Micro-electromechanical system (MEMS) based current and magnetic field sensor having improved sensitivities
View Patent ↗A micro-electromechanical system (MEMS) based current & magnetic field sensor includes a MEMS-based magnetic field sensing component a structural component comprising a silicon substrate and a compliant layer comprising a material selected from the group consisting of silicon dioxide and silicon nitride, a magnetic-to-mechanical converter coupled to the structural component to provide a mechanical indication of the magnetic field, and a strain responsive component coupled to the structural component to sense the mechanical indication and to provide an indication of the current in the current carrying conductor in response thereto.
1. A micro-electromechanical system (MEMS) current and magnetic field sensor for sensing a magnetic field produced by a current carrying conductor, comprising:
a structural component comprising a silicon substrate, and a compliant layer comprising a material selected from the group consisting of silicon dioxide and silicon nitride;
a magnetic-to-mechanical converter coupled to the structural component to provide a mechanical indication of the magnetic field; and
a strain responsive component coupled to the structural component to sense the mechanical indication and to provide an indication of the current in the current carrying conductor in response thereto.
2. The micro-electromechanical system of claim 1 , wherein the compliant layer comprises at least one low stress silicon layer having a residual stress of less than about 100 mega pascals.
3. The micro-electromechanical system current and magnetic field sensor of claim 2 , wherein the low stress silicon region comprises a first silicon nitride layer.
4. The micro-electromechanical system current and magnetic field sensor of claim 3 , wherein the low stress silicon region further comprises a second silicon nitride layer of formula Si x N y where the ratio x:y is between about 0.75 and 1.
5. The micro-electromechanical system current and magnetic field sensor of claim 4 , wherein the ratio of x:y is equal to 1.
6. The micro-electromechanical system current and magnetic field sensor of claim 4 , wherein the ratio of x:y is equal to 0.9.
7. The micro-electromechanical system current and magnetic field sensor of claim 4 , wherein the ratio of x:y is equal to 0.8.
8. The micro-electromechanical system current and magnetic field sensor of claim 4 , wherein the ratio of x:y is equal to 0.75.
9. The micro-electromechanical system current and magnetic field sensor of claim 4 , wherein the first silicon nitride layer comprises a thickness of about 100 Angstrom to about 500 Angstrom and the second silicon nitride layer comprises a thickness of about 1000 Angstroms to about 10000 Angstroms.
10. The micro-electromechanical system current and magnetic field sensor of claim 1 , wherein the strain responsive component comprises a piezo resistive element.
11. The micro-electromechanical system current and magnetic field sensor of claim 10 , further comprising an adhesion layer between the piezo resistive element and the low stress silicon region.
12. The micro-electromechanical system current and magnetic field sensor of claim 11 , wherein the adhesion layer comprises at least one material selected from the group consisting of chromium, titanium, and tungsten and combinations and alloys thereof.
13. The micro-electromechanical system current and magnetic field sensor of claim 1 , wherein the structural component comprises a spring element selected from the group consisting of a cantilever, a deflectable membrane, a torsion element and combinations thereof.
14. The micro-electromechanical system current and magnetic field sensor of claim 13 , wherein the strain responsive component comprises a strain concentrator.
15. The micro-electromechanical system current and magnetic field sensor of claim 1 , wherein the structural component is configured to register a bending action responsive to the mechanical indication from the magnetic-to-mechanical converter.
16. The micro-electromechanical system current and magnetic field sensor of claim 1 , wherein the structural component is configured to register a bending action and a twisting action responsive to the mechanical indication from the magnetic-to-mechanical converter.
17. The micro-electromechanical system current and magnetic field sensor of claim 16 , wherein the structural component comprises:
a first spring element; and
a torsion element coupled to the spring element, wherein the first spring element is displaced about the torsion element responsive to the mechanical indication to concurrently effect the bending action and the twisting action.
18. The micro-electromechanical system current and magnetic field sensor of claim 17 , further comprising a hinge element coupled between the spring element and the torsion element such that as the spring element is displaced responsive to the mechanical indication, the bending action is registered by the hinge element and the twisting action is concurrently registered by the torsion element.
19. The micro-electromechanical system current and magnetic field sensor of claim 18 , wherein the strain responsive component comprises a piezo resistive device coupled to the torsion element.
20. The micro-electromechanical system current and magnetic field sensor of claim 16 , wherein the structural component comprises:
a spring element having a first end configured to experience a first stress responsive to the mechanical indication and a second end configured to receive a second stress responsive to the mechanical indication, wherein the second stress is substantially opposite in direction to the first stress; and
a torsion element coupled to the spring element and about which the first and second ends of the spring element are displaced in response to the first and second stresses, wherein the torsion element is configured to register at least the twisting action.
21. The micro-electromechanical system current and magnetic field sensor of claim 20 , further comprising a first hinge element coupled between the first end of the spring element and the torsion element and a second hinge element coupled between the second end of the spring element and the torsion element.
22. The micro-electromechanical system current and magnetic field sensor of claim 21 , wherein the strain responsive component comprises at least one piezo resistive device coupled to the torsion element.
23. A method for fabricating a micro-electromechanical system (MEMS) magnetic field sensing component comprising:
providing a substrate including a compliant layer comprising a material selected from the group consisting of silicon dioxide and silicon nitride;
forming a strain responsive component on the substrate;
forming a magnetic-to-mechanical converter on the substrate; and
removing at least a portion of the substrate to release a spring element formed at least partly by the compliant layer.
24. The method of claim 23 , wherein the compliant layer comprises at least one low stress silicon layer having a residual stress of less than about 100 mega pascals.
25. The method of claim 23 , wherein providing a substrate including at least one low stress silicon layer comprises:
providing a silicon substrate; and
coating the silicon substrate with a low stress silicon layer wherein the low stress silicon layer comprises a material selected from the group consisting of silicon dioxide and silicon nitride.
26. The method of claim 25 , wherein removing at least a portion of the substrate to form a spring element comprises:
removing from a first side of the substrate at least a portion of the substrate located at least partially below the spring element; and
removing from a second side of the substrate a portion of the low stress silicon layer such that the spring element is released.
27. The method of claim 23 , wherein the low stress silicon layer comprises silicon nitride of formula Si x N y where the ratio of x:y is equal to a value within the range of about 0.75 to 1.
28. The method of claim 27 , wherein the ration of x:y is a discrete value selected from the group consisting of 0.75, 0.8, 0.9, and 1.
29. The method of claim 23 , wherein forming a strain responsive component on the substrate comprises:
depositing a layer of amorphous polysilicon on an upper side of the substrate; and
doping the polysilicon to create a piezo resistive element out of the polysilicon.
30. The method of claim 29 , wherein the layer of polysilicon has a thickness of about 2500 A.
31. The method of claim 23 , wherein forming a magnetic-to-mechanical converter on the substrate comprises:
depositing an adhesion layer on the substrate; and
depositing a conductive material on top of the adhesion layer.
32. The method of claim 31 , wherein the adhesion layer comprises at least one material selected from the group consisting of chromium, titanium, and tungsten and combinations and alloys thereof, and the conductive metal comprises at least one material selected from the group consisting of gold and polysilicon.