Systems and methods for controlling soft bias thickness for tunnel magnetoresistance readers

Abstract

Systems and methods for controlling a thickness of a soft bias layer in a tunnel magnetoresistance (TMR) reader are provided. One such method involves providing a magnetoresistive sensor stack including a free layer and a bottom shield layer, performing contiguous junction milling on the sensor stack, depositing an insulating layer on the sensor stack, depositing a spacer layer on the insulating layer, performing an angled milling sub-process to remove preselected portions of the spacer layer, depositing a soft bias layer on the sensor stack, and depositing a top shield layer on the sensor stack and the soft bias layer. The method can further involve adjusting an alignment of a top surface of the spacer layer with respect to the free layer. In one such case, the top surface of the spacer layer is adjust to be below the free layer.

What is claimed is: 
     
         1 . A method for controlling a thickness of a soft bias layer during fabrication of a tunnel magnetoresistance reader, the method comprising:
 providing a magnetoresistive sensor stack comprising a free layer and a bottom shield layer;   performing a contiguous junction milling on the sensor stack;   depositing an insulating layer on the sensor stack;   depositing a spacer layer on the insulating layer, wherein the spacer layer is entirely below the free layer;   performing an angled milling sub-process to remove preselected portions of the spacer layer;   depositing a soft bias layer on the sensor stack, wherein at least a portion of the soft bias layer is on the spacer layer; and   depositing a top shield layer on the sensor stack and the soft bias layer.   
     
     
         2 . The method of  claim 1 , wherein the performing the angled milling sub-process to remove the preselected portions of the spacer layer comprises adjusting an alignment of a top surface of the spacer layer with respect to the free layer. 
     
     
         3 . The method of  claim 1 , wherein the sensor stack comprises:
 an anti-ferromagnetic pinning layer on the bottom shield layer;   a pinned layer on the anti-ferromagnetic pinning layer;   a barrier layer on the pinned layer;   the free layer on the barrier layer; and   a capping layer on the free layer.   
     
     
         4 . The method of  claim 3 :
 wherein the bottom shield layer comprises one or more materials selected from the group consisting of NiFe, NiCo, CoFe, NiFeCo, CoB, CoFeB, and combinations thereof;   wherein the anti-ferromagnetic pinning layer comprises one or more materials selected from the group consisting of IrMn, IrMnCr, and combinations thereof;   wherein the pinned layer comprises one or more materials selected from the group consisting of CoFe, CoB, CoFeB, and combinations thereof;   wherein the barrier layer comprises one or more materials selected from the group consisting of MgO, AlOx, and combinations thereof, where x is a positive integer;   wherein the free layer comprises one or more materials selected from the group consisting of NiFe, NiCo, CoFe, Fe, NiFeCo, CoB, CoFeB, Ru, Ta, and combinations thereof; and   wherein the capping layer comprises one or more materials selected from the group consisting of Ru, Ta, Ti, MgO, and combinations thereof.   
     
     
         5 . The method of  claim 4 , wherein the spacer layer comprises one or more non-magnetic materials. 
     
     
         6 . The method of  claim 5 , wherein the spacer layer comprises one or more materials selected from the group consisting of NiFeCr, NiCr, Ta, Ru, Cr, and oxides of NiFeCr, NiCr, Ta, and Cr, and combinations thereof. 
     
     
         7 . The method of  claim 6 , wherein the soft bias layer comprises one or more materials selected from group consisting of NiFe, NiCo, CoFe, NiCoFe, CoB, CoFeB, Ru, and combinations thereof. 
     
     
         8 . The method of  claim 6 , wherein the insulating layer comprises one or more materials selected from group consisting of alumina, MgO, SiN, SiO2, and combinations thereof. 
     
     
         9 . The method of  claim 1 :
 wherein the sensor stack comprises angled sides such that a width of the sensor stack narrows as the sensor stack extends in a direction substantially perpendicular to the bottom shield layer; and   wherein the performing the angled milling sub-process to remove preselected portions of the spacer layer comprises removing portions of the spacer layer along the angled sides of the sensor stack.   
     
     
         10 . The method of  claim 9 , wherein the removing portions of the spacer layer along the angled sides of the sensor stack comprises removing portions of the spacer layer along the angled sides of the sensor stack that are above the free layer. 
     
     
         11 . The method of  claim 1 :
 wherein the sensor stack comprises angled sides such that a width of the sensor stack narrows as the sensor stack extends in a direction substantially perpendicular to the bottom shield layer; and   wherein the performing the angled milling sub-process to remove preselected portions of the spacer layer comprises removing portions of the insulating layer along the angled sides of the sensor stack.   
     
     
         12 . The method of  claim 1 :
 wherein the providing the magnetoresistive sensor stack comprising the free layer and the bottom shield layer comprises providing the magnetoresistive sensor stack comprising the free layer and the bottom shield layer and providing a resist layer on the sensor stack; and   the method further comprising:
 removing, after the depositing the soft bias layer on the sensor stack, a portion of the soft bias layer and a portion of the resist layer. 
   
     
     
         13 . The method of  claim 12 , wherein the removing the portion of the soft bias layer and the portion of the resist layer comprises:
 performing a reactive ion etching of a top surface area of the sensor stack; and   planarizing the top surface area of the sensor stack.   
     
     
         14 . The method of  claim 1 , wherein the spacer layer consists of a substantially flat layer. 
     
     
         15 . The method of  claim 1 :
 wherein a soft bias structure adjacent to the sensor stack comprises:
 a portion of the bottom shield layer; 
 the insulating layer; 
 the spacer layer; 
 the soft bias layer; 
 the top shield layer; and 
 an air bearing surface; 
   wherein a rear area of the soft bias structure is substantially free of the soft bias layer;   wherein the soft bias structure is positioned between the rear area and the air bearing surface; and   wherein a portion of the insulating layer forms the rear area of the soft bias structure.   
     
     
         16 . The method of  claim 1 :
 wherein a soft bias structure adjacent to the sensor stack comprises:
 a portion of the bottom shield layer; 
 the insulating layer; 
 the spacer layer; 
 the soft bias layer; 
 the top shield layer; and 
 an air bearing surface; and 
   wherein a depth of the spacer layer from the air bearing surface is greater than a depth of the soft bias layer from the air bearing surface.   
     
     
         17 . The method of  claim 16 , wherein a depth of the insulating layer from the air bearing surface is greater than the depth of the spacer layer from the air bearing surface. 
     
     
         18 . The method of  claim 1 , wherein the spacer layer is comprised of non-magnetic materials. 
     
     
         19 . The method of  claim 1 :
 wherein the depositing the spacer layer on the insulating layer comprises depositing the spacer layer directly on the insulating layer;   wherein the depositing the soft bias layer on the sensor stack comprises depositing the soft bias layer directly on the sensor stack; and   wherein the depositing the top shield layer on the sensor stack and the soft bias layer comprises depositing the top shield layer directly on the sensor stack and the soft bias layer.   
     
     
         20 . The method of  claim 19 , wherein the spacer layer is comprised of non-magnetic materials.