Trapezoidal back bias and trilayer reader geometry to enhance device performance

Abstract

A magnetoresistive sensor having a trilayer sensor stack with two ferromagnetic freelayers separated by a nonmagnetic spacer layer is disclosed. The sensor is biased with a back biasing magnet adjacent a back of the trilayer sensor. The back biasing magnet, the trilayer sensor stack, or both have substantially trapezoidal shapes to enhance the biasing field and to minimize noise. In some embodiments, the trilayer sensor or back bias magnet have a shape designed to stabilize a micromagnetic “C” shape or concentrate magnetic flux in the trilayer sensor stack.

1 . A magnetoresistive sensor comprising:
 a trilayer sensor stack comprising two ferromagnetic freelayers separated by a nonmagnetic spacer; and   a back biasing magnet adjacent a back end of the trilayer sensor stack;   wherein at least one of the trilayer sensor stack and the back biasing magnet has a shape that stabilizes a micromagnetic “C” state or concentrates magnetic flux in the trilayer sensor stack.   
     
     
         2 . The magnetoresistive sensor of  claim 1  wherein the back bias magnet has a substantially trapezoidal shape. 
     
     
         3 . The magnetoresistive sensor of  claim 2  wherein the trilayer sensor stacks have a substantially trapezoidal shape. 
     
     
         4 . The magnetoresistive sensor of  claim 1  wherein the trilayer sensor stack has a substantially rectangular shape. 
     
     
         5 . The magnetoresistive sensor of  claim 1 , wherein the nonmagnetic spacer layer of the trilayer sensor stack is an insulator layer and the trilayer sensor stack is a tunneling magnetoresistive sensor. 
     
     
         6 . The magnetoresistive sensor of  claim 1 , wherein the biasing magnet provides vertical bias to the trilayer sensor stack. 
     
     
         7 . The magnetoresistive sensor of  claim 1 , wherein the biasing magnet is a hard magnetic material. 
     
     
         8 . The magnetoresistive sensor of  claim 7 , wherein the hard magnetic material is a cobalt-platinum based alloy or iron-platinum based alloy. 
     
     
         9 . The magnetoresistive sensor of  claim 1 , wherein the back biasing magnet is isolated from the trilayer sensor stack by an insulating layer. 
     
     
         10 . The magnetoresistive sensor of  claim 1 , wherein the ferromagnetic layers in the trilayer sensor stack are selected from the group consisting of nickel-iron, copper-iron, and nickel-iron-copper alloys. 
     
     
         11 . The magnetoresistive sensor of  claim 1 , and further comprising:
 lateral side shields adjacent both sides of the trilayer sensor stack and the back biasing magnet.   
     
     
         12 . The magnetoresistive sensor of  claim 11 , wherein the lateral side shields are isolated from the trilayer sensor stack and the vertical biasing magnet by a side shield insulating layer comprising aluminum oxide. 
     
     
         13 . A magnetoresistive sensor comprising:
 a trilayer sensor stack comprising two ferromagnetic layers separated by a nonmagnetic spacer layer, and having a front width proximate an air bearing surface and a back width distal from the air bearing surface; and   a back biasing magnet adjacent the back width of the trilayer sensor stack, the back biasing magnet having a front width that is about the same as the back width of the trilayer stack, and a back width; wherein at least the back biasing magnet has a trapezoidal shape.   
     
     
         14 . The magnetoresistive sensor of  claim 13  wherein the back width of the trilayer sensor stack is larger than the front width of the trilayer stack. 
     
     
         15 . The magnetoresistive sensor of  claim 13  wherein the back biasing magnet provides bias to the trilayer sensor stack in a direction generally perpendicular to the air bearing surface. 
     
     
         16 . The magnetoresistive sensor of  claim 13  wherein the back width of the biasing magnet is larger than its front width. 
     
     
         17 . The magnetoresistive sensor of  claim 13  and further comprising:
 lateral side shields adjacent both sides of the trilayer sensor stack and the back biasing magnet. 
 
     
     
         18 . The magnetoresistive sensor of  claim 13  wherein the back width of the trilayer sensor stack is about the same as the front width of the trilayer sensor stack. 
     
     
         19 . A magnetoresistive sensor comprising:
 a trilayer sensor stack comprising first and second free layers separated by a nonmagnetic spacer;   a permanent magnet located on an opposite side of the trilayer sensor stack as an air bearing surface, the permanent magnet having a front side width less than a back side width wherein a front side is closest to the trilayer sensor stack;   a first and second side shield adjacent the trilayer sensor stack and permanent magnet;   a top shield adjacent the first free layer; and   a bottom shield adjacent the second free layer.   
     
     
         20 . The magnetoresistive sensor of  claim 19 , wherein the trilayer sensor stack has a front side width less than the back side width and a front side is closest to the air bearing surface.