U.S. patent application number 16/388487 was filed with the patent office on 2020-10-22 for reducing demolding stress at edges of gratings in nanoimprint lithography.
The applicant listed for this patent is Facebook Technologies, LLC. Invention is credited to Giuseppe CALAFIORE.
Application Number | 20200333527 16/388487 |
Document ID | / |
Family ID | 1000005132209 |
Filed Date | 2020-10-22 |
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United States Patent
Application |
20200333527 |
Kind Code |
A1 |
CALAFIORE; Giuseppe |
October 22, 2020 |
REDUCING DEMOLDING STRESS AT EDGES OF GRATINGS IN NANOIMPRINT
LITHOGRAPHY
Abstract
A nano-structure includes an outer area at an edge of the
nano-structure. A width of the outer area defined by a distance
from the edge of the nano-structure is less than 100 .mu.m. A depth
of the nano-structure in the outer area changes gradually between
0% and at least 50% of a maximum depth of the nano-structure. A
method includes forming an etch mask on a substrate and etching the
substrate with the etch mask using an ion beam to form a
nano-structure in the substrate. The etch mask includes an outer
area near an edge of the etch mask. A width of the outer area
defined by a distance from the edge of the etch mask is less than
100 .mu.m. A duty cycle of the etch mask in the outer area changes
gradually between at least 10% and at least 90%.
Inventors: |
CALAFIORE; Giuseppe;
(Redmond, WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Facebook Technologies, LLC |
Menlo Park |
CA |
US |
|
|
Family ID: |
1000005132209 |
Appl. No.: |
16/388487 |
Filed: |
April 18, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03F 7/0002 20130101;
G02B 6/0035 20130101; G02B 6/0016 20130101; G02B 2027/0178
20130101; G02B 6/0065 20130101; G02B 27/0172 20130101; G03F 7/0005
20130101 |
International
Class: |
F21V 8/00 20060101
F21V008/00; G02B 27/01 20060101 G02B027/01; G03F 7/00 20060101
G03F007/00 |
Claims
1. A nano-structure, comprising: an outer area at an edge of the
nano-structure, wherein: a width of the outer area defined by a
distance from the edge of the nano-structure is less than 100
.mu.m; and a depth of the nano-structure in the outer area changes
gradually between 0% and at least 50% of a maximum depth of the
nano-structure.
2. The nano-structure of claim 1, wherein the depth of the
nano-structure in the outer area gradually decreases towards the
edge of the nano-structure.
3. The nano-structure of claim 1, wherein the maximum depth of the
nano-structure is at least 100 nm.
4. The nano-structure of claim 1, wherein the depth of the
nano-structure in the outer area gradually changes from 400 nm or
less to 5 nm or less.
5. The nano-structure of claim 1, wherein the nano-structure
comprises: a plurality of ridges; and a plurality of trenches each
defined by two adjacent ridges, wherein: the depth of the
nano-structure is defined by a depth of each of the plurality of
trenches; and the depth of at least one trench of the plurality of
trenches changes gradually in the outer area between 0% and at
least 50% of a maximum depth of the at least one trench.
6. The nano-structure of claim 5, wherein at least one of the
plurality of ridges has a slant angle of greater than 30.degree.,
greater than 45.degree., or greater than 60.degree..
7. The nano-structure of claim 1, wherein the nano-structure
comprises a surface-relief grating configured to couple light into
and/or out of a substrate, and wherein the surface-relief grating
comprises a resin.
8. The nano-structure of claim 1, wherein the nano-structure
comprises a mold for nano-imprint lithography, and wherein the mold
comprises a resin.
9. The nano-structure of claim 1, wherein the nano-structure
comprises a mold for nano-imprint lithography, and wherein the mold
comprises a semiconductor, an oxide, or a metal.
10. The nano-structure of claim 1, wherein a duty cycle of the
nano-structure in the outer area changes gradually between at least
10% and at least 90%.
11. The nano-structure of claim 10, wherein the duty cycle of the
nano-structure gradually increases towards the edge of the
nano-structure.
12. The nano-structure of claim 1, wherein the outer area surrounds
less than an entire periphery of the nano-structure.
13. A method comprising: forming an etch mask on a substrate,
wherein the etch mask comprises an outer area near an edge of the
etch mask, and wherein: a width of the outer area defined by a
distance from the edge of the etch mask is less than 100 .mu.m; a
duty cycle of the etch mask in the outer area changes gradually
between at least 10% and at least 90%; and etching the substrate
with the etch mask using an ion beam to form a nano-structure in
the substrate.
14. The method of claim 13, wherein the duty cycle of the etch mask
gradually increases towards the edge of the etch mask.
15. The method of claim 14, wherein an etch depth in the substrate
gradually decreases towards an edge of the nano-structure.
16. The method of claim 15, wherein the etch depth decreases from
400 nm or less to 5 nm towards the edge of the nano-structure.
17. The method of claim 13, wherein the substrate comprises a
semiconductor, an oxide, or a metal, the method further comprising:
forming a stamp using the nano-structure in the substrate, wherein
the stamp comprises a resin.
18. The method of claim 17, further comprising: forming a
surface-relief grating using the stamp, wherein a depth of the
surface-relief grating decreases gradually towards an edge of the
surface-relief grating.
19. The method of claim 18, wherein the surface-relief grating
comprises: a plurality of ridges; a plurality of trenches each
defined by two adjacent ridges; wherein: the depth of the
surface-relief grating is defined by a depth of each of the
plurality of trenches; and the depth of at least one trench of the
plurality of trenches gradually decreases in the outer area from at
least 50% to 0% of a maximum depth of the at least one trench.
20. The method of claim 19, wherein at least one of the plurality
of ridges has a slant angle of greater than 30.degree., greater
than 45.degree., or greater than 60.degree..
Description
BACKGROUND
[0001] An artificial reality system, such as a head-mounted display
(HMD) or heads-up display (HUD) system, generally includes a
display configured to present artificial images that depict objects
in a virtual environment. The display may display virtual objects
or combine real objects with virtual objects, as in virtual reality
(VR), augmented reality (AR), or mixed reality (MR) applications.
For example, in an AR system, a user may view both images of
virtual objects (e.g., computer-generated images (CGIs)) and the
surrounding environment by, for example, seeing through transparent
display glasses or lenses (often referred to as optical
see-through) or viewing displayed images of the surrounding
environment captured by a camera (often referred to as video
see-through).
[0002] One example optical see-through AR system may use a
waveguide-based optical display, where light of projected images
may be coupled into a waveguide (e.g., a substrate), propagate
within the waveguide, and be coupled out of the waveguide at
different locations. In some implementations, the light may be
coupled out of the waveguide using a diffractive optical element,
such as a grating. The grating may diffract both the light of the
projected image and light from the surrounding environment (e.g.,
from a light source, such as a lamp). The diffracted light from the
surrounding environment may appear as a ghost image to the user of
the AR system. In addition, due to the wavelength dependent
characteristics of the grating, ghost images of different colors
may appear at different locations or angles. These ghost images may
negatively impact the user experience of using an artificial
reality system.
SUMMARY
[0003] This disclosure relates generally to waveguide-based
near-eye display systems. More specifically, this disclosure
relates to nanoimprint lithography (NIL) molding techniques for
manufacturing surface-relief structures, such as straight or
slanted surface-relief gratings used in a near-eye display
system.
[0004] In NIL molding, an NIL mold (e.g., a soft stamp or any other
working stamp having a nano-structure) may be pressed against an
NIL resin layer for molding a nano-structure (e.g., a grating) in
the NIL resin layer. To limit damage of the nano-structures of the
NIL mold and the imprinted resin layer during demolding, in some
embodiments, the depth of the nano-structure of the NIL mold may
gradually change at the edges of the NIL mold. The edge area having
the gradual depth change may be small so as to reduce the effect of
the gradual depth change in the imprinted nano-structure on the
performance of the imprinted nano-structure.
[0005] In some embodiments, reactive ion etch (RIE) lag effect may
be utilized to etch nano-structures with a large gradual depth
change in a small area near the edges of the nano-structures (e.g.,
in a master mold). The etch mask used for etching the nanostructure
in the master mold may be modified to include a large gradual
change in duty cycle in a small area such that a large change in
etch depth in a small area in the etched nano-structure in the
master mold can be achieved due to the RIE lag effect. The master
mold may then be used to produce soft stamps and/or surface-relief
structures having nanostructures having a large change in depth in
a small area.
[0006] In some embodiments, a nano-structure may include an outer
area at an edge of the nano-structure. A width of the outer area
defined by a distance from the edge of the nano-structure may be
less than 100 .mu.m. A depth of the nano-structure in the outer
area may change gradually between 0% and at least 50% of a maximum
depth of the nano-structure.
[0007] In some embodiments, the depth of the nano-structure in the
outer area may gradually decrease towards the edge of the
nano-structure. In some embodiments, the maximum depth of the
nano-structure may be at least 100 nm. In some embodiments, the
depth of the nano-structure in the outer area may gradually change
from 400 nm or less to 5 nm or less.
[0008] In some embodiments, the nano-structure may include a
plurality of ridges and a plurality of trenches each defined by two
adjacent ridges. The depth of the nano-structure may be defined by
a depth of each of the plurality of trenches. The depth of at least
one trench of the plurality of trenches may change gradually in the
outer area between 0% and at least 50% of a maximum depth of the at
least one trench. In some embodiments, at least one of the
plurality of ridges may have a slant angle of greater than
30.degree., greater than 45.degree., or greater than
60.degree..
[0009] In some embodiments, the nano-structure may include a
surface-relief grating configured to couple light into and/or out
of a substrate, and wherein the surface-relief grating may include
a resin. In some embodiments, the nano-structure may include a mold
for nano-imprint lithography, and the mold may include a resin. In
some embodiments, the nano-structure may include a mold for
nano-imprint lithography, and the mold may include a semiconductor,
an oxide, or a metal.
[0010] In some embodiments, a duty cycle of the nano-structure in
the outer area may change gradually between at least 10% and at
least 90%. In some embodiments, the duty cycle of the
nano-structure may gradually increase towards the edge of the
nano-structure. In some embodiments, the outer area surrounds less
than an entire periphery of the nano-structure.
[0011] In some embodiments, a method may include forming an etch
mask on a substrate and etching the substrate with the etch mask
using an ion beam to form a nano-structure in the substrate. The
etch mask may include an outer area near an edge of the etch mask.
A width of the outer area defined by a distance from the edge of
the etch mask may be less than 100 .mu.m. A duty cycle of the etch
mask in the outer area may change gradually between at least 10%
and at least 90%.
[0012] In some embodiments, the duty cycle of the etch mask may
gradually increase towards the edge of the etch mask. In some
embodiments, an etch depth in the substrate may gradually decrease
towards an edge of the nano-structure. In some embodiments, the
etch depth may decrease from 400 nm or less to 5 nm towards the
edge of the nano-structure.
[0013] In some embodiments, the substrate may include a
semiconductor, an oxide, or a metal. The method may further include
forming a stamp using the nano-structure in the substrate, and the
stamp may include a resin. In some embodiments, the method may
further include forming a surface-relief grating using the stamp. A
depth of the surface-relief grating may decrease gradually towards
an edge of the surface-relief grating. In some embodiments, the
surface-relief grating may include a plurality of ridges and a
plurality of trenches each defined by two adjacent ridges. The
depth of the surface-relief grating may be defined by a depth of
each of the plurality of trenches. The depth of at least one trench
of the plurality of trenches may gradually decrease in the outer
area from at least 50% to 0% of a maximum depth of the at least one
trench. In some embodiments, at least one of the plurality of
ridges may have a slant angle of greater than 30.degree., greater
than 45.degree., or greater than 60.degree..
[0014] This summary is neither intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used in isolation to determine the scope of the
claimed subject matter. The subject matter should be understood by
reference to appropriate portions of the entire specification of
this disclosure, any or all drawings, and each claim. The
foregoing, together with other features and examples, will be
described in more detail below in the following specification,
claims, and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Illustrative embodiments are described in detail below with
reference to the following figures.
[0016] FIG. 1 is a simplified diagram of an example near-eye
display according to certain embodiments.
[0017] FIG. 2 is a cross-sectional view of an example near-eye
display according to certain embodiments.
[0018] FIG. 3 is an isometric view of an example waveguide display
according to certain embodiments.
[0019] FIG. 4 is a cross-sectional view of an example waveguide
display according to certain embodiments.
[0020] FIG. 5 is a simplified block diagram of an example
artificial reality system including a waveguide display.
[0021] FIG. 6 illustrates an example optical see-through augmented
reality system using a waveguide display according to certain
embodiments;
[0022] FIG. 7 illustrates propagations of display light and
external light in an example waveguide display.
[0023] FIG. 8 illustrates an example slanted grating coupler in an
example waveguide display according to certain embodiments.
[0024] FIGS. 9A and 9B illustrate an example process for
fabricating a slanted surface-relief grating by molding according
to certain embodiments. FIG. 9A shows a molding process. FIG. 9B
shows a demolding process.
[0025] FIGS. 10A-10D illustrate an example process for fabricating
a soft stamp used to make a slanted surface-relief grating
according to certain embodiments. FIG. 10A shows a master mold.
FIG. 10B illustrates the master mold coated with a soft stamp
material layer. FIG. 10C illustrates a lamination process for
laminating a soft stamp foil onto the soft stamp material
layer.
[0026] FIG. 10D illustrates a delamination process, where the soft
stamp including the soft stamp foil and the attached soft stamp
material layer is detached from the master mold.
[0027] FIGS. 11A-11D illustrate an example process for fabricating
a slanted surface-relief grating using a soft stamp according to
certain embodiments. FIG. 11A shows a waveguide coated with an
imprint resin layer. FIG. 11B shows the lamination of the soft
stamp onto the imprint resin layer. FIG. 11C shows the delamination
of the soft stamp from the imprint resin layer. FIG. 11D shows an
example of an imprinted slanted grating formed on the
waveguide.
[0028] FIG. 12 is a simplified flow chart illustrating an example
method of fabricating a slanted surface-relief grating using
nanoimprint lithography according to certain embodiments.
[0029] FIG. 13A is a top view of an example soft stamp that has
been laminated onto an imprint resin layer.
[0030] FIG. 13B is a cross-sectional side view taken along line
13B-13B of FIG. 13A, illustrating a portion of the imprint resin
layer and the soft stamp of FIG. 13A that has been partially
delaminated.
[0031] FIG. 13C is a cross-sectional side view similar to FIG. 13B,
illustrating a portion of the imprint resin layer and the soft
stamp of FIG. 13A that has been further delaminated.
[0032] FIG. 14A is a top view of another example soft stamp that
has been laminated onto an imprint resin layer according to certain
embodiments.
[0033] FIG. 14B is a cross-sectional side view taken along line
14B-14B of FIG. 14A, illustrating a portion of the imprint resin
layer and the soft stamp of FIG. 14A that has been partially
delaminated according to certain embodiments.
[0034] FIG. 14C is a cross-sectional side view similar to FIG. 14B,
illustrating a portion of the imprint resin layer and the soft
stamp of FIG. 14A that has been further delaminated according to
certain embodiments.
[0035] FIGS. 15A and 15B are a side view and a top view,
respectively, of a master mold material layer and a master mold
mask for fabricating a master mold according to certain
embodiments.
[0036] FIGS. 15C, 15D, and 15E are various cross-sectional views of
a master mold fabricated using the master mold mask shown in FIGS.
15A and 15B according to certain embodiments. The cross-sectional
views shown in FIGS. 15C, 15D, and 15E are taken along line
15C-15C, line 15D-15D, and line 15E-15E of FIG. 15B,
respectively.
[0037] FIG. 16 illustrates an example of a reactive ion etching lag
curve that represents the relationship between duty cycles and etch
depths.
[0038] FIG. 17 is a simplified flow chart illustrating an example
method of fabricating a slanted surface-relief grating using
nanoimprint lithography according to certain embodiments.
[0039] FIG. 18 is a simplified block diagram of an example
electronic system of an example near-eye display for implementing
some of the examples disclosed herein.
[0040] The figures depict embodiments of the present disclosure for
purposes of illustration only. One skilled in the art will readily
recognize from the following description that alternative
embodiments of the structures and methods illustrated may be
employed without departing from the principles, or benefits touted,
of this disclosure.
[0041] In the appended figures, similar components and/or features
may have the same reference label. Further, various components of
the same type may be distinguished by following the reference label
by a dash and a second label that distinguishes among the similar
components. If only the first reference label is used in the
specification, the description is applicable to any one of the
similar components having the same first reference label
irrespective of the second reference label.
DETAILED DESCRIPTION
[0042] This disclosure relates generally to waveguide-based
near-eye display system. More specifically, this disclosure relates
to nanoimprint techniques for manufacturing surface-relief
structures, such as straight or slanted surface-relief gratings
used in a near-eye display system. The surface-relief structures
may be fabricated using many different nanofabrication techniques.
For example, in some implementations, the surface-relief structures
may be fabricated using lithography and etching techniques. In some
implementations, the surface-relief structures may be fabricated
using nanoimprint lithography (NIL) molding techniques. NIL molding
may significantly reduce the cost of the surface-relief
structures.
[0043] In NIL molding, a substrate may be coated with an NIL resin
layer. An NIL mold (e.g., a soft stamp including a polymeric
material or any other working stamp) with straight or slanted
structures may be pressed against the NIL resin layer for molding a
grating in the NIL resin layer. A soft stamp (e.g., made of
polymers) may offer more flexibility during the molding and
demolding processes. The NIL resin layer may be cured subsequently
using, for example, heat and/or ultraviolet (UV) light. The NIL
mold may then be detached or delaminated from the NIL resin layer,
and structures that are complementary to the structures of the NIL
mold may be formed in the NIL resin layer.
[0044] During delamination (or demolding) of the soft stamp, a
delamination front or crack may be created between surfaces of the
soft stamp and the NIL resin layer. At the beginning of the
demolding, the delamination front or crack may uniformly propagate
at a flat interface between the soft stamp and the NIL resin layer
because there may not be nano-structures at edges of the soft
stamp. However, when the delamination front or crack reaches the
edges of the nano-structures, the stress in the nano-structures of
the soft stamp or the resin layer may change suddenly as the
contact surface area between the soft stamp and the NIL resin layer
may increase suddenly due to the nano-structures. As such, the
nano-structures on the soft stamp or the resin layer may be damaged
due to the stress.
[0045] Thus, it may be desirable to have a gradual change in the
depth of the nano-structures at the edges of the soft stamp. In
addition, it may be desirable that the edge area having the gradual
change in the depth of the nano-structures is small in order to
reduce the effect of the gradual change in the depth of the
nano-structures on the performance of the nano-structures, such as
straight or slanted surface-relief gratings. However, it may be
challenging to fabricate a master mold having nano-structures with
a large gradual depth change in a small area at (e.g., within about
0.1-100 .mu.m from) the edges of the nano-structures using existing
etching techniques.
[0046] According to certain embodiments, to etch nano-structures
with a large gradual depth change in a small area near the edges of
the nano-structures (e.g., in a master mold), the edges of the mask
used for etching the master mold may be modified to include a large
gradual change in duty cycle in a small area. When the mask is used
for etching the nano-structure, the reactive ion etch (RIE) lag
effect may cause the areas with different duty cycles to be etched
at different rates and therefore have different depths. For
example, areas with larger duty cycles (narrower trenches) may be
etched at lower rates because of mean free path shortening and more
ineffective transport of the etched species. On the other hand,
areas with smaller duty cycles (wide trenches) may be etched at
faster rates because it is easier to remove the etched species when
the duty cycles are small. As such, a large gradual change in duty
cycle in a small area on the mask corresponding to the edges of the
nano-structure in the master mold may cause a large gradual depth
change in a small area near the edges of the etched nano-structure.
In this way, the stress may change gradually within a short
distance near the edges of the nano-structure to avoid a sudden
change and damage of the imprinted nano-structure or the working
stamp.
[0047] In the following description, for the purposes of
explanation, specific details are set forth in order to provide a
thorough understanding of examples of the disclosure. However, it
will be apparent that various examples may be practiced without
these specific details. For example, devices, systems, structures,
assemblies, methods, and other components may be shown as
components in block diagram form in order not to obscure the
examples in unnecessary detail. In other instances, well-known
devices, processes, systems, structures, and techniques may be
shown without necessary detail in order to avoid obscuring the
examples. The figures and description are not intended to be
restrictive. The terms and expressions that have been employed in
this disclosure are used as terms of description and not of
limitation, and there is no intention in the use of such terms and
expressions of excluding any equivalents of the features shown and
described or portions thereof.
[0048] FIG. 1 is a simplified diagram of an example near-eye
display 100 according to certain embodiments. Near-eye display 100
may present media to a user. Examples of media presented by
near-eye display 100 may include one or more images, video, and/or
audio. In some embodiments, audio may be presented via an external
device (e.g., speakers and/or headphones) that receives audio
information from near-eye display 100, a console, or both, and
presents audio data based on the audio information. Near-eye
display 100 is generally configured to operate as an artificial
reality display. In some embodiments, near-eye display 100 may
operate as an augmented reality (AR) display or a mixed reality
(MR) display.
[0049] Near-eye display 100 may include a frame 105 and a display
110. Frame 105 may be coupled to one or more optical elements.
Display 110 may be configured for the user to see content presented
by near-eye display 100. In some embodiments, display 110 may
include a waveguide display assembly for directing light from one
or more images to an eye of the user.
[0050] FIG. 2 is a cross-sectional view 200 of near-eye display 100
illustrated in FIG. 1. Display 110 may include may include at least
one waveguide display assembly 210. An exit pupil 230 may be
located at a location where a user's eye 220 is positioned when the
user wears near-eye display 100. For purposes of illustration, FIG.
2 shows cross-section sectional view 200 associated with user's eye
220 and a single waveguide display assembly 210, but, in some
embodiments, a second waveguide display may be used for the second
eye of the user.
[0051] Waveguide display assembly 210 may be configured to direct
image light (i.e., display light) to an eyebox located at exit
pupil 230 and to user's eye 220. Waveguide display assembly 210 may
include one or more materials (e.g., plastic, glass, etc.) with one
or more refractive indices. In some embodiments, near-eye display
100 may include one or more optical elements between waveguide
display assembly 210 and user's eye 220.
[0052] In some embodiments, waveguide display assembly 210 may
include a stack of one or more waveguide displays including, but
not restricted to, a stacked waveguide display, a varifocal
waveguide display, etc. The stacked waveguide display is a
polychromatic display (e.g., a red-green-blue (RGB) display)
created by stacking waveguide displays whose respective
monochromatic sources are of different colors. The stacked
waveguide display may also be a polychromatic display that can be
projected on multiple planes (e.g. multi-planar colored display).
In some configurations, the stacked waveguide display may be a
monochromatic display that can be projected on multiple planes
(e.g. multi-planar monochromatic display). The varifocal waveguide
display is a display that can adjust a focal position of image
light emitted from the waveguide display. In alternate embodiments,
waveguide display assembly 210 may include the stacked waveguide
display and the varifocal waveguide display.
[0053] FIG. 3 is an isometric view of an embodiment of a waveguide
display 300. In some embodiments, waveguide display 300 may be a
component (e.g., waveguide display assembly 210) of near-eye
display 100. In some embodiments, waveguide display 300 may be part
of some other near-eye displays or other systems that may direct
image light to a particular location.
[0054] Waveguide display 300 may include a source assembly 310, an
output waveguide 320, and a controller 330. For purposes of
illustration, FIG. 3 shows waveguide display 300 associated with a
user's eye 390, but in some embodiments, another waveguide display
separate, or partially separate, from waveguide display 300 may
provide image light to another eye of the user.
[0055] Source assembly 310 may generate image light 355 for display
to the user. Source assembly 310 may generate and output image
light 355 to a coupling element 350 located on a first side 370-1
of output waveguide 320. In some embodiments, coupling element 350
may couple image light 355 from source assembly 310 into output
waveguide 320. Coupling element 350 may include, for example, a
diffraction grating, a holographic grating, one or more cascaded
reflectors, one or more prismatic surface elements, and/or an array
of holographic reflectors. Output waveguide 320 may be an optical
waveguide that can output expanded image light 340 to user's eye
390. Output waveguide 320 may receive image light 355 at one or
more coupling elements 350 located on first side 370-1 and guide
received image light 355 to a directing element 360.
[0056] Directing element 360 may redirect received input image
light 355 to decoupling element 365 such that received input image
light 355 may be coupled out of output waveguide 320 via decoupling
element 365. Directing element 360 may be part of, or affixed to,
first side 370-1 of output waveguide 320. Decoupling element 365
may be part of, or affixed to, a second side 370-2 of output
waveguide 320, such that directing element 360 is opposed to
decoupling element 365. Directing element 360 and/or decoupling
element 365 may include, for example, a diffraction grating, a
holographic grating, a surface-relief grating, one or more cascaded
reflectors, one or more prismatic surface elements, and/or an array
of holographic reflectors.
[0057] Second side 370-2 of output waveguide 320 may represent a
plane along an x-dimension and a y-dimension. Output waveguide 320
may include one or more materials that can facilitate total
internal reflection of image light 355. Output waveguide 320 may
include, for example, silicon, plastic, glass, and/or polymers.
Output waveguide 320 may have a relatively small form factor. For
example, output waveguide 320 may be approximately 50 mm wide along
the x-dimension, about 30 mm long along the y-dimension, and about
0.5 to 1 mm thick along a z-dimension.
[0058] Controller 330 may control scanning operations of source
assembly 310. Controller 330 may determine scanning instructions
for source assembly 310. In some embodiments, output waveguide 320
may output expanded image light 340 to user's eye 390 with a large
field of view (FOV). For example, expanded image light 340 provided
to user's eye 390 may have a diagonal FOV (in x and y) of about 60
degrees or greater and/or about 150 degrees or less. Output
waveguide 320 may be configured to provide an eyebox with a length
of about 20 mm or greater and/or equal to or less than about 50 mm,
and/or a width of about 10 mm or greater and/or equal to or less
than about 50 mm.
[0059] FIG. 4 is a cross-sectional view 400 of the waveguide
display 300. Waveguide display 300 may include source assembly 310
and output waveguide 320. Source assembly 310 may generate image
light 355 (i.e., display light) in accordance with scanning
instructions from controller 330. Source assembly 310 may include a
source 410 and an optics system 415. Source 410 may include a light
source that generates coherent or partially coherent light. Source
410 may include, for example, a laser diode, a vertical cavity
surface emitting laser, and/or a light emitting diode.
[0060] Optics system 415 may include one or more optical components
that can condition the light from source 410. Conditioning light
from source 410 may include, for example, expanding, collimating,
and/or adjusting orientation in accordance with instructions from
controller 330. The one or more optical components may include one
or more lenses, liquid lenses, mirrors, apertures, and/or gratings.
Light emitted from optics system 415 (and also source assembly 310)
may be referred to as image light 355 or display light.
[0061] Output waveguide 320 may receive image light 355 from source
assembly 310. Coupling element 350 may couple image light 355 from
source assembly 310 into output waveguide 320. In embodiments where
coupling element 350 includes a diffraction grating, the
diffraction grating may be configured such that total internal
reflection may occur within output waveguide 320, and thus image
light 355 coupled into output waveguide 320 may propagate
internally within output waveguide 320 (e.g., by total internal
reflection) toward decoupling element 365.
[0062] Directing element 360 may redirect image light 355 toward
decoupling element 365 for coupling at least a portion of the image
light out of output waveguide 320. In embodiments where directing
element 360 is a diffraction grating, the diffraction grating may
be configured to cause incident image light 355 to exit output
waveguide 320 at angle(s) of inclination relative to a surface of
decoupling element 365. In some embodiments, directing element 360
and/or the decoupling element 365 may be structurally similar, and
may switch their roles for different portions of image light
355.
[0063] Expanded image light 340 exiting output waveguide 320 may be
expanded along one or more dimensions (e.g., elongated along the
x-dimension). In some embodiments, waveguide display 300 may
include a plurality of source assemblies 310 and a plurality of
output waveguides 320. Each of source assemblies 310 may emit a
monochromatic image light corresponding to a primary color (e.g.,
red, green, or blue). Each of output waveguides 320 may be stacked
together to output an expanded image light 340 that may be
multi-colored.
[0064] FIG. 5 is a simplified block diagram of an example
artificial reality system 500 including waveguide display assembly
210. System 500 may include near-eye display 100, an imaging device
535, and an input/output interface 540 that are each coupled to a
console 510.
[0065] As described above, near-eye display 100 may be a display
that presents media to a user. Examples of media presented by
near-eye display 100 may include one or more images, video, and/or
audio. In some embodiments, audio may be presented via an external
device (e.g., speakers and/or headphones) that may receive audio
information from near-eye display 100 and/or console 510 and
present audio data based on the audio information to a user. In
some embodiments, near-eye display 100 may act as an artificial
reality eyewear glass. For example, in some embodiments, near-eye
display 100 may augment views of a physical, real-world
environment, with computer-generated elements (e.g., images, video,
sound, etc.).
[0066] Near-eye display 100 may include waveguide display assembly
210, one or more position sensors 525, and/or an inertial
measurement unit (IMU) 530. Waveguide display assembly 210 may
include source assembly 310, output waveguide 320, and controller
330, as described above.
[0067] IMU 530 may include an electronic device that can generate
fast calibration data indicating an estimated position of near-eye
display 100 relative to an initial position of near-eye display 100
based on measurement signals received from one or more position
sensors 525.
[0068] Imaging device 535 may generate slow calibration data in
accordance with calibration parameters received from console 510.
Imaging device 535 may include one or more cameras and/or one or
more video cameras.
[0069] Input/output interface 540 may be a device that allows a
user to send action requests to console 510. An action request may
be a request to perform a particular action. For example, an action
request may be to start or end an application or to perform a
particular action within the application.
[0070] Console 510 may provide media to near-eye display 100 for
presentation to the user in accordance with information received
from one or more of: imaging device 535, near-eye display 100, and
input/output interface 540. In the example shown in FIG. 5, console
510 may include an application store 545, a tracking module 550,
and an engine 555.
[0071] Application store 545 may store one or more applications for
execution by the console 510. An application may include a group of
instructions that, when executed by a processor, may generate
content for presentation to the user. Examples of applications may
include gaming applications, conferencing applications, video
playback application, or other suitable applications.
[0072] Tracking module 550 may calibrate system 500 using one or
more calibration parameters and may adjust one or more calibration
parameters to reduce error in determination of the position of
near-eye display 100. Tracking module 550 may track movements of
near-eye display 100 using slow calibration information from
imaging device 535. Tracking module 550 may also determine
positions of a reference point of near-eye display 100 using
position information from the fast calibration information.
[0073] Engine 555 may execute applications within system 500 and
receives position information, acceleration information, velocity
information, and/or predicted future positions of near-eye display
100 from tracking module 550. In some embodiments, information
received by engine 555 may be used for producing a signal (e.g.,
display instructions) to waveguide display assembly 210. The signal
may determine a type of content to present to the user.
[0074] There may be many different ways to implement the waveguide
display. For example, in some implementations, output waveguide 320
may include a slanted surface between first side 370-1 and second
side 370-2 for coupling image light 355 into output waveguide 320.
In some implementations, the slanted surface may be coated with a
reflective coating to reflect light towards directing element 360.
In some implementations, the angle of the slanted surface may be
configured such that image light 355 may be reflected by the
slanted surface due to total internal reflection. In some
implementations, directing element 360 may not be used, and light
may be guided within output waveguide 320 by total internal
reflection. In some implementations, decoupling elements 365 may be
located near first side 370-1.
[0075] In some implementations, output waveguide 320 and decoupling
element 365 (and directing element 360 if used) may be transparent
to light from the environment, and may act as an optical combiner
to combine image light 355 and light from the physical, real-world
environment in front of near-eye display 100. As such, the user can
view both artificial images of artificial objects from source
assembly 310 and real images of real objects in the physical,
real-world environment.
[0076] FIG. 6 illustrates an example optical see-through augmented
reality system 600 using a waveguide display according to certain
embodiments. Augmented reality system 600 may include a projector
610 and a combiner 615. Projector 610 may include a light source or
image source 612 and projector optics 614. In some embodiments,
image source 612 may include a plurality of pixels that displays
virtual objects, such as an LCD display panel or an LED display
panel. In some embodiments, image source 612 may include a light
source that generates coherent or partially coherent light. For
example, image source 612 may include a laser diode, a vertical
cavity surface emitting laser, and/or a light emitting diode. In
some embodiments, image source 612 may include a plurality of light
sources each emitting a monochromatic image light corresponding to
a primary color (e.g., red, green, or blue). In some embodiments,
image source 612 may include an optical pattern generator, such as
a spatial light modulator. Projector optics 614 may include one or
more optical components that can condition the light from image
source 612, such as expanding, collimating, scanning, or projecting
light from image source 612 to combiner 615. The one or more
optical components may include one or more lenses, liquid lenses,
mirrors, apertures, and/or gratings. In some embodiments, projector
optics 614 may include a liquid lens (e.g., a liquid crystal lens)
with a plurality of electrodes that allows scanning of the light
from image source 612.
[0077] Combiner 615 may include an input coupler 630 for coupling
light from projector 610 into a substrate 620 of combiner 615.
Input coupler 630 may include a volume holographic grating, a
diffractive optical elements (DOE) (e.g., a surface-relief
grating), or a refractive coupler (e.g., a wedge or a prism). Input
coupler 630 may have a coupling efficiency of greater than 30%,
50%, 75%, 90%, or higher for visible light. As used herein, visible
light may refer to light with a wavelength between about 380 nm to
about 750 nm. Light coupled into substrate 620 may propagate within
substrate 620 through, for example, total internal reflection
(TIR). Substrate 620 may be in the form of a lens of a pair of
eyeglasses. Substrate 620 may have a flat or a curved surface, and
may include one or more types of dielectric materials, such as
glass, quartz, plastic, polymer, poly(methyl methacrylate) (PMMA),
crystal, or ceramic. A thickness of the substrate may range from,
for example, less than about 1 mm to about 10 mm or more. Substrate
620 may be transparent to visible light. A material may be
"transparent" to a light beam if the light beam can pass through
the material with a high transmission rate, such as larger than
60%, 75%, 80%, 90%, 95%, or higher, where a small portion of the
light beam (e.g., less than 60%, 25%, 20%, 10%, 5%, or less) may be
scattered, reflected, or absorbed by the material. The transmission
rate (i.e., transmissivity) may be represented by either a
photopically weighted or an unweighted average transmission rate
over a range of wavelengths, or the lowest transmission rate over a
range of wavelengths, such as the visible wavelength range.
[0078] Substrate 620 may include or may be coupled to a plurality
of output couplers 640 configured to extract at least a portion of
the light guided by and propagating within substrate 620 from
substrate 620 and direct extracted light 660 to an eye 690 of the
user of augmented reality system 600. As input coupler 630, output
couplers 640 may include grating couplers (e.g., volume holographic
gratings or surface-relief gratings), prisms, or DOEs. Output
couplers 640 may have different coupling (e.g., diffraction)
efficiencies at different locations. Substrate 620 may also allow
light 650 from environment in front of combiner 615 to pass through
with little or no loss. Output couplers 640 may allow light 650 to
pass through with little loss. For example, in some
implementations, output couplers 640 may have a low diffraction
efficiency for light 650 as described below such that light 650 may
be refracted or otherwise pass through output couplers 640 with
little loss. In some implementations, output couplers 640 may have
a high diffraction efficiency for light 650 and may direct light
650 to certain desired directions (i.e., diffraction angles) with
little loss. As a result, the user may be able to view combined
images of the environment in front of combiner 615 and virtual
objects projected by projector 610.
[0079] FIG. 7 illustrates propagations of incident display light
740 and external light 730 in an example waveguide display 700
including a waveguide 710 and a grating coupler 720.
[0080] Waveguide 710 may be a flat or curved transparent substrate
with a refractive index n.sub.2 greater than the free space
refractive index n.sub.1 (i.e., 1.0). Grating coupler 720 may
include, for example, a Bragg grating or a surface-relief
grating.
[0081] Incident display light 740 may be coupled into waveguide 710
by, for example, input coupler 630 of FIG. 6 or other couplers
(e.g., a prism or slanted surface) described above. Incident
display light 740 may propagate within waveguide 710 through, for
example, total internal reflection. When incident display light 740
reaches grating coupler 720, incident display light 740 may be
diffracted by grating coupler 720 into, for example, a 0.sup.th
order diffraction (i.e., reflection) light 742 and a -1st order
diffraction light 744. The 0.sup.th order diffraction may continue
to propagate within waveguide 710, and may be reflected by the
bottom surface of waveguide 710 towards grating coupler 720 at a
different location. The -1st order diffraction light 744 may be
coupled (e.g., refracted) out of waveguide 710 towards the user's
eye, because a total internal reflection condition may not be met
at the bottom surface of waveguide 710 due to the diffraction angle
of the -1' order diffraction light 744.
[0082] External light 730 may also be diffracted by grating coupler
720 into, for example, a 0.sup.th order diffraction light 732 or a
-1.sup.st order diffraction light 734. The 0.sup.th order
diffraction light 732 or the -1st order diffraction light 734 may
be refracted out of waveguide 710 towards the user's eye. Thus,
grating coupler 720 may act as an input coupler for coupling
external light 730 into waveguide 710, and may also act as an
output coupler for coupling incident display light 740 out of
waveguide 710. As such, grating coupler 720 may act as a combiner
for combining external light 730 and incident display light 740 and
send the combined light to the user's eye.
[0083] In order to diffract light at a desired direction towards
the user's eye and to achieve a desired diffraction efficiency for
certain diffraction orders, grating coupler 720 may include a
blazed or slanted grating, such as a slanted Bragg grating or
surface-relief grating, where the grating ridges and trenches (or
grooves) may be tilted relative to the surface normal of grating
coupler 720 or waveguide 710.
[0084] FIG. 8 illustrates an example slanted grating 820 in an
example waveguide display 800 according to certain embodiments.
Waveguide display 800 may include slanted grating 820 on a
waveguide 810, such as substrate 620. Slanted grating 820 may act
as a grating coupler for couple light into or out of waveguide 810.
In some embodiments, slanted grating 820 may include a periodic
structure with a periodp. For example, slanted grating 820 may
include a plurality of ridges 822 and trenches or grooves 824
between ridges 822. Each period of slanted grating 820 may include
a ridge 822 and a trench or groove 824, which may be an air gap or
a region filled with a material with a refractive index n.sub.g2.
The ratio between the width of a ridge 822 and the grating periodp
may be referred to as duty cycle. Slanted grating 820 may have a
duty cycle ranging, for example, from about 10% to about 90% or
greater. In some embodiments, the duty cycle may vary from period
to period. In some embodiments, the period p of the slanted grating
may vary from one area to another on slanted grating 820, or may
vary from one period to another (i.e., chirped) on slanted grating
820.
[0085] Ridges 822 may be made of a material with a refractive index
of n.sub.g1, such as silicon containing materials (e.g., SiO.sub.2,
Si.sub.3N.sub.4, SiC, SiO.sub.xN.sub.y, or amorphous silicon),
organic materials (e.g., spin on carbon (SOC) or amorphous carbon
layer (ACL) or diamond like carbon (DLC)), inorganic metal oxide
layers (e.g., TiO.sub.x, AlO.sub.x, TaO.sub.x, HfO.sub.x, etc.), or
a combination thereof. Each ridge 822 may include a leading edge
830 with a slant angle .alpha. and a trailing edge 840 with a slant
angle .beta.. In some embodiments, leading edge 830 and training
edge 840 of each ridge 822 may be parallel to each other. In other
words, slant angle .alpha. is approximately equal to slant angle
.beta.. In some embodiments, slant angle .alpha. may be different
from slant angle .beta.. In some embodiments, slant angle .alpha.
may be approximately equal to slant angle .beta.. For example, the
difference between slant angle .alpha. and slant angle .theta. may
be less than 20%, 10%, 5%, 1%, or less. In some embodiments, slant
angle .alpha. and slant angle .theta. may range from, for example,
about 30.degree. or less to about 70.degree. or larger. In some
embodiments, the slant angle .alpha. and/or slant angle .theta. may
be greater than 30.degree., 45.degree., 50.degree., 70.degree., or
larger.
[0086] The slanted grating 820 may be fabricated using many
different nanofabrication techniques. The nanofabrication
techniques generally include a patterning process and a
post-patterning (e.g., overcoating) process. The patterning process
may be used to form slanted ridges 822 of the slanted grating 820.
There may be many different nanofabrication techniques for forming
the slanted ridges 822. For example, in some implementations, the
slanted grating 820 may be fabricated using lithography techniques
including slanted etching. In some implementations, the slanted
grating 820 may be fabricated using nanoimprint lithography (NIL)
from a master mold.
[0087] The post-patterning process may be used to overcoat the
slanted ridges 822 and/or to fill the trenches or grooves 824
between the slanted ridges 822 with a material having a refractive
index n.sub.g2 different from the refractive index n.sub.g1 of the
slanted ridges 822. The post-patterning process may be independent
from the patterning process. Thus, a same post-patterning process
may be used on slanted gratings fabricated using any pattering
technique.
[0088] Techniques and processes for fabricating the slanted grating
coupler described below are for illustration purposes only and are
not intended to be limiting. A person skilled in the art would
understand that various modifications may be made to the techniques
described below. In some implementations, some operation described
below may be omitted. In some implementations, additional
operations may be performed to fabricate the grating coupler. For
example, in some implementations, the surface of a mold or some
other structures may be coated or plated prior to imprinting to
reduce wearing of the mold, improve product quality, and reduce
manufacturing cost. For example, in some implementations, an
anti-sticking layer may be coated on the mold before the molding
(or imprinting) process.
[0089] FIGS. 9A and 9B illustrate an example process for
fabricating a slanted surface-relief grating by direct molding
according to certain embodiments. In FIG. 9A, a waveguide 910 may
be coated with a NIL resin layer 920. NIL resin layer 920 may
include, for example, a butyl-acrylate-based resin doped with a
sol-gel precursor (e.g., titanium butoxide), a monomer containing a
reactive functional group for subsequent infusion processes (such
as acrylic acid), and/or high refractive index nanoparticles (e.g.,
TiO.sub.2, GaP, HfO.sub.2, GaAs, etc.). In some embodiments, NIL
resin layer 920 may include polydimethylsiloxane (PDMS) or another
silicone elastomer or silicon-based organic polymer. NIL resin
layer 920 may be deposited on waveguide 910 by, for example,
spin-coating, lamination, or ink injection. A NIL mold 930 with
slanted ridges 932 may be pressed against NIL resin layer 920 and
waveguide 910 for molding a slanted grating in NIL resin layer 920.
NIL resin layer 920 may be cured subsequently (e.g., cross-linked)
using heat and/or ultraviolet (UV) light.
[0090] FIG. 9B shows the demolding process, during which NIL mold
930 is detached from NIL resin layer 920 and waveguide 910. As
shown in FIG. 9B, after NIL mold 930 is detached from NIL resin
layer 920 and waveguide 910, a slanted grating 922 that is
complementary to slanted ridges 932 in NIL mold 930 may be formed
in NIL resin layer 920 on waveguide 910.
[0091] In some embodiments, a master NIL mold (e.g., a hard mold
including a rigid material, such as Si, SiO.sub.2, Si.sub.3N.sub.4,
or a metal) may be fabricated first using, for example, slanted
etching, micromachining, or 3-D printing. A soft stamp may be
fabricated using the master NIL mold, and the soft stamp may then
be used as the working stamp to fabricate the slanted grating. In
such a process, the slanted grating structure in the master NIL
mold may be similar to the slanted grating of the grating coupler
for the waveguide display, and the slanted grating structure on the
soft stamp may be complementary to the slanted grating structure in
the master NIL mold and the slanted grating of the grating coupler
for the waveguide display. Compared with a hard stamp or hard mold,
a soft stamp may offer more flexibility during the molding and
demolding processes.
[0092] FIGS. 10A-10D illustrate an example process 1000 for
fabricating a soft stamp used for making a slanted surface-relief
grating according to certain embodiments. FIG. 10A shows a master
mold 1010 (e.g., a hard mold or hard stamp). Master mold 1010 may
include a rigid material, such as a semiconductor substrate (e.g.,
Si or GaAs), an oxide (e.g., SiO.sub.2, Si.sub.3N.sub.4, TiO.sub.x,
AlO.sub.x, TaO.sub.x, or HfO.sub.x), or a metal plate. Master mold
1010 may be fabricated using, for example, a slanted etching
process using reactive ion beams or chemically assisted reactive
ion beams, a micromachining process, or a 3-D printing process. As
shown in FIG. 10A, master mold 1010 may include a slanted grating
1020 that may in turn include a plurality of slanted ridges 1022
with gaps 1024 between slanted ridges 1022.
[0093] FIG. 10B illustrates master mold 1010 coated with a soft
stamp material layer 1030. Soft stamp material layer 1030 may
include, for example, a resin material or a curable polymer
material. In some embodiments, soft stamp material layer 1030 may
include polydimethylsiloxane (PDMS) or another silicone elastomer
or silicon-based organic polymer. In some embodiment, soft stamp
material layer 1030 may include ethylene tetrafluoroethylene
(ETFE), perfluoropolyether (PFPE), or other fluorinated polymer
materials. In some embodiments, soft stamp material layer 1030 may
be coated on master mold 1010 by, for example, spin-coating or ink
injection.
[0094] FIG. 10C illustrates a lamination process for laminating a
soft stamp foil 1040 onto soft stamp material layer 1030. A roller
1050 may be used to press soft stamp foil 1040 against soft stamp
material layer 1030. The lamination process may also be a
planarization process to make the thickness of soft stamp material
layer 1030 substantially uniform. After the lamination process,
soft stamp foil 1040 may be tightly or securely attached to soft
stamp material layer 1030.
[0095] FIG. 10D illustrates a delamination process, where a soft
stamp including soft stamp foil 1040 and attached soft stamp
material layer 1030 is detached from master mold 1010. Soft stamp
material layer 1030 may include a slanted grating structure that is
complementary to the slanted grating structure on master mold 1010.
Because the flexibility of soft stamp foil 1040 and attached soft
stamp material layer 1030, the delamination process may be
relatively easy compared with a demolding process using a hard
stamp or mold. In some embodiments, a roller (e.g., roller 1050)
may be used in the delamination process to ensure a constant or
controlled delamination speed. In some embodiments, roller 1050 may
not be used during the delamination. In some implementations, an
anti-sticking layer may be formed on master mold 1010 before soft
stamp material layer 1030 is coated on master mold 1010. The
anti-sticking layer may also facilitate the delamination process.
After the delamination of the soft stamp from master mold 1010, the
soft stamp may be used to mold the slanted grating on a waveguide
of a waveguide display.
[0096] FIGS. 11A-11D illustrate an example process 1100 for
fabricating a slanted surface-relief grating using a soft stamp
according to certain embodiments. FIG. 11A shows a waveguide 1110
coated with an imprint resin layer 1120. Imprint resin layer 1120
may include, for example, a butyl-acrylate based resin doped with a
sol-gel precursor (e.g., titanium butoxide), a monomer containing a
reactive functional group for subsequent infusion processes (such
as acrylic acid), and/or high refractive index nanoparticles (e.g.,
TiO.sub.2, GaP, HfO.sub.2, GaAs, etc.). In some embodiments,
imprint resin layer 1120 may include polydimethylsiloxane (PDMS) or
another silicone elastomer or silicon-based organic polymer. In
some embodiments, imprint resin layer 1120 may include ethylene
tetrafluoroethylene (ETFE), perfluoropolyether (PFPE), or other
fluorinated polymer materials. Imprint resin layer 1120 may be
deposited on waveguide 1110 by, for example, spin-coating,
lamination, or ink injection. A soft stamp 1130 including slanted
ridges 1132 attached to a soft stamp foil 1140 may be used for the
imprint.
[0097] FIG. 11B shows the lamination of soft stamp 1130 onto
imprint resin layer 1120. Soft stamp 1130 may be pressed against
imprint resin layer 1120 and waveguide 1110 using a roller 1150,
such that slanted ridges 1132 may be pressed into imprint resin
layer 1120. Imprint resin layer 1120 may be cured subsequently. For
example, imprint resin layer 1120 may be cross-linked using heat
and/or ultraviolet (UV) light.
[0098] FIG. 11C shows the delamination of soft stamp 1130 from
imprint resin layer 1120. The delamination may be performed by
lifting soft stamp foil 1140 to detach slanted ridges 1132 of soft
stamp 1130 from imprint resin layer 1120. Imprint resin layer 1120
may now include a slanted grating 1122, which may be used as the
grating coupler or may be over-coated to form the grating coupler
for the waveguide display. As described above, because of the
flexibility of soft stamp 1130, the delamination process may be
relatively easy compared with a demolding process using a hard
stamp or mold. In some embodiments, a roller (e.g., roller 1150)
may be used in the delamination process to ensure a constant or
controlled delamination speed. In some embodiments, roller 1150 may
not be used during the delamination.
[0099] FIG. 11D shows an example imprinted slanted grating 1122
formed on waveguide 1110 using soft stamp 1130. As described above,
slanted grating 1122 may include ridges and gaps between the ridges
and thus may be over-coated with a material having a refractive
index different from imprint resin layer 1120 to fill the gaps and
form the grating coupler for the waveguide display.
[0100] In various embodiments, the period of the slanted grating
may vary from one area to another on slanted grating 1122, or may
vary from one period to another (i.e., chirped) on slanted grating
1122. Slanted grating 1122 may have a duty cycle ranging, for
example, from about 10% to about 90% or greater. In some
embodiments, the duty cycle may vary from period to period. In some
embodiments, the depth or height of the ridges of slanted grating
1122 may be greater than 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, or
higher. The slant angles of the leading edges of the ridges of
slanted grating 1122 and the slant angles of the trailing edges of
the ridges of slanted grating 1122 may be greater than 30.degree.,
45.degree., 60.degree., or higher. In some embodiments, the leading
edge and training edge of each ridge of slanted grating 1122 may be
parallel to each other. In some embodiments, the difference between
the slant angle of the leading edge of a ridge of slanted grating
1122 and the slant angle of the trailing edge of the ridge of
slanted grating 1122 may be less than 20%, 10%, 5%, 1%, or
less.
[0101] FIG. 12 is a simplified flow chart 1200 illustrating example
methods of fabricating a slanted surface-relief grating using
nanoimprint lithography according to certain embodiments. As
described above, different generations of NIL stamps may be made
and used as the working stamp to mold the slanted gratings. For
example, in some embodiments, a master mold (i.e., generation 0
mold, which may be a hard mold) may be used as the working stamp to
mold the slanted grating directly. In some embodiments, a hybrid
stamp (e.g., a generation 1 hybrid mold or stamp) may be fabricated
using the master mold and may be used as the working stamp for
nanoimprinting. In some embodiments, a generation 2 hybrid mold (or
stamp) may be made from the generation 1 mold, and may be used as
the working stamp for the nanoimprinting. In some embodiments, a
generation 3 mold, a generation 4 mold, and so on, may be made and
used as the working stamp.
[0102] At block 1210, a master mold with a slanted structure may be
fabricated using, for example, a slanted etching process that uses
reactive ion beams or chemically-assisted reactive ion beams, a
micromachining process, or a 3-D printing process. The master mold
may be referred to as the generation 0 (or Gen 0) mold. The master
mold may include quartz, fused silica, silicon, other metal-oxides,
or plastic compounds. The slanted structure of the master mold may
be referred to as having a positive (+) tone. The master mold may
be used as a working stamp for molding the slanted grating directly
(i.e., hard NIL) at block 1220. As described above, when the master
mold is used as the working stamp, the slanted structure of the
master mold may be complementary to the desired slanted grating.
Alternatively, the master mold may be used to make a hybrid stamp
as the working stamp for molding the slanted grating. The slanted
structure of the hybrid stamp may be similar to the desired slanted
grating or may be complementary to the desired slanted grating,
depending on the generation of the hybrid stamp.
[0103] At block 1220, a slanted grating may be molded in, for
example, a resin layer using the master mold as described above
with respect to, for example, FIGS. 9A and 9B. The resin layer may
be coated on a waveguide substrate, and may include, for example, a
butyl-acrylate based resin doped with a resin comprising a sol-gel
precursor (e.g., titanium butoxide), a monomer containing a
reactive functional group for subsequent infusion processes (such
as acrylic acid), and/or high refractive index nanoparticles (e.g.,
TiO.sub.2, GaP, HfO.sub.2, GaAs, etc.). The master mold may be
pressed against the resin layer. The resin layer may then be cured
to fix the structure formed within the resin layer by the master
mold. The master mold may be detached from the resin layer to form
a slanted grating within the resin layer. The slanted grating
within the resin layer may have a negative (-) tone compared with
the slanted structure of the master mold.
[0104] Alternatively, at block 1230, a hybrid stamp (e.g., a hard
stamp, a soft stamp, or a hard-soft stamp) with a slanted structure
may be fabricated using the master mold as described above with
respect to, for example, FIG. 10A-10D or the process described with
respect to, for example, FIGS. 11A-11D. For example, the process of
fabricating the hybrid stamp may include coating the master mold
with a soft stamp material, such as a resin material described
above. A soft stamp foil may then be laminated on the soft stamp
material, for example, using a roller. The soft stamp foil and the
attached soft stamp material may be securely attached to each other
and may be detached from the master mold to form the soft stamp.
The hybrid stamp fabricated at block 1230 may be referred to as a
generation 1 (or Gen 1) stamp. The slanted grating within the Gen 1
stamp may have a negative (-) tone compared with the slanted
structure of the master mold.
[0105] At block 1240, a slanted surface-relief grating may be
imprinted using the Gen 1 stamp as described above with respect to,
for example, FIGS. 11A-11D. For example, a waveguide substrate may
be coated with an imprint resin layer. The Gen 1 stamp may be
laminated on the imprint resin layer using, for example, a roller.
After the imprint resin layer is cured, the Gen 1 stamp may be
delaminated from the imprint resin layer to form a slanted grating
within the imprint resin layer. The slanted grating within the
imprint resin layer may have a positive tone.
[0106] Alternatively, in some embodiments, at block 1250, a second
generation hybrid stamp (Gen 2 stamp) may be fabricated using the
Gen 1 stamp using a process similar to the process for fabricating
the Gen 1 stamp as described above with respect to, for example,
FIGS. 7A-8D. The slanted structure within the Gen 2 stamp may have
a positive tone.
[0107] At block 1260, a slanted surface-relief grating may be
imprinted using the Gen 2 stamp as described above with respect to,
for example, FIGS. 11A-11D. For example, a waveguide substrate may
be coated with an imprint resin layer. The Gen 2 stamp may be
laminated on the imprint resin layer using, for example, a roller.
After the imprint resin layer is cured, the Gen 2 stamp may be
delaminated from the imprint resin layer to form a slanted grating
within the imprint resin layer. The slanted grating within the
imprint resin layer may have a negative tone.
[0108] Alternatively, in some embodiments, at block 1270, a second
generation (Gen 2) daughter mold may be fabricated using the Gen 1
stamp using a process similar to the process for fabricating the
Gen 1 stamp as described above with respect to, for example, FIGS.
10A-11D. The slanted structure within the Gen 2 daughter mold may
have a positive tone.
[0109] At block 1280, a third generation hybrid stamp (Gen 3 stamp)
may be fabricated using the Gen 2 daughter mold using a process
similar to the process for fabricating the Gen 1 stamp or the Gen 2
daughter mold as described above with respect to, for example,
FIGS. 10A-11D. The slanted structure within the Gen 3 stamp may
have a negative tone.
[0110] At block 1290, a slanted surface-relief grating may be
imprinted using the Gen 3 stamp as described above with respect to,
for example, FIGS. 11A-11D. For example, a waveguide substrate may
be coated with an imprint resin layer. The Gen 3 stamp may be
laminated on the imprint resin layer using, for example, a roller.
After the imprint resin layer is cured, the Gen 3 stamp may be
delaminated from the imprint resin layer to form a slanted grating
within the imprint resin layer. The slanted grating within the
imprint resin layer may have a positive tone.
[0111] Even though not shown in FIG. 12, in some embodiments, a
fourth generation hybrid stamp, a fifth generation hybrid stamp,
and so on, may be fabricated using a similar process, and may be
used as the working stamp for imprinting the slanted grating.
[0112] Optionally, at block 1295, the slanted grating may be
over-coated with a material having a refractive index different
from the slanted grating (e.g., the imprint resin layer). For
example, in some embodiments, a high refractive index material,
such as Hafnia, Titania, Tungsten oxide, Zirconium oxide, Gallium
sulfide, Gallium nitride, Gallium phosphide, silicon, or a high
refractive index polymer, may be used to over-coat the slanted
grating and fill the gaps between the slanted grating ridges. In
some embodiments, a low refractive index material, such as silicon
oxide, magnesium fluoride, porous silica, or fluorinated low index
monomer (or polymer), and the like, may be used to over-coat the
slanted grating and fill the gaps between the slanted grating
ridges.
[0113] One challenge associated with fabrication of nano-structures
using nanoimprint techniques, such as fabrication of slanted
gratings having a wide range of duty cycles, small periods, high
aspect ratios, and/or small feature size (or critical dimension),
is to avoid breaking the grating ridges of the soft stamp and/or
the imprinted slanted structures during delamination (or
demolding). For example, when the slanted structure to be molded
has a large slant angle (e.g., greater than 30.degree., 45.degree.,
or 60.degree.), a high depth (e.g., >100 nm), a high aspect
ratio (e.g., 3:1, 5:1, 10:1, or larger), and/or a large or small
duty cycle (e.g., below 30% or greater than 70%), either the
slanted structure in the soft stamp or the slanted structure in the
imprint resin layer may experience large stress during the
delamination of the soft stamp. The stress may be caused by the
deformation (bending) of the slanted structure and/or the surface
adhesion or friction between the soft stamp and the resin layer.
The surface friction or adhesion may be caused by, for example, Van
der Waals forces, mechanical interlock forces, chemical bonding
forces, etc. In some cases, the stress may be large enough to cause
damages in the slanted structure, including breaking some ridges in
the soft stamp and/or the imprinted nano-structure.
[0114] FIG. 13A is a top view of an example soft stamp 1330 that
has been laminated onto an imprint resin layer 1320. It should be
noted that FIG. 13A is not a true top view as the nano-structures
or slanted ridges 1332 of soft stamp 1330 and the nano-structures
or a slanted grating 1322 imprinted in imprint resin layer 1320,
both of which are below a soft stamp foil 1340 are also shown. For
purpose of description, the area of soft stamp 1330 in which
slanted ridges 1332 are formed is referred to as a nano-structure
area 1370. Although a circular soft stamp 1330 and a rectangular
nano-structure area 1370 are illustrated in FIG. 13A, soft stamp
1330, as well as nano-structure area 1370, may be of any shape,
depending on the particular application.
[0115] FIG. 13B is a cross-sectional side view taken along line
13B-13B of FIG. 13A, illustrating a portion of imprint resin layer
1320 and soft stamp 1330 that has been partially delaminated. FIG.
13C is a cross-sectional side view similar to FIG. 13B,
illustrating a portion of imprint resin layer 1320 and soft stamp
1330 that has been further delaminated. To carry out the
delamination or demolding process, soft stamp foil 1340 may be
lifted in a manner such that delamination occurs in a direction
that is generally along slanted ridges 1332 on soft stamp 1330 (or
trenches defined by adjacent slanted ridges 1332) as indicated by
the arrows A in FIG. 13A so as to reduce delamination stress.
During the delamination or demolding process, a delamination front
1360 (or crack) is created between the interface of soft stamp 1330
and imprint resin layer 1320 and propagates in the direction
indicated by the arrows A in FIG. 13A. FIGS. 13B and 13C thus
illustrate cross-sectional side views along the delamination
propagation direction (or along slanted ridges 1332 on soft stamp
1330).
[0116] As shown in FIGS. 13A and 13B, at the beginning of
delamination, delamination front 1360 may uniformly propagate at a
flat interface between soft stamp 1330 and imprint resin layer 1320
because there may not be any nano-structures near the edge of soft
stamp 1330.
[0117] However, as shown in FIG. 13C, as delamination front 1360
reaches the edge of nano-structure area 1370 of soft stamp 1330 and
continues to propagate, the stress in slanted ridges 1332 of soft
stamp 1330 and slanted grating 1322 in imprint resin layer 1320 may
change or increase suddenly as the contact surface area between
soft stamp 1330 and imprint resin layer 1320 increases suddenly.
The sudden increase in surface area and adhesion causes the
delamination front 1360 to undergo a sharp change in velocity,
which generates forces that are directly dispersed on the
nano-structures. The resulting stress may cause damages to slanted
ridges 1332 on soft stamp 1330 and/or slanted grating 1322 formed
in imprint resin layer 1320.
[0118] In some instances, it may be difficult to reduce or
eliminate the stress caused by, e.g., surface adhesion or friction
due to Van der Waals forces, mechanical interlock forces, chemical
bonding forces, etc. However, the change or increase in the stress
when delamination front reaches the slanted ridges of a soft stamp
may be controlled by modifying the structural profile of the
slanted ridges of the soft stamp. For example, the sudden increase
in the stress may be limited or reduced by having a gradual change
in the height of the slanted ridges (or the depth of the trenches)
of the soft stamp near the edges of the nano-structure area (e.g.,
nano-structure area 1370) of the soft stamp as discussed below.
[0119] FIG. 14A is a top view of another example soft stamp 1430
that has been laminated onto an imprint resin layer 1420. FIG. 14A
is not a true top view as the nano-structures or slanted ridges
1432 of soft stamp 1430 and the nano-structures or a slanted
grating 1422 imprinted in imprint resin layer 1420, both of which
are below a soft stamp foil 1440, are also shown. Soft stamp 1430
includes a nano-structure area 1470 in which slanted ridges 1432
are formed. Although a circular soft stamp 1430 and a rectangular
nano-structure area 1470 are illustrated in FIG. 14A, soft stamp
1430, as well as nano-structure area 1470, may be of any shape,
depending on the particular application.
[0120] Soft stamp 1430 shown in FIG. 14A differs from soft stamp
1330 shown in FIG. 13A in that the height of slanted ridges 1432
(or the depth of the trenches each defined by two adjacent slanted
ridges 1432) of soft stamp 1430 near the edges of nano-structure
area 1470 is relatively small so as to reduce the surface area
between slanted ridges 1432 and slanted grating 1422 near the edges
of nano-structure area 1470, thereby avoiding the sudden change in
the stress that slanted ridges 1432 and slanted grating 1422 may
experience when a delamination front 1460 approaches the edges of
nano-structure area 1470. The height of slanted ridges 1432 (or
depth of trenches) may then be gradually increased to a desired
height (or depth) to imprint a grating having desired operational
ridge height(s) (or trench depth(s)) according to various device
performance considerations. Consequently, nano-structure area 1470
may include an inner or operational area 1472 having ridge heights
(or trench depths) based on device performance considerations, and
may further include an outer or transition area 1474 surrounding
operational area 1472 and having a varying ridge height (or trench
depth) based on the delamination considerations.
[0121] FIG. 14B is a cross-sectional side view taken along line
14B-14B of FIG. 14A, illustrating a portion of imprint resin layer
1420 and soft stamp 1430 that has been partially delaminated. FIG.
14C is a cross-sectional side view similar to FIG. 14B,
illustrating a portion of imprint resin layer 1420 and soft stamp
1430 that has been further delaminated. As shown in FIGS. 14B and
14C, soft stamp 1430 includes a varying ridge height (or trench
depth) near the edges of nano-structure area 1470 (shown in FIG.
14A). The distance or width D shown in FIG. 14B represents a width
of transition area 1474 (shown in FIG. 14A) within which the height
of slanted ridges 1432 gradually increases to a desired height (or
the depth of the trenches gradually increases to a desired depth)
as required per device performance requirements. Depending on the
application, in various embodiments, the distance D or the width of
transition area 1474 may be defined as the distance within which
the height of slanted ridges 1432 (or the depth of trenches)
gradually increases to at least 70%, at least 80%, at least 90%, at
least 95%, or 100% of a maximum ridge height (or maximum trench
depth) of soft stamp 1430. The maximum ridge height (or maximum
trench depth) may be a maximum ridge height (or maximum trench
depth) determined by the device performance requirements. Depending
on the application, the maximum ridge height (or maximum trench
depth) may be at least 50 nm, at least 100 nm, at least 200 nm, or
at least 300 nm, or at least 400 nm.
[0122] Because the change or increase in the ridge height (or
trench depth) is gradual near the edges of soft stamp 1430, the
change or increase in the surface area, as well as the change or
increase in surface adhesion, etc., between slanted ridges 1432 and
slanted grating 1422 is gradual. Thus, as delamination front 1460
approaches the edges of nano-structure area 1470, the derivative of
the velocity changes smoothly, which results in minimum stress
dispersed on the nano-structures. The gradual change reduces or
avoids damage to slanted ridges 1432 of soft stamp 1430 and slanted
grating 1422 in imprint resin layer 1420.
[0123] As shown in FIG. 14A, transition area 1474 is formed along
the entire periphery of nano-structure area 1470. With such a
configuration, when the delamination or demolding process is about
to complete and delamination front 1460 reaches the edges of
nano-structure area 1470 from the inside of nano-structure area
1470, the ridge height of slanted ridges 1432 gradually decreases.
The gradual decrease in the ridge height limits the stress that
slanted ridges 1432 of soft stamp 1430 and slanted grating 1422 of
imprint resin layer 1420 may experience when the delamination
process is about to complete. In some embodiments, transition area
1474 may be formed less than the entire periphery, but only along
select portion or portions of the periphery of nano-structure area
1470, depending on the particular application.
[0124] Because the variation in ridge height (or trench depth) in
the transition area modifies the device design, and such
modification may be unnecessary from the device's optical
performance perspective. Thus, to minimize the impact to the
optical function and to reduce the size of the added footprint, the
width of the transition area may be configured as narrow as
possible. As discussed above, a soft stamp may be fabricated using
a master mold (e.g., a hard mold or hard stamp). To fabricate a
soft stamp having a ridge height (or trench depth) of a large
variation within a small transition area or short distance, a
master mold having a large variation in ridge height (or trench
depth) within a small area or short distance is needed. As also
discussed above, the master mold may be fabricated using various
etching techniques, such as a slanted etching process that uses
high energy ions, which may be projected towards the master mold
material layer in the form of reactive ion beams or
chemically-assisted reactive ion beams, etc. However, it can be
challenging to achieve a large variation in etch depth within a
small area or short distance, especially when the nano-structures
to be fabricated are slanted.
[0125] FIGS. 15A and 15B are a side view and a top view,
respectively, of a master mold material layer 1510 (or master mold
substrate) and a master mold mask 1520 for fabricating a master
mold (e.g., a hard mold or hard stamp) that has a large etch depth
variation within a very small area or short distance near the edges
of nano-structures of the master mold. FIGS. 15A and 15B show that
the nano-structures will be fabricated throughout the entire area
of master mold material layer 1510, but, in some other embodiments,
the nano-structures may be fabricated in only a selected area or
areas as shown in FIG. 14A.
[0126] Master mold material layer 1510 may include a rigid
material, such as a semiconductor substrate (e.g., Si or GaAs), an
oxide (e.g., SiO.sub.2, Si.sub.3N.sub.4, TiO.sub.x, AlO.sub.x,
TaO.sub.x, or HfO.sub.x), or a metal plate. Master mold mask 1520
may be fabricated from a lithography material layer, such as a
photoresist layer. The lithography material layer may be formed on
master mold material layer 1510 by deposition, such as spin
coating, physical/chemical vapor deposition, or other deposition
techniques. Master mold mask 1520 may be formed from the
lithography material layer using any appropriate lithography
process. For example, the lithography process may be performed
using an electron beam, focus ion beam, photolithography stepper,
nano-imprint tool, etc. In one example, a photomask with a
two-dimensional pattern similar to (or complementary to) the
pattern shown in FIG. 15B may be used to expose the lithography
material layer (e.g., a positive-tone or negative tone photoresist
layer) to form master mold mask 1520 on master mold material layer
1510 after the photoresist development. After the lithography
process, master mold mask 1520 having a desired pattern is formed
in the lithography material layer and can be used as the etch mask
for subsequent etching of master mold material layer 1510 to form
the master mold. Although FIG. 15A illustrates that the formed
features, i.e., ridges 1522, of master mold mask 1520 stand in a
substantially upright position on the top surface of master mold
material layer 1510, slanted ridges of master mold mask 1520 may be
formed in master mold material layer 1510 in some embodiments to
reduce shadowing effect and/or extend duty cycle range during
etching, etc.
[0127] Generally, the pattern of ridges 1522 can be fabricated with
high resolution and high accuracy due to the various lithography
techniques available for processing the lithography material layer
(or the photoresist layer). As will be explained further below,
through manipulation of the pattern of ridges 1522 of master mold
mask 1520, desired characteristics or pattern of the ridges of the
master mold can be achieved, which may be difficult to achieve
otherwise.
[0128] FIG. 16 illustrates an example of an RIE lag curve, which
represents the relationship between duty cycles and etch depths of
structures etched using reactive ion etching. Specifically, the
horizontal axis represents the duty cycle values, which range from
0% to 100%. As discussed above, for a pattern having ridges and
trenches, the duty cycle refers to the ratio between the width of a
ridge and the combined width of the ridge and the adjacent trench
(i.e., a period). The vertical axis represents the etch depth that
can be achieved for each duty cycle using RIE after a same etch
duration. It should be noted that the ME lag curve shown in FIG. 16
is for illustration purposes only and may only illustrate a general
trend. Depending on the materials to be etched, the etch system
used, the etchants used, and/or the etching conditions, the ME lag
curve may vary from one etching condition to another etching
condition.
[0129] As shown in FIG. 16, as the duty cycle increases (i.e., the
width of the ridge increases and/or the width of the trench
decreases), for a given etch duration, the etch depth that can be
achieved by an RIE process gradually decreases. This is because
there are abundant ions for the etch reaction to occur regardless
of large or small duty cycles, but the ion mean free path is
shorter inside small trenches, which lowers the effectiveness of
the etch. Also, etch by-products may not be transported outside the
etched trenches efficiently when the duty cycle is relatively
large. The lag in the by-product transport to the trench opening
may result in a lower etch depth when the duty cycle is larger,
which may be referred to as the RIE lag effect.
[0130] With continued reference to FIG. 16, when the duty cycle
changes from, e.g., below about 50% to about 90% or higher, the
etch depth can reduce significantly. It should be noted that
although FIG. 16 illustrates that when the duty cycle is about 50%
or below, the effect of duty cycle on the etch depth may be
relatively small in some embodiments, in some other embodiments,
the effect of duty cycle on the etch depth may still be significant
even when the duty cycle is below 50%, below 40%, or below 30%
since the etch depth also depends on the grating pitch or periods.
For example, for gratings having a common duty cycle but different
grating periods, the grating having the larger period will have a
wider trench, which will lead to a deeper etch. Thus, as the
grating period changes, the RIE lag curve may start to drop at a
duty cycle different from that shown in FIG. 16.
[0131] Given this relationship between duty cycle and etch depth,
the pattern of master mold mask 1520 near the edge of master mold
mask 1520 may be fine-tuned to have a varying duty cycle so as to
achieve a varying etch depth near the edge of the master mold to be
formed, which in turn can be used to fabricate a soft stamp with a
varying ridge height near the edges of the soft stamp. Moreover,
because the pattern of master mold mask 1520 can be fined-tuned
with high resolution and high accuracy as discussed above, the
desired variation in the duty cycle of master mold mask 1520 can be
achieved within a very small area or short distance from the edge
of master mold mask 1520.
[0132] Referring back to FIG. 15B, master mold mask 1520 may
include an inner or operational area 1524 and an outer or
transition area 1526 along the edges or periphery of master mold
mask 1520 and surrounding operational area 1524. Within operational
area 1524, the duty cycle of the pattern corresponds to the duty
cycle determined by the device performance considerations, which
may or may not be a varying duty cycle. Within transition area
1526, the duty cycle may gradually decrease from the edges of
master mold mask 1520 towards operational area 1524, or stated
differently, the duty cycle may gradually increase towards the
edges of master mold mask 1520.
[0133] Although only eight ridges 1522 are shown in FIG. 15B for
purpose of illustration, master mold mask 1520 may include many
more ridges 1522, and may include tens, hundreds, or more of ridges
1522 depending on the application, and ridges 1522 may be formed
within close proximity to each other. Thus, the duty cycle at the
edge of master mold mask 1520 may be as high as over 50%, over 60%,
over 70%, over 80%, over 90%, over 95%, or close to 100%. The duty
cycle from the edges of master mold mask 1520 to the edges of
operational area 1524 may gradually change from over 90% to below
50%, below 40%, below 30%, below 20%, below 10%, or other desired
duty cycle values. Further, as discussed above, the pattern of
ridges 1522 can be fine-tubed with high resolution and high
accuracy. Thus, the gradual change of the duty cycle from over 90%
to below 10% can be achieved within a very short distance D, as
shown in FIG. 15B. In some embodiments, the distance D may range
from 0.1 to 100 .mu.m.
[0134] As discussed above, when the duty cycle changes from a
relatively low value, e.g., below 10%, below 30%, or below 50%, to
90% or higher, the etch depth can reduce significantly. Thus, by
configuring the pattern in transition area 1526 appropriately, a
varying etch depth with a large or great variation can be achieved
within a very small area or distance D (e.g., from 0.1 to 100
.mu.m). In some embodiments, the duty cycle of ridges 1522 at the
outer edges of transition area 1526 (i.e., the edges of master mold
mask 1520) may be as high as 80%, 85%, 90%, 95%, or close to 100%,
whereas the duty cycle of ridges 1522 at the inner edges of
transition area 1526 (i.e., the edges of operational area 1524) may
be lower than 95%, such as below or about 90%, below or about 80%,
below or about 70%, below or about 60%, below or about 50%, below
or about 40%, below or about 30%, below or about 20%, below or
about 10%, or lower.
[0135] The transition of the duty cycle from the outer edges of
transition area 1526 to the inner edges of transition area 1526 can
be gradual or smooth as shown in FIG. 15B, and can be achieved
within a distance of 100 .mu.m or less. Thus, when an ion beam etch
process is subsequently performed to form the master mold, a
varying etch depth can be achieved at the edges of the master mold
fabricated. The varying etch depth achieved in turn translates to a
varying ridge height (or varying trench depth) near the edges of a
soft stamp fabricated from the master mold. A varying grating
height near the edges of the imprint resin layer, such as shown in
FIGS. 14A-14C, may be obtained using the soft stamp or the master
mold directly.
[0136] In some embodiments, the etch depth in master mold material
layer 1510 proximate the outer edges of transition area 1526 may be
as shallow as a few nanometers or tens of nanometers (e.g., below 5
nm, below 10 nm, below 50 nm, below 100 nm, etc.), whereas the etch
depth in master mold material layer 1510 proximate the inner edges
of transition area 1526 may be as deep as over tens of nanometers
or hundreds of nanometers (e.g., over 50 nm, over 100 nm, over 200
nm, over 300 nm, over 400 nm, etc.). Thus, the etch depth may
change from a few nanometers to a few hundred of nanometers (e.g.,
from 5 nm to 400 nm or any other range depending on the
application) within a distance of 100 .mu.m or less. A ratio of the
etch depth at the outer edge of transition area 1526 to the etch
depth at the inner edge of transition area 1526 may range from
100:1 to 2:1, from 90:1 to 2:1, 80:1 to 2:1, 70:1 to 2:1, 60:1 to
2:1, 50:1 to 2:1, 40:1 to 2:1, 30:1 to 2:1, 20:1 to 2:1, 10:1 to
2:1, 8:1 to 2:1, 6:1 to 2:1, 5:1 to 2:1, 4:1 to 2:1, or 3:1 to 2:1.
Accordingly, a soft stamp fabricated from the master mold may have
a varying ridge height (or varying trench depth) transitioning from
a few nanometers to a few hundred of nanometers within a short
distance of 100 .mu.m or less. A slanted grating fabricated using
such a soft stamp and/or master mold may have a varying grating
height only along the edges of the device, which may have a minimal
effect on the overall performance of the grating and/or the overall
size of the device incorporating such grating. The damage that may
be caused by the stress during delamination, however, may be
significantly reduced or limited.
[0137] FIGS. 15C, 15D, and 15E illustrate cross-sectional views of
a master mold 1530 that has been formed in master mold material
layer 1510 using, e.g., ME, taken along line 15C-15C, line 15D-15D,
and line 15E-15E of FIG. 15B, respectively. Although FIGS. 15C and
15D illustrate slanted ridges which may be formed using a slanted
ME process by projecting high energy ions towards master mold
material layer 1510 at a slant angle with respect to the top
surface of master mold material layer 1510, upright ridges that has
a substantially zero slant angle may also be fabricated using the
master mold mask 1520 to achieve a large ridge height (or trench
depth) variation within a short distance near the edge of master
mold material layer 1510.
[0138] As shown in FIGS. 15C and 15D, the duty cycle of ridges 1522
of master mold mask 1520 near the outer edge of transition area
1526 is greater than the duty cycle of ridges 1522 of master mold
mask 1520 near the inner edge of transition area 1526.
Consequently, a less etch depth into master mold material layer
1510 near the outer edge of transition area 1526 as shown in FIG.
15C may be obtained, whereas a greater etch depth into master mold
material layer 1510 near the inner edge of transition area 1526 as
shown in FIG. 15D may be obtained. Depending on the application,
the ridge height (or trench depth) may gradually increase to at
least 70%, at least 80%, at least 90%, at least 95%, or 100% of a
maximum ridge height (or maximum trench depth) at the inner edge of
transition area 1526. In some embodiments, the maximum ridge height
(or maximum trench depth) may be a maximum ridge height (or maximum
trench depth) determined by the device performance requirements.
Depending on the application, the maximum ridge height (or maximum
trench depth) may be at least 50 nm, at least 100 nm, at least 200
nm, or at least 300 nm, or at least 400 nm.
[0139] FIG. 15E illustrates an example etch profile of one trench
etched in master mold material layer 1510. As shown, a great
variation in the etch depth is achieved within a short distance
from either edge of the master mold 1530 fabricated. Although FIGS.
15B and 15E illustrate a master mold mask 1520 that has a
relatively small duty cycle within operational area 1524 as
compared to the duty cycle in transition area 1526, which results
in a greater etch depth within operational area 1524, it should be
noted that operational area 1524 may include a duty cycle that may
be greater than, less than, or similar to the duty cycle in
transition area 1526. Further, the duty cycle within operational
area 1524 may also vary. A master mold with a desired ridge height
variation near its edge or periphery can be fabricated independent
of the ridge configuration inside and further away from the edge or
periphery of the master mold. In other words, the method or
technique described herein can be used to fabricate master molds of
any configuration that may be determined based on various device
performance considerations.
[0140] Further, although the fabrication of the master mold is
described using RIE as an example fabrication technique, the master
mold can be fabricated using various other fabrication techniques,
such as micromachining process, 3-D printing process, focus ion
beam milling process, sputtering, etc. Regardless of the
fabrication processes or techniques employed for fabricating such
master mold, as long as the large variation of the ridge height
dimension can be effectuated within a short distance or small area
near the edge of the master mold, a soft stamp and/or other slanted
surface-relief structure may be fabricated using the master mold
with limited or minimal damage to the slanted ridges of the soft
stamp and/or the slanted surface-relief structure caused by stress
during the delamination process.
[0141] FIG. 17 is a simplified flow chart 1700 illustrating an
example method of fabricating a slanted surface-relief grating
using nanoimprint lithography according to certain embodiments.
[0142] At block 1710, a master mold mask is formed on a master mold
material layer or master mold substrate. The master mold mask may
be formed in a lithography material layer, such as a photoresist
layer, which may be deposited on the master mold material layer by
spin coating or other deposition techniques. The master mold mask
may then be formed from the lithography material layer using an
electron beam, focus ion beam, photolithography stepper,
nano-imprint tool, or any appropriate lithography process. The
master mold mask formed may include a varying duty cycle near the
edge of the master mold mask, such as master mold mask 1520
described above with reference to FIGS. 15A-E. The area or distance
cross which such duty cycle variation occurs may be very small,
such as between 0.1 to 100 .mu.m.
[0143] At block 1720, a master mold (which may be a hard mold) with
nano-structures, such as slanted ridges, may be fabricated in the
master mold material layer using the master mold mask as an etch
mask. The master mold may be etched using a slanted ME process that
utilizes high energy ions, which may be projected towards the
master mold material layer in the form of reactive ion beams,
chemically-assisted reactive ion beams, etc., at a slant angle
relative to a top surface of the master mold material layer. The
master mold material layer may include quartz, fused silica,
silicon, other metal-oxides, or plastic compounds.
[0144] The master mold fabricated at block 1720 may include a
varying ridge height near its edge due to the varying etch depth
resulted from the varying duty cycle of the master mold mask. The
achieved varying ridge height may gradually increase from the edge
of the master mold towards an inner region of the master mold, or
stated differently, gradually decrease towards the edge of the
master mold. The distance across which such ridge height variation
occurs can be very small and may be limited to be below 100 such as
0.1 to 10 Similar to the duty cycle of the master mold mask, the
duty cycle of the master mold also changes gradually near its edge.
Thus, the duty cycle of the master mold at its edge may be as high
as over 70%, over 80%, over 90%, over 95%, or higher, and may be
gradually reduced to any desired value depending on the device
performance requirement, such as below 90%, below 80%, below 70%,
below 60%, below 50%, below 40%, below 30%, below 20%, below 10%,
or lower towards the inner region of the master mold. The master
mold may be referred to as the generation 0 (or Gen 0) mold. The
slanted ridges of the master mold may be referred to as having a
positive (+) tone.
[0145] At block 1730, a soft stamp with slanted ridges may be
fabricated using the master mold fabricated at block 1720. The
process of fabricating the soft stamp may include coating the
master mold with a soft stamp material, such as a resin imprint
material described herein. A soft stamp foil may then be laminated
on the soft stamp material, for example, using a roller. The soft
stamp foil and the attached soft stamp material may be securely
attached to each other and may be detached from the master mold to
form the soft stamp.
[0146] Because the structures formed in the soft stamp material are
complementary to the structures of the master mold, the soft stamp
formed at block 1730 also includes a varying ridge height near its
edge. The achieved varying ridge height may gradually increase from
the edge of the soft stamp towards an inner region of the soft
stamp, or stated differently, gradually decrease towards the edge
of the soft stamp. The distance across which such ridge height
variation occurs can be limited to be below 100 .mu.m, such as 0.1
to 10 .mu.m. The soft stamp fabricated at block 1730 may be
referred to as a generation 1 (or Gen 1) stamp.
[0147] The slanted ridges of the Gen 1 stamp may have a negative
(-) tone compared with the slanted structure of the Gen 0 mold
(i.e., the master mold). Thus, instead of having a gradually
increasing duty cycle towards the edge as Gen 0 mold does, the duty
cycle of the soft stamp gradually decreases towards the edge of the
soft stamp. The duty cycle of the soft stamp at its edge may be as
low as below 30%, below 20%, below 10%, or even lower, and may be
gradually increased to any desired value as required by the device
performance, such as above 10%, above 20%, above 30%, above 40%,
above 50%, above 60%, above 70%, above 80%, above 90% or even
higher towards the inner region of the soft stamp.
[0148] At block 1740, a slanted surface-relief grating may be
imprinted using the Gen 1 stamp. For example, a waveguide substrate
may be coated with an imprint resin layer. The imprint resin layer
may include, for example, a butyl-acrylate based resin doped with a
sol-gel precursor (e.g., titanium butoxide), a monomer containing a
reactive functional group for subsequent infusion processes (such
as acrylic acid), and/or high refractive index nanoparticles (e.g.,
TiO.sub.2, GaP, HfO.sub.2, GaAs, etc.). In some embodiments, the
imprint resin layer may include polydimethylsiloxane (PDMS) or
another silicone elastomer or silicon-based organic polymer. In
some embodiments, the imprint resin layer may include ethylene
tetrafluoroethylene (ETFE), perfluoropolyether (PFPE), or other
fluorinated polymer materials. The Gen 1 stamp may be laminated on
the imprint resin layer using, for example, a roller, such as shown
in FIG. 14A. After the imprint resin layer is cured by UV light
and/or heat, the Gen 1 stamp may be delaminated from the imprint
resin layer, such as illustrated in FIGS. 14B and 14C, to form a
slanted grating within the imprint resin layer.
[0149] The slanted grating within the imprint resin layer may have
a positive (+) tone and may substantially correspond to the slanted
structure of the master mold. Thus, the imprinted grating may
include a varying grating depth near its edge that gradually
increases from the edge of the slanted grating towards an inner
region of the slanted grating, or stated differently, gradually
decreases towards the edge of the slanted grating. The imprinted
grating may further include a varying duty cycle that gradually
decreases from the edge of the slanted grating towards the inner
region of the slanted grating, or stated differently, increases
towards the edge of the slanted grating. Although the varying
grating depth and/or varying duty cycle can be limited to a very
small distance within the edge of the slanted grating imprinted,
the method illustrated by flow chart 1700 may include an optional
operation to trim or remove the edge area that includes the varying
grating depth and/or varying duty cycle, if desired.
[0150] At block 1750, the slanted grating may be over-coated with a
material having a refractive index different from the slanted
grating (e.g., the imprint resin layer). For example, in some
embodiments, a high refractive index material may be used to
over-coat the slanted grating with a relatively low refractive
index and fill the gaps between the slanted grating ridges. The
high refractive index material may include high refractive index
metal or metal compounds, such as Hafnia, Titania, Tungsten oxide,
Zirconium oxide, Gallium sulfide, Gallium nitride, Gallium
phosphide, etc., silicon, a high refractive index polymer, or a
combination of a high refractive index polymer and one or more of
the aforementioned high refractive index metal compounds, and the
like. In some embodiments, a low refractive index material may be
used to over-coat the slanted grating having a relatively high
refractive index and fill the gaps between the slanted grating
ridges. The low refractive index material may include silicon
oxide, magnesium fluoride, porous silica, or fluorinated low index
monomer (or polymer), and the like.
[0151] Although a soft stamp is described as an example stamp
fabricated at block 1730 using the master mold, the master mold may
be used to make a hybrid stamp (e.g., a hard stamp, a soft stamp,
or a hard-soft stamp). Further, different generations of NIL stamps
may be made and used as the working stamp to mold the slanted
gratings. For example, in some embodiments, the master mold may be
used as the working stamp to mold the slanted grating directly. In
some embodiments, in addition to the generation 1 stamp, a
generation 2 stamp may be made from the generation 1 stamp as shown
at block 1760, and may be used as the working stamp for the
nanoimprinting as shown at block 1770. In some embodiments, a
generation 3 stamp, a generation 4 stamp, and so on, may be made
and used as the working stamp. The varying ridge height may be
transferred from the master mold to the generation 1 stamp, to the
generation 2 stamp, to the generation 3 stamp, to the generation 4
stamp, and so on, and may be imprinted into the imprint resin layer
to reduce stress the imprinting stamp and the imprinted structure
may experience during delamination.
[0152] Embodiments of the invention may be used to implement
components of an artificial reality system or may be implemented in
conjunction with an artificial reality system. Artificial reality
is a form of reality that has been adjusted in some manner before
presentation to a user, which may include, for example, a virtual
reality (VR), an augmented reality (AR), a mixed reality (MR), a
hybrid reality, or some combination and/or derivatives thereof.
Artificial reality content may include completely generated content
or generated content combined with captured (e.g., real-world)
content. The artificial reality content may include video, audio,
haptic feedback, or some combination thereof, and any of which may
be presented in a single channel or in multiple channels (such as
stereo video that produces a three-dimensional effect to the
viewer). Additionally, in some embodiments, artificial reality may
also be associated with applications, products, accessories,
services, or some combination thereof, that are used to, for
example, create content in an artificial reality and/or are
otherwise used in (e.g., perform activities in) an artificial
reality. The artificial reality system that provides the artificial
reality content may be implemented on various platforms, including
a head-mounted display (HMD) connected to a host computer system, a
standalone HMD, a mobile device or computing system, or any other
hardware platform capable of providing artificial reality content
to one or more viewers.
[0153] FIG. 18 is a simplified block diagram of an example
electronic system 1800 of an example near-eye display (e.g., HMD
device) for implementing some of the examples disclosed herein.
Electronic system 1800 may be used as the electronic system of an
HMD device or other near-eye displays described above. In this
example, electronic system 1800 may include one or more
processor(s) 1810 and a memory 1820. Processor(s) 1810 may be
configured to execute instructions for performing operations at a
number of components, and can be, for example, a general-purpose
processor or microprocessor suitable for implementation within a
portable electronic device. Processor(s) 1810 may be
communicatively coupled with a plurality of components within
electronic system 1800. To realize this communicative coupling,
processor(s) 1810 may communicate with the other illustrated
components across a bus 1840. Bus 1840 may be any subsystem adapted
to transfer data within electronic system 1800. Bus 1840 may
include a plurality of computer buses and additional circuitry to
transfer data.
[0154] Memory 1820 may be coupled to processor(s) 1810. In some
embodiments, memory 1820 may offer both short-term and long-term
storage and may be divided into several units. Memory 1820 may be
volatile, such as static random access memory (SRAM) and/or dynamic
random access memory (DRAM) and/or non-volatile, such as read-only
memory (ROM), flash memory, and the like. Furthermore, memory 1820
may include removable storage devices, such as secure digital (SD)
cards. Memory 1820 may provide storage of computer-readable
instructions, data structures, program modules, and other data for
electronic system 1800. In some embodiments, memory 1820 may be
distributed into different hardware modules. A set of instructions
and/or code might be stored on memory 1820. The instructions might
take the form of executable code that may be executable by
electronic system 1800, and/or might take the form of source and/or
installable code, which, upon compilation and/or installation on
electronic system 1800 (e.g., using any of a variety of generally
available compilers, installation programs,
compression/decompression utilities, etc.), may take the form of
executable code.
[0155] In some embodiments, memory 1820 may store a plurality of
application modules 1822 through 1824, which may include any number
of applications. Examples of applications may include gaming
applications, conferencing applications, video playback
applications, or other suitable applications. The applications may
include a depth sensing function or eye tracking function.
Application modules 1822-1824 may include particular instructions
to be executed by processor(s) 1810. In some embodiments, certain
applications or parts of application modules 1822-1824 may be
executable by other hardware modules 1880. In certain embodiments,
memory 1820 may additionally include secure memory, which may
include additional security controls to prevent copying or other
unauthorized access to secure information.
[0156] In some embodiments, memory 1820 may include an operating
system 1825 loaded therein. Operating system 1825 may be operable
to initiate the execution of the instructions provided by
application modules 1822-1824 and/or manage other hardware modules
1880 as well as interfaces with a wireless communication subsystem
1830 which may include one or more wireless transceivers. Operating
system 1825 may be adapted to perform other operations across the
components of electronic system 1800 including threading, resource
management, data storage control and other similar
functionality.
[0157] Wireless communication subsystem 1830 may include, for
example, an infrared communication device, a wireless communication
device and/or chipset (such as a Bluetooth.RTM. device, an IEEE
802.11 device, a Wi-Fi device, a WiMax device, cellular
communication facilities, etc.), and/or similar communication
interfaces. Electronic system 1800 may include one or more antennas
1834 for wireless communication as part of wireless communication
subsystem 1830 or as a separate component coupled to any portion of
the system. Depending on desired functionality, wireless
communication subsystem 1830 may include separate transceivers to
communicate with base transceiver stations and other wireless
devices and access points, which may include communicating with
different data networks and/or network types, such as wireless
wide-area networks (WWANs), wireless local area networks (WLANs),
or wireless personal area networks (WPANs). A WWAN may be, for
example, a WiMax (IEEE 802.16) network. A WLAN may be, for example,
an IEEE 802.11x network. A WPAN may be, for example, a Bluetooth
network, an IEEE 802.15x, or some other types of network. The
techniques described herein may also be used for any combination of
WWAN, WLAN, and/or WPAN. Wireless communications subsystem 1830 may
permit data to be exchanged with a network, other computer systems,
and/or any other devices described herein. Wireless communication
subsystem 1830 may include a means for transmitting or receiving
data, such as identifiers of HMD devices, position data, a
geographic map, a heat map, photos, or videos, using antenna(s)
1834 and wireless link(s) 1832. Wireless communication subsystem
1830, processor(s) 1810, and memory 1820 may together comprise at
least a part of one or more of a means for performing some
functions disclosed herein.
[0158] Embodiments of electronic system 1800 may also include one
or more sensors 1890. Sensor(s) 1890 may include, for example, an
image sensor, an accelerometer, a pressure sensor, a temperature
sensor, a proximity sensor, a magnetometer, a gyroscope, an
inertial sensor (e.g., a module that combines an accelerometer and
a gyroscope), an ambient light sensor, or any other similar module
operable to provide sensory output and/or receive sensory input,
such as a depth sensor or a position sensor. For example, in some
implementations, sensor(s) 1890 may include one or more inertial
measurement units (IMUs) and/or one or more position sensors. An
IMU may generate calibration data indicating an estimated position
of the HMD device relative to an initial position of the HMD
device, based on measurement signals received from one or more of
the position sensors. A position sensor may generate one or more
measurement signals in response to motion of the HMD device.
Examples of the position sensors may include, but are not limited
to, one or more accelerometers, one or more gyroscopes, one or more
magnetometers, another suitable type of sensor that detects motion,
a type of sensor used for error correction of the IMU, or some
combination thereof. The position sensors may be located external
to the IMU, internal to the IMU, or some combination thereof. At
least some sensors may use a structured light pattern for
sensing.
[0159] Electronic system 1800 may include a display module 1860.
Display module 1860 may be a near-eye display, and may graphically
present information, such as images, videos, and various
instructions, from electronic system 1800 to a user. Such
information may be derived from one or more application modules
1822 to 1824, virtual reality engine 1826, one or more other
hardware modules 1880, a combination thereof, or any other suitable
means for resolving graphical content for the user (e.g., by
operating system 1825). Display module 1860 may use liquid crystal
display (LCD) technology, light-emitting diode (LED) technology
(including, for example, OLED, ILED, mLED, AMOLED, TOLED, etc.),
light emitting polymer display (LPD) technology, or some other
display technology.
[0160] Electronic system 1800 may include a user input/output
module 1870. User input/output module 1870 may allow a user to send
action requests to electronic system 1800. An action request may be
a request to perform a particular action. For example, an action
request may be to start or end an application or to perform a
particular action within the application. User input/output module
1870 may include one or more input devices. Example input devices
may include a touchscreen, a touch pad, microphone(s), button(s),
dial(s), switch(es), a keyboard, a mouse, a game controller, or any
other suitable device for receiving action requests and
communicating the received action requests to electronic system
1800. In some embodiments, user input/output module 1870 may
provide haptic feedback to the user in accordance with instructions
received from electronic system 1800. For example, the haptic
feedback may be provided when an action request is received or has
been performed.
[0161] Electronic system 1800 may include a camera 1850 that may be
used to take photos or videos of a user, for example, for tracking
the user's eye position. Camera 1850 may also be used to take
photos or videos of the environment, for example, for VR, AR, or MR
applications. Camera 1850 may include, for example, a complementary
metal-oxide-semiconductor (CMOS) image sensor with a few millions
or tens of millions of pixels. In some implementations, camera 1850
may include two or more cameras that may be used to capture 3-D
images.
[0162] In some embodiments, electronic system 1800 may include a
plurality of other hardware modules 1880. Each of other hardware
modules 1880 may be a physical module within electronic system
1800. While each of other hardware modules 1880 may be permanently
configured as a structure, some of other hardware modules 1880 may
be temporarily configured to perform specific functions or
temporarily activated. Examples of other hardware modules 1880 may
include, for example, an audio output and/or input module (e.g., a
microphone or speaker), a near field communication (NFC) module, a
rechargeable battery, a battery management system, a wired/wireless
battery charging system, etc. In some embodiments, one or more
functions of other hardware modules 1880 may be implemented in
software.
[0163] In some embodiments, memory 1820 of electronic system 1800
may also store a virtual reality engine 1826. Virtual reality
engine 1826 may execute applications within electronic system 1800
and receive position information, acceleration information,
velocity information, predicted future positions, or some
combination thereof of the HMD device from the various sensors. In
some embodiments, the information received by virtual reality
engine 1826 may be used for producing a signal (e.g., display
instructions) to display module 1860. For example, if the received
information indicates that the user has looked to the left, virtual
reality engine 1826 may generate content for the HMD device that
mirrors the user's movement in a virtual environment. Additionally,
virtual reality engine 1826 may perform an action within an
application in response to an action request received from user
input/output module 1870 and provide feedback to the user. The
provided feedback may be visual, audible, or haptic feedback. In
some implementations, processor(s) 1810 may include one or more
GPUs that may execute virtual reality engine 1826.
[0164] In various implementations, the above-described hardware and
modules may be implemented on a single device or on multiple
devices that can communicate with one another using wired or
wireless connections. For example, in some implementations, some
components or modules, such as GPUs, virtual reality engine 1826,
and applications (e.g., tracking application), may be implemented
on a console separate from the head-mounted display device. In some
implementations, one console may be connected to or support more
than one HMD.
[0165] In alternative configurations, different and/or additional
components may be included in electronic system 1800. Similarly,
functionality of one or more of the components can be distributed
among the components in a manner different from the manner
described above. For example, in some embodiments, electronic
system 1800 may be modified to include other system environments,
such as an AR system environment and/or an MR environment.
[0166] The methods, systems, and devices discussed above are
examples. Various embodiments may omit, substitute, or add various
procedures or components as appropriate. For instance, in
alternative configurations, the methods described may be performed
in an order different from that described, and/or various stages
may be added, omitted, and/or combined. Also, features described
with respect to certain embodiments may be combined in various
other embodiments. Different aspects and elements of the
embodiments may be combined in a similar manner. Also, technology
evolves and, thus, many of the elements are examples that do not
limit the scope of the disclosure to those specific examples.
[0167] Specific details are given in the description to provide a
thorough understanding of the embodiments. However, embodiments may
be practiced without these specific details. For example,
well-known circuits, processes, systems, structures, and techniques
have been shown without unnecessary detail in order to avoid
obscuring the embodiments. This description provides example
embodiments only, and is not intended to limit the scope,
applicability, or configuration of the invention. Rather, the
preceding description of the embodiments will provide those skilled
in the art with an enabling description for implementing various
embodiments. Various changes may be made in the function and
arrangement of elements without departing from the spirit and scope
of the present disclosure.
[0168] Also, some embodiments were described as processes depicted
as flow diagrams or block diagrams. Although each may describe the
operations as a sequential process, many of the operations may be
performed in parallel or concurrently. In addition, the order of
the operations may be rearranged. A process may have additional
steps not included in the figure. Furthermore, embodiments of the
methods may be implemented by hardware, software, firmware,
middleware, microcode, hardware description languages, or any
combination thereof. When implemented in software, firmware,
middleware, or microcode, the program code or code segments to
perform the associated tasks may be stored in a computer-readable
medium such as a storage medium. Processors may perform the
associated tasks.
[0169] It will be apparent to those skilled in the art that
substantial variations may be made in accordance with specific
requirements. For example, customized or special-purpose hardware
might also be used, and/or particular elements might be implemented
in hardware, software (including portable software, such as
applets, etc.), or both. Further, connection to other computing
devices such as network input/output devices may be employed.
[0170] With reference to the appended figures, components that can
include memory can include non-transitory machine-readable media.
The term "machine-readable medium" and "computer-readable medium,"
as used herein, refer to any storage medium that participates in
providing data that causes a machine to operate in a specific
fashion. In embodiments provided hereinabove, various
machine-readable media might be involved in providing
instructions/code to processing units and/or other device(s) for
execution. Additionally or alternatively, the machine-readable
media might be used to store and/or carry such instructions/code.
In many implementations, a computer-readable medium is a physical
and/or tangible storage medium. Such a medium may take many forms,
including, but not limited to, non-volatile media, volatile media,
and transmission media. Common forms of computer-readable media
include, for example, magnetic and/or optical media such as compact
disk (CD) or digital versatile disk (DVD), punch cards, paper tape,
any other physical medium with patterns of holes, a RAM, a
programmable read-only memory (PROM), an erasable programmable
read-only memory (EPROM), a FLASH-EPROM, any other memory chip or
cartridge, a carrier wave as described hereinafter, or any other
medium from which a computer can read instructions and/or code. A
computer program product may include code and/or machine-executable
instructions that may represent a procedure, a function, a
subprogram, a program, a routine, an application (App), a
subroutine, a module, a software package, a class, or any
combination of instructions, data structures, or program
statements.
[0171] Those of skill in the art will appreciate that information
and signals used to communicate the messages described herein may
be represented using any of a variety of different technologies and
techniques. For example, data, instructions, commands, information,
signals, bits, symbols, and chips that may be referenced throughout
the above description may be represented by voltages, currents,
electromagnetic waves, magnetic fields or particles, optical fields
or particles, or any combination thereof.
[0172] Terms, "and" and "or" as used herein, may include a variety
of meanings that are also expected to depend at least in part upon
the context in which such terms are used. Typically, "or" if used
to associate a list, such as A, B, or C, is intended to mean A, B,
and C, here used in the inclusive sense, as well as A, B, or C,
here used in the exclusive sense. In addition, the term "one or
more" as used herein may be used to describe any feature,
structure, or characteristic in the singular or may be used to
describe some combination of features, structures, or
characteristics. However, it should be noted that this is merely an
illustrative example and claimed subject matter is not limited to
this example. Furthermore, the term "at least one of" if used to
associate a list, such as A, B, or C, can be interpreted to mean
any combination of A, B, and/or C, such as A, AB, AC, BC, AA, ABC,
AAB, AABBCCC, etc.
[0173] Further, while certain embodiments have been described using
a particular combination of hardware and software, it should be
recognized that other combinations of hardware and software are
also possible. Certain embodiments may be implemented only in
hardware, or only in software, or using combinations thereof. In
one example, software may be implemented with a computer program
product containing computer program code or instructions executable
by one or more processors for performing any or all of the steps,
operations, or processes described in this disclosure, where the
computer program may be stored on a non-transitory computer
readable medium. The various processes described herein can be
implemented on the same processor or different processors in any
combination.
[0174] Where devices, systems, components or modules are described
as being configured to perform certain operations or functions,
such configuration can be accomplished, for example, by designing
electronic circuits to perform the operation, by programming
programmable electronic circuits (such as microprocessors) to
perform the operation such as by executing computer instructions or
code, or processors or cores programmed to execute code or
instructions stored on a non-transitory memory medium, or any
combination thereof. Processes can communicate using a variety of
techniques, including, but not limited to, conventional techniques
for inter-process communications, and different pairs of processes
may use different techniques, or the same pair of processes may use
different techniques at different times.
[0175] The specification and drawings are, accordingly, to be
regarded in an illustrative rather than a restrictive sense. It
will, however, be evident that additions, subtractions, deletions,
and other modifications and changes may be made thereunto without
departing from the broader spirit and scope as set forth in the
claims. Thus, although specific embodiments have been described,
these are not intended to be limiting. Various modifications and
equivalents are within the scope of the following claims.
* * * * *