Current-perpendicular-to-plane magnetoresistive device with oxidized free layer side regions and method for its fabrication

Abstract

A current-perpendicular-to the-plane (CPP) magnetoresistive device has two ferromagnetic layers separated by a nonmagnetic spacer layer with the free ferromagnetic layer having a central region of ferromagnetic material and nonmagnetic side regions formed of one or more oxides of the ferromagnetic material. One type of CPP device is a magnetic tunnel junction (MTJ) magnetoresistive read head in which the lower pinned layer has a width and height greater than the width and height, respectively, of the overlying central region of the upper free layer, with the side regions of the free layer being oxidized and therefore nonmagnetic. The MTJ read head is formed by patterning resist in the shape of the free layer central region over the stack of layers in the MTJ, ion milling or etching the stack down into the free layer, and then exposing the stack to oxygen to oxidize the ferromagnetic material in the side regions not covered by the resist.

What is claimed is:  
     
         1 . A magnetic tunnel junction device comprising: 
 a substrate;    a pinned ferromagnetic layer on the substrate and having a width in a first dimension in the plane of the pinned layer and a magnetization direction oriented in a preferred direction and substantially prevented from rotation in the presence of an applied magnetic field in the range of interest;    an insulating tunnel barrier layer on the pinned layer;    a free ferromagnetic layer on the tunnel barrier layer and having a width defined by side edges and less than the width of the pinned layer, the free layer having a magnetization direction substantially free to rotate in the presence of an applied magnetic field in the range of interest; and    a nonmagnetic side region located on the tunnel barrier layer on each side of and adjacent to the side edges of the free layer, each side region being formed of one or more oxides of the same ferromagnetic material present in the free layer.    
     
     
         2 . The magnetic tunnel junction device according to  claim 1  wherein the magnetization directions of the pinned and free ferromagnetic layers are substantially parallel or antiparallel to one another in the absence of an applied magnetic field.  
     
     
         3 . The magnetic tunnel junction device according to  claim 1  wherein the magnetization directions of the pinned and free ferromagnetic layers are substantially perpendicular to one another in the absence of an applied magnetic field.  
     
     
         4 . The magnetic tunnel junction device according to  claim 1  wherein the pinned layer has a height in a second dimension in the plane of the pinned layer perpendicular to said first dimension and wherein the free layer has a height less than the height of the pinned layer.  
     
     
         5 . The magnetic tunnel junction device according to  claim 1  further comprising a capping layer on the free layer.  
     
     
         6 . The magnetic tunnel junction device according to  claim 1  further comprising a layer of antiferromagnetic material on the substrate below the pinned layer for pinning the magnetization of the pinned layer by antiferromagnetic exchange coupling.  
     
     
         7 . The magnetic tunnel junction device according to  claim 1  wherein the tunnel barrier layer is formed substantially of alumina.  
     
     
         8 . The magnetic tunnel junction device according to  claim 1  further comprising an insulating cover on each insulating side region and formed of material having a composition different from the composition of the side region.  
     
     
         9 . The magnetic tunnel junction device according to  claim 1  wherein the substrate is a magnetic shield layer formed on the trailing surface of a head carrier.  
     
     
         10 . The magnetic tunnel junction device according to  9  further comprising a nonmagnetic electrically conductive lead layer on the shield layer.  
     
     
         11 . The magnetic tunnel junction device according to  claim 1  wherein the free layer is formed of an alloy comprising Co and Fe, and wherein the nonmagnetic side regions are formed of one or more oxides of Co and Fe.  
     
     
         12 . The magnetic tunnel junction device according to  claim 1  wherein the free layer is formed of an alloy comprising Ni and Fe, and wherein the nonmagnetic side regions are formed of one or more oxides of Ni and Fe.  
     
     
         13 . The magnetic tunnel junction device according to  claim 1  wherein the free layer is formed of an alloy comprising Co, Ni and Fe, and wherein the nonmagnetic side regions are formed of one or more oxides of Co, Ni and Fe.  
     
     
         14 . A magnetic tunnel junction read head for sensing data recorded on a magnetic recording disk, the head comprising: 
 a first magnetic shield layer;    a fixed ferromagnetic layer over the shield layer and having a width W along a dimension corresponding to the trackwidth TW dimension of the disk and a height H along a dimension substantially perpendicular to the TW dimension, the magnetization of the fixed layer being fixed in a direction along its height;    an insulating tunnel barrier layer on the fixed ferromagnetic layer;    a free ferromagnetic layer formed of an alloy comprising the elements of Fe and one or more of Co and Ni on the tunnel barrier layer and having a width TW defined by side edges and less than W and a stripe height SH less than H, the free layer having a magnetization direction in the TW dimension in the absence of an applied field, the magnetization direction of the free layer being substantially free to rotate in the presence of magnetic fields from the disk;    a nonmagnetic side region located on the tunnel barrier layer on each side of and adjacent to the side edges of the free layer, each side region being formed of one or more oxides of the elements in the alloy of said ferromagnetic free layer; and    a second magnetic shield layer over the free layer and nonmagnetic side regions.    
     
     
         15 . The magnetic tunnel junction read head according to  claim 14  further comprising a first nonmagnetic electrically conductive bottom lead layer between the first shield layer and the fixed layer, and a second nonmagnetic electrically conductive top lead layer between the free layer and the second shield layer.  
     
     
         16 . The magnetic tunnel junction read head according to  claim 15  further comprising an antiferromagnetic layer on the bottom lead layer, the fixed layer being located on and in contact with the antiferromagnetic layer and exchange coupled with the fixed layer for pinning the magnetization of the fixed layer in said direction along its height.  
     
     
         17 . The magnetic tunnel junction read head according to  claim 14  wherein H/W is greater than one.  
     
     
         18 . A current-perpendicular to the plane magnetoresistive sensor comprising: 
 a substrate;    a pinned ferromagnetic layer on the substrate and having a width in a first dimension in the plane of the pinned layer and a magnetization direction oriented in a preferred direction and substantially prevented from rotation in the presence of an applied magnetic field in the range of interest;    a nonmagnetic spacer layer on the pinned layer;    a free ferromagnetic layer on the spacer layer and having a width defined by side edges and less than the width of the pinned layer, the free layer having a magnetization direction substantially free to rotate in the presence of an applied magnetic field in the range of interest; and    a nonmagnetic side region located on the spacer layer on each side of and adjacent to the side edges of the free layer, each side region being formed of one or more oxides of the same ferromagnetic material present in the free layer.    
     
     
         19 . The sensor according to  claim 18  wherein the spacer layer is electrically insulating.  
     
     
         20 . The sensor according to  claim 18  wherein the spacer layer is electrically conducting.  
     
     
         21 . A method for making a current-perpendicular to the plane magnetoresistive sensor comprising: 
 depositing on a substrate in succession a layer of antiferromagnetic material, a first layer of ferromagnetic material, a spacer layer of nonmagnetic material, a second layer of ferromagnetic material, and a layer of capping material;    providing a mask over a central region of the capping layer and underlying central region of the second ferromagnetic layer;    removing the capping layer and a portion of the second ferromagnetic layer in side regions not covered by the mask;    oxidizing the remaining material in the second ferromagnetic layer in the side regions not covered by the mask; and    removing the mask.    
     
     
         22 . The method according to  claim 21  further comprising depositing over the oxidized side regions electrically insulating cover material different from the material of the oxidized side regions.  
     
     
         23 . The method according to  claim 21  wherein depositing the nonmagnetic spacer layer comprises depositing electrically insulating material.  
     
     
         24 . The method according to  claim 23  wherein depositing electrically insulating material comprises depositing a layer of aluminum and then oxidizing the aluminum.