U.S. patent application number 11/017470 was filed with the patent office on 2006-09-21 for methods for making large dimension, flexible piezoelectric ceramic tapes.
This patent application is currently assigned to PALO ALTO RESEARCH CENTER INCORPORATED. Invention is credited to Steven A. Buhler, Scott A. Elrod, KarlA Littau, Scott E. Solberg, Michael C. Weisberg, William S. Wong, Baomin Xu.
Application Number | 20060211217 11/017470 |
Document ID | / |
Family ID | 32771496 |
Filed Date | 2006-09-21 |
United States Patent
Application |
20060211217 |
Kind Code |
A1 |
Xu; Baomin ; et al. |
September 21, 2006 |
METHODS FOR MAKING LARGE DIMENSION, FLEXIBLE PIEZOELECTRIC CERAMIC
TAPES
Abstract
A method for producing a detection/test tape includes depositing
a material onto a surface of at least one first substrate to form a
plurality of element structures. Electrodes are deposited on a
surface of each of the plurality of element structures, and the
element structures are bonded to a second substrate, where the
second substrate is conductive or has a conductive layer, and the
second substrate is carried on a carrier plate. The at least one
first substrate is removed from the element structures and second
side electrodes are deposited on a second surface of each of the
plurality of element structures. An insulative material is inserted
around the element structures to electrically isolate the two
substrates used to bond the element structures. A second side of
the element structures is then bonded to another substrate, where
the other substrate is conductive or has a conductive layer.
Thereafter, the carrier plate carrying the second substrate is
removed.
Inventors: |
Xu; Baomin; (Cupertino,
CA) ; Buhler; Steven A.; (Sunnyvale, CA) ;
Wong; William S.; (San Carlos, CA) ; Weisberg;
Michael C.; (Woodside, CA) ; Solberg; Scott E.;
(Mountain View, CA) ; Littau; KarlA; (Palo Alto,
CA) ; Elrod; Scott A.; (La Honda, CA) |
Correspondence
Address: |
Mark S. Svat;FAY, SHARPE, FAGAN, MINNICH & McKEE, LLP
SEVENTH FLOOR
1100 SUPERIOR AVENUE
CLEVELAND
OH
44114-2579
US
|
Assignee: |
PALO ALTO RESEARCH CENTER
INCORPORATED
|
Family ID: |
32771496 |
Appl. No.: |
11/017470 |
Filed: |
December 20, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10376527 |
Feb 25, 2003 |
6964201 |
|
|
11017470 |
Dec 20, 2004 |
|
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|
Current U.S.
Class: |
438/455 ;
257/E27.006 |
Current CPC
Class: |
G01N 29/245 20130101;
H01L 41/314 20130101; H01L 27/20 20130101; G01L 1/16 20130101; H01L
41/313 20130101; G01N 2291/02827 20130101; B06B 1/0622 20130101;
G01N 2291/2694 20130101; G01N 29/2475 20130101 |
Class at
Publication: |
438/455 |
International
Class: |
H01L 21/30 20060101
H01L021/30 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. A method of producing a detection/test tape comprising;
depositing a material onto a surface of at least one first
substrate to form a plurality of element structures, wherein the
depositing step used to form the plurality of element structures
includes direct marking methods; depositing electrodes on a surface
of each of the plurality of element structures; bonding the element
structures to a second substrate, the second substrate being
conductive or having a conductive layer and the second substrate
being carried on a carrier plate; removing the at least one first
substrate from the element structures; depositing second side
electrodes on a second surface of each of the plurality of element
structures; bonding a second side of the element structures to a
third substrate, the third substrate being conductive or having a
conductive layer; and removing the carrier plate.
23. The method according to claim 22, wherein an insulative
material is inserted in the gaps between the element structures to
electrically isolate the two substrates or surface conductive
layers of the two substrates used to bond the element
structures.
24. (canceled)
25. (canceled)
26. (canceled)
27. (canceled)
28. (canceled)
29. (canceled)
30. The method according to claim 22, wherein the direct marking
methods include at least one of screen printing, jet printing or
acoustic printing.
31. A method of producing a detection/test tape comprising:
depositing a material onto a surface of at least one first
substrate to form a plurality of element structures; depositing
electrodes on a surface of each of the plurality of element
structures; bonding the element structures to a second substrate,
the second substrate being conductive or having a conductive layer
and the second substrate being carried on a carrier plate; removing
the at least one first substrate from the element structures;
depositing second side electrodes on a second surface of each of
the plurality of element structures; bonding a second side of the
element structures to a third substrate, the third substrate being
conductive or having a conductive layer, wherein at least one of
the second substrate or the third substrate is at least one of
flexible or partially flexible; and removing the carrier plate.
32. The method according to claim 22, wherein the bonding step
includes the use of at least one of nonconductive epoxy bonding
containing conductive particles, a nonconductive epoxy alone,
wherein electrical contact between the electrodes of the element
structures and at least one of the second substrate or third
substrate is maintained.
33. The method according to claim 22, wherein the bonding step
includes a thin film metal bonding.
34. A method of producing a detection/test tape comprising:
depositing a material onto a surface of at least one first
substrate to form a plurality of element structures; depositing
electrodes on a surface of each of the plurality of element
structures; bonding the element structures to a second substrate,
the second substrate being conductive or having a conductive layer
and the second substrate being carried on a carrier plate, wherein
the step of bonding the element structures to the second substrate,
includes the second substrate being a final target substrate,
wherein the bond is intended to be permanent; removing the at least
one first substrate from the element structures; depositing second
side electrodes on a second surface of each of the plurality of
element structures; bonding a second side of the element structures
to a third substrate, the third substrate being conductive or
having a conductive layer; and removing the carrier plate.
35. The method according to claim 22, wherein the step of bonding
the element structures to at least one second substrate, includes
the second substrate being a transfer substrate, wherein the bond
is a temporary bond.
36. The method according to claim 35, further including, bonding
element structures to a final target substrate, wherein the bond is
intended to be permanent; and removing the at least one transfer
substrate from the element structures.
37. The method according to claim 36, further including performing
a property test on the element structures before bonding the
element structures to a final target substrate.
38. A method of producing a detection/test tape comprising:
depositing a material onto a surface of at least one first
substrate to form a plurality of element structures, wherein the
element structures are made from one of piezoelectric or other
functional ceramic, including at least one of antiferroelectric
material, electrostrictive material, and magnetostrictive
materials; depositing electrodes on a surface of each of the
plurality of element structures; bonding the element structures to
a second substrate, the second substrate being conductive or having
a conductive layer and the second substrate being carried on a
carrier plate; removing the at least one first substrate from the
element structures; depositing second side electrodes on a second
surface of each of the plurality of element structures; bonding a
second side of the element structures to a third substrate, the
third substrate being conductive or having conductive layer; and
removing the carrier plate.
39. The method according to claim 22, wherein if more than one
first substrate is used, the materials, shapes and thicknesses of
the elements on these substrates are either the same or
different.
40. A method of producing a detection/test tape comprising:
depositing a material onto a surface of at least one first
substrate to form a plurality of element structures; depositing
electrodes on a surface of each of the plurality of element
structures; bonding the element structures to a second substrate,
the second substrate being conductive or having a conductive layer
and the second substrate being carried on a carrier plate; removing
the at least one first substrate from the element structures,
further including, removing the at least one first substrate via a
liftoff procedure using a radiation source; depositing second side
electrodes on a second surface of each of the plurality of element
structures; bonding a second side of the element structures to a
third substrate, the third substrate being conductive or having a
conductive layer; and removing the carrier plate.
41. A method of producing a detection/test tape comprising:
depositing a material onto a surface of at least one first
substrate to form a plurality of element structures; depositing
electrodes on a surface of each of the plurality of element
structures; bonding the element structures to a second substrate,
the second substrate being conductive or having a conductive layer
and the second substrate being carried on a carrier plate; removing
the at least one first substrate from the element structures;
depositing second side electrodes on a second surface of each of
the plurality of element structures; bonding a second side of the
element structures to a third substrate, the third substrate being
conductive or having a conductive layer; bonding a second plurality
of element structures to another surface of the third substrate,
the other surface of the third substrate being conductive or having
a conductive layer; removing the at least one first substrate from
the second plurality of elements structures, depositing electrodes
on a second surface of each of the second plurality of element
structures; bonding a second side of the second plurality of
element structures to a fourth substrate, the fourth substrate
being conductive or having a conductive layer; and removing the
carrier plate.
42. The method according to claim 40, wherein the at least one
first substrate is transparent.
43. The method according to claim 40, wherein the radiation source
is a laser.
44. The method according to claim 31, wherein an insulative
material is inserted in the gaps between the element structures to
electrically isolate the two substrates or surface conductive
layers of the two substrates used to bond the element
structures.
45. The method according to claim 31, wherein the bonding step
includes the use of at least one of nonconductive epoxy bonding
containing conductive particles, a nonconductive epoxy alone,
wherein electrical contact between the electrodes of the element
structures and at least one of the second substrate or third
substrate is maintained.
46. The method according to claim 31, wherein the bonding step
includes a thin film metal bonding.
Description
BACKGROUND OF THE INVENTION
[0001] Piezoelectric ceramics are commonly being used as sensors,
actuators and transducers because of their strong electromechanical
coupling effect.
[0002] A detection/test system, which combines such sensors,
actuators, transducers with feedback or feed-forward control
circuitry, is an important technology for many industry and
military applications. One particular application is the active
control of vibrations. For example, active control of the vibration
inside the body of an airplane can greatly reduce the noise in the
passenger cabin. Active control of the vibration of the wings can
greatly reduce the damping by airflow and thus increase the
efficiency of the airplane. Relatedly, active control of the
vibration of a submarine can greatly reduce the acoustic noise it
generates and thus greatly reduce its chance of being detected.
Another application of detection/test systems is real-time
structural health monitoring. For example, embedded sensors and
transducers in a structure can produce in-site detection of cracks
in the structures and thus predict and assist in avoiding critical
failure of the structure.
[0003] A significant drawback of piezoelectric ceramics is that it
is difficult to make a thin, large sheet (at many inches to several
feet scale), due to the brittle nature of the material. Due to this
limitation, it cannot be mounted to a curved surface or embedded in
a structure which needs to be flexible. Unfortunately, many real
world applications require detecting and testing of curved surfaces
and/or flexible structure, thus the mentioned brittleness greatly
limits the applications of piezoelectric ceramic materials in
detection/test systems.
[0004] An alternative is to use piezoelectric polymers which are
flexible and can be manufactured in large scale. Unfortunately, the
piezoelectric effect of piezoelectric polymers is weak--about
one-tenth of piezoelectric ceramics--and the materials are very
soft.
[0005] One path taken to develop a detector/test system is
represented by research at Stanford University and which is coined
as the Stanford Multi-Actuator-Receiver Transduction Layer (SMART
layer). Particularly, a manufacturing method has been proposed for
integrating a network of distributed piezoceramic actuators/sensors
onto laminated carbon/epoxy composite structures. The network of
built-in actuators/sensors is used to monitor the health of the
host composite structure by acquiring information about the
condition of the structure throughout its life. The manufacturing
method applies a printed circuit board technique to fabricate a
thin flexible layer with a network of piezoceramics. It is used as
an extra ply that is either inserted into or bonded onto the
surface of a composite laminate to give it actuating and sensing
capabilities. More particularly, the system implements the use of a
flexible printed circuit, commonly referred to as "Flex." The
proposed concept used the Flex technique to make a large, thin
flexible layer that contains a network of distributed piezoceramics
connected by printed circuits.
[0006] However, the fabrication techniques for the SMART layer are
labor intensive and restrictive in design choices. Particularly,
the disclosed fabrication process for the SMART layer do not lend
itself to obtaining of a flexible tape with high density elements
and a variety of geometric shapes for those elements, which in turn
permits more versatile functional capabilities. It also does not
consider use of elements within a thickness range of about 10
.mu.m, or greater, formed by a direct marking technology.
SUMMARY OF THE INVENTION
[0007] A flexible detection/test tape includes a first flexible
conductive layer, and a second flexible conductive layer positioned
opposite the first conductive layer. A plurality of at least one of
sensors, actuators or transducers are positioned between and are
bonded to the first flexible conductive layer and the second
flexible conductive layer. An insulative material is inserted
around the plurality of at least one of the sensors, actuators or
transducers. An electrical contact network connects to the first
flexible conductive layer and the second flexible conductive layer,
whereby power and control signals are provided to the flexible
detection test tape.
[0008] In an alternative embodiment, a method for producing a
detection/test tape includes depositing a material onto a surface
of a first substrate to form a plurality of element structures.
Electrodes are deposited on a surface of each of the plurality of
element structures, and the element structures are bonded to a
second substrate, where the second substrate is conductive or has a
conductive layer, and the second substrate is carried on a carrier
plate. The first substrate is removed from the element structures
and second side electrodes are deposited on a second surface of
each of the plurality of element structures. An insulative material
is inserted around the element structures to electrically isolate
the two substrates used to bond the element structures. A second
side of the element structures is then bonded to another substrate,
where the other substrate is conductive or has a conductive layer.
Thereafter, the carrier plate carrying the second substrate is
removed.
SUMMARY OF THE DRAWINGS
[0009] The invention may take form in various components and
arrangements of components, and in various steps and arrangements
of steps. The drawings are only for purposes of illustrating
preferred embodiments and are not to be construed as limiting the
invention.
[0010] FIG. 1 is a high level process flow for piezoelectric
detection/test tape production;
[0011] FIG. 2 is a high level process flow for piezoelectric
detection/test tape production including attachment of the
piezoelectric elements to a transfer substrate prior to completion
of the tape production process;
[0012] FIG. 3 illustrates a piezoelectric element array on a top
surface of a carrier substrate;
[0013] FIGS. 4A and 4B show alternative embodiments of a
piezoelectric element array deposited with electrodes and other
thin film metals for bonding, the piezoelectric element array is on
a top surface of a carrier substrate;
[0014] FIG. 5A illustrates an embodiment of a bonding of
piezoelectric elements to a conductive final target using a thin,
nonconductive epoxy bonding containing sub-.mu.m (micrometer)
conductive balls;
[0015] FIG. 5B shows a thin nonconductive epoxy bonding
process;
[0016] FIG. 5C is an enlarged view of a section of FIG. 5B;
[0017] FIG. 5D illustrates a bonding of piezoelectric elements to a
conductive final target substrate using thin film intermetallic
transient liquid phase bonding;
[0018] FIG. 6A depicts a bonding to a conductive transfer substrate
using removable conductive tape bonding;
[0019] FIG. 6B illustrates a bonding of the piezoelectric elements
to the transfer substrate which is an Indium-Tin-Oxide (ITO)-coated
glass using thin, nonconductive epoxy bonding containing sub-.mu.m
conductive balls;
[0020] FIG. 7A illustrates radiation of a beam through the carrier
substrate during a liftoff process;
[0021] FIG. 7B depicts a heat transfer for the liftoff process;
[0022] FIGS. 8A and 8B are alternative designs for bonding the
elements array to a final target substrate or a transfer
substrate;
[0023] FIG. 9A illustrates bonding the piezoelectric elements array
to a final target substrate using thin, nonconductive epoxy bonding
containing sub-.mu.m conductive balls, where the piezoelectric
elements array is bonded to the transfer substrate using removable
conductive tape bonding;
[0024] FIG. 9B is a bonding of the piezoelectric elements array to
the final target substrate using thin film intermetallic transient
liquid phase bonding, where the piezoelectric elements array is
bonded to the transfer substrate using removable conductive tape
bonding;
[0025] FIG. 9C is a bonding of the piezoelectric elements array to
the final target substrate using thin, nonconductive epoxy bonding
containing sub-.mu.m conductive balls, where the piezoelectric
elements array is bonded to an ITO-coated glass using the thin,
nonconductive epoxy bonding containing sub-.mu.m conductive
balls;
[0026] FIG. 9D depicts bonding the piezoelectric elements array to
the final target substrate using thin film intermetallic transient
liquid phase bonding, where the piezoelectric elements array is
bonded to the ITO-coated glass using the thin, nonconductive epoxy
bonding containing sub-.mu.m conductive balls;
[0027] FIG. 9E depicts bonding the two elements arrays to a final
target substrate using thin, nonconductive epoxy bonding containing
sub-.mu.m conductive balls, where the elements array is bonded to
the transfer substrate using removable conductive tape bonding; the
two elements arrays are deposited on two substrates and then
transferred to two transfer substrates;
[0028] FIG. 9F depicts bonding the two elements arrays to a final
target substrate using thin, nonconductive epoxy bonding containing
sub-.mu.m conductive balls, where the elements array is bonded to
the transfer substrate using removable conductive tape bonding; the
two elements arrays, with two different thicknesses for the
elements from one array to the other, are deposited on two
substrates and then transferred to two transfer substrate;
[0029] FIGS. 10A and 10B depict alternative embodiments of a
partially constructed system, wherein filler is inserted;
[0030] FIG. 11 is chart depicting transmission wavelength of a
laser used in a process of the present application;
[0031] FIG. 12 depicts one embodiment wherein the second final
target substrate is bonded to the piezoelectric elements;
[0032] FIG. 13 is a cross section view for one embodiment of a
completed piezoelectric tape according to the present
application;
[0033] FIG. 14 is a sectional view along section line A-A of FIG.
13;
[0034] FIG. 15 is a sectional view at lines A-A, for another
embodiment of a piezoelectric ceramic tape.
[0035] FIG. 16 is a further A-A sectional view of a further
embodiment of a piezoelectric ceramic tape according to the present
application;
[0036] FIG. 17 depicts a polymer tape with a patterned
metallization layer which may be implemented as a metal surface in
accordance with the concepts of the present application;
[0037] FIG. 18A is the A-A sectional view of the fourth embodiment
of a piezoelectric ceramic tape;
[0038] FIG. 18B depicts a polymer tape with a patterned
metallization layer which could be used as the second final target
substrate for the fourth embodiment;
[0039] FIG. 19 is yet a further cross section view for one
embodiment of a completed piezoelectric tape according to the
present application;
[0040] FIG. 20 is a two-layer piezoelectric tape which may be
accomplished in accordance with the concepts of the present
application.
DETAILED DESCRIPTION OF THE INVENTION
[0041] The present application provides for flexible detection/test
tape and processes to make such a tape. In one design, a plurality
of piezoelectric ceramic elements are sandwiched between two
conductive layers, such as two metallized polymer films or tapes,
two metal foils, or one metallized polymer tape and one metal foil.
The configuration provides the assemblied piezoelectric tape with
flexibility and a potential dimension of several feet or more in
scale. As will be described in greater detail, the metallization
layer in the polymer film can be patterned in such ways that the
piezoelectric elements can be connected to external circuitry as
individual elements, as several groups, of elements, or as a single
group. Thus the piezoelectric tape can work simultaneously as
sensors, actuators or transducers. The area density and the shape
of the piezoelectric elements can be varied locally to meet the
application requirements. Also, since the disclosed manufacturing
process permits for a high density of elements, the operational
functionality of the tape will not be significantly less than a
sheet of piezoelectric elements. The piezoelectric ceramic tapes
can be made by a process which combines screen printing or other
direct marking method, high temperature sintering, tape polishing,
laser or other radiation liftoff, a thin layer bonding which can
remain electric contact between the bonded parts. Specifics of the
process will now be described.
[0042] FIG. 1 illustrates a high level process flow 10 for a first
embodiment of a manufacturing process according to the concepts of
the present application. While the following discussion focuses on
producing piezoelectric thick film elements (with thickness between
10 and 100 .mu.m), it is to be appreciated the disclosed processes
may be used with other materials and may also be used for
production of thin-film elements (with thickness less than 10
.mu.m) and elements with thicknesses greater than 100 .mu.m to
millimeter in scale. Also, the following techniques are intended to
be applicable to the generation of individual elements and arrays
of elements.
[0043] Initially, piezoelectric ceramic thick film elements are
fabricated by depositing the piezoelectric material onto an
appropriate substrate by use of a direct marking technology 12. In
the deposition techniques employed, ceramic type powders are used
in a preferred embodiment. The fabrication process includes
sintering the material preferably at a temperature of approximately
1100 to 1350.degree. C. for densification, although other
temperature ranges may also be used in appropriate circumstances.
Following the fabrication process the surface of the formed
structures of piezoelectric elements are polished 14, preferably
using a dry tape polishing technique. Once the piezoelectric
elements have been polished and cleaned, electrodes are deposited
on the surface of the piezoelectric elements 16. Next, the
piezoelectric elements are permanently bonded to a final target
substrate 18. The final target substrate is flexible and conductive
or has a surface conductive layer, such as a metal foil or a
metallized polymer tape. In order to easily carry during the
fabrication process, the flexible target substrate can be put on
another rigid carrier plate. Typically, the composition of the
piezoelectric ceramic elements is doped or undoped PZT (lead
zirconate titanate), but any other piezoelectric materials, such as
lead titanate, lead zirconate, lead magnesium titanate and its
solid solutions with lead titanate, lithium niobate, lithium
tantanate, and others may be used.
[0044] At this point, the substrate on which the piezoelectric
elements were deposited is removed through a liftoff process using
radiation energy such as from a laser or other appropriate device
20. The releasing process involves exposure of the piezoelectric
elements to a radiation source through the substrate, to break an
attachment interface between the substrate and the piezoelectric
elements. Additional heating is implemented, if necessary, to
complete removal of the substrate. Once the liftoff process has
been completed, a second electrode is deposited on a second surface
of the piezoelectric material 22. Thereafter, poling of the
elements under high voltage obtains piezoelectric properties in the
material 24. The electric property, for example, a dielectric
property, of each element is then measured 26 to identify if the
elements meet required criteria. An insulative filler is inserted
between the piezoelectric elements 28, whereafter the piezoelectric
elements are bonded to the second final target substrate 30. Again
the second final target substrate is flexible, such as a metal foil
or metallized polymer tape. The assembled arrangement can then be
removed from the carrier plate 32.
[0045] Turning to FIG. 2, illustrated is a second high-level
process flow 40 for a second embodiment of the present application.
This process differs from FIG. 1 in that the bonding is to a
transfer substrate rather than to a final target substrate. Thus,
the fabrication step 42, the tape polishing step 44 and the
electrode depositing step 46 are performed in the same manner as
steps 12, 14 and 16 of FIG. 1. At bonding step 48, the bonding is
to a transfer substrate, as this connection is not intended to be
permanent. Thereafter, the liftoff step 50, the second electrode
deposition step 52, the poling step 54 and electric property test
step 56, which correlate to steps 20, 22, 24 and 26 of FIG. 1, are
performed.
[0046] The piezoelectric elements are then bonded to a final target
substrate 58, in a procedure similar in design to step 18 of FIG.
1. Following bonding step 58, the transfer substrate is removed 60.
Thereafter, the steps of inserting an insulative filler 62, bonding
to the second final target substrate 64 and removal of the carrier
plate 66, are performed similar to steps 28, 30 and 32 of FIG. 1.
When bonding to a final target substrate, a thin high strength
bonding layer is used to minimize or avoid undesirable mechanical
damping or absorption of the bonding layer. This bonding will,
however, also permit maintaining of electrical contact between the
metal electrodes on the piezoelectric elements and the final target
substrates or a conductive surface of the final target
substrates.
[0047] Employing the process of FIG. 2, only fully tested thick
film elements and arrays will be bonded to final target substrates,
thus avoiding yield loss of the piezoelectric tape.
[0048] The processes of FIGS. 1 and 2 are appropriate for the
production of a flexible piezoelectric ceramic tape in high volume,
high usable yields, i.e. greater than 60 percent and more
preferably over 90 percent, and still yet more preferably greater
than 98 percent.
[0049] With attention to FIG. 3, which illustrates steps 12 and 42
in greater detail, piezoelectric ceramic elements 72 are deposited
on an appropriate substrate 74, and then sintered at 1100 to
1350.degree. C. for densification. The depositing step may be
achieved by a number of direct marking processes including screen
printing, jet printing, ballistic aerosol marking (BAM) or acoustic
ejection, among others. Using these techniques permits flexibility
as to the type of piezoelectric element configurations and
thicknesses. For example, when the piezoelectric elements are made
by screen printing, the screen printing mask (mesh) can be designed
to have various shapes or openings resulting in a variety of shapes
for the piezoelectric elements, such as rectangular, square,
circular, ring, among others. Using single or multiple printing
processes, the thickness of the piezoelectric elements can be from
10 .mu.m to millimeter scale. Use of these direct marking
techniques also permits generation of very fine patterns and high
density elements.
[0050] The substrate used in the processes of this application will
have certain characteristics, due to the high temperatures involved
and--as will be discussed in greater detail--the fact that the
substrate is to be transparent for the liftoff process.
Specifically, the substrate is to be transparent at the wavelengths
of radiation beam emitted from the radiation source, and is to be
inert at the sintering temperatures so as not to contaminate the
piezoelectric materials. A particularly appropriate substrate is
sapphire. Other potential substrate materials include transparent
alumina ceramics, aluminum nitride, magnesium oxide, strontium
titanate, among others. In one embodiment of the process, the
substrate selected is transparent for an excimer laser operating at
a wavelength of 308 nm, and does not have any requirement on its
crystallographic orientation. It is preferable that the selected
substrate material be reusable, which will provide an economic
benefit to the process.
[0051] After fabrication of the elements has been completed, the
process moves to step 14 (or 44), where the top surface of the
piezoelectric elements are polished through a tape polishing
process to remove any possible surface damage layer, such as due to
lead deficiency. This step ensures the quality of the piezoelectric
elements and homogenizes the thickness of piezoelectric elements.
By having a homogenized thickness, each of the piezoelectric
elements of an array will bond to the final target substrate or the
transfer substrate even when a very thin epoxy bonding layer or a
thin film intermetallic transient liquid phase bonding layer is
used.
[0052] In one preferred embodiment, the tape polishing step is a
dry tape polishing process that provides a planar flat polish out
to the edge of the surfaces of the piezoelectric elements, which
avoids a crowning effect on the individual elements. Compared to
wet polishing processes, the dry tape polishing does not cause
wearing of the edges of the piezoelectric elements, making it
possible to fabricate high-quality, thickness and shape-identical
piezoelectric elements. Once polishing has been completed, the
surface is cleaned, in one instance by application of a cleaning
substance.
[0053] After polishing and cleaning, the process moves to step 16
(or 46) where, as shown in FIG. 4A, metal electrodes 76 such as
Cr/Ni or other appropriate materials, are deposited on the surface
of the piezoelectric elements by techniques such as sputtering or
evaporation with a shadow mask. The electrodes can also be
deposited by one of the direct marking methods, such as screen
printing, and sintered at suitable temperatures. Alternatively,
when using a thin film intermetallic transient liquid phase bonding
process, certain low/high melting-point metal thin film layers may
be used as the electrodes for the piezoelectric elements, thus in
some cases it is not necessary to deposit the extra electrode layer
such as Cr/Ni. However, preferably the thin film intermetallic
transient liquid phase bonding process is undertaken after metal
electrode deposition, such as Cr/Ni deposition. While this process
will be discussed in greater detail below, generally a thin film
layer of high melting-point metal 78 (such as silver (Ag), gold
(Au), Copper (Cu), Palladium (Pd)) and a thin film layer of low
melting-point metal 79 (such as Indium (In), Tin (Sn)) may be
deposited on the piezoelectric elements (or the substrate) and a
thin layer of high melting-point metal (such as Ag, Au, Cu, Pd) may
be deposited on the substrate (or the piezoelectric elements).
These materials are then used to form a bond. Also a multilayer
structure with alternating low melting-point metal/high
melting-point metal thin film layers can be used.
[0054] For some uses, such as when the final target substrate or
system is not expensive, the piezoelectric elements are directly
bonded to the final target substrate (step 18 of FIG. 1). For
example, as depicted in FIG. 5A, the final target substrate 82 is a
flexible and conductive material, such as a metal foil (thus it can
also be used as common electrode). The final target substrate 82
could also be carried on a carrier plate 80 during the process. The
placement of final target substrate 82 to carrier plate 80 may be
an action where no bonding material is used between the two
components. In alternative embodiments some type of removable
adhesive may be used to ensure placement of the metal foil.
[0055] The bonding to piezoelectric elements 72 is accomplished by
using a nonconductive epoxy layer 84 which can be as thin as less
than 1 .mu.m. The thin epoxy contains sub-.mu.m conductive
particles, which in one embodiment may be conductive balls (such as
Au balls) 85 so the epoxy is conductive in the Z direction (the
direction perpendicular to the surface of metal foil). Thus it can
keep the electric contact between the surface electrode of the
piezoelectric elements and the metal foil. The concentration of the
conductive balls can be controlled in such a range that the cured
thin epoxy is conductive in the Z direction but not conductive in
the lateral directions, as done for the anisotropic conductive
films. The shrinkage of the epoxy maintains contact between the
surfaces and the balls in the Z direction.
[0056] In an alternative embodiment shown in FIGS. 5B and 5C,
conductive balls 85 are removed, and bonding is accomplished using
the nonconductive epoxy layer 84 alone. As shown in more detail by
FIG. 5C, with controlled suitable surface roughness or asperity of
the piezoelectric elements and/or the final target substrate,
electrical contact is maintained via electrical contact points 86,
formed when the surface of the electrode 84 and metal foil 82 are
moved into contact.
[0057] In a further embodiment, bonding to the final target may be
accomplished by using the previously mentioned thin film
intermetallic transient liquid phase metal bonding, employing in
one embodiment a high melting-point metal (such as Ag, Cu, Pd, Au,
etc.)-low melting-point metal (such as In, Sn) intermetallic
compound bonding layer or alloy 88, FIG. 5D.
[0058] More particularly, for thin film intermetallic transient
liquid phase metal bonding, a high melting-point metal thin layer
such as a Pd thin layer is deposited on the target substrate. Next
the piezoelectric elements are moved into contact with the Pd thin
layer and heated under pressure above the melting point of the low
melting-point metal (In), e.g., about 200.degree. C. By this
operation the high melting-point metal/low melting-point metal/high
melting-point metal combination such as the Pd/I/Pd layer (a high
melting-point metal/low melting-point metal such as Pd/In layer was
previously deposited on the piezoelectric elements as shown in FIG.
4B) will form the high melting-point metal-low melting-point metal
intermetallic compound bonding layer or alloy 88. This compound or
alloy may be a PdIn.sub.3 alloy layer which is about 1 .mu.m-thick,
which acts to bond piezoelectric elements 72 and target substrate
82. Functionally, the low melting-point metal diffuses into the
high melting-point metal to form the compound/alloy.
[0059] As the melting point of the formed intermetallic compound
phase can be much higher than that of the low melting-point metal,
the working temperature of the bonding layer can be much higher
than the temperature used to form the bonding. For example, when
Indium (In) is used as the low melting-point metal and Palladium
(Pd) is used as the high melting-point metal, the bonding can be
finished below or at 200.degree. C. as the melting point of In is
about 156.degree. C. However, the working temperature of the formed
intermetallic compound bonding layer, PdIn.sub.3, can be well above
200.degree. C. because the melting point of PdIn.sub.3 is about
664.degree. C. The thickness of the bonding layer could be from 1
to 10 .mu.m, but a thinner bonding layer (e.g., about 1 .mu.m) is
expected for this purpose. Further, the amount of high and low
melting-point metals can be controlled so they will be totally
consumed to form the intermetallic bonding layer.
[0060] Alternatively, when the final target substrate is expensive,
or the final target substrate is so large (to fabricate a very
large piezoelectric tape) that the piezoelectric elements have to
be fabricated on more than one substrate, bonding of the
piezoelectric elements to the final target substrate is delayed.
Incorporation of the steps in FIG. 2 minimizes yield loss of the
final target substrate or the large area piezoelectric tape, which
might otherwise occur due to piezoelectric elements fabrication
failures. Therefore, the process of FIG. 2 temporarily bonds the
piezoelectric elements to a transfer substrate in step 48, and then
finishes piezoelectric elements production and testing. Only a
fully tested piezoelectric thick film array of elements is then
permanently bonded to the target substrate.
[0061] The temporary bonding process step 48 of FIG. 2, is
illustrated by FIGS. 6A and 6B. In FIG. 6A, the bonding operation
uses a removable conductive bonding epoxy, such as a removable
conductive tape 90, including 9712, 9713 and 9719 conductive tape
from 3M Corporation. The transfer substrate 92 can be a metallized
glass with surface conductive layer 94, such as a metallization
layer. In an alternative embodiment depicted in FIG. 6B, the
bonding operation uses thin nonconductive epoxy 84 containing
sub-.mu.m conductive balls 85, to bond to a transfer substrate 98
such as a glass having an ITO coating 100.
[0062] Once the piezoelectric elements have been either permanently
bonded to a final target substrate (step 18 of FIG. 1) or
temporarily bonded to a transfer substrate (step 48 of FIG. 2), the
next step is to release the piezoelectric elements 72 from
substrate 74. The releasing of substrate 74 is accomplished by a
liftoff operation as depicted in FIGS. 7A and 7B. The following
description is based on the arrangement of FIG. 5A. However, it is
applicable to all provided alternatives. Substrate 74 is first
exposed to a radiation beam (such as a laser beam) from a radiation
source (such as an excimer laser source) 102, having a wavelength
at which the substrate 74 is substantially transparent. In this way
a high percentage of the radiation beam passes through the
substrate 74 to the interface of the substrate and elements 72 at
the surface of the substrate. The energy at the interface acts to
break down the physical attachment between these components.
Following operation of the radiation exposure, and as shown in FIG.
7B, heat is applied by a heater 104. While the temperature provided
by the heater will vary depending on the situation, in one
embodiment a temperature of between 40 to 50.degree. C. is
sufficient to provide easy detachment of any remaining contacts to
fully release the piezoelectric elements 72 from substrate 74.
Desirably, the substrate is of a material that allows it to be
re-used after a cleaning of its surface.
[0063] In one experiment performed by the inventors, the radiation
source is an excimer laser source and the laser energy required to
achieve separation by the present procedure has been measured at
about one-half what is mentioned as needed in the Cheung et al.
patent. This is considered in part due to the wavelength used in
the experiment (e.g., 308 nm), and also that the piezoelectric
elements were printed on substrates, therefore more weakly bound to
the substrate compared to the epitaxially grown single crystal
films used in the previous work by Cheung et al.
[0064] Exposure to the radiation source does raise the potential of
damage to the surface of the piezoelectric elements, this potential
damage should however be no more than to a thickness of about 0.1
.mu.m. Since the thickness of the piezoelectric elements, in most
embodiments, will be larger than 10 .mu.m, the effect of the
surface damage layer can be ignored. However, if otherwise
necessary or when piezoelectric elements of less than 10 .mu.m are
formed by these processes, any surface damage layer can be removed
by appropriate processes including ion milling or tape polishing.
It is to be appreciated FIGS. 7A and 7B are simply used as
examples, and the described liftoff process may take place using
alternatively described arrangements. Also, for convenience FIGS.
7A and 7B correspond to the structure of FIG. 5A. However, the same
types of procedures may be applied to FIGS. 5B, 5D, 6A, 6B or other
relevant arrangements in accord with the present teachings.
[0065] Next, as depicted in FIGS. 8A and 8B, second side surface
electrodes 106, such as Cr/Ni, are deposited on the released
surfaces of elements 72 with a shadow mask or by other appropriate
method in accordance with step 22 of FIG. 1 or step 52 of FIG. 2.
After second electrode deposition, the processes move to steps 24
and 54, respectively, where the piezoelectric elements 72 are poled
under a voltage 108 sufficient, as known in the art, to obtain
piezoelectric properties. After poling, the electric property, for
example, the dielectric property, of the elements are measured
(step 26 of FIG. 1; step 56 of FIG. 2) to identify if the
piezoelectric elements meet expected quality criteria. FIG. 8A
corresponds to the arrangements shown in FIG. 5A, and FIG. 8B
corresponds to the arrangement of FIG. 6A, following release of the
substrates.
[0066] For the case where the piezoelectric thick film array of
elements is temporally bonded to a transfer substrate such as by
the process of FIG. 2, steps 58 and 60 are undertaken. In the
following these steps are implemented using selected ones of the
alternative arrangements previously described. It is to be
understood the present discussion is applicable for all disclosed
alternative designs.
[0067] By use of temporary bonding, it is only after electric
property measurement is made that the piezoelectric array is bonded
to the final target substrate.
[0068] Step 58 of FIG. 2 may be accomplished in the same manner as
bonding step 18 of FIG. 1. FIGS. 9A-9D, show alternative bonding
methods, including a thin nonconductive epoxy bonding containing
sub-.mu.m conductive balls (FIG. 5A) and a thin film intermetallic
transient liquid phase bonding (FIG. 5D). Still further, the
process could employ the thin nonconductive epoxy bonding of FIGS.
5B and 5C. When this process is used, the surface roughness of the
piezoelectric elements and/or the substrate is preferably in a
range of about 0.5 to 5 .mu.m, depending on the film thickness, the
nature of the substrate, as well as the intended use. The second
surface of the piezoelectric elements could be very smooth due to
the smooth nature of the substrate surface. This means that, after
liftoff, rough tape polishing, sandblasting or other methods may be
needed to increase the surface roughness. It is to be understood
the surface roughness will be a small fraction of the overall
thickness of the piezoelectric element and/or substrate. The
specific roughness being selected in accordance with a particular
implementation.
[0069] If the thin film intermetallic transient liquid phase
bonding is used, similar to previous steps, a high melting-point
metal/low melting-point metal such as Pd/In is deposited on the
second surface of the piezoelectric elements and a thin high
melting-point metal such as Pd layer is deposited on the surface of
the final target substrate. Deposition of the high
melting-point/low melting-point metal layers on the piezoelectric
elements can be done either after the poling and electric property
test or before the poling and electric property test but after the
electrode deposition.
[0070] It is to be appreciated that to make the flexible
piezoelectric tape the final target substrate needs to be flexible
and the final target substrate or the surface of the final target
substrate needs to be conductive. Typically, the final target
substrate could be a metal foil or a polymer tape with metallized
surface layer. If appropriate, the final target substrate may also
be put on rigid carrier plate 80, as shown in FIG. 5A, for easy
carrying during the fabrication process. FIGS. 9A-9D are related to
the process of FIG. 2, where the first bonding step is to a
temporary connection, and the final target substrate 110 has a
surface conductive layer 116.
[0071] With more particular attention to FIG. 9A, to bond the
piezoelectric elements 72 to final target substrate 110,
nonconductive epoxy 84 containing sub-.mu.m conductive balls 85 is
interposed between a surface of the conductive layer 116 of the
final target substrate 110 and piezoelectric elements 72 with
electrodes 106. The opposite side surfaces of the piezoelectric
elements 72 (i.e., having electrodes 76) are already temporarily
bonded to the transfer substrate 92 (via conductor 94) through the
use of a removable conductive tape 90.
[0072] FIG. 9B illustrates an alternative bonding of the
piezoelectric elements 72 to final target substrate 110 using thin
film intermetallic transient liquid phase bonding 88, where the
piezoelectric elements 72 are bonded to the transfer substrate 92
using removable conductive tape 90.
[0073] The alternative bonding of FIG. 9C, shows the elements 72
bonded to the final target substrate 110 using thin nonconductive
epoxy bonding 84 containing sub-.mu.m conductive balls 85. In this
design, elements 72 are bonded to an ITO coated 100 glass substrate
98 using the thin nonconductive epoxy 84 containing sub-.mu.m
conductive balls 85.
[0074] Depicted in FIG. 9D is an arrangement where the elements 72
are bonded to the final target substrate 110 using thin film
intermetallic transient liquid phase bonding 88, where the
piezoelectric elements 72 are bonded to ITO coated 100 glass 98
using the thin nonconductive epoxy 84 containing sub-.mu.m
conductive balls 85.
[0075] In some instances when fabricating a large piezoelectric
tape, the final target substrate may be larger than the substrate
available to deposit the piezoelectric elements. Alternatively, for
economic reasons a relatively small substrate may be preferred to
deposit the piezoelectric elements. In these situations, step 42 of
FIG. 2 (or Step 12 of FIG. 1) may be accomplished by depositing the
piezoelectric elements on several substrates. Thereafter processing
steps 44 and 46 are performed. Since the piezoelectric elements
will be on several substrates, step 48 will include bonding the
piezoelectric elements to several transfer substrates. Then,
following processing steps 50-56, in step 58 the several transfer
substrates will be bonded to the same final target substrate. The
foregoing process not only permit formation of large piezoelectric
tapes and the use of small substrates, it also permits the
attachment of different piezoelectric materials, such as soft PZT
and hard PZT, or other functional ceramic materials, such as
antiferroelectric materials, electrostrictive materials and
magnetostrictive materials, on the same final target substrate.
This means that the tape can contain different piezoelectric
materials and/or other functional ceramic materials. For
fabricating antiferroelectric elements and electrostrictive
elements, the poling step (step 54) is not necessary.
[0076] Additionally, when bonded to the same final target
substrate, if the distances between elements on one transfer
substrate and another transfer substrate are sufficient, the
thicknesses of the elements may be different from one transfer
substrate to another, and a second flexible substrate (explained in
details later) can still be bonded to the surface of all the
elements. This means that the tape can contain elements with
different thicknesses.
[0077] To illustrate the above concepts, FIG. 9E depicts two
transfer substrates 92, and 93. Transfer substrate 92 has
piezoelectric elements 72 bonded on it using removable conductive
tape 90, and transfer substrate 93 has elements 73 (which may be
another kind of piezoelectric material or other functional ceramic
materials) bonded on it using removable conductive tape 91. The
elements 72 and 73 are bonded to the same final target substrate
110 using the thin nonconductive epoxy bonding 84 containing
sub-.mu.m conductive balls 85. FIG. 9F depicts transfer substrates
92 and 93, where transfer substrate 92 has elements 72 bonded on it
using removable conductive tape 90, and transfer substrate 93 has
elements 71, which have thicknesses different from elements 72,
bonded using removable conductive tape 91. Elements 72 and 71 are
bonded to the same final target substrate using the thin
nonconductive epoxy bonding 84 containing sub-.mu.m conductive
balls 85. The distance between elements 71 and 72 is large enough
so the second flexible substrate can be bonded to all elements.
[0078] Once the final target substrate has been bonded to the
elements, the process proceeds to step 60 and the transfer
substrates (such as 92, 93) are removed, as shown in FIGS. 10A and
10B. For the case where the piezoelectric elements are bonded to
the transfer substrate using removable conductive epoxy, such as
tape, after permanent bonding to the final target is achieved, the
tape and the transfer substrate can be easily peeled off from the
piezoelectric elements. The present process makes it easy to take
off the conductive tape. This is because the conductive tape uses
filled acrylic, such as the 3M 9712, 9713 and 9719 conductive
tapes, which lose most of their adhesion after being heated at a
temperature of between 150 and 200.degree. C. The time needed for
application of the heat will depend upon the specific application.
In some applications this level of heat may be applied during the
process to bond the piezoelectric elements 72 to the final target
substrate.
[0079] For the case where the piezoelectric elements 72 are bonded
to the ITO coated glass using the thin nonconductive epoxy, the
piezoelectric elements can be released from the ITO coated glass by
using the liftoff operation in a manner similar as in steps 20 or
50 where the radiation source is a laser. This is possible as the
epoxy will also absorb the laser light, thus the laser exposure
will burn off the epoxy and release the piezoelectric elements from
the glass substrate. As the melting point of epoxy is much lower
than that of the metal and ITO electrodes, the laser exposure
intensity may be controlled so it will only burn off the epoxy and
not cause any damage on the metal and ITO electrodes.
[0080] It should be noted that when using laser liftoff techniques
to release the piezoelectric elements from ITO-coated glass, in one
embodiment an excimer laser with relatively longer wavelength, such
as Nd:YAG laser (.lamda.=355 nm) and XeF (.lamda.=351 nm) is to be
used. This is because, as shown in FIG. 11, the transmission of
light through ITO on glass will drop sharply around .lamda.=300 nm,
but around .lamda.=350 nm the transmission can be about 80%. With
such high transmission, the laser exposure can be controlled so
that only the epoxy is destroyed and damage to the ITO and metal
electrodes does not occur.
[0081] After removing the transfer carrier, solvent such as acetone
or other appropriate substance may be used to clean off the
residual of the conductive tape or the epoxy. Thereafter in step 28
(or 62), and as illustrated in FIGS. 10A and 10B, a filler material
114 is inserted between the piezoelectric elements 72. The filler
114 may be any appropriate insulative material including a punched
polymer tape with openings slightly larger than the dimension of
the piezoelectric elements 72.
[0082] Once the filler has been inserted, the process moves to step
30 (or 62) where, as depicted in FIG. 12, the second final target
substrate 118 is bonded to the top of a second surface of the
piezoelectric elements. Again the second final target substrate is
flexible and the final target substrate or the surface of the final
target substrate is conductive. Typically, the final target
substrate could be a metal foil or a polymer tape with metallized
surface layer. It is to be appreciated that FIG. 12 corresponds to
the configuration of FIG. 10A, and the second final target
substrate 118 has a surface conductive layer 119. However, the
concept is also applicable to FIG. 10B, and other configurations
which may be constructed according to the present application. In
this embodiment, bonding is accomplished by thin nonconductive
epoxy bonding 84 containing sub-.mu.m conductive balls 85. However,
it is to be appreciated other ones of the previously mentioned
bonding techniques may also be used.
[0083] Lastly, the carrier plate 80 is removed (step 32, FIG. 1 or
step 66, FIG. 2). It should be noticed that, while the carrier
plate is not shown in FIGS. 9A-D, FIGS. 10A-B and FIG. 12, a rigid
carrier plate (e.g., see FIGS. 5A-5B and 8A) may be located under
the final target substrate to support the final target substrate
and for carrying the final target substrate during the fabrication
process.
[0084] FIG. 13 shows one embodiment of a flexible tape 120
manufactured in accordance with the present application. FIG. 14
provides a A-A section view 120 of FIG. 13. In this configuration,
a plurality of elements 72, such as piezoelectric elements, are
sandwiched between final target substrate 82 and the second final
target substrate 118. Substrates 82 and 118 are flexible and
conductive or have a surface conductive layer. The procedure to
make this tape is the same as the procedure to make the embodiment
shown in FIG. 12 (therefore, final target substrate 110 with
conductive surface 116 could just as easily have been used instead
of substrates 82 or 118), but in this embodiment the final target
substrate 82 is a conductive material or conductive layer, such as
a metal foil, thus it does not have another conductive surface
layer, and the second final target substrate 118 is an insulative
material with a surface conducting layer 119, such as a metallized
polymer tape.
[0085] For this design, the piezoelectric elements 72 are
homogeneously distributed. It is to be appreciated that layers 82
and 118 are used as illustrative examples only, and other
conductive material or material with surface conductive layer may
also be used. Filler 114, such as punched mylar or teflon or other
insulative material is positioned between the piezoelectric
elements as insulation. The metallization layer 119 on polymer tape
118 is not patterned, thus all the piezoelectric elements 72 are
connected together. Inclusion of electrical connectors 122 permit
for the application of power and/or control signals. More
particularly, known feedback or feed-forward control circuitry 123
is provided to control operation of the piezoelectric elements 72.
Layers 82 and 118 are depicted as being bonded via the previously
described thin nonconductive epoxy 84 bonding process containing
sub-.mu.m conductive-balls 85. However, it is to be understood that
any of the previously described bonding techniques may be
employed.
[0086] The primary use of filler material 114 is to electrically
isolate the (first) final substrate and the second final substrate
or the surface conductive layers of these substrates from each
other. However, it is to be understood insertion of the filler
material is optional. For example, if the density of the elements
is sufficiently high so that gaps between the elements are small
enough that it is not possible to have an electric short circuit
between the (first) final substrate and the second final substrate
or their surface conductive layers even without any material
filling the gaps between the elements, the insertion of filler
material may be avoided. Also, filler material may not be used if
the surface conductive layer of the substrate is patterned so there
is no surface conductive layer in the areas which are not to be
bonded to the piezoelectric elements.
[0087] FIG. 15 is an A-A section view 130 for another embodiment of
the tape of FIG. 13. This drawing emphasizes piezoelectric elements
may be made as narrow and long strips 134, with the filler 136
configured to match this design. In this embodiment, the tape 130
can work as an active fiber composite, used in structures which
require flexibility only along one direction, such as a cylindrical
structure.
[0088] FIG. 16 is a third embodiment of an A-A sectional view 140.
This drawing shows that the density of piezoelectric elements in an
area can be changed (i.e., the elements do not need to be evenly
distributed in an area), and the piezoelectric elements may be
formed in a variety of shapes 142. Thus the function of the
piezoelectric tape can be locally adjusted. Filler 144 is
distributed around and between the elements.
[0089] FIG. 17 is a polymer tape 150 with a patterned metallization
layer 152. Depending on the shape and distribution of the
piezoelectric elements, and the design of outside circuits, the
metallization layer can be patterned on the polymer tape 150 to
connect the piezoelectric elements to external circuits, via
circuit lines 154, individually or group by group, where the number
of piezoelectric elements between groups can be different. With
such circuit connection it is possible to simultaneously have some
piezoelectric elements work as sensors, some as actuators, and some
as transducers. Thus the piezoelectric tape itself is a
detection/test panel or skin. For example, this purpose can be
realized if the metallization layer 152 as shown in this figure is
bonded to the piezoelectric elements shown in FIG. 16.
[0090] FIG. 18A is a fourth embodiment of an A-A section view 180.
This drawing emphasizes that in one tape it can have elements with
different compositions (such as soft PZT and hard PZT) or some of
the elements may be of piezoelectric material and other elements of
other functional ceramic materials such as antiferroelectric
material or electrostrictive material. For example, elements 72 are
one kind of piezoelectric material and elements 73 are another kind
of piezoelectric material or antiferroelectric or electrostrictive
material. These different materials are made on different
substrates and finally bonded to the same final target substrate,
as previously described. These elements (made from different
materials) can be connected together to a single outside circuit.
However, more preferably they will be connected to the different
outside circuits for different functions. For example, tape 190 can
have a patterned metallization layer 192 shown in FIG. 18B. When
this tape is used as the second final target substrate to bond the
elements shown in FIG. 18A, all the elements 72 will work as a
group and be connected to one outside circuit, and the elements 73,
made from another kind of piezoelectric material or other
functional ceramic material (such as antiferroelectric material or
electrostrictive material) will work as another group and be
connected to a separate outside circuit.
[0091] FIG. 19 shows a further embodiment of a flexible tape 200
manufactured in accordance with the present application. In this
configuration, a plurality of elements 72 and 71 are sandwiched
between the final target substrate 82 and the second final target
substrate 118. Substrates 82 and 118 are flexible and conductive or
have a surface conductive layer. Shown in this embodiment the final
target substrate 82 is a conductive material or conductive layer,
such as a metal foil, thus it does not have another conductive
surface layer. Final target substrate 118 is an insulative material
with a surface conducting layer 119, such as a metallized polymer
tape. However, unlike FIG. 13, the elements 72 and 71 in this
embodiment have different thicknesses, and are fabricated on
different substrates, but are finally bonded to the same final
target substrate, as previously described. The distance between
elements 72 and elements 71 is large enough so the second final
target substrate (which is flexible) 118 can be bonded to both
elements 72 and 71. Again while these elements with different
thicknesses can be connected to a single external circuit together,
more preferably they are connected to different external circuits
for different functions. For example, when the polymer tape 190
shown in FIG. 18B is used as the second final target substrate to
bond the elements shown in FIG. 19, elements 72 work as a group and
are connected to a single external circuit, and the elements 71 are
connected to a separate external circuit, in order to work as a
group.
[0092] FIG. 20 is a double piezoelectric tape 160 made from two
layers of single piezoelectric tape 162, 164 as configured, for
example, in FIG. 13. In one embodiment, a double surface metallized
polymer tape 166 is used to connect the two layers 162, 164. In
this embodiment, metallization layers 167, 168, and 119 are
individually numbered. While in this embodiment these metallization
layers cover the whole surface of the polymer tape 166 and 118,
depending on applications the metallization layers 167, 168, and
119 can be different materials, can be patterned and their
patterned configurations can be different from one to another.
Multilayer piezoelectric elements can also be made in accordance
with the teachings of the present application.
[0093] The various embodiments of a ceramic tape as shown in FIGS.
13-20 are flexible tapes having the capability of selective
operations, formed from the various piezoelectric elements provided
as representative examples in these figures.
[0094] A further consideration in the construction of the tapes, is
the placement of the piezoelectric elements in relation to the
neutral plane of the tape. For a film or solid piece of material,
the neutral plane is that location at which the sheer forces will
move to zero during a bending operation. Particularly, it is the
region inside the tape where the compressive force and the tensile
force will cancel each other so as to eliminate sheer stress. Once
the characteristics of the materials are known, such as the elastic
modulus of the materials, it is possible to determine where a
neutral plane will exist using well-known calculations. This
information may be used in the present application to place the
piezoelectric material relative to the plane to either increase or
decrease the sensitivity of the piezoelectric elements, or to
adjust the radius of curvature for the tape. Determinations on the
placement of the piezoelectric element will be driven by the
intended use of the tape. Particularly, placing the elements at the
neutral plane will permit for an increase in the radius of
curvature of the tape, thereby allowing the tape to be wrapped
around a more tightly curved object. However, the tradeoff in
providing this ability could cause a decrease in the sensitivity of
readings that may be obtained.
[0095] The invention has been described with reference to the
preferred embodiments. Obviously, modifications and alterations
will occur to others upon reading and understanding the preceding
detailed description. It is intended that the invention be
construed as including all such modifications and alterations
insofar as they come within the scope of the appended claims or the
equivalents thereof.
* * * * *