MTJ sensor including domain stable free layer
View Patent ↗By subdividing the free layer of a GMR/TMR device into multiple sub-elements that share common top and bottom electrodes, a magnetic detector is produced that is domain stable in the presence of large stray fields, thereby eliminating the need for longitudinal bias magnets. Said detector may be used to measure electric currents without being affected by local temperature fluctuations and/or stray fields.
1. A magnetic field sensor having a domain stable free layer, comprising:
an array of magneto-resistive elements on a conductive substrate, each of said magneto-resistive elements having a width dimension along a first axis and a length dimension along a second axis with a length-to-width ratio of at least 1.2, said length dimension being at most 1.0 micron;
each of said magneto-resistive elements further comprising a magnetic reference layer having a fixed magnetization whose direction is along said first axis;
a magnetic free layer having uniaxal anisotropy along said second axis; and
a separation layer between said magnetic reference layer and said magnetic free layer.
2. The magnetic field sensor of claim 1 wherein said plurality of independent magnetic sensor stacks numbers from 2 to about 2000 stacks.
3. The magnetic field sensor of claim 1 wherein each of said magneto-resistive elements has a shape selected from the group consisting of ellipse-like shapes including ellipses, rectangles having curved corners, eye shapes, and diamond-like shapes.
4. The magnetic field sensor of claim 1 wherein said magnetic reference layer is a pinned layer in a synthetic antiparallel configuration.
5. The magnetic field sensor of claim 1 wherein said separation layer is an oxide selected from the group consisting of AlOx, TiOx, HfOx, MgO, and laminations of one or more of said oxides, whereby said magnetic field sensor is an MTJ device.
6. The magnetic field sensor of claim 1 wherein said separation layer is a nitride selected from the group consisting of AlNx, TiNx, HfNx, MgN x , and laminations of one or more of said nitrides, whereby said magnetic field sensor is an MTJ device.
7. The magnetic field sensor structure of claim 1 wherein said separation layer is a conductive material selected from the group consisting of Cu, Au, Ag, and multi-layers thereof, whereby said magnetic field sensor is a CPP GMR device.
8. The magnetic field sensor of claim 1 wherein said magnetic free layer is ferromagnetic or ferrimagnetic and has an anisotropy substantially along said second axis and that is perpendicular to said fixed magnetization direction.
9. The magnetic field sensor of claim 1 wherein said magnetic free layer has a synthetic anti-parallel configuration with a non-zero net magnetic moment and has an anisotropy substantially along said second axis perpendicular to said fixed magnetization direction.
10. A magnetic field sensor having a domain stable free layer, comprising:
an antiferromagnetic layer on a lower conductive layer;
a pinned magnetic reference layer, having a magnetization direction, on said antiferromagnetic layer;
a separation layer on said magnetic reference layer;
a magnetic free layer on said separation layer;
a capping layer on said magnetic free layer;
said magnetic reference, separation, free, and capping layers having the form of a plurality of independent sensor stacks, each such stack having, in plan view, a width dimension along a first axis and a length dimension along a second axis, with a length-to-width ratio sufficient to support an anisotropy field, and a length dimension no greater than a domain wall width and perpendicular to said pinned magnetization direction whereby all free layers of said sensor stacks are domain stable when exposed to a magnetic field;
said lower conductive layer having the form of a bottom electrode that is common to all said sensor stacks;
a dielectric layer that fills all space between said sensor stacks, including covering all sidewalls; and
a top electrode that contacts said capping layer whereby it is common to all said sensor stacks.
11. The magnetic field sensor described in claim 10 wherein said plurality of independent magnetic sensors numbers in a range of from 2 to about 2000 stacks.
12. The magnetic field sensor described in claim 10 wherein said length-to-width ratio is at least 1.2, and said shape is selected from the group consisting of ellipse-like shapes including ellipses, rectangles having curved corners, eye shapes, and diamond-like shapes, and said length dimension is at most 1 micron.
13. The magnetic field sensor described in claim 10 wherein said sensor stacks are disposed to lie along a single straight line.
14. The magnetic field sensor described in claim 10 wherein said sensor stacks are disposed to lie along two or more parallel lines.
15. The magnetic field sensor described in claim 10 wherein said separation layer is a tunneling insulation layer whereby said magnetic field sensor is an MTJ device.
16. The magnetic field sensor described in claim 10 wherein said separation layer is a conductive layer whereby said magnetic field sensor is a CPP GMR device.