Xmr monocell sensors, systems and methods

Abstract

Embodiments relate to magnetoresistive (xMR) sensors. In an embodiment, an xMR stack structure is configured to form two different xMR elements that can be coupled to form a locally differential Wheatstone bridge. The result is a highly sensitive magnetic sensor with small dimensions and robustness against thermal drift and sensor/encoder pitch mismatch that can be produced using standard processing equipment. Embodiments also relate to methods of forming and patterning the stack structure and sensors that provide information regarding direction in addition to speed.

What is claimed is: 
     
         1 . A magnetic field sensor comprising:
 a first magnetoresistive (xMR) sensor element configured to have a first response to a magnetic field; and   a second xMR sensor element configured to have a second response to the magnetic field different from the first response, wherein the first and second xMR sensor elements having the same reference magnetization direction.   
     
     
         2 . The magnetic field sensor of  claim 1 , wherein one of the first response or the second response provides a signal with a positive sign and the other of the first response or the second response provides a signal with a negative sign. 
     
     
         3 . The magnetic field sensor of  claim 1 , wherein a magnetic moment of a freelayer system of the first xMR sensor element is different from a magnetic moment of a freelayer system of the second xMR sensor element. 
     
     
         4 . The magnetic field sensor of  claim 3 , wherein the freelayer system of the first xMR sensor element comprises a first freelayer and a second freelayer that are antiferromagnetically coupled. 
     
     
         5 . The magnetic field sensor of  claim 3 , wherein the freelayer systems of the second xMR sensor element comprises a single freelayer. 
     
     
         6 . The magnetic field sensor of  claim 1 , wherein the first and second xMR sensor elements comprise giant magnetoresistive (GMR) sensor elements. 
     
     
         7 . The magnetic field sensor of  claim 1 , wherein the first and second xMR sensor elements are arranged in a Wheatstone bridge comprising a third xMR element and a fourth xMR element coupled to the first and second xMR elements, the third xMR sensor element exhibiting the same behavior as the first xMR sensor element and the fourth xMR sensor element exhibiting the same behavior as the second xMR sensor element. 
     
     
         8 . The magnetic field sensor of  claim 7 , wherein the first, second, third and fourth xMR sensor elements are arranged in an area that has width less than about 1 millimeter (mm) wide. 
     
     
         9 . The magnetic field sensor of  claim 8 , wherein the width is less than about 10 micrometers (μm). 
     
     
         10 . The magnetic field sensor of  claim 8 , wherein the area is less than about 50 μm high. 
     
     
         11 . The magnetic field sensor of  claim 1 , wherein the first and second xMR sensor elements comprise reference system stacks having the same reference magnetization direction. 
     
     
         12 . The magnetic field sensor of  claim 1 , further comprising at least one additional xMR sensor element spaced apart from the first Wheatstone bridge. 
     
     
         13 . The magnetic field sensor of  claim 12 , wherein an output signal of the at least one additional xMR sensor element is offset corrected such that a zero transition of the output signal occurs at the same field as an output signal of the first Wheatstone bridge. 
     
     
         14 . The magnetic field sensor of  claim 12 , further comprising circuitry coupled to the at least one additional xMR sensor element and configured to evaluate a sign of an output signal of the at least one additional xMR sensor element at a zero crossing of the first Wheatstone bridge. 
     
     
         15 . The magnetic field sensor of  claim 12 , wherein the at least one additional xMR sensor element comprises first, second, third and fourth sensor elements coupled in a second Wheatstone bridge. 
     
     
         16 . The magnetic field sensor of  claim 12 , wherein the first and second Wheatstone bridges are substantially identical. 
     
     
         17 . The magnetic field sensor of  claim 12 , wherein the first Wheatstone bridge is configured to provide speed information and the at least one additional xMR sensor element is configured to provide direction information. 
     
     
         18 . The magnetic field sensor of  claim 12 , wherein the at least one additional xMR sensor element is spaced apart from the first Wheatstone bridge by less than about 500 micrometers (μm). 
     
     
         19 . The magnetic field sensor of  claim 18 , wherein the at least one additional xMR sensor element is spaced apart from the first Wheatstone bridge by less than about 200 μm. 
     
     
         20 . A magnetic field sensor comprising:
 a first sensor element arrangement configured to sense a magnetic field at a first location; and   at least one additional xMR sensor element configured to provide direction information related to the magnetic field and spaced apart from the first sensor element arrangement.   
     
     
         21 . The magnetic field sensor of  claim 20 , wherein the sensor element arrangement comprises a Wheatstone bridge configured to provide speed information related to a sensed magnetic field and comprising first, second, third and fourth magnetoresistive (xMR) sensor elements, the first and second xMR sensor elements formed to have a first response to the magnetic field and the third and fourth xMR sensor elements formed to have a second response to the magnetic field different from the first response. 
     
     
         22 . The magnetic field sensor of  claim 20 , wherein the at least one additional xMR sensor element is spaced apart from the first Wheatstone bridge on the same sensor die. 
     
     
         23 . The magnetic field sensor of  claim 20 , wherein the at least one additional xMR sensor element comprises a second Wheatstone bridge. 
     
     
         24 . The magnetic field sensor of  claim 23 , wherein the first and second Wheatstone bridges are substantially identical. 
     
     
         25 . A method comprising:
 forming first and second magnetoresistive stacks by forming a reference system and a free-layer system for each of the first and second magnetoresistive stacks such that the free-layer system of the first magnetoresistive stack includes first and second free-layers, and the free-layer system of the second magnetoresitive stack includes only one of the first or second free-layers.   
     
     
         26 . The method of  claim 25 , further comprising depositing a first free-layer in at least first and second portions, and selectively removing the first free-layer in the first portion while maintaining the first free-layer in the second portion. 
     
     
         27 . The method of  claim 25 , wherein forming the first and second magnetoresistive stacks comprises depositing layers for the reference systems of the first and second magnetoresistive stacks in common deposition steps. 
     
     
         28 . The method of  claim 25 , further comprising:
 forming a magnetoresistive stack (xMR) comprising a freelayer system and a reference system coupled by a spacer layer, the freelayer system comprising first and second freelayers;   selectively etching the stack to remove the second freelayer from a first portion of the stack while maintaining the second freelayer in a second portion of the stack; and   patterning the stack to form at least two xMR elements, a first xMR element comprising the first portion of the stack, and a second xMR element comprising the second portion of the stack.   
     
     
         29 . The method of  claim 25 , further comprising:
 forming a first free-layer;   selectively removing the first free-layer in at least a first portion while maintaining the first free-layer in a second portion;   depositing a second free-layer in at least the first and second portions; and   depositing additional layers to form a reference system.   
     
     
         30 . The method of  claim 25 , further comprising applying an external magnetic field to impress a reference magnetization in the same direction for the reference systems of the first and second magnetoresistive stacks.