Spin-transfer torque magnetoresistive memory device with a free layer stack including multiple spacers and methods of making the same

Patent metadata

Field	Value
Publication number	US-2022139435-A1
Application number	US-202217575840-A
Country	US
Kind code	A1
Filing date	Jan 14, 2022
Priority date	Sep 3, 2019
Publication date	May 5, 2022
Grant date	—

Abstract

A spin-transfer torque (STT) magnetoresistive memory device includes a first electrode, a second electrode, and a magnetic tunnel junction located between the first electrode and the second electrode. The magnetic tunnel junction includes a reference layer having a fixed magnetization direction, a free layer stack, and a nonmagnetic tunnel barrier layer located between the reference layer and the free layer stack. The free layer stack has a total thickness of less than 2 nm, and contains in order, a proximal ferromagnetic layer located proximal to the nonmagnetic tunnel barrier layer, a first non-magnetic metal sub-monolayer, an intermediate ferromagnetic layer, a second non-magnetic metal sub-monolayer, and a distal ferromagnetic layer.

First claim

What is claimed is:

1 . A spin-transfer torque (STT) magnetoresistive memory device, comprising:
a first electrode; a second electrode; and a magnetic tunnel junction located between the first electrode and the second electrode, the magnetic tunnel junction comprising a reference layer having a fixed magnetization direction, a free layer stack, and a nonmagnetic tunnel barrier layer located between the reference layer and the free layer stack, wherein the free layer stack comprises, in order, a proximal ferromagnetic layer located proximal to the nonmagnetic tunnel barrier layer, an intermediate ferromagnetic layer, a non-magnetic metal layer, and a distal ferromagnetic layer.

2 . The STT magnetoresistive memory device of claim 1 , wherein the proximal ferromagnetic layer comprises a proximal CoFeB layer, the intermediate ferromagnetic layer comprises an intermediate CoFe layer, the non-magnetic metal layer comprises a tungsten layer, and the distal ferromagnetic layer comprises a distal CoFe layer.

3 . The STT magnetoresistive memory device of claim 2 , wherein the proximal CoFeB layer includes boron at an atomic concentration in a range from 10% to 30%, cobalt at an atomic concentration in a range from 12% to 20%, and iron at an atomic concentration in a range from 55% to 75%.

4 . The STT magnetoresistive memory device of claim 3 , wherein the intermediate CoFe layer and the distal CoFe layer include cobalt at an atomic concentration in a range from 15% to 35% and iron at an atomic concentration in a range from 70% to 85%.

5 . The STT magnetoresistive memory device of claim 2 , wherein the nonmagnetic tunnel barrier layer comprises magnesium oxide.

6 . The STT magnetoresistive memory device of claim 2 , further comprising a magnesium oxide capping layer located over the free layer stack.

7 . The STT magnetoresistive memory device of claim 6 , further comprising a non-magnetic electrically conductive layer stack comprising, from one side to another, a first ruthenium layer, a tantalum layer, and a second ruthenium layer.

8 . The STT magnetoresistive memory device of claim 2 , wherein the tungsten layer comprises a sub-monolayer.

9 . The STT magnetoresistive memory device of claim 1 , further comprising a magnesium layer located between the intermediate ferromagnetic layer and a non-magnetic metal layer.

10 . The STT magnetoresistive memory device of claim 1 , wherein:
the STT magnetoresistive memory device comprises a STT MRAM cell that includes only one magnetic tunnel junction; the free layer stack has a saturation magnetization of at least about 1,500 emu/cm 3 ; and the free layer stack has a total thickness of less than 2 nm.

11 . A method of forming a spin-transfer torque (STT) magnetoresistive memory device, comprising:
forming a reference layer having a fixed magnetization direction; forming a nonmagnetic tunnel barrier layer over the reference layer; and forming a free layer stack on the non-magnetic tunnel barrier layer by sequentially forming a proximal ferromagnetic layer, an intermediate ferromagnetic layer, a non-magnetic metal layer, and a distal ferromagnetic layer.

12 . The method of claim 11 , wherein the proximal ferromagnetic layer comprises a proximal CoFeB layer, the intermediate ferromagnetic layer comprises an intermediate CoFe layer, the non-magnetic metal layer comprises a tungsten layer, and the distal ferromagnetic layer comprises a distal CoFe layer.

13 . The method of claim 12 , wherein the proximal CoFeB layer includes boron at an atomic concentration in a range from 10% to 30%, cobalt at an atomic concentration in a range from 12% to 20%, and iron at an atomic concentration in a range from 55% to 75%.

14 . The method of claim 13 , wherein the intermediate CoFe layer and the distal CoFe layer include cobalt at an atomic concentration in a range from 15% to 35% and iron at an atomic concentration in a range from 70% to 85%.

15 . The method of claim 12 , wherein the nonmagnetic tunnel barrier layer comprises magnesium oxide.

16 . The method of claim 12 , further comprising a magnesium oxide capping layer located over the free layer stack.

17 . The method of claim 16 , further comprising a non-magnetic electrically conductive layer stack comprising, from one side to another, a first ruthenium layer, a tantalum layer, and a second ruthenium layer.

18 . The method of claim 12 , wherein the tungsten layer comprises a sub-monolayer.

19 . The method of claim 12 , further comprising forming a magnesium layer on a top surface of the intermediate CoFe layer.

20 . The method of claim 19 , wherein the magnesium layer is removed during formation of the tungsten layer by tungsten atoms impinging on the magnesium layer.

Assignees

• Western Digital Tech Inc

Inventors

• Santos Tiffany
• Smith Neil

Classifications

• H10N50/85

  Materials of the active region · CPC title

• G11C11/161 Primary

  details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell · CPC title

• H01F10/329

  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

• H01F41/302

  for applying spin-exchange-coupled multilayers, e.g. nanostructured superlattices (spin-exchange-coupled multilayers H01F10/32) · CPC title

• H01F10/3259

  Spin-exchange-coupled multilayers comprising at least a nanooxide layer [NOL], e.g. with a NOL spacer · CPC title