U.S. patent application number 14/488539 was filed with the patent office on 2016-03-17 for electrowetting element and manufacture method.
The applicant listed for this patent is Amazon Technologies, Inc.. Invention is credited to Sukhdip Sandhu, Lara Tauk.
Application Number | 20160077324 14/488539 |
Document ID | / |
Family ID | 54207468 |
Filed Date | 2016-03-17 |
United States Patent
Application |
20160077324 |
Kind Code |
A1 |
Tauk; Lara ; et al. |
March 17, 2016 |
ELECTROWETTING ELEMENT AND MANUFACTURE METHOD
Abstract
An electrowetting element includes a support plate with a layer
with a first surface for adjoinment by a fluid. The layer is formed
at least partly of a material having a backbone which is
substantially apolar and at least one chain pendant from the
backbone and terminating with a substantially polar group.
Inventors: |
Tauk; Lara; (Eindhoven,
NL) ; Sandhu; Sukhdip; (Eindhoven, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Amazon Technologies, Inc. |
Reno |
NV |
US |
|
|
Family ID: |
54207468 |
Appl. No.: |
14/488539 |
Filed: |
September 17, 2014 |
Current U.S.
Class: |
359/290 ;
252/500; 427/58 |
Current CPC
Class: |
B01L 2400/0427 20130101;
G09G 3/348 20130101; B32B 2307/728 20130101; G02B 26/005 20130101;
G02B 26/02 20130101; B32B 2307/73 20130101; G02B 26/004 20130101;
C09D 5/00 20130101 |
International
Class: |
G02B 26/00 20060101
G02B026/00 |
Claims
1. An electrowetting element comprising: a support plate having a
layer with a first surface for adjoinment by a fluid, wherein the
layer is formed at least partly of a material having a backbone
which is substantially apolar and at least one chain pendant from
the backbone and terminating with a substantially polar group.
2. An electrowetting element according to claim 1, wherein the
material is at least one of: an ionomer, an amphiphile, a material
with the substantially apolar backbone being hydrophobic, or a
material with the substantially polar group being hydrophilic.
3. An electrowetting element according to claim 1, wherein the
material has the following formula: R.sup.1-A.sub.n-R.sup.2,
wherein R.sup.1 is a first terminus group; R.sup.2 is a second
terminus group; n is an integer equal to or greater than 2; and
each said A is independently selected from the group consisting of:
R.sup.3 having the formula --CF.sub.2CF.sub.2--, or R.sup.4 having
the formula --CFR.sup.5CF.sub.2--, wherein R.sup.5 has the formula
-L-Q, wherein L is a linker group and Q is a substantially polar
group, and wherein A.sub.n includes at least one of R.sup.3 and at
least one of R.sup.4.
4. An electrowetting element according to claim 3, wherein said
linker group L of at least one of said R.sup.5 is independently
selected from the group consisting of: a single bond, a straight
chain alkylene group, a branched alkylene group, a straight chain
fluoroalkylene group, a branched fluoroalkylene group, a
perfluorinated straight chain alkylene group, or a perfluorinated
branched alkylene group.
5. An electrowetting element according to claim 3, wherein said
linker group L of at least one of said R.sup.5 is independently
selected from the group consisting of: a straight chain alkylene
group containing 2 to 10 carbon atoms, a straight chain
fluoroalkylene group containing 2 to 10 carbon atoms, or a
perfluorinated straight chain alkylene group containing 2 to 10
carbon atoms.
6. An electrowetting element according to claim 3, wherein said
linker group L of at least one of said R.sup.5 has the following
formula: --R.sup.6R.sup.7R.sup.8--, wherein R.sup.6 is one of: a
single bond, a straight chain alkylene group, a branched alkylene
group, a straight chain fluoroalkylene group, a branched
fluoroalkylene group, a perfluorinated straight chain alkylene
group, or a perfluorinated branched alkylene group; wherein R.sup.7
has one of the following formula: --CHR.sup.9--, --CFR.sup.9, or
--CR.sup.9R.sup.9--, wherein each said R.sup.9 is independently
selected from the group consisting of: a straight chain alkyl
group, a branched alkyl group, a straight chain fluoroalkyl group,
a branched fluoroalkyl group, a perfluorinated straight chain alkyl
group, or a perfluorinated branched alkyl group; and wherein
R.sup.8 is a straight chain alkylene group, a straight chain
fluoroalkylene group, or a perfluorinated straight chain alkylene
group.
7. An electrowetting element according to claim 6, wherein said
R.sup.8 of at least one of said linker group L independently
contains 1 to 8 carbon atoms.
8. An electrowetting element according to claim 6, wherein said
R.sup.8 of at least one of said linker group comprises at least 5
atoms.
9. An electrowetting element according to claim 3, wherein said
linker group L of at least one of said R.sup.5 is independently one
of: an ether group, a fluoroether group, a perfluorinated ether
group, or a group having one of the following formula:
--O(CH.sub.2).sub.z--, --O(CF.sub.2).sub.z--,
--(OCH.sub.2CH.sub.2).sub.x--, --OR.sup.6R.sup.7OR.sup.8--,
--O(R.sup.6R.sup.7O).sub.zR.sup.8--, or
--OR.sup.6R.sup.7(OCH.sub.2CH.sub.2).sub.x--. wherein R.sup.6 is
one of: a single bond, a straight chain alkylene group, a branched
alkylene group, a straight chain fluoroalkylene group, a branched
fluoroalkylene group, a perfluorinated straight chain alkylene
group, or a branched perfluorinated alkylene group; wherein R.sup.7
has one of the following formula: --CHR.sup.9--, or
--CR.sup.9R.sup.9--, or is one of a straight chain alkylene, a
straight chain fluoroalkylene, or a perfluorinated straight chain
alkylene, wherein each said R.sup.9 is independently one of: a
straight chain alkyl group, a branched alkyl group, a straight
chain fluoroalkyl group, a branched fluoroalkyl group, a
perfluorinated straight chain alkyl group, or a perfluorinated
branched alkyl group; wherein R.sup.8 is a straight chain alkylene
group, a straight chain fluoroalkylene group, or a perfluorinated
straight chain alkylene group; wherein z is an integer with a value
selected from the range 1 to 8; and wherein x is an integer with a
value selected from the range 1 to 3.
10. An electrowetting element according to claim 9, wherein each
said R.sup.8 independently contains 1 to 8 carbon atoms.
11. An electrowetting element according to claim 9, wherein each
said R.sup.8 independently comprises at least 5 atoms.
12. An electrowetting element according to claim 3, wherein each
said Q independently comprises a hydrogen atom bonded to one of: an
oxygen atom, a nitrogen atom, or a sulphur atom.
13. An electrowetting element according to claim 3, wherein each
said Q is independently selected from the group consisting of:
--OH, --COOH, SO.sub.3H, NH.sub.2, or CONH.sub.2.
14. An electrowetting element according to claim 3, wherein a ratio
R.sup.3:R.sup.4 is in the range of 1:2 to 4:1.
15. An electrowetting element according to claim 3, wherein said
A.sub.n comprises at least one alternating sequence of said R.sup.3
and said R.sup.4.
16. An electrowetting element according to claim 3, wherein a
polymer molecule of the ionomer has a molecular weight of 400 to
400,000 Daltons.
17. An electrowetting element according to claim 3, wherein the
first terminus group is selected from the group consisting of: H,
F, or an initiating group formed by an initiator for initiating a
polymerisation reaction to form a polymer molecule of said
material; and wherein the second terminus group is selected from
the group consisting of: H, F, or a terminating group formed by a
terminator for terminating a polymerisation reaction to form a
polymer molecule of said material.
18. An electrowetting element according to claim 1, comprising at
least one wall formed on a second surface of the layer, the second
surface being more wettable to water than the first surface.
19. An electrowetting element according to claim 18, wherein in a
region of the layer forming the first surface, one or more side
chain of said at least one side chain is orientated such that the
respective substantially polar functional group is located away
from the first surface, and in a region of the layer forming the
second surface, a further one or more of said at least one side
chain is orientated such that the respective substantially polar
functional group is located within a material forming the at least
one wall.
20. A method of manufacturing a support plate for an electrowetting
element comprising: i) providing a surface for forming a layer of
the support plate thereon; ii) applying a layer material on said
surface, the layer material having a substantially apolar backbone
and at least one pendant chain terminating with a substantially
polar group; and iii) forming the layer on said surface from said
layer material applied on the surface.
21. A method according to claim 20, wherein upon said forming the
layer on said surface, the layer provides a first surface of the
support plate having a wettability for adjoining a fluid of an
electrowetting element.
22. A method according to claim 20 comprising: iv) applying a wall
material on a first surface and a second surface of the layer, for
forming at least one wall on the second surface, the layer material
reconfiguring upon said applying the wall material, to provide the
first surface and the second surface with a more wettable surface
to the wall material than before said applying the wall
material.
23. A method according to claim 22, the layer material
reconfiguring including the layer material reconfiguring to at
least partly insert at least one said substantially polar group
into the wall material applied on the second surface.
24. A method according to claim 22, including removing wall
material applied to the first surface during iv), the layer
material reconfiguring to provide the first surface with a
wettability for adjoining a fluid of an electrowetting element, the
first surface being more wettable for said fluid than said second
surface.
Description
BACKGROUND
[0001] Known electrowetting display devices include two support
plates. In examples, a pattern of walls is arranged on one of the
support plates, the pattern defining picture elements of the
display device. An area defined by the walls of a picture element,
also known as a pixel, is called the display area, over which a
display effect occurs. The walls of the picture elements may be
made of a hydrophilic material. The area of the support plate in
the display area may to a large extent be hydrophobic for a proper
operation of the picture element. During manufacture the area of
the support plate where the picture elements are located is covered
by a hydrophobic layer. The walls are made on this layer by
depositing a layer of wall material on the hydrophobic layer and
patterning the layer of wall material using for example a
photolithographic method.
[0002] To improve adhesion between the layer of wall material and
the hydrophobic layer, it is known to lower the hydrophobicity of
the hydrophobic layer prior to applying the layer of wall material.
After the formation of the walls, the area of the hydrophobic layer
between the walls is annealed to regain its hydrophobicity.
However, the quality of display devices made using this method is
not optimum.
[0003] It is desirable to provide an improved method for
manufacturing an electrowetting display device.
BRIEF DESCRIPTION OF DRAWINGS
[0004] FIG. 1 shows schematically an example electrowetting display
element;
[0005] FIG. 2 shows a plan view of the example display element;
and
[0006] FIG. 3 is a flow diagram showing an example method of
manufacture.
DETAILED DESCRIPTION
[0007] Details of substituent groups and atoms which will be
referred to herein are first described. These meanings apply unless
explicitly stated to the contrary.
[0008] An alkyl group as referred to herein is a straight chain or
a branched alkyl group, not a cyclic group as these are too
restrictive in terms of flexibility of a linker side chain L
described below.
[0009] A fluoroalkyl group as referred to herein is a straight
chain or a branched alkyl group in accordance with the description
of an alkyl group given in the paragraph above with at least one of
the hydrogen atoms replaced by a fluorine atom (F), and with at
least one hydrogen atom not being replaced.
[0010] A perfluorinated alkyl group as referred to herein is a
straight chain or a branched alkyl group in accordance with the
description of an alkyl group given in the paragraph above with
each of the hydrogen atoms replaced by a fluorine atom (F).
[0011] An alkylene group as referred to herein is a straight chain
or a branched divalent aliphatic hydrocarbon group having the
general formula --C.sub.mH.sub.2m--.
[0012] A fluoroalkylene group referred to herein is a straight
chain or a branched alkylene group in accordance with the
description of an alkylene group given in the paragraph above with
at least one of the hydrogen atoms replaced by a fluorine atom (F),
and with at least one hydrogen atom not being replaced.
[0013] A perfluorinated alkylene group referred to herein is a
straight chain or a branched alkylene group in accordance with the
description of an alkylene group given in the paragraph above with
each of the hydrogen atoms replaced by a fluorine atom (F).
[0014] An ether group referred to herein is a functional group
including the formula --CH.sub.2OCH.sub.2--.
[0015] A fluoroether group is an ether group described above but
with at least one hydrogen atom H replaced by a fluorine atom F,
but with at least one hydrogen atom H not replaced.
[0016] A perfluorinated ether group is an ether group described
above but with all hydrogen atoms H replaced by a fluorine atom
F.
[0017] Examples will now be described.
[0018] FIG. 1 shows a diagrammatic cross-section of part of an
example of an electrowetting display device 1, including a
plurality of picture elements or display elements 2, one of which
is shown in the Figure and which may also be referred to as an
electrowetting cell, an electrowetting element or an electrowetting
pixel. The lateral extent of the display element is indicated in
the Figure by two dashed lines 3, 4. The display elements comprise
a first support plate 5 and a second support plate 6. The support
plates may be separate parts of each display element, but the
support plates may be shared in common by the plurality of display
elements. The support plates may include a glass or polymer
substrate 6, 7 and may be rigid or flexible.
[0019] The display device has a viewing side 8 on which an image or
display formed by the display device can be viewed and a rear side
9. In the Figure a surface of the first support plate 5, which
surface is in this example a surface of the substrate 7, defines
the rear side 9; a surface of the second support plate 6, which
surface is in this example a surface of the substrate 6, defines
the viewing side; alternatively, in other examples, a surface of
the first support plate may define the viewing side. The display
device may be of the reflective, transmissive or transflective
type. The display device may be an active matrix driven display
device. The plurality of display elements may be monochrome. For a
colour display device the display elements may be divided in
groups, each group having a different colour; alternatively, an
individual display element may be able to show different
colours.
[0020] A space 10 of each display element between the support
plates is filled with two fluids: a first fluid 11 and a second
fluid 12 at least one of which may be a liquid. The second fluid is
immiscible with the first fluid. Therefore, the first fluid and the
second fluid do not substantially mix with each other and in some
examples do not mix with each other to any degree. The
immiscibility of the first and second fluids is due to the
properties of the first and second fluids, for example their
chemical compositions; the first and second fluids tend to remain
separated from each other, therefore tending not to mix together to
form a homogeneous mixture of the first and second fluids. Due to
this immiscibility, the first and second fluids meet each other at
an interface labelled 55 in FIG. 1 for when no voltage is applied
and labelled 57 for when a voltage is applied, which interface
defines a boundary between the volume of the first fluid and the
volume of the second fluid; this interface or boundary may be
referred to as a meniscus. With the first and second fluids
substantially not mixing with each other, it is envisaged in some
examples that there may be some degree of mixing of the first and
second fluids, but that this is considered negligible in that the
majority of the volume of first fluid is not mixed with the
majority of the volume of the second fluid.
[0021] The second fluid is electrically conductive and/or polar and
may be water, or a salt solution such as a solution of potassium
chloride in water. The second fluid may be transparent; it may
instead be coloured, for example, or absorbing. The first fluid,
which is electrically non-conductive, may for example be an alkane
like decane or hexadecane, silicone oil or decalin (otherwise known
as bicyclo-4,4,0-decane).
[0022] The first fluid may absorb at least a part of the optical
spectrum. The first fluid may be transmissive for a part of the
optical spectrum, forming a colour filter. For this purpose the
first fluid may be coloured by addition of pigment particles or a
dye. Alternatively, the first fluid may be black, i.e. absorb
substantially all parts of the optical spectrum, or reflecting. A
reflective first fluid may reflect the entire visible spectrum,
making the layer appear white, or part of it, making it have a
colour.
[0023] The support plate 5 includes a layer with a surface for
adjoinment by a fluid such as the first fluid described herein. In
examples described herein, the layer is an insulating layer 13. The
insulating layer may be transparent or reflective. The insulating
layer 13 may extend between walls of a display element. To avoid
short circuits between the second fluid 12 and electrodes arranged
under the insulating layer, layers of the insulating layer may
extend uninterrupted over a plurality of display elements 2, as
shown in the Figure. The insulating layer has a surface 14 facing,
i.e. closest to, the space 10 of the display element 2. An extent
of the surface corresponding to the extent of the display area
described below is referred to herein as the first surface and is
in this example hydrophobic. The thickness of the insulating layer
may be less than 2 micrometers and may be less than 1
micrometer.
[0024] The insulating layer in examples described herein is formed
of a different material, which for example is an ionomer, compared
with known examples. This will be explained in further detail
further below. The insulating layer may be formed solely of such a
different material; alternatively, the insulating layer may be
formed of a layer 15 of the different material and a barrier layer
16 with predetermined dielectric properties, the different material
15 facing, i.e. being closer to, the space 10, as shown in the
Figure. The layer of different material is schematically
illustrated in FIG. 1. The barrier layer 16 may have a thickness,
taken in a direction perpendicular the plane of the substrate,
between 50 nanometers and 500 nanometers and may be made of an
inorganic material like silicon oxide or silicon nitride or a stack
of these (for example, silicon oxide-silicon nitride-silicon oxide)
or an organic material like polyimide or Parylene.
[0025] In the absence of an applied voltage, the hydrophobic
character of the first surface causes the first fluid 11 to adhere
preferentially to the insulating layer 13, since the first fluid
has a higher wettability with respect to the surface of the
insulating layer 13 than the second fluid 12. Wettability relates
to the relative affinity of a fluid for the surface of a solid.
Wettability may be measured by the contact angle between the fluid
and the surface of the solid. The contact angle is determined by
the difference in surface tension between the fluid and the solid
at the fluid-solid boundary. For example, a high difference in
surface tension can indicate hydrophobic properties.
[0026] Each display element 2 includes a first electrode 17 as part
of the support plate 5. In examples shown there is one such
electrode 17 per element. The electrode 17 is electrically
insulated from the first and second fluids by the insulating layer
13; electrodes of neighbouring display elements are separated by a
nonconducting layer. In some examples, further layers may be
arranged between the insulating layer 13 and the electrode 17. The
electrode 17 can be of any desired shape or form. The electrode 17
of a display element is supplied with voltage signals by a signal
line 18, schematically indicated in the Figure.
[0027] The support plate 6 for example includes a second electrode
19, which may extend between walls of a display element or extend
uninterruptedly over a plurality of display elements 2, as shown in
the Figure. The electrode 19 is in electrical contact with the
conductive second fluid 12 and is common to all display elements.
The electrode may be made of for example the transparent conductive
material indium tin oxide (ITO). A second signal line 20 is
connected to the electrode 19. Alternatively, the electrode may be
arranged at a border of the support plates, where it is in
electrical contact with the second fluid. This electrode may be
common to all elements, when they are fluidly interconnected by and
share the second fluid, uninterrupted by walls. The display element
2 can be controlled by a voltage V applied between the signal lines
18 and 20. The signal line 18 can be coupled to a matrix of control
lines on the substrate 7. The signal line 20 is coupled to a
display driving system.
[0028] The first fluid 11 in this example is confined to one
display element by walls 21 that follow the cross-section of the
display element. The cross-section of a display element may have
any shape; when the display elements are arranged in a matrix form,
the cross-section is usually square or rectangular. Although the
walls are shown as structures protruding from the insulating layer
13 and formed on a second surface of the insulating layer 13, they
may instead be a surface layer of the support plate that repels the
first fluid, such as a hydrophilic or less hydrophobic layer. The
walls may extend from the first to the second support plate but may
instead extend partly from the first support plate to the second
support plate as shown in FIG. 1. The extent of the display
element, indicated by the dashed lines 3 and 4, is defined by the
center of the walls 21. The area of the first surface between the
walls of a display element, i.e. the first surface, indicated by
the dashed lines 22 and 23, is called the display area 24, over
which a display effect occurs. The area of the second surface on
which the walls are formed may be referred to as the wall area. The
display effect depends on an extent that the first and second
fluids adjoin the surface defined by the display area, in
dependence on the magnitude of the applied voltage V described
above. The magnitude of the applied voltage V therefore determines
the configuration of the first and second fluids within the
electrowetting element. In other words, the display effect depends
on the configuration of the first and second fluid in the display
element, which configuration depends on the magnitude of the
voltage applied to the electrodes of the display element. The
display effect gives rise to a display state of the display element
for an observer looking at the display device. When switching the
electrowetting element from one fluid configuration to a different
fluid configuration the extent of second fluid adjoining the
display area surface may increase or decrease, with the extent of
first fluid adjoining the display area surface decreasing or
increasing, respectively.
[0029] FIG. 2 shows a matrix of rectangular picture elements in a
plan view of the hydrophobic first surface of the first support
plate. The extent of the central picture element in FIG. 2,
corresponding to the dashed lines 3 and 4 in FIG. 1, is indicated
by the dashed line 26. Line 27 indicates the inner border of a
wall; the line is also the edge of the display area 23.
[0030] When a zero or substantially zero voltage is applied between
the electrodes 17 and 19, i.e. when the electrowetting element is
in an off state, the first fluid 11 forms a layer between the walls
21, as shown in the FIG. 1. Application of a voltage will contract
the first fluid, for example against a wall as shown by the dashed
shape 25 in FIG. 1 or FIG. 2. The controllable shape of the first
fluid, in dependence on the magnitude of applied voltage, is used
to operate the picture element as a light valve, providing a
display effect over the display area 23. For example, switching the
fluids to increase adjoinment of the second fluid with the display
area may increase the brightness of the display effect provided by
the element.
[0031] This display effect determines the display state an observer
will see when looking towards the viewing side of the display
device. The display state can be from black to white with any
intermediate grey state; in a colour display device, the display
state may also include colour.
[0032] In known electrowetting display devices, the layer is formed
of a hydrophobic material, for example Teflon.RTM. AF1600. However,
in examples described herein, it has now been found that a
different material may be used than for example Teflon AF1600, for
at least partly forming a layer, for example a layer such as the
insulating layer 13 and for providing the hydrophobic surface for
adjoinment by the first fluid and, depending on the magnitude of
the applied voltage, the second fluid. This different material is a
material having at least one molecule with a backbone which is
substantially apolar (i.e. non-polar) and at least one chain
pendant from (i.e. extending or hanging from) the backbone and
terminating with a substantially polar group. The material may
therefore be a polymer in examples. In some examples the material
may be considered an amphiphile, i.e. an amphiphilic material,
which has a substantially polar region and a substantially
non-polar region. In some examples such an amphiphilic material may
be an ionomer, i.e. an ionomeric material, where the substantially
polar group is ionisable, i.e. the substantially polar group is
capable of dissociating to form an anion and a cation. An example
of such an ionisable group is a carboxylic acid group, i.e.
--COOH.
[0033] The substantially polar functionality is for example
provided by the presence of at least one polar functional group in
a molecule of the material; a polarity in examples depends on the
electronegativity of two atoms bonded together. For example, a
polar functional group comprises a hydrogen atom H bonded to an
oxygen atom O or a nitrogen atom N or a sulphur atom S; in some
examples, as described above for ionomeric materials, this polar
group may tend to dissociate. A polar functional group, such as
those just described, may have an affinity for being wet by a
material for forming a wall of an electrowetting element, for
example a photoresist material such as SUB; this property is used
in examples to provide the wettability of the second surface, for
adhering at least one wall as described above to the insulating
layer. Further details of forming such a wall are described further
below. In examples, the polar functional group may provide a
hydrophilic functionality, i.e. a tendency to mix with or be wetted
by water, i.e. the polar functional group may have an affinity for
being wet by water, rather than for repelling water.
[0034] The substantially non-polar functionality is for example
provided by the presence of at least one apolar, i.e. non-polar,
part of a molecule of the material. Such non-polar functionality is
in examples provided by the presence of non-polar groups of atoms,
i.e. groups which are not polar. Examples of such non-polar groups
include a C--H group, i.e. a hydrogen H atom bonded to a carbon C
atom, a C--C group, i.e. a carbon atom C bonded to a carbon atom C,
and/or a C--F group, i.e. a carbon atom C bonded to a fluorine atom
F. In examples, the non-polar functionality may provide a
hydrophobic functionality, i.e. a property of part of the molecule
for repelling water; in other words an aversion for being wetted by
or mixing with water. The non-polar functionality may therefore
provide an affinity for being wet by the first fluid when no, i.e.
a zero, voltage is applied to the electrowetting element; this
property is used in examples to provide the wettability of the
first surface for adjoining the first fluid, as described
above.
[0035] In known methods, which use for example Teflon.RTM. 1600 to
provide a hydrophobic layer as part of the insulating layer, a
surface of the hydrophobic layer needs to be treated, for example
using reactive ion etching (RIE), to reduce its hydrophobicity, so
that a hydrophilic wall material may then be applied to the surface
of the hydrophobic layer. Otherwise, without this treatment, the
hydrophobic nature of the surface is unfavourable for adhering with
the wall material; this can result in poorly formed and/or poorly
attached walls on the hydrophobic material. Further, once the
hydrophobicity has been reduced, remnants of wall material, such as
SU8, may remain attached to parts of the surface of the hydrophobic
material within the display area, thus contaminating the display
area and potentially interfering with fluid switching in the
electrowetting element. Moreover, once the walls have been formed,
it is necessary to restore hydrophobicity of the surface of the
hydrophobic layer within the display area; this may be done using a
reflow step by exposing the hydrophobic layer to a temperature
which may be higher than that using a wall formation process.
However, this reflow may not fully restore the hydrophobicity of
the surface to the level of hydrophobicity before the treatment to
reduce the hydrophobicity.
[0036] Using the different material, for example the ionomeric
material, as described above, in a material forming a layer
providing a surface of the display area, i.e. the first surface
described above and providing a surface on which the walls are
formed, i.e. the second surface described above, allows a new
method of manufacturing a support plate of an electrowetting
element to be used. This will be described later. The properties of
the different material mean that in examples it is unnecessary to
treat a surface of a layer of the different material to reduce its
hydrophobicity for then forming the walls thereon; instead, the
polar functionality of the different material molecule for example
gives a suitable affinity for the wall material, leading to good
adhesion of wall material to the second surface. The polar
functionality in examples may be considered to mimic a surface of a
layer of Teflon.RTM. 1600 for example after the known method of
treating the surface using RIE to provide a less hydrophobic
surface for applying the walls to. Moreover, in examples, the first
surface remains less wettable for the wall material, due to the
presence of the apolar part of the different material molecule, and
more wettable for the first fluid. This can simplify a method of
manufacturing a support plate as it is not necessary also to
perform a reflow step, or equivalent, to restore a hydrophobicity
of a surface for adjoining the first fluid in the electrowetting
element. Further, this can reduce adhesion of remnants of wall
material to the display area, giving better display and/or
switching performance to the electrowetting element. For example;
the first surface may be hydrophobic whilst the second surface is
hydrophilic, without requiring any heat treatment to restore a
hydrophobicity of the material. Instead, as explained further
below, the different material molecule can configure itself, for
example by orientating different parts of the molecule to provide
the different surface wettability properties of the first and
second surfaces. For example, due to the presence of external
forces, for example dipole forces provided by polar groups in a
wall material, an attraction to a wall material when applied on a
surface of the different material, polar functional groups may
orientate themselves towards, and possibly to at least partly
insert themselves within, the wall material such as SU8 which has
polar properties. Further, for example, due to the presence of a
layer such as the barrier layer underneath the layer comprising the
different material, non-polar parts of the different material
molecules may orientate themselves towards the first surface, for
example due to an attraction of the polar functional groups to the
underlying material forming the barrier layer. The different
material therefore can, depending on the orientation of the polar
functional groups, provide both a surface such as the first surface
which is more wettable to the first fluid and less wettable to the
wall material and also a surface such as the second surface which,
compared with the first surface, is more wettable to the wall
material and less wettable to the first fluid.
[0037] In examples the polar functionality described above may be
considered to be substantially polar and the apolar functionality
described above may be considered to be substantially apolar.
Substantially in such examples means for example that the polar and
apolar parts of the molecules are polar and apolar respectively, in
accordance for example with the different atom to atom bonds which
are considered polar or non-polar as explained above, but moreover
such that the substantially polar and substantially apolar parts of
the molecule perform the functions described herein, for example in
relation to interacting with wall material when applied to a
surface of the different material. Moreover, the term substantially
is used to account for any transient and relatively minor changes
in polarity due to movement of electrons within the molecule.
[0038] In some examples, the different material has the following
formula: R.sup.1-A.sub.n-R.sup.2, wherein R.sup.1 is a first
terminus group; R.sup.2 is a second terminus group; n is an integer
equal to or greater than 2; and each A is independently selected
from the group consisting of: R.sup.3 having the formula
--CF.sub.2CF.sub.2--, which may be considered a first monomer, or
R.sup.4 having the formula --CFR.sup.5CF.sub.2--, which may be
considered a second monomer, wherein R.sup.5 has the formula -L-Q,
wherein L is a linker group and Q is a substantially polar group,
and wherein A.sub.n includes at least one of R.sup.3 and at least
one of R.sup.4. The linker group L is in examples sufficiently long
and flexible such that the position of the substantially polar
group Q may change, relative to the backbone, depending on external
forces. A polarity of the linker group L may be selected depending
on the desired properties of the material.
[0039] In examples, the linker group L of at least one of R.sup.5
is independently selected from the group consisting of: a single
bond, a straight chain alkylene group, a branched alkylene group, a
straight chain fluoroalkylene group, a branched fluoroalkylene
group, a perfluorinated straight chain alkylene group, or a
perfluorinated branched alkylene group.
[0040] In examples, the linker group L of at least one, for example
all, of R.sup.5 is independently selected from the group consisting
of: a straight chain alkylene group containing, i.e. having, 2 to
10 carbon atoms, a straight chain fluoroalkylene group containing 2
to 10 carbon atoms, or a perfluorinated straight chain alkylene
group containing 2 to 10 carbon atoms. The number range 2 to 10
carbon atoms includes all integer numbers within the range, i.e. 2,
3, 4, 5, 6, 7, 8. 9 and 10. It has been found that this range of
carbon atoms provides suitable flexibility and length for the
linker group L. In some examples the linker group may contain 2 to
3, 4 to 5, 6 to 7, or 8 to 10 carbon atoms; depending on the
specific formulation of the first and second fluids for example and
the wall material being used, these sub-ranges of carbon atoms
provide desired properties of the material for wall adhesion for
the second surface and hydrophobicity for the first surface, for
example.
[0041] In examples, the linker group L of at least one, for example
all, of R.sup.5 has the following formula:
--R.sup.6R.sup.7R.sup.8--, wherein R.sup.6 is one of: a single
bond, a straight chain alkylene group, a branched alkylene group, a
straight chain fluoroalkylene group, a branched fluoroalkylene
group, a perfluorinated straight chain alkylene group, or a
perfluorinated branched alkylene group; in any such examples other
than the single bond example, R.sup.6 may contain for example 1, 2,
3, 4 or 5 carbon atoms. In some examples, where R.sup.6 is a
straight chain alkylene group, which may be a fluoroalkylene or
perfluorinated, R.sup.6 contains one carbon atom C. This has been
found to give favourable flexibility properties to the side chain,
but in further examples a different number of carbon atoms for
forming the R.sup.6 group are envisaged.
[0042] In such examples, R.sup.7 may have one of the following
formula: --CHR.sup.9--, --CFR.sup.9, or --CR.sup.9R.sup.9--,
wherein each said R.sup.9 is independently selected from the group
consisting of: a straight chain alkyl group, a branched alkyl
group, a straight chain fluoroalkyl group, a branched fluoroalkyl
group, a perfluorinated straight chain alkyl group, or a
perfluorinated branched alkyl group. In examples R.sup.9 is a
methyl group, i.e. R.sup.9 contains one carbon atom C, which is
found to give favourable properties in terms of flexibility of the
side chain. Other examples are envisaged with R.sup.9 containing a
different number of carbon atoms.
[0043] Further, in such examples, R.sup.8 may be a straight chain
alkylene group, a straight chain fluoroalkylene group, or a
perfluorinated straight chain alkylene group. R.sup.8 of at least
one, for example all, of the linker group L may in some examples
independently contain 1 to 8 carbon atoms. This provides a suitable
extent of flexibility to the end of the side chain and therefore
gives more freedom for repositioning of the polar functional group
Q, depending on external forces. The range 1 to 8 carbon atoms
includes integer values within the range, i.e. 1, 2, 3, 4, 5, 6, 7,
8. In some examples R.sup.8 contains 1 to 3, 4 to 5, or 6 to 8
carbon atoms. Again, depending on the specific formulation of the
first and second fluids for example and the wall material being
used, for example, these sub-ranges of carbon atoms provide desired
properties of the material for wall adhesion for the second surface
and hydrophobicity for the first surface, for example.
[0044] In some examples, R.sup.8 of at least one, for example all,
of linker group L comprises at least 5 atoms. For example, each
linker group L may comprise 6 atoms, which corresponds with an
example where R.sup.8 is an ethylene group which may be a
fluoroethylene group or perfluorinated. For example, where R.sup.8
is a perfluorinated alkylene group, R.sup.8 has the formula
--CF.sub.2CF.sub.2-- and therefore comprises at least 6 atoms. With
at least 5 atoms in some examples, the side chain provides suitable
flexibility at its end, for repositioning of the polar functional
group Q.
[0045] In some examples, the linker group L of at least one, for
example all, of R.sup.5 is independently one of: an ether group,
for example containing 1 to 8 carbon atoms (i.e. 1, 2, 3, 4, 5, 6,
7, or 8 carbon atoms), a fluoroether group for example containing 1
to 8 carbon atoms (i.e. 1, 2, 3, 4, 5, 6, 7, or 8 carbon atoms), a
perfluorinated ether group for example containing 1 to 8 carbon
atoms (i.e. 1, 2, 3, 4, 5, 6, 7, or 8 carbon atoms), or a group
having one of the following formula: --O(CH.sub.2).sub.z--,
--O(CF.sub.2).sub.z--, --(OCH.sub.2CH.sub.2).sub.x--,
--OR.sup.6R.sup.7OR.sup.8--, --O(R.sup.6R.sup.7O).sub.zR.sup.8--,
or --OR.sup.6R.sup.7(OCH.sub.2CH.sub.2).sub.x--, wherein R.sup.6 is
one of: a single bond, a straight chain alkylene group, a straight
chain fluoroalkylene group, or a perfluorinated straight chain
alkylene group, for example an example of R.sup.6 described
previously.
[0046] In examples, R.sup.7 has one of the following formula:
--CHR.sup.9--, or --CR.sup.9R.sup.9--, or R.sup.7 is one of a
straight chain alkylene, a straight chain fluoroalkylene, or a
perfluorinated straight chain alkylene.
[0047] In some such examples, at least one, for example all, of
each R.sup.9 is independently one of: a straight chain alkyl group,
a branched alkyl group, a straight chain fluoroalkyl group, a
branched fluoroalkyl group, a perfluorinated straight chain alkyl
group, or a perfluorinated branched alkyl group. In some examples
R.sup.9 is a methyl group, which in some examples helps to maintain
flexibility of the side chains.
[0048] In some further such examples, R.sup.8 is a straight chain
alkylene group, a straight chain fluoroalkylene group, or a
perfluorinated straight chain alkylene group. In some examples,
each R.sup.8 independently contains 1 to 8 carbon atoms, i.e. a
value 1, 2, 3, 4, 5, 6, 7, or 8 and may have a value within a
sub-range containing 1 to 3, 4 to 5, or 6 to 8 carbon atoms. Again,
1 to 8 carbons gives the side chain a suitable flexibility for
positioning the polar functional group Q. Further, each R.sup.8 in
some examples independently comprises at least 5 atoms, similar to
the explanation given above in relation to the linker group
comprising at least 5 atoms. In some examples, R.sup.7 and R.sup.8
are respectively a straight chain alkylene group and a
perfluorinated straight chain alkylene group.
[0049] z is an integer with a value selected from the range 1 to 8,
i.e. a value 1, 2, 3, 4, 5, 6, 7, or 8 and may have a value within
a sub-range containing 1 to 3, 4 to 5, or 6 to 8 carbon atoms.
Again, 1 to 8 carbons gives the side chain a suitable flexibility
for positioning the polar functional group Q.
[0050] x is an integer with a value selected from the range 1 to 3,
i.e. a value 1, 2, or 3 --(OCH.sub.2CH.sub.2)-- groups.
[0051] In some specific examples, the linker group L has one of the
following formula: --OCF.sub.2CF(CF.sub.3)O(CF.sub.2).sub.1-8--;
--OCF.sub.2C(CF.sub.3).sub.2O(CF.sub.2).sub.1-8--;
--OCF.sub.2CF.sub.2O(CF.sub.2).sub.1-8--;
--O(CF.sub.2CF.sub.2O).sub.1-8(CF.sub.2).sub.1-8--,
--OCF.sub.2CF(CF.sub.3).sub.2O(CH.sub.2).sub.1-8--;
--OCF.sub.2C(CF.sub.3).sub.2O(CH.sub.2).sub.1-8--;
--OCF.sub.2CF.sub.2O(CH.sub.2).sub.1-8--.
[0052] In some other specific examples, the linker group L has one
of the following formula:
--OCF.sub.2CF(CF.sub.3)(OCH.sub.2CH.sub.2).sub.1-3--;
--OCF.sub.2C(CF.sub.3).sub.2(OCH.sub.2CH.sub.2).sub.1-3--;
--OCF.sub.2CF.sub.2(OCH.sub.2CH.sub.2).sub.1-3--;
--O(CF.sub.2CF.sub.2O).sub.1-8(OCH.sub.2CH.sub.2).sub.1-3--.
[0053] As explained above, a polar group Q, for example each polar
group Q, comprises for example a hydrogen atom H bonded to an
oxygen atom O, a nitrogen atom N, or a sulphur atom S. In some
examples, each Q for each side chain is independently selected from
the group consisting of: --OH, i.e. a hydroxyl group, --COOH, i.e.
a carboxylic acid, SO.sub.3H, i.e. a sulphonic acid, NH.sub.2, i.e.
a primary amine, or CONH.sub.2, i.e. an amide. In specific
examples, for example those described herein, with the linker group
L including the group (OCH.sub.2CH.sub.2).sub.x--, with .sub.x
having an integer value in the range 1 to 3, the polar group Q is
--OH. Known fluoropolymers for forming a hydrophobic layer of an
electrowetting element lack any such polar groups.
[0054] In an example, the A.sub.n material has the following
formula:
R.sup.1--[(CF.sub.2CF.sub.2).sub.f(CF(OCF.sub.2CF(CF.sub.3)OCF.sub.2CF.su-
b.2COOH)CF.sub.2).sub.1-f)]--R.sup.2 which is an example of an
ionomer. Therefore, R.sup.3 is --(CF.sub.2CF.sub.2)--, i.e. a first
monomer of a polymer of the material and R.sup.4 is
--(CF(OCF.sub.2CF(CF.sub.3)OCF.sub.2CF.sub.2COOH)CF.sub.2)--, i.e.
a second monomer of the material. f represents a proportion, for
example a fraction, of the first monomers in the polymer and
therefore the proportion, for example a fraction of second monomers
in the polymer is 1-f. This example may be referred to as the
polymer with the trade name Flemion.TM. which is an example of an
ionomer and which is supplied by Asahi Glass of 1-5-1, Marunouchi,
Chiyoda-ku, Tokyo 100-8405, Japan.
[0055] Flemion.TM. is similar to the polymer with the trade name
Nafion.TM. except that in Nafion.TM. the --COOH group is instead
SOOOH. Nafion.TM. is supplied by Dupont of Wilmington, Del.,
U.S.A.
[0056] The skilled person will readily be aware how to synthesise a
material in accordance with examples described herein. For example,
Flemion.TM. may be used, suitably prepared for coating an
underlying surface of a support plate as will be explained below.
Examples of a method of synthesising a monomer of Flemion.TM., in
accordance with the journal article with reference Modern
Chlor-Alkali Technology 1992, pp 59-67, the contents of which are
included herein by way of reference, are now described:
##STR00001##
[0057] In another example, Nafion.TM. may be modified as the
skilled person will understand to substitute the --SOOOH group with
a required polar functional group, such as --COOH or --OH. In other
examples, a method similar to that used to synthesise Nafion.TM.
may be used, modified accordingly, in accordance with the skilled
person's understanding. An example of a method for synthesising a
monomer of Nafion.TM. is now described:
##STR00002##
The above illustrates the principle of the preparation of Nafion
membrane according to D. J. Connolly and W. F. Gresham, U.S. Pat.
No. 3,282,875 (1966). Further details of an example of synthesising
Nafion.TM. may be found in the journal article with reference:
Journal of New Materials for Electrochemical Systems 1, 47-66
(1998).
[0058] Another reaction which may be used to synthesise
perfluorinated monomers according to examples described herein is
now described in relation to Nafion.TM., though it is to be
appreciated that the method may be modified accordingly for
different perfluorinated monomers, as the skilled person will
understand. Reference is made to the book `Fluorinated Ionomers`,
Second Ed., Walther Gro, page 15, the contents of which is enclosed
herein. These reactions are catalysed by fluoride ions; caesium
fluoride (CsF) is preferred due to its solubility in solvents such
as diglyme, tetraglyme, acetonitrile and adiponitrile.
Tetrafluoroethane (TFE) sultone can be used for the reaction
directly or after fluoride ion catalysed ring opening, as will
become clear from the following diagrams.
##STR00003##
[0059] Another synthesis method which may be used to synthesise a
material of examples described herein, modified accordingly as the
skilled person will understand, is now given in relation to the
preparation of PFA, and is taken from the journal Applied Sciences
2012, 2, page 258:
##STR00004##
[0060] Depending on the proportions of monomers which are
polymerised to form the material, the proportions of different
types of monomers in the polymer may be controlled. For example, a
ratio of the number of R.sup.3 monomers and R.sup.4 monomers, i.e.
the ratio R.sup.3:R.sup.4 is in the range of 1:2 to 4:1. i.e. the
fraction of the number of R.sup.3/R.sup.4 may be in the range of
0.5 to 4. It is desirable to control the proportion of
substantially polar groups in the polymer molecule to for example
permit suitable application, for example spreading, of a wall
material on the material forming the layer 15.
[0061] The total number of R.sup.3 and R.sup.4 monomers in the
polymer may be controlled in dependence on the synthesis method.
For example, the polymer may have a molecular weight of 400 to
400,000 Daltons. For example, the number of monomers may be
comparable with that of Nafion.TM.. The polymerisation and
synthesis may be controlled to determine the properties of the
polymer molecules; for example, a suitable viscosity may be
necessary for the method of applying the material to an underlying
surface during manufacture. Such a viscosity may for example be a
dynamic viscosity of 125 centipoise at room temperature of 21
degrees Celsius.
[0062] However, it may be desirable that the material is not too
viscous, otherwise this may affect the ability of the molecules to
reconfigure when applying the wall material, as explained further
below.
[0063] In some examples, the material may be synthesised such that
at least some parts of the molecule and in some examples
substantially all (for example 95% or more) of the molecule is
formed by an alternating sequence of the R.sup.3 and R.sup.4
groups, for example having the following formula which may have
further sequential repetitions of the --(R.sup.3R.sup.4)-- dimer.
In other examples, the R.sup.3 and R.sup.4 monomers may not form an
alternating sequence and may instead, at least in parts, form a
random sequence.
[0064] In examples, the first terminus group is selected from the
group consisting of: H, F, or an initiating group formed by an
initiator for initiating a polymerisation reaction to form a
polymer molecule of the material. Further, in examples, the second
terminus group is selected from the group consisting of: H, F, or a
terminating group formed by a terminator for terminating a
polymerisation reaction to form a polymer molecule of the material.
An example of those groups could be pentafluoroethylene (TFE) with
the formula CF.sub.3CF.sub.2-- or heptafluoropropylene with the
formula CF.sub.3CF.sub.2CF.sub.2--.
[0065] An example of a method of manufacturing a support plate for
at least one electrowetting element will now be described with
reference to features of FIGS. 1 and 2 and also to FIG. 3. During
the manufacturing process of the display device, the first support
plate may be manufactured entirely, or may be provided during the
manufacturing process as a partly or completely assembled support
plate. When manufacturing the first support plate according to an
example the substrate 7 is provided. An electrode layer comprising
at least one electrode 17, corresponding to the first electrode
described above, is provided on the substrate 7. A material for
forming the at least one electrode is provided on a surface for
example that of the substrate and the material is patterned for
forming the at least one electrode according to a desired pattern.
Where the first electrode material is for example ITO, a plasma
enhanced chemical vapour deposition technique or a DC (direct
current) magnetron sputtering technique may be used, as the skilled
person would know.
[0066] Subsequently, the insulating layer 13, which in this example
includes the barrier layer 16 and the layer comprising the
different material, is provided on the first electrode structure.
With the barrier layer being formed of a dielectric material, in
examples, a dielectric material is provided on the material
patterned for forming the electrode, thereby forming a layer of the
dielectric material on the electrode. This providing of the
dielectric material, for example to form the barrier layer, may be
provided using Chemical Vapour Deposition (CVD) or Physical Vapour
Deposition (PVD) for example sputter deposition or electron beam
evaporation where temperature, pressure and power are controlled
appropriately, as would be understood by the skilled person. The
layer 15 comprising the different material may then be formed on a
surface of in this example the barrier layer, or in other examples
on the electrode layer, for example by applying the material for
forming the layer using for example a wet coating process such as
slit coating, flexoprinting, spin coating or dip coating as is well
known in the art. This therefore forms a layer of the material
comprising the different material on the surface of the barrier
layer in this example. The layer 15 in the examples given here is a
continuous uninterrupted layer of the first support plate common to
all picture elements.
[0067] In examples, after the layer 15 has been formed, the layer
of the different material, which is for example ionomeric, provides
a surface which is in this example is a wettability suitable for
adjoining a fluid of the electrowetting element described above,
such as the first fluid; the surface may therefore be hydrophobic.
This is for example due to an attraction of the polar groups of the
molecules being attracted to the underlying material on which the
layer of material is formed. Thus, in a region of the layer for
forming the first surface, the molecules are configured such that
at least one side chain of the molecules is orientated away from
the surface of the material layer, towards the bulk of the
material, such that the polar functional group(s) are located away
from the first surface.
[0068] At least one wall may then be formed, for example by
photolithography using a SU8 photoresist material, which would be
well known to the skilled person. More specifically, a wall
material may be spread across at least part of the surface of the
layer of the different material and then patterned using for
example photolithography with ultraviolet light applied
selectively, using a mask, to the applied wall material. After then
hard baking the patterned wall material, the patterned wall
material is developed, leaving the formed walls. In examples
described herein, the wall material is patterned so as to form at
least one wall on the second surface. Thus, a wall material may be
applied on a second surface of the layer of material, for example
an ionomeric material described herein, the second surface being a
surface on which the walls are to be formed. In examples, when
applying the wall material, a first surface of the layer of
material is also covered by the wall material, but is later removed
during the development step, which can cause the side chains to
reorientate themselves from being with the polar groups attracted
to the applied wall material to point towards the bulk of the layer
15, away from the first surface, thus providing a hydrophobic first
surface. The first surface as explained above corresponds to the
display area.
[0069] In more detail, upon applying the wall material on the
second surface, the different material, for example the ionomeric
material of examples described herein, in the underlying layer
reconfigures in a region of the layer forming the second surface to
provide the second surface with a more wettable surface to the wall
material than the first surface. Thus, after forming the at least
one wall, the second surface may be more wettable to water than the
first surface without any treatment of the surface of the layer
being necessary before applying the wall material, for example
using RIE. The reconfiguring occurs due to an attraction between
the polar functional groups of the material and the wall material
applied on the second surface. Therefore, in examples, this
attraction causes one or more further side chains of the molecules
pendant from the substantially apolar backbone to, at the second
surface, at least partly insert themselves and therefore insert the
polar functional group(s) of the pendant side chain within the wall
material applied on the second surface. This insertion of the polar
groups into the wall material in examples improves adhesion of the
wall material to the underlying layer. Moreover, the polar groups
may help to spread the wall material at least on the second
surface, due to their attraction to the wall material, thus
improving a closeness of join between the wall material and the
second surface.
[0070] After applying the wall material, the wall material when it
is a photoresist is developed using an appropriate masking and
development technique, as explained above and as the skilled person
will understand. This may require a hard baking step to harden the
wall material applied on the second surface, which hard baking may
be performed at a temperature of approximately 180 degrees Celsius.
It is noted that, compared to known techniques, it is not then
necessary to perform a reflow step at a higher temperature, since
the first surface of the layer of material is suitable for its
function in the electrowetting element upon the material having
been applied to form the layer. Thus in examples a better quality
display area is provided, for example due to not having to treat
the display area with RIE and also for example as there is
therefore no consequential contamination of the display area with
wall material. By using the different material of examples
described herein, a simpler manufacturing technique compared with
known techniques may be used.
[0071] Once the first support plate is manufactured it may be
assembled with a pre-manufactured second support plate, to assemble
one or more electrowetting elements by attaching the first and
second support plates together, for example using an adhesive seal
at an outermost perimeter of an array of the one or more
electrowetting elements, after having provided the first and second
fluids in the space to be formed between the first and second
support plates. The skilled person will readily appreciate suitable
techniques for this.
[0072] It is to be noted that the phrase "wall material" is used to
cover a material from which at least one wall is to be formed, for
example a pre-cursor wall material, a material which forms at least
one wall after a wall formation process and any intermediate
material formed during formation of at least one wall. It is also
to be appreciated that other manufacturing methods may be used to
manufacture the first support plate.
[0073] The above examples are to be understood as illustrative
examples. Further examples are envisaged. For example, although
examples are described above in relation to a display element, it
is envisaged that use of a different material as described herein,
for example an ionomeric material, may be used in other types of
electrowetting element, for example an electrowetting lens.
[0074] It is to be understood that any feature described in
relation to any one example may be used alone, or in combination
with other features described, and may also be used in combination
with one or more features of any other of the examples, or any
combination of any other of the examples. Furthermore, equivalents
and modifications not described above may also be employed without
departing from the scope of the accompanying claims.
* * * * *