Magnetoresistive Z-axis gradient sensor chip

A magnetoresistive Z-axis gradient sensor chip for detecting a gradient in an XY plane of a Z-axis magnetic field generated by a magnetic medium where the gradient in the XY plane of the Z-axis magnetic field represents a difference for the Z-axis field in the XY plane at a gradient feature distance in an X-axis direction, wherein the magnetoresistive Z-axis gradient sensor chip comprises:

• a silicon (Si) substrate having a surface in the XY plane and perpendicular to the Z-axis magnetic field,
• a magnetoresistive Z axis sensor on the surface of the Si substrate, the magnetoresistive Z axis sensor including a first region and a second region, the magnetoresistive Z-axis sensor including magnetoresistive sensor units and flux guide devices, wherein each of the magnetoresistive sensor units on the surface of the Si substrate is fabricated with a pin layer orientation in either a positive X-axis direction to cause the sensor unit to have a positive X-axis sensing direction or orientated in a negative X-axis direction to cause the sensor unit to have a negative X-axis sensing direction, wherein the flux guide devices comprise a soft magnetic material and are separate structures that are not interconnected by the soft magnetic material, wherein each of the flux guide devices has an elongated shape with a central, major axis in a Y-axis direction and a minor axis in the X-axis direction, and wherein each of the flux guide devices is configured to convert the Z-axis magnetic field into X-axis components in opposite X-axis directions, and wherein each of the flux guide devices corresponds to a set of the magnetoresistive sensor units positioned to sense the X-axis components of the converted Z-axis magnetic field, wherein the corresponding set of the magnetoresistive sensor units include first and second subsets of magnetoresistive sensor units symmetrically positioned across a plane in the Y-axis direction and Z-axis-direction that passes through the central, major axis, and the first and second subsets of magnetoresistive sensor units have opposite pin layer orientations;
• wherein the positive and negative X-axis sensing directions of the magnetoresistive sensor units are parallel to the surface of the Si substrate and perpendicular to the Y-axis direction, and wherein corresponding ones of the flux guide devices are above or below corresponding ones of the magnetoresistive sensor units and are configured to convert the Z-axis magnetic field into the opposite X-axis directions for sensing by the corresponding ones of the magnetoresistive sensing units;
• wherein the flux guide devices are separated into two sets of respective one or more flux guide devices, wherein the two sets include a first set of the one or more flux guide devices in the first region and a second set of the one or more flux guide devices in the second region, wherein the two sets are symmetrically positioned about a Y-axis line of symmetry between the two sets,
• wherein the magnetoresistive sensor units are electrically interconnected into a full-bridge gradiometer having four full-bridge arms, wherein each of the full-bridge arms in the full-bridge gradiometer includes a linear arrangement of magnetoresistive sensor units extending in the Y-axis direction,
• wherein the four full-bridge arms include a first full-bridge arm connected to a second full-bridge arm at a first node, the second full-bridge arm connected to a third full-bridge arm at a second node, the third full-bridge arm connected to a fourth full-bridge arm at a third node, and the fourth full-bridge arm connected to the first full-bridge arm at a fourth node, and
• wherein opposite ones of the four full-bridge arms are not connected at one of the first, second, third and fourth nodes, are respectively positioned above or below the first set of one or more flux guide devices in the first region and the second set of one or more flux guide devices in the second region and are separated in the X-axis direction by the gradient feature distance, wherein the opposite ones of the four full-bridge arms include the first and second subsets of magnetoresistive sensor units, respectively, having opposite pin layer orientations.