U.S. patent application number 16/249292 was filed with the patent office on 2019-08-01 for rare earth reduced garnet systems and related microwave applications.
The applicant listed for this patent is Skyworks Solutions, Inc.. Invention is credited to David Bowie CRUICKSHANK, Michael David HILL, Iain Alexander MACFARLANE, Brian MURRAY, Rickard Paul O'DONOVAN.
Application Number | 20190237840 16/249292 |
Document ID | / |
Family ID | 47296684 |
Filed Date | 2019-08-01 |
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United States Patent
Application |
20190237840 |
Kind Code |
A1 |
CRUICKSHANK; David Bowie ;
et al. |
August 1, 2019 |
RARE EARTH REDUCED GARNET SYSTEMS AND RELATED MICROWAVE
APPLICATIONS
Abstract
Disclosed are synthetic garnets and related devices that can be
used in radio-frequency (RF) applications. In some embodiments,
such RF devices can include garnets having reduced or substantially
nil Yttrium or other rare earth metals. Such garnets can be
configured to yield high dielectric constants, and ferrite devices,
such as TM-mode circulators/isolators, formed from such garnets can
benefit from reduced dimensions. Further, reduced or nil rare earth
content of such garnets can allow cost-effective fabrication of
ferrite-based RF devices. In some embodiments, such ferrite devices
can include other desirable properties such as low magnetic
resonance linewidths. Examples of fabrication methods and
RF-related properties are also disclosed.
Inventors: |
CRUICKSHANK; David Bowie;
(Rockville, MD) ; O'DONOVAN; Rickard Paul;
(Dunmanway, IE) ; MACFARLANE; Iain Alexander;
(Midleton, IE) ; MURRAY; Brian; (Belgooly, IE)
; HILL; Michael David; (Frederick, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Skyworks Solutions, Inc. |
Woburn |
MA |
US |
|
|
Family ID: |
47296684 |
Appl. No.: |
16/249292 |
Filed: |
January 16, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15003446 |
Jan 21, 2016 |
10230146 |
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16249292 |
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13484018 |
May 30, 2012 |
9263175 |
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15003446 |
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61493942 |
Jun 6, 2011 |
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61648892 |
May 18, 2012 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01F 1/346 20130101;
H01F 10/24 20130101; H01P 1/387 20130101; C30B 29/28 20130101 |
International
Class: |
H01P 1/387 20060101
H01P001/387; H01F 1/34 20060101 H01F001/34; H01F 10/24 20060101
H01F010/24 |
Claims
1. (canceled)
2. A modified synthetic garnet material comprising: a
vanadium-doped garnet represented by the formula
Y.sub.2.15-2xBi.sub.0.5Ca.sub.0.35+2xZr.sub.0.35V.sub.xFe.sub.4.65-xO.sub-
.12, x being greater than or equal to 0.1 and less than or equal to
0.8, the vanadium being in a tetrahedral site of the garnet and
calcium charge balancing the vanadium.
3. The modified synthetic garnet material of claim 2 wherein x is
less than or equal to 0.5.
4. The modified synthetic garnet material of claim 3 wherein x is
0.5.
5. The modified synthetic garnet material of claim 4 wherein a 3 dB
linewidth of the modified synthetic garnet material is about
50.
6. The modified synthetic garnet material of claim 2 wherein a
dielectric constant and a density of the modified synthetic garnet
material remains substantially the same with changing values of
x.
7. The modified synthetic garnet material of claim 2 wherein a
density of the modified synthetic garnet material is about 50.
8. The modified synthetic garnet material of claim 2 wherein a
dielectric constant of the modified synthetic garnet material is
below 25.
9. The modified synthetic garnet material of claim 2 wherein a 4
PiMs of the modified synthetic garnet material decreases with
increasing values of x.
10. A method of modifying a garnet material, the method comprising:
substituting at least some iron from a garnet material with
vanadium to form a synthetic garnet material having a composition
Y.sub.2.15-2xBi.sub.0.5Ca.sub.0.35+2xZr.sub.0.35V.sub.xFe.sub.4.65-xO.sub-
.12, x being greater than or equal to 0.1 and less than or equal to
0.8, the vanadium being added to a tetrahedral site of the
garnet.
11. The method of claim 10 further comprising forming a
radiofrequency component from the synthetic garnet material.
12. The method of claim 10 wherein the radiofrequency component is
a circulator.
13. The method of claim 10 wherein x is less than or equal to
0.5.
14. The method of claim 13 wherein x is 0.5.
15. The method of claim 10 further comprising mixing raw materials
to form the garnet material.
16. The method of claim 10 further comprising heat treating the
synthetic garnet material at a temperature of between 800 and
1000.degree. C.
17. A radiofrequency system comprising: at least one circulator
including a vanadium-doped garnet represented by the formula
Y.sub.2.15-2xBi.sub.0.5Ca.sub.0.35+2xZr.sub.0.35V.sub.xFe.sub.4.65-xO.sub-
.12, x being greater than or equal to 0.1 and less than or equal to
0.8, the vanadium being added to a tetrahedral site of the
garnet.
18. The radiofrequency system of claim 17 wherein the circulator is
incorporated into an antenna.
19. The radiofrequency system of claim 17 wherein the circulator is
incorporated into a base station.
20. The radiofrequency system of claim 17 wherein x is less than or
equal to 0.5.
21. The radiofrequency system of claim 20 wherein x is 0.5.
Description
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS
[0001] Any and all applications for which a foreign or domestic
priority claim is identified in the Application Data Sheet as filed
with the present application are hereby incorporated by reference
under 37 CFR 1.57.
BACKGROUND
Field
[0002] The present disclosure generally relates to synthetic garnet
systems and related radio-frequency (RF) applications.
Description of the Related Art
[0003] Various crystalline materials with magnetic properties have
been used as components in electronic devices such as cellular
phones, biomedical devices, and RFID sensors. Garnets are
crystalline materials with ferrimagnetic properties particularly
useful in RF electronics operating in the lower frequency portions
of the microwave region. Many microwave magnetic materials are
derivatives of Yttrium Iron Garnet (YIG), a synthetic form of
garnet widely used in various telecommunication devices largely
because of its favorable magnetic properties such as narrow line
absorption at its ferromagnetic resonance frequency. YIG is
generally composed of Yttrium, Iron, Oxygen, and possibly doped
with one or more other rare earth metals such as the Lanthanides or
Scandium. However, the supply of rare earth elements such as
Yttrium has recently become increasingly restricted, thus resulting
in correspondingly steep increases in cost. As such, there is a
need to find a cost-effective substitute for rare earth elements in
synthetic garnet structures that does not compromise the magnetic
properties of the material and can be used for microwave
applications.
SUMMARY
[0004] The compositions, materials, methods of preparation,
devices, and systems of this disclosure each have several aspects,
no single one of which is solely responsible for its desirable
attributes. Without limiting the scope of this invention, its more
prominent features will now be discussed briefly.
[0005] Any terms not directly defined herein shall be understood to
have all of the meanings commonly associated with them as
understood within the art. Certain terms are discussed below, or
elsewhere in the specification, to provide additional guidance to
the practitioner in describing the compositions, methods, systems,
and the like of various embodiments, and how to make or use them.
It will be appreciated that the same thing may be said in more than
one way. Consequently, alternative language and synonyms may be
used for any one or more of the terms discussed herein. No
significance is to be placed upon whether or not a term is
elaborated or discussed herein. Some synonyms or substitutable
methods, materials and the like are provided. Recital of one or a
few synonyms or equivalents does not exclude use of other synonyms
or equivalents, unless it is explicitly stated. Use of examples in
the specification, including examples of terms, is for illustrative
purposes only and does not limit the scope and meaning of the
embodiments herein.
[0006] Embodiments disclosed herein include methods for modifying
synthetic garnets used in RF applications to reduce or eliminate
Yttrium (Y) or other rare earth metals in the garnets without
adversely affecting the magnetic properties of the material. In
some embodiments, modified synthetic garnet compositions with
significantly reduced rare earth content are designed with
properties suitable for use as ferrite materials in devices such as
isolators and circulators, which are necessary components in all
cellular base stations.
[0007] Some embodiments include methods of substituting at least
some of the Yttrium (Y) in a garnet structure with other chemicals,
such as a combination of Bismuth and one or more high valency ions.
The substitute chemicals are selected to reduce the content of Y
without adversely affecting the performance of the material. The
rare earth substitutions described herein substantially reduce the
need for Yttrium Oxides in the synthesis of certain garnet
structures such as Yttrium Iron Garnets (YIG), and provide modified
crystalline materials useful in a variety of electronic
applications including but not limited to uses in devices for
cellular base stations.
[0008] In one embodiment, the method for modifying synthetic
garnets comprises substituting Bismuth (Bi) for some of the Yttrium
(Y) on the dodecahedral sites of the garnet structure and
introducing high valency non-magnetic ions, preferably greater than
+3, to the octahedral sites to replace some of the Iron (Fe) in the
garnet. The quantity and combination of substitute ions and
processing techniques are selected to ensure that the resulting
material has high magnetization with low linewidth, along with
reduced Yttrium (Y) content. In some embodiments, Calcium (Ca) is
also introduced to the dodecahedral sites of the garnet structure
for charge compensation induced by the high valency ions while at
the same time replace some or all of the remaining Yttrium (Y). In
some other embodiments, the method further comprises introducing
one or more high valency ions, such as Vanadium (V.sup.5+), to the
tetrahedral sites of the garnet structure to further reduce the
saturation magnetization of the resulting material.
[0009] In one implementation, the modified synthetic crystalline
material is represented by the formula
Bi.sub.xCa.sub.y+2xY.sub.1-x-y-2zFe.sub.5-y-zZr.sub.yV.sub.zO.sub.12,
wherein x is greater than or equal to 0.5 and less than or equal to
1.4, y is greater than or equal to 0.3 and less than or equal to
0.55, and z is greater than or equal to 0 or less than or equal to
0.6. Bi and Ca are placed on the dodecahedral sites, Zr is placed
on the octahedral sites, and V is placed on the tetrahedral sites.
In some versions, small amounts of Niobium (Nb) may be placed on
the octahedral site and small amounts of Molybdenum (Mo) on the
tetrahedral site. Preferably, the modified crystalline material has
a magnetic resonance linewidth of less than or equal to 11
Oersted.
[0010] In another embodiment, the modified synthetic crystalline
material is represented by the formula
Bi(Y,Ca).sub.2Fe.sub.4.2M.sup.I.sub.0.4M.sup.II.sub.0.4O.sub.12,
where M.sup.I is the octahedral substitution for Fe and can be
selected from the group consisting of In, Zn, Mg, Zr, Sn, Ta, Nb,
Fe, Ti, Sb, and combinations thereof where M.sup.II is the
tetrahedral substitution for Fe and can be selected from the group
consisting of: Ga, W, Mo, Ge, V, Si, and combinations thereof.
[0011] In yet another implementation, the modified synthetic
crystalline material is represented by the formula
Bi.sub.0.9Ca.sub.0.9xY.sub.2.1-0.9x(Zr.sub.0.7Nb.sub.0.1).sub.xFe.sub.5-0-
.8xO.sub.12, wherein x is greater than or equal to 0.5 and less
than or equal to 1.0.
[0012] In yet another implementation, the modified synthetic
crystalline material is represented by the formula
Bi.sub.xY.sub.3-x-0.35Ca.sub.0.35Zr.sub.0.35Fe.sub.4.65O.sub.12,
where x is greater than or equal to 0.5 and less than or equal to
1.0, more preferably x is greater or equal to 0.6 and less than or
equal to 0.8.
[0013] In yet another implementation, the modified synthetic
crystalline material is represented by the formula
Y.sub.2.15-2xBi.sub.0.5Ca.sub.0.35+2xZr.sub.0.35V.sub.xFe.sub.4.65-xO.sub-
.12, wherein x is greater than or equal to 0.1 and less than or
equal to 0.8.
[0014] In yet another implementation, a modified Yttrium based
garnet structure is provided. The modified Yttrium based garnet
structure comprises Bismuth (Bi.sup.3+) and Calcium (Ca.sup.2+)
doped dodecahedral sites, and tetravalent or pentavalent ion doped
octahedral sites, wherein Bi.sup.3+ occupies about 0 to 100 atomic
percent of the dodecahedral sites, Ca.sup.2+ occupies about 0 to 90
atomic percent of the dodecahedral sites, wherein the tetravalent
or pentavalent ions occupy about 0 to 50 atomic percent of the
octahedral sites, wherein said modified synthetic Yttrium based
garnet structure has a magnetic resonance linewidth of between 0
and 50 Oersteds. In some implementations, the modified Yttrium
based garnet structure further comprises Vanadium (V.sup.5+) doped
tetrahedral sites, wherein V.sup.5+ occupies about 0 to 50 atomic
percent of the tetrahedral sites. Preferably, Yttrium occupies the
balance of the dodecahedral sites of the modified Yttrium based
garnet structure. In some implementations, the modified Yttrium
based garnet structure is incorporated as a ferrite material in RF
devices such isolators, circulators, or resonators.
[0015] Advantageously, the substitution allows the use of
tetravalent, pentavalent, and other ions on the octahedral site of
the garnet structure, resulting in potentially high magnetization
with low linewidth, along with reduced Y content.
[0016] In some implementations, the present disclosure relates to a
synthetic garnet material having a structure including dodecahedral
sites, with Bismuth occupying at least some of the dodecahedral
sites. The garnet material has a dielectric constant value of at
least 21.
[0017] In some embodiments, the dielectric constant value can be in
a range of 25 to 32. In some embodiments, the garnet can be
represented by the formula Bi.sub.3-x(RE or
Ca).sub.xFe.sub.2-y(Me).sub.yFe.sub.3-z(M').sub.zO.sub.12 where x
is greater than or equal to 1.6 and less than or equal to 2.0, RE
represents a rare earth element, and each of Me and Me' represents
a metal element. The value of x can be approximately 1.6. The metal
element Me can include Zr and the value of y can be greater than or
equal to 0.35 and less than or equal to 0.75. The value of y can be
approximately 0.55. The metal element Me' can include V and the
value of z can be greater than or equal to 0 and less than or equal
to 0.525. The value of z can be approximately 0.525 such that the
garnet is substantially free of rare earth and the formula is
Bi.sub.1.4Ca.sub.1.6Zr.sub.0.55V.sub.0.525Fe.sub.3.925O.sub.12. For
such an example composition, the dielectric constant value can be
approximately 27. In some embodiments, the garnet material can have
a ferrimagnetic resonance linewidth value that is less than 12
Oersted.
[0018] According to a number of implementations, the present
disclosure relates to a method for fabricating synthetic garnet
material having dodecahedral sites, octahedral sites, and
tetrahedral sites. The method includes introducing Bismuth into at
least some of the dodecahedral sites. The method further includes
introducing high-polarization ions into at least some of either or
both of the octahedral and tetrahedral sites to yield a dielectric
constant value of at least 21 for the garnet material.
[0019] In some embodiments, the high-polarization ions can include
non-magnetic ions. The non-magnetic ions can include Zirconium in
octahedral sites in concentration selected to maintain a low
magnetic resonance linewidth. The magnetic resonance linewidth can
be less than or equal to 12 Oersted. The non-magnetic ions can
include Vanadium in tetrahedral sites.
[0020] In some embodiments, the dielectric constant value can be in
a range of 25 to 32. In some embodiments, the introduction of
Bismuth and high-polarization ions can result in the garnet
material being substantially free of rare earth.
[0021] In a number of implementations, the present disclosure can
include a circulator that includes a conductor having a plurality
of signal ports. The circulator further includes one or more
magnets configured to provide a magnetic field. The circulator
further includes one or more ferrite disks disposed relative to the
conductor and the one or more magnets so that a radio-frequency
(RF) signal is routed selectively among the signal ports due to the
magnetic field. Each of the one or more ferrite disks has an
enhanced dielectric constant value of at least 21 and at least some
garnet structures. The garnet structures include dodecahedral
sites, and at least some of the dodecahedral sites are occupied by
Bismuth.
[0022] In some embodiments, the garnet structures can be
substantially free of Yttrium. In some embodiments, the garnet
structures can be substantially free of rare earth elements.
[0023] In some embodiments, the ferrite disk can be a circular
shaped disk. In some embodiments, the circular shaped ferrite disk
can have a diameter that is reduced by a factor of square root of
(.epsilon./.epsilon.'), where .epsilon. is the dielectric constant
in a range of 14 to 16, and .epsilon.' is the enhanced dielectric
constant. In some embodiments, the circulator can be a transverse
magnetic (TM) mode device.
[0024] In accordance with some implementations, the present
disclosure relates to a packaged circulator module that includes a
mounting platform configured to receive one or more components
thereon. The packaged circulator module further includes a
circulator device mounted on the mounting platform. The circulator
device includes a conductor having a plurality of signal ports. The
circulator device further includes one or more magnets configured
to provide a magnetic field. The circulator further includes one or
more ferrite disks disposed relative to the conductor and the one
or more magnets so that a radio-frequency (RF) signal is routed
selectively among the signal ports due to the magnetic field. Each
of the one or more ferrite disks has an enhanced dielectric
constant value of at least 21 and at least some garnet structures.
The garnet structures include dodecahedral sites and at least some
thereof occupied by Bismuth. The packaged circulator module further
includes a housing mounted on the mounting platform and dimensioned
to substantially enclose and protect the circulator device.
[0025] In some implementations, the present disclosure relates to a
radio-frequency (RF) circuit board that includes a circuit
substrate configured to receive a plurality of components. The
circuit board further includes a plurality of circuits disposed on
the circuit substrate and configured to process RF signals. The
circuit board further includes a circulator device disposed on the
circuit substrate and interconnected with at least some of the
circuits. The circulator device includes a conductor having a
plurality of signal ports. The circulator device further includes
one or more magnets configured to provide a magnetic field. The
circulator further includes one or more ferrite disks disposed
relative to the conductor and the one or more magnets so that a
radio-frequency (RF) signal is routed selectively among the signal
ports due to the magnetic field. Each of the one or more ferrite
disks has an enhanced dielectric constant value of at least 21 and
at least some garnet structures. The garnet structures include
dodecahedral sites and at least some thereof occupied by Bismuth.
The circuit board further includes a plurality of connection
features configured to facilitate passing of the RF signals to and
from the RF circuit board.
[0026] According to some implementations, the present disclosure
relates to a radio-frequency (RF) system that includes an antenna
assembly configured to facilitate transmission and reception of RF
signals. The system further includes a transceiver interconnected
to the antenna assembly and configured to generate a transmit
signal for transmission by the antenna assembly and process a
received signal from the antenna assembly. The system further
includes a front end module configured to facilitate routing of the
transmit signal and the received signal. The front end module
includes one or more circulators, with each circulator including a
conductor having a plurality of signal ports. The circulator
further includes one or more magnets configured to provide a
magnetic field. The circulator further includes one or more ferrite
disks disposed relative to the conductor and the one or more
magnets so that a radio-frequency (RF) signal is routed selectively
among the signal ports due to the magnetic field. Each of the one
or more ferrite disks had an enhanced dielectric constant value of
at least 21 and at least some garnet structures. The garnet
structures include dodecahedral sites and at least some thereof
occupied by Bismuth.
[0027] In some embodiments, the system can include a base station.
In some embodiments, the base station can include a cellular base
station.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 schematically shows how materials having one or more
features described herein can be designed, fabricated, and
used.
[0029] FIG. 2 depicts a Yttrium based garnet crystal lattice
structure;
[0030] FIG. 3 is an example graph depicting variations of material
properties versus varying levels of Vanadium in crystalline
compositions represented by the formula
Y.sub.2.15-2xBi.sub.0.5Ca.sub.0.35+2xZr.sub.0.35V.sub.xFe.sub.4.65-xO.sub-
.12, where x=0.1 to 0.8.
[0031] FIG. 4 is an example graph depicting variations of material
properties versus varying levels of (Zr, Nb) in crystalline
compositions represented by the formula
Bi.sub.0.9Ca.sub.0.9xY.sub.2.1-0.9x(Zr.sub.0.7Nb.sub.0.1).sub.xFe.sub.5-0-
.8xO.sub.12, where x=0.5 to 1.0.
[0032] FIGS. 5A-5G are example graphs depicting the relationship
between firing temperature and various properties at varying levels
of Vanadium in crystalline compositions represented by the formula
Bi.sub.0.9Ca.sub.0.9+2xZr.sub.0.7Nb.sub.0.1V.sub.xFe.sub.4.2-xO.sub.12
where x=0-0.6.
[0033] FIG. 6 is an example graph depicting best linewidth versus
composition of varying Vanadium content in crystalline compositions
represented by the formula
Bi.sub.0.9Ca.sub.0.9+2xZr.sub.0.7Nb.sub.0.1V.sub.xFe.sub.4.2-xO.sub.12
where x=0-0.6.
[0034] FIG. 7 is an example graph illustrating the properties of
crystal compositions represented by the formula
Bi.sub.1.4Ca.sub.1.05-2xZr.sub.0.55V.sub.xFe.sub.4.45-xO.sub.12,
where x=0-0.525.
[0035] FIG. 8 illustrates an example process flow for making a
modified synthetic garnet having one or more features described
herein.
[0036] FIG. 9 shows an example ferrite device having one or more
garnet features as described herein.
[0037] FIG. 10 shows various properties as functions of Zr content
for an example composition
Bi.sub.0.5Y.sub.2.5-xCa.sub.xZr.sub.xFe.sub.5-xO.sub.12 where
Bi.sup.+3 content is substantially fixed at approximately 0.5 while
Zr.sup.+4 content is varied from 0 to 0.35.
[0038] FIG. 11 shows various properties as functions of Bi content
for an example composition
Bi.sub.xY.sub.2.65-xCa.sub.0.35Zr.sub.0.35Fe.sub.4.65O.sub.12 where
Zr.sup.+4 content is substantially fixed at approximately 0.35
while Bi.sup.+3 content is varied.
[0039] FIG. 12 shows dielectric constant and density as functions
of Bi content for the example composition of FIG. 11.
[0040] FIG. 13 shows plots of various properties as functions of Zr
content that extends beyond the 0.35 limit of the example
composition of FIG. 10.
[0041] FIG. 14 shows plots of various properties as functions of
V.sup.+5 content when Bi content is approximately 1.4 and Zr
content is approximately 0.55 for the example composition of FIG.
13.
[0042] FIGS. 15A and 15B show examples of size reduction that can
be implemented for ferrite devices having one or more features as
described herein.
[0043] FIGS. 16A and 16B show an example circulator/isolator having
ferrite devices as described herein.
[0044] FIG. 17 shows insertion loss plots and return loss plots for
two example 25 mm circulators, where one is based on a YCaZrVFe
garnet system with dielectric constant of 14.4, and another is
based on a Yttrium free BiCaZrVFe garnet system with dielectric
constant of 26.73.
[0045] FIGS. 18A and 18B show s-parameter data for an example 10 mm
circulator device having the high-dielectric Yttrium free BiCaZrVFe
garnet system of FIG. 17.
[0046] FIG. 19 shows an example of a packaged circulator
module.
[0047] FIG. 20 shows an example RF system where one or more of
circulator/isolator devices as described herein can be
implemented.
[0048] FIG. 21 shows a process that can be implemented to fabricate
a ceramic material having one or more features as described
herein.
[0049] FIG. 22 shows a process that can be implemented to form a
shaped object from powder material described herein.
[0050] FIG. 23 shows examples of various stages of the process of
FIG. 22.
[0051] FIG. 24 shows a process that can be implemented to sinter
formed objects such as those formed in the example of FIGS. 22 and
23.
[0052] FIG. 25 shows examples of various stages of the process of
FIG. 24.
DETAILED DESCRIPTION OF SOME EMBODIMENTS
[0053] The headings provided herein, if any, are for convenience
only and do not necessarily affect the scope or meaning of the
claimed invention.
[0054] FIG. 1 schematically shows how one or more chemical elements
(block 1), chemical compounds (block 2), chemical substances (block
3) and/or chemical mixtures (block 4) can be processed to yield one
or more materials (block 5) having one or more features described
herein. In some embodiments, such materials can be formed into
ceramic materials (block 6) configured to include a desirable
dielectric property (block 7), a magnetic property (block 8) and/or
an advanced material property (block 9).
[0055] In some embodiments, a material having one or more of the
foregoing properties can be implemented in applications (block 10)
such as radio-frequency (RF) application. Such applications can
include implementations of one or more features as described herein
in devices 12. In some applications, such devices can further be
implemented in products 11. Examples of such devices and/or
products are described herein.
[0056] Disclosed herein are methods of modifying synthetic garnet
compositions, such as Yttrium Iron Garnet (YIG), to reduce or
eliminate the use of rare earth metals in such compositions. Also
disclosed herein are synthetic garnet materials having reduced or
no rare earth metal content, methods of producing the materials,
and the devices and systems incorporating such materials. The
synthetic garnet materials prepared according to embodiments
described in the disclosure exhibit favorable magnetic properties
for microwave magnetic applications. These favorable properties
include but are limited to low magnetic resonance line width,
optimized density, saturation magnetization and dielectric loss
tangent. Applicants have surprisingly found that when garnet
compositions are doped with certain combinations of ions and
prepared using certain processing techniques, a significant amount
if not all of the rare earth elements can be substituted and yet
still result in microwave magnetic crystalline materials with
comparable, if not superior, performance characteristics as
commercially available garnets containing Yttrium (Y) or other rare
earth elements.
[0057] Synthetic garnets typically have the formula unit of
A.sub.3B.sub.5O.sub.12, where A and B are trivalent metal ions.
Yttrium Iron Garnet (YIG) is a synthetic garnet having the formula
unit of Y.sub.3Fe.sub.5O.sub.12, which includes Yttrium (Y) in the
3+ oxidation state and Iron (Fe) in the 3+ oxidation state. The
crystal structure of a YIG formula unit is depicted in FIG. 2. As
shown in FIG. 2, YIG has a dodecahederal site, an octahedral site,
and a tetrahedral site. The Y ions occupy the dodecahedral site
while the Fe ions occupy the octahedral and tetrahedral sites. Each
YIG unit cell, which is cubic in crystal classifications, has eight
of these formula units.
[0058] The modified synthetic garnet compositions, in some
embodiments, comprise substituting some or all of the Yttrium (Y)
in Yttrium Iron Garnets (YIG) with a combination of other ions such
that the resulting material maintains desirable magnetic properties
for microwave applications. There have been past attempts toward
doping YIG with different ions to modify the material properties.
Some of these attempts, such as Bismuth (Bi) doped YIG, are
described in "Microwave Materials for Wireless Applications" by D.
B. Cruickshank, which is hereby incorporated by reference in its
entirety. However, in practice ions used as substitutes may not
behave predictably because of, for example, spin canting induced by
the magnetic ion itself or by the effect of non-magnetic ions on
the environment adjacent magnetic ions, reducing the degree
alignment. Thus, the resulting magnetic properties cannot be
predicted. Additionally, the amount of substitution is limited in
some cases. Beyond a certain limit, the ion will not enter its
preferred lattice site and either remains on the outside in a
second phase compound or leaks into another site. Additionally, ion
size and crystallographic orientation preferences may compete at
high substitution levels, or substituting ions are influenced by
the ion size and coordination of ions on other sites. As such, the
assumption that the net magnetic behavior is the sum of independent
sub-lattices or single ion anisotropy may not always apply in
predicting magnetic properties.
[0059] Considerations in selecting an effective substitution of
rare earth metals in YIG for microwave magnetic applications
include the optimization of the density, the magnetic resonance
linewidth, the saturation magnetization, the Curie temperature, and
the dielectric loss tangent in the resulting modified crystal
structure. Magnetic resonance is derived from spinning electrons,
which when excited by an appropriate radio frequency (RF) will show
resonance proportional to an applied magnetic field and the
frequency. The width of the resonance peak is usually defined at
the half power points and is referred to as the magnetic resonance
linewidth. It is generally desirable for the material to have a low
linewidth because low linewidth manifests itself as low magnetic
loss, which is required for all low insertion loss ferrite devices.
The modified garnet compositions according to preferred embodiments
of the present invention provide single crystal or polycrystalline
materials with reduced Yttrium content and yet maintaining low
linewidth and other desirable properties for microwave magnetic
applications.
[0060] In some embodiments, a Yttrium based garnet is modified by
substituting Bismuth (Bi.sup.3+) for some of the Yttrium (Y.sup.3+)
on the dodecahedral sites of the garnet structure in combination
with introducing one or more ions, such as divalent (+2), trivalent
(+3), tetravalent (+4), pentavalent (+5) or hexavalent (+6)
non-magnetic ions to the octahedral sites of the structure to
replace at least some of the Iron (Fe.sup.3+). In a preferred
implementation, one or more high valency non-magnetic ions such as
Zirconium (Zr.sup.4+) or Niobium (Nb.sup.5+) can be introduced to
the octahedral sites.
[0061] In some embodiments, a Yttrium based garnet is modified by
introducing one or more high valency ions with an oxidation state
greater than 3+ to the octahedral or tetrahedral sites of the
garnet structure in combination with substituting Calcium
(Ca.sup.2+) for Yttrium (Y.sup.3+) in the dodecahedral site of the
structure for charge compensation induced by the high valency ions,
hence reducing the Y.sup.3+ content. When non-trivalent ions are
introduced, valency balance is maintained by introducing, for
example, divalent Calcium (Ca.sup.2+) to balance the non-trivalent
ions. For example, for each 4+ ion introduced to the octahedral or
tetrahedral sites, one Y.sup.3+ ion is substituted with a Ca.sup.2+
ion. For each 5+ ion, two Y.sup.3+ ions are replaced by Ca.sup.2+
ions. For each 6+ ion, three Y.sup.3+ ions are replaced by
Ca.sup.2+ ions. For each 6+ ion, three Y.sup.3+ ions are replaced
by Ca.sup.2+ ions. In one implementation, one or more high valence
ions selected from the group consisting of Zr.sup.4+, Sn.sup.4+,
Ti.sup.4+, Nb.sup.5+, Ta.sup.5+, Sb.sup.5+, W.sup.6+, and Mo.sup.6+
is introduced to the octahedral or tetrahedral sites, and divalent
Calcium (Ca.sup.2+) is used to balance the charges, which in turn
reduces Y.sup.3+ content.
[0062] In some embodiments, a Yttrium based garnet is modified by
introducing one or more high valency ions, such as Vanadium
(V.sup.5+), to the tetrahedral site of the garnet structure to
substitute for Fe.sup.3+ to further reduce the magnetic resonance
linewidth of the resulting material. Without being bound by any
theory, it is believed that the mechanism of ion substitution
causes reduced magnetization of the tetrahedral site of the
lattice, which results in higher net magnetization of the garnet,
and by changing the magnetocrystalline environment of the ferric
ions also reduces anisotropy and hence the ferromagnetic linewidth
of the material.
[0063] In some embodiments, Applicant has found that a combination
of high Bismuth (Bi) doping combined with Vanadium (V) and
Zirconium (Zr) induced Calcium (Ca) valency compensation could
effectively displace all or most of the Yttrium (Y) in microwave
device garnets. Applicants also have found that certain other high
valency ions could also be used on the tetrahedral of octahedral
sites and that a fairly high level of octahedral substitution in
the garnet structure is preferred in order to obtain magnetic
resonance linewidth in the 5 to 20 Oersted range. Moreover, Yttrium
displacement is preferably accomplished by adding Calcium in
addition to Bismuth to the dodecahedral site. Doping the octahedral
or tetrahedral sites with higher valency ions, preferably greater
than 3+, would allow more Calcium to be introduced to the
dodecahedral site to compensate for the charges, which in turn
would result in further reduction of Yttrium content.
Modified Synthetic Garnet Compositions:
[0064] In one implementation, the modified synthetic garnet
composition may be represented by general Formula I:
Bi.sub.xCa.sub.y+2xY.sub.1-x-y-2zFe.sub.5-y-zZr.sub.yV.sub.zO.sub.12,
where x=0 to 3, y=0 to 1, and z=0 to 1.5, more preferably x=0.5 to
1.4, y=0.3 to 0.55, and z=0 to 0.6. In a preferred implementation,
0.5 to 1.4 formula units of Bismuth (Bi) is substituted for some of
the Yttrium (Y) on the dodecahedral site, 0.3 to 0.55 formula units
of Zirconium (Zr) is substituted for some of the Iron (Fe) on the
octahedral site. In some embodiments, up to 0.6 formula units of
Vanadium (V) is substituted for some of the Iron (Fe) on the
tetrahedral site. Charge balance is achieved by Calcium (Ca)
substituting for some or all of the remaining Yttrium (Y). In some
other embodiments, small amounts of Niobium (Nb) may be placed on
the octahedral site and small amounts of Molybdenum (Mo) may be
placed on the tetrahedral site.
[0065] In another implementation, the modified synthetic garnet
composition may be represented by general Formula II:
Bi.sub.xY.sub.3-x-0.35Ca.sub.0.35Zr0.35Fe.sub.4.65O.sub.12, where
x=0.5 to 1.0, preferably x=0.6 to 0.8, more preferably x=0.5. In
this implementation, 0.5 to 1.0 formula units of Bismuth (Bi) is
substituted for some of the Yttrium (Y) on the dodecahedral site
and Zirconium (Zr) is substituted for some of the Iron (Fe) on the
octahedral site. Calcium (Ca.sup.2+) is added to the dodecahedral
site to replace some of the remaining Y to balance the Zr charges.
Bi content can be varied to achieve varying material properties
while Zr is held fixed at Zr=0.35.
[0066] In another implementation, the modified garnet composition
may be represented by general Formula III:
Bi(Y,Ca).sub.2Fe.sub.4.2M.sup.I.sub.0.4M.sup.II.sub.0.4O.sub.12,
where M.sup.I is the octahedral substitution for Fe and can be
selected from one or more of the following elements: In, Zn, Mg,
Zr, Sn, Ta, Nb, Fe, Ti, and Sb, where M.sup.II is the tetrahedral
substitution for Fe and can be selected from one or more of the
following elements: Ga, W, Mo, Ge, V, Si.
[0067] In another implementation, the modified synthetic garnet
composition may be represented by general Formula IV:
Y.sub.2.15-2xBi.sub.0.5Ca.sub.0.35+2xZr.sub.0.35V.sub.xFe.sub.4.65-xO.sub-
.12, wherein x=0.1 to 0.8. In this implementation, 0.1 to 0.8
formula units of Vanadium (V) is added to the tetrahedral site to
substitute for some of the Iron (Fe), and Calcium (Ca) is added to
balance the V charges and replace some of the remaining Y while the
levels of Bi and Zr remain fixed similar to Formula III. FIG. 3
illustrates variations of material properties in connection with
varying levels of V. As shown in FIG. 3, the dielectric constant
and density of the material remain largely constant with varying
levels of V. Increasing levels of V reduces the 4 PiMs by about 160
Gauss for each 0.1 of V. As further shown in FIG. 3, there are no
appreciable changes in 3 dB linewidth up to V=0.5.
[0068] In another implementation, the modified synthetic garnet
composition may be represented by Formula V:
Bi.sub.0.9Ca.sub.0.9xY.sub.2.1-0.9x(Zr.sub.0.7Nb.sub.0.1).sub.xFe.sub.5-0-
.8xO.sub.12, wherein x=0.5 to 1.0. In this implementation, the
octahedral substitution is made with two high valency ions:
Zr.sup.4+ and Nb.sup.5+ with Bi held constant at 0.9. FIG. 4
illustrates variations of material properties in connection with
varying levels of (Zr, Nb). As shown in FIG. 4, the magnetic
resonance linewidth decreased with higher octahedral substitutions.
The magnetization also fell as the increase in total non-magnetic
ions overcomes the higher non-magnetic octahedral
substitutions.
[0069] In another implementation, the modified synthetic garnet
composition may be represented by Formula VI:
Bi.sub.0.9Ca.sub.0.9+2xY.sub.2.1-0.9-2xZr.sub.0.7Nb.sub.0.1V.sub.xFe.sub.-
4.2-xO.sub.12, where V=0-0.6. In this implementation, Vanadium is
introduced to the octahedral site in addition to Zr and Nb. When
V=0.6, Y is completely replaced. FIGS. 5A-5G illustrate the
relationship between firing temperatures and various material
properties as V level increases from 0 to 0.6. As illustrated, the
3 dB linewidth, measured in accordance with ASTM A883/A883M-01,
tends to remain below 50 Oe at all V levels at firing temperatures
below 1040.degree. C. FIG. 6 illustrates the best linewidth at
varying firing temperatures versus composition at varying levels of
V of one preferred embodiment. In some implementations, the
linewidth can be further reduced by annealing the material. The
effect of annealing on linewidth of
Bi.sub.0.9Ca_Zr.sub.0.7Nb.sub.0.1V.sub.xFe.sub.4.2-xO.sub.12, where
x=0.1 to 0.5 is illustrated in Table 1 below.
TABLE-US-00001 TABLE 1 Linewidth (Oe) and Curie Temp. (.degree. C.)
Data for
Bi.sub.0.9Ca.sub.0.9+2xY.sub.2.1-0.9-2x(Zr,Nb).sub.0.8V.sub.xFe.sub.4.2-x-
O.sub.12 Heat Treatment Heat Heat (Calcined Treatment 3 dB 3 dB
Treatment 3 dB Blend + 3 dB 3 dB after (Initial before after
(Calcined before 3 dB after Extended before extended Curie Formula
Blend) anneal anneal Blend) anneal anneal Milling) anneal anneal
Temp V = 0.5 1050 39 25 1030 38 20 1030 38 17 108 V = 0.4 1050 44
27 1030 48 18 1030 42 16 112 V = 0.3 1050 52 32 1030 46 19 1030 48
15 111 V = 0.2 1050 59 43 1030 55 21 1030 62 17 108 V = 0.1 1050 78
62 1030 61 24 1030 55 21 107
[0070] In another implementation, the modified synthetic garnet
composition may be represented by Formula VI:
Bi.sub.1.4Ca.sub.1.05-2xZr.sub.0.55V.sub.xFe.sub.4.45-xO.sub.12,
where x=0-0.525. In this implementation, the level of Bi doping is
increased while the level of octahedral substitution is decreased.
The material formed has higher Curie temperature and low linewidth.
The Vanadium (V) content is varied from 0 to 0.525. When V=0.525,
the composition is free of Yttrium. The resulting material achieved
a linewidth of 20 Oe without subsequently heat treatment. FIG. 7
illustrates the properties of the material with varying amount of
V. As shown in FIG. 7, V drops the dielectric constant rapidly,
about 1 unit for each 0.1 of V in the formula unit, and drops the
magnetization by about 80 Gauss for each 0.1 of V. Optimizing the
processing parameters such as firing conditions have produced
linewidth as low as 11 or V at or close to 0.525, which is free of
Y. These values are comparable to commercially available Calcium
Yttrium Zirconium Vanadium garnets of the same magnetization.
[0071] In another implementation, the modified synthetic garnet
composition may be represented by Formula VII:
Y.sub.2CaFe.sub.4.4Zr.sub.0.4Mo.sub.0.2O.sub.12. In this
implementation, high valency ion Molybdenum (Mo) is added to the
tetrahedral site to create a single phase crystal. In other
implementations, the modified synthetic garnet compositions can be
represented by a formula selected from the group consisting of:
BiY.sub.2Fe.sub.4.6In.sub.0.4O.sub.12,
BiCa.sub.0.4Y.sub.1.6Fe.sub.4.6Zr.sub.0.4O.sub.12,
BiCa.sub.0.4Y.sub.1.6Fe.sub.4.6Ti.sub.0.4O.sub.12,
BiCa.sub.0.8Y.sub.1.2Fe.sub.4.6Sb.sub.0.4O.sub.12,
BiY.sub.2Fe.sub.4.6Ga.sub.0.4O.sub.12,
BiCa.sub.1.2Y.sub.0.8Fe.sub.4.2In.sub.0.4Mo.sub.0.4O.sub.12,
BiY.sub.1.2Ca.sub.0.8Fe.sub.4.2Zn.sub.0.4Mo.sub.0.4O.sub.12,
BiY.sub.1.2Ca.sub.0.8Fe.sub.4.2Mg.sub.0.4Mo.sub.0.4O.sub.12,
BiY.sub.0.4Ca.sub.1.6Fe.sub.4.2Zr.sub.0.4Mo.sub.0.4O.sub.12,
BiY.sub.0.4Ca.sub.1.6Fe.sub.4.2Sn.sub.0.4Mo.sub.0.4O.sub.12,
BiCa.sub.2Fe.sub.4.2Ta.sub.0.4Mo.sub.0.4O.sub.12,
BiCa.sub.2Fe.sub.4.2Nb.sub.0.4Mo.sub.0.4O.sub.12,
BiY.sub.0.8Ca.sub.1.2Fe.sub.4.6Mo.sub.0.4O.sub.12, and
BiY.sub.0.4Ca.sub.1.6Fe.sub.4.2Ti.sub.0.4Mo.sub.0.4O.sub.12.
Preparation of the Modified Synthetic Garnet Compositions:
[0072] The preparation of the modified synthetic garnet materials
can be accomplished by using known ceramic techniques. A particular
example of the process flow is illustrated in FIG. 8.
[0073] As shown in FIG. 8, the process begins with step 106 for
weighing the raw material. The raw material may include oxides and
carbonates such as Iron Oxide (Fe.sub.2O.sub.3), Bismuth Oxide
(Bi.sub.2O.sub.3), Yttrium Oxide (Y.sub.2O.sub.3), Calcium
Carbonate (CaCO.sub.3), Zirconium Oxide (ZrO.sub.2), Vanadium
Pentoxide (V.sub.2O.sub.5), Yttrium Vanadate (YVO.sub.4), Bismuth
Niobate (BiNbO.sub.4), Silica (SiO.sub.2), Niobium Pentoxide
(Nb.sub.2O.sub.5), Antimony Oxide (Sb.sub.2O.sub.3), Molybdenum
Oxide (MoO.sub.3), Indium Oxide (In.sub.2O.sub.3), or combinations
thereof. In one embodiment, raw material consisting essentially of
about 35-40 wt % Bismuth Oxide, more preferably about 38.61 wt %;
about 10-12 wt % Calcium Oxide, more preferably about 10.62 wt %;
about 35-40 wt % Iron Oxide, more preferably about 37 wt %, about
5-10 wt % Zirconium Oxide, more preferably about 8.02 wt %; about
4-6 wt % Vanadium Oxide, more preferably about 5.65 wt %. In
addition, organic based materials may be used in a sol gel process
for ethoxides and/or acrylates or citrate based techniques may be
employed. Other known methods in the art such as co-precipitation
of hydroxides may also be employed as a method to obtain the
materials. The amount and selection of raw material depend on the
specific formulation.
[0074] After the raw material is weighed, they are blended in Step
108 using methods consistent with the current state of the ceramic
art, which can include aqueous blending using a mixing propeller,
or aqueous blending using a vibratory mill with steel or zirconia
media. In some embodiments, a glycine nitrate or spray pyrolysis
technique may be used for blending and simultaneously reacting the
raw materials.
[0075] The blended oxide is subsequently dried in Step 110, which
can be accomplished by pouring the slurry into a pane and drying in
an oven, preferably between 100-400.degree. C. or by spray drying,
or by other techniques known in the art.
[0076] The dried oxide blend is processed through a sieve in Step
112, which homogenizes the powder and breaks up soft agglomerates
that may lead to dense particles after calcining.
[0077] The material is subsequently processed through a
pre-sintering calcining in Step 114. Preferably, the material is
loaded into a container such as an alumina or cordierite sagger and
heat treated in the range of about 800-1000.degree. C., more
preferably about 900-950.degree. C. Preferably, the firing
temperature is low as higher firing temperatures have an adverse
effect on linewidth.
[0078] After calcining, the material is milled in Step 116,
preferably in a vibratory mill, an attrition mill, a jet mill or
other standard comminution technique to reduce the median particle
size into the range of about 0.5 micron to 10 microns. Milling is
preferably done in a water based slurry but may also be done in
ethyl alcohol or another organic based solvent.
[0079] The material is subsequently spray dried in Step 118. During
the spray drying process, organic additives such as binders and
plasticizers can be added to the slurry using techniques known in
the art. The material is spray dried to provide granules amenable
to pressing, preferably in the range of about 10 microns to 150
microns in size.
[0080] The spray dried granules are subsequently pressed in Step
120, preferably by uniaxial or isostatic pressing to achieve a
pressed density to as close to 60% of the x-ray theoretical density
as possible. In addition, other known methods such as tape casting,
tape calendaring or extrusion may be employed as well to form the
unfired body.
[0081] The pressed material is subsequently processed through a
calcining process in Step 122. Preferably, the pressed material is
placed on a setter plate made of material such as alumina which
does not readily react with the garnet material. The setter plate
is heated in a periodic kiln or a tunnel kiln in air or pressure
oxygen in the range of between about 850.degree. C.-100.degree. C.
to obtain a dense ceramic compact. Other known treatment techniques
such as induction heat may also be used in this step.
[0082] The dense ceramic compact is machined in the Step 124 to
achieve dimensions suitable or the particular applications.
[0083] Radio-frequency (RF) applications that utilize synthetic
garnet compositions can include ferrite devices having relatively
low magnetic resonance linewidths (e.g., approximately 11 Oe or
less) as described in reference to FIGS. 2-8. RF applications can
also include devices, methods, and/or systems having or related to
garnet compositions having reduced or substantially nil reduced
earth content. As described herein, such garnet compositions can be
configured to yield relatively high dielectric constants; and such
a feature can be utilized to provide advantageous functionalities.
It will be understood that at least some of the compositions,
devices, and methods described in reference to FIGS. 2-8 can be
applied to such implementations.
[0084] FIG. 9 shows a radio-frequency (RF) device 200 having garnet
structure and chemistry, and thus a plurality of dodecahedral
structures, octahedral structures, and tetrahedral structures. The
device 200 can include garnet structures (e.g., a garnet structure
220) formed from such dodecahedral, octahedral, and tetrahedral
structures. Disclosed herein are various examples of how
dodecahedral sites 212, octahedral sites 208, and tetrahedral sites
204 can be filled by or substituted with different ions to yield
one or more desirable properties for the RF device 200. Such
properties can include, but are not limited to desirable RF
properties and cost-effectiveness of manufacturing of ceramic
materials that can be utilized to fabricate the RF device 200. By
way of an example, disclosed herein are ceramic materials having
relatively high dielectric constants, and having reduced or
substantially nil rare earth contents.
[0085] Some design considerations for achieving such features are
now described. Also described are example devices and related RF
performance comparisons. Also described are example applications of
such devices, as well as fabrication examples.
Rare Earth Garnets:
[0086] Garnet systems in commercial use typically belong to a
series of compositions that can be expressed as Y.sub.3-x(RE or
Ca).sub.xFe.sub.2-y(Me).sub.yFe.sub.3-z(M').sub.zO.sub.12, where
"RE" represents a non-Y rare earth element. The non-Y rare earth
element (RE) can be, for example, Gd for temperature compensation
of magnetization, with small amounts of Ho sometimes used for high
power doping purposes. Rare earths are typically trivalent and
occupy dodecahedral sites. "Me" in octahedral sites is typically
non-magnetic (e.g., typically Zr.sup.+4, although In.sup.+3 or
Sn.sup.+4 can been used, typically at around y=0.4 in the formula).
"Me'" in tetrahedral sites is typically non-magnetic (e.g.,
typically Al.sup.+3 or V.sup.+5, where z can vary from 0 to around
1 in the formula to give a range of magnetizations). Ca.sup.+2 is
typically used in dodecahedral sites for valency compensation when
the octahedral or tetrahedral substitution is an ion of
valency>3. Based on the foregoing, one can see that such
commercial garnet systems contain greater than 40% Y or other RE
elements, with the balance mainly Fe.sup.+3 on octahedral and
tetrahedral sites.
Ferrite Device Design Considerations:
[0087] Magnetization (4.pi.M.sub.s) of ferrite devices for RF
applications such as cellular infrastructure typically operate at
400 MHz to 3 GHz in an above-resonance mode. To achieve typical
bandwidths of about 5 to 15%, magnetizations in a range of
approximately 1,000 to 2,000 Gauss (approximately 0.1 to 0.2 Tesla)
are desired.
[0088] Magnetic losses associated with ferrite devices can be
determined by a ferrimagnetic resonance linewidth .DELTA.H.sub.o.
Values for such linewidth are typically less than about 30 Oersted
(about 0.377 Ampere-turns/meter), and are typically equivalent to
K.sub.1/M.sub.s, where K.sub.1 is a first order magnetocrystalline
anisotropy, determined by the anisotropy of the Fe.sup.+3 ion in
two of its sites if non-magnetic Y is the only RE. There can also
be a fractional porosity (p) contribution to linewidth,
approximately 4.pi.M.sub.s.times.p.
[0089] Dielectric losses associated with ferrite devices are
typically selected so that loss tangent .delta. satisfies a
condition tan .delta.<0.0004. The Curie temperature associated
with ferrite devices can be expected to exceed approximately
160.degree. C. for the above range of magnetizations.
Bismuth Garnets:
[0090] Single crystal materials with a formula
Bi.sub.(3-2x)Ca.sub.2xFe.sub.5-xV.sub.xO.sub.12 have been grown in
the past, where x was 1.25. A 4.pi.M.sub.s value of about 600 Gauss
was obtained (which is suitable for some tunable filters and
resonators in a 1-2 GHz range), with linewidths of about 1 Oersted,
indicating low intrinsic magnetic losses for the system. However,
the level of Bi substitution was only about 0.5 in the formula.
[0091] Attempts to make single phase polycrystalline materials
(with a formula Bi.sub.3-2xCa.sub.2xV.sub.xFe.sub.5-xO.sub.12)
similar to the single crystal materials were successful only in a
region of x>0.96, effectively confining the 4.pi.M.sub.s to less
than about 700 Oersted and resulting in poor linewidths (greater
than 100 Oersted). Small amounts of Al.sup.+3 reduced the linewidth
to about 75 Oersted, but increased Al.sup.+3 reduced 4.pi.M.sub.s.
Bi substitution was only about 0.4 in the formula for these
materials.
[0092] For Faraday rotation devices, the Faraday rotation can be
essentially proportionate to the level of Bi substitution in
garnets, raising interest in increasing the level of substitution.
Anisotropy is generally not a major factor for optical
applications, so substitution on the octahedral and tetrahedral
site can be based on maximizing the rotation. Thus, in such
applications, it may be desirable to introduce as much Bi.sup.+3
into the dodecahedral site as possible. The maximum level of
Bi.sup.+3 can be influenced by the size of the dodecahedral rare
earth trivalent ion, and can vary between 1.2 and 1.8 in the
formula.
[0093] In some situations, the level of Bi.sup.+3 substitution can
be affected by substitutions on the other sites. Because Bi.sup.+3
is non-magnetic, it can influence the Faraday rotation through its
effect on the tetrahedral and octahedral Fe.sup.+3 ions. Since this
is thought to be a spin-orbital interaction, where Bi.sup.+3
modifies existing Fe.sup.+3 pair transitions, one can expect both a
change in the anisotropy of the Fe.sup.+3 ions and optical effects
including large Faraday rotation. The Curie temperature of
Bi.sup.+3 substituted YIG can also increase at low Bi.sup.+3
substitution.
Bi Substitution in Polycrystalline Garnets:
[0094] To see the effects (e.g., low magnetocrystalline anisotropy
and hence low magnetic losses) that can result from combinations of
Bi.sup.+3 on the dodecahedral site and Zr.sup.+4 on the octahedral
site, following approaches were tested. The first example
configuration included fixed Bi and variable Zr in a formula
Bi.sub.0.5Y.sub.2.5-xCa.sub.xZr.sub.xFe.sub.5-xO.sub.12, where x
varied from approximately 0 to 0.35. The second example
configuration included fixed Zr and variable Bi in a formula
Bi.sub.xY.sub.2.65-xCa.sub.0.35Zr.sub.0.35Fe.sub.4.65O.sub.12,
where x varied from approximately 0.5 to 1.4.
[0095] FIG. 10 shows various properties as functions of Zr content
for the first configuration
(Bi.sub.0.5Y.sub.2.5-xCa.sub.xZr.sub.xFe.sub.5-xO.sub.12) where
Bi.sup.+3 content was fixed at approximately 0.5 while Zr.sup.+4
content was varied from 0 to 0.35. From the plots, one can see that
the 0.5 Bi material at zero Zr has a relatively high linewidth
(near 80 Oe after porosity correction). This is in contrast to
standard Y.sub.3Fe.sub.5O.sub.12, which has a much lower corrected
value of about 17 Oe, indicating that non-magnetic Bi.sup.+3 can
substantially raise the magnetocrystalline anisotropy, K.sub.1
contribution from the octahedral and tetrahedral Fe.sup.+3.
[0096] One can also see, as found in Bi-free garnet, that the
introduction of increasing amounts of Zr.sup.+4 progressively
lowers the anisotropy contribution, and very low linewidths are
found at Zr=0.35, albeit with some reduction in Curie temperature.
The expected result is a higher Curie temperature from the Bi
content being offset by the Zr contribution.
[0097] As further shown in FIG. 10, although the 4.pi.M.sub.s value
generally increases with Zr content, the effect on the
K.sub.1/M.sub.s contribution is overwhelmingly on K.sub.1,
representing a significant technical breakthrough.
[0098] FIG. 11 shows various properties as functions of Bi content
for the second configuration
(Bi.sub.xY.sub.2.65-xCa.sub.0.35Zr.sub.0.35Fe.sub.4.65O.sub.12)
where Zr.sup.+4 content was fixed at approximately 0.35 while
Bi.sup.+3 content was varied. FIG. 12 shows dielectric constant and
density as functions of Bi content for the same configuration. One
can see that a large increase in dielectric constant occurs when Bi
content is greater than approximately 1. In some implementations,
such an increased dielectric constant can be utilized to yield RF
devices having desirable features.
[0099] It appeared that the maximum Bi.sup.+3 content was 1.4 in
the formula, and therefore can be a optimum or desired amount to
replace Y.sup.+3, at least in the range of Zr.sup.+4 substitution
examined. At the example desired Bi content of 1.4, there was a
desire to optimize the Zr.sup.+4 content to reduce or minimize the
linewidth without substantially reducing the Curie temperature.
Also considered was a possibility of implementing a range of
V.sup.+5 substitutions which can yield a range of magnetizations
without much reduction in Curie temperature (e.g., as found in
Y-based Zr or In Ca--V garnets).
[0100] Based at least in part on the foregoing, the following
substitutions were tested to optimize or improve Bi-substituted
garnet compositions. For example, by using Ca.sup.+2 to balance
V.sup.+5, more Y could be displaced, at a rate of 2 Ca.sup.+2 for 1
V.sup.+5. In another example, Zr.sup.+4 can yield 1:1 substitution
of Ca.sup.+2 for Y; thus, if Nb.sup.+5 could be used instead on the
octahedral site, more Y could be removed from the compositions.
[0101] FIG. 13 shows plots of various properties as functions of Zr
content that extends beyond the 0.35 limit described in reference
to FIG. 10. Such measurements were based on the foregoing selection
of Bi content (approximately 1.4) to refine or optimize the Zr
content. Based on such measurements, an example Zr content of 0.55
was selected to test effects of variation of V.sup.+5 content.
[0102] FIG. 14 shows plots of various properties as functions of
V.sup.+5 content. For such measurements, Bi content was held as
approximately 1.4, and Zr content was held at approximately 0.55.
It is noted that at the maximum V.sup.+5 substitution, the example
composition
(Bi.sub.1.4Ca.sub.1.6Zr.sub.0.55V.sub.0.525Fe.sub.3.925O.sub.12) is
substantially free of rare earth.
[0103] In the context of RF applications, following observations
can be made for the foregoing example rare earth-free composition
(Bi.sub.1.4Ca.sub.1.6Zr.sub.0.55V.sub.0.525Fe.sub.3.925O.sub.12).
Dielectric constant is approximately 27; and this is thought to be
due to the "lone pair" of electrons on Bi.sup.+3 which can greatly
increase the polarizability of the ion. Dielectric loss is less
than 0.0004, which is useful for most applications. Magnetic loss
(as linewidth) is approximately 11 Oersted, which is comparable
with the best Y based garnets. 4.pi.M.sub.s is approximately 1150
Gauss, which is useful for many RF devices such as those used in
cellular infrastructures. Curie temperature is approximately
160.degree. C., which is useful for most applications.
Examples of Devices Having Rare Earth Free or Reduced Garnets
[0104] As described herein, garnets having reduced or no rare earth
content can be formed, and such garnets can have desirable
properties for use in devices for applications such as RF
applications. In some implementations, such devices can be
configured to take advantage of unique properties of the Bi.sup.+3
ion.
[0105] For example, the "lone pair" of electrons on the Bi.sup.+3
ion can raise the ionic polarizability and hence the dielectric
constant. This is consistent with the measurement observed in
reference to FIG. 14. In that example, the dielectric constant
roughly doubled, from 15 to 27 as one went from standard YCaZrV
garnets to BiCaZrV garnets when Bi was at maximum substitution at
1.4 in the formula. Such an increase in dielectric constant can be
utilized in a number of ways.
[0106] For example, because the center frequency of a ferrite
device (such as a garnet disk) operating in a split polarization
transverse magnetic (TM) mode is proportional to
1/(.epsilon.).sup.1/2, doubling the dielectric constant (.epsilon.)
can reduce the frequency by a factor of square root of 2
(approximately 1.414). As described herein in greater detail,
increasing the dielectric constant by, for example, a factor of 2,
can result in a reduction in a lateral dimension (e.g., diameter)
of a ferrite disk by factor of square root of 2. Accordingly, the
ferrite disk's area can be reduced by a factor of 2. Such a
reduction in size can be advantageous since the device's footprint
area on an RF circuit board can be reduced (e.g., by a factor of 2
when the dielectric constant is increased by a factor of 2).
Although described in the context of the example increase by a
factor of 2, similar advantages can be realized in configurations
involving factors that are more or less than 2.
Reduced Size Circulators/Isolators Having Ferrite with High
Dielectric Constant:
[0107] As described herein, ferrite devices having garnets with
reduced or no rare earth content can be configured to include a
high dielectric constant property. Various design considerations
concerning dielectric constants as applied to RF applications are
now described. In some implementations, such designs utilizing
garnets with high dielectric constants may or may not necessarily
involve rare earth free configurations.
[0108] Values of dielectric constant for microwave ferrite garnets
and spinels commonly fall in a range of 12 to 18 for dense
polycrystalline ceramic materials. Such garnets are typically used
for above ferromagnetic resonance applications in, for example, UHF
and low microwave region, because of their low resonance linewidth.
Such spinels are typically used at, for example, medium to high
microwave frequencies, for below resonance applications, because of
their higher magnetization. Most, if not substantially all,
circulators or isolators that use such ferrite devices are designed
with triplate/stripline or waveguide structures.
[0109] Dielectric constant values for low linewidth garnets is
typically in a range of 14 to 16. These materials can be based on
Yttrium iron garnet (YIG) with a value of approximately 16, or
substituted versions of that chemistry with Aluminum or, for
example, Zirconium/Vanadium combinations which can reduce the value
to around 14. Although for example Lithium Titanium based spinel
ferrites exist with dielectric constants up to close to 20, these
generally do not have narrow linewidths; and thus are not suitable
for many RF applications.
[0110] As described herein, garnets made using Bismuth substituted
for Yttrium can have much higher dielectric constants. Also as
described herein, when Zirconium is used in tandem with Bismuth
substitution to maintain low linewidths, then the dielectric
constant of the garnet can increase as shown by way of examples in
Table 2.
TABLE-US-00002 TABLE 2 Den- Dielectric 4.pi. M.sub.s Linewidth sity
Composition Constant (Gauss) (Oersted) (g/cc)
Bi.sub.0.5Ca.sub.0.35Y.sub.2.15Zr.sub.0.35Fe.sub.4.65O.sub.12 18.93
1985 25 5.485
Bi.sub.0.9Ca.sub.0.35Y.sub.1.75Zr.sub.0.35Fe.sub.4.65O.sub.12 21.35
1925 67 5.806
Bi.sub.1.4Ca.sub.0.35Y.sub.1.25Zr.sub.0.35Fe.sub.4.65O.sub.12 31.15
1857 52 6.041
[0111] Table 2 shows that it is possible to more than double the
dielectric constant of garnets. In some implementations, an
increase in dielectric constant can be maintained for compositions
containing Bismuth, including those with other non-magnetic
substitution on either or both of the octahedral and tetrahedral
sites (e.g., Zirconium or Vanadium, respectively). By using ions of
higher polarization, it is possible to further increase the
dielectric constant. For example, Niobium or Titanium can be
substituted into the octahedral or tetrahedral site; and Titanium
can potentially enter both sites.
[0112] In some implementations, a relationship between ferrite
device size, dielectric constant, and operating frequency can be
represented as follows. There are different equations that can
characterize different transmission line representations. For
example, in above-resonance stripline configurations, the radius R
of a ferrite disk can be characterized as
R=1.84/[2.pi.(effective permeability).times.(dielectric
constant)].sup.1/2 (1)
where (effective permeability)=H.sub.dc+4.pi.M.sub.s/H.sub.dc, with
H.sub.dc being the magnetic field bias. Equation 1 shows that, for
a fixed frequency and magnetic bias, the radius R is inversely
proportional to the square root of the dielectric constant.
[0113] In another example, in below-resonance stripline
configurations, a relationship for ferrite disk radius R similar to
Equation 1 can be utilized for weakly coupled quarter wave
circulators where the low bias field corresponds to below-resonance
operation. For below-resonance waveguide configurations (e.g., in
disk or rod waveguides), both lateral dimension (e.g., radius R)
and thickness d of the ferrite can influence the frequency.
However, the radius R can still be expressed as
R=.lamda./[2.pi.(dielectric
constant).sup.1/2][((.pi.R)/(2d)).sup.2+(1.84).sup.2].sup.1/2,
(2)
which is similar to Equation 1 in terms of relationship between R
and dielectric constant.
[0114] The example relationship of Equation 2 is in the context of
a circular disk shaped ferrites. For a triangular shaped resonator,
the same waveguide expression can used, but in this case, A
(altitude of the triangle) being equal to 3.63.times..lamda./2.pi.
applies instead of the radius in the circular disk case.
[0115] In all of the foregoing example cases, one can see that by
increasing the dielectric constant (e.g., by a factor of 2), one
can expect to reduce the size of the ferrite (e.g., circular disk
or triangle) by a factor of square root of 2, and thereby reduce
the area of the ferrite by a factor of 2. As described in reference
to Equation 2, thickness of the ferrite can also be reduced.
[0116] In implementations where ferrite devices are used as RF
devices, sizes of such RF devices can also be reduced. For example,
in a stripline device, a footprint area of the device can be
dominated by the area of the ferrite being used. Thus, one can
expect that a corresponding reduction in device size would be
achieved. In a waveguide device, a diameter of the ferrite being
used can be a limiting factor in determining size. However, a
reduction provided for the ferrite diameter may be offset by the
need to retain waveguide-related dimensions in the metal part of
the junction.
Examples of Reduced-Size Ferrite Having Yttrium Free Garnet
[0117] As described herein, ferrite size can be reduced
significantly by increasing the dielectric constant associated with
garnet structures. Also as described herein, garnets with reduced
Yttrium and/or reduced non-Y rare earth content can be formed by
appropriate Bismuth substitutions. In some embodiments, such
garnets can include Yttrium-free or rare earth free garnets. An
example RF device having ferrite devices with increased dielectric
constant and Yttrium-free garnets is described in reference to
FIGS. 15-17.
[0118] FIGS. 15A and 15B summarize the example ferrite size
reductions described herein. As described herein and shown in FIG.
15A, a ferrite device 200 can be a circular-shaped disk having a
reduced diameter of 2R' and a thickness of d'. The thickness may or
may not be reduced. As described in reference to Equation 1, the
radius R of a circular-shaped ferrite disk can be inversely
proportional to the square root of the ferrite's dielectric
constant. Thus, the increased dielectric constant of the ferrite
device 200 is shown to yield its reduced diameter 2R'.
[0119] As described herein and shown in FIG. 15B, a ferrite device
200 can also be a triangular-shaped disk having a reduced side
dimension of S' and a thickness of d'. The thickness may or may not
be reduced. As described in reference to Equation 2, the altitude A
of a triangular-shaped ferrite disk (which can be derived from the
side dimension S) can be inversely proportional to the square root
of the ferrite's dielectric constant. Thus, the increased
dielectric constant of the ferrite device 200 is shown to yield its
reduced dimension S'.
[0120] Although described in the context of example circular and
triangle shaped ferrites, one or more features of the present
disclosure can also be implemented in other shaped ferrites.
[0121] To demonstrate the foregoing effect of the dielectric
constant on the operating frequency (and size in some
implementations), circulator (sometimes also referred to as an
isolator) devices were built. One circulator was built with a
current ferrite available as TransTech TTVG1200 (17.56 mm diameter,
1 mm thickness). Another circulator was built with a Yttrium free
ferrite with the same dimensions. For the purpose of description,
such a Yttrium free ferrite is referred to as "TTHiE1200." Each of
the two example circulators has a diameter of about 25 mm.
[0122] The TTVG1200 ferrite has a Yttrium Calcium Zirconium
Vanadium Iron garnet configuration, and a typical dielectric
constant of approximately 14.4. The Yttrium free ferrite
(TTHiE1200) has a Bismuth Calcium Zirconium Vanadium Iron garnet
configuration containing not more than approximately 1% rare earth
oxides, and a dielectric constant of approximately 26.73.
[0123] Additional details concerning the foregoing example
circulators are described in reference to FIGS. 16A and 16B, in
which a "ferrite" can be the first type (TTVG1200) or the second
type (TTHiE1200).
[0124] FIGS. 16A and 16B show an example of a circulator 300 having
a pair of ferrite disks 302, 312 disposed between a pair of
cylindrical magnets 306, 316. Each of the ferrite disks 302, 312
can be a ferrite disk having one or more features described herein.
FIG. 16A shows an un-assembled view of a portion of the example
circulator 300. FIG. 16B shows a side view of the example
circulator 300.
[0125] In the example shown, the first ferrite disk 302 is shown to
be mounted to an underside of a first ground plane 304. An upper
side of the first ground plane 304 is shown to define a recess
dimensioned to receive and hold the first magnet 306. Similarly,
the second ferrite disk 312 is shown to be mounted to an upper side
of a second ground plane 314; and an underside of the second ground
plane 314 is shown to define a recess dimensioned to receive and
hold the second magnet 316.
[0126] The magnets 306, 316 arranged in the foregoing manner can
yield generally axial field lines through the ferrite disks 302,
312. The magnetic field flux that passes through the ferrite disks
302, 312 can complete its circuit through return paths provided by
320, 318, 308 and 310 so as to strengthen the field applied to the
ferrite disks 302, 312. In some embodiments, the return path
portions 320 and 310 can be disks having a diameter larger than
that of the magnets 316, 306; and the return path portions 318 and
308 can be hollow cylinders having an inner diameter that generally
matches the diameter of the return path disks 320, 310. The
foregoing parts of the return path can be formed as a single piece
or be an assembly of a plurality of pieces.
[0127] The example circulator device 300 can further include an
inner flux conductor (also referred to herein as a center
conductor) 322 disposed between the two ferrite disks 302, 312.
Such an inner conductor can be configured to function as a
resonator and matching networks to the ports (not shown).
[0128] FIG. 17 shows insertion loss plots and return loss plots for
the two above-described 25 mm circulators (based on the TTVG1200
ferrite (YCaZrVFe garnet, dielectric constant of 14.4), and based
on the Yttrium free ferrite (TTHiE1200) (BiCaZrVFe garnet,
dielectric constant of 26.73)). Frequencies and loss values for
edges of the loss curves of the two circulators ("TTVG1200" and
"TTHiE1200") are indicated by their respective trace markers shown
in FIG. 17 and listed in Table 3.
TABLE-US-00003 TABLE 3 Marker Trace Frequency Loss value 1
Insertion loss (Y-free TTHiE1200) 1.77 GHz -0.40 dB 2 Insertion
loss (Y-free TTHiE1200) 2.23 GHz -0.39 dB 3 Insertion loss
(TTVG1200) 2.41 GHz -0.39 dB 4 Insertion loss (TTVG1200) 3.01 GHz
-0.41 dB 5 Return loss (Y-free TTHiE1200) 1.77 GHz -19.87 dB 6
Return loss (Y-free TTHiE1200) 2.23 GHz -16.64 dB 7 Return loss
(TTVG1200) 2.41 GHz -16.37 dB 8 Return loss (TTVG1200) 3.01 GHz
-18.75 dB
[0129] Based on the foregoing measurements, one can see that the
TTVG1200 configuration has a center operating frequency of about
2.7 GHz, and the TTHiE1200 configuration has a center operating
frequency of about 2.0 GHz. The ratio of center operating
frequencies between TTHiE1200 and TTVG1200 configurations is
approximately 0.74. It is noted that a theoretical reduction in
frequency due to a higher dielectric constant can be calculated
(e.g., using Bosma's equations) as being proportional to square
root of the ratios of the dielectric constants. Thus, such a
calculation yields sqrt(14.4/26.73)=0.734, which is in good
agreement with the measured reduction of 0.74.
[0130] For the example 25 mm circulators having the TTHiE1200 and
TTVG1200 configurations, a comparison of intermodulation yields the
following measurements. For 2.times.40 W tones at room temperature,
the TTVG1200 configuration yields an intermodulation performance of
approximately -78 dBc at 2.7 GHz, and the TTHiE1200 configuration
yields an intermodulation performance of approximately -70 dBc at
1.8 GHz. It is noted that such results are expected due to the
reduction in the biasing magnetic field.
[0131] To further characterize the TTHiE1200 ferrite as described
herein, a smaller 10 mm circulator was made using a TTHiE1200
ferrite disk (radius of approximately 7.00 mm, thickness of
approximately 0.76 mm). FIGS. 18A and 18B show s-parameter data for
the 10 mm device at operating temperatures of 25.degree. C. and
100.degree. C., respectively. Intermodulation measurements were
also made for the 10 mm device at 25.degree. C. For 2.times.15 W
tones, intermodulation values are listed in Table 4, where various
parameters are indicated in the "Parameter" column.
TABLE-US-00004 TABLE 4 Inter- modu- lation Parameter (dBc) 2
.times. 15 W @ 2110 & 2115 MHz, 3.sup.rd Order IMD @ 2105 MHz
-59.9 2 .times. 15 W @ 2110 & 2115 MHz, 3.sup.rd Order IMD @
2120 MHz -58.8 2 .times. 15 W @ 2138 & 2143 MHz, 3.sup.rd Order
IMD @ 2133 MHz -57.5 2 .times. 15 W @ 2138 & 2143 MHz, 3.sup.rd
Order IMD @ 2148 MHz -56.7 2 .times. 15 W @ 2165 & 2170 MHz,
3.sup.rd Order IMD @ 2160 MHz -56.0 2 .times. 15 W @ 2165 &
2170 MHz, 3.sup.rd Order IMD @ 2175 MHz -54.9
[0132] Based on FIGS. 18A and 18B, one can see that the s-parameter
data appears to be generally positive. Based on Table 4, IMD
performance is generally what is expected for this size package.
For example, typical IMD performance for a 20 mm device is about
-70 dBc, and about -60 dBc for a 15 mm device.
[0133] Various examples of new garnet systems and devices related
thereto are described herein. In some embodiments, such garnet
systems can contain high levels of Bismuth, which can allow
formation of low loss ferrite devices. Further, by selected
addition of other elements, one can reduce or eliminate rare earth
content of garnets, including commercial garnets. Reduction or
elimination of such rare earth content can include, but is not
limited to, Yttrium. In some embodiments, the garnet systems
described herein can be configured to significantly increase (e.g.,
double) the dielectric constant of non-Bi garnets, thereby offering
the possibility of significantly decreasing (e.g., halving) the
printed circuit "footprint" of ferrite devices associated with
conventional garnets.
[0134] In some implementations as described herein, a synthetic
garnet material can include a structure having dodecahedral sites,
with Bismuth occupying at least some of the dodecahedral sites. In
some embodiments, such a garnet material can have a dielectric
constant value of at least 18.0, 19.0, 20.0, 21.0, 22.0, 23.0,
24.0, 25.0, 26.0, or 27.0.
[0135] In some embodiments, ferrite-based circulator devices having
one or more features as described herein can be implemented as a
packaged modular device. FIG. 19 shows an example packaged device
400 having a circulator device 300 mounted on a packaging platform
404 and enclosed by a housing structure 402. The example platform
404 is depicted as including a plurality of holes 408 dimensioned
to allow mounting of the packaged device 400. The example packaged
device 400 is shown further include example terminals 406a-406c
configured to facilitate electrical connections.
[0136] In some embodiments, a packaged circulator/isolator such as
the example of FIG. 19 can be implemented in a circuit board or
module. Such a circuit board can include a plurality of circuits
configured to perform one or more radio-frequency (RF) related
operations. The circuit board can also include a number of
connection features configured to allow transfer of RF signals and
power between the circuit board and components external to the
circuit board.
[0137] In some embodiments, the foregoing example circuit board can
include RF circuits associated with a front-end module of an RF
apparatus. As shown in FIG. 20, such an RF apparatus can include an
antenna 412 that is configured to facilitate transmission and/or
reception of RF signals. Such signals can be generated by and/or
processed by a transceiver 414. For transmission, the transceiver
414 can generate a transmit signal that is amplified by a power
amplifier (PA) and filtered (Tx Filter) for transmission by the
antenna 412. For reception, a signal received from the antenna 412
can be filtered (Rx Filter) and amplified by a low-noise amplifier
(LNA) before being passed on to the transceiver 414. In the example
context of such Tx and Rx paths, circulators and/or isolators 400
having one or more features as described herein can be implemented
at or in connection with, for example, the PA circuit and the LNA
circuit.
[0138] In some embodiments, circuits and devices having one or more
features as described herein can be implemented in RF applications
such as a wireless base-station. Such a wireless base-station can
include one or more antennas 412, such as the example described in
reference to FIG. 20, configured to facilitate transmission and/or
reception of RF signals. Such antenna(s) can be coupled to circuits
and devices having one or more circulators/isolators as described
herein.
[0139] As described herein, terms "circulator" and "isolator" can
be used interchangeably or separately, depending on applications as
generally understood. For example, circulators can be passive
devices utilized in RF applications to selectively route RF signals
between an antenna, a transmitter, and a receiver. If a signal is
being routed between the transmitter and the antenna, the receiver
preferably should be isolated. Accordingly, such a circulator is
sometimes also referred to as an isolator; and such an isolating
performance can represent the performance of the circulator.
[0140] FIGS. 21-25 show examples of how ferrite devices having one
or more features as described herein can be fabricated. FIG. 16
shows a process 20 that can be implemented to fabricate a ceramic
material having one or more of the foregoing properties. In block
21, powder can be prepared. In block 22, a shaped object can be
formed from the prepared powder. In block 23, the formed object can
be sintered. In block 24, the sintered object can be finished to
yield a finished ceramic object having one or more desirable
properties.
[0141] In implementations where the finished ceramic object is part
of a device, the device can be assembled in block 25. In
implementations where the device or the finished ceramic object is
part of a product, the product can be assembled in block 26.
[0142] FIG. 21 further shows that some or all of the steps of the
example process 20 can be based on a design, specification, etc.
Similarly, some or all of the steps can include or be subjected to
testing, quality control, etc.
[0143] In some implementations, the powder preparation step (block
21) of FIG. 21 can be performed by the example process described in
reference to FIG. 14. Powder prepared in such a manner can include
one or more properties as described herein, and/or facilitate
formation of ceramic objects having one or more properties as
described herein.
[0144] In some implementations, powder prepared as described herein
can be formed into different shapes by different forming
techniques. By way of examples, FIG. 22 shows a process 50 that can
be implemented to press-form a shaped object from a powder material
prepared as described herein. In block 52, a shaped die can be
filled with a desired amount of the powder. In FIG. 23,
configuration 60 shows the shaped die as 61 that defines a volume
62 dimensioned to receive the powder 63 and allow such power to be
pressed. In block 53, the powder in the die can be compressed to
form a shaped object. Configuration 64 shows the powder in an
intermediate compacted form 67 as a piston 65 is pressed (arrow 66)
into the volume 62 defined by the die 61. In block 54, pressure can
be removed from the die. In block 55, the piston (65) can be
removed from the die (61) so as to open the volume (62).
Configuration 68 shows the opened volume (62) of the die (61)
thereby allowing the formed object 69 to be removed from the die.
In block 56, the formed object (69) can be removed from the die
(61). In block 57, the formed object can be stored for further
processing.
[0145] In some implementations, formed objects fabricated as
described herein can be sintered to yield desirable physical
properties as ceramic devices. FIG. 24 shows a process 70 that can
be implemented to sinter such formed objects. In block 71, formed
objects can be provided. In block 72, the formed objects can be
introduced into a kiln. In FIG. 25, a plurality of formed objects
69 are shown to be loaded into a sintering tray 80. The example
tray 80 is shown to define a recess 83 dimensioned to hold the
formed objects 69 on a surface 82 so that the upper edge of the
tray is higher than the upper portions of the formed objects 69.
Such a configuration allows the loaded trays to be stacked during
the sintering process. The example tray 80 is further shown to
define cutouts 83 at the side walls to allow improved circulation
of hot gas at within the recess 83, even when the trays are stacked
together. FIG. 25 further shows a stack 84 of a plurality of loaded
trays 80. A top cover 85 can be provided so that the objects loaded
in the top tray generally experience similar sintering condition as
those in lower trays.
[0146] In block 73, heat can be applied to the formed objects so as
to yield sintered objects. Such application of heat can be achieved
by use of a kiln. In block 74, the sintered objects can be removed
from the kiln. In FIG. 25, the stack 84 having a plurality of
loaded trays is depicted as being introduced into a kiln 87 (stage
86a). Such a stack can be moved through the kiln (stages 86b, 86c)
based on a desired time and temperature profile. In stage 86d, the
stack 84 is depicted as being removed from the kiln so as to be
cooled.
[0147] In block 75, the sintered objects can be cooled. Such
cooling can be based on a desired time and temperature profile. In
block 206, the cooled objects can undergo one or more finishing
operations. In block 207, one or more tests can be performed.
[0148] Heat treatment of various forms of powder and various forms
of shaped objects are described herein as calcining, firing,
annealing, and/or sintering. It will be understood that such terms
may be used interchangeably in some appropriate situations, in
context-specific manners, or some combination thereof.
[0149] Unless the context clearly requires otherwise, throughout
the description and the claims, the words "comprise," "comprising,"
and the like are to be construed in an inclusive sense, as opposed
to an exclusive or exhaustive sense; that is to say, in the sense
of "including, but not limited to." The word "coupled", as
generally used herein, refers to two or more elements that may be
either directly connected, or connected by way of one or more
intermediate elements. Additionally, the words "herein," "above,"
"below," and words of similar import, when used in this
application, shall refer to this application as a whole and not to
any particular portions of this application. Where the context
permits, words in the above Detailed Description using the singular
or plural number may also include the plural or singular number
respectively. The word "or" in reference to a list of two or more
items, that word covers all of the following interpretations of the
word: any of the items in the list, all of the items in the list,
and any combination of the items in the list.
[0150] The above detailed description of embodiments of the
invention is not intended to be exhaustive or to limit the
invention to the precise form disclosed above. While specific
embodiments of, and examples for, the invention are described above
for illustrative purposes, various equivalent modifications are
possible within the scope of the invention, as those skilled in the
relevant art will recognize. For example, while processes or blocks
are presented in a given order, alternative embodiments may perform
routines having steps, or employ systems having blocks, in a
different order, and some processes or blocks may be deleted,
moved, added, subdivided, combined, and/or modified. Each of these
processes or blocks may be implemented in a variety of different
ways. Also, while processes or blocks are at times shown as being
performed in series, these processes or blocks may instead be
performed in parallel, or may be performed at different times.
[0151] The teachings of the invention provided herein can be
applied to other systems, not necessarily the system described
above. The elements and acts of the various embodiments described
above can be combined to provide further embodiments.
[0152] While certain embodiments of the inventions have been
described, these embodiments have been presented by way of example
only, and are not intended to limit the scope of the disclosure.
Indeed, the novel methods and systems described herein may be
embodied in a variety of other forms; furthermore, various
omissions, substitutions and changes in the form of the methods and
systems described herein may be made without departing from the
spirit of the disclosure. The accompanying claims and their
equivalents are intended to cover such forms or modifications as
would fall within the scope and spirit of the disclosure.
* * * * *