U.S. patent application number 12/475920 was filed with the patent office on 2009-12-03 for method of assembling an electrode array that includes a plastically deforamble carrier.
Invention is credited to Robert Brindley, John Janik.
Application Number | 20090293270 12/475920 |
Document ID | / |
Family ID | 40933554 |
Filed Date | 2009-12-03 |
United States Patent
Application |
20090293270 |
Kind Code |
A1 |
Brindley; Robert ; et
al. |
December 3, 2009 |
METHOD OF ASSEMBLING AN ELECTRODE ARRAY THAT INCLUDES A PLASTICALLY
DEFORAMBLE CARRIER
Abstract
A method of assembling an implantable electrode array from a
coupon (108) formed from plastically deformable material. Layers of
material are disposed on the coupon to form the electrodes (48) and
conductors (62) of one or more electrode arrays. Sections of the
coupon on which the electrodes and conductors are removed, along
with the electrodes and conductors to form the electrode arrays.
The removed sections of the coupon thus function as plastically
deformable carriers (74) for the arrays (40).
Inventors: |
Brindley; Robert; (Delton,
MI) ; Janik; John; (Hudsonville, MI) |
Correspondence
Address: |
INTEL. PROP./ RND;STRYKER CORPORATION
4100 EAST MILHAM AVE.
KALMAZOO
MI
49001-6197
US
|
Family ID: |
40933554 |
Appl. No.: |
12/475920 |
Filed: |
June 1, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61057684 |
May 30, 2008 |
|
|
|
Current U.S.
Class: |
29/829 |
Current CPC
Class: |
C23C 14/0005 20130101;
Y10T 29/49124 20150115; A61N 1/0543 20130101; A61N 1/0541 20130101;
A61N 1/0551 20130101; A61N 1/05 20130101; A61B 2562/125 20130101;
A61N 1/0529 20130101 |
Class at
Publication: |
29/829 |
International
Class: |
H05K 3/00 20060101
H05K003/00; A61N 1/05 20060101 A61N001/05 |
Claims
1. A method of assembling an implantable electrode array including
the steps of: applying at least one layer of insulating material
and at least one layer of conductive material in separate process
steps to a section of the coupon formed from plastically deformable
material so as to form on the coupon at least one electrode and at
least one conductor, wherein the at least one electrode and the at
least one conductor occupy a section of the coupon that is less
than the whole of the coupon; separating from the coupon the
section of the coupon upon which the at least one electrode and at
least one conductor are formed so that the section of the coupon
functions as a carrier for an implantable electrode array that
further includes at least one electrode and at least one conductor
on the carrier.
2. The method of assembling an implantable electrode array of claim
1, wherein, prior to said step of applying the at least one layer
of insulating material and one layer of conductive material to the
coupon, the at least one section of the coupon that is to function
as the electrode array carrier is shaped to at least partially
define the carrier, and after said shaping, remains attached to the
coupon.
3. The method of assembling an implantable electrode array of claim
2, wherein: in said step of shaping the coupon to at least
partially define the electrode array carrier, slots are formed in
the coupon to define the carrier and at least one tab intersects
the slots to connect the at least one carrier to an adjacent
section of the coupon; and after said step of applying the at least
one layer of insulating material and one layer of conductive
material to the coupon, as part of said step of separating the
carrier from the rest of the coupon, the at least one tab
connecting the carrier to the coupon is removed.
4. The method of assembling an implantable electrode array of claim
1, wherein: during said step of applying the at least one layer of
insulating material and one layer of conductive material to the
coupon, the insulating material and conductive material form, on
plural sections of the coupon, assemblies consisting of at least
one electrode and at least one conductor; and during said step of
separating from the coupon the section of the coupon upon which the
at least one electrode and at least one conductor are formed,
separating from the coupon the plural sections of the coupons on
which the electrode and conductor assemblies are formed so that
removed section of the coupon functions as an electrode array
assembly.
5. The method of assembling an implantable electrode of claim 1,
wherein: prior to said step of applying the at least one layer of
insulating material and one layer of conductive material to the
coupon, the coupon is mounted to a rigid substrate; and during said
step of applying the at least one layer of insulating material and
one layer of conductive material to the coupon, the insulating
material and conductive material is applied to a surface of the
carrier opposite a surface of the carrier mounted to the substrate;
and after said step of applying the at least one layer of
insulating material and one layer of conductive material to the
coupon, the coupon is released from the substrate.
6. The method of assembling an implantable electrode of claim 1,
wherein, the coupon lies in a plane; prior to said step of applying
the at least one layer of insulating material and one layer of
conductive material to the coupon, the section of the coupon on
which the insulating material and conductive material is applied is
at least partially shaped to define the carrier and, in said
shaping, is shaped to extend out the plane of the coupon; the
coupon, including the at least partially shaped carrier, is mounted
to a planar substrate and, as a consequence of said step of
mounting the coupon, the at least partially shaped carrier is
flexed back into the plane of the coupon; during said step of
applying the at least one layer of insulating material and one
layer of conductive material to the coupon, the insulating material
and conductive material is applied to a surface of the at least
partially shaped carrier opposite a surface of the carrier mounted
to the substrate; and after said step of applying the at least one
layer of insulating material and one layer of conductive material
to the coupon, the coupon is released from the substrate.
7. The method of assembling an implantable electrode array of claim
1, wherein: prior to said step of applying the at least one layer
of insulating material and one layer of conductive material to the
coupon, the at least one section of the coupon that is to be
occupied by the at least one electrode and the at least one
conductor is shaped to at least partially shaped to define the
carrier wherein during said shaping, the carrier is formed to have
at least one tab that is partially separated from adjacent portions
of the carrier; and during said step of applying the at least one
layer of insulating material and one layer of conductive material
to the coupon, the conductive material is applied to the
carrier-defining section of the coupon to form an electrode on the
carrier tab.
8. The method of assembling an implantable electrode array of claim
1, wherein the coupon is formed from a superelastic material.
9. A method of assembling an implantable electrode array, said
method including the steps of: at least partially shaping a carrier
formed of superelastic material so that the carrier has a
non-planar shape; bonding the carrier to a rigid planar substrate
so that as a result of said bonding, the carrier flexes into a
planar shape; while the carrier is bonded to the substrate,
applying at least one layer of insulating material and at least one
layer of conductive material in separate process steps to the
carrier so as to form on the carrier at least one electrode and at
least one conductor; and after said formation of said at least one
electrode and said conductor on the carrier, releasing the carrier
from the substrate so that carrier and at least one electrode and
at least one conductor formed thereon function as an electrode
array assembly and, as a result of said releasing of the carrier
from the substrate, the carrier at least partially returns to the
non-planar shape the carrier had prior to said step of bonding the
carrier to the substrate.
10. The method of assembling an implantable electrode array of
claim 9, wherein said carrier is formed from a nickel titanium
alloy.
11. The method of assembling an implantable electrode array of
claim 9, wherein: during said step of at least partially shaping
said carrier, the carrier is shaped to have at least one tab that
is partially separated from adjacent portions of the carrier; and
during said step of applying the at least one layer of insulating
material and one layer of conductive material to the coupon, the
conductive material is applied to the carrier to form an electrode
on the tab.
12. The method of assembling an implantable electrode array of
claim 9, wherein: the carrier is part of a coupon that is larger in
size than the carrier; in said step of bonding the carrier to the
rigid substrate, the coupon is bonded to the substrate; and in said
step of applying at least one layer of insulating material and at
least one layer of conductive material to the carrier, the
insulating material and conductive material is applied to form the
at least one electrode and the at least one conductor to a section
of the coupon that defines the carrier; and said method further
includes the step of separating the carrier-defining section of the
coupon from an adjacent section of the coupon.
13. The method of assembling an implantable electrode array of
claim 12 wherein: said step of separating the carrier-defining
section of the coupon from the adjacent section of the coupon
occurs prior to said step of releasing the carrier from said
substrate.
14. The method of assembling an implantable electrode array of
claim 13, wherein, prior to bonding the coupon to the rigid
substrate, said coupon is at least partially shaped to define the
carrier.
15. A method of assembling an implantable electrode array including
the steps of: bonding a carrier formed of flexible material to a
rigid substrate; while the carrier is bonded to the rigid
substrate, applying at least one layer of insulating material and
at least one layer of conductive material in separate steps to an
exposed face of the carrier to form at least one electrode and at
least conductor on the carrier; and after said formation of said at
least one electrode and said conductor on the carrier, releasing
the carrier from the substrate so that carrier and at least one
electrode and at least one conductor formed thereon function as an
electrode array assembly.
16. The method of assembling an implantable electrode array of
claim 15, wherein the carrier bonded to the rigid substrate is
formed from material that is plastically deformable.
17. The method of assembling an implantable electrode array of
claim 15, wherein the carrier bonded to the rigid substrate is a
polyamide film.
18. The method of assembling an implantable electrode array of any
one of claim 15, wherein: the carrier is part of a coupon that is
larger in size than the carrier; in said step of bonding the
carrier to the rigid substrate, the coupon is bonded to the
substrate; in said step of applying at least one layer of
insulating material and at least one layer of conductive material
to the carrier, the insulating material and conductive material is
applied to a section of the coupon; and said method further
includes the step of separating the carrier-defining section of the
coupon from an adjacent section of the coupon.
19 The method of assembling an implantable electrode array of claim
18, wherein: said step of separating the carrier-defining section
of the coupon from an adjacent section of the coupon occurs prior
to said step of releasing the carrier from said substrate.
20. The method of assembling an implantable electrode array of
claim 18, wherein, prior to bonding the coupon to the substrate,
said coupon is at least partially shaped to define the carrier.
Description
RELATIONSHIP TO EARLIER FILED APPLICATION
[0001] This application claims priority from and is nonprovisional
of U.S. Patent Application No. 61/057,684 filed 30 May 2008.
FIELD OF THE INVENTION
[0002] This invention is generally related to a method of
assembling electrodes arrays that include plastically deformable
carriers. More particularly, this application is directed to a
method that facilitates the batch, simultaneous assembly of plural
electrode arrays.
BACKGROUND OF THE INVENTION
[0003] A number of medical procedures involve implanting an
electrode array in a patient to accomplish a desired therapeutic
effect. Generally, the electrode array includes a non-conductive
carrier on which typically two or more electrodes are disposed.
Once the electrode array is implanted, current is flowed from at
least one of the electrodes, through the adjacent tissue, to at
least one of the other electrodes. The current flow through the
tissue stimulates the tissue to accomplish a desired therapeutic
result. For example, an electrode array positioned adjacent the
heart may flow currents to stimulate the appropriate contraction
and expansion of the heart muscles. There is an increasing interest
in implanting electrode arrays adjacent neurological tissue so that
the resultant current flow stimulates a desired neurological
effect. Thus, the current flowed between the electrodes of such an
array can be used to reduce the sensation of chronic pain perceived
by the brain. Alternatively, the current flow stimulates a feeling
of satiation as part of an appetite suppression/weight management
therapy. In another application, the current is flowed to muscles
associated with the bladder or the anal sphincter to assist in
control of incontinence.
[0004] Implicit for the above therapies to work, the current must
flow through very small sections of tissue through which such flow
will cause the desired result. Likewise, the current should not be
flowed through adjacent tissue if such flow would result in
undesirable side effects. Even if the flow of the current through
some tissue does not result in undesirable side effects, such
current flow is a needless sink of power. Accordingly, for an
implanted electrode array to provide the greatest benefit, it is
necessary that the electrodes be positioned as closely as possible
adjacent the tissue through which the current is to be flowed.
[0005] One means to accomplish the goal of precisely targeted
current flow is to provide the electrode array with a matrix, rows
and columns, of spaced apart electrodes. The array is implanted
over a relatively large section of tissue that includes the tissue
through which the current flow will offer the desired therapeutic
effect. Once the array is implanted, the current is flowed between
different combinations of electrodes. As a result of the current
flowing between different electrodes, the current flows through
different sections of the underlying tissue. The response of the
patient to the current flow through the different sections of
tissue is monitored to determine through which section of tissue
the current flow has the most beneficial effects and/or most
tolerable side effects. This type of electrode assembly thus
provides relatively precise targeting of current flow through
tissue so that such flow has the greatest potential for positive
results and minimal adverse effects.
[0006] For the above electrode array assembly to potentially be of
benefit, the assembly should occupy a relatively large surface
area. The above type of assembly are for example known to have a
width of 0.25 cm or more and a length of 0.5 cm or larger. To
position this type of electrode array assembly against target
tissue, it is suggested that a surgical procedure is required in
which an incision is cut in the patient to access the surface of
the tissue over which the assembly is to be positioned. The
assembly is then fitted over the tissue and the incision cut in the
overlying tissue is closed.
[0007] An electrode array assembly designed to eliminate having to
expose a patient to the above surgical trauma is disclosed by the
Applicants' Patent Application FOLDABLE, IMPLANTABLE ELECTRODE
ARRAY ASSEMBLY AND TOOL FOR IMPLANTING SAME, U.S. Pat. App. No.
61/034,367, filed 6 Mar. 2008, the contents of which are published
in PCT Pat. App. No. PCT/US2009/033769, PCT. Pub. No. ______ and
U.S. Pat. Pub. No. ______, and which is explicitly incorporated
herein by reference. The electrode array assembly of this invention
includes a carrier formed from superelastic material. A
superelastic material is a material that though rigid, will, after
being subjected to relatively high degree of bending or folding,
substantially return to its initial shape. The superelastic
material forming the carrier of the disclosed electrode assembly is
a nickel titanium alloy. Another feature of using the nickel
titanium alloy as the carrier is that this material is plastically
deformable, the carrier can be formed into a particular shape
without fracturing. Other components of the electrode array
assembly, the electrodes and the conductors that extend to the
electrodes, are disposed on the carrier.
[0008] Since the carrier is formed from a shape memory material,
the electrode array assembly can be folded or rolled into a
delivery cannula that has a width appreciably less than the width
of the assembly itself. Thus, an electrode assembly having a width
of 12 mm can be rolled or folded to fit in a delivery cannula
having a major diameter of 6 mm or smaller. This means that one can
implant the electrode assembly of this invention, by forming a
relatively small portal in the body that is directed to the site at
which the assembly is to be implanted. The delivery cannula, with
the electrode assembly contained therein, is inserted in the portal
and directed to the target site. The electrode assembly is then
discharged, deployed, from the cannula. Upon deployment, owing to
the presence of the superelastic carrier, the electrode assembly,
when disposed over the tissue, unfolds or unrolls to its initial
shape. Current is then flowed between different sets of electrodes
to determine which current flow has the most beneficial and/or less
adverse effect.
[0009] An advantage of the above electrode array assembly is that
it only requires the formation of a relatively small opening in the
patient to be properly positioned. The trauma and side effects
associated with surgical procedures in which larger openings are
created are eliminated.
[0010] For the above electrode array assembly to have appreciable
therapeutic utility, it is desirable to have means that makes it
possible to efficiently fabricate the assembly.
SUMMARY OF THE INVENTION
[0011] This invention relates generally to a method for assembling
an electrode array assembly that includes a carrier formed from
superelastic material. The method of this invention facilitates the
simultaneous, batch fabrication of plural electrode array
assemblies.
[0012] One aspect of the method of this invention is that the
conductive components forming an electrode array assembly are
fabricated over or otherwise bonded to a layer of material that
eventually functions as the superelastic carrier.
[0013] Another aspect of the method of this invention is that,
during the fabrication process, a backing is disposed below the
superelastic carrier. The backing provides rigidity to the carrier
so the carrier can withstand the forces of the processes in which
the conductive components are fabricated over or otherwise bonded
to the carrier.
[0014] Another aspect of the method of this invention is that the
method makes it possible to in a single set of fabrication
sub-steps, simultaneously assembly plural electrode array
assemblies.
[0015] A further aspect of this invention is the method makes it
possible to, using two-dimensional fabrication techniques, form an
electrode array assembly on a carrier that already has features in
three dimensions; length, width and height in/out of a reference
plane.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention is pointed out with particularity in the
claims. The above and further features and advantages of this
invention are understood by reference to the following Detailed
Description in conjunction with the accompanying drawings in
which:
[0017] FIG. 1 is a plan view of an electrode assembly constructed
in accordance with this invention wherein certain normally covered
components are shown exposed for purposes of illustration;
[0018] FIG. 1A is a front view of an electrode assembly of this
invention depicting how the assembly may have an arcuate
profile;
[0019] FIG. 2 is a cross sectional view of a single electrode of
the electrode assembly of FIG. 1;
[0020] FIG. 3 is a plan view of a sheet, a coupon, of superelastic
material on which plural carriers are formed;
[0021] FIG. 4A is a plan view of an enlarged section of the coupon
of superelastic material showing how the proximal front end of the
carrier is retained to the sheet;
[0022] FIG. 4B is a plan view of an enlarged sections of the sheet
of superelastic material showing how the distal rear end of the
carrier is retained to the coupon;
[0023] FIG. 4C is a plan view of a single carrier wherein the slits
that define the waste slugs that are eventually separated from the
carrier are shown;
[0024] FIG. 5 is a perspective view illustrating how, while
retained to the sheet of superelastic material, the individual
carriers are curved;
[0025] FIG. 5A is a perspective view of an individual carrier of
FIG. 5;
[0026] FIG. 6 is a cross sectional view of a section of the sheet
of superelastic material showing the coating on the sheet and one
of the carriers on the sheet;
[0027] FIG. 7 is a cross sectional view of the section of the sheet
of superelastic material bound to a support wafer;
[0028] FIG. 8 is a cross sectional view of the section of the sheet
of superelastic material with a layer of parylene over the formally
exposed surface of the sheet;
[0029] FIGS. 9, 10, 11 and 12 are cross sectional views of the
section of the sheet of superelastic material showing the
fabrication of the components forming the electrode array assembly
on one of the carriers of the sheet;
[0030] FIG. 13 is a cross sectional view of the essentially
fabricated electrode array assembly showing one of the
sheet-to-carrier retaining tabs immediately prior to the removal of
the tab;
[0031] FIG. 14 is a cross sectional view of the section of the
sheet of superelastic material of FIG. 13 illustrating the
separation between the electrode array assembly and the sheet after
removal of the tab and underlying parylene-C layer;
[0032] FIG. 15 is a cross sectional view of the section of the
electrode array assembly and surrounding sheet of FIG. 14
illustrating lift off of the assembly after removal of the
sacrificial layer;
[0033] FIGS. 16A and 16B are, respectively, plan and cross
sectional views of a portion of the coupon illustrating an initial
step in the formation of the coupon-to-carrier tabs and the
carrier-to-slug tabs formed on the coupon;
[0034] FIGS. 17A and 17B are, respectively, plan and cross
sectional views of a portion of the coupon illustrating one of the
coupon-to-carrier tabs after the formation of the carrier from a
section of the coupon;
[0035] FIG. 18 is a cross sectional view illustrating the perimeter
of the electrode array assembly of this invention after the layers
of insulating material and the tab are separated from the
surrounding coupon; and
[0036] FIGS. 19A and 19B are cross sectional views illustrating how
the electrode and conductor intermediate layers can are fabricated
so as to have different thicknesses.
DETAILED DESCRIPTION
I. Electrode Array Assembly
[0037] FIG. 1 is a plan view of an electrode array assembly 40
fabricated according to the method of this invention. Assembly 40
includes a head 42. Spaced from the head 42 is a foot 46. A number
of parallel, spaced apart legs 44a-e extend rearward from the
distal end of the head 42 to connect the foot 46 to the head. A
number of columns of spaced-apart electrodes 48 are disposed on
assembly head 42. Each column of electrodes includes a number of
longitudinally spaced apart electrodes 48. For ease of
illustration, in FIG. 1, only the first and fifth columns of
electrodes 48 are shown; only two electrodes in each column are
identified. Each electrode 48 in the first four (4) columns of
electrodes, when viewed from the left side to the right side of the
drawing, is disposed on a tab 50 formed in the head 42. Each tab 50
is defined by a three sided-slot 52 that extends through the head
42. In the illustrated version of the invention, an auxiliary tab
54 is formed in the head forward of the proximal most electrode 48
in the first, second and fourth columns of electrodes. Each
auxiliary tab 54 is defined by a slot 56 that extends through
assembly head 42. Supplementary slots 58 extend from the first
column auxiliary tab 54 and the forward most tab 52 of the fourth
column of tabs 52.
[0038] A conductor 62 extends to each electrode 48. (For ease of
illustration, only two conductors 62 are shown.) Each conductor 62
extends from the assembly head, over one of the legs 44a, 44b, 44c,
44d or 44e to assembly foot 46.
[0039] Foot 46 is formed to define a center opening 64. Center
opening 46 is dimensioned to receive a cable assembly not
illustrated and not part of this invention. The individual assembly
conductors 62 are connected to conductors internal to the cable.
The cable conductors supply current that is applied through
conductors 62 to the electrodes 48 to cause current flow between
the electrodes. U.S. Pat. App. No. 60/871,675 filed 22 Dec. 2006,
refilled as PCT App. No. PCT/US2007/088580 and U.S. Pat. App. No.
______ and published, respectively, as PCT Pub. No. WO 2008/080073
A2 and U.S. Pat. Pub. No. ______, the contents of which are each
hereby explicitly incorporated by reference, describes an
alternative means to provide current to the electrodes 48. The
assembly of this document discloses how components external to the
electrode array assembly 40 supply both power for sourcing current
through the electrodes 48 and instructions that indicate between
which electrodes the current should be flowed. Signals that contain
both the power and instructions are supplied to components mounted
to the assembly foot 46, (components not illustrated and not part
of this invention). In these constructions of the electrode array
assembly 40, conductors 62 extend to these components. Again, it
should be appreciated that the methods by which current is sourced
to the electrodes 48 and the structural features on the assembly 40
that facilitate such current sourcing are not relevant to this
invention.
[0040] As seen best in FIG. 2, assembly 40 includes a carrier 74
formed from material that is plastically deformable and, in many
versions of the invention, superelastic. For this assembly, the
carrier is considered "plastically deformable" if the shape of the
carrier can be altered by stressing, heat treatment or by chemical
or metallurgical transformation to take on a formed shape without
fracturing. The carrier is considered to be "superelastic" if,
after being shaped, the carrier can be bent, folded or otherwise
deflected and, upon being released from the stress of the forces
applying this deflection, return to its formed shape. Carrier 74,
as is all the components forming assembly 40, is formed from
material that is biocompatible, that is material that, when
implanted in living tissue, typically does not become a source of
infection. In some versions of the invention carrier 74 is a layer
of nitinol, a nickel titanium alloy. Carrier 74 has a thickness of
50 microns. Disposed below and around the sides of carrier 74 is a
lower insulating layer 72 formed from electrically insulating
material. In one version of the invention, insulating layer 72 is a
polyxylene polymer film, such as parylene-C. Lower insulating layer
72 has a thickness of at least 1 micron. An upper insulating layer
76 is disposed on top of the carrier 74. Upper insulating layer 76
can be formed from the same material from which lower insulating
layer 72 is formed. Upper insulating layer 76 has a thickness of at
least 1 micron.
[0041] Electrodes 48 and conductors 62 are formed above the upper
insulating layer 76. Each electrode 48 can have surface area as
small as 50 microns.sup.2 and, in some versions of the invention,
as small as 10 microns.sup.2. The minimal on-carrier separation
between each electrode can be as small as 15 microns and in some
versions of the invention, as small a distance as 5 microns.
[0042] Each electrode 48 includes a conductive base pad 80 from
which a number of conductive buttons 90 project. Each base pad 80
includes a bottom layer 82, an intermediate layer 84 and a top
layer 86. The base pad bottom and top layers 82 and 86,
respectively, are formed from chrome. In some versions of the
invention, electrode base pad bottom layer 82 and top layer 86 each
have a thickness of at least 500 Angstroms. Bottom layer 82 and top
layer 86 are provided because chrome bonds to both polyxylene
polymer and gold. Gold is the material from which base pad
intermediate layer 84 is formed. Often, intermediate layer 84 has a
thickness of 5 microns or less. Intermediate layer 84, as discussed
below, is also integral with the conductors 62. The various
sections of intermediate layer 84 functions as the low resistance
components of the electrodes 48 and the conductors 62.
[0043] Each conductive button 90 typically has a circular cross
sectional profile in the lateral plane. The diameter of the button
is typically is at least 10 microns. In many versions of the
invention, the cross-sectional diameter of the button 90 is between
and 20 and 30 microns. The minimal separation between adjacent
buttons 90 is 0.5 microns. In some versions of the invention, the
separation is 1.0 or more microns. In some versions of the
invention, each button 90 is formed from iridium and has a
thickness of at least 1000 Angstroms.
[0044] While not illustrated, it should be understood that each
conductor 62 is formed from a chrome bottom layer, a gold
intermediate layer and a chrome top layer. Conductors 62 are formed
simultaneously with the electrode base pads 80. Accordingly, the
conductor base layers are contiguous with and have the same
thickness as the electrode base pad base layers 82. The conductor
intermediate layers are contiguous with and have the same thickness
as the electrode base pad intermediate layers 84. The conductor top
layers are contiguous with and have the same thickness as the
electrode base pad top layers 86.
[0045] An electrically non-conductive shell 98 is disposed over
conductors 62 and the surfaces of the electrode base pads 80 that
are button-free. Portions of the shell 98 also extend around the
outer perimeters of the buttons 90. Openings 102 in the shell
expose faces of the buttons 90 located inward from the outer
perimeters of the buttons 90. Shell 98, like insulating layers 72
and 76, is formed from parylene-C polyxylene polymer film.
[0046] FIG. 2 is a cross sectional view along a line at least
parallel to the longitudinal axis of a single one of the electrodes
48. Accordingly, also seen FIG. 2 are the parallel side sections of
slot 52 that define the tab 50 (FIG. 1) on which the electrode 48
is seated.
[0047] As represented by FIG. 1A, in some versions of the
invention, at least head 42 of electrode array assembly 40 has an
arcuate lateral cross section profile. Electrodes 48 are disposed
on the inwardly curved surface of the carrier 74. In FIG. 1A, the
extent to which electrodes 48 extend outward of the adjacent
section of shell 98 is exaggerated for purposes of illustration.
This embodiment of the invention is provided when assembly 40 is to
be positioned over the surface of a section of tissue that itself
is curved. The curvature of assembly 40 thus minimizes the gap
between the electrodes 48 and the underlying tissue. The
minimization of this gap reduces the loss of current flow between
the electrodes and the tissue. For example, an electrode array
assembly intended to be placed over the spinal dura may be provided
with the above-described profile.
II. Method of Assembly
[0048] A process to manufacture electrode array assembly 40 using a
method of this invention can start with the formation of the
carrier. As seen by reference to FIG. 3 a sheet of the superelastic
material, referred to as a coupon 108, is shaped to define at least
one if not a plurality of carriers 74.
[0049] According to the present invention, using a photo etch
process or other processes, the coupon 108 is formed with a number
of through openings that define both the perimeters of the
individual carriers 74 and the features of each carrier. The
perimeter, the outer shape of an individual carrier 74, is defined
by a slot 120, seen in FIGS. 4A and 4B in the coupon 108. In this
step, slot 120 is not formed so as to completely sever the carrier
74 from the surrounding section of the coupon 108. Instead, slot
120 is broken into sections by a number of retaining tabs 122 that
extend between the carrier and the surrounding section of the
coupon (individual slot sections not identified). As seen by FIG.
4A, a first retaining tab 122 extends between the most proximal end
of the carrier head 112 and the rest of the coupon 108. From FIG.
4B, it can be seen that second and third spaced apart retaining
tabs 122 extend from the distal end of foot 116 to the adjacent
section of coupon 108.
[0050] In the process in which the perimeter of the carrier 74 is
formed, the carrier 74 is further formed in this process to define
a head 112, legs 114 and a foot 116. Carrier head 112, legs 114 and
foot 116 become portions of, respectively, the assembly head 42,
legs 44 and foot 46.
[0051] Formed simultaneously with slot 120 are slots 124, 126 and
128. Each one of the slots 124, 126 and 128 is formed wholly within
the portion of the coupon that is a carrier 74. Each slot 124
defines one of the tabs 130 or 132 on the carrier 74. As is
apparent in the following description, each carrier tab 130 becomes
one of the electrode assembly tabs 50. Each carrier tab 132 becomes
one of the electrode assembly auxiliary tabs 54. Slots 124 also
define the carrier portions of the assembly auxiliary slots 58.
[0052] Each slot 126 defines what becomes a void space between
adjacent legs 114 of the carrier. For purposes of later
identification, each section of superelastic material defined by
one of the slots 126 can be considered a slug 134. Slot 128 defines
what becomes a rectangular opening in the carrier foot 116. For
purposes of later identification, the rectangular section of
superelastic material defined by slot 128 is identified as slug
135. Slots 126 and 128, like slot 120 are not closed loop slots.
Instead, retaining tabs 127 break up each slot 126 and 128 into at
least two if not more sub slots (individual sub-slots not
identified).
[0053] Slots 120, 124, 126 and 128 are all typically no more than 4
microns wide. In some preferred methods of manufacture, slots 120,
124, 126 and 128 are 2 microns wide or smaller in width. The small
widths of slots 120, 124, 126, and 128 substantially eliminates the
instances of, during the subsequent fabrication processes, photo
resists and other coatings developing a relatively thick bead on
the surface of the carrier immediately behind the perimeter of the
slot. Such beads can develop as a result of surface tension if the
slots are relatively wide across.
[0054] Simultaneously with the forming of the individual carriers
74 and their feature-defining slots, alignment features are also
formed in the coupon 108. In FIG. 3, openings 129 in carrier free
sections of the coupon serve as the alignment features. This
shaping of coupon 108 may be performed simultaneously with the
process in which slots 120, 124, 126 and 128 are formed. In many
method of assembly of this invention, the alignment features are
slots formed in the sections of the coupon that do not function as
carriers. The alignment features facilitate the precise overly of
masks over the coupon 108 so that the subsequent layers of material
are accurately laid down.
[0055] Once slots 120, 124, 126 and 128 and the alignment features
are formed in coupon 108, the carriers 74 are shape formed so that
at least the heads 112 have the desired concavo-convex profile as
seen in FIG. 5. This step may be performed by pressing the
individual carriers between opposed dies that are appropriately
shaped. Once the carriers are so pressed, heat is applied to set
the carriers. The heat may be sourced from heaters in the
individual dies, external heaters or heat transferred from liquid
surrounding the dies. As a consequence of the simultaneous bending
and heating of the carriers, the carriers develop the desired
curved shape, undergo the desired plastic deformation. As seen in
the detailed view of FIG. 5A, as a consequence of this process, the
head 112 of each carrier 74 essentially has a pair of opposed wings
133. Each wing 133 extends along the side of the head 112 and
curves away from the plane of the coupon 108.
[0056] As represented by FIG. 6, the underside of coupon 108,
including the suspended carriers 74, is provided with a parylene-C
coating 136. Here the "underside" of the sheet is understood to be
the surface of sheet where in the carrier heads 112 have their
convex profile. The parylene-C is deposited on the coupon 108 and
carriers using a vapor deposition process. Parylene-C polymer is a
conformal coating. Therefore, the even thought the carrier heads
112 have curved wings 133, the parylene-C still covers these
portions of the carriers 74a. Parylene-C coating 136 has a
thickness of at least 1 micron.
[0057] During the above process step it should be appreciated that
slugs 134 and 135 remain attached to the individual carriers 74.
Accordingly, whenever a material such as parylene is coated over
the whole of a carrier 74, the material is also coated over slugs
134 and slug 135.
[0058] Coupon 108, with the carrier 74 still attached, is then
bonded to a silicon wafer 140. Prior to this step, it should be
appreciated that the silicon wafer 140 is prepared for this bonding
process. This preparation includes initially forming a layer of
silicon oxide 142 over silicon wafer 140. Silicon oxide layer 142
has a thickness of at least 1 micron. As will be apparent below,
silicon oxide layer 142 functions as a sacrificial layer for the
assembly process.
[0059] A layer 144 of parylene-C having a thickness of 1 micron is
then formed over silicon oxide layer 142. Parylene-C layer 144 is
formed over silicon oxide layer 142 by a vapor deposition
process.
[0060] Once the parylene-C layer 144 is formed over layer 142,
coupon 108 is ready for bonding to wafer 140. Coupon 108, including
carriers 74 and associated slugs 134 and 135, is bonded to the
wafer 140 so the parylene-C coating 136 of coupon 108 is bonded to
the parylene-C layer 144 of wafer 140. This bonding process is
performed by wafer level parylene-to-parylene bonding or microwave
bonding. As a consequence of this bonding process, the wings 133 of
the individual carriers 74 flatten out so as return to the plane of
coupon 108, FIG. 7. FIG. 7, and subsequent FIGS. 8-12, are lateral
cross sectional views across a single carrier and the surrounding
sections of the coupon 108 adjacent the carrier. The two outer most
slots represent the gap between the electrode array assembly under
fabrication and the adjacent section of the coupon 108. The four
slots between the outermost slots are void spaces that eventually
become portions of the tab-defining slots 52.
[0061] In FIG. 7, dashed line 143 represents the separation between
the parylene-C coating 136 of the carrier 74 and the parylene-C
layer of 144 of the silicon wafer 108. These two layers 136 and 144
of parylene-C are eventually become the lower insulating layer 72
of the electrode array assembly 40. Accordingly, in subsequent
FIGS. 8-15, these layers of a common material, the parylene-C, are
shown as a single layer and are identified as insulating layer
72.
[0062] As a consequence of the bonding of coupon 108 and the
carriers 74 formed thereon to the silicon wafer 140, the wafer
functions as a substrate. This substrate supports both the carriers
74 and the subsequent materials bonded to the carrier during the
remainder of the electrode array assembly fabrication process.
[0063] Fabrication of electrode array assemblies 40 continues with
the deposition of a parylene-C layer 146 over the exposed upper
surface of coupon 108 and carriers 74, illustrated by FIG. 8.
Parylene-C layer 146 has a thickness of at least 1 micron and is
deposited over the coupon 108, including carriers 74 using a vapor
deposition process. While not illustrated, is should be understood
that the parylene-C forming layer 146 also coats the side surfaces
of the carriers 74 around slots 120, 124, 126 and 128.
[0064] Once layer 146 is formed over the carriers 74, semiconductor
and microcomponent fabrication processes are then employed to
fabricate the electrodes 50, the conductors 62 and shell over the
carriers 74a. Each step of the process is conducted simultaneously
on each carrier 74 integral with coupon 108. In brief, layers of
chrome and gold are applied over and selectively removed from the
carriers to form the conductors 62 and electrode base pads 80 as
seen in FIG. 9. The incorporated-by-reference U.S. Provisional Pat.
App. No. 61/034,367 and PCT Pat. App. No. PCT/US2009/033769 provide
more detailed explanations of the process steps by which these
components of the electrode array assembly 40 are formed. Thus, it
should be understood that after the chrome of the bottom layer 82
is applied, a small seed layer of gold, layer 83, seen only in
FIGS. 19A and 19B, is applied prior to the step of plating
intermediate layer 84.
[0065] Fabrication of the one or more electrode array assemblies 40
continues with the fabrication of the iridium buttons 90 over the
electrode base pads 80. This process begins with the formation of a
mask 150 over each partially fabricated assembly, FIG. 10. Mask 150
has a thickness greater than that of the conductive buttons 90.
While mask 150 covers most of each assembly, there are openings 152
over the surfaces of the electrode base pad chrome top layers 86
where the buttons are to be formed.
[0066] Once mask 150 is formed, iridium is sputtered over the one
or more partially fabricated assemblies 40. A fraction of this
iridium enters the mask openings 152 to define the conductive
buttons 90. Not shown is the iridium that is deposited over the
mask. Once the iridium is deposited, mask 150 is removed. the
removal of masks 150 leaves only buttons 90 extend above the chrome
top layers 90 of the electrode base pads 90, FIG. 11. For ease of
illustration in FIGS. 10-12, only three buttons 90 are shown with
each electrode. In practice, each row of buttons typically contains
appreciably more buttons 90.
[0067] During the above fabrication steps of this invention,
iridium is not deposited on the top layers of the conductors
62.
[0068] Once electrode buttons 90 are formed, a layer 158 of
parylene-C that becomes shell 98 is deposited over the whole of the
partially fabricated assembly, FIG. 12. More particularly, the
parylene-C layer 158 is deposited over the exposed surfaces of
parylene-C layer 146 and the conductors 68. The parylene-C of layer
158 has a thickness slightly greater than that of the conductive
buttons 90 Accordingly, while not illustrated, it should be
understood that the parylene-C of layer 158 is initially applied to
completely cover the conductive buttons 90. Once layer 158 is
applied, openings 102 are formed in the layer to expose the outer
faces of the conductive buttons 90. More particularly, the
parylene-C of layer 158 is removed so that, post removal, at least
a portion of the parylene-C, as seen in FIG. 2, extends around the
outer parameters of the faces of the conductive buttons 90. Thus,
layer 158 becomes the outer shell 98. Accordingly, in FIGS. 13-15
this layer of parylene is relabeled as shell 98 in FIGS. 13-15.
[0069] Shell 98 thus does more than function as the non-conductive
outer shell of the electrode assembly 40. In the process of
removing parylene-C layer 158 to form the shell, openings 102 are
formed so as to not wholly expose the faces of the underlying
buttons. Instead, openings 102 have a diameter less than that of
the conductive buttons. Consequently, as mentioned above, shell 98
projects over the outer perimeter of the buttons 90. Shell 98 thus
also holds the conductive buttons 90 to the electrode base pads 80
with which the buttons are associated.
[0070] The formation of shell 98 completes the component-addition
processes of the fabrication of electrode array assembly 40.
Assembly 40, more particularly, the assembly carrier 74, is then
removed from the coupon 108 and the underlying silicon wafer
140.
[0071] The removal process starts with the removal of the
parylene-C from over the retaining tabs 122 and 127, step not
shown. Consequently, above each opening 120 there is a parylene-C
free void space. This void space, represented by identification
number 162 in FIG. 13 is shown above one of the retaining tabs 122
that extend across each opening. In FIG. 13, the retaining tab 122
is the section of the superelastic material between the two dashed
lines. The assembly to the left of the tab 122 is the essentially
fabricated electrode array assembly 40. The assembly to the right
of the tab includes the portion of the coupon 108 and surrounding
parylene-C that is left behind after the lift off process. Since
FIGS. 13-15 only represent the section of the assembly adjacent the
end of the foot 46, not seen in these Figures are the layers of
material forming the electrodes or conductors. The cross sectional
view of a retaining tab 127 and the associated slug 134 or 135 is
essentially identical to that of the depiction of tab 122 in FIG.
13. Accordingly, as the removal processes are identical, the
removal of the tabs 127 is not illustrated. Below each retaining
tab 122 and 127 a section of parylene-C is present as a result of
the bonding of the parylene-C layers 136 and 144 forming lower
insulating layer 72.
[0072] The coupon and carrier forming superelastic forming tabs 122
and 127 is removed by a chemical etching process or a mechanical
process. Once tabs 122 and 127 are removed, the parylene below
where the tabs were present is removed. As a consequence of these
processes, the assembly appears as in FIG. 14. Opening 162, which
is part of a slot 120 of FIGS. 4A and 4B now forms a continuous
separation between the electrode array assembly and the surrounding
section of the parylene-coated coupon 108. While not shown, it
should be appreciated that as a result of these material removal
processes, each of slots 126 and 128 also is transformed into a
closed loop slot. As a consequence of the closing of each of the
slots 126 and 128 slugs 134 and 135 are separated from the
fabricated electrode array 40 assembly that surrounds the slugs. In
addition to the slugs 134 and 135 of superelastic material
separating from the associated electrode array assembly in these
processes, the material deposited above each slug is also separated
from the assembly 40. At this stage of the process, the electrode
array assembly 40 and the material laden slugs within the assembly
are still bonded to the silicon wafer 140.
[0073] Final separation of the assembly 40 from the workpiece is
performed by removal of sacrificial layer 142. This removal process
is not selective so that removal of layer 142 also results in the
separation of coupon 108 from wafer 140 as seen in FIG. 15. As a
consequence of the removal of sacrificial layer 142, the electrode
array assembly 40 is wholly separated from both coupon 108 and
wafer 140. Assembly 40 is then lifted off from the wafer 140 and
away from sheet. Since the material-coated slugs 134 and 135 were
previously separated from the assembly 40, the slugs are left
behind on the wafer to define the void spaces between the assembly
legs 44 and center opening 64 of assembly foot 46.
[0074] As a consequence of the electrode array assembly 40 being
lifted off wafer 140, the assembly head 42 develops the curved
profile of carrier head 112 as represented by FIG. 1A. This
curvature is not seen in FIG. 15 because the cross sectional view
this Figure is a longitudinal slice view; the curvature is along
the lateral axis of the assembly 40. The electrodes 48 and
conductors 60 are disposed on the inwardly curved face of the
assembly 40.
[0075] Once electrode array assembly 40 is lifted off wafer 140,
the assembly is ready for further processing the specifics of which
are not relevant to this invention. This further processing can
involve folding the electrode array assembly along a number of fold
lines parallel to the longitudinal axis of the assembly. The folded
assembly is then placed into a delivery cannula. When the assembly
is deployed from the delivery cannula against a section of tissue,
owing to carrier 74 being formed from super-elastic material, the
assembly unfolds to the curved shape. This facilitates surface
contact between the conductive buttons 90 of the electrodes 48 and
the underlying tissue.
[0076] An advantage of assembling electrode array assembly 40
according to the method of this invention is that the conductive
elements of the assembly are formed directly on the superelastic
carrier 74. This eliminates the process steps associated with
bonding a first subassembly that includes the electrodes and
conductors to a second subassembly that includes the super elastic
carrier.
[0077] Another feature of this invention is that silicon wafer 140
functions as a structural backing, a substrate, for the assembly 40
while the assembly is being fabricated. The silicon wafer 140,
owing to its mechanical strength, withstands the pressures of the
process steps associated with the fabrication of the various
components of the assembly on the carrier 74. Since the wafer 140
absorbs these stresses without bending or breaking, the need to
provide the carrier with sufficient strength so it can withstand
these stresses is eliminated. Avoiding having to provide a carrier
that can withstand these stresses likewise avoids the increased
carrier thickness reduced carrier elasticity that results from
having to design the carrier to resist these forces.
[0078] Another benefit of the method of this invention is that
plural carriers 74 can be formed on a single coupon 108 of super
elastic material. While the carriers 74 remain attached to the
coupon 108, the remaining components forming each electrode array
assembly 40 can be fabricated over the individual carriers. Thus,
the method of this invention, in addition to simplifying the
process steps associated with the assembly of a single electrode
array assembly 40, also makes it possible to batch fabricate plural
assemblies 40.
III. Alternative Versions
[0079] It should be appreciated that the foregoing is direct to one
specific method of assembly of this invention. Alternative versions
of the invention are possible.
[0080] Other methods of this invention may have less than, more
than or different process steps than what has been disclosed. For
example, in some versions of the invention, the formation of the
carriers 74 starts with the formation of the tabs that hold the
carriers to the coupons and that hold the slugs 134 and 135 to the
carriers. This is seen in FIGS. 16A and 16B. As illustrated in
these Figures, the portions of the coupon 108 are partially etched
(not completely etched through) to define notches 172 (one shown).
Each notch 172 has a depth that is between 25 and 75% of the total
thickness of the coupon 108. Often, the notches 172 have a depth
between 40 and 60% of the total thickness of the coupon 108.
Notches 172 are formed in the coupon over the sections of the
coupon that become the tabs.
[0081] Once notches 172 are formed, coupon 108 is shaped to form
the slots 120, 124, 126 and 128 that define the inner and outer
perimeters of each carrier 74. This etching removes material
through the whole of the thickness of the coupon 108. This etching
step is specifically not performed on the sections of the coupon
108 that define the bases of the notches 172. Consequently, the
coupon 108 develops the shape as depicted in FIGS. 17A and 17B. In
FIG. 17A the sections of a slot 120 that defines the carrier head
is shown. For ease of illustration, only a few of the slots 124 in
this portion of the head are shown. As seen in FIG. 17B, as a
consequence of these two carrier material removal etches,
coupon-to-carrier tabs and carrier-to-slug tabs are defined, a
single coupon-to-carrier tab 122A being illustrated. Given the
previous formation of notches 172 each, these tabs have a thickness
between 25 to 75% of the thickness of the coupon 108. Each of these
tabs has a face that is coplanar with one of the faces of the
coupon 108. If the carriers are plastically deformed, bent, the
tabs are located so the tab faces coplanar with the coupon 108 are
coplanar with the coupon face that is concave face with regard to
the bend of the carrier away from the coupon. With respect to FIG.
5A, this mean that the tabs have faces that are coplanar with the
faces of the carrier 74 and coupon 108 opposite the face seen in
this Figure.
[0082] An advantage of employing reduced thickness tabs to hold the
carriers 74 to coupons 108 and the slugs 134 and 135 to the
carriers 74 is seen by reference to FIG. 18. Here, the results of
the etching process used to removing a tab 122A from the coupon 108
are shown. In most etching processes, the removal, the etching away
of the material forming the tab is not simply along a line
perpendicular to the mask opening through which the etchant is
applied. Instead, the etching forms a boundary surface of this
material that flares inward from the perimeter of the mask opening.
As a consequence of the boundary forming along this non-linear
path, the remaining material forms an outwardly projecting crest
176. In the method of the invention, the thickness of the tabs that
need to be removed is less than the thickness of the coupon 108.
Consequently, both the extent the distance to which the crest 176
extends outwardly and the acuteness of the angle of the crest are
reduced relative to that of a crest formed as a result of the
etching away a tab having a thickness equal to that of the coupon
108. The minimization of both the extent the crest 176 extends
beyond the rest of the assembly 40 and the angle of this crest
reduces the likelihood that, when the assembly is implanted, the
crest inadvertently injures adjacent tissue.
[0083] Likewise, in some versions of the invention, two or more
layers of the insulating material and conductive material used to
form the electrodes and conductors of each array 40 may initially
formed as a subassembly that is not on the coupon 108. Once this
subassembly is formed, it is bonded to the coupon 108.
[0084] There is no requirement that, in all versions of the
invention, all described process steps be executed or that the
process steps be executed in the order described. For example, in
some methods of this invention, prior to the formation of the one
or more carriers on the coupon, the materials forming the array
electrodes and conductors are bonded to sections of the coupon 108
that later become the one or more carriers 74. Once these materials
are applied to the coupon, the sections of the coupons over which
these materials are applied are first severed from and then removed
from the remainder of the coupon. Each of these removed sections of
the coupon 108 becomes a carrier 74 for one of the electrode arrays
40. Alternatively, after some of the layers of the material forming
the array electrodes 48, conductors 62 and insulating layers may
first be disposed on one or more sections of the coupon 108, the
coupon is then shaped to form the one or more carriers 74. After
these process steps are completed, additional materials are
disposed on the carriers 74 to complete the process of forming the
individual electrode arrays 40.
[0085] Also, depending on the materials from which the electrode
arrays 40 are formed, the final step in the removal of the assembly
from the workpiece to which the assembly is held during the
fabrication may be the removal of the retaining tabs that hold the
assembly to the sheet of plastically deformable material.
[0086] Alternatively, depending on the nature of the plastically
deformable material, once the electrode assembly is fabricated, the
whole of the surrounding sections of plastically deformable
material are removed from the support substrate. Once this step is
performed, the sacrificial layer is removed. An advantage of this
version of the invention is that it reduces the extent to which a
precise lift off process is required to remove the electrode array
assembly from the support substrate.
[0087] Similarly, there is no requirement that in all versions of
the invention, the carrier 74 be curved or that the carrier be
formed from a plastically deformable material. In alternative
applications of this invention, it may be desirable to fabricate
the electrode array assembly on a carrier that has a high degree of
flexibility and resists tearing, for example a polyamide film. This
is so the assembly could be disposed over tissue that has a
relatively bumpy or irregular surface pattern. Using the method of
this invention, the carrier can be bonded to the support wafer or
other rigid substrate prior to the formation of the conductive
components on top of the carrier. Once the assembly is fabricated,
the assembly is removed from the support wafer. In these versions
of the method of the invention, the only component attached to the
substrate is the flexible carrier without any surrounding
coupon.
[0088] Likewise, materials other than the described materials can
function as the base materials from which the components of each
electrode array assembly 40 are fabricated. Thus, the carrier 74
may be formed out of a superelastic material other than a nickel
titanium alloy. Again, some versions of the invention, this
material may need only be material that can be flexible or
plastically deformed and not superelastic. In some versions of the
invention, the material from which the carrier may be formed may be
non-conductive. If such a material is employed as the carrier, it
could eliminate the need to provide a layer of non-conductive
material between the carrier and the conductive components. Thus,
it should be understood, less or more layers of material that what
has been described with respect to the exemplary version of the
invention may be needed to fabricate an electrode array assembly 40
in other versions of this invention. Materials other than chrome
may be used as adhesion layers around the gold layers. For example,
in some versions of the invention the adhesion layer may be formed
from titanium.
[0089] Likewise, the actual process steps used to apply the
material that forms the layers of insulating and conductive
materials on the carriers 74 may vary with the nature of the
materials. In some versions of the invention, it may be desirable
to prepare the surface of the carrier to ensure and/or improve the
adhesion of insulating material to the carrier. For example, it may
be desirable to deposit an oxide layer on the surface of a Nitinol
carrier/coupon to ensure the adhesion of the parylene to this
structure.
[0090] In some versions of the invention, each electrode conductive
button may include a pedestal formed from a first material and a
head, that forms the exposed face of the button, formed from a
second material. Thus, in some versions of the invention, the
pedestal is formed from titanium. The head can be formed from
iridium. Alternatively, in some versions of the invention, instead
of having individual conductive buttons, each electrode may have a
sheet of material the exposed face of which functions as the
interface surface across which current is flowed to/from the
adjacent tissue. This sheet can, for example be a layer of iridium,
iridium oxide, platinum or platinum oxide. In some embodiments of
this version of the invention, the shell is formed with openings
through which individual sections of this sheet are exposed.
Alternatively, in some embodiments of this version of this
invention, substantially 30% or more or even 50% or more of the
whole of this material is exposed as a continuous surface to form
the exposed face of the electrode. Again, it may be appropriate to
have a layer of intermediate material between the conductive base
of the electrode and the material forming the exposed head of the
electrode.
[0091] In some versions of this invention, the conductive buttons
are formed by a combination of these processes. Specifically,
conductive posts formed from the one, two or even more layers of
material are formed on base pads of the electrodes. These posts may
have cross sectional shapes that are circular or polygonal in
shape. Insulating material is disposed over these posts. Portions
of the exposed faces of these posts are exposed to form the
conductive surfaces of the electrode. The area of each of these
exposed faces, conductive surfaces, is typically less than the
cross sectional area of the post with which the face is
integral.
[0092] It should likewise be appreciated that this invention is not
directed to electrode array assemblies having the above-described
shape. For example, it may not be necessary to form the assembly
and underlying carrier 74 with spaced-apart legs that extend from
the section on which the electrodes are formed. Similarly, it may
not be necessary to provide an opening in the assembly or carrier
for receiving the cable that includes the current-supplying
conductors that are connected to the individual electrodes.
Likewise in not all versions of the invention are the electrodes
formed on tabs that are separate from the surrounding sections of
the carrier.
[0093] Similarly, there is no requirement that, in all versions of
the invention, a silicon wafer serve as the support substrate. In
some versions of the invention a rigid polymer or other plastic may
serve this function. In this version and other versions of the
invention, an adhesive may be used to releasably bond the
insulating layer to the support substrate. Then once the electrode
array assembly/assemblies is/are fabricated, the adhesive bond is
broken either chemically or mechanically to remove the
assembly/assemblies from the support substrate.
[0094] Also, it should be appreciated that, unless specifically set
forth in the claims, the dimensions of the various components and
material layers are for purposes of example only and are not
limiting. Thus, in some versions of the invention, the gold
intermediate layer 84 of the electrode bond pad may have a
thickness of 10 microns or more and some versions of the invention
a thickness of 20 microns or more. A reason it may be desirable to
proved the electrodes with relatively thick intermediate layers is
to increase the radiopacity of the assembly 40
[0095] In these and other versions of the invention, the thickness
of the gold intermediate layers of the conductors 62 is less than
that of the electrodes 48. One process for fabricating an electrode
array having these characteristics is described by initial
reference to FIG. 19A. This Figure represents that, in a first
plating process, spaced apart layers of gold, layers 84a, (one
shown) are applied to the assembly under formation. In FIG. 19A,
the layer 84a is shown deposited above the thin gold seed layer 83
that is disposed above the bottom (adhesion) layer 82. In this
step, the layers 84a are applied so as to not extend over the outer
perimeters of the seed layers 83 that define the outer perimeters
of the electrodes 48. Instead, layers 84a are applied so as to have
an outer surface that is recessed approximately 25 microns inwardly
from outer edges of the adjacent portions of the seed layers 83. In
this plating step, layers 84a are applied to have a thickness equal
to the difference between the desired thickness of the intermediate
layers for the electrodes 48 and the thickness of the intermediate
layers of the conductors 62.
[0096] In a second plating step, represented by FIG. 19B, gold is
applied over the seed layers 83 to form the intermediate layers 84b
of the conductors 62. In this plating step, the gold forming layers
84b is applied to further cover the outer surfaces of electrode
intermediate layers 84a (single layer 84b shown). Often the gold
forming the layers 84b is formed to have thickness of approximately
2 microns. The deposit of the second gold of the layers 84b over
the previously formed gold of layers 84a of the electrodes
effectively welds the two gold layers together. The gold forming
the intermediate layers, the combination of layers 84a and 84b, can
be considered welded to the gold of the conductors 62, the layers
84b. In this process, the gold of layer 84b is applied so that it
covers the exposed portions of the seed layers 83 that are between
the outer edges of the seed layer and the adjacent surfaces of the
gold layers 84a.
[0097] At the completion of the above process steps, the
gold-on-gold layers 84a and 84b can be considered to be the thick
intermediate conductive layers of the electrodes 48. The gold
layers 84b are the thin intermediate conductive layers of the
conductors 62.
[0098] Likewise, it should be understood electrode array assemblies
can be fabricated according to this invention that include just a
single column of electrodes. This type of assembly may have a nerve
cuff. It should therefore be appreciated that to fit around a
nerve, this assembly may have a width as small as 0.25 mm. This
invention can also be used to form an implantable electrode array
assembly that has a single electrode 48 with a single complementary
conductor 62.
[0099] Alternatively, instead of forming the assembly of this
invention so it curves around an axis parallel to the longitudinal
axis of the assembly, the curvature is around an axis parallel to
the lateral axis. Still in some versions of the invention, the axis
of curvature may be off angle to both the longitudinal and lateral
axes of the assembly. Likewise, in some versions of the invention,
depending of the application of the electrode array assembly, the
carrier may be formed to have plural sections with different
curvatures.
[0100] Therefore, it is an object of the appended claims to cover
all such variations and modifications that come within the true
spirit and scope of this invention.
* * * * *