Methods of manufacturing a magnetic field sensor
A semiconductor process integrates three bridge circuits, each include magnetoresistive sensors coupled as a Wheatstone bridge on a single chip to sense a magnetic field in three orthogonal directions. The process includes various deposition and etch steps forming the magnetoresistive sensors and a plurality of flux guides on one of the three bridge circuits for transferring a “Z” axis magnetic field onto sensors orientated in the XY plane.
1. A method of manufacturing an integrated magneto-resistive sensor, the method comprising:
forming a first plurality of magneto-resistive sensor elements on a first insulating material, wherein forming the first plurality of magneto-resistive sensor elements includes:
forming a first reference layer,
forming a first intermediate layer on the first reference layer, and
forming a first sensing layer on the first intermediate layer;
forming a first bridge circuit by electrically interconnecting the magneto-resistive sensor elements of the first plurality of magneto-resistive sensor elements;
depositing a second insulating material over the first plurality of magneto-resistive sensor elements;
etching a plurality of first trenches in the second insulating material, wherein each first trench includes at least two side walls, and wherein each first trench is juxtaposed to and laterally offset from an associated magneto-resistive sensor element of the first plurality of magneto-resistive sensor elements; and
forming a plurality of first flux guides in the plurality of first trenches, wherein each first flux guide includes a magnetic material deposited on the at least two side walls of an associated first trench.
2. The method of claim 1 , wherein the magnetic material is one or more of nickel, a nickel alloy, iron, an iron alloy, cobalt, and a cobalt alloy.
3. The method of claim 1 , wherein the magnetic material comprises a material with a magnetic permeability of greater than 100.
4. The method of claim 1 , wherein the magneto-resistive sensor elements comprise magnetic tunnel junctions.
5. The method of claim 1 , wherein the first reference layer includes a pinning direction; and
wherein forming the first sensing layer of the first plurality of magneto-resistive sensor elements includes:
depositing the magnetic material over the first intermediate layer; and
patterning the magnetic material into the sensing layer, wherein the magnetic material includes an easy axis of a magnetization direction that is orthogonal to the pinning direction of the first reference layer.
6. The method of claim 1 , wherein the first intermediate layer includes an insulating material.
7. The method of claim 1 , wherein forming the plurality of first flux guides in the plurality of first trenches further includes:
back sputtering at least a portion of the magnetic material thereof from the bottom of each first trench and onto the at least two side walls thereof.
8. The method of claim 1 , wherein forming the plurality of first flux guides in the plurality of first trenches further includes:
depositing a dielectric material over the magnetic material and in each trench of the plurality of first trenches.
9. The method of claim 1 , further comprising:
depositing a third insulating material over the second insulating material and the first flux guides.
10. The method of claim 1 , wherein each first flux guide is deposited completely within an associated first trench.
11. The method of claim 1 , wherein forming the plurality of first flux guides in the plurality of first trenches further includes:
depositing a conductive material over the magnetic material and in each trench of the plurality of first trenches.
12. The method of claim 1 , further comprising:
etching a plurality of second trenches in the first insulating material, wherein each second trench includes at least two side walls; and
forming a plurality of second flux guides in the plurality of second trenches by depositing the magnetic material into the plurality of second trenches, wherein each second flux guide includes the magnetic material deposited on the at least two side walls of each second trench, and wherein each magneto-resistive sensor element of the first plurality of magneto-resistive sensor elements is juxtaposed to and laterally offset from an associated second flux guide.
13. The method of claim 1 , further comprising:
forming a second plurality of magneto-resistive sensor elements on the first insulating material, including:
forming a second reference layer having a first pinning direction,
forming a second intermediate layer on the second reference layer, and
forming a second sensing layer on the second intermediate layer; and
forming a second bridge circuit by electrically interconnecting the magneto-resistive sensor elements of the second plurality of magneto-resistive sensor elements.
14. The method of claim 13 , further comprising:
forming a third plurality of magneto-resistive sensor elements on the first insulating material, including:
forming a third reference layer having a second pinning direction that is different from the first pinning direction;
forming a third intermediate layer on the third reference layer, and
forming a third sensing layer on the third intermediate layer; and
forming a third bridge circuit by electrically interconnecting the magneto-resistive sensor elements of the third plurality of magneto-resistive sensor elements.