U.S. patent application number 13/897199 was filed with the patent office on 2013-09-19 for method of constructing inductors and transformers.
This patent application is currently assigned to Infineon Technologies Austria AG. The applicant listed for this patent is Infineon Technologies Austria AG. Invention is credited to Ulrich Schwarzer, Marco Seibt, Bernhard Strzalkowski.
Application Number | 20130241685 13/897199 |
Document ID | / |
Family ID | 42063228 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130241685 |
Kind Code |
A1 |
Strzalkowski; Bernhard ; et
al. |
September 19, 2013 |
Method of Constructing Inductors and Transformers
Abstract
An embodiment of the invention relates to an apparatus including
a magnetic device and a related method. A multilayer substrate is
constructed with a winding formed in a metallic layer, an
electrically insulating layer above the metallic layer, and a via
formed in the electrically insulating layer to couple the winding
to a circuit element positioned on the multilayer substrate. A
depression is formed in the multilayer substrate, and a polymer
solution, preferably an epoxy, containing a ferromagnetic component
such as nanocrystaline nickel zinc ferrite is deposited within a
mold positioned on a surface of the multilayer substrate above the
winding and in the depression. An integrated circuit electrically
coupled to the winding may be located on the multilayer substrate.
The multilayer substrate may be a semiconductor substrate or a
printed wiring board, and the circuit element may be an integrated
circuit formed on the multilayer substrate.
Inventors: |
Strzalkowski; Bernhard;
(Muenchen, DE) ; Seibt; Marco; (Villach, AT)
; Schwarzer; Ulrich; (Warstein, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Infineon Technologies Austria AG |
Villach |
|
AT |
|
|
Assignee: |
Infineon Technologies Austria
AG
Villach
AT
|
Family ID: |
42063228 |
Appl. No.: |
13/897199 |
Filed: |
May 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12262816 |
Oct 31, 2008 |
8446243 |
|
|
13897199 |
|
|
|
|
Current U.S.
Class: |
336/200 ;
29/602.1 |
Current CPC
Class: |
H01F 41/046 20130101;
H05K 1/165 20130101; H01F 27/2804 20130101; H01F 2017/002 20130101;
H05K 2201/0187 20130101; H05K 2201/09672 20130101; H05K 1/0298
20130101; H05K 2201/086 20130101; H01F 17/0013 20130101; Y10T
29/4902 20150115; H01F 2017/0066 20130101 |
Class at
Publication: |
336/200 ;
29/602.1 |
International
Class: |
H01F 27/28 20060101
H01F027/28; H01F 41/04 20060101 H01F041/04 |
Claims
1. An apparatus, comprising: a multilayer substrate comprising a
first winding of a magnetic device formed in a first metallic layer
of the multilayer substrate; a first electrically insulating layer
formed above the first metallic layer; a first via formed in the
first electrically insulating layer, wherein the first via is
configured to couple the first winding to a connection for a
circuit element positioned on the multilayer substrate; a
depression formed in the multilayer substrate; and a ferromagnetic
material disposed on a surface of the multilayer substrate above
the first winding and in the depression, wherein the first winding
is not completely encircled by the ferromagnetic material.
2. (canceled)
3. The apparatus as claimed in claim 1, wherein the ferromagnetic
material comprises nanocrystaline nickel zinc ferrite.
4. The apparatus as claimed in claim 1, wherein the depression
incompletely penetrates the multilayer substrate.
5. (canceled)
6. The apparatus as claimed in claim 1, wherein the multilayer
substrate comprises a printed wiring board.
7. The apparatus as claimed in claim 1, further comprising an
integrated circuit located on the multilayer substrate and
electrically coupled to the first winding.
8. The apparatus as claimed in claim 7, wherein the apparatus
comprises a power conversion device.
9. The apparatus as claimed in claim 1, further comprising: a
second insulating layer formed on the multilayer substrate below
the first metallic layer; a second winding of the magnetic device
formed in a second metallic layer of the multilayer substrate,
wherein the second metallic layer is formed on the multilayer
substrate below the second insulating layer; and a second via
formed in the second insulating layer, wherein the second via
electrically couples the second winding to the first winding.
10. The apparatus as claimed in claim 9, wherein the first via and
the second via are metallic vias.
11. The apparatus as claimed in claim 9, further comprising: a
third insulating layer formed on the multilayer substrate below the
second metallic layer; a third metallic layer formed on the
multilayer substrate below the third insulating layer, wherein the
third metallic layer forms a further winding of the magnetic device
electrically insulated from the first winding; and a third via
formed in the third insulating layer, wherein the third via
provides an electrical coupling of the further winding to a further
connection configured to be coupled to a further circuit element
located on the multilayer substrate.
12. The apparatus as claimed in claim 11, wherein the multilayer
substrate comprises a semiconductor substrate, and wherein the
circuit element comprises an integrated circuit formed on the
multilayer substrate.
13. A method of forming an apparatus, the method comprising:
forming a first metallic layer of a multilayer substrate; forming a
first winding of a magnetic device in the first metallic layer;
forming a first electrically insulating layer above the first
metallic layer; forming a first via in the first electrically
insulating layer to couple the first winding to a connection
configured to be coupled to a circuit element; forming a depression
in the multilayer substrate; and forming a ferromagnetic material
on a surface of the multilayer substrate above the first winding
and in the depression, wherein the first winding is not completely
encircled by the ferromagnetic material.
14. (canceled)
15. The method as claimed in claim 13, wherein the ferromagnetic
material comprises nanocrystaline nickel zinc ferrite.
16. The method as claimed in claim 13, wherein the depression
incompletely penetrates the multilayer substrate.
17. (canceled)
18. The method as claimed in claim 13, wherein the multilayer
substrate comprises a printed wiring board.
19. The method as claimed in claim 13, wherein the apparatus
comprises a power conversion device.
20. The method as claimed in claim 13, further comprising: forming
a second insulating layer on the multilayer substrate below the
first metallic layer; forming a second metallic layer on the
multilayer substrate below the second insulating layer; forming a
second winding of the magnetic device in the second metallic layer;
and forming a second via in the second insulating layer to
electrically couple the second winding to the first winding.
21. A power converter, comprising: a magnetic circuit element
comprising a multilayer substrate comprising a first winding formed
in a first metallic layer of the multilayer substrate, a first
electrically insulating layer formed above the first metallic
layer, a first via formed in the first electrically insulating
layer, wherein the first via is configured to couple the first
winding to a first connection, a depression formed in the
multilayer substrate, and a ferromagnetic material disposed on a
surface of the multilayer substrate above the first winding and in
the depression, wherein the first winding is not completely
encircled by the ferromagnetic material; and a switch coupled to
the first connection.
22. The power converter of claim 21, wherein the ferromagnetic
material is a polymer solution containing a ferromagnetic component
that is deposited on the surface of the multilayer substrate and in
the depression.
23. The power converter of claim 21, wherein the magnetic circuit
further comprises: a second insulating layer formed on the
multilayer substrate below the first metallic layer; a second
winding of the magnetic device formed in a second metallic layer of
the multilayer substrate, wherein the second metallic layer id
formed on the multilayer substrate below the second insulating
layer; and a second via formed in the second insulating layer,
wherein the second via electrically couples the second winding to
the first winding.
24. The power converter of claim 21, wherein the magnetic circuit
comprises an inductor.
Description
[0001] This is a continuation application of U.S. application Ser.
No. 12/262,816, filed on Oct. 31, 2008, entitled "Method of
Constructing Inductors and Transformers," which application is
hereby incorporated herein by reference in its entirety.
TECHNICAL FIELD
[0002] An embodiment of the invention relates generally to
constructing magnetic devices, and in particular, to forming a
magnetic device such as an inductor or a transformer on a
substrate, such as a printed wiring board or a semiconductor
substrate.
BACKGROUND
[0003] With the increasing complexity and level of integration of
electronic products, there is a growing need for distributed and
independent power conversion devices, such as point-of-load voltage
sources, to provide the well-regulated bias voltages for the highly
integrated semiconductor devices that are commonly used. Highly
integrated semiconductor devices frequently operate from
specialized bias voltages. The power conversion devices must be
economical and formed with very small dimensions to meet the size
and portability needs of these markets, particularly markets that
include portable and compact products such as cellular telephones
and personal computers.
[0004] A power converter is conventionally formed with discrete
magnetic devices such as transformers and inductors that are
necessary in the design to achieve high power conversion
efficiency. Such magnetic devices generally consist of electrically
conductive windings, a body ("bobbin") to support the windings, and
a ferromagnetic core to provide a sufficiently high level of
magnetic flux density for a given level of current in the windings.
The assembly is generally mounted on a printed wiring board ("PWB")
for interconnection with other circuit elements.
[0005] A known technique to form magnetic devices is to employ
planar windings that are formed directly in the buried metallic
layers of a PWB. Exemplary magnetic cores that can be used with
such structures are "EI" and "EE" core forms, so named for the
corresponding shapes of the letters "E" and "I," and produced by
companies such as EPCOS and Philips. To insert and secure such
cores to a PWB, apertures with complex and precise shapes must be
milled in the PWB. Milling of such apertures in a PWB is generally
a more costly mechanical operation than, for example, drilling of
holes.
[0006] Power converters are also manufactured with discrete
magnetic devices in an integrated circuit-size ("IC") package, such
as the DCR010505 power converter produced by Texas Instruments,
Inc., to achieve a small physical size, as described by Geoff Jones
in the paper entitled "Miniature Solutions for Voltage Isolation,"
Texas Instruments' Analog Applications Journal, dated 3Q2005, pages
13-17. However, such power converters are generally larger than the
needs of the more challenging markets for compact circuit devices,
particularly for low power applications, and are produced at costs
that do not meet the needs of high-volume production.
[0007] To produce inductors and transformers with small dimensions,
studies have been undertaken to incorporate buried copper
conductors within surrounding layers of a ferromagnetic film, for
example, the study described by K. Yamaguchi, et al., in the paper
entitled "Characteristic of a Thin Film Microtransformer with
Circular Spiral Coils," published in the IEEE Transaction on
Magnetics, Vol. 29, No. 5, Sep. 1993. The fabrication procedure
described by Yamaguchi includes depositing a sputtered magnetic
film that is then patterned using a photoresist. Copper windings
are deposited by an electroplating process to produce a compact
magnetic design. However, the overall process is not practical for
a high-volume, low-cost production sequence in view of the
complexity of the manufacturing steps that are necessary to produce
a workable product.
[0008] Thus, there is a need for a process and related method to
produce a magnetic device with very small physical dimensions that
are adaptable to high volume and low cost manufacturing processes
to meet the more challenging market needs that lie ahead that
avoids the disadvantages of conventional approaches.
SUMMARY OF THE INVENTION
[0009] In accordance with an exemplary embodiment, an apparatus
including a magnetic device and a related method are provided. In
an embodiment, a multilayer substrate is constructed with a first
winding formed in a first metallic layer of the multilayer
substrate, a first electrically insulating layer formed above the
first metallic layer, and a first via formed in the first
electrically insulating layer. The first via couples the first
winding to a circuit element positioned on the multilayer
substrate. A depression is formed in the multilayer substrate, and
a polymer solution containing a ferromagnetic component is
deposited on a surface of the multilayer substrate above the first
winding and in the depression. The polymer solution is preferably
an epoxy, but another polymer solution may be used. The
ferromagnetic component preferably contains nanocrystaline nickel
zinc ferrite, but another ferromagnetic material may be used. In an
embodiment, the depression incompletely penetrates the multilayer
substrate. Preferably, the polymer solution is deposited within a
mold positioned on a surface of the multilayer substrate to form
the shape of the polymer solution after curing. The multilayer
substrate may be a printed wiring board. In an embodiment, an
integrated circuit is located on the multilayer substrate that is
electrically coupled to the first winding. In an embodiment, the
apparatus may be formed as a power conversion device. In a further
embodiment, a second insulating layer is formed on the multilayer
substrate below the first metallic layer, and a second winding of
the magnetic device is formed in a second metallic layer of the
multilayer substrate to form additional turns for a winding of the
magnetic device. The second metallic layer is formed on the
multilayer substrate below the second insulating layer, and a
second via is formed in the second insulating layer. The second via
electrically couples the second winding to the first winding.
Preferably, the first via and the second via are metallic vias. In
a further embodiment, a third insulating layer is formed on the
multilayer substrate below the second metallic layer, and a third
metallic layer is formed on the multilayer substrate below the
third insulating layer. The third metallic layer forms a further
winding of the magnetic device dielectrically insulated from the
first winding to form dielectrically insulated transformer
windings. A third via is formed in the third insulating layer to
provide an electrical coupling of the further winding to a further
circuit element located on the multilayer substrate. In an
embodiment, the multilayer substrate is a semiconductor substrate,
and the circuit element is an integrated circuit formed on the
multilayer substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the claims. In
the figures, identical reference symbols generally designate the
same component parts throughout the various views, and may be
described only once in the interest of brevity. For a more complete
understanding of the invention, reference is now made to the
following descriptions taken in conjunction with the accompanying
drawings, in which:
[0011] FIGS. 1A, 1B, and 1C illustrate planar-view drawings
showing, respectively, the form and arrangement of spiral, planar
coils in an upper metallic layer, a lower metallic layer, and the
placement of the windings relative to each other, constructed
according to an embodiment;
[0012] FIG. 2 illustrates a planar-view drawing of an electrical
apparatus including a magnetic device formed with spiral windings
formed in a two-sided PWB, constructed according to an
embodiment;
[0013] FIG. 3 illustrates an elevation-view drawing of a planar
transformer formed on a four-layer PWB, constructed according to an
embodiment;
[0014] FIG. 4 illustrates an elevation-view drawing showing the use
of molds to shape magnetic layers deposited about planar windings,
constructed according to an embodiment;
[0015] FIG. 5 illustrates an elevation-view drawing showing the
structure of a magnetic device wherein a magnetic layer is formed
on a semiconductor substrate, constructed according to an
embodiment;
[0016] FIG. 6 illustrates a transformer formed on a semiconductor
substrate including a primary winding formed on metallic layers
that are dielectrically isolated from a secondary winding formed on
metallic layers, constructed according to an embodiment; and
[0017] FIG. 7 illustrates a simplified schematic diagram of a
switch-mode power converter including an exemplary magnetic circuit
element, constructed according to an embodiment.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0018] The making and using of the presently preferred embodiments
are discussed in detail below. It should be appreciated, however,
that the present invention provides many applicable inventive
concepts that can be embodied in a wide variety of specific
contexts. The specific embodiments discussed are merely
illustrative of specific ways to make and use the invention, and do
not limit the scope of the invention.
[0019] The present invention will be described with respect to
exemplary embodiments in a specific context, namely a magnetic
device formed on a substrate with planar windings that produce a
magnetic field enhanced by a molded ferromagnetic structure.
[0020] An embodiment of the invention may be applied to various
electronic power conversion arrangements, for example, to an
integrated isolated or nonisolated power converter configured to
power an electronic load. Other devices including a magnetic
element can be constructed and applied using processes as
introduced herein in different contexts using inventive concepts
described herein, for example, a filtering arrangement used to
shape a spectral characteristic of an analog signal.
[0021] As introduced herein, windings of a compact, integrated
magnetic device such as a transformer or an inductor are formed on
a substrate such as a PWB or a semiconductor substrate. The
windings are structured so that no additional electrically
conductive lines or other interconnections such as wire bonds are
needed to interconnect the metallic layers forming the internal
windings of the magnetic device, enabling thereby the production of
low-profile structures. To extend the magnetic path of the
ferromagnetic layers in various areas of the spiral coils forming
the windings, a number of drilled holes and trenches that may not
penetrate the substrate are formed. The winding areas are then
covered with a polymer solution that contains a soft ferrite such
as the nanocrystaline ferrite FeSiBCuNb or nanocrystaline nickel
zinc ferrite to form the magnetic core of the medic device. The
polymer solution is of a sufficiently low viscosity so that the
formed depressions, i.e., the holes and trenches, are readily
filled. An exemplary polymer solution such as I-8606M is available
from Asahi Kasei, and an exemplary powdered ferrite such as
Vitroperm is available from Vacuumschmelze GmbH. The relative
permeability value and the saturation flux density of the
ferrite-mold compound are dependent on the powder filling content.
For a low viscosity polymer, a suitable filling fraction, without
limitation, is 60% to 85% of the polymer volume; the relative
permeability of the molded material may typically vary from 10 to
40 for the cited powder fraction. The saturation flux density can
be expressed according to Kelly, A. W, et al., as described in the
paper entitled "Plastic-Iron-Powder Distributed-Air-Gap Magnetic
Material," IEEE Power Electronics Specialists Conference, 11 Jun.
1990, pages 25-34, by the equation:
B.sub.sat=B.sub.sat-fill[x+(1-x).rho..sub.pol/.rho..sub.fill],
[1]
where
[0022] B.sub.sat-fill=saturation flux density of the filler
(ferrite powder)
[0023] x=filler fraction by polyimide volume
[0024] .rho..sub.pol=mass density of the polyimide
[0025] .rho..sub.fill=mass density of the ferrite powder
[0026] The required properties of the magnetic core for optimal
energy conversion are influenced by the number of vias at the
periphery of the winding and by the thickness of the magnetic
layer. For economical implementation of the magnetic circuit, the
vias in the middle area of the magnetic device and at the level of
winding may be advantageously formed of the same size. The diameter
and number of vias formed to contain the polymer solution should be
selected in view of expected current levels in the magnetic device
to manage saturation of the magnetic material using analytical
techniques well known in the art. The sum of the areas of the outer
vias is preferably equal to the area of the large via formed in the
middle of the magnetic device.
[0027] Turning now to FIGS. 1A, 1B, and 1C, illustrated are
drawings showing, respectively, the structure and arrangement of
spiral, planar coils in an upper metallic layer, a lower metallic
layer, and the placement of the windings relative to each other to
provide efficient utilization of board area on the internal
metallization layers forming a magnetic device, constructed
according to an embodiment. Although round spiral structures for
the windings are illustrated in the figures herein, other winding
structures may be employed within the broad scope of the present
invention, such as hexagonal spiral structures. The spiral coils of
the upper 3 and the lower 5 spiral metal layers are laid out with
opposite geometric winding sense. The inner ends of the upper coil
3 and lower coil 5 are coupled by via 18. This creates a stacked
winding, wherein each layer produces a magnetic flux with the same
winding sense with respect to flux generation. No other connection
is necessary to interconnect the inner end terminal of each
winding. This creates a compact, low-profile, planar coil, wherein
a higher number of winding turns is produced compared to a
single-layer winding arrangement. Accordingly, no connection is
needed to form the mid-point (or other tap location) of the
winding. The coil ends 15 and 16 are coupled to other electrical
circuits, for example, to the integrated circuit IC1 illustrated
and described hereinbelow with reference to FIGS. 2 and 3.
[0028] Turning now to FIG. 2, illustrated is a planar-view drawing
of an embodiment of an electrical circuit including a magnetic
device formed with spiral windings formed in a two-sided or
multilayer PWB 201. The interconnection 15 and 16 between the
windings and an IC (IC1) placed on the PWB are shown. The windings
are covered with a ferromagnetic layer 101. The ferromagnetic layer
101 fills the inner via 14 and the outer vias such as the outer via
13. The ferromagnetic layer 101 is created by applying a polymer
solution such as an epoxy or other plastic material mixed with a
ferromagnetic powder, as described previously hereinabove.
[0029] Turning now to FIG. 3, illustrated is an elevation drawing
of an embodiment of a planar transformer 302 formed in a four-layer
PWB 301. The transformer consists of the following layers and
structures:
[0030] layers 101 and 1011: ferromagnetic layers,
[0031] layer 102: isolation layer (the first passivation layer
above the first metallic layer of the first winding),
[0032] layer 103: first metallic layer of the first winding,
[0033] layer 104: isolation layer between the first and the second
metallic layers of the first winding,
[0034] layer 105: second metallic layer of the first winding,
[0035] layer 106: substrate/isolation layer of the PWB,
[0036] layer 107: second metallic layer of the second winding,
[0037] layer 108: isolation layer between the first and the second
metallic layers of the second winding,
[0038] layer 109: first metallic layer of the second winding,
[0039] layer 1010: isolation layer (the second passivation layer
below the first metallic layer of the second winding,
[0040] 12 and 18: vias between upper and lower metallic layers of
the first and second windings,
[0041] 13: outer completely or incompletely drilled via through
PWB,
[0042] 14: inner completely or incompletely drilled via through
PWB, and
[0043] 15 and 16: ends forming the interconnections with the first
winding.
[0044] In order not to saturate the ferrite layer in the area of
the via 13, the viscosity of the solution is preferably selected so
that it will be disposed in the region of the via 13 with a
thickness that is no less than a certain amount such as the
distance D indicated in FIG. 3. The distance D is selected to
manage saturation of the magnetic layer; preferably, it is not less
than the diameter of via 13. In order to produce increased
electrical breakdown voltage between the windings, the holes are
not drilled completely through the PWB, as indicated by the
separation distance d in FIG. 3. The distance d can also be used to
control the effective transformer air gap for the path of the
magnetic flux.
[0045] Turning now to FIG. 4, illustrated is an elevation drawing
showing an embodiment of the use of molds to shape and control
dimensions of the magnetic layers about the planar windings. As
illustrated in FIG. 4, the windings of the magnetic device are
coupled to integrated circuits IC1 and IC2, such as by winding end
15 that may be formed with a via. A mold for the polymer solution,
illustrated as the mold with top and bottom portions identified
with reference designation 19 with apertures 20, is placed above
the upper and lower surfaces of the PWB 401. The polymer solution
containing the ferromagnetic component is introduced through the
apertures 20 under pressure to fill the mold and the vias in the
PWB.
[0046] By selection of the height D and the diameter diam of the
mold, the magnetic and electrical characteristics of the core can
be determined. If the polymer solution containing the ferromagnetic
component is controllably introduced through the vias 14 and 18,
the structure of the resulting ferrite core can be constructed with
repeatable magnetic and electrical characteristics.
[0047] A magnetic device as introduced herein can be characterized,
without limitation, as follows: It is not necessary for the
magnetic flux of a winding to be completely enclosed in a magnetic
layer to obtain a high quality inductor with sufficiently high
inductance values for a particular application. A portion of the
magnetic flux may lie in air or in other non-ferromagnetic
material. The effective permeability of the magnetic path will be
increased nonetheless by the presence of the ferromagnetic
material, which results in increased inductance of a planar
inductor winding formed in the magnetic device. The longer the path
of the magnetic flux lies in a ferromagnetic layer, the greater is
the resulting device inductance. In this way, an inductance value
and a power density of a magnetic device formed with a planar
winding can be substantially increased over a comparable device
formed without added ferromagnetic material.
[0048] Turning now to FIG. 5, illustrated is an elevation drawing
showing an exemplary embodiment of the structure of a magnetic
device, wherein a magnetic layer 101 is formed on a semiconductor
substrate 21. The magnetic device is coupled to an integrated
circuit 501 by means of vias formed through the isolation layers of
the semiconductor device. Unlike the structure of the magnetic
devices illustrated in FIGS. 4 and 5, the magnetic flux of the
device illustrated in FIG. 6 is less contained within a high
permeability magnetic layer, such as the magnetic layers 101 and
1011 illustrated in FIGS. 3 and 4, but traverses longer,
low-permeability paths, such as the paths between the trenches 13
and 14. Nonetheless, a sufficiently high permeability path can be
obtained to construct a practical high-frequency magnetic device.
The trenches 13 and 14 are etched using integrated circuit etching
techniques well known in the art, such as, without limitation, by
deposition of a photoresist layer, patterning the photoresist
layer, reactive-ion etching, and deposition of a metallic layer on
the walls of holes and trenches so formed, in the processing steps
after forming layers 102 through 106 on the semiconductor substrate
21. Then the magnetic layer 101 is deposited and structured. The
deposition of a thin magnetic layer can be performed employing RF
sputtering in a PVD (plasma vacuum deposition) process. Structuring
of the layer can by realized by means of a photoresist lift-off
method. Another method is direct deposition of a photoresist
containing a magnetic powder to fill the trenches and to build the
upper magnetic layer. The thickness of the layer may be controlled
by the rotational speed of the wafer. Structuring of the
photoresist then follows. The remaining photoresist structure is
preferably not ashed. Instead of the last photoresist, the
polyimide containing the magnetic powder can be used. In this way a
magnetic circuit is created wherein a magnetic field surrounds a
compact, planar winding, and the magnetic field is partially
conducted within a high permeability ferromagnetic structure. The
magnetic field lines that are conducted between the trenches such
as trenches 13 and 14 are conducted through the isolation layers
104 and 106 and the substrate 21 of a semiconductor device. It is
also possible to etch vias 13 and 14 entirely though the substrate.
In this case, the coupling factor between the primary and secondary
winding becomes larger, as well as the primary winding
inductance.
[0049] Turning now to FIG. 6, illustrated is an exemplary
embodiment of a transformer formed on semiconductor substrate 21
including a primary winding formed on metallic layers 103 and 105
that is dielectrically isolated from a secondary winding formed on
metallic layers 107 and 109. As illustrated in FIG. 5, the magnetic
device may be coupled by means of vias formed through the isolation
layers of the semiconductor device to an integrated circuit formed
on the substrate. Similar to the magnetic device illustrated in
FIG. 5, the magnetic flux of the device illustrated in FIG. 6 is
only partially contained within a high permeability magnetic
layer.
[0050] Referring now to FIG. 7, illustrated is a simplified
schematic diagram of a switch-mode power converter 700, including a
magnetic circuit element L.sub.filter, constructed according to an
embodiment. The switch-mode power converter 700, a power conversion
device, is an exemplary application of a low-profile magnetic
element such as the inductor L.sub.filter coupled to circuit
elements on a PWB or on another substrate such as a semiconductor
substrate. The power converter includes a controller 701
constructed as an integrated circuit that regulates the power
converter output voltage. The power converter provides dc power to
a load R.sub.load (not shown) that may be coupled to output
terminals 703 and 704. While the illustrated power converter
employs a buck converter topology, those skilled in the art should
understand that other power converter topologies are well within
the broad scope of the present invention.
[0051] The power converter receives an input dc voltage V.sub.input
from a source of electrical power 702 at an input thereof and
provides a regulated output voltage V.sub.output at output
terminals 703 and 704. In keeping with the principles of a buck
converter topology, the output voltage V.sub.output is generally
less than the input voltage V.sub.input such that a switching
operation of the power switch Q can regulate the output voltage
V.sub.output.
[0052] During a first portion of a high-frequency switching cycle
of the power converter, the power switch Q, which may be formed as
a power MOSFET, is enabled to conduct in response to a gate drive
signal G.sub.D, coupling the input voltage V.sub.input to the
filter inductor L.sub.filter, enabling thereby a current to flow
through the filter inductor L.sub.filter. During the first portion
of the high-frequency switching cycle, an inductor current flowing
through the output filter inductor L.sub.filter increases as
current flows from the input to the output of the power train. An
ac component of the inductor current is filtered by the output
filter capacitor C.sub.filter.
[0053] During a complementary portion of the switching cycle, the
power switch Q is transitioned to a non-conducting state, and a
freewheeling diode D.sub.fr coupled to the filter inductor
L.sub.filter becomes forward biased. The diode D.sub.fr provides a
current path to maintain continuity of inductor current flowing
through the filter inductor L.sub.filter. During the complementary
portion of the switching cycle, the inductor current flowing
through the filter inductor L.sub.filter decreases. In general, the
first portion of the high-frequency switching cycle of the power
switch Q may be adjusted to regulate the output voltage
V.sub.output of the power converter.
[0054] The controller 701 of the power converter receives the
output voltage V.sub.output of the power converter and a desired
system voltage. The controller 701 adjusts the first portion of the
high-frequency switching cycle to regulate the output voltage
V.sub.output at the desired system voltage.
[0055] The concept has thus been introduced of constructing a
multilayer substrate with a first winding of a magnetic device
formed in a first metallic layer of the multilayer substrate, a
first electrically insulating layer formed above the first metallic
layer, and a first via formed in the first electrically insulating
layer. The first via couples the first winding to a circuit element
positioned on the multilayer substrate. A depression is formed in
the multilayer substrate, and a polymer solution containing a
ferromagnetic component is deposited on a surface of the multilayer
substrate above the first winding and in the depression. In an
embodiment, the polymer solution is an epoxy. In an embodiment, the
ferromagnetic component contains nanocrystaline nickel zinc
ferrite. In an embodiment, the depression incompletely penetrates
the multilayer substrate. In an embodiment, the polymer solution is
deposited within a mold positioned on a surface of the multilayer
substrate to form the shape of the polymer solution after curing.
In an embodiment, the multilayer substrate comprises a printed
wiring board. In an embodiment, an integrated circuit is located on
the multilayer substrate that is electrically coupled to the first
winding. In an embodiment, the apparatus is a power conversion
device. In a further embodiment, a second insulating layer is
formed on the multilayer substrate below the first metallic layer,
and a second winding of the magnetic device is formed in a second
metallic layer of the multilayer substrate. The second metallic
layer is formed on the multilayer substrate below the second
insulating layer, and a second via is formed in the second
insulating layer. The second via electrically couples the second
winding to the first winding. In an embodiment, the first via and
the second via are metallic vias. In a further embodiment, a third
insulating layer is formed on the multilayer substrate below the
second metallic layer, and a third metallic layer is formed on the
multilayer substrate below the third insulating layer. The third
metallic layer forms a further winding of the magnetic device
electrically insulated from the first winding. A third via is
formed in the third insulating layer to provide an electrical
coupling of the further winding to a further circuit element
located on the multilayer substrate. In an embodiment, the
multilayer substrate is a semiconductor substrate, and the circuit
element is an integrated circuit formed on the multilayer
substrate.
[0056] Another exemplary embodiment provides a method of forming an
apparatus. In an embodiment, the method includes forming a first
metallic layer of a multilayer substrate, and forming a first
winding of a magnetic device in the first metallic layer. The
method further includes forming a first electrically insulating
layer above the first metallic layer, and positioning a circuit
element on the multilayer substrate. The method further includes
forming a first via in the first electrically insulating layer to
couple the first winding to the circuit element, and forming a
depression in the multilayer substrate. The method further includes
depositing a polymer solution containing a ferromagnetic component
on a surface of the multilayer substrate above the first winding
and in the depression. In an embodiment, the polymer solution
includes an epoxy. In an embodiment, the ferromagnetic component
includes nanocrystaline nickel zinc ferrite. In an embodiment, the
depression incompletely penetrates the multilayer substrate. In an
embodiment, the method further includes positioning a mold on a
surface of the multilayer substrate and depositing the polymer
solution in the mold. In an embodiment, the multilayer substrate
comprises a printed wiring board. In an embodiment, the apparatus
comprises a power conversion device. In an embodiment, the method
further includes forming a second insulating layer on the
multilayer substrate below the first metallic layer, and forming a
second metallic layer on the multilayer substrate below the second
insulating layer. The method further includes forming a second
winding of the magnetic device in the second metallic layer, and
forming a second via in the second insulating layer to electrically
couple the second winding to the first winding. In an embodiment,
the first via and the second via are metallic vias. In an
embodiment, the method further includes forming a third insulating
layer on the multilayer substrate below the second metallic layer
and forming a third metallic layer on the multilayer substrate
below the third insulating layer. The method further includes
forming a further winding of the magnetic device in the third
metallic layer electrically insulated from the first winding, and
locating a further circuit element on the multilayer substrate. The
method further includes forming a third via in the third insulating
layer to provide an electrical coupling of the further winding to
the further circuit element. In an embodiment, the multilayer
substrate is formed as a semiconductor substrate, and the circuit
element is an integrated circuit formed on the multilayer
substrate.
[0057] Although processes for forming a device containing a
magnetic element and related methods have been described for
application to electronic power conversion, it should be understood
that other applications of these processes such as for analog
signal filtering are contemplated within the broad scope of the
invention, and need not be limited to electronic power conversion
applications employing processes introduced herein.
[0058] Although the invention has been shown and described
primarily in connection with specific exemplary embodiments, it
should be understood by those skilled in the art that diverse
changes in the configuration and the details thereof can be made
without departing from the essence and scope of the invention as
defined by the claims below. The scope of the invention is
therefore determined by the appended claims, and the intention is
for all alterations that lie within the range of the meaning and
the range of equivalence of the claims to be encompassed by the
claims.
* * * * *