm;
the ferromagnetic oscillation layer has a thickness in a range from 2 nm to 15 nm;
the nonmagnetic coupling layer has a thickness in a range from 0.4 nm to 2 nm; and
the assist layer has a thickness in a range from 2 nm to 100 nm.

13. The spin torque oscillator of claim 1 , wherein:
the first electrode comprises the ferromagnetic material having the fixed magnetization; the ferromagnetic electrode layer comprises a first ferromagnetic electrode layer;
the ferromagnetic pillar comprises a first ferromagnetic pillar; and
sidewalls of the device layer stack are vertically coincident with a sidewall of the first ferromagnetic pillar.

14. The spin torque oscillator of claim 13 , wherein:
the second electrode also comprises the ferromagnetic material having the fixed magnetization;
the second electrode comprises a second ferromagnetic electrode layer and a second ferromagnetic pillar protruding toward the device layer stack;
the second ferromagnetic pillar has substantially a same lateral width as a lateral width of the device layer stack such that sidewalls of the device layer stack are vertically coincident with a sidewall of the second ferromagnetic pillar; and
a lateral width of the second ferromagnetic electrode layer is larger than the lateral width of the second ferromagnetic pillar, such that a ring shaped horizontal surface of the second ferromagnetic electrode layer surrounds a base of the second ferromagnetic pillar to provide a second notch at a junction of the second ferromagnetic ele

Assignees

• Western Digital Tech Inc

Inventors

• Zheng Yuankai
• Gao Zheng
• Okamura Susumu
• Freitag James

Classifications

• B82Y25/00

  Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance · CPC title

• H03B15/006

  using spin transfer effects or giant magnetoresistance · CPC title

• H01F10/3254

  the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ] · CPC title

• H01F10/329 Primary

  Spin-exchange coupled multilayers wherein the magnetisation of the free layer is switched by a spin-polarised current, e.g. spin torque effect · CPC title

• H01F10/3272

  by use of anti-parallel coupled [APC] ferromagnetic layers, e.g. artificial ferrimagnets [AFI], artificial [AAF] or synthetic [SAF] anti-ferromagnets · CPC title