Method of manufacturing a magnetic memory device having buffer layer

Abstract

The disclosed technology generally relates to magnetic memory devices, and more particularly to spin transfer torque magnetic random access memory (STT-MRAM) devices having a magnetic tunnel junction (MTJ), and further relates to methods of fabricating the STT-MRAM devices. In an aspect, a magnetoresistive random access memory (MRAM) device has a magnetic tunnel junction (MTJ). The MTJ includes a magnetic reference layer comprising CoFeB, a magnetic free layer comprising CoFeB, and a barrier layer comprising MgO. The barrier layer is interposed between the magnetic reference layer and the magnetic free layer. The barrier layer has a thickness adapted to tunnel electrons between the magnetic reference layer and the magnetic free layer sufficient to cause a change in the magnetization direction of the variable magnetization under a bias. The MTJ further comprises a buffer layer comprising one or more of Co, Fe, CoFe and CoFeB, where the buffer layer is doped with one or both of C and N.

What is claimed is: 
     
         1 . A method of manufacturing a magnetoresistive random access memory (MRAM), the MRAM having a magnetic tunnel junction (MTJ), the method comprising:
 forming a magnetic reference layer comprising CoFeB and having a fixed magnetization direction;   forming a barrier layer, comprising MgO, on the magnetic reference layer;   forming a magnetic free layer, comprising CoFeB, on the barrier layer, wherein the magnetic free layer has a variable magnetization direction that changes under a write bias, wherein the barrier layer is interposed between the magnetic reference layer and the magnetic free layer,   wherein the barrier layer has a thickness adapted to tunnel electrons between the magnetic reference layer and the magnetic free layer at a current density sufficient to cause a magnetization direction of the magnetic free layer to change under a write bias; and   forming one or more buffer layers over one or both of opposing surfaces of the barrier layer, wherein each of the one or more buffer layers comprises one or more of Co, Fe, CoFe and CoFeB, and is doped with one or both of C and N.   
     
     
         2 . The method according to  claim 1 , wherein each of the one or more buffer layers is doped with the one or both of C and N at a concentration of 1 to 8 atomic percent. 
     
     
         3 . The method according to  claim 1 , wherein forming the one or more buffer layers comprises forming one of the one or more buffer layers adjacent to and on a same side of the barrier layer as the magnetic reference layer. 
     
     
         4 . The method according to  claim 3 , wherein the one of the one or more buffer layers is interposed between the barrier layer and the magnetic reference layer. 
     
     
         5 . The method according to  claim 3 , wherein the magnetic reference layer comprises a plurality of layers, wherein one of the plurality of layers is the one of the one or more buffer layers. 
     
     
         6 . The method according to  claim 3 , wherein forming the one or more buffer layers further comprises forming another one of the one or more buffer layers adjacent to and on a same side of the barrier layer as the magnetic free layer. 
     
     
         7 . The method according to  claim 1 , wherein forming the one or more buffer layers comprises forming one of the one or more buffer layers adjacent to and on a same side of the barrier layer as the magnetic free layer. 
     
     
         8 . The method according to  claim 7 , wherein the one of the one or more buffer layers is interposed between the barrier layer and the magnetic free layer. 
     
     
         9 . The method according to  claim 7 , wherein the magnetic free layer comprises a plurality of layers, wherein one of the plurality of layers is the one of the one or more buffer layers. 
     
     
         10 . The method according to  claim 1 , further comprising annealing the MTJ at a temperature sufficient to cause one or more of the barrier layer, the magnetic reference layer and the magnetic free layer to crystallize into a body-centered cubic structure. 
     
     
         11 . The method according to  claim 10 , wherein annealing the MTJ comprises causing crystallization of the magnetic reference layer and/or the magnetic free layer to initiate subsequent to initiation of crystallization of the barrier layer. 
     
     
         12 . The method according to  claim 1 , wherein the one or more buffer layers serve as a diffusion barrier, such that one or both of the magnetic free layer and the magnetic reference layer are substantially free of atomic elements diffused from the barrier layer, and that the barrier layer is substantially free of atomic elements diffused from the one or both of the magnetic reference layer and the magnetic free layer. 
     
     
         13 . A method of manufacturing a magnetoresistive random access memory (MRAM) device, the method comprising:
 forming a magnetic tunnel junction (MTJ) comprising a magnetic reference layer and a magnetic free layer interposed by a barrier layer,   wherein forming the MTJ further comprises forming one or more buffer layers over one or both opposing surfaces of the barrier layer, wherein each of the one or more buffer layers comprises one or more of Co, Fe, CoFe and CoFeB, and is doped with one or both of C and N.   
     
     
         14 . The method according to  claim 13 , wherein each of the one or more buffer layers is doped with one or both of C and N at a concentration of 1 to 8 atomic percent. 
     
     
         15 . The method according to  claim 13 , wherein each of the one or more buffer layers has a thickness of 0.2 nm-2 nm. 
     
     
         16 . The method according to  claim 13 , further comprising annealing the MTJ at a temperature sufficient to cause one or more of the barrier layer, the magnetic reference layer and the magnetic free layer that are amorphous as-deposited to crystallize. 
     
     
         17 . The method according to  claim 13 , wherein the one or more buffer layers serve as a diffusion barrier, such that one or both of the magnetic free layer and the magnetic reference layer are substantially free of atomic elements diffused from the barrier layer, and the barrier layer is substantially free of atomic elements diffused from the one or both of the magnetic reference layer and the magnetic free layer. 
     
     
         18 . The method according to  claim 17 , wherein the magnetic reference layer and the magnetic free layer comprise boron (B), and wherein the one or more buffer layers are adapted to impede diffusion therethrough of at least boron (B), such that after annealing, a concentration of B in the barrier layer is less than 10% of B in the magnetic reference layer and the magnetic free layer. 
     
     
         19 . The method according to  claim 17 , wherein the barrier layer comprises an oxide, and wherein the one or more buffer layers are adapted to impede diffusion therethrough of at least oxygen (O), such that after annealing, a concentration O in one or both of the magnetic reference layer and the magnetic free layer is less than 10% of O in the barrier layer. 
     
     
         20 . The method according to  claim 13 , wherein one or both of the magnetic reference layer and the magnetic free layer comprises a plurality of layers, and wherein one of the plurality of layers is one of the one or more buffer layers.