Title: Fabrication approaches for the formation of planar inductors and transformers
Abstract: This invention relates to the fabrication of planar inductive components whereby the design in cross-section describes a conductor surrounded by magnetic material along the length of the conductor; an electrical insulator is placed between the conductor and the magnetic material. Cases also apply where more than one independent conductor is used. The planar form allows integration of inductive components with integrated circuits. These inductive components can be embedded in other materials. They can also be fabricated directly onto parts.
Patent Number: 6,990,725 Issued on 01/31/2006 to Fontanella, et al.
| Inventors:
|
Fontanella; Mark D. (111 Manor Ave., Wellesley, MA 02482);
Greiff; Paul (2 Cameron Rd., Wayland, MA 01778);
Cardarelli; Donato (16 Ledgetree Rd., Medfield, MA 02052);
Walsh; Joseph G. (1753 Beacon St., #1, Brookline, MA 02445)
|
| Appl. No.:
|
265170 |
| Filed:
|
October 4, 2002 |
| Current U.S. Class: |
29/602.1; 29/604; 29/605; 29/606; 29/829; 156/89.11; 156/89.12; 156/250; 257/531; 336/176; 336/200; 336/229; 438/238; 438/381; 438/788; 438/792 |
| Current Intern'l Class: |
H01F 7/06 (20060101) |
| Field of Search: |
29/6021,604,605,606,829
336/176,200,229
156/891.1,891.2,250,891
257/531
438/238,381,788,792
|
References Cited [Referenced By]
U.S. Patent Documents
| 5062197 | Nov., 1991 | Ngo et al.
| |
| 5479695 | Jan., 1996 | Grader et al.
| |
| 5787071 | Jul., 1998 | Basso et al.
| |
| 6233834 | May., 2001 | Walsh.
| |
| Foreign Patent Documents |
| 01110714 | Apr., 1989 | JP.
| |
Other References
An evaluation of suitability of electromagnetic integration in single switch
single stage unity power factor correction converters Gerber, M.B.; Hofsajer, I.W.;
AFRICON, 1999 IEEE, vol.: 2, Sep. 28-Oct. 1, 1999; pp.: 605-610.
|
Primary Examiner: Tugbang; A. Dexter
Assistant Examiner: Kim; Paul D.
Attorney, Agent or Firm: Dingman; Brian M.
Goverment Interests
STATEMENT OF FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
This invention was made with Government support under contract number DTRA01-99-C-0186
awarded by BMDO. The Government has certain rights in the invention.
Parent Case Text
CROSS REFERENCED TO RELATED APPLICATION
This application claims priority of Provisional application Ser. No. 60/327,486,
filed Oct. 5, 2001 entitled "Fabrication Approaches for the Formation of Planar
Inductors and Transformers".
Claims
What is claimed is:
1. A method of fabricating a planar inductive component having one or more conductive
windings, a magnetic core co-linear with and surrounding all windings, and an insulator
separating each winding from any other winding and from the magnetic core, the
method comprising:
providing a component support member defining a non-magnetic top surface;
sequentially overlaying at least part of the top surface of the support member
with a first layer of magnetic material, a first layer of insulating material,
and a layer of conductive material;
removing portions of the conductive material layer down to the underlying insulating
material to leave the inductive component winding;
overlaying the exposed first layer of insulating material and the winding with
a second layer of insulating material;
creating spaced, elongated, parallel deposition channels through both layers
of insulating material to the underlying first layer of magnetic material, the
deposition channels on opposite sides of and spaced from the winding; and
overlaying the exposed insulating material and the exposed first layer of magnetic
material with magnetic material, to complete the magnetic core.
2. The method of claim 1 wherein the magnetic material overlaying step comprises
depositing a seed conductive layer before overlaying the magnetic material, to
allow electrodeposition of the magnetic material.
3. The method of claim 1 wherein overlaying with magnetic material comprises
filling the deposition channels with magnetic material.
4. The method of claim 1 wherein overlaying with magnetic material comprises
conformal coating.
5. The method of claim 4 wherein the conformal coating comprises a series of
thin magnetic laminations separated by non-magnetic layers.
6. The method of claim 5 wherein the thin non-magnetic layers are also non-conductive.
Description
BACKGROUND OF THE INVENTION
Planar inductors and transformers have many advantages. Such are disclose
in U.S. Pat. No. 6,233,834, the disclosure of which is incorporated herein by reference.
However, approaches for fabricating these planar devices on or in chips would provide
several advantages.
SUMMARY OF THE INVENTION
This invention addresses the fabrication of planar inductive components based
on a linear, thin design topology that enables greater flexibility in how the components
are used, structurally and electrically. The components can be formed in a variety
of ways that suit the application: onto a part of a sensor, integrated with Integrated
Circuits (IC) on the same chip, embedded in circuit boards or device packaging,
embedded within the volume of the IC chip to be accessed through vias, formed as
discrete components for conventional electronics applications.
The inductive components are linear because their inductance varies proportionately
with length. Unlike wire-wound inductive coils that occupy an appreciable volume
on a circuit board location, the linear devices of this invention are planar and
wire-like and can be distributed over available space.
The planar topology of this invention is practical to fabricate thus enabling
large-scale production and low cost.
The inductive components of this invention include inductors, transformers, differential
current transformers (DCT), isolation transformers, chokes, filters, mixers, etc.
This invention features a method of fabricating an embedded planar inductive
component having one or more conductive windings, a magnetic core co-linear with
and surrounding all windings, and an insulator separating each winding from any
other winding and from the magnetic core, the method comprising providing a substrate
defining first and second surfaces; creating one or more spaced, elongated conductive
pads on one surface of the substrate; overlaying the pads and at least part of
the one substrate surface with a first insulating layer; overlaying the first insulator
layer with a first layer of magnetic material; depositing a second insulating layer
on at least part of the other surface of the substrate; creating parallel, spaced,
elongated, magnetic material deposition channels through spaced portions of the
second insulating layer and through the underlying substrate and first insulating
layer, ending at the first layer of magnetic material, with one channel on each
side of and spaced from a pad; creating another parallel channel through the second
insulating layer over and extending to an underlying conductive pad; filling the
magnetic material channels with the magnetic material; filling the channel extending
to the conductive pad with conductive material, to form the winding, the winding
having an exposed surface; creating an insulator parallel to and between the winding
and the magnetic material channels; overlaying at least the exposed surface of
the winding with the insulator to form a third insulating layer; and overlaying
at least the third insulating layer and the magnetic material in the magnetic material
channels with a second layer of magnetic material that is in contact with the magnetic
material in the magnetic material channels, to form the magnetic core.
The magnetic material overlaying steps may each comprise depositing a seed conductive
layer before overlaying the magnetic material, to allow electrodeposition of the
magnetic material. The first and second surfaces of the substrate may each be at
the bottom of wells in the substrate. The first insulating layer may fill one well,
and the second insulating layer may fill the other well. The first layer of magnetic
material may be larger than the first insulating layer, so that it also overlays
a part of the substrate. The second layer of magnetic material may be larger than
the third insulating layer, so that it also overlays a part of the substrate. The
substrate may be conductive, and, before any channel is filled, the exposed substrate
material may be treated to decrease its conductivity. The substrate may comprise
silicon, and the treatment may comprise oxidation. The layers of magnetic material
may each comprise a series of thin magnetic laminations separated by thin non-magnetic,
non-conducting layers.
Also featured is a method of fabricating an embedded planar inductive component
having one or more conductive windings, a magnetic core co-linear with and surrounding
all windings, and an insulator separating each winding from any other winding and
from the magnetic core, the method comprising providing a substrate defining first
and second surfaces; creating one or more spaced, elongated conductive pads on
one surface of the substrate; overlaying the pads and at least part of the one
substrate surface with a first insulating layer; overlaying the first insulator
layer with a first layer of magnetic material; depositing a second insulating layer
on at least part of the other surface of the substrate; creating parallel, spaced,
elongated first deposition channels through spaced portions of the second insulating
layer and through the underlying substrate and the first insulating layer, ending
at the first layer of magnetic material, with one channel on each side of and spaced
from a pad; creating another parallel channel through the second insulating layer
over and extending to an underlying conductive pad; filling the channel extending
to the conductive pad with conductive material, to form the winding, the winding
having an exposed surface; overlaying onto the exposed surface of the winding,
and depositing into the deposition channels, an insulator; creating through the
middle of the deposited insulator in the first deposition channels, a narrower
magnetic material deposition channel extending to the first layer of magnetic material,
to leave the first deposition channels lined with insulator that, along with the
insulator overlaying the exposed surface of the winding, forms a third insulating
layer; and conformally coating at least the second insulating layer with a second
layer of magnetic material that is in contact with the first layer of magnetic
material, to form the magnetic core.
The magnetic material conformal coating step may comprises depositing a seed
conductive layer before conformally coating the magnetic material, to allow electrodeposition
of the magnetic material.
Also featured is a method of fabricating a planar inductive component having
one or more conductive windings, a magnetic core co-linear with and surrounding
all windings, and an insulator separating each winding from any other winding and
from the magnetic core, the method comprising providing a component support member
defining a non-magnetic top surface; sequentially overlaying at least part of the
top surface of the support member with a first layer of magnetic material, a first
layer of insulating material, and a layer of conductive material; removing portions
of the conductive material layer down to the underlying insulating material to
leave the inductive component winding; overlaying the exposed first layer of insulating
material and the winding with a second layer of insulating material; creating spaced,
elongated, parallel deposition channels through both layers of insulating material
to the underlying first layer of magnetic material, the deposition channels on
opposite sides of and spaced from the winding; and overlaying the exposed insulating
material and the exposed first layer of magnetic material with magnetic material,
to complete the magnetic core.
Also featured is a method of fabricating a planar inductive component having
one or more conductive windings, a magnetic core co-linear with and surrounding
all windings, and an insulator separating each winding from any other winding and
from the magnetic core, the method comprising: providing a first layer of magnetic
material covered by a first layer of insulating material, covered by a conductor
layer, covered by a second layer of insulating material, covered by a second layer
of magnetic material; creating parallel, spaced elongated first deposition channels
through the second layers of magnetic material and insulating material, the conductor
layer and the first layer of insulating material, ending at the lower magnetic
layer; depositing into the first channels an insulating material; creating through
the middle of the deposited insulating material in the first channels, narrower
magnetic material deposition channels extending through the entire deposited insulating
material thickness to the lower layer of magnetic material, to leave the first
channels lined with insulating material, and expose the lower layer of magnetic
material; and overlaying the magnetic material deposition channels and the exposed
lower layer of magnetic material with magnetic material, to complete the magnetic core.
Still further, this invention features a method of fabricating a planar inductive
component having one or more conductive windings, a magnetic core co-linear with
and surrounding all windings, and an insulator separating each winding from any
other winding and from the magnetic core, the method comprising providing a substrate
covered by an upper magnetic material layer, covered by the winding encapsulated
along its length with an insulating material to create an intermediate with an
exposed insulating surface; creating parallel, spaced, elongated deposition channels
through the insulating material to the underlying magnetic material layer, the
deposition channels on opposite sides of and spaced from the winding; and overlaying
the exposed insulating material and the exposed underlying magnetic material layer
with magnetic material, to complete the magnetic core.
Also featured is a method of fabricating a planar inductive component having
one or more conductive windings, a magnetic core co-linear with and surrounding
all windings, and an insulator separating each winding from any other winding and
from the magnetic core, the method comprising providing an intermediate comprising
a conductive layer in contact with an insulating material layer overlaid with a
layer of magnetic material defining a series of elongated, spaced gaps through
to the insulating material layer; creating a series of parallel channels from the
gaps, through the adjacent insulating material layer, to the adjacent winding layer;
depositing magnetic material into the channels; removing portions of the winding
layer aligned with the filled channels to leave an exposed surface comprising the
one or more windings, each winding spaced from channels on either side of the winding;
overlaying on the exposed surface an insulating material, leaving the magnetic
material in the channels uncovered; and overlaying magnetic material on the insulating
material on the exposed surface, and on the uncovered magnetic material in the
channels, to complete the magnetic core.
Also featured in the invention is a method of fabricating a planar inductive
component having one or more conductive windings, a magnetic core co-linear with
and surrounding all windings, and an insulator separating each winding from any
other winding and from the magnetic core, the method comprising providing a supportive
substrate; defining an elongated channel in a surface of the substrate; lining
the channel with an insulator; filling the lined channel with a conductor to create
the winding; creating on at least part of the substrate surface over the winding,
a layer of insulating material, to surround the winding with an insulator; creating
parallel, elongated, spaced deposition channels through the insulating layer and
spaced on either side of the winding, the channels extending into the substrate
and completely under the winding, while providing spaced supports from the substrate
to the insulator; and depositing completely surrounding the winding and its surrounding
insulating layer, a layer of magnetic material, to form the magnetic core.
Featured as well is a method of fabricating a planar inductive component
having one or more conductive windings, a magnetic core co-linear with and surrounding
all windings, and an insulator separating each winding from any other winding and
from the magnetic core, the method comprising providing an intermediate comprising
the winding encapsulated along its length by an insulator; creating parallel, spaced,
elongated deposition channels in the insulator on each side of and spaced from
the winding; and depositing into the channels a magnetic material, to form at least
part of the magnetic core.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages will occur to those skilled in the art
from the following descriptions of the preferred embodiments, and the accompanying
drawings, in which:
FIG. 1 is a schematic cross-sectional view of a one-to-one transformer having
a unit length with two conductor windings.
FIG. 2 is a schematic cross-sectional view of an inductor having a unit length.
FIG. 3 is a schematic cross-sectional view of an inductor having a unit length,
with magnetic laminations added to reduce eddy currents.
FIG. 4 is a schematic rendition of an inductor meandered to obtain the required
length; the meander results in a planar rectangular arrangement for a differential
current transformer.
FIG. 5 depicts successive steps in a schematic process for the fabrication of
an inductive component embedded within the volume of a silicon wafer; the inductive
component has vertical magnetic core segments.
FIG. 6 depicts successive steps in a schematic process for the fabrication of
an inductive component embedded within the volume of a silicon wafer; the inductive
component has conformally-formed magnetic core segments.
FIG. 7 depicts successive steps in a schematic process for the fabrication of
an inductive component embedded within the volume of a silicon wafer; the inductive
component has vertical magnetic core segments and insulation wall structures.
FIG. 8 depicts successive steps in a schematic process for the fabrication of
an inductive component onto the surface of a substrate; the inductive component
has vertical magnetic core segments.
FIG. 9 depicts successive steps in a schematic process for the fabrication of
an inductive component onto the surface of a substrate; the inductive component
has conformally-formed magnetic core segments.
FIG. 10 depicts successive steps in a schematic process for the fabrication
of an inductive component with vertical magnetic core segments by starting with
a laminated stack of magnetic, electrically insulating and electrically conductive layers.
FIG. 11 depicts successive steps in a schematic process for the fabrication
of an inductive component with conformally-formed magnetic core segments by starting
with a laminated stack of magnetic, electrically insulating and electrically conductive layers.
FIG. 12 depicts successive steps in a schematic process for the fabrication
of an inductive component with vertical magnetic core segments by starting with
a printed circuit embedded in electrically insulating cladding.
FIG. 13 depicts successive steps in a schematic process for the fabrication
of an inductive component with conformally-formed magnetic core segments by starting
with a printed circuit embedded in electrically insulating cladding.
FIG. 14 depicts successive steps in a schematic process for the fabrication
of an inductive component with vertical magnetic core segments and conductor windings
with a trapezoidal cross section.
FIG. 15 depicts successive steps in a schematic process for the fabrication
of an inductive component with conformally-formed magnetic core segments and conductor
windings with a trapezoidal cross section.
FIG. 16 depicts successive steps in a schematic process for the fabrication
of an inductive component by etching into one surface of the silicon wafer to form
channel wells, filling the channel wells to form windings, undercutting the channel
wells and coating all around with insulation and magnetic materials; one surrounding
layer of the magnetic core is shown.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
This invention applies to the fabrication of planar inductive components for
which the magnetic core encircles the conductor winding (or a number of independent
conductor windings) along its (their) length, and an electrical insulator separates
the conductor windings themselves, and separates the conductor windings from the
magnetic core. The topology can be wire-like having a cross-section that is essentially
uniform along the component length. The desired inductance is achieved by varying
the length of the component. The conductor windings, the insulator structure and
the magnetic core are collinear.
One-To-One Ratio Transformer
A one-to-one ratio transformer
43 of unit length is shown in FIG. 1. It
includes a single primary conductor winding
44 and a single secondary conductor
winding
46. An electrical insulator
48 separates the conductor windings
from each other and from the magnetic core. The magnetic core
50 encircles
the insulator and conductor windings.
Inductor
An inductor configuration
52 of unit length is shown in FIG. 2. It consists
of a single conductor winding
54 enclosed by an insulator
56. Both
the conductor winding and insulator are encircled by the magnetic core
58.
FIG. 3 shows a magnetically laminated core
60 with
4 magnetic layers
62. The magnetic layers are separated by layers of material
64 that
is non-magnetic and ideally non-conducting electrically.
Meandering Form
To achieve the desired inductance, the inductive component must have the proper
length. A top view of a DCT
70 (Differential Current Transformer,
3
conductors) is shown in FIG. 4 for a planar, rectangular component shape. The conductors
and magnetic core are shown to meander
72 back and forth from side to side
to achieve the necessary length. The thin cross-section
74 of the side-view
is shown. The external connections to the DCT can be made at the pads
76,
77, and
78. In the meander detail shown in the enlarged view
79,
are indicated a first primary
80, a second primary
81 and the secondary
82. The DCT is not limited to the rectangular shape shown, however, and
can in fact meander along arbitrary paths and form any planar shape according to
available space. An electrical insulator
83 separates the conductor windings
from each other and the conductor windings from the magnetic core
84. Magnetic
laminations are present but not shown.
General Fabrication Procedure
This invention relates to methods for fabricating planar inductors and transformers
of which the inductor, the one-to-one transformer, the DCT and the inductor with
laminations are examples. Other fabrication procedures that include different materials
and fabrication technologies will occur to those skilled in the art. The devices
are preferably symmetric about the winding(s). The described channels are parallel,
and evenly spaced, to accomplish the symmetry.
Permalloy is one example of a magnetic core material that can be deposited
by electrodeposition. SU-8, a negative photoresist, is one example of an electrical
insulator material. SU-8 is attractive because it can be used to form electroplating
molds that can be retained as part of the finished component. In these components
the molds are also referred to as channels since they are long and narrow. Copper
is an example of an electrically conductive material for forming windings.
Magnetic laminations are not shown in the fabrication procedures discussed.
When laminations are necessary, the magnetic core is formed in multi-layers of
magnetic material separated by thin non-magnetic, and preferably electrically non-conducting, layers.
The continuous magnetic circuit is completed in all cases by making certain that
each segment of the magnetic core encircling the conductor winding makes a continuous
magnetic contact with the next segment.
The deposition of materials can be accomplished by several technologies. Electroplating,
vapor deposition and sputtering are three examples. Others will occur to those
skilled in the art. Similarly, there are different methods for cutting into materials
to form channels. Reactive Ion Etching is suitable for silicon. Other technologies
such as chemical etching are possible. Different materials can be cut by different
technologies and these will be apparent to those skilled in the different technologies.
Fabrication Approaches
1. Fabrication Within the Volume of a Silicon Wafer
This is an approach to embedding inductive components within the volume of a
silicon wafer. Embedding enables:
- use of the silicon wafer volume,
- fabrication of Integrated Circuits (IC) next to inductive components,
- minimum device height over the silicon surface.
Embedding by this approach can also be accomplished into materials other
than silicon by applying cutting technologies appropriate to the material. Deposition
technologies and the use of the SU-8 can be common.
1a. Vertical Magnetic Core Segments (FIG. 5)
In this approach, vertical magnetic core segments are used to connect lower and
top magnetic core segments to complete the magnetic circuit around the winding.
The fabrication steps shown in FIG. 5 are as follows:
- Step a: Start with the silicon wafer 10. Etch the silicon on
the first surface of the wafer to create a channel well 11.
- Step b: Pattern and metalize within the channel well to form conductor
footings 12. Sputter deposition is a way to deposit the conductor footing material.
- Step c: Fill the channel well with SU-8 photoresist to form a first
SU-8 layer 14.
- Step d: Deposit over the first wafer surface, by electroplating, a magnetic
material such as Permalloy to form the first core segment 16 after a seed
layer has been applied to the surface (the seed layer is not shown). This completes
the first surface of the wafer. Sputter deposition and electroless deposition are
ways to apply the seed layer.
- Step e: On the second surface of the wafer, etch the silicon surface
to create a channel well 17. Fill the channel well with SU-8 to form the
second SU-8 layer.
- Step f: Pattern and expose the SU-8 layer on the second surface of the
wafer to form an SU-8 mask. Etch the uncovered silicon down to the conductor footing
to form conductor winding channels 18 and down to the first SU-8 layer to
form magnetic core channels 20. The part of the first SU-8 layer at the
bottom of the magnetic core channel is then removed to expose the first magnetic
core segment. Etching of the silicon is accomplished by Reactive Ion Etching (RIE).
Oxidize the silicon channel walls to form an electrically-insulating oxide for
electrical isolation (oxide not shown).
- Step g: Connect electrically to the first magnetic core segment 16
on the first wafer surface and electroplate Permalloy to fill the magnetic core
channel up to the top surface of the second SU-8 layer on the second wafer surface
to form vertical magnetic core segments 22.
- Step h: Connect electrically to the conductor footing 12 and
electroplate copper to fill the conductor channel to the top of the silicon surface
as shown to form a conductor winding 24. Complete the fill of the conductor
channel 25 with SU-8 to the top surface of the second SU-8 layer on the
second wafer surface. Planarize the second surface to expose the vertical magnetic
core segment.
- Step i: Deposit the magnetic core segment 26 on the second wafer
surface after a seed layer has been applied over the surface. This completes the core.
1b. Conformal Formation of Magnetic Core Segments (FIG. 6)
In this approach, magnetic core segments are formed by the conformal deposition
of magnetic material about non-planar structures. This is a practical approach
to the formation of magnetic laminations that requires the alternate deposition
of magnetic and non-magnetic layers. In the ideal case, conformal deposition forms
one continuous magnetic structure (circuit) about the winding followed by a continuous
non-magnetic layer and so on. The fabrication steps shown in FIG. 6 are as follows:
- Steps a-e: Same as Fabrication 1a.
- Step f: Pattern and expose the SU-8 layer on the second surface of the
wafer to form an SU-8 mask. Etch the uncovered silicon down to the conductor footing
to form conductor winding channels 30 and down to the first SU-8 layer to
form wider magnetic core channels 28. The part of the first SU-8 layer at
the bottom of the magnetic core channel is then removed to expose the first magnetic
core segment. Etching of the silicon is accomplished by Reactive Ion Etching (RIE).
Oxidize the silicon channel walls to form an oxide for electrical isolation (oxide
not shown).
- Step g: Connect electrically to the conductor footing 12 and
electroplate copper to fill the conductor channel to the top of the second silicon
surface, as shown, to form conductor winding 32. Fill with SU-8 34
the wide magnetic channel and complete the fill of the conductor channel up to
the top surface of the second SU-8 layer. Planarize if necessary.
- Step h: Pattern and expose the SU-8 located above the wide channels.
Within the wide channels, the exposed SU-8 forms vertical insulation sidewalls
35. The unexposed SU-8 is removed to form the narrower channel down to the
lower magnetic core.
- Step i: Apply a seed layer conformally over all surfaces (seed layer
is not shown) including surfaces of the narrower channel. Connect electrically
to the first magnetic core segment and electroplate magnetic material over all
surfaces to form the conformal core segment 38.
1c. Extra Insulation (FIG. 7)
The inductive component resulting from Fabrication Process 1a can be improved
by providing insulation sidewalls between the silicon and the vertical magnetic
core segments, in addition to oxide. The fabrication steps shown in FIG. 7 are
as follows:
- Step a: Same as in Fabrication 1a.
- Step b: Same as in Fabrication 1a, with added electrical
insulation footings 15 located on both sides of the conductor footings.
The insulation footing prevents the exposure of the magnetic segment and the filling
of insulation channels during the electroplating of the vertical magnetic segments
in a later step.
- Steps c-e: Same as in Fabrication 1a.
- Step f: Pattern and expose the SU-8 layer on the second surface of the
insulation footing wafer to form an SU-8 mask. Etch the uncovered silicon down
to the conductor footing to form conductor winding channels 40, down to
the insulation footing to form the insulation channels 41 and down to the
first SU-8 layer to form the magnetic core channels 42. The part of the
first SU-8 layer at the bottom of the magnetic channel is removed to expose the
first magnetic core. The insulation footing material needs to be resistant to the
method used to remove the SU-8. Oxidize the channel walls to provide electrical
insulation from the silicon material.
- Step g: Connect electrically to the first magnetic core segment 16
on the first wafer surface and electroplate Permalloy to fill the magnetic core
channels up to the top surface of the second SU-8 layer on the second wafer surface
to form vertical magnetic core segments 45.
- Step h: Connect electrically to the conductor footing 12 and
electroplate copper to fill the conductor channel to the top of the silicon surface
as shown to form a conductor winding 47. Fill with SU-8 49 the insulation
channel and complete the fill of the conductor channel up to the top surface of
the second SU-8 layer. Planarize to expose the vertical magnetic core segment.
- Step i: Deposit the magnetic core segment 51 on the second wafer
surface after a seed layer has been applied over the surface.
2. Fabrication onto Substrates
In this approach, layers are deposited onto a substrate prior to cutting and filling.
2a. Vertical Magnetic Segments (FIG. 8)
The fabrication steps shown in FIG. 8 are as follows:
- Step a: Deposit a magnetic material layer 53 onto a substrate
55 that is non magnetic and ideally non-conducting electrically. An electrical
insulator layer (not shown) can be deposited onto the conductive substrate prior
to the first step if necessary. Deposit an electrical insulator layer 57
over the magnetic layer. SU-8 is an example of an electrical insulator material
that can be used that also serves as a photoresist.
- Step b: Deposit an electrical conductor material 59 onto the
SU-8 layer. Copper is an example of an electrical conductor material.
- Step c: Pattern the copper layer and etch to form a conductor winding 61.
- Step d: Apply a top SU-8 layer 65 sufficiently thick so as to
be planar and encapsulate the conductor windings.
- Step e: Pattern and expose the SU-8. The unexposed regions are etched
down to the lower magnetic layer to form vertical magnetic channels 6. The
exposed regions form the electrical insulation structure 7 that surrounds
the conductor windings and remains part of the inductive component.
- Step f: Electrically connect to the lower magnetic layer and electroplate
Permalloy into the magnetic channels up to the top surface of the SU-8 to form
vertical magnetic segments 8. Planarize if necessary.
- Step g: Apply a seed layer over the top surface. Electrically connect
to the lower magnetic layer and electroplate with Permalloy to form the top magnetic
layer 9.
2b. Conformal Deposition of Magnetic Material (FIG. 9)
The fabrication steps shown in FIG. 9 are as follows:
- Steps a-d: Same as Fabrication 2a.
- Step e: Pattern with wider channels and expose the SU-8 layer. The unexposed
regions are etched down to the lower magnetic layer to form vertical magnetic channels
66. The exposed regions form the electrical insulation structure 67
that surrounds the conductor windings and remains part of the inductive component.
- Step f: Electrically connect to the lower magnetic layer and electroplate
Permalloy conformally over all surfaces after a seed layer is applied to form the
conformal magnetic segment 68.
3. Fabrication by Layering of Prefabricated Sheet Stock as a First Step
This approach is a means to achieve construction of inductive components by
starting with a stack of layers of different materials, etching channels into the
stack and filling the channels by electroplating or other means. One starting stack
comprises five layers having different material properties as listed from the bottom:
magnetic, electrical insulator, conductor, electrical insulator and magnetic. Other
stacks are possible. The stacks can be pre-made by lamination of sheet stock of
the proper materials, or can be fabricated by sequential deposition of the materials.
The main advantages to this approach are:
- a. the stack starts with materials of known thickness and properties,
- b. the vertical magnetic channels are filled with one, continuous electrodeposition step.
3a. Vertical Magnetic Segments (FIG. 10)
The fabrication steps shown in FIG. 10 are as follows:
- Step a: The starting material is a stack of five layers 90 that
are bonded together. The layers are preferably prefabricated as sheet stock. They
include a magnetic material 91, an electrical insulator 92, an electrical
conductor 93, an electrical insulator 94 and a magnetic material 95.
- Step b: Pattern and chemically etch the top magnetic layer to form a
metallic mask 98.
- Step c: Using the magnetic layer as a mask, remove material vertically
down to the bottom magnetic layer to form channels 99. The conductive winding
96 is formed as part of this step.
- Step d: Fill the channels with SU-8 photoresist 100.
- Step e: Pattern and expose the SU-8. The exposed region of the SU-8
forms vertical insulator wall structures 103 on either side of the conductor.
The unexposed SU-8 is removed down to the lower magnetic layer to form narrower
vertical magnetic channels 102.
- Step f: Apply the seed layer to the top surface. Connect electrically
to the lower magnetic layer and electroplate within the channel to form the vertical
magnetic segment 104 followed by the electroplating of the top surface by
additionally connecting electrically to the top magnetic layer
3b. Conformal Deposition of Magnetic Material (FIG. 11)
The fabrication steps shown in FIG. 11 are as follows:
- Steps a-d: Same as Fabrication 3a steps.
- Step e: Pattern and expose the SU-8 for a wider channel 106.
The exposed region forms vertical insulation wall structures 108. The unexposed
region is etched down to the lower magnetic layer.
- Step f: Apply a seed layer conformally over all surfaces. Connect electrically
to the lower magnetic material and deposit magnetic material 110 by electroplating
conformally over all surfaces.
3c: Starting Layer Stack is Formed by Sequential Deposition
Sputtering and electrodeposition are two ways to deposit layers. The five
materials are deposited sequentially one on top of the other to form the starting
stack. Fabrications 3a and 3b can be followed. Advantages to this approach are
that bonding is not necessary and thinner layers can be used.
4. Starting Material is a Printed Circuit Embedded in Insulation Cladding
Two approaches are possible: vertical walls and conformal. The advantage to this
approach is that the copper patterning with insulation can be prefabricated. The
fabrication procedure is as follows:
4a. Vertical Magnetic Segments (FIG. 12)
The fabrication steps shown in FIG. 12 are as follows:
- Step a: The starting material 112 is a copper circuit 114
embedded within an electrical insulator cladding 116.
- Step b: A magnetic layer 118 is separately applied to a substrate
120. The layer can be pre-formed or deposited. The starting material 112
is then bonded to the magnetic layer on the substrate. Note that steps a and b
could also be accomplished by sequential deposition.
- Step c: The electrical insulator material between the copper is patterned
and etched to form channels 122 down to the magnetic layer.
- Step d: Connect electrically to the magnetic layer and electroplate
to fill within the channel to form vertical magnetic segments 124.
- Step e: Apply a seed layer over the top surface. Connect electrically
to the magnetic layer and electroplate over the top surface to form the top magnetic
layer 126.
4b. Conformal Deposition of Magnetic Material (FIG. 13)
The fabrication steps shown in FIG. 13 are as follows:
- Steps a-c: Same as Fabrication 4a.
- Step d: Apply a seed layer conformally over all surfaces. Connect electrically
to the lower magnetic layer and electroplate to form the conformal magnetic layer 128.
5. Fabrication with Kapton and Copper.
In this procedure Kapton is selected because it is an electrical insulator, can
be matched to the thermal expansion coefficient of copper and can be chemically
etched. A laser can also be used to cut the Kapton.
5a. Vertical Magnetic Walls (FIG. 14)
The fabrication steps shown in FIG. 14 are as follows:
- Step a: A copper conductor layer 130 is applied to a Kapton electrically
insulating substrate 131. Copper in sheet stock can be bonded to Kapton
or copper can be deposited onto the Kapton.
- Step b: A magnetic layer 132 such as Permalloy is applied to
the second side of the Kapton (shown from below). Permalloy can be applied in sheet
form and bonded, or it can be deposited after a seed layer is applied. In this
case, the magnetic lower layer is patterned and etched to form a channel 133.
- Step c: Using the channel in the magnetic lower layer, the Kapton is
etched to extend the channel depth to the conductor layer. The channel is then
electroplated to filling with magnetic material to form a vertical magnetic segment
134 after a seed layer is applied and an electrical connection made to the
conductor layer.
- Step d: Using resist and patterning, a chemical etch is used to form
the trapezoidal copper winding 136.
- Step e: An electrical insulator such as SU-8 138 is allowed to
flow and become planar to cover the copper winding.
- Step f: A vertical channel 140 is patterned and etched in the
SU-8. The channel is located above the magnetic posts 141 from below.
- Step g: After electrical connection is made to the magnetic layer, the
channels are plated to complete the upper portion of the vertical magnetic segment 142.
- Step h: A seed layer is applied to the top surface. After electrically
connecting to the magnetic layer, magnetic material is electroplated over the top
surface to form the top magnetic layer 144.
5b. Conformal Application of Magnetic Material (FIG. 15)
The fabrication steps shown in FIG. 15 are as follows:
- Step a: A copper conductor layer 130 is applied to a Kapton electrically
insulating substrate 131. Copper in sheet stock can be bonded to Kapton
or copper can be deposited onto the Kapton.
- Step b: The Kapton is patterned and etched to form channels 135.
- Step c: After a seed layer is applied to the Kapton surface, a magnetic
material is electroplated conformally over the Kapton surface and channel walls
to form the lower magnetic layer 137.
- Step d: Using resist and patterning, a chemical etch is used to form
the trapezoidal copper winding 136.
- Step e: A conformal electrical insulator 146 is applied to the
top surface.
- Step f: The portion 148 of the conformal insulator above the
magnetic vertical channel is removed. A laser is one means to accomplish this.
- Step g: A seed layer is applied to the top surface. An electrical connection
is made to the lower magnetic layer and the top surface is electroplated conformally
to form the top magnetic layer 150.
6. Fabrication on One Side of a Silicon Wafer (FIG. 16)
This approach allows for the formation of the inductive component on one side
of the silicon wafer while keeping the other side untouched. The other side can
then be fully used for IC fabrication. The IC and component can then be connected
through vias in the silicon. The fabrication steps shown in FIG. 16 are as follows:
- Step a: Form an oxide layer 152 on the surface of the wafer 154.
Then pattern and etch the oxide to form a mask. Etch into the silicon using the
oxide mask to form conductor channels 156. Etching into the silicon can
be accomplished using Deep Reactive Ion Etching (DRIE). Form an oxide coating 158
on the channel walls to provide electrical isolation.
- Step b: Apply a seed layer to the conductor channel and electroplate
copper into the channel to form a conductor winding 160. Remove oxide from
the silicon surface.
- Step c: Apply a photoresist 161 to the top layer that can be
left in place to form an insulation layer above the conductor.
- Step d: Pattern the resist and etch silicon channels 162 on both
sides of the conductor to a depth below the conductor channel.
- Step e: Apply an undercutting etch to deepen the channels and etch beneath
the conductor channels to form a large well 166. Xenon Difluoride is one
etching system that can be used. The winding is suspended from the silicon through
oxide and silicon infrastructure that is not removed (not shown). A seed layer
is applied all around the winding. After electrical connection, to the seed layer,
the magnetic material layer 168 is electroplated all around the winding.
Other embodiments will occur to those skilled in the art, and are within the
scope of the following claims.
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