U.S. patent application number 11/568584 was filed with the patent office on 2007-07-19 for electrowetting cell and method of manufacturing thereof.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS, N.V.. Invention is credited to Klaas Willem Kerkhof, Roel Rudolf Maria Tijburg, Piet Van Der Meer, Wilhelmus Antonius Martinus Van Der Zanden, Godefridus Johannes Verhoeckx, Johannus Wilhelmus Weekamp.
Application Number | 20070163875 11/568584 |
Document ID | / |
Family ID | 34966271 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163875 |
Kind Code |
A1 |
Van Der Meer; Piet ; et
al. |
July 19, 2007 |
Electrowetting cell and method of manufacturing thereof
Abstract
The electrowetting cell (15) comprises an outer wall (90) and an
inner wall (80), said outer wall (90) being provided with
extensions (85, 86) extending at opposing sides of the inner wall
(80). The cell (15) is further provided with a membrane (45) for
volume expansion and is sealed through an electroplated layer
(95).
Inventors: |
Van Der Meer; Piet;
(Eindhoven, NL) ; Tijburg; Roel Rudolf Maria;
(Eindhoven, NL) ; Kerkhof; Klaas Willem;
(Eindhoven, NL) ; Verhoeckx; Godefridus Johannes;
(Eindhoven, NL) ; Van Der Zanden; Wilhelmus Antonius
Martinus; (Eindhoven, NL) ; Weekamp; Johannus
Wilhelmus; (Eindhoven, NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS,
N.V.
GROENEWOUDSEWEG 1
EINDHOVEN
NL
5621 BA
|
Family ID: |
34966271 |
Appl. No.: |
11/568584 |
Filed: |
May 3, 2005 |
PCT Filed: |
May 3, 2005 |
PCT NO: |
PCT/IB05/51435 |
371 Date: |
November 2, 2006 |
Current U.S.
Class: |
204/247.4 |
Current CPC
Class: |
G02B 26/005 20130101;
G02B 3/14 20130101 |
Class at
Publication: |
204/247.4 |
International
Class: |
C25C 7/00 20060101
C25C007/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 7, 2004 |
EP |
04101996.9 |
Nov 19, 2004 |
EP |
04105940.3 |
Mar 24, 2005 |
EP |
05102398.4 |
Claims
1. An electrowetting cell comprising a body section provided with a
substrate and at least one side wall, which substrate and side wall
jointly define a cavity containing electrowetting fluids and
further comprising at least one end section securable to the body
section, wherein the at least one side wall of the body section
comprises an inner wall and an outer wall, wherein a portion of
which end section is part of the inner wall, the outer wall
securing the end section and the body section by means of
extensions extending at a first and a second side of the outer cell
over opposed sides of the inner wall.
2. An electrowetting cell as claimed in claim 1, wherein the inner
wall comprises a portion of the substrate.
3. An electrowetting cell as claimed in claim 2, wherein the inner
wall further comprises a spacer of an electrically insulating
material between said portion of the substrate and said portion of
the end section.
4. An electrowetting cell as claimed in claim 1, wherein the
extension of the outer wall extending at the first side of the
inner wall is a clamping body that is attached to the outer
wall.
5. An electrowetting cell as claimed in claim 4, wherein the
clamping body is attached to the outer wall by means of a metal
layer that is grown on the extension and on the outer wall.
6. An electrowetting cell as claimed in claim 1, wherein a first
and a second electrode that are in contact with at least one of the
electrowetting fluids are defined at opposed sides of the cavity at
the substrate and at the end section.
7. An electrowetting cell as claimed in claim 6, wherein the
substrate is provided with an aperture, at an end of which said
electrode is present.
8. An electrowetting cell as claimed in claim 1, wherein the end
section comprises a flexible membrane allowing for volume expansion
of the closed cavity.
9. An electrowetting cell as claimed in claim 2, wherein the
extension at the second side of the inner wall is attached to the
substrate through a metal layer that is grown on both.
10. An electrowetting cell comprising a body section provided with
a substrate and at least one side wall, which substrate and side
wall jointly define a cavity containing electrowetting fluids and
further comprising at least one end section secured to the body
section, wherein the end section is attached to the body section
with a metal layer that is applied on a surface of both the end
section and the joint section.
11. An electrowetting cell as claimed in claim 1, comprising an
overlapping a part of the outer wall and in the inner wall or the
substrate or end section, wherein in the overlapping part at least
one of the adjacent surfaces comprises a sealant for sealing the
overlapping part under pressure.
12. An electrowetting cell as claimed in claim 11, wherein the
sealant comprises an organic composite, such as a composite
comprising a plastic or rubber.
13. An electrowetting cell as claimed in claim 11, wherein the
sealant has electrically conductive properties.
14. An electrowetting cell as claimed in claim 11, wherein the
sealant comprises a nickel-PTFE composite, such as niflon.
15. An electrowetting cell as claimed in claim 11, wherein in the
sealant is obliged by means of a depositing or growth process.
16. A method of manufacturing an electrowetting cell comprising a
body section provided with a substrate and a side wall having an
inner wall and an outer wall, said outer wall being provided with a
first and a second extension extending at opposed sides of the
inner wall, which substrate and side wall jointly define a cavity
containing a first and a second electrowetting fluid, which method
comprises the steps of: providing an outer wall and a substrate,
resulting in the cavity; filling the cavity with the first and the
second electrowetting fluid; providing the end section in the
cavity such that it is immersed in at least one of the fluids at a
desired distance to the substrate, portions of the substrate and
the end section and optionally an intermediate spacer forming the
inner wall; securing the end section to the body section in that
the first extension of the outer wall is positioned on top of the
end section.
17. A method as claimed in claim 16, wherein the extension is a
separate clamping body that is connected to the outer wall only
after having been positioned on the end section.
18. A method as claimed in claim 17, wherein the clamping body and
the outer wall are connected with a metal layer grown on their
surfaces.
19. An image capture device or an image sensor incorporating an
electrowetting cell as claimed in claim 1.
20. An optical scanning device comprising an electrowetting cell as
claimed in claim 1.
21. A display device incorporating an electrowetting cell as
claimed in claim 1.
Description
[0001] The invention relates to an electrowetting cell comprising a
body section provided with a substrate and at least one side wall,
which substrate and side wall jointly define a cavity containing
electrowetting fluids and further comprising at least one end
section secured to the body section.
[0002] The invention also relates to a method of manufacturing an
electrowetting cell comprising a body section provided with a
substrate and a side wall, which substrate and side wall jointly
define a cavity containing a first and a second electrowetting
fluid.
[0003] Electrowetting cells are cells in which light is refracted
by a meniscus between two immiscible fluids. One of the two fluids
is electrically insulating and the other is electrically
conducting. The shape of the meniscus is variable under the
influence of a voltage between two electrodes, one of which is
connected to the electrically conducting fluid and the other to a
surface of the body. Such cells are known and can for instance be
applied as lenses or displays. In the case of the application of a
cell, there is a light-path through the body section.
[0004] Such an electrowetting cell is for instance known from WO-A
03/069380. This patent application discloses a lens in which an
inner surface of the at least one side wall is covered by a
hydrophobic fluid contact layer. When no voltage is applied, the
wettability of the fluid contact layer with respect to the
electrically insulating fluid differs from the wettability of the
fluid contact layer with respect to the electrically conducting
fluid. Under influence of the applied voltage a change of the
wettability occurs. This leads to a change of a contact angle of
the meniscus at a line of contact between the fluid contact layer
and the fluids, whereby the shape of the meniscus is adjusted.
Hence, the shape of the meniscus is dependent on the applied
voltage.
[0005] As the electrowetting cell has optical properties and
includes fluids, it is of primary importance for an adequate
operation that a complete filling of the cell is achieved and that
no fluid can leak out of the cell after closing the cell. The cell
disclosed in the prior art does not give any solution how to
achieve such a complete filling and a prevention of fluid
leakage.
[0006] It is therefore a first object of the invention to provide
an electrowetting cell of the kind mentioned in the opening
paragraph, which can be completely filled and that is protected
against fluid leakage after closing of the cell.
[0007] It is a second object to provide a method of the kind
mentioned in the opening paragraph, with which the complete filling
can be achieved in an industrially viable manner.
[0008] The first object is achieved in that the at least one side
wall of the body section comprises an inner wall and an outer wall,
a portion of which end section is part of the inner wall, thus
securing the end section and the body section, and which outer wall
is provided with extensions extending at a first side and a second,
to the first opposed side of the inner wall.
[0009] The second object is achieved in a cell with an inner and an
outer wall, said outer wall having a first and second extension
extending at opposite sides of the inner wall, which method
comprises the steps of: [0010] providing an outer wall and a
substrate, resulting in the cavity; [0011] filling the cavity with
the first and the second electrowetting fluid; [0012] providing the
end section in the cavity such that it is immersed in at least one
of the fluids at a desired distance to the substrate, portions of
the substrate and the end section and optionally an intermediate
spacer forming the inner wall; and [0013] securing the end section
to the body section in that the first extension of the outer wall
is positioned on top of the end section.
[0014] The solution of the present invention is a cell with a
double wall. The outer wall provides stability and adequate
sealing, whereas the inner wall is built up from the constituent
elements that are assembled consecutively. Due to the consecutive
assembly and the double wall, the electrowetting fluids can be
provided before the end section. As a result, the end section can
be immersed in the fluid, practically the fluid with the lowest
density. Some fluid will flow to above the end section, but is
nevertheless kept within the outer wall. The immersion leads to the
required complete filling. An adequate sealing is then arrived at,
in that the outer wall is present at the opposite sides of the
inner wall. The outer wall of the package will then comprise only
two major materials, that can be attached to each other in a good
manner. A suitable combination is metal and glass.
[0015] The substrate could be part of the outer wall, but is
preferably a separate part of which an portion is part of the inner
wall. A spacer may be present between the portions of the substrate
and the end section. This is suitable but not necessary. The
advantage of such spacer is that it can be provided with any
desired surfacial coating, such as the above mentioned fluid
contact layer. Advantageously, the spacer is provided with a gap at
its bottom side. This allows a reduction of the height of the
cell.
[0016] Several embodiments can be envisaged for the first extension
that is provided on top of the end section. It may for instance be
a flexible extension of the outer wall. It may alternatively be a
metal layer that is positioned through a deposition technique,
probably with the help of a tool exerting pressure.
[0017] In a preferred embodiment, the first extension is a clamping
body that is assembled on top of the end section as a separate
component and--simultaneously or consecutively--connected to the
outer wall. This allows an efficient assembly method. Reliable
connection can be realized in both mechanical and chemical means,
such as locking features, additional clamps, adhesive layers and
sealing layers. Advantageously, use is made of a joining and
protective layer that is grown on said surfaces. The grown layer is
bonded to the surfaces chemically. It has the same coefficient of
thermal expansion and it is not sensitive for inelastic and
irreversible expansion under the influence of temperature. The
grown layer can be grown to a desired thickness, therewith
smoothening out gaps and height differences. Moreover, such a grown
layer is quite inert, particularly if provided with an oxide, that
may be a native oxide. Finally, the grown layer is not sensitive to
attack by any of the electrowetting fluids and does not have an
open or porous structure that would allow diffusion of molecules.
With such a sealing, particularly together with a substrate and end
section of glass, the resulting cell is closed hermetically.
[0018] A particularly suitable technique hereto is electroplating.
This technique has the advantage that it can be applied at bulk
level, by immersing the complete cell into a bath. Such an
immersion of the complete cell moreover has the advantage that the
grown layer extends on the complete outer wall and on both
extensions at either side of the inner wall. Herewith the clamping
character of the outer wall is strengthened.
[0019] In a further embodiment, a first and a second electrode that
are in contact with at least one of the electrowetting fluids are
defined at opposed sides of the cavity at the substrate and at the
end section. At least two electrodes are needed in the
electrowetting cell so as to apply the voltage needed to set the
shape of the meniscus. Such electrodes can be applied at the inner
walls, at opposite sides of the meniscus. In this embodiment
however, the electrodes are present at the end section and at the
substrate. This actually allows the use of a metal encapsulation
without an isolated connection for one of the electrodes.
[0020] Preferably, the substrate is provided with an aperture, at
an end of which said electrode is present. The electrode may be
present both at a surface of the substrate facing the meniscus and
at an opposite surface facing away from the meniscus. The latter
modification is most preferred, as there is no need to fill said
aperture with metal herein: the fluid fills the aperture. Moreover,
the manufacture of this electrode can be integrated with the
provision of metal strips that are used for the attachment of the
outer wall to the substrate, and hence provide an adequate
sealing.
[0021] It is preferred that the package is provided with a volume
expansion member. Such an expansion member is for instance known
from JP-A 2002/162506. This known package comprises a specific
chamber that is present adjacent to the substrate, and is separated
from the cell with a flexible cover. On increase of the pressure in
the cell, the flexible cover may be deformed or even be stretched
out, so as to form a curved surface extending into the said
chamber. The invention offers the possibility to locate such a
chamber between the inner wall and the outer wall.
[0022] A more preferable embodiment of the volume expansion member
is a flexible membrane that is part of the end section. In this
manner, a larger part of the end section--that is: the part that is
present in the light path--is moved. Hence, a substantial volume
increase can be compensated. The flexible membrane is particularly
ring-shaped. The end section is thus divided into an outer edge, a
membrane and an inner portion. The standard position of the end
section need not to be planar herein. As will be explained with
respect to the Figures, it is particularly such that the outer edge
is pushed downwards under the pressure of the clamping body. This
moreover results in a pressurized package. Although not preferred,
it is not excluded that the outer edge portion of the end section
comprises an other material than the inner portion.
[0023] The membrane is made of metal by far preference. Such a
material withstands the fluids effectively. It has the additional
advantage that the membrane can be used as one of the electrodes of
the cell. If the connection between clamping body and outer wall is
provided by electroplating or the like, the membrane will be
provided with a metal layer too. A suitable thickness of the
membrane layer that has sufficient stability on the one hand and
sufficient flexibility on the other hand, is in the order of 5-30
microns, and more preferably between 15 and 25 microns. This is
also dependent of the material of the membrane. In order to limit
the thickness of the membrane, it may be provided with an
insulating coating.
[0024] The substrate and the end section are preferably glass
plates. Glass is inert against the electrowetting fluids. It can be
treated with techniques such as powder blasting, and metal layers
can be attached to it. If desired, one or both glass plates may be
provided with coatings and surface layers, including IR-coatings,
UV-absorption coatings, antireflection coatings, but also lenses.
Such lenses can be made of surface layers with the replica
technique. Alignment features may be included in such replica made
surface layers. This allows a proper alignment of the cell with
further lenses at the bottom and the top side.
[0025] If the cell of the invention is used as a lens, it is
suitable assembled with further lenses to obtain a desired path. It
is not excluded that two electrowetting lenses are part of the
assembly; in fact this provides zoom properties. An alternative
embodiment is however a stacked electrowetting lens. This stacked
electrowetting lens can be suitable made with the method of the
invention.
[0026] In a first embodiment of stacked cell manufacture, the
substrate is present located in the middle of the stacked cell
construction. A first assembly and filling takes then place on the
one side of the substrate, and a second assembly and filling takes
place on the opposed second side after finalizing the assembly and
filling at the first side. Preferably both opposite end section are
provided with flexible membrane for compensation of volume
expansion. The outer wall is provided in this construction with an
extension to support the substrate, half way the stacked cell.
[0027] In a second embodiment of the stacked cell manufacture, the
two cells are provided within the outer wall one after the other.
The end section of the first cell may be the substrate of the
second cell, but that is not necessary. Most simply, a spacer is
provided instead of the clamping body. On this spacer, that may
well be connected to the outer wall by electroplating, a further
substrate and the further elements of the second cell are provided
consecutively. Such a construction moreover allows that the
electrodes are located in the substrates and the end sections
without the need for mutual coupling.
[0028] Instead for stacking of several electrowetting cells, the
outer wall may be applied for stacking of one electrowetting cell
and further optical and/or non-optical elements. In addition to
separate lenses and filters, it is envisaged that an image sensor
is assembled in this manner, separated from the electrowetting lens
at a desired distance with any spacer or the like. Such an
integration is most effectively with an image sensor in which the
bond pads are located at a surface opposite to the optically active
surface. Alternatively, the image sensor can be assembled on top of
an interposer substrate, that is provided with through-holes so as
to bring the contacts to a side opposite from the optically active
surface. The use of interposer substrates is known per se in the
art of semiconductor packaging.
[0029] It is an advantage of the method of the invention that it
can be carried out at a wafer-level or a bulk level. The outer wall
may be part of a plate, such as a printed circuit board with
apertures. It can be separated into individual packages only after
the filling and encapsulating steps. However, even if the
manufacture of the cells is carried out individually, the
electroplating steps can occur in a bath, allowing the simultaneous
electroplating of a plurality of devices.
[0030] In a further preferred embodiment, at least one of the
overlapping surfaces of the outer wall and the inner wall or the
substrate or end section comprises a sealant for sealing the
overlapping part under pressure. An advantage thereof is that the
cell is being sealed during the assembly thereof. In other words,
the cell is sealed while the closing extension is applied to the
cell. It is to be kept in mind that leakage of fluids has to be
prevented all around the overlapping surfaces. The sealing of this
embodiment prevents leakage of fluids through passages that are
formed by irregularities in the adjacent surfaces. A further
advantage of this embodiment is that, because leakage is prevented
after assembly, the surface of the exterior of the cell will remain
free of liquids migrating from the inside after cleaning of the
cell. Therefore, the application of the, preferably, metal layer as
described in the above is not hampered by newly leaking fluids.
[0031] Advantages of a sealant comprising an organic composite such
as plastic or rubber is that such materials are easily deformed and
or pressed into areas wherein the adjacent surfaces are further
away from each other, which areas are most prone to leakage.
Preferably the sealant has electrically conductive properties which
enables the process of electroplating by means of the positing
technique such as electro galvanizing directly onto the sealant.
Applying the electroplating directly on the sealant speeds of up
the electroplating process over the gap between adjacent wall
parts.
[0032] The invention is further related to a manufacturing method
and a cell of the kind mentioned in the opening paragraph, in which
a hermetic sealing is provided. This is achieved in that the end
section is attached to the body section with a metal layer that is
applied on a surface of both the end section and the joint section.
As is explained above, the application of a metal layer will lead
to a hermetic sealing. A clamping is achieved if the metal layer,
or the construction of which the metal layer is part extends on
both sides of the cell. A preferred application method is
electroplating, but other methods such as sol-gel deposition of
metal, sputtering or chemical vapor deposition, or combinations of
such deposition methods, are not excluded. The metal layer will
suitably be attached to metal parts at the surface of the end
section and at the surface of the body section.
[0033] The cell may be used as a lens for use in a camera, in an
optical recording apparatus or any other optical equipment. The
cell may be assembled with further lenses, to obtain an optical
path as needed, or even to obtain a zoom lens. Alternatively, the
cell is used as a display, in which case only one of the substrate
and the end section needs to be optically transparent. The cell may
be further used as a sensor.
[0034] These and other aspects of the cell and the method of the
invention will be further elucidated with reference to the Figures,
in which:
[0035] FIG. 1 shows a diagrammatical cross-sectional view of the
cell of the invention, in which only the left part is depicted;
[0036] FIGS. 2-7 show diagrammatic cross-sectional views of
consecutive stages in the manufacturing of the end section used in
the cell;
[0037] FIGS. 8-16 show diagrammatic cross-sectional views of
consecutive stages in the method of manufacturing of the cell, in
which Figs. Only the left part of the cell is depicted.
[0038] FIG. 17 shows a diagrammatical cross-sectional view of a
second embodiment of the cell of the invention.
[0039] FIGS. 18-19 shows a diagrammatical cross-sectional view of a
third embodiment of the cell of the invention.
[0040] The Figures are diagrammatic and not drawn to scale. The
same reference numbers in different Figures refer to like
parts.
[0041] FIG. 1 shows an embodiment of an electrowetting cell 15
according to the invention. In this FIG. 1 only a partial
cross-sectional view is shown, i.e. only the left part of the cell
15. The cell 15 is however built up symmetrically, such that the
non-shown right part is the mirror of the left part. The lens
includes fluid chamber, with a first fluid 51 and a second fluid 52
that are non-miscible and contact each other over a meniscus 14.
The first fluid 51 is in this example a silicone oil, an alkane or
another suitable electrically insulating fluid. The second fluid 52
is in this example water containing a salt solution or another
suitable electrically conducting fluid. The sides of the chamber
are provided with an electrically insulating layer 8 and a fluid
contact layer 10, for instance parylene.
[0042] According to this embodiment, the body section 17 comprises
an inner wall 80 and an outer wall 90, and--at the second side 112
of the cell 15--the second cover plate 6. The inner wall 80
comprises an electrically insulating member 8 that is coated with a
fluid contact layer 10. The inner wall 80 also comprises a portion
of the end section 4. This end section (or first cover plate) 4
comprises a ring-shaped glass member 81 that is through an
expandable joint 45 connected to an inner portion. In a preferred
embodiment, this ring-shaped glass member 81 and the inner portion
of the end section 4 are manufactured from a single glass plate, as
will be explained with reference to FIGS. 2 to 7. The inner wall,
80 further comprises the end 61 of the second cover plate 6. This
second cover plate 6 is provided with a through hole 62, an
electrode 2, and a metallization 63. In an alternative embodiment,
the plate 6 may be replaced by a construction similar or identical
to that at the first side 111 of the cell 15, i.e. a ring-shaped
glass member, an expandable joint and a cover plate.
[0043] These three sections of the inner wall 80--the ring-shaped
glass member 81, the--also ring-shaped--insulating member 8 and the
end 61--are clamped between a protrusion 85 of the outer wall 90
and a ring-shaped closing member 86. The closing member 86 is
herein a piece of metal, but can be anything with an electrically
conducting surface. The outer wall 90 comprises an inner core of
plastic or other material 92 that is provided with a metallized
surface 91. This metallized surface 91 also circumferes the
metallization 63 of the second cover plate 6. In this manner, a
mechanically stable connection is provided.
[0044] The inner wall 80 and the outer wall 90 are attached to each
other, as well as to the joint 45 and the end section 4, in that a
sealing layer 95 is present around it. The sealing layer 95 can be
made of a suitable material. Polymeric coating of rubber, epoxy or
the like, as are known per se as protective coating may be used. It
is however preferred that the sealing layer 95 comprises a metal.
This allows the provision of a package that is hermetical and not
prone to diffusion of air, water or fluid. A particularly preferred
method for the provision of this metal sealing layer 95 is
electroplating. This method can be carried out at three-dimensional
surfaces, e.g. in a bath.
[0045] FIGS. 2 to 7 show in schematic cross-sectional views
consecutive steps in a method of manufacturing of the substrate 200
with an integrated membrane 210, to be applied as expandable joint
46. FIG. 20 shows the substrate 200, with a first surface 201 and
an opposed second surface 202. The substrate 200 is in this example
a glass plate with a suitable thickness, for instance in the order
of 0.1 mm.
[0046] FIG. 3 shows the substrate 200, after that a photoresist 205
is applied at both surfaces 201, 202. Photoresist materials are
known per se in the art.
[0047] FIG. 4 shows the substrate 200 after patterning and
developing the photoresist 205. The patterning at the first side
201 results in an aperture 214. The patterning at the second side
202 has resulted therein, that also the surface 215 of the
photoresist 205 is given a three-dimensional structure. This
surface 215 is in this example in the form of an undulating
surface. This surface structure can be provided with forging or
another manner of mechanical deformation. Alternatively, use is
made of advanced photolithographical techniques. In an even further
embodiment, use is made of a molding technique to provide the
photoresist layer 205 in the desired shape. As will be understood,
no specific photoresist material is needed in such a case.
[0048] FIG. 5 shows the substrate 200 after that a membrane layer
225 is applied. The membrane layer comprises for instance a metal
with some elasticity, although any other material is suitable, as
long as it is compatible with the photoresist layer 205. Many
metals turn out to have sufficient flexibility if applied as a thin
layer. Examples include gold, copper, nickel, aluminum, as well as
suitable alloys thereof. A metal layer may be applied with a
suitable deposition technique, such as sputtering, chemical vapor
deposition and also wet-chemical techniques. In this example, the
membrane layer 225 is shown to be patterned, but that is not
necessary.
[0049] FIG. 6 shows the substrate 200 after that it has been
patterned through the patterned photoresist 205 at the first side
201. In the case of a glass plate 200 the technique of power
blasting can be applied advantageously, which however does not
exclude any other technique such as etching.
[0050] FIG. 7 shows the substrate 200 after that the photoresist
205 is removed, and a substrate 200 with an integrated membrane 220
results. As will be clear, the substrate 200 may extend in lateral
directions. The membrane 220 may have any suitable shape.
Particularly preferred is a ring-shape. The substrate may contain a
plurality of membranes, and be suitable for wafer-level processing
in a further step, or be separated. Such a separation step could
also be applied before the removal of the photoresist 205. Although
not shown here, it is not excluded that the substrate comprises
further layers at its first or second side 201, 202. If a
semiconductor substrate is used as the substrate 200, semiconductor
elements such as diodes and transistors or trench capacitors may be
defined herein.
[0051] FIGS. 8 to 16 show diagrammatical cross-sectional views of
the method of manufacturing the electrowetting cell 15. Shown here
is the manufacture of the embodiment of FIG. 1, but modifications
and alternatives are possible within the scope of the present
invention.
[0052] FIG. 8 shows the first step in the assembly. Herein, a glass
substrate 6 is provided into a ring-shaped member 90. The
ring-shaped member 90 acts as outer wall, and is provided with an
electrically conducting surface. It is not necessary though allowed
that the complete surface is electrically conducting. The member 90
is provided with an extension 85, that is present at a first side
112 of the substrate 6, and is in contact with a adhesion layer 63
of the substrate 6. The adhesion layer 63 is here a metal, such as
copper. An electrode 2 is present at the same first side 112 of the
substrate 6. This electrode 2 covers an aperture 62 in the
substrate 6. The aperture 62 may be filled with electrically
conducting material, but that is not the case in this example. The
aperture 62 is--contrarily to for instance the outer wall 90--not
ring-shaped, but provided locally only. Instead of glass use can be
made of another material. In case that the cell is not a lens,
there is no need that the substrate is optically transparent. In
order to keep the substrate 6 and the outer wall attached, use is
for instance made of an adhesive layer.
[0053] FIG. 9 shows the result after a second step in the assembly.
Herein, the substrate 6 and the outer wall 90 are connected to each
other with a metal layer 91. This metal layer 91 is suitable
provided with electroplating in a bath. The metal layer 91 extends
around the outer wall 90, and is connected to the adhesion layer 63
of the substrate. The connection is present not only at the first
side 112 of the substrate, but also at a side face 115. Shown here,
but not in further Figures is the fact that the electrode 2 will be
provided with an electroplated layer as well. The position of this
electrode 2 is chosen such that no bridge is formed between the
electrode and the outer wall. An insulating coating may be provided
at the electrode 2 in order to prevent the thickening thereof.
[0054] FIG. 10 shows the result after that an electrically
conducting fluid 52 is provided into the outer wall 90 and on the
second side 113 of the substrate 6. The fluid 52 is in this example
an aqueous salt solution. Alcohols and the like may be used as
additional solvents. The fluid extends into the aperture 62,
therewith making contact to the electrode 2. The electrode 2 acts
at the same time as a closure of the cell.
[0055] FIG. 11 shows the result after the provision of the
electrically insulating fluid 51. This is an oil, for instance an
alkane or a silicone oil. In view of its lower density, it is
provided after the electrically conducting fluid 51. The shown
shapes of the meniscus and the adhesion to the second side 113 of
the substrate 6 are purely diagrammatical and do not necessarily
correspond to any physical effect.
[0056] FIG. 12 shows the result after the insertion of a spacer 8.
This is in this case a ring-shaped electrically insulating member 8
that is provided with a fluid contact layer 10 of parylene. The
spacer 8 has a surface 9 that may have a modified surface structure
or layer for proper adhesion to the electroplated layer 91 of the
outer wall 90. This surface structure or layer can be of any
chemical kind, but also mechanical, such as a locking feature.
Additionally, the spacer 8 is provided with a gap 64. This gap 64
has as a first advantage that the electrode 2 can be provided below
this spacer 8. Hence, the electrode 2 is located outside the light
path, which reduces the diameter of the cell. A second advantage of
the gap is a modification of the angle of the meniscus 14 between
the electrically conducting fluid 52 and the electrically
insulating fluid 51. As a result, the minimum thickness of the cell
is reduced. The spacer 8 forms with an outer edge 61 of the
substrate part of the inner wall.
[0057] FIG. 13 shows the cell 15 after a sixth step in the
manufacturing. This step involves the assembly of the end section
4. The end section 4 includes an inner portion, a membrane 45 and
an outer portion 81. A pressure tool 70 is provided at a first side
111 of the end section 4. Preferably, the end section 4 is provided
with a layer of the electrically insulating fluid at its second
side 114 before the actual assembly. This ensures that no air
bubbles will be formed during the assembly. The end section 4 is
immersed in the fluid 51 during the assembly. As a result thereof,
a surplus layer 55 of the fluid is formed at the first side of the
end section. The electrically insulating fluid 51 is able to flow
from the second side 114 to the first side 111 of the end section
4, as a narrow channel is left between the outer portion 81 and the
outer wall 90.
[0058] FIG. 14 shows the cell 15 after that the outer portion 81 of
the end section 4 is secured to the body section. This body section
comprises in fact both the spacer 8 and the outer wall 90. This is
carried out by insertion of a clamping body 86. That clamps and/or
puts the outer portion 81 downwards to the spacer 8. As a result
the membrane 45 is put into a slightly bent position. The clamping
body has a surface that is in contact with the electroplated
surface layer 91 of the outer wall 90. It is preferably provided
with one or more locking features. If desired, it may be designed
to extend into the channel 89 between the outer portion 81 and the
outer wall 90. In this operation, the inner wall 80 is formed,
constituted by the adhesion layer 63, the outer portion 61 of the
substrate 6, the spacer 8, the outer portion 81 of the end section
4 and the clamping body 86.
[0059] FIG. 15 shows the cell 15 after removal of the tool 70 and
the surplus 55 of the electrically insulating fluid 51. The removal
step is followed by a cleaning step, so that the surfaces of the
clamping body 86 and the membrane 45 are sufficiently clean for
subsequent steps.
[0060] FIG. 16 shows the cell 15 after the last important step in
the manufacture. In this step, the connection between the clamping
body 86 and the outer wall 90 is strengthened by the provision of a
sealing layer 95. The sealing layer 95 is preferably provided with
electroplating in a suitable bath. Alternatively, it may be any
other protective layer known per se in the art, such as an
epoxy-based layer. The sealing layer 95 extends in this example to
the membrane 45 but that is not essential. Preferably, the sealing
layer 95 is provided in a suitable thickness so as to fill any
corners and provide a smoothened outer surface. The sealing layer
95 extends in this example from the first side 111 of the end
section to the first side 112 of the substrate. This is
advantageous, in that it therewith has a clamping character as
well, and unifies the outer wall 90 with its extensions 85, 86.
[0061] FIG. 17 shows a diagrammatical, cross-sectional view of a
second embodiment of the cell of the invention. Not shown in this
embodiment are any electroplated sealing layers that cover the
extension 85 of the outer wall 80. In this embodiment, the core 92
of the outer wall is a metallic tray, which inherently comprise the
protrusion 85. The second cover plate 6 with the through-hole 62,
the body member 8 and the first cover plate 4 are herein assembled
in the manner described with reference to FIGS. 8 to 16. The body
member 8 will generally operate as one of the electrodes, and it is
for instance connected to the tray 92, that acts as a contact.
[0062] The first cover plate 4 is herein a continuous plate that is
chosen to be sufficiently thin so as to be bendable under stress.
In this example, use is made of a plate of glass. A cavity 41 is
present between the body member 8 and the first cover plate 4.
Under expansion of at least one of the fluids 51,52--particularly
at a temperature increase--the first cover plate 4 will bend so as
to enlarge the volume in the cell. Under shrinkage of at least one
of the fluids 51,52 the first cover plate will bend so as to
diminish the volume in the cell. Since the electrically insulating
fluid 51 is preferably an oil and has a larger coefficient of
thermal expansion than the aqueous second fluid 52, it is
preferably that the bendable first cover plate 4 is present at the
side of the electrically insulating fluid 51.
[0063] FIG. 18 shows a further embodiment of the electrowetting
cell according to the present invention. The left side of the
embodiment is shown in greater detail in FIG. 19. In this
embodiment, the outer wall is formed by a cylindrical wall part 92
as well as to ring shaped closing members 86,12. Between the ring
shaped closing members 86,12, to glass plates 4,6 and an annular or
ring shaped insulating member 8 are enclosed in a manner similar to
the other embodiments.
[0064] Before the assembly of this embodiment, the cylindrical wall
part 92 is provided with a layer 91 comprising niflon. Niflon is a
composite of Teflon and nickel which composite is electrically
conductive. Another example of such a composite comprises Teflon
and copper. Because such a layer is electrically conductive, and
the final metallic layer 95, which is also applied in the other
embodiments, can directly grow onto the niflon layer 91 when the
use is made of a plating technique based on electricity such as
electro galvanizing. Also the annular members 12,86 are provided
with niflon layers 11,13.
[0065] The embodiment is assembled as follows. The assembly is
started with just the cylindrical wall part 92. The ring shaped
closing member 12 is inserted in to the cylindrical wall part. On
top of the ring shaped closing member 12, the glass plate or
substrate 6 is attached by means of an adhesive. On top of the
glass plate or substrate 6, the annular or ring shaped insulating
member 8 is placed. Then the first and second liquids are provided
into the cavity and the cover plate is placed on top of the liquids
in a manner similar as described with the earlier embodiments.
[0066] The sealant or niflon layer has advantages in that the
materials are pressed into uneven parts of the overlapping
surfaces, which spreading can be improved by moving two adjacent
surfaces relative to each other during or after the joining
process. Such a relative movements can be achieved by means of
rotating and/or repeatedly sliding surfaces relative to each other.
The sealant is preferably applied onto either of the adjacent
surfaces by means of a depositing or growth process such as a
galvanizing process. Such a process allows for accurately
depositing a thin layer or a labyrinth of material suitable for the
purpose of sealing a very narrow closure, which is present between
the adjacent surfaces in the embodiment.
[0067] Several additional features described in connection with
other embodiments are also applicable in this embodiment.
[0068] Although not shown here, very good results have been
obtained with the electroplated sealing layer. It is not excluded
that this electroplated sealing layer is also applicable in other
configurations of fluid containing cells, and that not for all
applications a cell with both an inner wall 80 and an outer wall 90
and an extension 85,86.
[0069] It is further understood, that the extensions 85, 86 of the
outer wall 80 extending at the first and second side 111, 112 are
not separate elements, but either protrusions to parts or
connections grown or deposited. Particularly, an electroplated
connection may be effective as such an extension 86.
* * * * *