Microfabricated system for magnetic field generation and focusing

• US 20050275497A1
• Filed: 11/12/2004
• Published: 12/15/2005
• Est. Priority Date: 06/09/2004
• Status: Active Grant

• Current Assignee: Agency For Science Technology and Research, Nanyang Technological University
• Original Assignee: Agency For Science Technology and Research
• Inventors: Ramadan, Qasem, Yu, Chen, Samper, Victor, Poenar, Daniel Puiu
• Granted Patent: US 7,791,440 B2
• Time in Patent Office: Days
• US Class Current: 336/200
• CPC Class Codes: H01F 2007/062 Details of terminals or connectors for electromagnets
• CPC Class Codes: H01F 2007/068 using printed circuit coils
• CPC Class Codes: H01F 2017/0086 on semiconductor substrate inductors for integrated circuits H01L28/10
• CPC Class Codes: H01F 41/046 structurally combined with ferromagnetic material
• CPC Class Codes: H01F 5/003 Printed circuit coils
• CPC Class Codes: H01H 50/005 using micromechanics
• CPC Class Codes: H01L 23/5227 Inductive arrangements or effects of, or between, wiring layers other inductive arrangements H01L23/645
• CPC Class Codes: H01L 23/645 Inductive arrangements H01L23/647, H01L23/66 take precedence
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 2924/3011 Impedance

Abstract

A method of forming, in or on a Si substrate, planar micro-coils with coil windings of high aspect ratio (>3) and a wide variety of geometric shapes. The micro-coils may be formed on a Si substrate and be embedded in a dielectric, or they may be formed in trenches within a Si substrate. The micro-coils may have field enhancing ferromagnetic pillars rising above the micro-coil plane, formed at positions of maximum magnetic field strength and the micro-coils may also include magnetic layers formed beneath the substrate and contacting the pillars to form a substantially closed pathway for the magnetic flux. The substrate may be thinned to membrane proportions. These micro-coils produce strong magnetic fields with strong field gradients and can be used in a wide variety of processes that involve the exertion of strong magnetic forces at small distances or the creation of magnetic wells for trapping and manipulating small particles.

Claims

1. A micro-coil device for the generation, focusing and manipulation of magnetic fields comprising:

a substrate having an upper and a lower surface;

a planar micro-coil, formed of a plated conductor having an aspect ratio greater than 3/1, said micro-coil being formed in a variety of geometrical shapes on the upper surface of said substrate or in a trench formed through said upper surface and said micro-coil having at least two ends;

a passivating oxide layer formed over said micro-coil;

a dielectric layer formed over said oxide layer; and

bonding pads for making electrical connections to said micro-coil formed on said coil ends or on conducting leads connected to said coil ends.

2. The device of claim 1 wherein the substrate is a silicon wafer having plane, parallel upper and lower surfaces, the upper surface being covered by a first layer of oxide and the lower surface being covered by a second layer of oxide and wherein said linear micro-coil is formed within a trench formed through said first oxide layer and terminating within said wafer.

3. The device of claim 2 wherein said trench has a width of approximately 3 microns and a depth of approximately 10 microns to provide a micro-coil of aspect ratio approximately 10/3.

4. The device of claim 1 further comprising at least one pillar formed of ferromagnetic material having a high permeability, said pillar having an upper and lower end, said pillar being located at a position of maximum magnetic field strength generated by the micro-coil and the lower end of said pillar contacting a patterned metal base formed on said oxide and the upper end of said pillar extending through said dielectric layer.

5. The device of claim 4 wherein said pillar is formed of the electroless plated ferromagnetic material NiCoP and said patterned base is a patterned bi-layer comprising a layer of Al formed on a layer of Ti.

6. The device of claim 1 wherein said dielectric layer is a layer of BCB formed to a thickness between approximately 2 and 5 microns.

19. The device of claim 1, wherein the coil is shaped as a curved spiral, a square spiral, a meander coil with rectangular loops, a pair of interdigitated meander coils, a pair of independent concentric circular spirals wherein an inner spiral is formed entirely within an outer spiral, a pair of interdigitated circular spirals, a meander coil with small rectangular loops formed within the larger loops, a meander coil with small circular or elliptical loops formed within the larger loops, a semi-spiral coil, an array of spirals having a common central axis, or as arrays of such shapes connected in series or in parallel.

22. The device of claim 1 wherein the bonding pads are formed as a patterned bilayer of Ti/Al formed over a Cu mesh of intersecting Cu filled trenches and are connected directly to said micro-coil ends or to conducting bridging leads that are connected to similar bonding-pads formed on said micro-coil ends.

7. A micro-coil device that includes a dielectric embedded micro-coil, for the generation, focusing and manipulation of magnetic fields comprising:

a substrate having an upper and a lower surface;

a planar linear micro-coil, formed of a plated conductor having an aspect ratio greater than 3/1, formed in a variety of geometrical shapes on the upper surface of said substrate, said coil having at least two ends;

a dielectric layer formed over said micro-coil and conformally covering said micro-coil; and

bonding pads for making electrical connections to said micro-coil, connected to said coil ends or to conducting leads that are connected to said coil ends.

8. The device of claim 7 wherein the substrate is a silicon wafer having plane, parallel upper and lower surfaces, the upper surface being covered by a first layer of oxide and the lower surface being covered by a second layer of oxide.

9. The device of claim 7 wherein said micro-coil is formed of plated Cu to a width of approximately 3 microns and a height of approximately 10 microns to provide an aspect ratio of approximately 10/3.

10. The device of claim 7 wherein a cavity is formed through said lower substrate surface and extends within said substrate to terminate beneath said upper substrate surface, said cavity removing a substantial portion of the substrate, thereby thinning the substrate and rendering it a flexible membrane.

11. The device of claim 7 further comprising at least one pillar formed of ferromagnetic material, said pillar having an upper and lower end, said pillar being formed at a position of maximum magnetic field strength generated by the micro-coil and the lower end of said pillar contacting a patterned metal base formed on said upper substrate surface and the upper end of said pillar extending above said dielectric layer.

12. The device of claim 10 further comprising at least one pillar formed of ferromagnetic material, said pillar having an upper and lower end, said pillar being formed at a position of maximum magnetic field strength generated by the micro-coil and the lower end of said pillar contacting a patterned metal base formed on said upper substrate surface and the upper end of said pillar extending above said dielectric layer.

13. The device of claim 11 wherein said pillar is formed of the electroless plated ferromagnetic material NiCoP and said patterned base is a patterned bilayer comprising a layer of Al formed on a layer of Ti.

14. The device of claim 11 wherein said pillar is formed to a height between approximately 10 and 50 microns and said patterned base has horizontal dimensions between approximately 10 and 90 microns.

15. The device of claim 12 wherein said pillar is formed of the electroless plated ferromagnetic material NiCoP and said patterned base is a patterned bi-layer comprising a layer of Al formed on a layer of Ti.

16. The device of claim 12 wherein said pillar is formed to a height between approximately 10 and 50 microns and said patterned base has horizontal dimensions between approximately 10 and 90 microns.

17. The device of claim 7 wherein the dielectric layer is a layer of BCB formed to a thickness between approximately 15 and 20 microns.

18. The device of claim 10 wherein the dielectric layer is a layer of BCB formed to a thickness between approximately 15 and 20 microns.

20. The device of claim 7, wherein the coil is shaped as a curved spiral, a square spiral, a meander coil with rectangular loops, a pair of interdigitated meander coils, a pair of independent concentric circular spirals wherein an inner spiral is formed entirely within an outer spiral, a pair of interdigitated circular spirals, a meander coil with small rectangular loops formed within the larger loops, a meander coil with small circular or elliptical loops formed within the larger loops, a semi-spiral coil, an array of spirals having a common central axis, or as arrays of such shapes connected in series or in parallel.

21. The device of claim 10, wherein the coil is shaped as a curved spiral, a square spiral, a meander coil with rectangular loops, a pair of interdigitated meander coils, a pair of independent concentric circular spirals wherein an inner spiral is formed entirely within an outer spiral, a pair of interdigitated circular spirals, a meander coil with small rectangular loops formed within the larger loops, a meander coil with small circular or elliptical loops formed within the larger loops, a semi-spiral coil, an array of spirals having a common central axis, or as arrays of such shapes connected in series or in parallel.

23. The device of claim 7 wherein the bonding pads are formed as a patterned bilayer of Ti/Al formed over a Cu mesh of intersecting Cu filled trenches and are connected directly to said micro-coil ends or to conducting bridging leads that are connected to similar bonding-pads formed on said micro-coil ends.

24. The device of claim 10 wherein the bonding pads are formed as a patterned bilayer of Ti/Al formed over a Cu mesh of intersecting Cu filled trenches and are connected directly to said micro-coil ends or to conducting bridging leads that are connected to similar bonding-pads formed on said micro-coil ends.

25. A micro-coil device having a micro-coil, a ferromagnetic pillar and a ferromagnetic backplate for the generation, focusing and manipulation of magnetic fields comprising:

a substrate having an upper and a lower surface;

a planar linear micro-coil, formed of a plated conductor having an aspect ratio greater than 3/1, said micro-coil being formed in a variety of geometrical shapes on the upper surface of said substrate or in a trench formed through said upper surface, said coil having at least two ends;

a cavity within the substrate, said cavity formed through an opening in the lower surface of said substrate and said cavity having sides and an upper surface within said substrate;

a ferromagnetic plated layer formed conformally filling said cavity, a lower surface of said layer being substantially co-planar with the lower surface of the substrate and an upper surface of said layer contacting the upper surface of said cavity;

an opening formed through the upper surface of the substrate, said opening extending through the substrate and exposing a portion of said ferromagnetic layer upper surface;

a ferromagnetic plated pillar formed within said opening, a lower end of said pillar contacting said exposed portion of the ferromagnetic layer and an upper end of said pillar extending above said substrate upper surface;

bonding pads for making electrical connections to said micro-coil connected to the ends of said micro-coil or to conducting leads that are connected to the ends of said micro-coil.

26. The device of claim 25 wherein the substrate is a silicon wafer having plane, parallel upper and lower surfaces, the upper surface being covered by a first layer of oxide and the lower surface being covered by a second layer of oxide and wherein said linear micro-coil is formed within a trench formed through said first oxide layer and terminating within said wafer.

27. The device of claim 26 wherein said trench has a width of approximately 3 microns and a depth of approximately 10 microns to provide a micro-coil of aspect ratio approximately 10/3.

28. The device of claim 26 wherein the micro-coil is covered by an oxide passivation layer.

29. The device of claim 25, wherein the coil is shaped as a curved spiral, a square spiral, a meander coil with rectangular loops, a pair of interdigitated meander coils, a pair of independent concentric circular spirals wherein an inner spiral is formed entirely within an outer spiral, a pair of interdigitated circular spirals, a meander coil with small rectangular loops formed within the larger loops, a meander coil with small circular or elliptical loops formed within the larger loops, a semi-spiral coil, an array of spirals having a common central axis, or as arrays of such shapes connected in series or in parallel.

30. The device of claim 25 wherein the backplate and pillar are formed of electroless plated NiCoP.

31. The device of claim 30 wherein the pillar is between approximately 55 and 100 microns in length and between approximately 10 and 100 microns in diameter.

32. The device of claim 25 wherein the bonding pads are formed as a patterned bilayer of Ti/Al formed over a Cu mesh of intersecting Cu filled trenches and are connected directly to said micro-coil ends or to conducting bridging leads that are connected to similar bonding-pads formed on said micro-coil ends.

33. A method of forming a micro-coil device for the generation, focusing and manipulation of magnetic fields comprising:

providing a substrate having upper and lower surfaces;

forming a geometrically patterned linear trench of depth d and width w, wherein d/w>

3, through said upper surface, said trench having side and bottom surfaces and at least two ends, said trench to be used in the formation of a micro-coil;

forming a grid of orthogonally intersecting trenches at the ends of said linear trench and at positions peripherally disposed thereto, said grid of trenches to be used in the formation of inner bonding pads and minor and major outer bonding pads;

conformally covering said upper surface and the side and bottom surfaces of said linear trench and said grid of trenches with a three-layer sequential deposition further comprising;

forming a first layer of oxide to a thickness t_o;

forming on said first oxide layer a barrier layer to a thickness t_b;

forming on said barrier layer a seed layer to a thickness t_s;

forming a first layer of conductor over said upper substrate surface, said layer also conformally covering said three layer deposition and filling all said trenches in a void-free manner;

removing that portion of said first conductor layer and sequential three-layer deposition that lies on the upper substrate surface, retaining that portion of said first conductor layer within said trenches, forming, thereby, a micro-coil conformally filling the trench, having ends that correspond to the ends of the trench and having an upper surface that is co-planar with the upper substrate surface and also forming a conductor filled mesh within each of said grid of trenches;

forming a second layer of oxide on said upper substrate, mesh and micro-coil surfaces, said layer being a passivation layer;

removing a portion of said second oxide layer above each mesh whereat subsequent electrical connections will be made, exposing clean conductor surfaces at those positions;

forming a second layer of conducting material on said second oxide layer, said second layer of conducting material contacting said mesh, said layer electrically contacting said micro-coil and forming a bonding-pad and said layer extending between bonding-pads;

coating the upper surface of the substrate and said bonding pads with a layer of dielectric polymer;

removing a portion of said polymer layer over the bonding pad.

34. The method of claim 33 wherein the substrate is a Si wafer having substantially planar and parallel upper and lower surfaces, and wherein a third oxide layer is formed on both of said surfaces.

35. The method of claim 33, wherein the geometrically patterned trench is shaped as a curved spiral, a square spiral, a meander coil with rectangular loops, a pair of interdigitated meander coils, a pair of independent concentric circular spirals wherein an inner spiral is formed entirely within an outer spiral, a pair of interdigitated circular spirals, a meander coil with small rectangular loops formed within the larger loops, a meander coil with small circular or elliptical loops formed within the larger loops, a semi-spiral coil, an array of spirals having a common central axis, or as arrays of such shapes connected in series or in parallel.

36. The method of claim 33 wherein the ratio d/w=10/3

37. The method of claim 33 wherein said conductor layer is a layer of Cu deposited by electroplating.

38. The method of claim 33 wherein t_o is approximately 1000 angstroms.

39. The method of claim 33 wherein the first barrier layer is a bi-layer of Ti/TiN, the TiN being formed to a thickness of approximately 300 angstroms, the Ti being formed to a thickness of approximately 200 angstroms and t_b, therefore, being approximately 500 angstroms.

40. The method of claim 33 wherein each of said bonding pads is formed as a conducting bilayer of horizontal cross-sectional surface area approximately 500 microns by 500 microns formed on a Cu mesh, wherein the bilayer comprises a layer of Ti formed to a thickness between approximately 200 and 2000 angstroms on which is formed a layer of Al of thickness between approximately 0.5 and 3 microns and wherein said Cu mesh comprises a grid of orthogonally intersecting trenches, of depth d and width w and filled with said plated Cu layer.

41. The method of claim 33 wherein the oxide passivation layer is approximately 1000 angstroms thick.

42. The method of claim 33 wherein said bonding pads are electrically connected to said micro-coil by Al bridging leads when said connection is to an end of the micro-coil that is interior to the periphery of said micro-coil.

43. The method of claim 33 further including the formation of a patterned bilayer on said oxide passivation layer as a base for the electroless plating of a ferromagnetic pillar, said patterned bilayer comprising a layer of Ti formed to a thickness between approximately 200 and 2000 angstroms on which is formed a layer of Al of thickness between approximately 0.5 and 3 microns.

44. The method of claim 43 wherein an opening above said pillar base is formed through said dielectric polymer layer and a ferromagnetic pillar is plated onto said base by electroless plating, said pillar passing through said opening and extending above said dielectric polymer layer.

45. The method of claim 44 wherein said ferromagnetic pillar is a pillar formed of NiCoP.

46. A method of forming a dielectric-embedded micro-coil and pillar device for the generation, focusing and manipulation of magnetic fields comprising:

providing a substrate having an upper and a lower surface;

forming a patterned layer of conductor over the upper substrate surface, said layer to act as a base for a subsequent plating process;

forming a first dielectric layer, to a thickness t₁, over the upper substrate surface and said patterned conductor layer;

forming an opening through the first dielectric layer, said opening exposing an upper surface of the patterned conductor layer;

plating by an electroless process, within said opening, a first portion of a ferromagnetic pillar on the patterned conductor layer, the height of said first pillar portion being t₁, the thickness of said first dielectric layer;

removing the first dielectric layer;

depositing a seed layer on the substrate surface, said seed layer being disposed about the patterned conductor layer, being thinner than said patterned conductor layer and being contiguous with it;

forming a second dielectric layer over the seed layer, the thickness of the second dielectric layer being t₂, which is greater than t₁;

forming a micro-coil trench through said second dielectric layer, said trench being patterned in a linear geometric shape having at least two ends, said trench terminating at said seed layer and said trench having a width w₂ that produces an aspect ratio of t₂/w₂>

3;

forming an array of trenches at the ends of said micro-coil trench and at positions peripherally disposed thereto, said array of trenches to be used in the formation of bonding pads;

forming a micro-coil by electroplating, on said seed layer, a void-free conducting layer conformally filling said trench, said micro-coil having ends corresponding to said trench ends and said conducting layer also filling said array of trenches to form a mesh;

removing a portion of the second dielectric layer above the pillar, exposing, thereby, an upper surface of said pillar;

forming, by electroless plating, a second pillar portion on said exposed first pillar portion upper surface, the total height of said first and second pillar portions being t₄;

removing the second dielectric layer and the seed layer, leaving only those portions of the seed layer that are beneath said micro-coil;

forming a third dielectric layer with thickness t₃ that is greater than t₂ but less than t₄, said third layer thereby conformally covering said micro-coil but not completely covering said second pillar portion;

forming openings in the third dielectric layer over said mesh, thereby exposing said mesh;

cleaning said mesh; and

forming an electrically conducting layer in said openings, the layer electrically contacting said mesh and forming a bonding pad.

47. The method of claim 46 wherein the patterned layer of conductor is a bilayer comprising a layer of Ti of thickness between approximately 200 and 2000 angstroms on which is formed a layer of Al of thickness between approximately 0.5 and 3 microns.

48. The method of claim 46, wherein the trench in said second dielectric layer is shaped as a curved spiral, a square spiral, a meander coil with rectangular loops, a pair of interdigitated meander coils, a pair of independent concentric circular spirals wherein an inner spiral is formed entirely within an outer spiral, a pair of interdigitated circular spirals, a meander coil with small rectangular loops formed within the larger loops, a meander coil with small circular or elliptical loops formed within the larger loops, a semi-spiral coil, an array of spirals having a common central axis, or as arrays of such shapes connected in series or in parallel.

49. The method of claim 46 wherein said first dielectric layer is a layer of BCB formed to a thickness, t₁ between approximately 12 and 15 microns, said second dielectric layer is a layer of BCB formed to a thickness t₂ between approximately 5 microns and 20 microns and said third dielectric layer is formed to a thickness t₄ between approximately 15 and 25 microns.

50. The method of claim 46 wherein said high aspect ratio is 10/3.

51. The method of claim 46 wherein w₂ is approximately 3 microns and t₂ is approximately 10 microns.

52. The method of claim 46 wherein the conducting layer is a layer of electroplated Cu of thickness between approximately 15 and 20 microns and said seed layer is a Cu seed layer of thickness between approximately 500 and 2000 angstroms.

53. The method of claim 46 wherein the pillar is formed of the electroless plated ferromagnetic material NiCoP.

54. The method of claim 46 wherein the bonding pads on ends of said micro-coil are formed as a bi-layer comprising a layer of Ti of thickness between approximately 200 and 2000 angstroms on which is formed a layer of Al of thickness between approximately 0.5 and 3 microns.

55. The method of claim 46 wherein said substrate is a Si wafer having plane, parallel upper and lower surfaces, on each of which surfaces are formed a layer of Si oxide on which is formed a layer of Si nitride.

56. The method of claim 46 further comprising thinning the substrate by etching, through the lower substrate surface to a depth below the upper substrate surface to produce a flexible membrane.

57. A method of forming a dielectric-embedded micro-coil device for the generation, focusing and manipulation of magnetic fields comprising:

providing a substrate having an upper and a lower surface;

depositing a seed layer on the substrate surface;

forming a first dielectric layer over the seed layer, the thickness of the first dielectric layer being t₁;

forming a micro-coil trench through said first dielectric layer, said trench being patterned in a linear geometric shape having at least two ends, said trench terminating at said seed layer and said trench having a width w₁ that produces an aspect ratio of t₁/w₁>

3;

forming an array of trenches at the ends of said micro-coil trench and at positions peripherally disposed thereto, said array of trenches to be used in the formation of bonding pads;

forming a micro-coil by electroplating, on said seed layer, a void-free conducting layer conformally filling said trench, said micro-coil having ends corresponding to said trench ends and said conducting layer also filling said array of trenches to form a mesh;

removing the first dielectric layer and the seed layer, leaving only those portions of the seed layer that are beneath said micro-coil and mesh;

forming a second dielectric layer with thickness t₂ that is greater than t₁, said second dielectric layer thereby conformally covering said micro-coil and mesh;

forming openings in the second dielectric layer over said mesh, thereby exposing said mesh;

cleaning said mesh; and

forming an electrically conducting layer in said openings, the layer electrically contacting said mesh and forming a bonding pad.

58. The method of claim 57, wherein the geometrically patterned trench is shaped as a curved spiral, a square spiral, a meander coil with rectangular loops, a pair of interdigitated meander coils, a pair of independent concentric circular spirals wherein an inner spiral is formed entirely within an outer spiral, a pair of interdigitated circular spirals, a meander coil with small rectangular loops formed within the larger loops, a meander coil with small circular or elliptical loops formed within the larger loops, a semi-spiral coil, an array of spirals having a common central axis, or as arrays of such shapes connected in series or in parallel.

59. The method of claim 57 wherein said first dielectric layer is a layer of BCB formed to a thickness, t₁ between approximately 15 and 20 microns and said second dielectric layer is a layer of BCB formed to a thickness t₂ between approximately 15 microns and 25 microns.

60. The method of claim 57 wherein said high aspect ratio is 10/3.

61. The method of claim 57 wherein w₁ is approximately 3 microns and t₁ is approximately 10 microns.

62. The method of claim 57 wherein the micro-coil conducting layer is a layer of electroplated Cu of thickness between approximately 10 and 20 microns and it is deposited on a Cu seed layer of thickness between approximately 500 and 2000 angstroms.

63. The method of claim 57 wherein said substrate is a Si wafer having plane, parallel upper and lower surfaces, on each of which surfaces are formed a layer of Si oxide over which is formed a layer of Si nitride.

64. The method of claim 57 further comprising thinning the substrate by etching, through the lower substrate surface to a depth below the upper substrate surface to produce a flexible membrane.

65. A method of forming a micro-coil, pillar and backplate within a substrate comprising:

providing a substrate having an upper and lower surface;

forming, through said upper surface, a linear, geometrically patterned micro-coil trench having at least two ends, having a depth d and width w, wherein the aspect ratio, d/w is greater than 3;

forming an array of trenches at the ends of said micro-coil trench and at positions peripherally disposed thereto, said array of trenches to be used in the formation of bonding pads;

conformally covering said upper substrate surface and the interior of said micro-coil trench and array of trenches with a three-layer sequential deposition further comprising;

forming a first layer of oxide to a thickness t_o;

forming on said first oxide layer a barrier layer to a thickness t_b;

forming on said barrier layer a seed layer to a thickness t_s;

forming a layer of conductor over said seed layer, said conductor layer also conformally filling the trenches in a void-free manner;

removing that portion of the conductor that lies on the upper substrate surface, retaining that portion of the conductor within the micro-coil trench and array of trenches, forming, thereby, a micro-coil conformally filling the trench, having ends that coincide with the ends of the trench and having an upper surface that is co-planar with the upper substrate surface and also forming a mesh within the array of trenches;

forming a second oxide layer over said substrate surface and co-planar micro-coil and mesh surfaces;

forming a cavity through the lower surface of said substrate, said cavity extending from the lower surface towards the upper surface and penetrating into the interior of the substrate to an approximate depth t_c;

forming a magnetic backplate within said cavity;

forming a plurality of openings within said second oxide layer, a first opening exposing a central portion of said substrate upper surface and the remainder of said openings exposing upper surface portions of the mesh;

cleaning the upper surface portions of said mesh; and

forming an electrically conducting layer in said openings, the layer electrically contacting said mesh and forming a bonding pad;

forming a dielectric layer of thickness t_d over the upper surface of said oxide layer, said dielectric layer having an upper surface;

forming a second trench extending vertically through said dielectric layer, said trench passing through the first opening in the oxide layer, through the Si substrate and terminating at the upper surface of said backplate, whereat it exposes a corresponding portion of said backplate upper surface;

forming an electroless plated pillar conformally filling said second trench, said pillar being plated onto said exposed upper surface portion of the backplate, said pillar extending vertically upward from the backplate and terminating at the upper surface of said dielectric layer; and

then

removing the dielectric layer.

66. The method of claim 65, wherein the geometrically patterned trench is shaped as a curved spiral, a square spiral, a meander coil with rectangular loops, a pair of interdigitated meander coils, a pair of independent concentric circular spirals wherein an inner spiral is formed entirely within an outer spiral, a pair of interdigitated circular spirals, a meander coil with small rectangular loops formed within the larger loops, a meander coil with small circular or elliptical loops formed within the larger loops, a semi-spiral coil, an array of spirals having a common central axis, or as arrays of such shapes connected in series or in parallel.

67. The method of claim 65 wherein said second oxide layer is formed to a thickness between approximately 500 angstroms and 1 micron.

68. The method of claim 65 wherein the pillar is formed of electroless plated NiCoP.

69. The method of claim 65 wherein the backplate is formed of electroless plated NiCoP.

70. The method of claim 65 wherein the ratio d/w is approximately 10/3.

71. The method of claim 65 wherein d is approximately 10 microns and w is approximately 3 microns.

72. The method of claim 65 wherein said conductor layer is a layer of Cu deposited by electroplating.

73. The method of claim 65 wherein t_o is approximately 1000 angstroms.

74. The method of claim 65 wherein the barrier layer is a bi-layer of Ti/TiN, the TiN being formed to a thickness of approximately 300 angstroms, the Ti being formed to a thickness of approximately 200 angstroms and t_b, therefore, being approximately 500 angstroms.

75. The method of claim 65 wherein the electrically conducting layer forming the bonding pads is a bilayer comprising a layer of Ti formed to a thickness between approximately 200 angstroms and 2000 angstroms on which is formed a layer of Al formed to a thickness between approximately 0.5 microns and 3 microns.

76. The method of claim 65 wherein the substrate lower surface is etched to a depth of approximately 550 microns.

77. The method of claim 65 wherein the substrate lower surface is etched using KOH, TMAH, NaOH, EDP, HNA, RIE, DRIE or plasma etching as an etchant.

78. The method of claim 65 wherein the dielectric layer is a layer of BCB formed to a thickness, t_d, between approximately 10 microns and 50 microns.

79. A method of micro-self-assembly using micro-coils comprising:

providing a plurality of micro-components;

providing a substrate having a plurality of receptor sites at which said micro-components are to be positioned and affixed;

coating at least a portion of said micro-components with a magnetic material, making said micro-components subject to magnetic forces;

positioning a plurality of micro-coils at locations on or within said substrate, a first portion of said micro-coils being positioned at said receptor sites, and a second portion of said micro-coils being positioned along paths leading to said receptor sites, said micro-coils capable of producing magnetic fields having gradients and potential wells when electrically energized;

immersing said substrate and said micro-components in a fluid;

sequentially energizing said micro-coils or a set of selected micro-coils, thereby guiding a selected micro-component or a set of such micro-components to a receptor site or set of receptor sites and trapping said micro-components at said receptor site or sites;

affixing, using a bonding process, said micro-component to said receptor site while said micro-coil remains energized.