Simplified double magnetic tunnel junctions

Abstract

A double magnetic tunnel junction includes a bottom reference layer having a first fixed magnetization and a first thickness and formed from at least one material. A first tunnel barrier is on the bottom reference layer. A free layer is on the first tunnel barrier and has a changeable magnetization. A second tunnel barrier is on the free layer. A multilayered top reference layer is formed 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, and equal to or greater than the third thickness.

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, and equal to or greater than the third thickness.   
     
     
         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 . 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. 
     
     
         10 . 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, 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;   a free layer on the first tunnel barrier having a changeable magnetization and is;   a second tunnel barrier on the free layer; and   a top reference layer having a fixed magnetization and a second thickness of that is smaller than the first thickness, 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.   
     
     
         11 . The memory device of  claim 10 , 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. 
     
     
         12 . The memory device of  claim 10 , wherein the spacer of the top reference layer includes a material selected from the group consisting of molybdenum, iridium, hafnium, platinum, and rhodium. 
     
     
         13 . The memory device of  claim 10 , wherein the second thickness of each MRAM cell is about 100 Å. 
     
     
         14 . The memory device of  claim 10 , 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.   
     
     
         15 . The memory device of  claim 10 , 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.   
     
     
         16 . 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, and about the same as the third thickness.   
     
     
         17 . The method of  claim 16 , 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.   
     
     
         18 . The method of  claim 17 , further comprising forming an oxide cap on the second magnetic layer. 
     
     
         19 . The method of  claim 16 , wherein the second thickness is about 20 Å. 
     
     
         20 . The method of  claim 16 , wherein forming the bottom reference layer comprises forming the bottom reference layer on a bottom electrode.