Magnetoresistive sensors having reduced AMR effects

Embodiments related to magnetoresistive angle sensor layouts having reduced anisotropic magneto resistance (AMR) effects. Embodiments provide magnetoresistive angle sensor layouts that reduce or eliminate distortion related to AMR effects, can be more easily scaled up or down, and are more compact to use available surface area more efficiently.

TECHNICAL FIELD

The invention relates generally to magnetoresistance sensors and more particularly to magnetoresistive angle sensor layouts having reduced anisotropic magneto resistance (AMR) effects.

BACKGROUND

Magnetoresistive sensors, such as giant magneto resistance (GMR) sensors, can be used in various angular position sensing applications, including steering angle sensing in automotive applications and in brushless DC motor commutation and rotary switch applications. In use, the resistance of GMR layers in a GMR angle sensor varies in response to an angle between the magnetization of a free layer and a reference direction. The reference direction can be defined by a hard, or permanent, magnetic magnetization of a reference layer of the angle sensor. The resistance of a GMR resistor can be expressed as:
R=R0*(1+GMR*cos(phi))
where phi is the angle between the magnetization of the reference layer and the magnetization of the free layer, R0 is the resistance at phi=90 degrees, and GMR is a dimensionless number specifying the strength of the GMR effect.

Anisotropic magneto resistance (AMR) sensors are also known and have a resistance that is a function of an angle between an applied magnetic field and current flow lines through a soft magnetic electrically conducting layer:
R=R0*(1+AMR*(cos(psi))2)
where psi is the angle between the current flowlines and the magnetization of the soft magnetic layer, R0 is the resistance at psi=90 degrees, and AMR is a dimensionless number specifying the strength of the AMR effect.

Both GMR and AMR resistors can generally comprise metallic thin films having small sheet resistances such that many strips arranged in serpentines are used to build up larger resistors. A drawback of GMR resistors, however, is that they also have small AMR effects, which can distort results. The resistance of a GMR resistor when considering the AMR effect can be expressed as:
R=R0*(1+GMR*cos(phi)+AMR*(cos(psi))2)

Therefore, there is a need for a GMR angle sensor having a reduced AMR effect.

SUMMARY

In an embodiment, a magnetoresistive sensor with a reference magnetization comprises a first half-bridge comprising a first meander coupled to a supply voltage terminal and a second meander coupled to a ground terminal; and a second half-bridge comprising a third meander and a fourth meander, the third meander coupled to the supply voltage terminal, and the fourth meander coupled to the ground terminal, wherein two of the first, second, third and fourth meanders are oriented to provide a first current flow direction, and the other two of the first, second, third and fourth meanders are oriented to provide a second current flow direction being substantially perpendicular to the first current flow direction, wherein a current flow direction of the second meander is substantially perpendicular to a current flow direction of the third meander, and wherein each current flow direction is generally transverse with respect to the respective meander.

In an embodiment, a magnetoresistive sensor having a reference magnetization, comprises a first reference layer portion having a first resistor and a second resistor disposed thereon, the first resistor coupled to a supply voltage terminal and comprising a first portion and a second portion, and the second resistor coupled to a ground terminal and comprising a third portion and a fourth portion; a second reference layer portion having a third resistor and a fourth resistor disposed thereon, the third resistor coupled to a supply voltage terminal and comprising a fifth portion and a sixth portion and forming a first half-bridge with the second resistor, and the fourth resistor coupled to a ground terminal and comprising a seventh portion and an eighth portion and forming a second half-bridge with the first resistor, wherein two of the first, second, third and fourth resistors are arranged to have a first current flow direction, and the other two of the first, second, third and fourth resistors are arranged to have a second current flow direction substantially perpendicular to the first current flow direction, and wherein a current flow direction of the second resistor is substantially perpendicular to a current flow direction of the third resistor.

In an embodiment, a method comprises providing a magnetoresistive sensor having a reference magnetization and a full-bridge layout; and coupling first and second resistors of the sensor to a supply voltage and third and fourth resistors of the sensor to ground, two of the first, second, third and fourth resistors configured to provide a first direction of current flow and the other two of the first, second, third and fourth resistors configured to provide a second direction of current flow substantially perpendicular to the first direction, the second and third resistors configured to provide substantially perpendicular directions of current flow to one another.

DETAILED DESCRIPTION

The invention relates to magnetoresistive angle sensor layouts having reduced AMR effects. Embodiments provide GMR angle sensor layouts that reduce or eliminate distortion related to AMR effects, can be more easily scaled up or down, and are more compact to use available surface area more efficiently.

FIG. 1depicts a layout of a GMR sensor100according to an embodiment. GMR sensor100comprises a full-bridge layout having two half-bridges. A first half-bridge includes top left (with respect to the orientation of the drawing on the page) meander102disposed on reference layer104acoupled in series with bottom right meander106disposed on reference layer104b. A second half-bridge includes top right meander108disposed on reference layer104bcoupled in series with bottom left meander110disposed on reference layer104a. Meanders102and108can also be referred to as vertical meanders, with respect to the orientation of the longer meander strips on the page, and meanders106and110as horizontal meanders, though in practice the orientations may not in fact be vertical or horizontal. The terms are therefore used herein for the sake of convenience and illustration and are not limiting.

The direction of magnetization of reference layers104aand104bvaries in embodiments. In the embodiment depicted, reference layer104ahas a magnetization going from left to right, while reference layer104bis the opposite. In an embodiment, reference layers104aand104bare disposed on a die surface (not depicted inFIG. 1).

Meanders102and108are coupled to a supply voltage Vs, while meanders106and110are coupled to ground and an output voltage Vo is measured between the meanders of each half-bridge. Thus, the current flows in the same direction in meanders102and108, and in meanders106and110, with the current flow direction in meanders102and108being perpendicular to that in meanders106and110. This configuration effectively cancels any AMR effects between the two half-bridges.

This can be seen by comparing GMR sensor100with an AMR sensor layout. Referring toFIG. 2, a layout of an AMR sensor120is depicted. In AMR sensor120, AMR contributions of each half-bridge are added given the rotated orientations of resistive half-bridge components. Comparing the layout of AMR sensor120with the layout of GMR sensor100, however, shows that the orientations of meanders108and110of GMR sensor100are reversed with respect to the orientation of the same meanders in AMR sensor120. Thus, the AMR contribution of the half-bridge of GMR sensor100comprising meanders108and110is subtracted instead of added as in AMR sensor120and thereby reduced or eliminated.

Another embodiment is depicted inFIG. 3. Similar to GMR sensor100ofFIG. 1, GMR sensor130cancels half-bridge AMR contributions as discussed above. The arrangement of GMR sensor130accomplishes this by having identical AMR contributions in both resistors of each half-bridge. In other words, each half-bridge has no AMR-related contribution because any contribution is canceled within the half-bridge, as compared to GMR sensor100in which any AMR contribution is canceled between the two half-bridges.

Another advantage provided by embodiments is a general immunity of the differential output signal to differing nominal resistances between the horizontal meanders (e.g., meanders106and110inFIG. 1) and vertical meanders (e.g., meanders102and108inFIG. 1). Variations in resistances can be caused, for example, by systemic differences in meander shape due to design, processing or manufacturing inconsistencies, among others. Thus, a design which is not sensitive to these differences provides advantages. In embodiments, therefore, the sizes and shapes of the vertical and horizontal meanders may vary, with or without intention. For example,FIG. 4depicts an embodiment of a GMR sensor140in which horizontal meanders106and110are shorter and narrower, with respect to the orientation on the page, than vertical meanders102and108. While the common mode of the output signal is affected, the differential output signal is not.

InFIG. 5, another embodiment is depicted. GMR angle sensor150includes four meanders102,106,108and110. Meander102includes a first portion102aand a second portion102b, wherein the portion102aand102bare arranged contiguously or serially. Meander108similarly includes portions108aand108b. Each portion102a,band108a,bis approximately square in circumference, such that each can be rotated 90 degrees to the orientations of lower meanders106and110. Meander portion110b, for example, corresponds to rotated meander portion102b. As in other embodiments, the direction of current flow through meanders102and108, both coupled to supply voltage Vs is the same, with the direction of current flow in meanders106and110also the same, but perpendicular with respect to that in meanders102and108.

In other embodiments, one or more of the meanders can otherwise vary in size, length and composition. For example, one or more of the meanders can have more or fewer turns and/or branches. The curved portions of one or more of the meanders can be angled, pointed, broader and/or narrower. The lengths of one or more of the meanders can vary, as can other physical characteristics. In general, however, the two meanders coupled to the supply voltage in a full-bridge layout of a GMR angle sensor have a first current flow direction while the other two meanders coupled to ground have a second current flow direction different from and perpendicular to the first current flow direction. Various embodiments of systems, devices and methods have been described herein. These embodiments are given only by way of example and are not intended to limit the scope of the invention. It should be appreciated, moreover, that the various features of the embodiments that have been described may be combined in various ways to produce numerous additional embodiments. Moreover, while various materials, dimensions, shapes, implantation locations, etc. have been described for use with disclosed embodiments, others besides those disclosed may be utilized without exceeding the scope of the invention.

Persons of ordinary skill in the relevant arts will recognize that the invention may comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the invention may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the invention may comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art.