Simplified double magnetic tunnel junctions

Patent metadata

Field	Value
Publication number	US-10468455-B2
Application number	US-201615096864-A
Country	US
Kind code	B2
Filing date	Apr 12, 2016
Priority date	Apr 12, 2016
Publication date	Nov 5, 2019
Grant date	Nov 5, 2019

Abstract

Double magnetic tunnel junctions and methods of forming the same include a bottom reference layer having a first fixed magnetization and a first thickness. A first tunnel barrier is formed on the bottom reference layer. A free layer is formed on the first tunnel barrier and has a changeable magnetization. A second tunnel barrier is formed on the free layer. A top reference layer is formed on the second tunnel barrier and has a second fixed magnetization that is opposite to the first fixed magnetization and a second thickness that is significantly smaller than the first thickness.

First claim

The invention claimed is:

1. A double magnetic tunnel junction, comprising:
a bottom reference layer having a first fixed magnetization and a first thickness, and formed from at least one material;
a first tunnel barrier on the bottom reference layer;
a free layer on the first tunnel barrier having a changeable magnetization and having a third thickness;
a second tunnel barrier on the free layer; and
a multilayered top reference layer on the second tunnel barrier having a second fixed magnetization that is opposite to the first fixed magnetization and a second thickness that is smaller than the first thickness, less than about 50 Angstroms, and equal to or greater than the third thickness, and formed from at least one material different from any material of the bottom reference layer.

2. The double magnetic tunnel junction of claim 1 , wherein the top reference layer comprises:
a first magnetic layer on the second tunnel barrier;
a spacer on the first magnetic layer; and
a second magnetic layer on the spacer.

3. The double magnetic tunnel junction of claim 2 , wherein the first magnetic layer and the second magnetic layer comprise one of cobalt, iron, cobalt-iron, cobalt-iron-boron.

4. The double magnetic tunnel junction of claim 2 , wherein the spacer includes a material selected from the group consisting of molybdenum, iridium, hafnium, platinum, and rhodium.

5. The double magnetic tunnel junction of claim 2 , wherein the top reference layer further comprises an oxide cap on the second magnetic layer.

6. The double magnetic tunnel junction of claim 1 , wherein the second thickness is about 20 Å.

7. The double magnetic tunnel junction of claim 1 , wherein the bottom reference layer comprises:
a superlattice formed from one of cobalt-platinum or cobalt-iridium; and
a synthetic anti-ferromagnetic spacer formed from one of ruthenium or iridium.

8. The double magnetic tunnel junction of claim 1 , further comprising:
a first electrode formed under the bottom reference layer; and
a second electrode formed on the top reference layer.

9. A memory device, comprising:
a plurality of magnetoresistive random access memory (MRAM) cells, each comprising:
a bottom reference layer having a fixed magnetization and a first thickness between about 21 and about 120 Angstroms, and formed from at least one material to form a synthetic anti-ferromagnetic structure;
a first tunnel barrier on the bottom reference layer including an insulating material that is between 5 and 20 Angstroms thick;
a free layer on the first tunnel barrier having a changeable magnetization and is between 10 and 30 Angstroms thick;
a second tunnel barrier on the free layer; and
a top reference layer having a fixed magnetization and a second thickness of about 20 Angstroms and that is smaller than the first thickness, and formed from at least one material different from any material of the bottom reference layer, comprising:
a first magnetic layer on the second tunnel barrier including cobalt or iron or an alloy thereof;
a spacer on the first magnetic layer including tungsten;
a second magnetic layer on the spacer including cobalt or iron or an alloy thereof; and
an oxide cap on the second magnetic layer having a thickness between 2 and 20 Angstroms; and
a plurality of control transistors, each connected to a respective MRAM cell, configured to control reading of information from and writing of information to the respective MRAM cell.

10. The memory device of claim 9 , wherein the first magnetic layer and the second magnetic layer of each top reference layer comprise one of cobalt, iron, cobalt-iron, cobalt-iron-boron.

11. The memory device of claim 9 , wherein the spacer of the top reference layer includes a material selected from the group consisting of molybdenum, iridium, hafnium, platinum, and rhodium.

12. The memory device of claim 9 , wherein the second thickness of each MRAM cell is about 100 Å.

13. The memory device of claim 9 , wherein the bottom reference layer of each MRAM cell comprises:
a superlattice formed from one of cobalt-platinum and cobalt-iridium; and
a rubidium synthetic anti-ferromagnetic spacer.

14. The memory device of claim 9 , wherein each MRAM cell further comprises:
a first electrode formed under the bottom reference layer; and
a second electrode formed on the top reference layer, wherein the first and second electrode are connected to the respective control transistor.

15. A method of forming a double magnetic tunnel junction, comprising:
forming a bottom reference layer having a first fixed magnetization and a first thickness, the bottom reference layer being formed from at least one material;
forming a first tunnel barrier on the bottom reference layer;
forming a free layer on the first tunnel barrier having a changeable magnetization and having a third thickness;
forming a second tunnel barrier on the free layer; and
forming a multilayered top reference layer on the second tunnel barrier having a second fixed magnetization that is opposite to the first fixed magnetization and a second thickness that is smaller than the first thickness, less than about 50 Angstroms, and about the same as the third thickness, wherein the multilayered top reference layer is formed from at least one material different from any material of the bottom reference layer.

16. The method of claim 15 , wherein forming the multilayered top reference layer comprises:
forming a first magnetic layer on the second tunnel barrier;
forming a spacer on the first magnetic layer; and
forming a second magnetic layer on the spacer.

17. The method of claim 16 , further comprising forming an oxide cap on the second magnetic layer.

18. The method of claim 15 , wherein the second thickness is about 20 Å.

19. The method of claim 15 , wherein forming the bottom reference layer comprises forming the bottom reference layer on a bottom electrode.

20. The double magnetic tunnel junction of claim 1 , wherein the bottom reference layer includes a thickness of about 80 Å to about 120 Å, and wherein the top multilayered reference layer includes a thickness of about 20 Å.

Assignees

• IBM
• Samsung Electronics Co Ltd

Inventors

• Hu Guohan
• Kim Younghyun
• Park Jeong-Heon
• Worledge Daniel

Classifications

• G11C11/161 Primary

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

• H01L43/08

  Electricity · mapped topic

• H01L43/12

  Electricity · mapped topic

• H01L27/226 Primary

  Electricity · mapped topic

• H01L43/10

  Electricity · mapped topic