U.S. patent application number 11/495213 was filed with the patent office on 2008-02-21 for multi-level layer.
This patent application is currently assigned to Hewlett-Packard Development Company LP. Invention is credited to Bradley D. Chung, Frank E. Glass, Qin Liu, John C. Rudin.
Application Number | 20080043166 11/495213 |
Document ID | / |
Family ID | 38963111 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080043166 |
Kind Code |
A1 |
Liu; Qin ; et al. |
February 21, 2008 |
Multi-level layer
Abstract
Various methods and apparatus relating to a multi-level layer
are disclosed.
Inventors: |
Liu; Qin; (Corvallis,
OR) ; Chung; Bradley D.; (Corvallis, OR) ;
Rudin; John C.; (Bristol, GB) ; Glass; Frank E.;
(Corvallis, OR) |
Correspondence
Address: |
HEWLETT PACKARD COMPANY
P O BOX 272400, 3404 E. HARMONY ROAD, INTELLECTUAL PROPERTY ADMINISTRATION
FORT COLLINS
CO
80527-2400
US
|
Assignee: |
Hewlett-Packard Development Company
LP
|
Family ID: |
38963111 |
Appl. No.: |
11/495213 |
Filed: |
July 28, 2006 |
Current U.S.
Class: |
349/56 |
Current CPC
Class: |
G02F 1/133345 20130101;
Y10T 428/31515 20150401; G02F 1/133371 20130101; G02F 2202/022
20130101 |
Class at
Publication: |
349/56 |
International
Class: |
G02F 1/1333 20060101
G02F001/1333 |
Claims
1. An apparatus comprising: a first electrode; a second electrode;
a first polymeric layer between the first electrode and the second
electrode, the first layer having portions, each portion including
a specific amount of a cross-linking agent, wherein each portion
has a distinct thickness for the specific amount of cross-linking
agent.
2. The apparatus of claim 1, wherein each set includes at least
three portions.
3. The apparatus of claim 1, wherein the first layer includes a
photo-polymer.
4. The apparatus of claim 1, wherein the first layer includes
bisphenol A epoxy resin.
5. The apparatus of claim 1, wherein the first layer includes at
least 20% by solids of bisphenol A diglycidyl ether (BADGE).
6. The apparatus of claim 1 further comprising an electro-optical
material between the first layer and the first electrode.
7. The apparatus of claim 6, wherein the first side of the first
layer includes multiple levels.
8. The apparatus of claim 6, wherein the second side of the layer
includes multiple levels.
9. The apparatus of claim 6, wherein the first layer is transparent
and wherein the first electrode element is transparent.
10. The apparatus of claim 6, wherein the first layer is
transparent and wherein the first electrode element is
reflective.
11. The apparatus of claim 6, wherein the first layer is
opaque.
12. The apparatus of claim 6 further comprising a second polymeric
layer on an opposite side of the electo-optical material as the
first polymeric layer, the second polymeric layer having second
substantially similar second sets of portions, each portion of the
second sets including a specific amount of a cross-linking agent,
wherein each portion of the second sets has a distinct thickness
for the specific amount of cross-linking agent
13. The apparatus of claim 12, wherein the second polymeric layer
includes multiple levels on the same side of the second polymeric
layer as the second electrode.
14. The apparatus of claim 12, wherein the second polymeric layer
includes multiple levels on the same side as the electro-optical
material.
15. The apparatus of claim 1, wherein at least a percentage of at
least one portion is ramped.
16. A method comprising: providing a layer of material; selectively
treating portions of the layer to form a pattern of multiple
substantially similar sets of portions, wherein each set includes
differently treated portions that exhibit different degrees of
material volatization from the layer to form different thicknesses
across the layer; and forming electrodes on opposite sides of the
layer.
17. A method comprising: providing a first layer of material;
selectively treating portions of the first layer such a differently
treated portions exhibit different degrees of material volatization
from the first layer to form a first structure having different
levels; and applying one or more second layers of one or more
materials over the levels and separating the first structure from
the one or more second layers to form a second structure having a
negative copy of the levels of the first structure.
18. The method of claim 17, wherein the levels include multiple
substantially similar sets of levels, each set including portions
having specific amounts of cross-linking agents, wherein each
portion has a distinct thickness for the specified amount of the
cross-linking agent.
19. The method of claim 17, wherein selectively treating comprises:
exposing the portions of the first layer to distinct exposure doses
of radiation; and heating the portions.
20. The method of claim 17 further comprising: providing a
substrate supporting a third layer of one or more materials; and
imprinting the third layer with the negative copy of the levels of
the first structure.
Description
CROSS-REFERENCE TO RELATED PATENT APPLICATION
[0001] The present application is related to co-pending U.S. patent
application Ser. No. 11/243,614,000 on Oct. 5, 2005 by Bradley D.
Chung et al. and entitled MULTI-LEVEL LAYER.
BACKGROUND
[0002] Applications sometimes require a layer or structure having
distinct levels or thicknesses. Existing methods for fabricating
such multiple levels require a relatively large number of process
steps, increasing fabrication costs and complexity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] FIGS. 1-4 are side elevational views schematically
illustrating one example of a method for forming a multi-level
layer according to one example embodiment.
[0004] FIG. 5A is a side elevational view schematically
illustrating an alternative method for forming the multi-level
layer of FIG. 4 according to one example embodiment.
[0005] FIG. 5B is a side elevational view schematically
illustrating another method for forming the multi-level layer of
FIG. 4 according to one example embodiment.
[0006] FIG. 6 is a graph illustrating a percent thickness change as
a function of different heating according to one example
embodiment.
[0007] FIG. 7 is a side elevational view schematically illustrating
another method for forming a multi-level layer according to one
example embodiment.
[0008] FIG. 8 is a graph illustrating the thickness of layers of
material having different levels of a monomer as a function of
radiation exposure according to one example embodiment.
[0009] FIG. 9 is a graph illustrating a percent thickness loss of a
material as a function of an added monomer according to one example
embodiment.
[0010] FIG. 10 is a top perspective view of a multi-level layer
according to one example embodiment.
[0011] FIG. 11 is a top perspective view of one set of portions of
the multi-level layer of FIG. 10 according to an example
embodiment.
[0012] FIG. 12 is a sectional view of a display pixel according to
an example embodiment.
[0013] FIG. 13 in a sectional view of another embodiment of a
display pixel according to an example embodiment.
[0014] FIG. 14 is a sectional view of another embodiment of a
display pixel according to an example embodiment.
[0015] FIG. 15 is a sectional view of another embodiment of a
display pixel according to an example embodiment.
[0016] FIG. 16 is a sectional view of another embodiment of a
display pixel according to an example embodiment.
[0017] FIG. 17 is a top plan view of another embodiment of the
multi-level layer of FIG. 10 according to an example
embodiment.
[0018] FIG. 18 is a sectional view of the multi-level layer of FIG.
17 according to an example embodiment.
[0019] FIGS. 19-22 are sectional views schematically illustrating
use of the multi-level layer of FIG. 18 to form another multi-level
layer according to an example embodiment.
[0020] FIGS. 23a-23e illustrate stages in the manufacture of a cell
wall assembly having busbars and electrode structures in a
predetermined alignment according to one example embodiment.
[0021] FIG. 24 illustrates a stage in the manufacture of a cell
wall assembly in accordance with another example embodiment.
[0022] FIG. 25 is a schematic sectional view through part of a
liquid crystal display device in accordance with another example
embodiment.
[0023] FIG. 26 is a schematic sectional view similar to that of
FIG. 25, through part of a device in accordance with another
example embodiment.
[0024] FIG. 27 is a similar view to FIG. 25, of another embodiment
of a liquid crystal display device in accordance with another
example embodiment.
DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS
[0025] FIGS. 1-4 schematically illustrate one example of a method
for forming a multi-level structure or layer 40 (shown in FIG. 4).
As shown by FIG. 1, a layer 20 of one or more materials is
initially provided. In the particular embodiment illustrated, layer
20 is formed upon substrate 22. In one embodiment, layer 20 is spun
upon substrate 22. In other embodiments, layer 20 may be deposited
or positioned adjacent to substrate 22 in other fashions.
[0026] Substrate 22 may constitute any structure configured to
support layer 20. Substrate 22 may be electrically conductive or
dielectric. Substrate 22 may be transparent, partially transmissive
or opaque.
[0027] Layer 20 constitutes one or more layers of one or more
materials configured to exhibit a loss or reduction in thickness
upon being heated. In one embodiment, layer 20 is formed from
materials configured to exhibit a loss or reduction in thickness
based at least in part upon exposure of layer 20 to radiation. In
one embodiment, layer 20 includes a material configured to exhibit
a loss of thickness based at least upon an extent to which layer 20
is heated. In the particular embodiment illustrated, layer 20
includes a material that exhibits a loss of thickness based upon
both a degree of exposure of the material to radiation and a
subsequent extent of heating of the material.
[0028] According to one embodiment, layer 20 includes a material
that exhibits a loss of thickness based upon a degree of exposure
to ultra-violet radiation. In one embodiment, layer 20 includes a
material that exhibits a loss of thickness based at least in part
upon heating of the material or layer to a temperature of at least
170 degrees Celsius. In one embodiment, layer 20 includes a
material configured to generate various amounts of at least one
cross-linking catalyst in response to being exposed to various
degrees of radiation, wherein the various amounts of cross-linking
catalysts generated results in different degrees of cross-linking
during heating such that different percentages of materials in the
layer are released, volatized or sublimed during heating.
[0029] In one embodiment, layer 20 includes a photo polymer that
generates a photo acid in response to being exposed to radiation,
such as ultra-violet radiation. In one embodiment, layer 20
includes a negative photo resist polymer. Layer 20 cross-links in
response to being heated. During such heating, one or more volatile
reactive molecules (VRMs) are released, volatized or sublimed from
the material, resulting in layer 20 exhibiting a loss of thickness.
The degree to which the VRMs are released, volatized or sublimed
from the remainder of layer 20 may vary depending upon the degree
to which the one or more VRMs are bound in the polymeric matrix as
a result of the level or degree of cross-linking. In one
embodiment, Layer 20 may include a volatile reactive molecule such
as a monomer. In one particular embodiment, layer 20 constitutes a
layer of a bisphenol-A novolac epoxy resin such as a fully
epoxidized bisphenol-A/formaldehyde novolac co-polymer combined
with an appropriate photo acid generator (one example is sometimes
referred to as SU8). One example of SU8 is: NANO SU8-5 commercially
available from MicroChem Corporation, Newton, Mass.
[0030] FIGS. 2 and 3 illustrate selectively exposing portions of
layer 20 to distinct exposure doses of radiation. As shown by FIG.
2, a first portion 24 of layer 20 is initially exposed to a first
dose 26 of radiation, such as UV radiation, while a remainder of
layer 20 remains unexposed to the dose 26 of radiation. In the
particular example illustrated, portions of layer 20 are
selectively exposed to dose 26 of radiation using a mask 28. Mask
28 is configured to substantially attenuate transmission of dose 26
of radiation. In one embodiment in which the radiation constitutes
ultra-violet radiation, mask 28 is configured to substantially
attenuate ultra-violet radiation. As a result of being exposed to
dose 26, portion 24 of layer 20 generates a cross-linking catalyst
such as photo acids 29 (schematically illustrated by hatching).
Unexposed portions of layer 20 generate little if any cross-linking
catalysts as illustrated and schematically represented by the less
dense hatching.
[0031] As shown by FIG. 3, portion 30 of layer 20 is exposed to
exposure dose 32, while portions 24 and 34 are not substantially
exposed to dose 32 of the radiation. As schematically illustrated,
dose 32 is relatively less than dose 26. In one embodiment, dose 32
may have a shorter duration. In another embodiment, dose 32 may
have a lesser intensity. As a result, portion 30 of layer 20
generates a lesser amount of one or more cross-linking catalysts
such as photo acids (as schematically represented by the lesser
dense hatching). As shown in FIG. 4, portion 34 generates little if
any cross-linking catalysts 29 (as schematically represented by the
even lesser dense hatching).
[0032] In the particular example illustrated, mask 36 is used to
substantially attenuate transmission of dose 32 of radiation to
portions 24 and 34 while permitting transmission of dose 32 to
portion 30. In other embodiments, selective exposure of layer 20 to
radiation may be performed in other manners.
[0033] As shown by FIG. 4, after selective exposure of portions of
layer 20 to radiation, such as ultra-violet radiation, layer 20 is
heated. As a result, cross-linking catalyst 29 in portions 24 and
30 (shown in FIG. 3) cause or initiate cross-linking of portions 24
and 30. As further shown by FIG. 4, a different amount of
cross-linking catalysts 29 in portions 24 and 30 result in portions
24 and 30 cross-linking to different extents as schematically
represented by the denser grid or matrix associated with portion 24
as compared to the lesser dense grid or matrix associated with
portion 30. As schematically represented by the lack of a grid or
matrix, portion 34 has an even lesser degree or extent of
cross-linking as compared to portion 30.
[0034] As further shown by FIG. 4, during heating, elements or
material 38 are released, volatized or sublimed from portions 30
and 34 to a greater extent as compared to any material that is
released, volatized or sublimed from portion 24. As shown by FIG.
4, the material or elements released, volatized or sublimed from
portion 34 exceeds that removed from portion 30. As a result,
portion 30 has a greater mass loss and reduction in thickness as
compared to portion 24. Likewise, portion 34 has a greater percent
mass loss and greater reduction in thickness as compared to portion
30. This results in the formation of distinct levels 42, 44 and 46
on portions 24, 30 and 34, respectively.
[0035] In one particular embodiment, the material 38 released,
volatized or sublimed from portions 30 and 34 constitutes a VRM
such as a monomer. In one embodiment in which layer 20 includes
SU8, material 38 constitutes bisphenol A diglycidyl ether (BADGE
monomer) in the SU8 material of layer 20. In other embodiments,
other VRMs, monomers or materials may be released, volatized or
sublimed from one or more of portions 24, 30 and 34 to form levels
42, 44 and 46.
[0036] The resulting multi-level layer 40 shown in FIG. 4 includes
distinct portions 24, 30 and 34. Each of portions 24, 30 and 34 has
a distinct level or degree of cross-linking. Each of portions 24,
30 and 34 also has a distinct remaining concentration and molecular
weight distribution of a VRM, such as a monomer material, that has
not been removed. In particular, each of portions 24, 30 and 34 may
have a distinct amount of VRM such as BADGE, remaining after the
heating step in FIG. 4. The distinct levels 42, 44 and 46 of layer
40 may serve one of several potential functions in several
applications as will be described hereafter.
[0037] FIGS. 5A and 5B illustrate alternative methods for
selectively exposing portions of layer 20 to distinct exposure
doses of radiation. FIG. 5A illustrates an alternative method of
exposing layer 20 to radiation in lieu of the steps illustrated in
steps 2 and 3. As shown in FIG. 5A, in lieu of masks 28 and 36
(shown and described with respect to FIGS. 2 and 3), mask 56 is
alternatively used to selectively expose portions of layer 20 to
distinct exposure doses of radiation. In particular, mask 56
includes portions 58, 60 and 64 which substantially correspond to
the desired size and shape of portions 24, 30 and 34 of layer 20.
Portions 58, 60 and 64 of mask 56 have distinct radiation
transmissiveness. In the particular example illustrated, portions
58, 60 and 64 are each configured to transmit different intensities
of ultra-violet radiation to layer 20. In the example shown,
portion 58 is configured to transmit the greatest intensity of UV
radiation to portion 24. Portion 60 is configured to transmit a
lesser intensity of UV radiation to portion 30. Portion 64 is
configured to transmit a level of ultra-violet radiation less than
both portions 58 and 60. In one embodiment, mask 56 constitutes a
grayscale mask such as a High Energy Beam Sensitive glass mask
commercially available from Canyon Materials, Inc., San Diego,
Calif.
[0038] As shown by FIG. 5A, mask 56 facilitates selective exposure
of portions 24, 30 and 34 with a single period of exposure of a
single dose 66 which is effectively filtered by mask 56 such that
portions 24, 30 and 34 receive distinct exposure doses 68, 70 and
substantially no dose, respectively, (as schematically illustrated
by bolts 68 and 70). Following the steps shown in FIG. 5A,
multi-level layer 40 (shown in FIG. 4) may be formed by heating
layer 20 of FIG. 5A.
[0039] FIG. 5B schematically illustrates another method of
selectively exposing portions of layer 20 to distinct exposure
doses of radiation. FIG. 5B schematically illustrates an
alternative to the step shown in FIG. 3. In particular, FIG. 5B
illustrates selectively exposing portions of layer 20 to distinct
exposure doses of radiation by varying the time of exposure that
different portions are exposed to radiation such as ultra-violet
radiation. As discussed above in FIG. 2, portion 24 of layer 20 is
exposed for a first period of time to radiation dose 26 while a
remainder of layer 20 has minimal or no exposure. As shown by FIG.
5B, in a subsequent step, portion 24 is once again exposed to dose
26 of ultra-violet radiation. However, portion 30 is also exposed
to dose 26 while portion 34 remains unexposed. In the particular
example shown, a mask 72 is utilized to expose portions 24 and 30
to radiation while substantially blocking or attenuating
transmission of UV radiation to portion 34. In other embodiments, a
single mask may be used where the mask is moved or reconfigured. In
other embodiments, the dose 26 of radiation applied to portions 24
and 30 in FIG. 5B may alternatively have a distinct intensity or
duration as compared to dose 26 that was applied in the step
illustrated in FIG. 2.
[0040] Because portion 24 is subjected to radiation for a longer
total period of time as compared to portions 30 and 34, a larger
amount of cross-linking catalysts are generated in portion 24.
Likewise, because portion 30 is exposed to a longer duration as
compared to portion 34, a greater amount of cross-linking catalysts
are generated in portion 30 as compared to portion 34. As discussed
above with respect to FIG. 4, the different levels of cross-linking
catalysts generated in portions 24, 30 and 34 result in distinct
degrees of thickness loss in portions 24, 30 and 34 to form levels
42, 44 and 46 in the finished multi-level layer 40 shown in FIG.
4.
[0041] Overall, the process or method shown in FIGS. 1-4, 5A and 5B
facilitates fabrication of a single layer of material having
multiple distinct levels with fewer individual processing steps and
at a lower cost. In particular, the method illustrated in FIGS.
1-4, 5A and 5B forms a multi-level layer 40 (shown in FIG. 4) which
utilizes a single coating process (FIG. 1). Because thickness
variations are achieved based upon different levels of
cross-linking and by volatizing materials from layer 20, developing
processes, etching processes and stripping processes may be
omitted. In addition, the described process utilizes minimal
consumables and may result in minimal process waste disposal. Using
grayscale masks, such as mask 56 shown in FIG. 5A, highly
repeatable analog changes in thickness may be achieved. In sum, the
general method described in FIGS. 1-4, 5A and 5B facilitates
low-cost fabrication of multi-level layers or structures.
[0042] FIG. 6 graphically illustrates thickness loss of a layer of
unexposed SU8 as a function of time and temperature at which the
layer was heated. As shown by FIG. 6, materials within the SU8
layer, such as a monomer BADGE, begin volatizing, subliming or
being released from the layer at a temperature of about 130
degrees. The degree to which such materials are released from the
layer to produce changes in thickness of the layer greatly
increases when the layer is heated at a temperature of at least
about 170 degrees. Heating the unexposed layer of SU8 at 250
degrees for 15 minutes yielded the greatest percent thickness loss
of the layer.
[0043] FIG. 7 schematically illustrates another method for forming
multi-level layer 40 shown in FIG. 4. As shown in FIG. 7, in lieu
of or in addition to exposing portions 24, 30 and 34 to distinct
doses of ultra-violet radiation to form distinct levels 42, 44 and
46 of layer 40 (shown in FIG. 4), portions 24, 30 and 34 may be
subjected to different amounts of heating by varying one or both of
the time and temperature at which portions 24, 30 and 34 are
heated.
[0044] In one embodiment, portions 24, 30 and 34 may be subjected
to different levels of heating using a heating device 80 which
includes an energy source 82 and one or more structures 84
(schematically illustrated) for applying different levels of heat
or different levels of energy as schematically represented by
arrows 86, 88 and 90 to portions 24, 30 and 34, respectively. In
one embodiment, energy source 82 may emit a substantially uniform
level of heat across layer 20 while structure 84 constitutes a
masking device that thermally insulates portions 24, 30 and 34 to
different extents from heat provided by the energy source 82. In
another embodiment, energy source 82 may emit distinct levels of
heat in distinct zones separated by heat shields and aligned with
portions 24, 30 and 34. In still another embodiment, heating device
80 may constitute a laser configured to selectively apply different
levels of energy to portions 24, 30 and 34 by varying the intensity
of the laser or the duration at which the laser is applied to
portions 24, 30 and 34. In one embodiment, the heat may be applied
to layer 20 without layer 20 being exposed to ultra-violet
radiation. In other embodiments, such selective heating of layer 20
may be performed after layer 20 has been exposed to ultra-violet
radiation. In embodiments in which different levels of heat or
energy are used to form different levels, an optional final two
steps of exposing of layer 20 to an unmasked dose of radiation
followed by heating of layer 20 to bind any remaining monomer into
place can be performed to substantially eliminate any further
monomer evaporation over time.
[0045] As shown in FIG. 6 above, subjecting unexposed SU8 to a
temperature of 250 degrees for about 15 minutes resulted in a 12
percent loss of overall thickness of the SU8 layer. In particular
applications, it may be beneficial to achieve greater percent
thickness losses.
[0046] FIG. 8 is a graph illustrating various thicknesses of layers
of SU8 having different amounts of added monomer, such as BADGE, as
a result of being exposed to UV radiation to different extents then
being heated at a temperature of at least 250 degrees C. for 2
minutes. In the example shown in FIG. 8, the layers are exposed to
UV light having a wavelength of 365 nanometers for different
periods of time given in milliseconds (ms). The intensity of the
light is such that energy is applied at a rate of 0.5 millijoules
per centimeter squared per millisecond. As shown by FIG. 8, for a
fixed amount of added monomer, higher exposure levels of SU8 to
ultra-violet radiation result in thicker final films after being
heated at a temperature of 250 C for at least 2 minutes. In
addition, as the amount of BADGE, as a percentage of total solids
of the SU8, is increased, the percent difference between the
thickness of two different areas subjected to fixed differences of
exposure to ultra-violet radiation and subsequently heated at the
same temperature for the same duration also increases. In
particular, it has been found that the percent thickness loss of
SU8 after being exposed and heated may be defined as follows:
L=Re.sup.-kd/(B+R)*100 where: [0047] L=percent loss of thickness;
[0048] B=a predetermined floor constant; [0049] R=a range constant;
[0050] k=a constant; and [0051] d =exposure dose
[0052] FIG. 9 graphically illustrates percentage thickness loss of
a layer of unexposed SU8 as a function of addition of a monomer
such as BADGE above the level of BADGE contained in commercially
available SU8. The level of BADGE contained in commercially
available SU8 is estimated to be between approximately 15-20
percent by mass. In the particular examples illustrated, the layer
of SU8 experienced an approximately 18 percent loss of thickness
upon being heated as compared to the same heating of the same SU8
that had been exposed to high doses of ultra-violet radiation,
where high is defined here as at least about 3000 ms. The 18
percent thickness loss exhibited by the unexposed SU8 of FIG. 8 as
compared to the approximately 12 percent thickness loss of the
unexposed SU8 of FIG. 6 is believed to be the result of the layer
of FIG. 9 being thinner, facilitating greater percentage
volatization of BADGE in the layer.
[0053] As further shown by FIG. 9, as the percent total solids of
BADGE is added to the SU8 layer, the relative percentage thickness
loss from portions of the layer that have been exposed to
approximately 3,000 ms of ultra-violet radiation as compared to
other portions of the same layer of SU8 that remain unexposed
increases. As shown by FIG. 9, the rate at which the percent
thickness loss increases is a linear function of the percent of
total solids of BADGE added to the SU8 material. As shown by FIG.
9, up to over 70 percent thickness loss may be achieved with the
addition of BADGE in the amount of approximately 60 percent of the
total solids (excluding solvents) of the SU8 layer.
[0054] Thus, as shown by FIG. 9, by adding BADGE or other monomers
to the negative resist polymer, such as SU8, percent thickness
losses may be increased to enhance height differences between
levels of a multi-level layer such as layer 40 shown in FIG. 4. In
other embodiments, in lieu of adding a VRM, such as BADGE to a
commercially available photo polymer such as SU8, materials having
appropriate concentrations of VRMs, such as monomers such as BADGE,
may be directly formed or synthesized to provide a volatile polymer
that has varying degrees of volatization upon being heated to
provide distinct thicknesses or levels.
[0055] FIGS. 10 and 11 illustrate multi-level layer 140, another
embodiment of multi-level layer 40 shown in FIG. 4. As shown by
FIG. 10, layer 140 includes a repeating pattern of groupings or
sets 141 of multiple distinct portions 124, 128, 130 and 134. As
shown by FIG. 11 which illustrates a single set 141, portions 124,
128, 130 and 134 have distinct thicknesses which results in each of
such portions having distinct levels. In particular, portions 124,
128, 130 and 134 include distinct levels 142, 144, 146 and 148,
respectively. In the example illustrated, each portion 124, 128,
130 and 134 has a specific amount of a cross-linking agent, wherein
each portion 124, 128 to 130 and 134 has a distinct thickness for
the specified amount of the cross-linking agent. Each of portions
124, 128, 130 and 134 also has a distinct remaining concentration
and molecular weight distribution of a VRM such as BADGE.
[0056] Portions 124, 128, 130 and 134 of each set 141 of layer 140
are formed according to one of the methods illustrated and
described with respect to FIGS. 1-4, 5A, 5B or 7. As a result,
layer 140 is formed utilizing a single coating process (FIG. 1).
Because such thickness variations are achieved based on different
levels of cross-linking and volatizing materials from layer 140,
developing processes, etching processes and stripping processes may
be omitted. In addition, layer 140 may be formed from a process
that utilizes minimal consumables and may result in minimal process
waste disposal. Utilizing grayscale masks, such as mask 56 shown in
FIG. 5A, highly repeatable analog changes in thickness may be
achieved. In addition, gradual sloped or ramped transitions 151
(shown in FIG. 10) between one or more of portions 124, 128, 130
and 134 may be formed. In particular embodiments, one or more of
portions 124, 128, 130 and 134 may themselves be at least
substantially ramped, sloped or tapered as shown by ramped portion
130' or 151 (shown in FIG. 10).
[0057] In the particular example illustrated, layer 140 includes a
photo polymer that generates a photo acid in response to being
exposed to radiation, such as ultra-violet radiation. In one
embodiment, layer 140 includes a negative photoresist polymer.
Layer 140 cross-links in response to being heated. During such
heating, one or more volatile reactive molecules are released,
volatizing or sublimed from the material, resulting in layer 140
further exhibiting in loss of thickness. The degree to which the
VRMs are released, volatized or sublimed from the remainder of
layer 140 may vary depending upon the degree to which the one or
more VRMs are bound in the polymer matrix as a result of the level
or degree of cross-linking. In one embodiment, layer 140 may
include a volatile reactive molecule such as a monomer. In one
embodiment, layer 140 constitutes a layer of a bisphenol-A novolac
epoxy resin such as a fully epoxidized bisphenol-A/formaldehyde
novolac co-polymer combined with an appropriate photo acid
generator (one example of which is sometimes referred to as
SU8).
[0058] In the example illustrated, levels 142, 144, 146 and 148 are
formed by applying distinct doses of ultraviolet radiation to each
of portions 124, 128, 130 and 134, respectively, prior to the
applying heat to layer 140. In one example embodiment, portioning
134 is exposed to an ultraviolet radiation dose of about 200
mJ/cm2. Portion 130 is exposed to an ultraviolet radiation dose of
about 250 mJ/cm2 which results in level 146, at its center,
extending at a height of about 71 nm above level 148 of portion
134. Portion 128 is exposed to an ultraviolet radiation dose of
about 350 mJ/cm2 which results in level 144, at its center,
extending at a height of about 194 nm above level 148 of portion
134. Portion 124 is exposed to an ultraviolet radiation dose of
about 550 mJ/cm.sup.2 which results in level 142 extending at a
height, at its center, of about 315 nm above level 148 of portion
134. In another embodiment, portions 124, 128, 130 and 134 are
exposed to appropriate levels of ultraviolet radiation such that
levels 142, 144, 146 and 148 have height variations of at least 100
nm between each level. In yet other embodiments, portions 124, 128,
130 and 134 may be exposed to other levels or doses of ultraviolet
radiation such that levels 142, 144, 146 and 148 have other
relative heights.
[0059] In further embodiments, an optional post expose bake then
develop step can be inserted immediately after exposure to
substantially remove portions that have been completely masked out
and therefore had no exposure. Subsequently, all portions can then
be heated to define the height variation that have been previously
described.
[0060] FIGS. 12-16 schematically illustrate various embodiments
including multi-level layer 140. In particular, FIGS. 12-16 are
sectional views of individual display pixels including one set 141
of multilevel layer 140 taken along line 12--12 of FIG. 11. FIG. 12
illustrates a pixel 199 of a display 200. Although layer 140 is
illustrated as including a single set 141 of portions 124, 128, 130
and 134, display 200 includes a layer 140 having a repeating
pattern of such sets 141 as shown in FIG. 10. In other embodiments,
display 200 may alternatively include a layer 140 having a single
set of portions 124, 128, 130 and 148. In yet other embodiments,
each set 141 may alternatively include greater or fewer than four
portions. In addition to multilevel layer 140, display 200 further
includes front substrate 202, electrode 204, alignment layers 206,
208, substrate 210, electrode 212, active layer 220, voltage driver
222 and controller 224.
[0061] Substrate 202 comprises one or more layers of one or more
materials serving as a base or foundation upon which electrode 204
and alignment layer 206 are formed. Front substrate 202 is formed
from an optically transparent and clear dielectric material. In one
embodiment, front substrate 202 may be formed from an optically
clear and flexible dielectric material that is birefringence free
such as polyethersulfone (PES). In other embodiments, that omit a
polarizer, transparent films or materials having birefringence such
as polyethyleneterephthalate (PET) may be employed. In other
embodiments, front substrate 202 may be formed from other
transparent dielectric materials that may be inflexible such as
glass.
[0062] Electrode 204 constitutes a layer of transparent or
translucent electrically conductive material formed upon substrate
202. Electrode 204 is configured to be charged to cooperate with
electrode 212 to create an electric field across active layer 220.
In one embodiment, electrode 204 may constitute a transparent
conductor such as indium tin oxide (ITO) or a conductive
transparent polymer such as Polyethylenedioxythiophene
polystyrenesulfonate: (PEDOT:PSS) which is commercially available
from HC Starck. In other embodiments the transparent conductive
coating may comprise other materials such as carbon nanotubes, zinc
oxide, tin oxide, zinc tin oxide, copper indium oxide, strontium
copper oxide, cadmium oxide and thin layers of metals such as Al,
Pt, Ag, Au, Cu. In other embodiments, electrode 204 may be formed
from other translucent or transparent electrically conductive
materials.
[0063] Alignment layer 206 comprises a layer of material upon
electrode 204 and in contact with active layer 220. Similarly,
alignment layer 208 comprises a layer of material overlying layer
140 and in contact with active layer 220. Alignment layers 206 and
208 cooperate to align liquid crystals of active layer 220. For
example, in those embodiments in which active layer 220 includes
twisted nematic liquid crystals, layers 206 and 208 cooperate to
align such liquid crystals in an appropriate orientation. In one
embodiment, layer 206 may comprise a rubbed polyimide having
parallel microscopic grooves in a first direction while layer 208
comprises a rubbed polyimide having parallel microscopic grooves in
a second direction orthogonal to the first direction. In other
embodiments, layers 206 and 208 may have other configurations for
aligning liquid crystals of active layer 220. In yet another
embodiment, the alignment layer may be composed of microstructures,
such as posts or grooves. In particular embodiments, layers 206 and
208 may be omitted where alignment of crystals of active layer 220
may be omitted. For example, alignment layers 206 and 208 may be
omitted in those embodiments in which active layer 220 comprises
polymer dispersed liquid crystal or the active layer is composed of
materials other than liquid crystals displays that requires
polarizers or any active layer materials which effect an optical
response.
[0064] Substrate 210 comprises one or more layers of one or more
materials configured to support electrode 212 and layer 140. In
embodiments where display 200 is a transmissive or backlit display,
substrate 210 is formed from one or more optically clear or
transparent materials. In one embodiment, substrate 210 may be
formed from an optically clear and flexible dielectric material
that is birefringence free such as polyethersulfone (PES). In other
embodiments, that omit a polarizer, transparent films or materials
having birefringence such as polyethyleneterephthalate (PET) may be
employed. In other embodiments, substrate 210 may be formed from
other transparent dielectric materials that may be inflexible such
as glass. In another embodiment where display 200 is a front lit
display, substrate 210 may be formed from one or more rigid opaque
dielectric materials.
[0065] Electrode 212 is similar to electrode 204. Electrode 212 is
configured to be charged to cooperate with electrode 204 to create
an electric field across active layer 220. In embodiments in which
display 200 comprises a backlit display, electrode 212 is formed
from one or more optically clear or transparent electrically
conductive materials such as ITO or PEDOT:PSS. In other embodiments
the transparent conductive coating may comprise other materials
such as carbon nanotubes, zinc oxide, tin oxide, zinc tin oxide,
copper indium oxide, strontium copper oxide, cadmium oxide and thin
layers of metals such as Al, Pt, Ag, Au, Cu. In embodiments where
display 200 is a front lit display, electrode 212 may be formed
from one or more transparent electrically conductive materials or
opaque electrically conductive materials. In such an embodiment,
electrode 212 may be formed from an electrically conductive
material that is also highly reflective.
[0066] Active layer 220 comprises a layer of any electro-optically
responsive material configured with alignment layers 206,208 to
change its optical behaviour in response to an applied electric
field. In one embodiment, the retardation of polarised light is
modified such that when viewed through a suitably aligned
polarising film, the display pixel can modulate the intensity of
transmitted or reflected light. In other embodiments, active layer
220 may contain re-orientable dichroic dye molecules or pigments
such that transmitted or reflected light is modulated without the
need for external polarizing elements. In further embodiments,
active layer 220 may modulate the scattering of incident light by
means of polymer dispersed liquid crystals. In yet further
embodiments, active layer 220 may modulate the spectral content
(i.e. color) of incident light. In still other embodiments, layer
220 may comprise other presently developed or future developed
materials configured to selectively block, absorb or attenuate
light
[0067] In one embodiment the electro-optical effect or state of
layer 220 has a optical threshold, and in a further example
embodiment, the electro-optical effect of layer 220 has state
memory (i.e. bistability) with a distinct threshold field level. By
this means, when a voltage is applied between electrodes 204, 212,
areas of the pixel which receive a field strength higher than the
memory threshold will change state, whereas areas which receive a
lower field will not. By design of the areas and thickness of the
structures 140, spatial greytone may be generated. This is
particularly beneficial to electro-optical effects or states which
have a distinct optical threshold such as, but not limted to,
ferroelectric liquid crystal, bistable nematic liquid crystal,
cholesteric texture liquid crystal, viologen based electro-chromic,
MEMS or micro-fluidic devices.
[0068] Active layer 220 extends between electrodes 204 and 212.
Active layer 220 includes regions 234, 238, 240 and 244. Regions
234, 238, 240 and 244 extend opposite to portions 124, 128, 130 and
134 of layer 140, respectively. Because layer 140 is a dielectric
material and because portions 124, 128, 130 and 134 have differing
thicknesses, regions 234-244 experience different electric fields
having different strengths even though a common voltage is created
between electrodes 204 and 212. As a result, regions 234-244 will
change between different electro-optical effects including but not
limited to different light attenuating states or different
wavelength absorbing states at different times or in response to
different voltages created between electrodes 204 and 212.
[0069] For example, because portion 134 has the smallest thickness,
region 244 experiences the strongest electrical field for a given
voltage between electrodes 204 and 212. As a result, region 244
will change between different electro-optical effects or states at
a lower voltage between electrodes 204, 212 as compared to regions
234-240. Similarly, region 240 will change at a lower voltage as
compared to regions 238 and 234 and region 238 will change at a
lower voltage as compared to region 234. Thus, the multiple
distinct thicknesses of layer 140 enable distinct regions of active
layer 220 and the associated pixel of display 200 to be selectively
actuated between different electro-optical states based upon the
voltage applied across electrodes 204 and 212 by both driver 222
and controller 224. The selective actuation of regions 234-244 may
be achieved without electrical switching elements provided for each
of regions 234-244, reducing the cost and complexity of display
200.
[0070] Voltage driver 222 comprises one or more devices or
structures configured to selectively apply voltages across the
electrodes 204 and 212 to control an electric field created across
active layer 220. In one embodiment, driver 222 may comprise one or
more voltage sources and one or more electrical switching elements,
such as transistors, metal-insulator-metal devices, diodes and the
like. Such electrical switching elements may be arranged as part of
an active-matrix control, wherein the electrical switching elements
are proximate each of the pixels or sets 141 or a passive control,
wherein the electrical switching elements are grouped together
distant the pixels or sets 141.
[0071] Controller 224 comprises a processing unit configured to
generate control signals based upon desired images to be displayed
by display 200, wherein driver 222, in response to such control
signals, creates appropriate voltages between electrodes 204 and
212 and across active layer 220. For purposes of this application,
the term "processing unit" shall mean a presently developed or
future developed processing unit that executes sequences of
instructions contained in a memory. Execution of the sequences of
instructions causes the processing unit to perform steps such as
generating control signals. The instructions may be loaded in a
random access memory (RAM) for execution by the processing unit
from a read only memory (ROM), a mass storage device, or some other
persistent storage. In other embodiments, hard wired circuitry may
be used in place of or in combination with software instructions to
implement the functions described. Controller 224 is not limited to
any specific combination of hardware circuitry and software, nor to
any particular source for the instructions executed by the
processing unit.
[0072] In operation, controller 224 generates control signals based
upon an image to be displayed by display 200. In response to such
control signals, driver 222 establishes a desired voltage across
electrodes 204 and 212 to selectively control how many of regions
234, 238, 240 and 244 of one or more sets 141 are actuated between
different light attenuating or absorbing states. For example, for a
particular pixel of display 200 having a particular set 141 of
portions of layer 140, a first voltage may be applied across
electrodes 204 and 212 to actuate region 244 while regions 234, 238
and 240 remain unactuated. To additionally actuate region 240 of
active layer 220, a larger voltage may be applied across electrodes
204 and 212. Likewise, even larger voltages may be applied across
electrodes 204 and 212 to additionally selectively actuate regions
238 and 234.
[0073] FIG. 13 schematically illustrates a single pixel 299 of
display 300, another embodiment of display 200. Pixel 299 is
similar to pixel 199 except that pixel 299 includes substrate 302,
adhesive 303, electrode 304 and active layer 320 in lieu of
substrate 202, electrode 204 and active layer 220, respectively,
omits alignment layers 206, 208 and additionally includes light
altering layer 314. Those remaining elements of pixel 299 and
display 300 which correspond to pixel 199 and display 200 are
numbered similarly.
[0074] Substrate 302 is similar to substrate 202 except that
substrate 302 supports layer 140 and electrode 304 which are joined
to substrate by adhesive layer 303. Like substrate 202, substrate
302 is formed from one or more layers of one or more optically
clear or transparent dielectric materials. In one embodiment,
substrate 302 may comprise an optically clear and flexible
dielectric material that is birefringence free such as
polyethersulfone (PES). In other embodiments, that omit a
polarizer, transparent films or materials having birefringence such
as polyethyleneterephthalate (PET) may be employed. In other
embodiments, substrate 302 may be formed from other transparent
dielectric materials that may be inflexible such as glass.
[0075] Adhesive layer 303 comprises a transparent adhesive. In one
embodiment, the adhesive may comprise a UV-curable material such as
NOA81 (Norland Optical Products), but alternatively may be thermal
or moisture cured.
[0076] Electrode 304 is similar to electrode 204 except that
electrode 304 is stepped as it extends over portions 124, 128, 130
and 134 of layer 140. Like electrode 204, electrode 304 is formed
from an optically clear or transparent electrically conductive
material. In one embodiment, electrode 304 may comprise a
transparent conductor such as ITO or PEDOT:PSS. In other
embodiments the transparent conductive coating may comprise other
materials such as carbon nanotubes, zinc oxide, tin oxide, zinc tin
oxide, copper indium oxide, strontium copper oxide, cadmium oxide
and thin layers of metals such as Al, Pt, Ag, Au, Cu. In other
embodiments, electrode 304 may be formed from other translucent or
transparent electrically conductive materials.
[0077] Active layer 320 comprises a layer of optical charge
responsive material configured to change from a transparent state,
allowing light to pass through active layer 320, to a generally
opaque state in which light is absorbed or otherwise attenuated by
layer 320 in response to changes in an applied voltage or charge.
In the particular example illustrated, active layer 320 comprises a
polymer-dispersed liquid crystal, permitting alignment layers 206,
208 (shown in FIG. 12) to be omitted. In other embodiments, active
layer 320 may comprise other optical charge responsive materials.
For example, active layer 320 may comprise a nematic liquid
crystal, wherein display 300 additionally includes alignment layers
206 and 208 (shown in FIG. 12). Like layer 220, layer 320 includes
regions 234, 238, 240 and 244 generally opposite to portions 124,
128, 130 and 134 of layer 140. As a result of the different
thicknesses of portions 124, 128, 130 and 134 spacing electrode 304
from active layer 320, regions 234, 238, 240 and 244 actuate or
change between different light attenuating states in response to
different applied voltages created between electrodes 304 and
212.
[0078] Light altering layer 314 comprises one or more layers of one
or more materials configured to alter or change light prior to or
after the transition of light across active layer 320. In one
embodiment in which display 300 comprises a backlit display, layer
314 may comprise a light filtering layer configured to filter
selected wavelengths of light. In such an embodiment, layer 314 may
include distinct portions 344, 348, 350 and 354 opposite to regions
234, 238, 240 and 244, respectively. Each portion 344-354 may be
configured to filter a different range of wavelengths of light. For
example, region 344 may filter red light, 348 may filter blue
light, region 350 may filter green light and region 354 may block
or reflect all light or filter other wavelengths of light. In other
embodiments in which displays 300 comprises a front lit display,
layer 314 may be configured to reflect selected wavelengths of
light or may be configured to reflect substantially all wavelengths
of light. In one embodiment, portions 344-354 of layer 314 may each
be configured to reflect different ranges of wavelengths of light.
In yet other embodiments, layer 314 may be configured to filter or
reflect a single color of light, wherein adjacent pixels have
layers 314 that filter or reflect other colors of light. For
example, in one embodiment, layer 314 may filter (in the case of a
backlit display) or reflect (in the case of a front lit display)
red light. Adjacent pixels may have layers 314 that filter or
reflect green light or blue light. In some embodiments, portions
344-354 may alternatively be configured to reflect the same
wavelengths of light. For example, in another embodiment,
substantially all of layer 314 may be white. In yet other
embodiments, layer 314 may be omitted.
[0079] FIG. 14 schematically illustrates one pixel 399 of display
400, another embodiment of display 200. Display 400 is similar to
display 200 (shown in FIG. 12) except that display 400 omits
alignment layers 206, 208, includes active layer 420 in lieu of
active layer 220 and additionally includes layer 440 and light
altering layer 314 (described above with respect to FIG. 13). Those
remaining elements of display 400 which correspond to elements of
display 200 are numbered similarly. Active layer 420 is similar to
active layer 320 of display 300 (shown and described with respect
to FIG. 13). In the example illustrated, active layer 420 comprises
a polymer-dispersed liquid crystal, permitting alignment layers 206
and 208 to be omitted. In other embodiments, active layer 420 may
comprise other materials configured to change between different
light attenuating or light absorbing states in response to
different electric fields. For example, in other embodiments,
active layer 420 may comprise other liquid crystals. In those
environments in which active layer 420 includes liquid crystals
that should be aligned, such as twisted nematic crystals, display
400 may additionally include alignment layers 206, 208 as described
above with respect to FIG. 12.
[0080] Active layer 420 includes regions 444, 448, 450 and 454.
Regions 444, 448, 450 and 454 experience different electrical
fields as a result of layers 140 and 440. Consequently, regions
444, 448, 450 and 454 change between different light attenuating or
light absorbing states at different times in response to different
voltages applied across electrodes 204 and 212.
[0081] Layer 440 is substantially similar to layer 140. Layer 440
is supported by substrate 202 and extends between electrode 204 and
active layer 420. Layer 440 is formed according to one of the
methods described above with respect to FIGS. 1-4, 5A, 5B or FIG.
7. As shown by FIG. 14, layer 440 includes distinct portions 464,
468, 470 and 474 which have different thicknesses and which extend
opposite to portions 124, 128, 130 and 134 of layer 140,
respectively.
[0082] Like layer 140, layer 440 controls the strength of the
electrical field experienced by active layer 420 even though a
common voltage is created between electrodes 204 and 212. As a
result, regions 444-454 will change between different light
attenuating states or wavelength absorbing states at different
times or in response to different voltages created between
electrodes 204 and 212. For example, because portion 474 has the
smallest thickness, region 454 experiences the strongest electrical
field for a given voltage between electrodes 204 and 212. As a
result, region 454 will change between different light attenuating
or absorbing states at a lower voltage between electrodes 204, 212
as compared to regions 444-450. Similarly, region 450 will change
at a lower voltage as compared to regions 444 and 448 and region
448 will change at a lower voltage as compared to region 444. Thus,
the multiple distinct thicknesses of layer 440 enable distinct
regions of active layer 420 and the associated pixel of display 400
to be selectively actuated between different light absorbing or
light attenuating states based upon the voltage applied across
electrodes 204 and 212 by both driver 222 and controller 224.
Because display 400 includes both layers 140 and 440, greater
electrical field variations between electrodes 204 and 212 may be
achieved, permitting selective actuation of regions 444-454 with
less costly and less precise voltage control. In addition, the
greater electric field variations facilitate the addition of more
selectively actuatable regions of active layer 420. The selective
actuation of regions 444-454 may be achieved without electrical
switching elements provided for each of regions 444-454, reducing
the cost and complexity of display 400.
[0083] FIG. 15 schematically illustrates an individual pixel 499 of
display 500, another embodiment of display 200. Display 500 is
substantially similar to display 400 except that display 500
includes substrate 510, adhesive layer 511, electrode 512 and
multi-level layer 540 in lieu of substrate 210, electrode 212 and
layer 140, respectively. Those remaining elements of display 500
which correspond to elements of display 400 are numbered similarly.
Like substrate 210, substrate 510 is formed from one or more layers
of one or more optically clear or transparent dielectric materials.
In one embodiment, substrate 510 may be formed from an optically
clear and flexible dielectric material that is birefringence free
such as polyethersulfone (PES). In other embodiments, that omit a
polarizer, transparent films or materials having birefringence such
as polyethyleneterephthalate (PET) may be employed. In other
embodiments, substrate 510 may be formed from other transparent
dielectric materials that may be inflexible such as glass. In yet
other embodiments in which display 500 is a front-lit display,
substrate 510 may be formed from an opaque or reflective dielectric
material.
[0084] Adhesive layer 511 connects and spaces electrode 512 and
substrate 510. Adhesive layer 511 comprises a transparent adhesive.
In one embodiment, the adhesive may comprise a UV-curable material
such as NOA81 (Norland Optical Products), but alternatively may be
thermal or moisture cured.
[0085] Electrode 512 is similar to electrode 212 except that
electrode 512 is stepped as it extends over portions 124, 128, 130
and 134 of layer 140. Like electrode 212, electrode 512 is formed
from an optically clear or transparent a likely conductive
material. In one embodiment, electrode 512 may constitute a
transparent conductor such as ITO or PEDOT:PSS. In other
embodiments the transparent conductive coating may comprise other
materials such as carbon nanotubes, zinc oxide, tin oxide, zinc tin
oxide, copper indium oxide, strontium copper oxide, cadmium oxide
and thin layers of metals such as Al, Pt, Ag, Au, Cu. In other
embodiments, electrode 512 may be formed from other translucent or
transparent electrically conductive materials. In still other
embodiments in which display 500 comprises a front-lit display,
electrode 512 may be formed from reflective or opaque electrically
conductive materials.
[0086] Layer 540 is substantially identical to layer 140 except
that layer 540 is inverted. Layer 540 includes portions 124, 128,
130 and 134 which extend opposite to portions 464, 468, 470 and 474
of layer 440. The differing thicknesses of portions 124, 128, 130
and 134 result in active layer 420 experiencing different electric
field strengths for a single given voltage between electrode 204
and electrode 512. As a result, regions 444-454 of active layer 420
may be selectively actuated between states by controlling the
voltage across electrodes 204 and 512.
[0087] FIG. 16 schematically illustrates pixel 599 of display 600,
another embodiment of display 200 (shown and described with respect
to FIG. 12). Display 600 is substantially similar to display 500 of
FIG. 15 except that display 600 includes substrate 602, adhesive
layer 603, electrode 604 and multi-level layer 640 in lieu of
substrate 202, electrode 204 and layer 440, respectively. Those
remaining elements of display 600 which correspond to elements of
display 500 are numbered similarly. Like substrate 202, substrate
602 is formed from one or more layers of one or more optically
clear or transparent dielectric materials. In one embodiment,
substrate 602 may be formed from an optically clear and flexible
dielectric material that is birefringence free such as
polyethersulfone (PES). In other embodiments, that omit a
polarizer, transparent films or materials having birefringence such
as polyethyleneterephthalate (PET) may be employed. In other
embodiments, substrate 602 may be formed from other transparent
dielectric materials that may be inflexible such as glass.
[0088] Adhesive layer 603 connects and spaces electrode 604 and
substrate 602. Adhesive layer 603 comprises a transparent adhesive.
In one embodiment, the adhesive may comprise a UV-curable material
such as NOA81 (Norland Optical Products), but alternatively may be
thermal or moisture cured.
[0089] Electrode 604 is similar to electrode 204 except that
electrode 604 is stepped as it extends over portions 464, 468, 470
and 474 of layer 640. Like electrode 204, electrode 604 is formed
from an optically clear or transparent a likely conductive
material. In one embodiment, electrode 604 may constitute a
transparent conductor such as ITO or PEDOT:PSS. In other
embodiments the transparent conductive coating may comprise other
materials such as zinc oxide, tin oxide, zinc tin oxide, copper
indium oxide, strontium copper oxide, cadmium oxide, carbon
nanotubes and thin layers of metals such as Al, Pt, Ag, Au, Cu. In
other embodiments, electrode 604 may be formed from other
translucent or transparent electrically conductive materials
[0090] Layer 640 is substantially identical to layer 440 except
that layer 640 is inverted. Layer 640 includes portions 464, 468,
470 and 474 which extend opposite to portions 124, 128, 130 and 134
of layer 540. The differing thicknesses of portions 464, 468, 470
and 474 result in active layer 420 experiencing different electric
field strengths for a single given voltage between electrode 604
and electrode 512. As a result, regions 444-454 of active layer 420
may be selectively actuated between states by controlling the
voltage across electrodes 604 and 512. In addition, because layer
420 has a substantially uniform thickness over the area of all the
pixies 600, improved performance and manufacturing efficiencies may
result.
[0091] FIGS. 17 and 18 illustrate multi-level layer 740, another
embodiment of multi-level layer 140. Multi-level layer 740 is
similar to layer 140 except that layer 140 includes a repeating
pattern of sets 741 of portions 724, 728, 730 and 734. Portion 724,
728, 730 and 734 are similar to portions 124, 128, 130 and 134 of
layer 140, respectively, except that portion 734 comprises the
floor of layer 740 extending between adjacent sets 741, that
portions of 724, 728 and 730 are stacked upon one another so as to
extend outwardly beyond one another and that portions 724, 728 and
730 are circular.
[0092] Like portions 124, 128 and 130 and 134, portion 724, 724,
730 and 734 have distinct thicknesses. In particular, each portion
724, 728, 730 and 734 has a specific amount of a cross-linking
agent, wherein each portion 724, 728, 730 and 734 has a distinct
thickness for the specified amount of the cross-linking agent. Each
of portions 724, 728, 730 and 734 also has a distinct remaining
concentration and molecular weight distribution of a VRM such as
BADGE.
[0093] Portions 724, 728, 730 and 734 of each set 741 of layer 740
are formed according to one of the methods illustrated and
described with respect to FIGS. 1-4, 5A, 5B or 7. As a result,
layer 740 is formed utilizing a single coating process (FIG. 1).
Because such thickness variations are achieved based on different
levels of cross-linking and volatizing materials from layer 740,
developing processes, etching processes and stripping processes may
be omitted.
[0094] Although portions 724, 728, 730 and 734 are illustrated as
being circular, in other embodiments, portions 724, 728 and 730 may
alternatively be square, rectangle or, triangular or have other
shapes. Although portions 724, 728 and 730 are illustrated as
having a common shape, in other embodiments, such portions may have
differing shapes from one another. Although each set 741 is
illustrated as having four distinct portions or levels, in other
embodiments, each set 741 may include greater or fewer number of
such portions.
[0095] FIGS. 19-22 illustrate the formation of a multi-level layer
840 (shown in FIG. 22) using multi-level layer 740 (shown in FIG.
18). As shown by FIG. 19, after layer 740 is formed, a layer 760 of
polymeric material is formed over layer 740. Layer 760 may comprise
a UV, thermal or moisture curable material. In other embodiments,
layer 760 may comprise one or more other polymeric materials.
[0096] As shown by FIG. 20, upon solidification or curing of layer
760, layer 760 is separated from layer 740. As shown by FIG. 21, a
layer 764 of dielectric material is formed upon a dielectric
substrate 766. Thereafter, layer 760 is imprinted or embossed
against layer 764 to form multi-level layer 840 upon substrate 766.
As shown by FIG. 22, upon solidification or curing of the imprinted
layer 764, layer 760 (shown in FIG. 21) is separated from layer 764
to produce multi-level layer 840. Multi-level layer 840 may be used
in lieu of layers 140, 440 and 540 in displays 200, 300, 400 and
500 as described above. Layer 760 may also be used for forming
additional multilevel layers 840. In such an embodiment, layer 764
and multilevel layer 840 may be formed from various dielectric
materials.
[0097] According to one embodiment, layer 764 comprises a layer of
a bisphenol-A novolac epoxy resin such as a fully epoxidized
bisphenol-A/formaldehyde novolac co-polymer combined with an
appropriate photo acid generator (an example of which is sometimes
referred to as SU8). In such an embodiment, layer 760 is formed
from one or more UV radiation transmitting materials, wherein layer
764, while imprinted by layer 760, is exposed to ultraviolet
radiation passing through layer 760. In particular embodiments,
layer 764 may be provided with appropriate levels of BADGE and
distinct portions 824, 828, 830 and 834 of layer 764 being
imprinted by layer 760 may be exposed to different doses of
ultraviolet radiation through layer 760 such that portions 824-834
undergo different degrees of cross-linking and underground
different degrees of volatization upon being subsequently heated so
as to enlarge thickness differences between portions 824, 828, 830
and 834 of the resulting multilevel layer 840.
[0098] FIGS. 23a-23e illustrate a method for forming a pixel 999 of
a display 1000 (shown in FIG. 25). A transfer carrier 901 is shown
in FIG. 23a. The carrier 901 comprises a base film 902 on which is
coated a planar conductive layer 903. The carrier 901 may be rigid
or flexible. In this example, the base film 902 comprises 150 .mu.m
thick PET and the conductive layer 903 is copper metal of about 1
.mu.m thickness. In this example, the copper layer 903 is optically
flat and has been passivated by immersion in 0.1 N potassium
dichromate solution for 5 minutes, rinsed with deionised water and
air-dried. Alternatively, the base film may itself be a
conductor.
[0099] Multi-level layer 740 (described above) is formed on the
surface of the conductive layer 903 A trench 906 is formed in layer
740. If necessary, the trench 906 is plasma-etched to remove
polymer from the bottom of the trench 906. Metal, in this example
nickel, is then electroplated into the trench 906 to form a busbar
908 (FIG. 23b). In one embodiment, the conductor 903 forms the
cathode of an electrolytic cell with a nickel anode and a nickel
sulphamate-based electrolyte. Plating may be carried out with DC,
with pulsed or biased AC current used to fill in the trenches 906
completely. Other existing electroplating or electroless plating
techniques may be employed. Suitable metals include nickel, copper
and gold. The busbars 908 are linear structures which will run
across the length or width of the display substrate (cell wall) to
which they are transferred. They are typically about 100 .mu.m
apart and up to many metres in length. The busbars 908 are about
5.times.5 .mu.m is cross-section and have a low resistance that in
use will apply an applied voltage evenly across the device. The
metal of the busbar 908 is opaque but it is small enough not to
reduce the aperture to a large extent.
[0100] To form electrode structures, a transparent conductor 910 is
deposited onto the multi-level layer 740 and busbars 908, as
illustrated in FIG. 23c. The conductor 910 may comprise indium
oxide, tin oxide, indium tin oxide (ITO) or the like, but is
preferably an organic conductor such as PEDOT:PSS (HC Starck
Baytron P), which may be applied by a printing technique such as
inkjet printing. The transparent conductor is then selectively
etched or bleached to provide transparent electrodes 910. Standard
photolithographic techniques can be used to prevent the conductor
contacting more than one busbar 908. In the preferred embodiment,
PEDOT:PSS is selectively bleached by UV light to form the electrode
structures. Alternatively, standard photoresists and etching or
chemical deactivation may be employed.
[0101] It will be understood that, for simplicity, only a single
multi-level layer 740, busbar 908 and electrode track 910 are
shown. A plurality of similar dielectric structures, busbars and
electrode structures will be formed, each electrode structure 910
typically comprising one of a series of parallel row or column
electrodes.
[0102] After forming the electrode structures 910, the resulting
structure is treated with a transparent adhesive 914 and the final
display substrate 912 is laminated and the adhesive 914 is cured
(FIG. 23d). In a preferred embodiment the adhesive 914 is a
UV-curable material such as NOA81 (Norland Optical Products) but
may be thermal- or moisture-cured. The display substrate 912 is
preferably a plastics material, for example, ZF-16 by Zeon
Chemical, PEN (DuPont Teijin Teonex Q65), PES (Sumitomo Bakelite)
or polyArylate (Ferrania SpA--Arylite), but could comprise glass,
preferably a UV-translucent glass.
[0103] The adhesions in the assembly shown in FIG. 23d are tuned
such that when the transfer carrier 901 is peeled off, the adhesion
breaks at the surface of the conducting carrier substrate 903. The
whole of the rest of the structure remains adhered to the display
substrate 912, as illustrated in the cell wall assembly 905 of FIG.
23e. This surface is flat so that the resulting LC layer will be a
constant thickness. The electrode structures 910, however, are
embedded at different distances from the cell wall 912. The
distances are set by the heights or thicknesses of portions 724,
728, 730 and 734 of layer 740 (now a dielectric covering layer for
the electrode structures 910).
[0104] In this embodiment, one of the layer 740 is the full
thickness of the busbar 908. It may be desirable to make the steps
less than the full thickness of the busbar 908 to avoid increasing
the switching threshold too much. The width of the step could be
kept small to minimise the non-switching region. Alternatively, the
initial trench 906 may be made somewhat shallower and the metal may
be overplated to form a busbar 908 that extends beyond the
dielectric structures 904 as illustrated in FIG. 24.
[0105] FIG. 25 ilustrates a display device 1000 having a pixel 999
with greyscale capability Pixel 999 comprises the cell wall
assembly 905 of FIG. 23e, including a first cell wall 912a and
first electrode structures 910a, formed as previously described and
in ohmic contact with the busbar 908. The pixel 999 in this example
is a liquid crystal display device and has a layer of electro-optic
material 920 which comprises a nematic LC. A first surface
alignment 918a is provided on the innermost surface of the cell
wall assembly 905. The surface alignment 918a in this example
comprises a PABN surface textured with posts to provide bistable
alignment to adjacent molecules of the nematic LC material 920.
Other bistable alignments could be used, or conventional alignment
materials such as rubbed polyimide if the display is monostable,
for example a supertwist or HAN cell.
[0106] A second cell wall 912b is of conventional construction,
being formed from a flat glass or plastics material and having
second electrode structures 910b formed thereon by a conventional
etch technique using ITO. A second surface alignment 918b is
provided on the second electrode structures 910b, in this example
inducing homeotropic alignment in adjacent LC molecules. Means for
distinguishing between different optical states are provided, in
this example polarisers 916 which are adhered to the outer surfaces
of the cell walls 912. It will be understood that surface
alignments 918 could be transposed; ie the PABN surface alignment
could be provided on the innermost surface of the second cell wall
and the homeotropic surface alignment could be provided on the
first cell wall assembly 905. The second cell wall 912b may be
spaced apart from the first cell wall assembly 905 by conventional
spacing means (not shown) for example microbeads or pieces of glass
fibre or polymer fibre. Suitable spacing means are well known to
those skilled in the art of LCD manufacture.
[0107] The inner surfaces of both cell walls 912 are substantially
planar and parallel to each other, and the layer of nematic LC
material 920 is of substantially constant thickness. The shortest
distance between the LC material 920 and one of the first electrode
structures 910a varies within the area of the pixel illustrated in
FIG. 25. Above a maximum threshold voltage all of the visible pixel
area is in an `on` state. For a bistable display, when the voltage
is reduced or removed the pixel remains in the `on` state. To
switch the pixel to an `off` state, a suitable pulse is
applied.
[0108] FIG. 26 illustrates pixel 999', another embodiment of pixel
999. The display pixel 999' of FIG. 26 is similar to that of FIG.
25 except that the second cell wall assembly 905b is constructed
similarly to that of the first cell wall assembly 905a. Multi-level
layer 740 separates the second electrode structures 910b from the
LC 920. The second cell wall assembly 905b may be constructed by a
similar transfer method to that used to make the first cell wall
assembly 905a. The transparent adhesive 914b of the second cell
wall assembly 905b may be formed of the same adhesive material as
the transparent adhesive 914a of the first cell wall assembly. In
this arrangement, the shortest distance between the LC material 920
and one of the first electrode structures 910a varies within the
area of the pixel, as does the shortest distance between the LC
material 920 and one of the second multi-level layer 740b. In this
arrangement the cell may be symmetrical in a plane through the LC
layer 920 parallel to the cell walls 912 and may be more easily
constructed because the electrode variation may be shared between
the two cell wall assemblies.
[0109] FIG. 27 illustrates pixel 999'', another embodiment of pixel
999 in which the polariser 916 on the upper cell wall 912a is
provided on an inner surface, in this example between the first
cell wall 912a and the adhesive 914, so that birefringence of the
first cell wall 912a does not affect the display appearance. The
switching voltage differs according to the shortest distance of the
electrode structure 910a and the LC molecules 920. Each Multi-level
layer 740 increases the switching threshold voltage. In order to
switch the LC between stable states the electric field applied
across the LC has to exceed a threshold. By putting the dielectric
step between the electrode and the LC the electric field
experienced by the LC will be reduced. Thus the applied voltage
needed to switch the LC can be controlled by varying the thickness
of the steps. In the illustration in FIG. 25, sufficient voltage
has been applied via electrode structures 910a and 910b to align LC
molecules 920a, in the outer regions, in the `on` state. The
applied voltage was insufficient to switch LC molecules 920b, in
inner regions, from the `off` state. Increasing the amplitude of a
switching pulse will cause more of the steps to switch and hence
increase the proportion of the device that switches into one of the
two states, ultimately reaching a fully-switched state as
illustrated in FIG. 25. The eye averages the areas of the pixel
that are in each state to give a perceived grey level. LC molecules
under the busbar 908 in FIG. 27 are switched, but are not visible
under the opaque busbar. The busbar is narrow (about 5 .mu.m) so is
not readily visible.
[0110] Although the present disclosure has been described with
reference to example embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the claimed subject matter.
For example, although different example embodiments may have been
described as including one or more features providing one or more
benefits, it is contemplated that the described features may be
interchanged with one another or alternatively be combined with one
another in the described example embodiments or in other
alternative embodiments. Because the technology of the present
disclosure is relatively complex, not all changes in the technology
are foreseeable. The present disclosure described with reference to
the example embodiments and set forth in the following claims is
manifestly intended to be as broad as possible. For example, unless
specifically otherwise noted, the claims reciting a single
particular element also encompass a plurality of such particular
elements.
* * * * *