U.S. patent application number 17/369301 was filed with the patent office on 2022-01-13 for anti-glare substrate for a display article including a textured region with primary surface features and secondary surface features imparting a surface roughness that increases surface scattering.
The applicant listed for this patent is Corning Incorporated. Invention is credited to Jiangwei Feng, Corinne Elizabeth Isaac, Shenping Li, Wageesha Senaratne, William Allen Wood.
Application Number | 20220009824 17/369301 |
Document ID | / |
Family ID | 1000005751234 |
Filed Date | 2022-01-13 |
United States Patent
Application |
20220009824 |
Kind Code |
A1 |
Feng; Jiangwei ; et
al. |
January 13, 2022 |
ANTI-GLARE SUBSTRATE FOR A DISPLAY ARTICLE INCLUDING A TEXTURED
REGION WITH PRIMARY SURFACE FEATURES AND SECONDARY SURFACE FEATURES
IMPARTING A SURFACE ROUGHNESS THAT INCREASES SURFACE SCATTERING
Abstract
A substrate for a display article is described herein that
includes (a) a primary surface; and (b) a textured region on at
least a portion of the primary surface; the textured region
comprising: (i) primary surface features, each comprising a
perimeter parallel to a base-plane extending through the substrate
disposed below the textured region, wherein the perimeter of each
of the primary surface features comprises a longest dimension of at
least 5 .mu.m; and (ii) one or more sections each comprising
secondary surface features having a surface roughness (R.sub.a)
within a range of 5 nm to 100 nm. In some instances, an arrangement
of the surface features reflect a random distribution. A method of
forming the same is disclosed.
Inventors: |
Feng; Jiangwei; (Painted
Post, NY) ; Isaac; Corinne Elizabeth; (Horseheads,
NY) ; Li; Shenping; (Painted Post, NY) ;
Senaratne; Wageesha; (Horseheads, NY) ; Wood; William
Allen; (Painted Post, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Corning Incorporated |
Corning |
NY |
US |
|
|
Family ID: |
1000005751234 |
Appl. No.: |
17/369301 |
Filed: |
July 7, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
63049843 |
Jul 9, 2020 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03C 15/00 20130101;
G02B 2207/101 20130101; G02B 1/118 20130101 |
International
Class: |
C03C 15/00 20060101
C03C015/00; G02B 1/118 20060101 G02B001/118 |
Claims
1. A substrate for a display article, the substrate comprising: a
primary surface; and a textured region on at least a portion of the
primary surface; the textured region comprising: primary surface
features, each comprising a perimeter parallel to a base-plane
extending through the substrate disposed below the textured region,
wherein the perimeter of each of the primary surface features
comprises a longest dimension of at least 5 .mu.m; and one or more
sections each comprising secondary surface features having a
surface roughness (R.sub.a) within a range of 5 nm to 100 nm.
2. The substrate of claim 1, wherein the primary surface features
form a pattern.
3. The substrate of claim 1, wherein the longest dimension of each
of the primary surface features is about the same.
4. The substrate of claim 1, wherein an arrangement of the surface
features reflect a random distribution.
5. The substrate of claim 1, wherein the perimeter of each primary
surface features is elliptical.
6. The substrate of claim 1, wherein the perimeter of each primary
surface features is circular.
7. The substrate of claim 1, wherein each primary surface feature
provides a surface, and the surface is either concave or
convex.
8. The substrate of claim 1, wherein the textured region further
comprises: a surrounding portion into which the primary surface
features are set or out of which the primary surface features
project.
9. The substrate of claim 1, wherein the primary surface features
that are adjacent to one another have perimeters that are separated
by a distance within a range of 1 .mu.m to 100 .mu.m; and the
primary surface features that are adjacent to one another are
separated by a center-to-center distance within a range of 5 .mu.m
to 150 .mu.m.
10. The substrate of claim 1, wherein each of the primary surface
features comprises a change in elevation perpendicular to the
base-plane that is within a range of 0.05 .mu.m to 0.50 .mu.m.
11. The substrate of claim 1, wherein each primary surface features
provides a surface, and the secondary surface features are disposed
on the surfaces of the primary surface features.
12. The substrate of claim 1 wherein the textured region further
comprises: a surrounding portion into which the primary surface
features are set into or out of which the primary surface features
project; wherein, each primary surface feature provides a surface,
wherein, the secondary surface features are disposed on both the
surrounding portion and on the surfaces of the primary surface
features, and wherein, the surface roughness at the surfaces of the
primary surface features is less than the surface roughness at the
surrounding portion.
13. The substrate of claim 1 further comprising: a surrounding
portion into which the primary surface features are set into or out
of which the primary surface features project; wherein, the
secondary surface features are disposed on the surfaces of the
primary surface features but not on the surrounding portion.
14. The substrate of claim 1, wherein the substrate comprises a
glass or glass-ceramic.
15. The substrate of claim 1, wherein the textured region exhibits
a transmission haze within a range of 1.5% to 3.5%; the textured
region exhibits a pixel power deviation within a range of 1.5% to
3.5%; the textured region exhibits a distinctness-of-image within a
range of 2.% to 5.0%; and the textured region exhibits a specular
reflectance within a range of 5 GU to 20 GU.
16. A method of forming a textured region of a substrate, the
method comprising: forming primary surface features into a primary
surface of a substrate according to a predetermined positioning of
each primary surface feature thus forming a textured region, each
primary surface feature comprising a largest dimension parallel to
a base-plane through the substrate disposed below the primary
surface of at least 5 .mu.m; and forming secondary surface features
into one or more sections of the textured region, thereby
increasing the surface roughness (R.sub.a) of the one or more
sections to within a range of 5 nm to 100 nm.
17. The method of claim 16 further comprising: determining the
positioning of each primary surface feature utilizing a spacing
distribution algorithm.
18. The method of claim 16, wherein forming the primary surface
features into the primary surface comprises contacting the primary
surface with an etchant while an etching mask is disposed on the
primary surface to permit only selective etching of the substrate
to form the primary surface features.
19. The method of claim 18, wherein the etchant comprises
hydrofluoric acid and nitric acid; and the etchant contacts the
substrate for a time period within a range of 10 seconds to 60
seconds.
20. The method of claim 16 further comprising: forming the etching
mask by exposing a photorsesist material disposed on the primary
surface of the substrate to a curing agent while a lithography mask
is disposed on the photoresist material, the lithography mask
comprising material and voids through the material to selectively
expose portions of the photoresist material to the curing agent,
wherein the voids of the lithography mask are positioned according
to the predetermined positioning of the primary surface
features.
21. The method of claim 16, wherein forming the secondary surface
features into one or more sections of the textured region comprises
contacting the textured region of the substrate with a second
etchant, different than the etchant used to form the primary
surface features.
22. The method of claim 21, wherein the second etchant comprises
acetic acid and ammonium fluoride.
23. The method of claim 16, wherein forming the primary surface
features into the primary surface comprises contacting the primary
surface with an etchant while an etching mask is disposed on the
primary surface to permit only selective etching of the substrate
to form the primary surface features, and forming the secondary
surface features into one or more sections of the textured region
comprises contacting the one or more sections of the textured
region of the substrate with a second etchant, different than the
etchant used to form the primary surface features, while the
etching mask used to form the primary surface features remains on
the substrate.
Description
CLAIM OF PRIORITY
[0001] This Application claims the benefit of priority to U.S.
Provisional Application No. 63/049,843, filed 9 Jul. 2020, the
content of which is incorporated herein by reference in its
entirety.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] The present application relates to, but does not claim
priority to, commonly owned and assigned U.S. patent application
Ser. No. ______ (D31977), entitled "TEXTURED REGION TO REDUCE
SPECULAR REFLECTANCE INCLUDING A LOW REFRACTIVE INDEX SUBSTRATE
WITH HIGHER ELEVATED SURFACES AND LOWER ELEVATED SURFACES AND A
HIGH REFRACTIVE INDEX MATERIAL DISPOSED ON THE LOWER ELEVATED
SURFACES" and filed on ______; U.S. patent application Ser. No.
______ (D32630/32632), entitled "TEXTURED REGION OF A SUBSTRATE TO
REDUCE SPECULAR REFLECTANCE INCORPORATING SURFACE FEATURES WITH AN
ELLIPTICAL PERIMETER OR SEGMENTS THEREOF, AND METHOD OF MAKING THE
SAME" and filed on ______; U.S. patent application Ser. No. ______
(D32647), entitled "DISPLAY ARTICLES WITH DIFFRACTIVE, ANTIGLARE
SURFACES AND THIN, DURABLE ANTIREFLECTION COATINGS" and filed on
______; and U.S. patent application Ser. No. ______ (D32623),
entitled "DISPLAY ARTICLES WITH DIFFRACTIVE, ANTIGLARE SURFACES AND
THIN, DURABLE ANTIREFLECTION COATINGS" and filed on ______. The
entire disclosures of each of the foregoing U.S. patent
applications, publications and patent documents are incorporated
herein by reference.
BACKGROUND
[0003] Substrates transparent to visible light are utilized to
cover displays of display articles. Such display articles include
smart phones, tablets, televisions, computer monitors, and the
like. The displays are often liquid crystal displays, organic light
emitting diodes, among others. The substrate protects the display,
while the transparency of the substrate allows the user of the
device to view the display.
[0004] The substrate reflecting ambient light, especially specular
reflection, reduces the ability of the user to view the display
through the substrate. Specular reflection in this context is the
mirror-like reflection of ambient light off the substrate. For
example, the substrate may reflect visible light reflecting off or
emitted by an object in the environment around the device. The
visible light reflecting off the substrate reduces the contrast of
the light from the display transmitting to the eyes of the user
through the substrate. At some viewing angles, instead of seeing
the visible light that the display emits, the user sees a
specularly reflected image. Thus, attempts have been made to reduce
specular reflection of visible ambient light off of the
substrate.
[0005] Attempts have been made to reduce specular reflection off of
the substrate by texturing the reflecting surface of the substrate.
The resulting surface is sometimes referred to as an "antiglare
surface." For examples, sandblasting and liquid etching the surface
of the substrate can texture the surface, which generally causes
the surface to reflect ambient light diffusely rather than
specularly. Diffuse reflection generally means that the surface
still reflects the same ambient light but the texture of the
reflecting surface scatters the light upon reflection. The more
diffuse reflection interferes less with the ability of the user to
see the visible light that the display emits.
[0006] Such methods of texturing (i.e., sandblasting and liquid
etching) generate features on the surface with imprecise and
unrepeatable geometry (the features provide the texture). The
geometry of the textured surface of one substrate formed via
sandblasting or liquid etching can never be the same as the
geometry of the textured surface of another substrate formed via
sandblasting or liquid etching. Commonly, only a statistical
quantification of the surface roughness (i.e., R.sub.a) of the
textured surface of the substrate is a repeatable target of the
texturing.
[0007] There are a variety of metrics by which the quality of the
"antiglare" surface is judged. Those metrics include (1) the
distinctness-of-image, (2) pixel power deviation, (3) apparent
Moire interference fringes, (4) transmission haze, (5) specular
reflection, and (6) reflection color artifacts.
Distinctness-of-image, which more aptly might be referred to as
distinctness-of-reflected-image, is a measure of how distinct an
image reflecting off the surface appears. The lower the
distinctness-of-image, the more the textured surface is diffusely
reflecting rather than specularly reflecting. Surface features can
magnify various pixels of the display, which distorts the image
that the user views. Pixel power deviation, also referred to as
"sparkle," is a quantification of such an effect. The lower the
pixel power deviation the better. Moire interference fringes are
large scale interference patterns, which, if visible, distort the
image that the user sees. Preferably, the textured surface produces
no apparent Moire interference fringes. Transmission haze is a
measure of how much the textured surface is diffusing the visible
light that the display emitted upon transmitting through the
substrate. The greater the transmission haze, the less sharp the
display appears (i.e., lowered apparent resolution). Specular
reflection reduction is again a measure of how much of the
reflected ambient light off the textured surface is specular. The
lower the better. Reflection color artifacts are a sort of
chromatic aberration where the textured surface diffracts light
upon reflection as a function of wavelength--meaning that the
reflected light, although relatively diffuse, appears segmented by
color. The less reflected color artifacts that the textured surface
produces the better. Some of these attributes are discussed in
greater detail below.
[0008] Targeting a specific surface roughness alone cannot optimize
all of those metrics simultaneously. A relatively high surface
roughness that sandblasting or liquid etching produces might
adequately transform specular reflection into diffuse reflection.
However, the high surface roughness can additionally generate high
transmission haze and pixel power deviation. A relatively low
surface roughness, while decreasing transmission haze, might fail
to sufficiently transform specular reflection into diffuse
reflection--defeating the "antiglare" purpose of the texturing.
[0009] Accordingly, a new approach to providing a textured region
of the substrate is needed--one that is reproducible from
substrate-to-substrate and one that causes the textured surface to
reflect ambient light sufficiently diffusely rather than specularly
so as to be "antiglare" (e.g., a low distinctness-of-image, low
specular reflection) but simultaneously also delivers low pixel
power deviation, low transmission haze, and low reflection color
artifacts.
SUMMARY
[0010] The present disclosure provides a new approach that
specifically places primary surface features having a specific
geometry throughout a textured region according to a predetermined
placement. The primary surface features cause the substrate to
reflect rather diffusely and are reproducible from
substrate-to-substrate because the placement of each primary
surface feature is by design. In addition, secondary surface
features are incorporated into the textured region to increase the
surface roughness to within a certain range. The increased surface
roughness imparts surface scattering to the textured region, which
generally lowers pixel power deviation and specular reflection, and
sometimes distinctness of image too.
[0011] According to a first aspect of the present disclosure, a
substrate for a display article, the substrate comprising: (a) a
primary surface; and (b) a textured region on at least a portion of
the primary surface; the textured region comprising: (i) primary
surface features, each comprising a perimeter parallel to a
base-plane extending through the substrate disposed below the
textured region, wherein the perimeter of each of the primary
surface features comprises a longest dimension of at least 5 .mu.m;
and (ii) one or more sections each comprising secondary surface
features having a surface roughness (R.sub.a) within a range of 5
nm to 100 nm.
[0012] According to a second aspect of the present disclosure, the
substrate of the first aspect, wherein the primary surface features
form a pattern.
[0013] According to a third aspect of the present disclosure, the
substrate of any one of the first through second aspects, the
longest dimension of each of the primary surface features is about
the same.
[0014] According to a fourth aspect of the present disclosure, the
substrate of the first aspect, wherein an arrangement of the
surface features reflect a random distribution.
[0015] According to a fifth aspect of the present disclosure, the
substrate of any one of the first through fourth aspects, wherein
the perimeter of each primary surface features is elliptical.
[0016] According to a sixth aspect of the present disclosure, the
substrate of any one of the first through fourth aspects, wherein
the perimeter of each primary surface features is circular.
[0017] According to a seventh aspect of the present disclosure, the
substrate of any one of the first through fourth aspects, wherein
each primary surface feature provides a surface, and the surface is
either concave or convex.
[0018] According to an eighth aspect of the present disclosure, the
substrate of any one of the first through seventh aspects, wherein
the textured region further comprises: a surrounding portion into
which the primary surface features are set or out of which the
primary surface features project.
[0019] According to a ninth aspect of the present disclosure, the
substrate of any one of the first through eighth aspects, wherein
(i) the primary surface features that are adjacent to one another
have perimeters that are separated by a distance within a range of
1 .mu.m to 100 .mu.m; and (ii) the primary surface features that
are adjacent to one another are separated by a center-to-center
distance within a range of 5 .mu.m to 150 .mu.m.
[0020] According to a tenth aspect of the present disclosure, the
substrate of any one of the first through ninth aspects, wherein
each of the primary surface features comprises a change in
elevation perpendicular to the base-plane that is within a range of
0.05 .mu.m to 0.50 .mu.m.
[0021] According to an eleventh aspect of the present disclosure,
the substrate of any one of the first through sixth and eighth
through tenth aspects, wherein (i) each primary surface features
provides a surface, and (ii) the secondary surface features are
disposed on the surfaces of the primary surface features.
[0022] According to a twelfth aspect of the present disclosure, the
substrate of any one of the first through sixth, ninth, and tenth
aspects, wherein the textured region further comprises: a
surrounding portion into which the primary surface features are set
into or out of which the primary surface features project; wherein,
each primary surface feature provides a surface, wherein, the
secondary surface features are disposed on both the surrounding
portion and on the surfaces of the primary surface features, and
wherein, the surface roughness at the surfaces of the primary
surface features is less than the surface roughness at the
surrounding portion.
[0023] According to a thirteenth aspect of the present disclosure,
the substrate of any one of the first through sixth, ninth, and
tenth aspects further comprises: a surrounding portion into which
the primary surface features are set into or out of which the
primary surface features project; wherein, the secondary surface
features are disposed on the surfaces of the primary surface
features but not on the surrounding portion.
[0024] According to a fourteenth aspect of the present disclosure,
the substrate of any one of the first through thirteenth aspects,
wherein the substrate comprises a glass or glass-ceramic.
[0025] According to a fifteenth aspect of the present disclosure,
the substrate of any one of the first through fourteenth aspects,
wherein (i) the textured region exhibits a transmission haze within
a range of 1.5% to 3.5%; (ii) the textured region exhibits a pixel
power deviation within a range of 1.5% to 3.5%; (iii) the textured
region exhibits a distinctness-of-image within a range of 2.0% to
5.0%; and (iv) the textured region exhibits a specular reflectance
within a range of 5 GU to 20 GU.
[0026] According to a sixteenth aspect of the present disclosure, a
method of forming a textured region of a substrate, the method
comprising: (i) forming primary surface features into a primary
surface of a substrate according to a predetermined positioning of
each primary surface feature thus forming a textured region, each
primary surface feature comprising a largest dimension parallel to
a base-plane through the substrate disposed below the primary
surface of at least 5 .mu.m; and (ii) forming secondary surface
features into one or more sections of the textured region, thereby
increasing the surface roughness (R.sub.a) of the one or more
sections to within a range of 5 nm to 100 nm.
[0027] According to a seventeenth aspect of the present disclosure,
the method of the sixteenth aspect further comprises: determining
the positioning of each primary surface feature utilizing a spacing
distribution algorithm.
[0028] According to an eighteenth aspect of the present disclosure,
the method of any one of the sixteenth through seventeenth aspects,
wherein forming the primary surface features into the primary
surface comprises contacting the primary surface with an etchant
while an etching mask is disposed on the primary surface to permit
only selective etching of the substrate to form the primary surface
features.
[0029] According to a nineteenth aspect of the present disclosure,
the method of the eighteenth aspect, wherein (i) the etchant
comprises hydrofluoric acid and nitric acid; and (ii) the etchant
contacts the substrate for a time period within a range of 10
seconds to 60 seconds.
[0030] According to a twentieth aspect of the present disclosure,
the method of any one of the sixteenth through nineteenth aspects
further comprising: forming the etching mask by exposing a
photorsesist material disposed on the primary surface of the
substrate to a curing agent while a lithography mask is disposed on
the photoresist material, the lithography mask comprising material
and voids through the material to selectively expose portions of
the photoresist material to the curing agent, wherein the voids of
the lithography mask are positioned according to the predetermined
positioning of the primary surface features.
[0031] According to a twenty-first aspect of the present
disclosure, the method of any one of the sixteenth through
twentieth aspects, wherein forming the secondary surface features
into one or more sections of the textured region comprises
contacting the textured region of the substrate with a second
etchant, different than the etchant used to form the primary
surface features.
[0032] According to a twenty-second aspect of the present
disclosure, the method of any one of the sixteenth through
twenty-first aspects, wherein the second etchant comprises acetic
acid and ammonium fluoride.
[0033] According to a twenty-third aspect of the present
disclosure, the method of any one of the sixteenth through
twenty-second aspects, wherein (i) forming the primary surface
features into the primary surface comprises contacting the primary
surface with an etchant while an etching mask is disposed on the
primary surface to permit only selective etching of the substrate
to form the primary surface features, and (ii) forming the
secondary surface features into one or more sections of the
textured region comprises contacting the one or more sections of
the textured region of the substrate with a second etchant,
different than the etchant used to form the primary surface
features, while the etching mask used to form the primary surface
features remains on the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] In the figures:
[0035] FIG. 1 is perspective view of a display article,
illustrating a substrate with a textured region disposed over a
display;
[0036] FIG. 2 is closer-up perspective view of area II of FIG. 1,
illustrating the textured region of the substrate of FIG. 1
including primary surface features that are arranged in a hexagonal
pattern;
[0037] FIG. 3 is an elevation view of a cross-section of the
substrate of FIG. 1 taken through line III-III of FIG. 2,
illustrating the textured region further including secondary
surface features, smaller than the primary surface features,
disposed on the textured region including the primary surface
features;
[0038] FIG. 4 is an overhead view of embodiments of a textured
region, illustrating the primary surface features having an
elliptical perimeter and projecting from a surrounding portion;
[0039] FIG. 5 is another overhead view of embodiments of a textured
region, illustrating the primary surface features having a
hexagonal perimeter that are arranged hexagonally but separated by
a distance (wall-to-wall) and a center-to-center distance;
[0040] FIG. 6 is a schematic flow chart of a method of forming the
textured region of FIG. 1, illustrating steps such as determining
the positioning of each primary surface feature using a spacing
distribution algorithm;
[0041] FIG. 7A, pertaining to a modeled Example 1, is a graph that
illustrates distinctness-of-image generally decreasing as a
function of (i) increasing change of elevation (height) of the
primary surface features and (ii) increasing sigma value assigned
for the secondary surface features, which is a measure of the
surface scattering that the secondary surface features impart to
the textured region;
[0042] FIG. 7B, pertaining to Example 1, is a graph that
illustrates the change in distinctness-of-image that the presence
of the secondary surface features impart compared to if there were
no secondary surface features, as a function of the assigned sigma
value and height of the primary surface features;
[0043] FIG. 7C, pertaining to Example 1, is a graph that
illustrates the sigma value that imparts the textured region with
the minimum distinctness-of-image value generally decreases as a
function of decreasing height of the primary surface features;
[0044] FIG. 7D, pertaining to Example 1, is a graph that
illustrates that pixel power deviation generally increases as a
function of height of the primary surface features and decreases as
a function of increasing sigma value assigned to the secondary
surface features;
[0045] FIG. 7E, pertaining to Example 1, is a graph that
illustrates pixel power deviation generally decreases as a function
of increasing sigma value and decreases as a function of decreasing
height of the primary surface features;
[0046] FIG. 7F, pertaining to Example 1, is a graph that
illustrates transmission haze generally increases as a function of
increasing sigma values assigned for the secondary surface
features;
[0047] FIG. 7G, pertaining to Example 1, is a graph that
illustrates transmission haze generally increasing as a function of
increasing sigma value assigned for the secondary surface features,
but only after a threshold minimum sigma value;
[0048] FIG. 8A, pertaining to Examples 2A-2D, reproduce atomic
force microscopy images of secondary surface features with various
topographies, a result of varying a composition of an etchant
utilized to form the secondary surface features;
[0049] FIG. 8B, pertaining to Examples 2A-2D, is a graph that
illustrates transmission haze generally increasing as a function of
increasing sigma (surface scattering) value, which were variable as
a function of etchant composition;
[0050] FIG. 9A, pertaining to Examples 3A-3B, is a graph that
illustrates pixel power deviation varying as a function of
orientation angle of the textured region (because of the hexagonal
perimeter) of the primary surface features, and the presence of the
secondary surface features lowering pixel power deviation compared
to when no such secondary surface features were present;
[0051] FIG. 9B, pertaining to Examples 3A-3B, is a schematic
diagram illustrating that orientation angle concerns the angle that
an edge of the substrate forms with the display beneath the
substrate;
[0052] FIG. 10A, pertaining to Examples 4A-4H, is a graph that
illustrates that the inclusion of the secondary surface features
resulted in a lower pixel power deviation and, further, that the
resulting pixel power deviation can vary depending on the surface
roughness (R.sub.a) that the secondary surface features impart, and
thus the composition of the etchant used to form the secondary
surface features;
[0053] FIG. 10B, pertaining to Examples 4A-4H, is a graph that
illustrates that the presence of the secondary surface features did
not change measured specular reflectance compared to substrates
that did not have the secondary surface features;
[0054] FIG. 10C, pertaining to Examples 4A-4H, is a graph that
illustrates that the presence of the secondary surface features
produced a lower distinctness-of-image compared to substrates that
did not have the secondary surface features;
[0055] FIG. 10D, pertaining to Examples 4A-4H, is a graph that
illustrates that the presence of the secondary surface features
produces greater transmission haze compared to substrates that did
not have the secondary surface features, and increasingly so as the
surface roughness (R.sub.a) that the secondary surface features
imparts increases;
[0056] FIG. 11A, pertaining to Examples 5A-5O, is a graph that
illustrates that the presence of secondary surface features
resulted in a lower pixel power deviation compared to substrates
that did not have the secondary surface features;
[0057] FIG. 11B, pertaining to Examples 5A-5O, is a graph that
illustrates that the presence of secondary surface features
resulted in a lower specular reflectance compared to substrates
that did not have the secondary surface features;
[0058] FIG. 11C, pertaining to Examples 5A-5O, is a graph that
illustrates that the presence of secondary surface features
resulted in a higher distinctness-of-image compared to substrates
that did not have the secondary surface features;
[0059] FIG. 11D, pertaining to Examples 5A-5O, is a graph that
illustrates that the presence of secondary surface features
resulted in a higher transmission haze compared to substrates that
did not have the secondary surface features;
[0060] FIG. 12A, pertaining to Examples 6A-6B, are atomic force
microscopy images of the primary surface features and the
surrounding portion (left) and the secondary surface features
(middle and right), for both when the secondary surface features
were disposed only on the primary surface features (top) and when
the secondary surface features were disposed over both the primary
surface features and the surrounding portion (bottom);
[0061] FIG. 12B, pertaining to Examples 6A-6B, is a graph
illustrating that incorporating the secondary surface features over
the entire textured region resulted in a lowed pixel power
deviation compared to substrates where the secondary surface
features were incorporated only on the primary surface
features;
[0062] FIG. 12C, pertaining to Examples 6A-6B, is a graph
illustrating that incorporating the secondary surface features over
the entire textured region resulted in a higher transmission haze
compared to substrates that incorporated the secondary surface
features only on the primary surface features;
[0063] FIG. 12D, pertaining to Examples 6A-6B, is a graph
illustrating that incorporating the secondary surface features over
the entire textured region did not substantially affect specular
reflectance compared to substrates that incorporated the secondary
surface features only on the primary surface features;
[0064] FIG. 12E, pertaining to Examples 6A-6B, is a graph
illustrating that incorporating the secondary surface features over
the entire textured region slightly affected specular reflectance
compared to substrates that incorporated the secondary surface
features only on the primary surface features, and increasingly so
as wavelength deviated from about 455 nm;
[0065] FIG. 13A, pertaining to Example 7, are white light
interferometer graphs illustrating the topography of the primary
surface features and the surrounding portion (top) and the
secondary surface features (bottom) disposed at the primary surface
features (left) and the surrounding portion (right); and
[0066] FIG. 13B, pertaining to Example 7, are atomic force
microscopy images of the secondary surface features disposed at a
primary surface feature (left) and the surrounding portion (right),
illustrating that the secondary surface features at the surrounding
portion imparted a higher surface roughness (R.sub.a) than the at
the primary surface features (because the surrounding portion was
not previously etched and thus more sensitive to the etching that
imparted the secondary surface features).
DETAILED DESCRIPTION
[0067] Referring now to FIG. 1, a display article 10 includes a
substrate 12. In embodiments, the display article 10 further
includes a housing 14 to which the substrate 12 is coupled and a
display 16 within the housing 14. In such embodiments, the
substrate 12 at least partially covers the display 16 such that
light that the display 16 emits transmits through the substrate
12.
[0068] The substrate 12 includes a primary surface 18, a textured
region 20 defined on the primary surface 18, and a thickness 22
that the primary surface 18 bounds in part. The primary surface 18
generally faces toward an external environment 24 surrounding the
display article 10 and away from the display 16. The display 16
emits visible light that transmits through the thickness 22 of the
substrate 12, out the primary surface 18, and into the external
environment 24.
[0069] Referring now to FIGS. 2-5, in embodiments, the textured
region 20 includes primary surface features 26. A base-plane 28
extends through the substrate 12 below the textured region 20. The
base-plane 28 provides a conceptual reference point and is not a
structural feature. Each primary surface feature 26 includes a
perimeter 30. The perimeter 30 is parallel to the base-plane 28.
The perimeter 30 has a longest dimension 32. For example, in the
embodiments illustrated at FIG. 2, the perimeter 30 is hexagonal
and thus the longest dimension 32 of the perimeter 30 is the long
diagonal of the hexagonal perimeter 30. The longest dimension 32 is
parallel to the base-plane 28 as well. The longest dimension 32 of
each primary surface feature 26 is at least 5 .mu.m. The perimeter
30 can be shaped other than hexagonal. In embodiments, the
perimeter 30 of each of the primary surface features 26 is
polygonal. In embodiments, the perimeter 30 of each of the primary
surface features 26 is elliptical (see, e.g., FIG. 4). In other
embodiments, the perimeter 30 of each of the primary surface
features 26 is circular.
[0070] In addition, the textured region 20 further includes one or
more sections 34 that have secondary surface features 36. The
secondary surface features 36 are smaller than the primary surface
features 26. The secondary surface features 36 impart a surface
roughness to the one or more sections 34 of the textured region 20.
The surface roughness imparted is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm,
30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75
nm, 80 nm, 85 nm, 90 nm, 95 nm, or 100 nm, or within any range
bounded by any two of those values (e.g., 5 nm to 100 nm, and so
on). As used herein, surface roughness (R.sub.a) is measured with
an atomic force microscope, such as an atomic force microscope
controlled by a NanoNavi control station distributed by Seiko
Instruments Inc. (Chiba, Japan), with a scan size of 5 .mu.m by 5
.mu.m. Surface roughness (R.sub.a), as opposed to other types of
surface roughness values such as R.sub.q, is the arithmetical mean
of the absolute values of the deviations from a mean line of the
measured roughness profile.
[0071] The positioning, perimeter 30, and longest dimension 32 of
each of the primary surface features 26 is by design, as opposed to
the purely uncontrolled and coincidental placement of surface
features via sandblasting or open etching (i.e., etching without a
mask that would define the placement of each surface feature). In
embodiments, such as those embodiments illustrated at FIG. 2, the
primary surface features 26 form a pattern. In other words, the
positioning of a grouping of the primary surface features 26
repeats at the textured region 20. The embodiments illustrated at
FIG. 2 are a hexagonal pattern. In embodiments, the longest
dimension 32 of each of the primary surface features 26 is about
the same or the same within manufacturing tolerances.
[0072] In other embodiments, such as those illustrated at FIG. 4,
the primary surface features 26 do not form a pattern--that is, the
arrangement of the surface features reflect a random distribution.
To not form a pattern, the primary surface features 26 can be
randomly distributed within certain constraints, such as a
center-to-center distance 38 that varies but is greater than a
minimum value. In addition, to not form a pattern, the longest
dimension 32 of each primary surface feature 26 can be aligned not
parallel to each other. A reason to avoid arranging the primary
surface features 26 not in a pattern is to avoid the textured
region 20 reflecting ambient light with Moire fringe interference
patterns. When the primary surface features 26 form a pattern, a
possible consequence is the generation of Moire fringe interference
patterns upon reflection of ambient light.
[0073] Each of the primary surface features 26 includes a surface
40 facing the external environment 24. The primary surface 18 of
the substrate 12 at the textured region 20 includes all of surfaces
40 that the primary surface features 26 provide. In embodiments,
such as those illustrated at FIGS. 3 and 4, the surface 40 of each
primary surface feature 26 is concave. In other embodiments, the
surface 40 of each primary surface feature 26 is convex. In
embodiment, the surfaces 40 of some primary surface features 26 of
the textured region 20 are concave, while the surfaces 40 of other
primary surface features 26 of the textured region 20 are convex.
In embodiments, the surface 40 of each primary surface feature 26
of the textured region 20 is planar and parallel to the base-plane
28.
[0074] In embodiments, the textured region 20 further includes a
surrounding portion 42 (see, e.g., FIGS. 4 and 5). In embodiments,
the primary surface features 26 project out from the surrounding
portion 42 away from the base-plane 28 and toward the external
environment 24. In embodiments, the primary surface features 26 are
set into the surrounding portion 42 toward the base-plane 28 and
away from the external environment 24. The elevation 44 (see FIG.
13A) of the surrounding portion 42 from the base-plane 28 may be
relatively constant within manufacturing capabilities. The
elevation 46 (see FIG. 13A) of the surfaces 40 of the primary
surface feature 26 may all be approximately the same, within
manufacturing capabilities. The textured region 20 may thus have a
bi-modal surface structure--with one or more surfaces (e.g., the
surfaces 40 of the primary surface features 26) having one mean
elevation (e.g., elevation 46), and one or more surfaces (e.g., the
surface provided by the surrounding portion 42) having a second
mean elevation (e.g., elevation 44).
[0075] In embodiments, the perimeters 30 of primary surface
features 26 that are adjacent are separated by a distance 48 (e.g.,
wall-to-wall distance). In embodiments, the distance 48 is 1 .mu.m,
2 .mu.m, 3 .mu.m, 4 .mu.m, 5 .mu.m, 6 .mu.m, 7 .mu.m, 8 .mu.m, 9
.mu.m, 10 .mu.m, 15 .mu.m, 20 .mu.m, 25 .mu.m, 30 .mu.m, 35 .mu.m,
40 .mu.m, 45 .mu.m, 50 .mu.m, 55 .mu.m, 60 .mu.m, 65 .mu.m, 70
.mu.m, 75 .mu.m, 80 .mu.m, 85 .mu.m, 90 .mu.m, 95 .mu.m, or 100
.mu.m, or within any range bounded by any two of those values
(e.g., 25 .mu.m to 75 .mu.m, 50 .mu.m to 60 .mu.m, 1 .mu.m to 100
.mu.m, and so on). In embodiments, primary surface features 26 that
are adjacent are separated by a center-to-center distance 38 of 5
.mu.m, 6 .mu.m, 7.mu.m, 8 .mu.m, 9 .mu.m, 10 .mu.m, 15 .mu.m, 20
.mu.m, 25 .mu.m, 30 .mu.m, 35 .mu.m, 40 .mu.m, 45 .mu.m, 50 .mu.m,
55 .mu.m, 60 .mu.m, 65 .mu.m, 70 .mu.m, 75 .mu.m, 80 .mu.m, 85
.mu.m, 90 .mu.m, 95 .mu.m, 100 .mu.m, 110 .mu.m, 120 .mu.m, 130
.mu.m, 140 .mu.m, or 150 .mu.m, or within any range bounded by any
two of those values (e.g., 100 .mu.m to 150 .mu.m, 5 .mu.m to 150
.mu.m and so on).
[0076] Each primary surface feature 26 has a change in elevation 50
perpendicular to the base-plane 28. For a primary surface feature
26 that is convex or projects from the surrounding portion 42, the
change in elevation 50 is the height of the primary surface feature
26. For a primary surface feature 26 that is concave or set into
the surrounding portion 42, the change in elevation 50 is the depth
of the primary surface feature 26. In embodiments, the change in
elevation 50 of each primary surface feature 26 is the same or
about the same (varies by 25% or less). In embodiments, the change
in elevation 50 of each primary surface feature 26 is 0.05 .mu.m,
0.10 .mu.m, 0.15 .mu.m, 0.20 .mu.m, 0.25 .mu.m, 0.30 .mu.m, 0.35
.mu.m, 0.40 .mu.m, 0.45 .mu.m, or 0.50 .mu.m, or within any range
bounded by any two of those values (e.g., 0.05 .mu.m to 0.50 .mu.m,
and so on). When the textured region 20 provides surfaces
structured in a bi-modal distribution of elevations, the change in
elevation 50 is the distance between the two elevations.
[0077] In embodiments, the one or more sections 34 that include the
secondary surface features 36 include the surfaces 40 of the
primary surface features 26. In other words, in those embodiments,
the secondary surface features 36 are disposed on the surface 40 of
the primary surface features 26. In embodiments, the secondary
surface features 36 are disposed on the surface 40 of the primary
surface features 26 but not the surrounding portion 42.
[0078] In embodiments, the one or more sections 34 that include the
secondary surface features 36 include the surrounding portion 42
and the surfaces 40 of the primary surface features 26. In other
words, in those embodiments, the secondary surface features 36 are
disposed on both the surrounding portion 42 and on the surfaces 40
of the primary surface features 26. In embodiments, the section 34
that includes the secondary surface features 36 is coextensive with
the textured region 20 meaning that the secondary surface features
36 are disposed throughout the entirety of the textured region 20.
In embodiments, the surface roughness (R.sub.a) at the surfaces 40
of the primary surface features 26 is less than the surface
roughness at the surrounding portion 42.
[0079] Through adjustment of the parameters of the primary surface
features 26, such as the change in elevation 50, longest dimension
32, shape of the perimeter 30, and center-to-center distance 38,
and the addition of the secondary surface features 36, the
distinctness-of-image, pixel power deviation, and transmission haze
that the textured region 20 generates can be optimized. In general,
incorporation of the primary surface features 26 alone would cause
the textured region 20 to reflect ambient light with a lower
distinctness-of-image but transmit light from the display 16 with a
higher pixel power deviation and higher transmission haze. The
larger the change in elevation 50 of the primary surface features
26, the larger these effects on distinctness of image, pixel power
deviation, and transmission haze. The incorporation of the
secondary surface features 36 mitigates the negative effect that
the primary surface features 26 might have on pixel power
deviation. The surface roughness that the secondary surface
features 36 impart increases the scattering of the textured region
20. This increased scattering increases the amount of diffuse
reflection that the textured region 20 generates upon reflecting
ambient light thus further lowering specular reflection and
rehabilitating (lowering) the pixel power deviation simultaneously,
and distinctness-of-image in some instances. Thus, the textured
region 20 can simultaneously generate low values for all of the
specular reflection, distinctness-of-image, pixel power deviation,
and transmission haze--something that previous methods of created
the textured region 20 could not achieve. In addition, the designer
of the textured region 20 has many more variables with which the
designer can work to optimize the textured region 20 for any given
application than with previous methods such as sandblasting or open
etching.
[0080] In embodiments, the substrate 12 includes a glass or
glass-ceramic. In embodiments, the substrate 12 is a
multi-component glass composition having about 40 mol % to 80 mol %
silica and a balance of one or more other constituents, e.g.,
alumina, calcium oxide, sodium oxide, boron oxide, etc. In some
implementations, the bulk composition of the substrate 12 is
selected from the group consisting of aluminosilicate glass, a
borosilicate glass, and a phosphosilicate glass. In other
implementations, the bulk composition of the substrate 12 is
selected from the group consisting of aluminosilicate glass, a
borosilicate glass, a phosphosilicate glass, a soda lime glass, an
alkali aluminosilicate glass, and an alkali aluminoborosilicate
glass. In further implementations, the substrate 12 is a
glass-based substrate, including, but not limited to, glass-ceramic
materials that comprise a glass component at about 90% or greater
by weight and a ceramic component. In other implementations of the
display article 10, the substrate 12 can be a polymer material,
with durability and mechanical properties suitable for the
development and retention of the textured region 20.
[0081] In embodiments, the substrate 12 has a bulk composition that
comprises an alkali aluminosilicate glass that comprises alumina,
at least one alkali metal and, in some embodiments, greater than 50
mol % SiO.sub.2, in other embodiments, at least 58 mol % SiO.sub.2,
and in still other embodiments, at least 60 mol % SiO.sub.2,
wherein the ratio (Al.sub.2O.sub.3 (mol %)+B.sub.2O.sub.3 (mol
%))/.SIGMA. alkali metal modifiers (mol %)>1, where the
modifiers are alkali metal oxides. This glass, in particular
embodiments, comprises, consists essentially of, or consists of:
about 58 mol % to about 72 mol % SiO.sub.2, about 9 mol % to about
17 mol % Al.sub.2O.sub.3; about 2 mol % to about 12 mol %
B.sub.2O.sub.3; about 8 mol % to about 16 mol % Na.sub.2O; and 0
mol % to about 4 mol % K.sub.2O, wherein the ratio (Al.sub.2O.sub.3
(mol %)+B.sub.2O.sub.3 (mol %))/.SIGMA. alkali metal modifiers (mol
%)>1, where the modifiers are alkali metal oxides.
[0082] In embodiments, the substrate 12 has a bulk composition that
comprises an alkali aluminosilicate glass comprising, consisting
essentially of, or consisting of: about 61 mol % to about 75 mol %
SiO.sub.2; about 7 mol % to about 15 mol % Al.sub.2O.sub.3; 0 mol %
to about 12 mol % B.sub.2O.sub.3; about 9 mol % to about 21 mol %
Na.sub.2O; 0 mol % to about 4 mol % K.sub.2O; 0 mol % to about 7
mol % MgO; and 0 mol % to about 3 mol % CaO.
[0083] In embodiments, the substrate 12 has a bulk composition that
comprises an alkali aluminosilicate glass comprising, consisting
essentially of, or consisting of: about 60 mol % to about 70 mol %
SiO.sub.2; about 6 mol % to about 14 mol % Al.sub.2O.sub.3; 0 mol %
to about 15 mol % B.sub.2O.sub.3; 0 mol % to about 15 mol %
Li.sub.2O; 0 mol % to about 20 mol % Na.sub.2O; 0 mol % to about 10
mol % K.sub.2O; 0 mol % to about 8 mol % MgO; 0 mol % to about 10
mol % CaO; 0 mol % to about 5 mol % ZrO.sub.2; 0 mol % to about 1
mol % SnO.sub.2; 0 mol % to about 1 mol % CeO.sub.2; less than
about 50 ppm As.sub.2O.sub.3; and less than about 50 ppm
Sb.sub.2O.sub.3; wherein 12 mol
%.ltoreq.Li.sub.2O+Na.sub.2O+K.sub.2O.ltoreq.20 mol % and 0 mol
%.ltoreq.MgO+Ca.ltoreq.10 mol %.
[0084] In embodiments, the substrate 12 has a bulk composition that
comprises an alkali aluminosilicate glass comprising, consisting
essentially of, or consisting of: about 64 mol % to about 68 mol %
SiO.sub.2; about 12 mol % to about 16 mol % Na.sub.2O; about 8 mol
% to about 12 mol % Al.sub.2O.sub.3; 0 mol % to about 3 mol %
B.sub.2O.sub.3; about 2 mol % to about 5 mol % K.sub.2O; about 4
mol % to about 6 mol % MgO; and 0 mol % to about 5 mol % CaO,
wherein: 66 mol %.ltoreq.SiO.sub.2+B.sub.2O.sub.3+CaO.ltoreq.69 mol
%; Na.sub.2O+K.sub.2O+B.sub.2O.sub.3+MgO+CaO+SrO>10 mol %; 5 mol
%.ltoreq.MgO+CaO+SrO.ltoreq.8 mol %;
(Na.sub.2O+B.sub.2O.sub.3)--Al.sub.2O.sub.3.ltoreq.2 mol %; 2 mol
%.ltoreq.Na.sub.2O--Al.sub.2O.sub.3.ltoreq.6 mol %; and 4 mol
%.ltoreq.(Na.sub.2O+K.sub.2O)--Al.sub.2O.sub.3.ltoreq.10 mol %.
[0085] In embodiments, the substrate 12 has a bulk composition that
comprises SiO.sub.2, Al.sub.2O.sub.3, P.sub.2O.sub.5, and at least
one alkali metal oxide (R.sub.2O), wherein
0.75>[(P.sub.2O.sub.5(mol %)+R.sub.2O (mol
%))/M.sub.2O.sub.3(mol %)].ltoreq.1.2, where
M.sub.2O.sub.3.dbd.Al.sub.2O.sub.3+B.sub.2O.sub.3. In embodiments,
[(P.sub.2O.sub.5(mol %)+R.sub.2O (mol %))/M.sub.2O.sub.3(mol %)]=1
and, in embodiments, the glass does not include B.sub.2O.sub.3 and
M.sub.2O.sub.3.dbd.Al.sub.2O.sub.3. The substrate 12 comprises, in
embodiments: about 40 to about 70 mol % SiO.sub.2; 0 to about 28
mol % B.sub.2O.sub.3; about 0 to about 28 mol % Al.sub.2O.sub.3;
about 1 to about 14 mol % P.sub.2O.sub.5; and about 12 to about 16
mol % R.sub.2O. In some embodiments, the glass substrate comprises:
about 40 to about 64 mol % SiO.sub.2; 0 to about 8 mol %
B.sub.2O.sub.3; about 16 to about 28 mol % Al.sub.2O.sub.3; about 2
to about 12 mol % P.sub.2O.sub.5; and about 12 to about 16 mol %
R.sub.2O. The substrate 12 may further comprise at least one
alkaline earth metal oxide such as, but not limited to, MgO or
CaO.
[0086] In some embodiments, the substrate 12 has a bulk composition
that is substantially free of lithium; i.e., the glass comprises
less than 1 mol % Li.sub.2O and, in other embodiments, less than
0.1 mol % Li.sub.2O and, in other embodiments, 0.01 mol %
Li.sub.2O, and in still other embodiments, 0 mol % Li.sub.2O. In
some embodiments, such glasses are free of at least one of arsenic,
antimony, and barium; i.e., the glass comprises less than 1 mol %
and, in other embodiments, less than 0.1 mol %, and in still other
embodiments, 0 mol % of As.sub.2O.sub.3, Sb.sub.2O.sub.3, and/or
BaO.
[0087] In embodiments, the substrate 12 has a bulk composition that
comprises, consists essentially of or consists of a glass
composition, such as Corning.RTM. Eagle XG.RTM. glass, Corning.RTM.
Gorilla.RTM. glass, Corning.RTM. Gorilla.RTM. Glass 2, Corning.RTM.
Gorilla.RTM. Glass 3, Corning.RTM. Gorilla.RTM. Glass 4, or
Corning.RTM. Gorilla.RTM. Glass 5.
[0088] In embodiments, the substrate 12 has an ion-exchangeable
glass composition that is strengthened by either chemical or
thermal means that are known in the art. In embodiments, the
substrate 12 is chemically strengthened by ion exchange. In that
process, metal ions at or near the primary surface 18 of the
substrate 12 are exchanged for larger metal ions having the same
valence as the metal ions in the substrate 12. The exchange is
generally carried out by contacting the substrate 12 with an ion
exchange medium, such as, for example, a molten salt bath that
contains the larger metal ions. The metal ions are typically
monovalent metal ions, such as, for example, alkali metal ions. In
one non-limiting example, chemical strengthening of a substrate 12
that contains sodium ions by ion exchange is accomplished by
immersing the substrate 12 in an ion exchange bath comprising a
molten potassium salt, such as potassium nitrate (KNO.sub.3) or the
like. In one particular embodiment, the ions in the surface layer
of the substrate 12 contiguous with the primary surface 18 and the
larger ions are monovalent alkali metal cations, such as Li.sup.+
(when present in the glass), Na.sup.+, K.sup.+, Rb.sup.+, and
Cs.sup.+. Alternatively, monovalent cations in the surface layer of
the substrate 12 may be replaced with monovalent cations other than
alkali metal cations, such as Ag.sup.+ or the like.
[0089] In such embodiments, the replacement of small metal ions by
larger metal ions in the ion exchange process creates a compressive
stress region in the substrate 12 that extends from the primary
surface 18 to a depth (referred to as the "depth of layer") that is
under compressive stress. This compressive stress of the substrate
12 is balanced by a tensile stress (also referred to as "central
tension") within the interior of the substrate 12. In some
embodiments, the primary surface 18 of the substrate 12 described
herein, when strengthened by ion exchange, has a compressive stress
of at least 350 MPa, and the region under compressive stress
extends to a depth, i.e., depth of layer, of at least 15 .mu.m
below the primary surface 18 into the thickness 22.
[0090] Ion exchange processes are typically carried out by
immersing the substrate 12 in a molten salt bath containing the
larger ions to be exchanged with the smaller ions in the glass. It
will be appreciated by those skilled in the art that parameters for
the ion exchange process, including, but not limited to, bath
composition and temperature, immersion time, the number of
immersions of the glass in a salt bath (or baths), use of multiple
salt baths, additional steps such as annealing, washing, and the
like, are generally determined by the composition of the glass and
the desired depth of layer and compressive stress of the glass as a
result of the strengthening operation. By way of example, ion
exchange of alkali metal-containing glasses may be achieved by
immersion in at least one molten bath containing a salt, such as,
but not limited to, nitrates, sulfates, and chlorides, of the
larger alkali metal ion. The temperature of the molten salt bath
typically is in a range from about 380.degree. C. up to about
450.degree. C., while immersion times range from about 15 minutes
up to about 16 hours. However, temperatures and immersion times
different from those described above may also be used. Such ion
exchange treatments, when employed with a substrate 12 having an
alkali aluminosilicate glass composition, result in a compressive
stress region having a depth (depth of layer) ranging from about 5
.mu.m up to at least 50 .mu.m, with a compressive stress ranging
from about 200 MPa up to about 800 MPa, and a central tension of
less than about 100 MPa.
[0091] As the etching processes that can be employed to create the
textured region 20 of the substrate 12 can remove alkali metal ions
from the substrate 12 that would otherwise be replaced by a larger
alkali metal ion during an ion exchange process, a preference
exists for developing the compressive stress region in the display
article 10 after the formation and development of the textured
region 20.
[0092] In embodiments, the display article 10 exhibits a pixel
power deviation ("PPD"). The details of a measurement system and
image processing calculation used to obtain PPD values described in
U.S. Pat. No. 9,411,180 entitled "Apparatus and Method for
Determining Sparkle," and the salient portions of which are related
to PPD measurements are incorporated by reference herein in their
entirety. Further, unless otherwise noted, the SMS-1000 system
(Display-Messtechnik & Systeme GmbH & Co. KG) is employed
to generate and evaluate the PPD measurements of this disclosure.
The PPD measurement system includes: a pixelated source comprising
a plurality of pixels (e.g., a Lenovo Z50 140 ppi laptop), wherein
each of the plurality of pixels has referenced indices i and j; and
an imaging system optically disposed along an optical path
originating from the pixelated source. The imaging system
comprises: an imaging device disposed along the optical path and
having a pixelated sensitive area comprising a second plurality of
pixels, wherein each of the second plurality of pixels is
referenced with indices m and n; and a diaphragm disposed on the
optical path between the pixelated source and the imaging device,
wherein the diaphragm has an adjustable collection angle for an
image originating in the pixelated source. The image processing
calculation includes: acquiring a pixelated image of the
transparent sample, the pixelated image comprising a plurality of
pixels; determining boundaries between adjacent pixels in the
pixelated image; integrating within the boundaries to obtain an
integrated energy for each source pixel in the pixelated image; and
calculating a standard deviation of the integrated energy for each
source pixel, wherein the standard deviation is the power per pixel
dispersion. As used herein, all PPD values, attributes and limits
are calculated and evaluated with a test set-up employing a display
device having a pixel density of 140 pixels per inch (PPI). In
embodiments, the display article 10 exhibits a PPD of 1.0%, 1.1%,
1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.25%, 2.5%,
2.75%, 3.0%, 3.25%, 3.5%, 3.75%, 4.0%, 4.25%, 4.5%, 4.75%, 5.0%,
5.5%, 6.0%, 6.5%, or within any range bounded by any two of those
values (e.g., 0.8% to 2.0%, 0.9% to 2.25%, 2.0% to 5.0%, 4.0% to
6.0%, and so on). In embodiments, the display article 10 exhibits a
PPD of less than 4.0%, less than 4.0%, less than 3.0%, or less than
2.0%.
[0093] In embodiments, the substrate 12 exhibits a
distinctness-of-image ("DOI"). As used herein, "DOI" is equal to
100*(R.sub.S-R.sub.3.0.degree.)/R.sub.S, where R.sub.S is the
specular reflectance flux measured from incident light (at
20.degree. from normal) directed onto the textured region 20, and
R.sub.0.3 is the reflectance flux measured from the same incident
light at 0.3.degree. from the specular reflectance flux, R.sub.S.
Unless otherwise noted, the DOI values and measurements reported in
this disclosure are obtained according to the ASTM D5767-18,
entitled "Standard Test Method for Instrumental Measurement of
Distinctness-of-Image (DOI) Gloss of Coated Surfaces using a
Rhopoint IQ Gloss Haze & DOI Meter" (Rhopoint Instruments
Ltd.). The values are reported here as "coupled" meaning that the
sample is coupled with index matching fluid to the back-side
surface of the substrate during the measurement to reduce backside
reflections. In embodiments, the substrate 12 exhibits a
distinctness-of-image ("DOI") of 15%, 20%, 25%, 30%, 35%, 40%, 45%,
50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 96%, 97%,
98%, 99%, or 99.9%, or within any range bounded by any two of those
values (e.g., 20% to 40%, 10% to 96%, 35% to 60%, and so on).
[0094] In embodiments, the substrate 12 exhibits a transmission
haze. As used herein, the term "transmission haze" refers to the
percentage of transmitted light scattered outside an angular cone
of about .+-.2.5.degree. in accordance with ASTM D1003, entitled
"Standard Test Method for Haze and Luminous Transmittance of
Transparent Plastics," the contents of which are incorporated by
reference herein in their entirety. Note that although the title of
ASTM D1003 refers to plastics, the standard has been applied to
substrates comprising a glass material as well. For an optically
smooth surface, transmission haze is generally close to zero. In
embodiments, the substrate 12 exhibits a transmission haze of 0.7%,
0.8%, 0.9%. 1.0%, 1.5%, 2%, 3%, 4%, or 5%, or within any range
bounded by any two of those values (e.g., 0.7% to 3%, 2% to 4%, and
so on).
[0095] In embodiments, the substrate 12 exhibits a specular
reflectance of 1 GU, 2 GU, 3 GU, 4 GU, 5 GU, 10 GU, 15 GU, 20 GU,
25 GU, 30 GU, 40 GU, 50 GU, 60 GU, 70 GU, 80 GU, or within any
range bounded by any two of those values (e.g., 1 GU to 3 GU, 5 GU
to 30 GU, 50 GU to 80 GU, and so on). In embodiments, the substrate
12 exhibits a specular reflectance that is less than less than 25
GU less than 20 GU, less than 15 GU, less than 10 GU, less than 5
GU, or less than 2 GU. Specular reflectance here, noted as
"c-Rspec" or "coupled Rspec" in the Examples that follow, refers to
the value obtained in gloss units (GU) using a Rhopoint IQ
goniophotometer. The values are indicative of how much specular
reflection is measured when the sample is optically coupled to a
perfect absorber. A value of 100 GU means 4.91% specular reflection
from a polished flat black glass surface of refractive index 1.567
at 20 degrees angle of incidence.
[0096] Referring now to FIGS. 6-10, a method 100 of forming the
textured region 20 is herein disclosed. At a step 102, the method
100 includes forming the primary surface features 26 into the
primary surface 18 of the substrate 12 according to a predetermined
positioning of each primary surface feature 26. The step 102, at
least for the moment, forms the textured region 20.
[0097] In embodiments, at a step 104, the method 100 further
includes determining the positioning of each primary surface
feature 26 utilizing a spacing distribution algorithm. Example
spacing distribution algorithms include Poisson disk sampling,
maxi-min spacing, and hard-sphere distribution. For example,
Poisson disk sampling inserts a first object (e.g., a point or a
circle with a diameter) into an area of a plane. Then the algorithm
inserts a second object within the area, placing the center at a
random point within the area. If the placement of the second object
satisfies the minimum center-to-center distance from the first
object, then the second object stays in the area. The algorithm
then repeats this process until no more such objects can be placed
within the area that satisfies the minimum center-to-center
distance. The result is a random distribution, but specific
placement, of the objects. From the random distribution but
specific placement of the objects, the positioning of the primary
surface features 26 are determined. For example, if the objects
positioned via the spacing distribution algorithm are points, then
the points can be the center of circles with a certain diameter, or
the center of hexagons with certain geometry. In other embodiments,
the points are triangulated, inellipses formed in the triangles,
and then the triangulations and points are removed leaving
ellipses, which can be shape of the primary surface features
26.
[0098] In embodiments, the step of 102 forming the primary surface
features 26 into the primary surface 18 includes contacting the
primary surface 18 with an etchant while an etching mask is
disposed on the primary surface 18 to permit only selective etching
of the substrate 12 to form the primary surface features 26. The
etching mask includes voids that allow the etchant to remove
material from the primary surface 18 of the substrate 12 and,
outside of the voids, the etching mask prevents the etchant from
contacting the primary surface 18 of the substrate 12. In
embodiments, the voids allow the etchant to remove material and
thereby to create the primary surface features 26 set into the
surrounding portion 42, which the etching mask protects from the
etchant. In embodiments, the voids allow the etchant to remove
material of the substrate 12 where the surrounding portion 42 is to
be but not where the primary surface features 26 are to be,
resulting in the primary surface features 26 projecting from the
surrounding portion 42. In short, the etching mask incorporates the
predetermined positioning of each primary surface feature 26 as
either a positive or negative.
[0099] In embodiments, the etchant includes one or more of
hydrofluoric acid and nitric acid. In embodiments, the etchant
includes both hydrofluoric acid and nitric acid. The etchant can be
sprayed onto the substrate 12 while the etching mask is on the
substrate 12. The substrate 12 with the etching mask can be dipped
into a vessel containing the etchant. In embodiments, the etchant
contacts the substrate 12 for a time period of 10 seconds, 20
seconds, 30 seconds, 40 seconds, 50 seconds, or 60 seconds, or
within any range bounded by any two of those values (e.g., 10
seconds to 60 seconds, and so on). After the period of time has
concluded, the substrate 12 is rinsed in deionized water and dried.
The longer the period of time that the etchant contacts the
substrate 12, the deeper the etchant etches into the substrate 12
and thus the greater the change in elevation 50 of the primary
surface features 26.
[0100] In embodiments, at a step 106, the method 100 further
includes forming the etching mask by exposing a photoresist
material disposed on the primary surface 18 of the substrate 12 to
a curing agent while a lithography mask is disposed on the
photoresist material. The thickness of the photoresist material can
vary from about 3 .mu.m to about 20 .mu.m depending on how the
photoresist material is added to the primary surface 18 of the
substrate 12. The photoresist material can be added via spin
coating (<3 .mu.m thickness), screen coating (<15 .mu.m
thickness), or as a dry film (<20 .mu.m thickness).
[0101] The lithography mask includes material and voids through the
material to selectively expose portions of the photoresist material
to the curing agent. The voids of the lithography mask are
positioned according to the predetermined positioning of the
primary surface features 26, either as a positive or negative. The
placement of each of the primary surface features 26 is determined,
such as with the spacing distribution algorithm and the lithography
mask incorporates that determined placement. The lithography mask
then allows selective curing of the etching mask, which then
incorporates that predetermined placement of the primary surface
features 26. Then finally the etching mask allows for selective
etching of the substrate 12, which translates the determined
placement of the primary surface features 26 onto the primary
surface 18 of the substrate 12 as the textured region 20. The
substrate 12 with the etching mask can be baked before the etching
mask contacts the etchant in order to ensure adhesion to the
substrate 12.
[0102] At a step 108, which occurs after the step 102, the method
100 further includes forming the secondary surface features 36 into
the one or more sections 34 of the textured region 20. This step
108 increases the surface roughness (R.sub.a) at the one or more
sections 34 to within the range of 5 nm to 100 nm. In embodiments,
the step 108 of forming the secondary surface features 36 into one
or more sections 34 of the textured region 20 comprises contacting
the one or more sections 34 of the textured region 20 of the
substrate 12 with a second etchant. The second etchant is different
than the etchant that was utilized to etch the primary surface
features 26 into the primary surface 18 of the substrate 12. In
embodiments, the second etchant includes acetic acid and ammonium
fluoride. In embodiments, the second etchant includes (in wt %): 85
to 98 acetic acid, 0.5 to 7.5 ammonium fluoride, and 0 to 11 water.
The water can be deionized water. In embodiments, the second
etchant contacts the one or more sections 34 for a time period
within a range of 15 seconds to 5 minutes. In embodiments, the
second etchant contacts the one or more sections 34 while the
etching mask used to form the primary surface features 26 remains
on the substrate 12. This would result in the increase of the
surface roughness (R.sub.a) of only the primary surface features 26
and not the surrounding portion 42, or only the surrounding portion
42 and not the primary surface features 26. After the period of
time has concluded the substrate 12 is rinsed with deionized water
and dried. Both etching steps 102, 108 can be conducted at room
temperature.
[0103] The method 100 is scalable and low-cost. In addition, the
method 100 is repeatable and is able to reproduce the textured
region 20 with the essentially the same geometry from substrate 12
to substrate 12. That is different than the previous methods, such
as sand-blasting or open etching, where the geometry of the
textured region 20 varied from one substrate 12 to the next.
EXAMPLES
[0104] Example 1--Example 1 is computer modeling that explores the
impact of the second surface features. Example 1 assumes that the
textured region is as illustrated in FIGS. 2 and 3, with primary
surface features arranged in a hexagonal pattern. Each primary
surface feature has a hexagonal perimeter and an aspheric surface
facing the external environment. Each aspheric surface is governed
by the equation:
z .function. ( r ) = r 2 R .function. [ 1 + 1 - ( 1 + .kappa. )
.times. r 2 R 2 ] .times. a 0 + .alpha. 4 .times. r 4 + a 6 .times.
r 6 + .times. .times. ##EQU00001##
[0105] where z(r) is the sag--the z-component of the displacement
of the surface from the vertex, at the distance from z axis. The
z-axis is perpendicular to the base-plane. The a.sub.0, a.sub.4,
a.sub.6 are all coefficients that describe the deviation of the
surface from the axially symmetric quadric surface specified by R
and .kappa.. If the coefficients are all zero, which they are
assumed to be here, then R is the radius of curvature and .kappa.
is the conic constant, as measured at the vertex. When the change
in elevation of the surface along the z-axis is a negative value,
then the surface of the primary surface features are concave. In
contrast, when the change in elevation of surface of the primary
surface features along the z-axis is positive, then the surface of
the primary surface features is convex.
[0106] Example 1 further assumes that the secondary surface
features generate a light scattering distribution that can be
described by the Gaussian scattering function:
I .function. ( .theta. ) = I 0 .times. exp .function. [ ( - 1 2 )
.times. ( .theta. .sigma. ) 2 ] ##EQU00002##
where, .theta. is the angle (degree) from the specular direction,
I(.theta.) is radiance in the .theta. direction, I.sub.0 is
radiance in the specular direction, and .sigma. (sigma) is the
standard deviation (or scattering factor) of the Gaussian
distribution, in degree. As .sigma. increases, the scattering angle
increases.
[0107] Zemax ray tracing software (Zemax, LLC of Kirkland, Wash.,
USA) was utilized to model distinctness-of-image, pixel power
deviation, and transmission haze as a function of change of
elevation (height) of the primary surface features and the .sigma.
provided by the secondary surface features. The modeling assumed
that the substrate had a thickness of 0.3 mm, that the refractive
index of the substrate was 1.49, and the substrate had no light
absorption.
[0108] FIG. 7A reproduces a graph of the calculations of the model
pertaining to distinctness-of-image. As the graph reveals,
increasing change in elevation (i.e., height or depth) of the
primary surface features decreases distinctness-of-image. When no
secondary surface features are present (sigma=0) on the primary
surface features, then the primary surface features do not begin to
decrease distinctness-of-image until the change in elevation
(height or depth) is greater than 0.08 .mu.m. However, when
secondary surface features are present on the primary surface
features, increasing height of the primary surface features
instantly causes a decrease in distinctness-of-image.
[0109] FIG. 7B reproduces a graph illustrating the difference the
presence of secondary surface features on the primary surface
features makes for decreasing distinctness-of-image compared to if
the secondary surface features were absent. When sigma=0.20 degree,
the presence of the secondary surface features further decreases
the distinctness-of-image, compared to if no secondary surface
features were present, for all heights of the primary surface
features from -0.24 .mu.m to +0.24 .mu.m. The presence of the
secondary surfaces features (providing .sigma.=0.20 degrees)
decreases the distinctness-of-image by a maximum of .about.29% when
the height of the primary surface features is .about.0.10 .mu.m,
compared to if no secondary surface features were present. When
.sigma.=0.41 degree, the presence of the secondary surface features
further decreases the distinctness-of-image, compared to if no
secondary surface features were present, for all heights of the
primary surface features from -0.27 .mu.m to +0.27. The presence of
the secondary surfaces features (providing .sigma.=0.41 degrees)
decreases the distinctness-of-image by a maximum of .about.25% when
the height of the primary surface features is .about.0.18 .mu.m,
compared to if no secondary surface features were present.
[0110] In short, for any given height/depth of the primary surface
features, there is an optimal .sigma. value to be incorporated as
the secondary surface features in order to maximize the
contribution that the secondary surface features has on decreasing
the distinctness-of-image. The graph reproduced at FIG. 7C reveals
the optimum value for .sigma., to minimize distinctness-of-image,
as a function of change in elevation (height) of the primary
surface features. The smallest distinctness-of-image values of 92%,
66%, 49% respectively for primary surface feature heights of 0.00
(flat), -0.10 .mu.m, and -0.14 .mu.m are achieved with .sigma.
being 0.14, 0.20, and 0.28 degree, respectively.
[0111] Next, the modeling software calculated pixel power deviation
as a function of the height of the primary surface features and
.sigma. value. FIGS. 7D and 7E each reproduce a graph of the
calculations. The graphs reveals that, as the height of the primary
surface features increases, the pixel power deviation increases.
However, as the value for .sigma. provided by the secondary surface
features increases, for any given height of the primary surface
features, the pixel power deviation decreases. The secondary
surface features cause scattering that evens the angular and
spatial distributions of the light transmitting through the primary
surface features and thus reduces the pixel power deviation. The
effect that the secondary surface features have on reducing pixel
power deviation becomes greater as the height of the primary
surface features increases. In short, the presence of the secondary
surface features on the primary surface features introduces surface
scattering that can reduce distinctness-of-image (for a given range
of heights of the primary surface features) and generally reduces
pixel power deviation.
[0112] Finally, the modeling software calculated transmission haze
as a function of the height of the primary surface features and
.sigma. value. FIGS. 7F and 7G each reproduce a graph of the
calculations. The graph of FIG. 7F reveals that increasing .sigma.
value increases generally increases pixel power deviation, and
increasing the height of the primary surface features magnifies the
affect that increasing .sigma. value on increasing pixel power
deviation (but only slightly). The graph of FIG. 7G reveals however
that .sigma. has to be above a certain value before .sigma. causes
an increase in pixel power deviation. In the instance of FIG. 7G,
where the primary surface features were assumed to have a height of
-0.1 .mu.m and a width of 100 .mu.m, the .sigma. only begins to
increase pixel power deviation when the value for .sigma. is about
0.35 or higher. The value for .sigma. can be greater than 0.35, in
order to further reduce pixel power deviation and
distinctness-of-image, if those benefits outweigh the increase in
transmission haze. For example, even at a .sigma. value of 0.7
degree, which maximizes the reduction in pixel power deviation and
distinctness-of-image, the transmission haze is only 20%, which may
be acceptable for a given application.
[0113] Thus, as long as the .sigma. value is configured to be right
below 0.35, the affect that the secondary features have on
decreasing distinctness-of-image and pixel power deviation does not
simultaneously cause an increase in transmission haze. For example,
when the height of the primary surface features are -0.1 .mu.m and
the .sigma. value is 0.41 degree, the calculated
distinctness-of-image is .about.74%, the pixel power deviation is
.about.2.5%, and the transmission haze is .about.1%. When the
height of the primary surface features are -0.1 .mu.m and the
.sigma. value is 0.2 degree, the calculated distinctness-of-image
is .about.64%, the pixel power deviation is .about.3.5%, and the
transmission haze is .about.0%. When the height of the primary
surface features are -0.08 .mu.m and the .sigma. value is 0.41
degree, the calculated distinctness-of-image is .about.85%, the
pixel power deviation is .about.2%, and the transmission haze is
.about.0%. When the height of the primary surface features are
-0.08 .mu.m and the .sigma. value is 0.20 degree, the calculated
distinctness-of-image is .about.73%, the pixel power deviation is
.about.2.5%, and the transmission haze is .about.0%.
[0114] In sum, the modeling demonstrates that the incorporation of
the secondary surface features on the primary surface features to
impart the surface roughness that causes a certain scattering level
can result in a low distinctness-of-image, low pixel power
deviation, and low transmission haze all simultaneously--something
not achievable with previous methods of forming the textured
region.
[0115] Examples 2A-2D--For Examples 2A-2D, four (4) samples of
glass were prepared. Each sample was etched with an etchant of
differing compositions to model the effect that the etchant would
have on the generation of secondary surface features to impart a
surface roughness within a range of 5 nm to 100 nm. All
compositions of the etchant included acetic acid and ammonium
fluoride (NH.sub.4F) in varying weight percentages. Table 1,
immediately, below summarizes the compositions of the four etchants
tested.
TABLE-US-00001 TABLE 1 Acetic Acid NH.sub.4F Water (Deionized)
Example (wt %) (wt %) (wt %) 2A 92 2 6 2B 92 6 2 2C 90 1 9 2D 96 4
0
Each etchant composition contacted the primary surface of the glass
substrate for a time period of 2 minutes.
[0116] After the etchant for each example etched the glass sample
for the 2-minute period of time, the surface roughness was
determined utilizing an atomic force microscope with a 5 .mu.m by 5
.mu.m scan size. Images that the atomic force microscope captured
for each example are reproduced at FIG. 8. The images show the
secondary surface features that impart the desired surface
roughness. Table 2 immediate below reports the measured surface
roughness for each sample. In addition, the .sigma. value, the
surface scattering factor, was measured for each sample. Here, the
measurement method of the surface scattering factor is as follows.
First, the transmission haze of a sample is measured. Then, a
raytracing model with Gaussian scattering function for describing
surface scattering is used to find proper surface scattering factor
which results the same transmission haze as the measured one. Those
values too are reported in Table 2 below.
TABLE-US-00002 TABLE 2 Example Surface Roughness (R.sub.a) (nm)
.sigma. (degrees) 2A 27.6 0.46 2B 19.3 0.42 2C 53.6 0.64 2D 11.2
0.34
[0117] In general, the higher the weight percentage of water, the
higher the surface roughness that was generated during the same two
minute period of time. In turn, the higher the surface roughness,
the higher the surface scattering .sigma. value. Thus, the surface
roughness can be controlled via manipulating the water content of
the composition of the etchant, and thus the acetic acid and
ammonium fluoride content of the composition of the etchant.
[0118] In addition, the transmission haze, coupled
distinctness-of-image, and pixel power deviation was measured for
each sample. Table 3, immediately below, reproduces the
results.
TABLE-US-00003 TABLE 3 Transmission Coupled Pixel Power Example
haze (%) DOI (%) Deviation (%) 2A 2.27 99.2 0.32 2B 1.16 99.58 1.07
2C 13.8 99.47 0.38 2D 0.12 99.48 0.31
Analysis of the results reveal that the higher the surface
roughness, the greater the transmission haze.
[0119] A graph reproduced at FIG. 8B reproduces the results. In
addition, a reproduced at FIG. 8D sets forth measured transmission
haze as a function of measured surface scattering .sigma. (sigma)
value for each sample, and then a line is modeled to fit the data.
The modeled line fitting measured data agrees with the ray
scattering model of Example 1 that indicated that the surface
scattering .sigma. value had to reach a certain value before it
began to impart increased transmission haze.
[0120] Examples 3A and 3B--Examples 3A and 3B demonstrate the
effect that the secondary surface features (imparting the surface
roughness) has on pixel power deviation for samples were primary
surface features are also present. For the samples of both Example
3A and 3B, primary surface features were etched into a glass
substrate. The composition of the etchant included 1 wt %
hydrofluoric acid (HF) and 2 wt % nitric acid (HNO.sub.3). The
etchant contacted the primary surface of the glass substrate for 25
seconds, resulting the primary surface features having a depth of
150 nm from a surrounding portion. A dry film resist etching mask
was utilized to position the primary surface features in a
hexagonal pattern set into the surrounding portion (see FIG. 5).
The perimeter of each primary surface feature was hexagonal as
well. Each primary surface feature was separated by a
center-to-center distance of 120 .mu.m. Adjacent primary surface
features were separated, perimeter to perimeter, by a distance of
55 .mu.m. One of the samples was retained as Example 3A and no
secondary surface features were subsequently added to the sample of
Example 3A
[0121] For Example 3B, the sample was subjected to a second etching
step to impart secondary surface features. The second etching step
used an etchant with a composition of 92 wt % acetic acid, 2 wt %
ammonium fluoride, and 6 wt % water (deionized). The etchant
contacted the primary surface with the primary surface features for
a period of time of 2 minutes. The etchant formed the secondary
surface features within the textured region, which imparted a
surface roughness (R.sub.a) of .about.28 nm.
[0122] The pixel power deviation that the samples of both Example
3A and Example 3B generated were measured. The measured pixel power
deviation was sensitive to the orientation of the sample to the
display pixel array, because the primary surface features had a
hexagonal perimeter. A graph reproduced at FIG. 9A reproduces the
measured pixel power deviation for both Examples 3A and 3B as a
function of the orientation angle 52 of the sample. The schematic
illustration at FIG. 9B shows what orientation angle means. In
short, the substrate is over the display, with the textured region
at the primary surface facing away from the display. The display
has pixels 54. The substrate forms the orientation angle relative
to the display. As the substrate is rotated relative to the display
about an axis extending through the substrate orthogonal to the
primary surface, the orientation angle changes.
[0123] Analysis of the graph of FIG. 9A reveals that the Example
3B, with the added secondary surface features over the primary
surface features to impart surface roughness, lowered the pixel
power deviation compared to Example 3A, which included only the
primary surface features. The secondary surface features lowered
the pixel power deviation by .about.0.2% to 2.5% (in absolute
terms), depending on orientation angle of the substrate relative to
the display. For example, at the orientation angle of 85%, the
pixel power deviation of Example 3A was 6.5%, while the pixel power
deviation of Example 3B was 4.0%, for a reduction (in absolute
terms) of 2.5%, (or a 41.7% relative reduction in pixel power
display, where 6.5%-4.0%=2.5% and 2.5%/6.5%*100% is 41.7%). The
results suggest that the effect that the secondary surface features
has on the pixel power deviation of the sample is a function of the
geometry of the primary surface features.
[0124] Examples 4A-4H--For each of Examples 4A-4H, a glass
substrate was obtained having dimensions of 4 mm by 4 mm by 0.7 mm.
The glass substrate was then subjected to a first etching step to
etch primary surface features set into a surrounding portion. Each
primary surface feature had a perimeter that was circular. The
diameter of the perimeter was 40 .mu.m. An etching mask was
utilized to place each of the primary surface features. The
placement of each of the primary surface features was generated
using a spacing distribution algorithm. The spacing distribution
algorithm required a minimum center-to-center distance between
circles of 50 .mu.m. The placement of the primary surface features
pursuant to the spacing distribution algorithm was thus randomized
and did not form a pattern. The placement of the primary surface
features made pursuant to the spacing distribution algorithm was
transferred to a lithograph mask, which was then used to cure AZ
4210 lithography ink disposed on the primary surface of the
substrate. The uncured portions of the lithograph ink was removed
and the cured portion remained as the etching mask. The primary
surface features occupied about 50% of the area of the textured
region, and the depth of the primary surface features was 0.18
.mu.m. The etchant of the first etching step comprised 1 wt %
hydrofluoric acid (HF) and 2 wt % nitric acid (HNO.sub.3). The
etchant contacted the substrate for a period of time to achieve the
target 150 nm depth based on etch rate. For of the samples were
then set aside as Example 4A-4D and not subjected to a second
etching step to impart secondary surface features.
[0125] The remaining four samples were assigned to be Examples
4E-4H and each subjected to a second etching step using an etchant
including acetic acid, ammonium fluoride, and water (deionized).
The etchant for Examples 4E and 4F had a composition of 92 wt %
acetic acid, 2 wt % ammonium fluoride, and 6 wt % water
(deionized). The second etching step for Examples 4E and 4F formed
secondary surface features that imparted a surface roughness (Ra)
of .about.28 nm. The etchant for Examples 4G and 4H had a
composition of 90 wt % acetic acid, 1 wt % ammonium fluoride, and 9
wt % water (deionized). In each of Examples 4E-4H, the etchant
contacted the sample of a time period of 2 minutes. The second
etching step for Examples 4G and 4H formed secondary surface
features that imparted a surface roughness (Ra) of .about.54
nm.
[0126] Referring now to FIGS. 10A-10D, the pixel power deviation
(FIG. 10A), the specular reflectance (FIG. 10B), the
distinctness-of-image (FIG. 10C), and the transmission haze (FIG.
10D) were measured for each example. The measurements are set forth
in the aforementioned graphs at FIGS. 10A-10D. Analysis of the
graphs reveal that the second etching step that formed the
secondary surface features that added surface roughness to the
textured region resulted in a lowering of pixel power deviation and
distinctness-of-image but resulted in increasing the transmission
haze. The higher surface roughness of that the secondary surface
features imparted to Examples 4G and 4H did not result in a
different scale of lowering of distinctness-of-image compared to
Examples 4E and 4F. However, the higher surface roughness of that
the secondary surface features imparted to Examples 4G and 4H did
result in a larger decrease in pixel power deviation compared to
Examples 4E and 4F but with a larger increase in transmission haze.
The addition of the secondary surface features did not appear to
affect measured specular reflectance.
[0127] Examples 5A-5O--For Examples 5A-5O, a spacing distribution
algorithm was utilized to randomly but specifically place points
within an area. Each of the points were to be separated by a
minimum distance of 105 .mu.m. The points were then triangulated,
an inellipse drawn in each triangle, and then the points and
triangles were removed. The longest dimension of the ellipses now
remaining in the area were scaled down so that the ellipses
occupied 50 percent of the area. The placement of the ellipses was
then transferred to a lithography mask. The lithography mask was
used to form an etching mask on the primary surface of a glass
substrate. Each substrate was then etched with the etching mask on
the substrate. The etchant utilized had a composition of 0.15 wt %
hydrofluoric acid and 1 wt % nitric acid. The etchant contacted the
primary surface with the etching mask for a period of time set
forth in Table 4 immediately below that varied among the samples.
The etchant formed primary surface features having an elliptical
perimeter set into a surrounding portion. The depth of the primary
surface features varied, and the depth for each sample is set forth
below.
TABLE-US-00004 TABLE 4 Etching Period of Time Depth of Primary
Surface Example (seconds) Features (.mu.m) 5A 212 0.186 5B 200
0.179 5C 165 0.1451 5D 150 0.1353 5E 140 0.1311 5F 178 0.1639 5G
178 0.1619 5H 167 0.1557 5I 167 0.1526 5J 133 0.1261 5K 133 0.1261
5L 150 0.1364 5M 178 0.1531 5N 167 0.1436 5O 167 0.1429
[0128] After removal of the etching mask, the samples of 5M-5O were
then subjected to a second etching step to form secondary surface
features at the primary surface. The second etching step used an
etchant with a composition of 92 wt % acetic acid, 2 wt % ammonium
fluoride, and 6 wt % water (deionized). The etchant contacted the
substrate for a time period of 120 seconds. The secondary surface
features so formed imparted a surface roughness (Ra) of .about.28
nm to the textured region at the primary surface.
[0129] The pixel power deviation, distinctness-of-image, specular
reflection, and transmission haze were measured for the sample of
each of Examples 5A-5O. The measured results are set forth in the
graphs of FIGS. 11A-11D, which plot the measured value as a
function of the depth of the primary surface features with the
elliptical perimeter. Analysis of the graphs reveal that the
secondary surface features to impart surface roughness of Examples
5M-5O resulted in a lower pixel power deviation and specular
reflectance compared to when no such secondary surface features
were included in Examples 5A-5L. However, the secondary surface
features to impart surface roughness of Examples 5M-5O resulted in
a higher distinctness-of-image and transmission haze compared to
when no such secondary surface features were included in Examples
5A-5L. In general, the introducing of the secondary surface
features to the primary surface features can be either increase or
decrease the distinctness-of-image, which depends on the design of
the primary surface features. Unlike the model of Example 1, the
design of the primary surface features of this experimental sample
resulted in the increasing of the distinctness-of-image.
[0130] Example 6A-6C--Examples 6A and 6B are two different sets of
samples, each with primary surface features having an elliptical
perimeter, just as in Examples 5A-5O. The difference was that for
the samples of Example 6A, the etching mask used while forming the
primary surface features was kept on the substrate while the second
etching step was performed to generate the secondary surface
features. For the samples of Example 6B, the etching mask was
removed before the second etching step was performed to generate
the secondary surface features. Thus, in the samples of Example 6A,
the secondary surface features and the added surface roughness were
formed only on surfaces provided by the primary surface features
and not the surrounding portion. In contrast, with the samples of
Example 6B, the secondary surface features and the added surface
roughness were formed on the entire textured region including both
the surrounding portion and the surfaces provided by the primary
surface features.
[0131] A scanning electron microscope captured images of a sample
from both Example 6A and Example 6B. The images are reproduced at
FIG. 12A. The images on the left show the primary surface features
with the elliptical perimeters set into the surrounding portion.
The images in the middle show the secondary surface features. The
images on the right show the etching depth of the secondary surface
features.
[0132] The pixel power deviation, transparency haze, and specular
reflectance of samples from both Examples 6A and 6B were measured.
A Rhopoint instrument was utilized to determine specular
reflectance. The graphs reproduced at FIGS. 12B-12D set forth the
measured data. Analysis of the graphs reveal that the samples of
Example 6B, where the etching mask was removed before the second
etching step to impart second surface features throughout the
entire textured region, resulted in a lower pixel power deviation
but higher transmission haze compared to the samples of Example 6A,
where the etching mask was maintained during the second etching
step and thus the second surface features were imparted only to the
surfaces provided by the primary surface features.
[0133] The Rhopoint instrument utilized to measure specular
reflectance did not measure a difference between the samples of
Examples 6A and 6B. However, the device could measure differences
in specular reflectance when a 6 degree angle of incidence for the
light to be reflected and a 2 degree aperture to measure the
specular reflectance. The graph reproduced at FIG. 12E shows the
measured data for samples of Examples 6A and 6B, as well as for a
sample (Example 6C) where only the primary surface features were
present and did not include the secondary surface features to
impart surface roughness. Analysis of the graph of FIG. 12E reveals
that the presence of the secondary surface features in Examples 6A
and 6B reduced specular reflectance compared to when the secondary
surface features were absent in Example 6C. The difference in
specular reflectance between Examples 6A and 6B is wavelength
dependent.
[0134] Example 7--For Example 7, a sample was prepared similar to
the samples Examples 5M-5O, where primary surface features with an
elliptical perimeter are set into a surrounding portion in a first
etching step forming textured region, and then secondary surface
features are etched throughout the entire textured region to
increase surface roughness. The sample so prepared was then
analyzed with a white light interferometer to measure the three
dimensional profile of the textured region. FIG. 13A illustrates
the three dimensional profile that was measured. The top half
illustrates relative elevation differences between primary surface
features and the surrounding portion. The bottom half illustrates
the topography of the secondary surface features, with the
topography of the secondary surface features added to the surfaces
that the primary surface features are provided illustrated at the
left, and the topography of the secondary surface features added to
the surrounding portion illustrated at the right. The three
dimensional profile of the secondary features within the primary
surface features is measurably different than the three dimensional
profile of the secondary features at the surrounding portion--with
the surrounding portion showing deeper secondary features.
[0135] An atomic force microscope was utilized to image and
determine the surface roughness (Ra) imparted by the secondary
surface features at both (i) a surface provided by a primary
surface feature and (ii) at the surrounding portion. The images are
reproduced at FIG. 13B. The image on the left is of the secondary
surface features at the surface provided by the primary surface
feature, and shows a surface roughness (R.sub.a) of 15.3 nm. The
image on the right is of the secondary surface features at the
surrounding portion, and shows a surface roughness (R.sub.a) of
33.5 nm. The image on the right and the higher surface roughness
(R.sub.a) value at the surrounding portion matches the topography
date illustrated at FIG. 13A. The surrounding portion was covered
by the etching mask during the formation of the primary surface
features and thus had not been contacted with an etchant, unlike
the primary surface features which were created by the first
etching step. Thus, it is believed that the surrounding portion,
previously untouched by an etchant, was more sensitive to the
second etching step to impart the secondary surface features.
* * * * *