TMR vortex layout for back bias sensors
According to one aspect of the disclosure, a sensor includes a substrate; a back bias magnet arranged to generate a bias field at least having components in a plane parallel to a surface of the substrate, the bias field having a horizontal symmetry axis within the plane; and a plurality of sensing element groups disposed at different locations on a surface of the substrate and laid out along a common line aligned with the horizontal symmetry axis of the back bias magnet, each of the plurality of sensing element groups having one or more tunneling magnetoresistance (TMR) vortices having an axis of maximum sensitivity aligned with the common line.
1 . A sensor comprising:
a substrate;
a back bias magnet arranged to generate a bias field at least having components in a plane parallel to a surface of the substrate, the bias field having a horizontal symmetry axis within the plane; and
a plurality of sensing element groups disposed at different locations on a surface of the substrate and laid out along a common line aligned with the horizontal symmetry axis of the back bias magnet, each of the plurality of sensing element groups having one or more tunneling magnetoresistance (TMR) vortices having an axis of maximum sensitivity aligned with the common line.
2 . The sensor of claim 1 wherein the plurality of sensing element groups include a first group and a second group, wherein one or more TMR vortices of the first group are electrically connected with one or more TMR vortices of the second group to form a bridge circuit.
3 . The sensor of claim 1 wherein the plurality of sensing element groups include a first group, a second group, and a third group, wherein one or more TMR vortices of the first group and one or one or more TMR vortices of the second group are electrically connected to form a first bridge circuit, and one or more TMR vortices of the second group and one or more TMR vortices of the third group are electrically connected to form a second bridge circuit.
4 . The sensor of claim 3 wherein the first group and the third group are equidistant from the second group along the common line.
5 . The sensor of claim 1 wherein one or more of the TMR vortices have a first pinning direction along the common line and one or more others of the TMR vortices have a second pinning direction along the common line opposite from the first pinning direction.
6 . The sensor of claim 5 wherein a number of the TMR vortices have a first pinning direction is equal to a number of the TMR vortices have a second pinning direction.
7 . The sensor of claim 1 wherein the back bias magnet comprises multiple smaller magnets arranged to generate said bias field.
8 . The sensor of claim 1 wherein the TMR vortices are formed as pillars on the substrate.
9 . The sensor of claim 8 wherein the pillars have a diameter less than or equal to 2 microns and the TMR vortices have a free layer with a thickness in a range 35-150 nm.
10 . The sensor of claim 1 wherein each of plurality of sensing element groups includes at least two interleaved TMR vortices.
11 . The sensor of claim 1 wherein the bias field has a magnitude of 30 Oersted or less along a direction perpendicular to the horizontal axis of symmetry at the locations of the plurality of sensing element groups.
12 . The sensor of claim 1 wherein the bias field is substantially zero along a direction parallel to the horizontal axis of symmetry at the locations of the plurality of sensing element groups.
13 . The sensor of claim 1 wherein the plurality of sensing element groups comprises a first sensing element group, a second sensing element group, and a third sensing element group, wherein the sensor comprises a heat source located on a perpendicular bisector of a line segment between the first sensing element group and the second sensing element group.
14 . The sensor of claim 13 wherein the sensor comprises another heat source located on a perpendicular bisector of a line segment between the second sensing element group and the third sensing element group.
15 . The sensor of claim 1 wherein the plurality of sensing element groups is a first plurality of sensing element groups, the sensor further comprising a second plurality of sensing element groups, wherein the first plurality of sensing element groups includes TMR vortices having a first diameter and the second plurality of sensing element groups includes TMR vortices having a second diameter different from the first diameter.
16 . The sensor of claim 15 wherein the TMR vortices having the first diameter have a first sensitivity and the TMR vortices having the second diameter have a second sensitivity different from the first sensitivity.
17 . The sensor of claim 15 wherein the TMR vortices having the first diameter are connected to form one or more first bridge circuits and the TMR vortices having the second diameter are connected to form one or more second bridge circuits.
18 . The sensor of claim 16 comprising switching circuitry configured to switch between the one or more first bridge circuits and the one or more second bridge circuits based on an amplitude of a sensed signal.
19 . The sensor of claim 18 wherein the switching circuitry is configured to switch between the one or more first bridge circuits and the one or more second bridge circuits in response to the amplitude of the sensed signal being greater than a predetermined threshold value.
20 . The sensor of claim 18 wherein the switching circuitry is configured to switch between the one or more first bridge circuits and the one or more second bridge circuits in response to the amplitude of the sensed signal being less than a predetermined threshold value.