Magnetic sensor design for suppression of barkhausen noise
View Patent ↗A semiconductor process and apparatus provide a high-performance magnetic field sensor from two differential sensor configurations ( 201, 211 ) which require only two distinct pinning axes ( 206, 216 ), where each differential sensor (e.g., 201 ) is formed from a Wheatstone bridge structure with four unshielded MTJ sensors ( 202 - 205 ), each of which includes a magnetic field pulse generator (e.g., 414 ) for selectively applying a field pulse to stabilize or restore the easy axis magnetization of the sense layers (e.g., 411 ) to eliminate micromagnetic domain switches during measurements of small magnetic fields.
1. A magnetic field sensor, comprising a differential sensor circuit formed over a substrate for detecting an applied magnetic field directed along a first axis, wherein the differential sensor circuit comprises a bridge structure of unshielded magnetic tunnel junction (MTJ) sensors formed with a plurality of pinned layers that are each magnetized in a single pinned direction and a corresponding plurality of unshielded sense layers, wherein the differential sensor circuit comprises:
a first unshielded MTJ sensor having a first unshielded sense layer with a first easy axis magnetic orientation, and
a second unshielded MTJ sensor having a second unshielded sense layer with a second easy axis magnetic orientation, where the first and second easy axis magnetic orientations are deflected equally and in opposite directions from the single pinned direction.
2. The magnetic field sensor of claim 1 , wherein the first easy axis magnetic orientation is deflected about negative 45 degrees from the single pinned direction, and the second easy axis magnetic orientation is deflected about 45 degrees from the single pinned direction.
3. The magnetic field sensor of claim 1 , wherein each unshielded sense layer comprises an anisotropic axis with a longer length dimension and a shorter width dimension, where the longer length dimension is aligned with an easy axis magnetic orientation for the unshielded sense layer.
4. The magnetic field sensor of claim 1 , further comprising an embedded magnetic field generator for each unshielded sense layer that is positioned to generate a magnetic field pulse that is aligned with an easy axis magnetic orientation for each unshielded sense layer.
5. The magnetic field sensor of claim 4 , wherein each embedded magnetic field generator comprises a conductive line positioned to conduct a current pulse that creates a magnetic field pulse for resetting a magnetic orientation of an associated unshielded sense layer.
6. The magnetic field sensor of claim 4 , wherein each embedded magnetic field generator is configured to apply a weak magnetic field along an easy axis magnetic orientation for each unshielded sense layer.
7. The magnetic field sensor of claim 1 , further comprising a second differential sensor circuit formed over the substrate for detecting the applied magnetic field directed along a second axis that is orthogonal to the first axis, wherein the second differential sensor circuit comprises a Wheatstone bridge structure of unshielded magnetic tunnel junction (MTJ) sensors formed with a second plurality of pinned layers that are each magnetized in a second pinned direction and a corresponding plurality of unshielded sense layers, where the single pinned direction for the first differential sensor circuit is orthogonal to the first axis, and the second pinned direction for the second differential sensor circuit is orthogonal to the second axis.
8. The magnetic field sensor of claim 7 , wherein the second differential sensor circuit comprises:
a third unshielded MTJ sensor having a third unshielded sense layer with a third easy axis magnetic orientation, and
a fourth unshielded MTJ sensor having a fourth unshielded sense layer with a fourth easy axis magnetic orientation,
where the third and fourth easy axis magnetic orientations are deflected equally and in opposite directions from the second pinned direction for the second differential sensor circuit.