U.S. patent application number 09/871251 was filed with the patent office on 2002-04-11 for surface mount rc devices.
Invention is credited to Blair, Andrew, Heistand, Robert H. II, Moore, Clare Ashley, Ritter, Andrew P., Strawhorne, Maureen.
Application Number | 20020041219 09/871251 |
Document ID | / |
Family ID | 23314104 |
Filed Date | 2002-04-11 |
United States Patent
Application |
20020041219 |
Kind Code |
A1 |
Ritter, Andrew P. ; et
al. |
April 11, 2002 |
Surface mount RC devices
Abstract
Both discrete and array RC components are described using
cofireable resistive material as part of internal electrodes of the
device. The devices include a sintered body of multilayer ceramic
material in which multiple first and second electrode layers are
stacked. Each of the first layers comprises at least one resistive
electrode pattern extending across the sintered body between
respective pairs of terminations. The second layers comprise an
electrode pattern extending transverse to the resistive electrode
pattern, such as between end terminations. In some embodiments,
opposing side electrodes serve as input and output terminals of a
respective feedthrough filter. In a feedthrough arrangement, the
third terminal may be provided by one or both of the end terminals.
The invention also describes an improved termination structure
including a layer made from a metal oxide material.
Inventors: |
Ritter, Andrew P.; (Surfside
Beach, SC) ; Blair, Andrew; (Coleraine, NIR) ;
Strawhorne, Maureen; (Coleraine, NIR) ; Moore, Clare
Ashley; (Coleraine, NIR) ; Heistand, Robert H.
II; (Pawleys Island, SC) |
Correspondence
Address: |
DORITY & MANNING
ATTORNEYS AT LAW, P.A.
P.O. Box 1449
Greenville
SC
29602
US
|
Family ID: |
23314104 |
Appl. No.: |
09/871251 |
Filed: |
May 31, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09871251 |
May 31, 2001 |
|
|
|
09335991 |
Jun 18, 1999 |
|
|
|
Current U.S.
Class: |
333/172 ;
333/185 |
Current CPC
Class: |
H01G 4/40 20130101; H03H
1/02 20130101; H05K 3/3442 20130101; H01C 13/02 20130101; H03H
2001/0085 20130101 |
Class at
Publication: |
333/172 ;
333/185 |
International
Class: |
H03H 007/01 |
Claims
What is claimed is:
1. An array device having a predetermined number of RC circuits in
a singular package, said device comprising: a device body defined
by a plurality of first ceramic layers and a plurality of second
ceramic layers arranged to form a stack; each of said first ceramic
layers having thereon a plurality of side-by-side first electrode
plates, said first electrode plates being at least partially formed
of a cofirable resistor material; each of said second ceramic
layers having a second electrode plate extending in a direction
transverse to said first electrode plates, a predetermined number
of said first ceramic layers being respectively adjacent to a
corresponding said second ceramic layer such that said first
electrode plates will oppose said second electrode plate to form
two plates of a capacitor of a respective RC circuit; and said
device body having a plurality of terminations on side surfaces
thereof, respective of said first electrode plates corresponding to
one of said RC circuits being electrically connected to at least
one of said terminations and said second electrode plates being
electrically connected to at least another of said
terminations.
2. An array device as set forth in claim 1, further comprising: a
plurality of third ceramic layers arranged in said stack with said
first ceramic layers and said second ceramic layers, said third
ceramic layers having thereon a plurality of side-by-side third
electrode plates at least partially formed of a cofirable resistor
material; a predetermined number of said third ceramic layers being
respectively adjacent to a corresponding one of said second ceramic
layers such that said third electrode plates will oppose said
second electrode plates to form two plates of a capacitor of a
respective RC circuit; and respective of said third electrode
plates corresponding to one of said RC circuits being connected to
a corresponding one of said terminations.
3. An array device as set forth in claim 2, wherein said first
ceramic layers are alternately stacked with said second ceramic
layers in a top portion of said device body and said third ceramic
layers are alternated with said second ceramic layers in a bottom
portion of said device body.
4. An array device as set forth in claim 3, wherein each of said
first electrode plates is electrically connected only to a
respective one of said terminations.
5. An array device as set forth in claim 4, comprising a total of
four of said side-by-side first electrode plates on each of said
first ceramic layers and a total of four of said side-by-side third
electrode plates on each of said third ceramic layers.
6. An array device as set forth in claim 4, wherein said cofirable
resistor material comprises ruthenium oxide.
7. An array device as set forth in claim 2, wherein each of said
first electrode plates is electrically connected between first and
second terminations, said first and second terminations being
located on opposite sides of said device body.
8. An array device as set forth in claim 2, wherein each of said
second electrode plates extend between third and fourth
terminations located at respective opposite ends of said device
body.
9. An array device as set forth in claim 2, wherein said second
electrode plates are formed of a substantially nonresistive
conductive material.
10. An array device as set forth in claim 9, wherein said
substantially nonresistive conductive material is selected from a
group consisting of Ag, Ag/Pd, Cu, Ni, Pt, Au and Pd.
11. An array device as set forth in claim 2, wherein said cofirable
resistor material comprises ruthenium oxide.
12. An array device as set forth in claim 2, further comprising at
least one blank ceramic layer located in said stack such that said
device will be provided with predetermined resistance and
capacitance values.
13. An array device as set forth in claim 2, wherein two of said
second electrode plates occupy respective topmost and bottommost
positions in said stack to enhance electrical shielding of an
interior thereof.
14. A composite RC device, said device comprising: a device body
defined by a plurality of first ceramic layers and a plurality of
second ceramic layers arranged to form a stack; each of said first
ceramic layers having thereon at least one first electrode plate;
each of said second ceramic layers having a second electrode plate,
a predetermined number of said first ceramic layers being
respectively adjacent to a corresponding said second ceramic layer
such that said first electrode plate will oppose said second
electrode plate to form two plates of a capacitor; said first
electrode plates or said second electrode plates being at least
partially formed of a cofirable resistor material; and said device
body having a pair of terminations electrically connected to said
first electrode plate on each of said first ceramic layers, and
further having at least one termination electrically connected to
said second electrode plate on each of said second ceramic layers
to provide a predetermined electrical function; wherein two of said
second electrode plates occupy respective topmost and bottommost
positions in said stack to enhance electrical shielding of an
interior thereof.
Description
[0001] This application is a divisional of U.S. Ser. No.
09/335,991, filed Jun. 18, 1999.
BACKGROUND OF THE INVENTION
[0002] The present invention relates generally to the art of
surface mount electronic components. More particularly, the
invention relates to electronic components of the type having a
multilayer ceramic structure.
[0003] Multilayer ceramic capacitors (MLCs) have enjoyed widespread
use in the electronics industry. These devices are generally
constructed having a plurality of ceramic-electrode layers arranged
in a stack. During manufacture, the stacked layers are pressed and
sintered to achieve a substantially unitary capacitor body. The
capacitor body is often rectangular in shape, with electrical
terminations of opposite polarity provided along respective sides
or at opposite ends. A single MLC package may contain one
capacitor, or an array of multiple capacitors.
[0004] For a variety of considerations, including a desire to
conserve circuit board "real estate," several types of integrated
passive devices (IPDs) have been provided. For example, integrated
RC devices, produced in a manner similar to MLCs, utilize a single
"package" to yield a desired filtering function. Often, the
capacitor of these devices will be made in a manner substantially
identical to discrete MLCs. The resistor, electrically connected to
the capacitor in a predetermined manner, is often applied to the
outer surface of the ceramic body.
SUMMARY OF THE INVENTION
[0005] The present invention recognizes various disadvantages of
prior art constructions and methods. Accordingly, it is an object
of the present invention to provide novel electronic devices having
a multilayer ceramic structure.
[0006] It is a further object of the present invention to provide
novel integrated passive devices (IPDs) for surface mount
applications.
[0007] It is an additional object of the present invention to
provide novel RC components having a multilayer ceramic
structure.
[0008] It is also an object of the present invention to provide a
multilayer ceramic device having a novel termination structure.
[0009] Some of these objects are achieved by a composite RC device
comprising a device body defined by a plurality of first ceramic
layers and a plurality of second ceramic layers arranged to form a
stack. Each of the first ceramic layers has at least one first
electrode plate thereon, and each of the second ceramic layers has
thereon a second electrode plate. A predetermined number of the
first ceramic layers are respectively adjacent to a corresponding
one of the second ceramic layers such. that the first electrode
plate will oppose the second electrode plate to form two plates of
a capacitor.
[0010] In the composite RC device, either or both of the first
electrode plates and the second electrode plates are at least
partially formed of a cofirable resistor material. In addition, the
device body has a pair of terminations electrically connected to
the first electrode plate on each of the first ceramic layers.
Furthermore, at least one termination is electrically connected to
the second electrode plate on each of the second ceramic layers to
provide a predetermined electrical function.
[0011] In some exemplary embodiments, each of the first ceramic
layers comprises a plurality of side-by-side first electrode
plates. These first electrode plates extend between respective
first and second terminations located on the device body. For
example, a total of four side-by-side first electrode plates may be
provided on each of the first ceramic layers.
[0012] Often, the second electrode plates may extend between third
and fourth terminations on the device body. In such cases, the
first electrode plates may extend in a direction transverse to the
second electrode plates. In addition, the first electrode plates
and the second electrode plates may each be formed having a wider
main plate portion with narrower tab portions at each end
thereof.
[0013] In other embodiments, each of the first ceramic layers may
comprise a single first electrode plate extending between first and
second terminations located on the device body. In this case, the
second electrode plates may extend between third and fourth
terminations on the device body. For example, the second electrode
plates may extend in a direction transverse to the first electrode
plates. Often, the first electrode plates and the second electrode
plates may each be formed having a wider main plate portion with
narrower tab portions at each end thereof.
[0014] Preferably, the first electrode plates include the cofirable
resistor material. Resistor materials suitable for this purpose may
include an appropriate metal oxide (such as ruthenium oxide) which,
depending on the exigencies of a particular application, may be
diluted with a suitable metal. The second electrode plates, on the
other hand, may be formed of a substantially nonresistive
conductive material. Materials suitable for this purpose may be
selected from a group consisting of Ag, Ag/Pd, Cu, Ni, Pt, Au, Pd
or other such metals.
[0015] In some exemplary embodiments, a least one blank ceramic
layer is located in the stack such that the device will be provided
with predetermined resistance and capacitance values. Often, the
terminations may comprise an inner layer having a metal oxide
material and an outer layer of solderable metal. In some exemplary
embodiments, two of the second electrode plates may occupy
respective topmost and bottommost positions in the stack to enhance
electrical shielding of an interior thereof.
[0016] Other objects of the invention are achieved by an array
device having a predetermined number of RC circuits in a singular
package. The device comprises a device body defined by a plurality
of first ceramic layers and a plurality of second ceramic layers
arranged to form a stack. Each of the first ceramic layers has a
plurality of side-by-side first electrode plates thereon, the first
electrode plates being at least partially formed of a cofirable
resistor material. Each of the second ceramic layers has a second
electrode plate extending in a direction transverse to the first
electrode plates. A predetermined number of the first ceramic
layers are respectively adjacent to a corresponding one of the
second ceramic layers such that the first electrode plates will
oppose the second electrode plate to form two plates of a capacitor
of a respective RC circuit.
[0017] The device body is also configured having a plurality of
terminations on side surfaces thereof. Respective first electrode
plates corresponding to one of the RC circuits are electrically
connected to at least one of the terminations. Furthermore, the
second electrode plates are electrically connected to at least
another of the terminations.
[0018] In some exemplary embodiments, a plurality of third ceramic
layers are arranged in the stack with the first ceramic layers and
second ceramic layers. The third ceramic layers have thereon a
plurality of side-by-side third electrode plates at least partially
formed of a cofirable resistor material. A predetermined number of
the third ceramic layers are respectively adjacent to a
corresponding one of the second ceramic layers such that the third
electrode plates will oppose the second electrode plates to form
two plates of a capacitor of a respective RC circuit. Respective
third electrode plates corresponding to one of the RC circuits are
connected to a corresponding one of the terminations.
[0019] In such embodiments, the first ceramic layers may be
alternately stacked with the second ceramic layers in a top portion
of the device body. The third ceramic layers may then be alternated
with the second ceramic layers in a bottom portion of the device
body.
[0020] Other objects of the present invention are achieved by a
miniature surface mount device comprising a device body having a
unitary structure characteristic of a plurality of stacked, pressed
and sintered ceramic-electrode layers. The device body includes at
least two electrical terminations located on side surfaces thereof.
Each of the terminations comprises an inner termination layer
having a metal oxide material and an outer termination layer of
solderable metal.
[0021] In some exemplary embodiments, the inner termination layer
comprises a metal oxide-glass frit layer substantially similar to a
material used to form resistive electrodes in the device. Often, it
will be desirable to provide an intermediate termination layer of a
conductive metal-glass frit between the inner termination layer and
the outer termination layer. For example, the intermediate
termination layer may comprise a silver-glass frit layer. In other
embodiments, the outer termination layer is directly juxtaposed to
the inner termination layer. Often, at least some ceramic-electrode
layers of the miniature surface mount device will comprise a metal
oxide electrode material, such as ruthenium oxide, mixed with a
glass frit binder.
[0022] Still further objects of the invention are achieved by a
method of fabricating a composite RC device. According to the
method, a plurality of first ceramic layers are provided having a
predetermined dielectric constant. A first selected electrode
pattern is entirely formed on the first ceramic layers of a
substantially nonresistive conductive material. In addition, a
plurality of second ceramic layers are provided having the
predetermined dielectric constant. A second selected electrode
pattern is entirely formed on the second ceramic layers of a
cofirable resistive material. The second electrode pattern is
further configured so as to yield a desired resistance value.
Furthermore, the first selected electrode pattern and the second
selected electrode pattern are configured to provide a particular
electrode overlap to yield a desired capacitance value.
[0023] Additional objects of the invention are achieved by a
composite RC device comprising a device body having a unitary
structure characteristic of a plurality of stacked, pressed and
sintered ceramic-electrode layers. The device body includes at
least two electrical terminations located on side surfaces thereof.
The ceramic-electrode layers include a plurality of first ceramic
layers having thereon a pair of first electrode plates extending to
a respective termination. The ceramic-electrode layers further
include a plurality of second ceramic layers having thereon a
second electrode plate formed of a resistive material. The second
ceramic layers are interleaved with the first ceramic layers to
produce overlaps between each of the second electrode plates and a
respective pair of the first electrode plates in an adjacent
ceramic-electrode layer.
[0024] Other objects, features and aspects of the present invention
are provided by various combinations and subcombinations of the
disclosed elements, which are discussed in greater detail
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] A full and enabling disclosure of the present invention,
including the best mode thereof, to one of ordinary skill in the
art, is set forth more particularly in the remainder of the
specification, including reference to the accompanying drawings, in
which:
[0026] FIG. 1 is a perspective view of a surface mount RC filter
array constructed in accordance with the present invention in
position on a circuit board;
[0027] FIG. 2 is an enlarged perspective view of the filter array
of FIG. 1;
[0028] FIG. 3 is a cross sectional view as taken along line 3-3 of
FIG. 1;
[0029] FIGS. 4A and 4B are plan views of a first layer and a second
layer as may be alternated and stacked to form the filter array of
FIG. 1;
[0030] FIG. 5 is an electrical schematic showing an equivalent
circuit realized by the filter array of FIG. 1;
[0031] FIGS. 6A and 6B are cross-sectional views similar to FIG. 3
illustrating the manner in which device capacitance can be adjusted
independently of device resistance in the array device of FIG.
1;
[0032] FIG. 7 is a perspective view of a discrete RC filter device
constructed in accordance with the present invention;
[0033] FIGS. 8A and 8B are plan views of a first layer and a second
layer as may be alternated and stacked to form the filter device of
FIG. 7;
[0034] FIG. 9 is a perspective view of an alternative RC filter
array constructed in accordance with the present invention;
[0035] FIGS. 10A, 10B and 10C are plan views of a first layer, a
second layer and a third layer as may be alternated and stacked to
form the RC filter array of FIG. 9;
[0036] FIG. 11 is a cross-sectional view as taken along line 11-11
of FIG. 9;
[0037] FIGS. 12A-B through 16A-B diagrammatically illustrate the
manner in which teachings of the present invention may be utilized
to achieve a variety of configurations without altering exterior
dimensions of the device;
[0038] FIG. 17 is a fragmentary view of a multilayer ceramic device
having a novel termination structure in accordance with the present
invention;
[0039] FIG. 18 is an enlarged view of the area so indicated in FIG.
17;
[0040] FIG. 19 is a view similar to FIG. 18 illustrating an
alternative termination structure; and
[0041] FIG. 20 is a cross-sectional view showing the interior
construction of a still further alternative device constructed in
accordance with the present invention.
[0042] Repeat use of reference characters in the present
specification and drawings is intended to represent same or
analogous features or elements of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0043] It is to be understood by one skilled in the art that the
present discussion is a description of exemplary embodiments only,
and is not intended as limiting the broader aspects of the present
invention, which broader aspects are embodied in the exemplary
constructions.
[0044] The present invention discloses various improvements in
surface mount RC devices made according to multilayer ceramic
techniques. Surface mount RC devices having internal resistor
structures are shown in commonly-assigned U.S. Pat. No. 5,889,445,
incorporated herein by reference. Generally, these devices are
constructed having a unitary body characteristic of a plurality of
stacked, pressed and sintered ceramic-electrode layers.
Terminations are applied to the surfaces of the body for electrical
connection to external circuitry. According to industry practice,
the size of such devices may be expressed as a number "XXYY," with
XX and YY being the length and width in hundredths of an inch. Some
typical sizes for devices of the present invention as expressed
under this practice are 0603, 0805, 1206, 1210 and 1812.
[0045] FIG. 1 illustrates a surface mount RC array 10 of the
present invention mounted to a circuit board 12. As can also be
seen in FIG. 2, array 10 includes a main body 14 of relatively
small size. A plurality of terminations 16a-d and 18a-d are located
on respective sides of main body 14, with terminations 20 and 22
being similarly located at respective ends thereof. While
terminations 20 and 22 are here shown only partially covering the
end of main body 14, it is contemplated that these terminations may
cover the entire end surface in some embodiments.
[0046] As shown in FIG. 1, the various terminations of the body 14
align with respective conductive paths, such as traces 24 and 26,
defined on the surface of circuit board 12. Electrical connection
between each termination and its associated conductive path may be
effected by soldering. Typically, circuit board 12 may be made from
a low-temperature organic material, with the solder being a low
temperature eutectic solder applied by wave or reflow soldering
techniques.
[0047] Referring now to FIG. 3, the internal construction of main
body 14 will be explained. As can be seen, main body 14 includes a
plurality of first electrode plates (such as plates 28d) situated
in opposed and spaced apart relation with a plurality of second
electrode plates 30. The electrode plates are separated by layers
of ceramic material to provide a predetermined dielectric constant.
Capacitor body 14 is typically made by stacking ceramic-electrode
layers formed using conventional dicing techniques, which are then
pressed and sintered in a kiln. Generally, main body 14 will
comprise approximately 5-50 ceramic-electrode layers stacked in
this manner.
[0048] As shown in FIG. 4A, each of the first electrode plates may
comprise a plurality of side-by-side electrode plates (designated
28a-d) formed on the surface of a first ceramic layer 31. In this
case, each of the first electrode plates is configured to have a
main plate portion (such as main plate portion 32) between a pair
of tab portions (such as tab portions 34). The tab portions extend
to, and are electrically connected with, respective pairs of side
terminations.
[0049] Referring now to FIG. 4B, each of the second electrode
plates 30 may be formed as a single electrode plate on the surface
of a second ceramic layer 38. As shown, electrode plate 30, which
has a main plate portion 40 between a pair of tab portions 42,
preferably extends in a direction transverse to the direction of
first electrode plates 28a-d. Tab portions 42 are electrically
connected with respective end terminations 20 and 22.
[0050] Preferably, electrode plates 28a-d are at least partially
formed of a cofirable resistor material, such as a combination
including a suitable metal oxide and glass frit. For example, some
presently preferred embodiments employ ruthenium oxide as the metal
oxide material. As a result, the electrode pattern not only serves
as one plate of a capacitor, but also serves as a resistor. The use
of a cofirable material permits single fire processing, which
simplifies processing in relation to many prior art
arrangements.
[0051] In the illustrated embodiment, electrode plates 28a-d are
entirely formed from the resistor material. The opposed capacitor
plates 30 are preferably formed of a conductive material from the
family of noble and base metals that are traditionally used in
cofired electronic components and packages. For example, capacitor
plates 30 may be formed from Ag, Ag/Pd, Cu, Ni, Pt, Au, Pd or the
like. In some embodiments, however, it may be desirable to also
form electrode plates 28a-d of the cofirable resistor material.
[0052] As will be appreciated, the illustrated embodiment provides
a total of four RC devices in a single package. Often, each pair of
side terminations will serve as the respective input and output
terminals of one RC device. One or both of the end terminals 20 and
22 may be grounded to provide a three-terminal feedthrough
arrangement, as schematically illustrated in FIG. 5.
[0053] In the illustrated embodiment, the R and C values of the
respective RC devices can be adjusted by varying the overall number
of ceramic layers. Due to the parallel arrangement of the
resistors, more plates 28 will yield a lower R value. Because
parallel capacitors are additive, fewer plates 30 will yield a
lower C value. The values of R and C can be adjusted independently
by selectively applying the "capacitor" or "resistor" layers.
[0054] This can be explained most easily with reference to FIGS. 6A
and 6B. In FIG. 6A, array 10 is constructed so that every potential
position for an electrode plate is populated. The resistance
between terminal 16d and 18d is determined by the single layer
resistance of each plate 28d, and the number of layers in parallel.
Capacitance is determined by the number of combinations of plates
28d and plates 30. Thus, device capacitance can be adjusted
independently of device resistance by altering the structure within
the cofired body. Specifically, it is possible to vary the values
of resistance and/or capacitance by interrupting the usual sequence
of the plates.
[0055] In this regard, FIG. 6B illustrates a device 10' wherein two
plate positions that could be occupied by a plate 30 are shown to
be vacant. As a result, device 10', otherwise identical to device
10, will exhibit a lower capacitance. Because the number of plates
28d remains the same, however, the resistance between terminations
16d and 18d remains unchanged.
[0056] FIG. 7 illustrates a discrete RC device 50 constructed in
accordance with the present invention. Like array 10, device 50
includes a device body 52 manufactured from a plurality of ceramic
electrode layers arranged to form a stack. A pair of terminations
54 and 56 are located on respective sides of device body 52, as
shown. Terminations 58 and 60 are located at the respective ends of
device body 52.
[0057] FIGS. 8A and 8B illustrate the ceramic layers that can be
alternated in the fabrication of device body 52. As shown in FIG.
8A, the first ceramic layer 62 has a first electrode plate 64
located thereon. The plates 64 are configured to extend between
terminations 58 and 60. Plate 64 may be formed entirely of a
cofireable resistor material as described above.
[0058] As shown in FIG. 8B, each of the second ceramic layers 66
includes a second ceramic plate 68, which serve as
counterelectrodes in the eventual capacitor. In this case, second
electrode plates 68 are configured to have a main plate portion 70
and a pair of tab portions 72. The tab portions 72 extend to
respective terminations 54 and 56 located on the lateral sides of
device body 52. Depending on the requirements of a particular
application, electrode plates 68 may be formed of a substantially
nonresistive material, or may be formed of a cofireable resistor
material.
[0059] FIG. 9 illustrates an alternative embodiment which is
similar in its external appearance to array 10. Specifically, FIG.
9 illustrates an array 80 having a device body 82 formed of a
plurality of ceramic-electrode layers arranged in a stack. The
lateral sides of body 82 carry a plurality of opposite terminations
84a-d and 86a-d.
[0060] In this case, array 80 is configured to yield a total of
eight different RC circuits in a single package. Instead of
three-terminal feedthrough arrangements as described above, the RC
circuits of array 80 are configured as two terminal series
circuits.
[0061] FIGS. 10A-10C illustrate the three different ceramic layers
that can be stacked in the manufacture of device body 82. As shown
in FIG. 10A, first ceramic layer 92 includes a total of four
electrode plates 94a-d. As shown, plates 94a-d are arranged side by
side, with the tab portion of every other plate extending to
opposite sides of the device. Thus, electrode plates 94a and 94c
will be electrically connected to terminations 84a and 84c, with
electrode plates 94b and 94d being connected to terminations 86b
and 86d, respectively.
[0062] Referring to FIG. 10B, the second ceramic layers 96 each
include an elongate electrode plate 98 extending to opposite ends
of device body 82. As such, electrode plates 98, which will serve
as counter electrodes in the multilayer capacitor structure, will
be electrically connected to terminations 88 and 90.
[0063] Referring now to FIG. 10C, third ceramic layer 100 includes
a plurality of third electrode plates 102a-d. Like electrode plates
94a-d, electrode plates 102a-d are arranged such that the tab
portion of every other plate extends to opposite sides of device
body 82. Thus, electrode plates 102a and 102c will be electrically
connected to terminations 86a and 86c, respectively. Similarly,
electrode plates 102b and 102d will be electrically connected to
terminations 84b and 84d.
[0064] Preferably, electrode plates 94a-d and 102a-d are formed of
a cofireable resistor material as described above. In such
embodiments, electrode plates 98 will often be formed of a
substantially nonresistive material. In this manner, each of the RC
circuits may have substantially equivalent values of both
resistance and capacitance.
[0065] Embodiments are also contemplated, however, in which only
electrode plates 98, or all of the electrode plates in the device,
are formed of the resistive material. Such a construction may be
advantageous to provide different values of resistance among the
various RC circuits in the array. For example, the interior
circuits may have a higher resistance value if electrode plates 98
are made of a resistive material, since there will be a longer
resistive path from the counterelectrode of the capacitor to the
end termination for these circuits.
[0066] FIG. 11 illustrates one stacking arrangement which may be
utilized to produce array 80. In this case, the first ceramic
layers are alternated with the second ceramic layers in the top
portion of the stack. In the bottom portion of the stack, the
second ceramic layers are alternated with the third ceramic layers.
According to one preferred arrangement, second electrodes 98 will
occupy both the topmost and bottommost positions in the stack. This
is advantageous to provide a degree of electrical shielding to the
interior of the device.
[0067] As noted above, the present invention provides a high degree
of flexibility in the manufacturing process. Depending on the
desired values of resistance and capacitance, ceramic layers may be
left blank, or the physical dimensions of the layers may be
changed. A wide variety of different circuits can be easily created
within a single component size. A series of examples will now be
described to demonstrate this flexibility.
[0068] FIGS. 12A and 12B are side and transverse sectional views,
respectively, diagrammatically illustrating the construction of a
typical multilayer ceramic capacitor 108. As can be seen, a
plurality of first polarity plates 110 are interleaved with a
plurality of second polarity plates 112, which extend to opposite
ends of body 114. In this prior art arrangement, the capacitor
plates are formed of a conductive material, such as Ag/Pd.
[0069] FIGS. 13A and 13B illustrate an RC device wherein the
opposite polarity plates are made from a cofireable resistive
material, such as ruthenium oxide and glass frit. Device 208 will
exhibit a capacitance substantially identical to that of device 108
but will have a much higher series resistance value.
[0070] FIGS. 14A and 14B illustrate a further alternative 308
wherein first polarity plates 310 are formed from the resistive
material. Second polarity plates 312, on the other hand, are formed
in this case from the conductive material. Device 308 will exhibit
a capacitance substantially identical to that of devices 108 and
208, but will exhibit a greatly reduced value of resistance.
[0071] FIGS. 15A and 15B illustrate an RC device 408 having first
polarity terminals 410 made from the resistive material. Electrode
plates 412, on the other hand, are formed of the conductive
material. In this case, electrode plates 412 are configured to
provide a smaller overlap area than in the embodiments discussed
above. As a result, device 408 will exhibit a smaller capacitance.
In addition, the resistance value will be lower than that of
devices 208 and 308 due to the shorter length of resistive
material.
[0072] FIGS. 16A and 16B illustrate a still further alternative
device 508, in which the first polarity electrode plates 510 are
made from the resistive material. Electrode plates 512, on the
other hand, are formed from the conductive material. It can be seen
that plates 510 are configured to have a length and area
approximately equivalent to plates 310 of device 308. Plates 512,
however, are configured to have a relatively narrow width. Thus, in
comparison to device 308, device 508 will exhibit a lower
capacitance value. The resistance value, however, will not be
substantially changed.
[0073] The following table represents theoretical capacitance and
resistance values that may be achieved in one family of examples as
described above, assuming use of ruthenium oxide as the resistive
material and Ag/Pd as the conductive material:
1 DEVICE RESISTANCE CAPACITANCE 108 0.006 Ohms 39.6 pF 208 80.1
Ohms 39.6 pF 308 43.0 Ohms 39.6 pF 408 26.3 Ohms 19.9 pF 508 35.3
Ohms 21.8 pF
[0074] Thus, within a single component size, the present invention
allows a wide variety of different RC circuits to be manufactured
to meet the needs of a particular application.
[0075] The above examples demonstrate that variations in plate
geometry can yield different resistance and capacitance values.
Further variations can be achieved, however, by altering the
materials from which the electrode plates are made. For example, a
conductive metal, such as silver, may be selectively added to the
metal oxide/glass frit material to lower the resistance of the
material.
[0076] The present invention also provides an improved termination
structure for use with a multilayer ceramic device. Referring now
to FIG. 17, a termination 120 of the present invention is shown
covering an end surface of a device body 122. As can be seen in
FIG. 18, termination 120 includes an inner termination layer 124
and an outer termination layer 126.
[0077] Where the device includes internal electrodes formed of a
ceramic material, such as the metal oxide and glass frit material
described above, inner layer 124 is preferably formed from a
chemically similar material. For example, in one preferred
implementation, the termination material may be made from about
equal parts of RuO.sub.2 and glass frit, which is fired onto the
body 122 when it is sintered. Although layer 124 is made from a
resistive material in this example, it will not add appreciable
resistance to the overall device. This is due to the relatively
small thickness of the resistive layer.
[0078] Termination layer 126, on the other hand, is typically
formed of SnPb, Ni or other solderable metal. Preferably, layer 126
is applied to the device body after sintering as has been done in
the past.
[0079] When the improved termination of the present invention is
used with an RC device having resistive electrodes, inner
termination layer 124 may be formed from an identical material.
Because the two materials are the same, the termination will
readily bond with the internal electrodes during the firing
process. This is in contrast with fired-on termination materials of
the prior art, such as a silver-glass frit material, which may not
readily adhere to a metal oxide electrode.
[0080] FIG. 19 illustrates an alternative termination structure
120' constructed in accordance with the present invention.
Termination structure 120' includes an inner termination layer 124'
and an outer termination layer 126' similar to layers 124 and 126,
respectively. In this case, an intermediate termination layer 128
is provided between termination layers 124' and 126'. Termination
layer 128 is formed of a prior art fired-on termination material of
conductive metal and glass frit. For example, a silver/glass frit
material of the type typically used in component terminations of
the prior art may be used for this purpose. Structure 120 may be
advantageous to provide a good bond to resistive internal
electrodes, while at the same time otherwise appearing as a
termination structure of the prior art.
[0081] An improved termination structure made in accordance with
the present invention has been found to offer a number of benefits
in certain applications. For example, where an internal electrode
of resistive material is used, the like material of the termination
structure provides excellent electrical contact. In addition, the
termination structure will provide excellent electrical contact to
conductive internal electrodes such as Ag/Pd electrodes and the
like. The termination structure will also achieve excellent
mechanical bond to the ceramic chip itself for a strong,
well-adhered termination. Moreover, the metal oxide termination
offers very well-matched thermal expansion properties between the
chip and termination to reduce thermal-cycle induced failures.
[0082] In the above embodiments, resistive electrodes have been
shown above as forming the entire electrode pattern. Embodiments
are contemplated, however, wherein part of the electrode is formed
from resistive material and part is formed from a traditional
conductive material. In this regard, a conductive tab may be
provided between the termination and an electrode plate formed of
resistive material. This may be particularly advantageous where it
is desired to utilize a traditional conductive metal/glass frit
termination material as the inner layer of the termination
structure. Alternatively, the electrode plate may be formed of a
conductive material, with the resistive material forming a series
resistor between it and the termination.
[0083] FIG. 20 illustrates a still further embodiment constructed
in accordance with the present invention. In this case, a device
130 is depicted having terminations 132 and 134 located at
respective ends of a sintered body 136. Each of the first ceramic
layers defines a pair of conductive capacitor plates 138a-b
extending to a respective termination. The second ceramic layers
each define a resistive plate 140 which is not directly connected
to either of the terminations. Instead, resistive plates 140 are
configured to overlap a portion of plates 138a-b to yield a
predetermined capacitance. Electrically, the resulting structure
will be equivalent to a series capacitor-resistor-capacitor,
wherein the resistance and capacitance values can be adjusted as
described above.
[0084] It can thus be seen that the present invention provides
improved RC devices that accomplish the various objectives set
forth above. While preferred embodiments of the invention have been
shown and described, modifications and variations may be made
thereto by those of ordinary skill in the art without departing
from the spirit and scope of the invention. It should also be
understood that aspects of the various embodiments may be
interchanged both in whole or in part. Furthermore, those of
ordinary skill in the art will appreciate that the foregoing
description is by way of example only, and is not intended to be
limitative of the invention so further described in the appended
claims.
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