Magnetic stacks with perpendicular magnetic anisotropy for spin momentum transfer magnetoresistive random access memory

Abstract

A magnetic tunnel junction (MTJ) includes a magnetic free layer, having a variable magnetization direction; an insulating tunnel barrier located adjacent to the free layer; a magnetic fixed layer having an invariable magnetization direction, the fixed layer disposed adjacent the tunnel barrier such that the tunnel barrier is located between the free layer and the fixed layer, wherein the free layer and the fixed layer have perpendicular magnetic anisotropy; and one or more of: a composite fixed layer, the composite fixed layer comprising a dusting layer, a spacer layer, and a reference layer; a synthetic antiferromagnetic (SAF) fixed layer structure, the SAF fixed layer structure comprising a SAF spacer located between the fixed layer and a second fixed magnetic layer; and a dipole layer, wherein the free layer is located between the dipole layer and the tunnel barrier.

1 . A magnetic tunnel junction (MTJ) for a magnetic random access memory (MRAM), comprising:
 a magnetic free layer, having a variable magnetization direction;   an insulating tunnel barrier located adjacent to the free layer;   a magnetic fixed layer having an invariable magnetization direction, the fixed layer disposed adjacent the tunnel barrier such that the tunnel barrier is located between the free layer and the fixed layer, wherein the free layer and the fixed layer have perpendicular magnetic anisotropy; and   one or more of:
 a composite fixed layer, the composite fixed layer comprising a dusting layer, a spacer layer, and a reference layer, wherein the spacer layer is located between the reference layer and the tunnel barrier, and wherein the dusting layer is located between the spacer layer and the tunnel barrier; 
 a synthetic antiferromagnetic (SAF) fixed layer structure, the SAF fixed layer structure comprising a SAF spacer located between the fixed layer and a second fixed magnetic layer, wherein the fixed layer and the second fixed magnetic layer are anti-parallely coupled through the SAF spacer; and 
 a dipole layer, wherein the free layer is located between the dipole layer and the tunnel barrier. 
   
     
     
         2 . The MTJ of  claim 1 , wherein the free layer comprises one of cobalt-iron-boron (CoFeB), pure iron (Fe), CoFeB|Fe and Fe|CoFeB. 
     
     
         3 . The MTJ of  claim 1 , further comprising a seed layer underneath the free layer, the seed layer comprising one of tantalum (Ta) or tantalum magnesium (TaMg), and wherein the seed layer has a thickness from about 0.5 nanometers (nm) to about 3 nm. 
     
     
         4 . The MTJ of  claim 1 , wherein the tunnel barrier comprises magnesium oxide (MgO). 
     
     
         5 . The MTJ of  claim 1 , wherein the dusting layer of the composite fixed layer comprises one of CoFeB, CoFe, Fe, bilayers of Fe|CoFeB, bilayers of CoFe|CoFeB, bilayers of CoFeB|Fe, and bilayers of CoFeB|CoFe. 
     
     
         6 . The MTJ of  claim 1 , wherein the dusting layer of the composite fixed layer has a thickness from about 0.5 nm to about 2 nm. 
     
     
         7 . The MTJ of  claim 1 , wherein the spacer layer of the composite fixed layer comprises a non-magnetic material. 
     
     
         8 . The MTJ of  claim 1 , wherein the spacer layer of the composite fixed layer comprises one of chromium (Cr), ruthenium (Ru), titanium nitride (TiN), titanium (Ti), vanadium (V), tantalum (Ta), tantalum nitride (TaN), aluminum (Al), magnesium (Mg) and MgO. 
     
     
         9 . The MTJ of  claim 1 , wherein the spacer layer of the composite fixed layer comprises a tri-layer structure comprising a center magnetic spacer layer disposed between two non-magnetic spacer layers. 
     
     
         10 . The MTJ of  claim 9 , wherein the center magnetic spacer layer comprises one of CoFeB, Fe, and CoFe. 
     
     
         11 . The MTJ of  claim 9 , wherein the center magnetic layer has a thickness from about 0.1 nm to about 0.5 nm. 
     
     
         12 . The MTJ of  claim 1 , wherein the fixed layer comprises one of cobalt-platinum (Co|Pt) and cobalt-palladium (Co|Pd). 
     
     
         13 . The MTJ of  claim 1 , wherein the SAF spacer comprises ruthenium, and wherein the second fixed magnetic layer comprises one of cobalt-nickel (Co|Ni), Co|Pd and Co|Pt. 
     
     
         14 . The MTJ of  claim 1 , wherein the dipole layer comprises one of cobalt chromium platinum (CoCrPt), Co|Ni, Co|Pd, and Co|Pt multilayers. 
     
     
         15 . The MTJ of  claim 14 , wherein the dipole layer further comprises a CoFeB layer. 
     
     
         16 . The MTJ of  claim 1 , wherein the fixed layer is magnetized in a direction opposite to a magnetization direction of the second fixed magnetic layer in the SAF structure. 
     
     
         17 . The MTJ of  claim 1 , wherein the MTJ comprises both the dipole layer and the SAF structure, and the dipole layer and the second fixed magnetic layer of the SAF structure are magnetized in the same direction, and the fixed layer is magnetized in a direction that is opposite to the magnetization direction of the dipole layer and the second fixed magnetic layer. 
     
     
         18 . The MTJ of  claim 1 , wherein the dipole layer is magnetized in a direction opposite to a magnetization direction of the fixed layer. 
     
     
         19 . A method of forming a magnetic tunnel junction (MTJ) for a magnetic random access memory (MRAM), the method comprising:
 forming a magnetic free layer having a variable magnetization direction;   forming a tunnel barrier over the free layer, the tunnel barrier comprising an insulating material;   forming a magnetic fixed layer having an invariable magnetization direction over the tunnel barrier, wherein the free layer and the fixed layer have perpendicular magnetic anisotropy; and   forming one or more of:
 a composite fixed layer, the composite fixed layer comprising a dusting layer, a spacer layer, and a reference layer, wherein the spacer layer is located between the reference layer and the tunnel barrier, and wherein the dusting layer is located between the spacer layer and the tunnel barrier; 
 a synthetic antiferromagnetic (SAF) fixed layer structure, the SAF fixed layer structure comprising a SAF spacer located between the fixed layer and a second fixed magnetic layer, wherein the fixed layer and the second fixed magnetic layer are anti-parallelly coupled through the SAF spacer; and 
 a dipole layer, wherein the free layer is located between the dipole layer and the tunnel barrier. 
   
     
     
         20 . The method of  claim 19 , wherein forming the free layer comprises growing the free layer on a seed layer comprising one of tantalum (Ta) or tantalum magnesium (TaMg), and wherein the seed layer has a thickness from about 0.5 nanometers (nm) to about 3 nm. 
     
     
         21 . The method of  claim 19 , wherein the tunnel barrier comprises magnesium oxide (MgO) and is formed by one of natural oxidation, radical oxidation, and radio frequency (RF) sputtering. 
     
     
         22 . The method of  claim 19 , wherein the fixed layer is magnetized in a direction opposite to a magnetization direction of the second fixed magnetic layer in the SAF structure. 
     
     
         23 . The method of  claim 19 , wherein the MTJ comprises both the dipole layer and the SAF structure, and the dipole layer and the second fixed magnetic layer of the SAF structure are magnetized in the same direction, and the fixed layer is magnetized in a direction that is opposite to the magnetization direction of the dipole layer and the second fixed magnetic layer. 
     
     
         24 . The method of  claim 19 , wherein the dipole layer is magnetized in a direction opposite to a magnetization direction of the fixed layer. 
     
     
         25 . The method of  claim 19 , wherein the free layer comprises one of cobalt-iron-boron (CoFeB), pure iron (Fe), CoFeB|Fe and Fe|CoFeB, and the fixed layer comprises one of cobalt-platinum (Co|Pt) and cobalt-palladium (Co|Pd).