U.S. patent application number 11/383794 was filed with the patent office on 2006-09-07 for microstructures with assisting optical lenses.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Rolf W. Biernath, David A. Engler, John C. Nelson.
Application Number | 20060198015 11/383794 |
Document ID | / |
Family ID | 25193044 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060198015 |
Kind Code |
A1 |
Engler; David A. ; et
al. |
September 7, 2006 |
Microstructures With Assisting Optical Lenses
Abstract
A microstructure to interact with electromagnetic waves by
changing optical aspect in selected areas in response to an
external signal, the microstructure comprising: a plurality of
responsive elements, each responsive element capable of presenting
at least two different optical aspects and changing between the
optical aspects based on an applied external signal, a support
substrate containing the responsive elements; and a plurality of
assisting optical lenses each optically enlarging an image from the
responsive elements associated with the assisting optical lens.
Inventors: |
Engler; David A.; (St. Paul,
MN) ; Biernath; Rolf W.; (St. Paul, MN) ;
Nelson; John C.; (The Sea Ranch, CA) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
25193044 |
Appl. No.: |
11/383794 |
Filed: |
May 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09805990 |
Mar 14, 2001 |
7057599 |
|
|
11383794 |
May 17, 2006 |
|
|
|
Current U.S.
Class: |
359/296 |
Current CPC
Class: |
G02B 26/026
20130101 |
Class at
Publication: |
359/296 |
International
Class: |
G02B 26/00 20060101
G02B026/00 |
Claims
1. A display which can communicate visual information by changing
color in selected areas responsive to an electromagnetic field, the
display comprising: a plurality of chromatic display particles
being visible on the surface of the display, each display particle
capable of presenting at least two different optical aspects and
changing between the optical aspects based on an applied
electromagnetic field, and being optically reflective and
substantially non-transmissive in each of the two optical aspects;
a support substrate containing the chromatic display particles, the
support substrate having a surface structure which defines
receiving positions for the particles; and an array of transparent
lenses displaced parallel to the support substrate, with each lens
corresponding to one receiving position and at least one particle,
wherein the lens, the receiving position and the particle or
particles in correspondence with lens together define a display
unit; wherein the support substrate has two major sides, one major
side being opaque.
2. The display of claim 1, wherein the opaque side of the support
substrate comprises an opaque cover plate bonded to the rest of the
support the substrate.
3. The display of claim 1, further comprising a filler material at
least partially surrounding each particle.
4. A display which can communicate visual information by changing
color in selected areas responsive to an electromagnetic field, the
display comprising: a plurality of chromatic display particles
being visible on the surface of the display, each display particle
capable of presenting at least two different optical aspects and
changing between the optical aspects based on an applied
electromagnetic field, and being optically reflective and
substantially non-transmissive in each of the two optical aspects;
a support substrate containing the chromatic display particles, the
support substrate having a surface structure which defines
receiving positions for the particles; an array of transparent
lenses displaced parallel to the support substrate, with each lens
corresponding to one receiving position and at least one particle,
wherein the lens, the receiving position and the particle or
particles in correspondence with lens together define a display
unit; and a filler material at least partially surrounding each
particle; wherein: the filler material exerts a force on the
particles, the force being sufficient to keep the particles
bistable but not excessive as to prevent the particles from
rotating upon the application of the electromagnetic field.
5. The display of claim 1, wherein: the chromatic display particles
have a particle size, and the receiving positions have a first
viewing aperture which is smaller than the particle size.
6. The display of claim 5, wherein each lens defines a second
viewing aperture which is greater than the first viewing
aperture.
7. As method of making a structure to interact with electromagnetic
waves, the method comprising: making a substrate, the substrate
having a plurality of cavities; placing a plurality of responsive
elements in the cavities, wherein the responsive elements are
rotating particles, and when placed in the cavities each responsive
element is optically anisotropic with respect to an electromagnetic
wave, with each responsive element capable of presenting at least
two different optical aspects and changing between the optical
aspects based on an external signals forming an array of optical
lenses directly on the substrate, each optical lens being connected
to a said cavity; and adding a filler material into each cavity,
the filler material being selected and positioned so that the
filler material exerts a force on the particles, the force being
sufficient to keep the particles bistable but not excessive as to
prevent the particles from a rotating upon the application of the
electromagnetic field.
8. The method of claim 7, wherein the structure is a visual display
and the responsive elements are optically anisotropic with respect
to a visible light.
9. The method of claim 7, wherein the external signal is an
electromagnetic field.
10. The method of claim 7 wherein the substrate is
three-dimensionally micro fabricated.
11. The method claim 7, wherein each lens is a converging lens.
12. The method of claim 7, wherein each optical lens enlarges an
image from at least a portion of the visible side of a said display
element associated with the optical lens.
13. The method of claim 7, wherein the step of forming an array of
lenses comprises: placing a top layer over the cavities, the top
layer comprising a lens-forming layer; and forming an array of
lenses from the lens-forming layer.
14. A method of making a visual display apparatus, the method
comprising: making a substrate, the substrate having a plurality of
cavities; placing a plurality of optically anisotropic display
elements in the cavities, and when placed in the cavities, each
display element having a visible side each display element capable
of presenting at least two different optical aspects and changing
between the optical aspects based on an external signal; directly
forming an array of optical lenses on the substrate, each optical
lens being individually connected to a display unit, each optical
lens further enlarging an image from at least a portion of the
visible side of each element belong to the corresponding display
unit; and making the visual display apparatus optically
non-transmissive.
15. The method of claim 14 wherein the display elements are
rotating particles.
16. The method of claim 14, wherein the particles are spheroid
balls,
17. The method of claim 14, wherein the substrate is
three-dimensionally micro fabricated.
18. The method of claim 14, wherein each lens is a converging
lens.
19. The method of claim 14, wherein: making the visual display
apparatus optically non-transmissive comprises adding an opaque
bottom layer or plate to a side of the substrate.
20. A method of making a visual display apparatus, the method
comprising: making a substrate, the substrate having a plurality of
cavities; placing a plurality of optically anisotropic display
elements in the cavities, and when placed in the cavities, each
display element having a visible side each display element capable
of presenting at least two different optical aspects and changing
between the optical aspects based on an external signal; adding an
array of optical lenses on the substrate, each optical lens being
individually connected to a display unit, each optical lens further
enlarging an image from at least a portion of the visible side of
each element belong to the corresponding display unit; and adding
an opaque bottom layer or plate to a side of the substrate to make
the visual display apparatus optically non-transmissive.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. Ser. No. 09/805990,
filed Mar. 14, 2001, now allowed, the disclosure of which is herein
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to microfabricated structures
to interact with electromagnetic waves and, more particularly to
addressable, reusable visual displays. Still more particularly, an
embodiment of the invention relates to pre-formed microstructured
substrates containing assisting optical lenses to enhance the
visual effect of visual displays, such as gyricon displays using
rotatable particles (e.g., rotary balls).
[0003] For purpose of illustration, the present application uses
structures of gyricon displays to demonstrate the concepts and the
benefits of the inventive structure.
[0004] A gyricon display, also called a twisting-particle display,
rotary ball display, particle display, dipolar particle light
valve, etc., is a type of addressable visual displays. A gyricon
display offers a technology for making a form of electric paper and
other reflective displays. Briefly, a gyricon display is an
addressable display made up of a multiplicity of optically
anisotropic particles, with each particle being selectively
rotatable to present a desired face to an observer. The rotary
particle can be of various shapes, such as spherical or
cylindrical. For convenience, balls, rather than cylinders, are
used in this description for illustrations.
[0005] Addressable visual displays typically have multiple display
units such as pixels or subpixels. A separate auxiliary optical
element is sometimes used in connection with each display to
enhance or create certain visual effect. U.S. Pat. No. 5,777,782 to
Sheridon, for example, discloses a gyricon or rotating-particle
display having an auxiliary optical structure which is a pre-formed
array of lenses indexed to gyricon particles. Although the Sheridon
patent relates to gyricon displays only, in principle the use of an
auxiliary optical structure is not limited to the gyricon displays.
A properly designed auxiliary optical structure may be used to
enhance or create certain visual effects in other types of visual
displays containing multiple display units, such as displays using
the electronic ink based on the electrophoretic principle made by E
Ink Corp. For purpose of illustration, however, the present
application uses structures of gyricon displays to demonstrate the
concepts and the benefits of the inventive structure.
[0006] A gyricon display, also called a twisting-particle display,
rotary ball display, particle display, dipolar particle light
valve, etc., offers a technology for making a form of electric
paper and other reflective displays. Briefly, a gyricon display is
an addressable display made up of a multiplicity of optically
anisotropic particles, with each particle being selectively
rotatable to present a desired face to an observer. The rotary
particle can be of various shapes, such as spherical or
cylindrical. For convenience, balls, rather than cylinders, are
used in this description for illustrations. Like ordinary paper,
electric paper preferably can be written on and erased, can be read
in ambient light, and can retain imposed information in the absence
of an electric field or other external retaining force. Also like
ordinary paper, electric paper preferably can be made in the form
of a lightweight, flexible, durable sheet that can be folded or
rolled into tubular form about any axis and can be conveniently
placed into a shirt or coat pocket and then later retrieved,
restraightened, and read substantially without loss of information.
Yet unlike ordinary paper, electric paper preferably can be used to
display full-motion and changing images as well as still images and
text. Thus, it is particularly useful for bistable displays where
real-time imagery is not essential, but also adaptable for use in
real-time imaging such as a computer display screen or a
television.
[0007] In the prior art, the black-and-white balls (particles) are
embedded in a sheet of optically transparent material, such as an
elastomer sheet. The elastomer sheet is then cured. After curing,
the elastomer sheet is placed in a plasticizer liquid, such as a
dielectric fluid. The dielectric plasticizer swells the elastomer
sheet containing the particles creating cavities larger than the
particles around the particles. The cavities are also filled with
the absorbed dielectric fluid. The fluid-filled cavities
accommodate the particles, one particle per cavity, so as to
prevent the particles from migrating within the sheet.
[0008] Besides being optically anisotropic, the particles are
electrically dipolar in the presence of the fluid. This may be
accomplished by simply including in one or both hemispheres
materials that impart an electrical anisotropy, or by coating one
or both sides of hemispheres with materials that impart electrical
anisotropy. The above charge activation agents may impart an
electrical anisotropy and an optical anisotropy at the same time.
For example, when each hemisphere of a gyricon particle is coated
with a material of a distinct electrical characteristic (e.g., Zeta
potential with respect to a dielectric fluid) corresponding to a
distinct optical characteristic the particles will have an
electrical anisotropy in addition to their optical anisotropy when
dispersed in a dielectric liquid. It is so because when dispersed
in a dielectric liquid the particles acquire an electric charge
related to the Zeta potential of their surface coating.
[0009] An optically anisotropic particle can be selectively rotated
within its respective fluid-filled cavity, for example by
application of an electric field, so as to present either its black
or white hemisphere to an observer viewing the surface of the
sheet. Under the action of an addressing electric field, such as
provided by a conventional matrix addressing scheme, selected ones
of the optically and electrically anisotropic particles are made to
rotate or otherwise shift their orientation within their cavities
to provide a display by the selective absorption and reflection of
ambient light. Since the particles need only rotate, not translate,
to provide an image, much faster imaging response is achieved than
with the display of U.S. Pat. No. 3,612,758.
[0010] When the electric field is applied to the sheet, the
adhesion of each particle to the cavity is overcome and the
particles are rotated to point either their black or white
hemispheres towards the transparent surface. Even after the
electric field is removed, the structures (particles in specific
orientations) will stay in position and thus create a bistable
display until the particles are dislodged by another electric
field. An image is formed by the pattern collectively created by
each individual black and white hemisphere. Thus, by the
application of an electric field addressable in two dimensions (as
by a matrix addressing scheme), the black and white sides of the
particles can be caused to appear as the image elements (e.g.,
pixels or subpixels) of a displayed image. These bistable displays
are particularly useful for remotely addressable displays that
require little power to switch and no power to maintain display
image for a long period of time (e.g., months).
[0011] Gyricon display technology is described further in U.S. Pat.
No. 4,126,854 (Sheridon, "Twisting Ball Panel Display") and U.S.
Pat. No. 5,389,945 (Sheridon, "Writing System Including Paper-Like
Digitally Addressed Media and Addressing Device Therefor"). Further
advances in black and white gyricon displays have been described in
U.S. Pat. No. 6,055,091 (Sheridon, "Twisting-Cylinder Display").
The aboveidentified patents are all hereby incorporated by
reference. The Sheridon patents disclosed a gyricon display which
uses substantially cylindrical bichromal particles rotatably
disposed in a substrate. The twisting cylinder display has certain
advantages over the rotating ball gyricon because the elements can
achieve a much higher packing density. The higher packing density
leads to improvements in the brightness of the twisting cylinder
display as compared to the rotating ball gyricon.
[0012] Gyricon displays are not limited to black and white images,
as gyricon and other display mediums are known in the art to have
incorporated color. Gyricons incorporating color have been
described in U.S. Pat. No. 5,760,761 titled "Highlight Color
Twisting Ball Display", U.S. Pat. No. 5,751,268 titled "Pseudo-Four
Color Twisting Ball Display", U.S. patent application Ser. No.
08/572,820 titled "Additive Color Transmissive Twisting Ball
Display", U.S. patent application Ser. No. 08/572,780 titled
"Subtractive Color Twisting Ball Display", U.S. Pat. No. 5,737,115
titled "Additive Color Tristate Light Valve Twisting Ball Display",
U.S. Pat. No. 6,128,124 titled "Additive Color Electric Paper
Without Registration or Alignment of Individual Elements" and
European Patent No. EP0902410 titled "Methods for Making Spinnable
Ball, Display Medium and Display Device". The above-identified
patents are all hereby incorporated by reference.
[0013] The above prior art all involve a process which is to
randomly pack the bichromal particles in an elastomeric matrix,
cure the elastomer, and subsequently swell the elastomer in the
dielectric oil. The process is laborious and time-consuming,
consisting of mixing of the particles into the elastomer, coating
the slurry into a sheet format, curing, and subsequently swelling
the sheet with the dielectric oil.
[0014] Furthermore, the display device of such an arrangement poses
problems in connection with the selection of a usable dielectric
liquid, stability upon changes in temperature, non-uniformity of
dimensions of the cavities, and the like. The material
considerations in the prior art are many, the primary issues being
tuning the swelling of the elastomer by the dielectric oil without
harming the dielectric oil compatibility with all the other
elements of the display package.
[0015] Furthermore, the above approach resulted ill less than
satisfactory contrast of the display, associated with the
relatively low reflectance of a gyricon display. It is commonly
believed that the best way to improve the reflectance of a gyricon
display is to make the display from a close packed arrangement of
bichromal particles. The closer packed the arrangement of
particles, the better the reflectance and the brighter the
appearance of the displays. To achieve a close packed arrangement,
the cavities in which the particles rotate should be close to each
other and each cavity should have little unfilled space when filled
with a particle, ideally no more empty space than what is necessary
to keep the particle therein rotatable. The prior art approaches,
however, had difficulties to achieve a high density of particles,
mainly due to the lack of controlling on the formation of
individual cavities. The result is typically that cavities are
either too large, or distributed too loosely in the elastomer with
large distances and thick walls between the individual cavities,
making it difficult to control the arrangement and packing density
of the display particle members to a sufficiently high value to
achieve a display of high quality, high resolution, and high
contrast.
[0016] As a related problem, in a typical conventional gyricon
display, bichromal particles are to dispersed throughout the
thickness of the substrate sheet, which is always thicker than two
particle diameters and is usually many diameters thick. Generally,
less than 20 percent of the upper surface area of the sheet is
covered by the bichromal particles in the layer closest to the
surface. Therefore, a display according to the above prior art has
multiple layers of particles instead of a single layer, making the
display thick and bulky, an undesirable feature especially for an
electronic paper. In the prior art designs, the multiple layer
configuration is on one hand necessary in order to increase the
reflectance (the reflectance of multiple layers of loosely packed
particles accumulatively approaches that of a closely packed single
layer) and on the other hand difficult to avoid due to the
characteristics of the prior art process of making a display.
[0017] To achieve higher packing density, the above method was
modified in U.S. Pat. No. 4,438,160 to Ishikawa et al, which patent
is hereby incorporated preference. In the Ishikawa patent, instead
of using the swelling method to create cavities larger than the
particles, the particles are coated with a layer of wax before
being placed in the elastomer. The wax is later melted away,
resulting in cavities that are larger than the particles.
Presumably, because it is easier to control the thickness of the
wax layer coated on the particles than to control the degree of
swelling the elastomer, it is also easier to achieve higher density
of particles by using the Ishikawa method. The actual improvement,
however, is not significant enough to solve the problem. See U.S.
Pat. No. 5,825,529 to Crowley, which patent is hereby incorporated
by reference.
[0018] To achieve still higher packing density, a gyricon display
can be constructed without elastomer and without cavities. U.S.
Pat. No. 5,825,529 to Crowley, for example, uses no elastomer
substrate. In the display in the Crowley patent, the bichromal
particles are placed directly in the dielectric fluid. The
particles and the dielectric fluid are then sandwiched between two
retaining members (egg. between the addressing electrodes). There
is no elastomer substrate. Electrodes serve both to address
particles and to retain particles and fluid in place. Particles and
fluid can be sealed in the display by seals at either end of the
display. In addition, the spacing between electrodes is set to be
as close to the diameter of particles as is possible consistent
with proper particle rotation, resulting a monolayer display. The
Crowley patent achieved a display with a closely packed monolayer
having a light reflectance that surpasses that of the multi-layer
displays in the prior art. The display in Crowley, however,
achieves a higher packing density by sacrificing structural
integrity. The Crowley display lacks internal support and has
insufficient to sealing. Particularly, the display will not work
when placed vertically.
[0019] More fundamentally, even with the above improved methods
making twisting particle displays the particles cannot be packed
together to completely fill the area of the display because of the
existence of interstices. Furthermore, regardless of which
microstructure is used, and regardless of how the particles are
packed, the particles often do not exactly rotate to the precise
orientation to have only the side with the desired optical
characteristics facing the viewer. Both partial filling and partial
rotating contribute to decreased image contrast in the following
manner: Gyricon displays use optically anisotropic particles that
are selectively rotatable to communicate visual information. For
example, in a display using bichromal spherical balls where each
ball defines a display unit which conveys the characteristic color
information of the spherical ball's hemisphere which is selectively
turned to face the viewer, the unit display area is typically the
projection area or image size of the ball. Due to the unfilled
spaces between the particles and also due to imperfect rotation
which may show wrong color or portions of contrasting (hence
cancelling) colors, each particle is surrounded by a peripheral
area which does not carry any color information of the particle
selectively rotated. Instead the peripheral area substantially
reflects the optical characteristic of the substrate which is
typically dark. This phenomenon causes decreased contrast. The same
phenomenon exists in displays where each unit display is defined by
multiple particles.
[0020] The auxiliary optical structure in U.S. Pat. No. 5,777,782
to Sheridon is not used to solve the above identified low contrast
problem. Rather it is used to focus a visual element of gyricon
particles to form a projected image on the other side of the
transmissive gyricon display. Furthermore, the auxiliary optical
structure in that patent is a pre-formed array of fly's-eye lenses
which need to be then precisely aligned in each of x, y and z
directions with the gyricon particles. Such requirement of
alignment or indexation between a pre-formed array of lenses and a
separately formed gyricon display structure is difficult and
costly.
BRIEF SUMMARY OF THE INVENTION
[0021] The present invention uses assisting optical elements to
enhance or improve optical effect of a microstructure such as
contrast of visual displays (e.g., a gyricon display). To enhance
contrast of a visual displays for example, an assisting optical
element is placed over or around each display unit to form an
enlarged image of at least a portion of the upper side of the
display elements ( such as the gyricon particles) in that display
unit so that the effective unit display area is larger than the
actual unit display area, therefore diminishing the effect of
imperfect orientation of the display elements and dark peripheral
effect caused by the substrate.
[0022] The assisting optical elements may be either reflective or
refractive in one preferred embodiment, optical lenses are directly
fabricated on the substrate containing the display elements (such
as gyricon particles). The lenses from enlarged images of the
surface of each particle when viewed from above. The inventive
assisting lens structure in accordance with the present invention
is not preformed separately from the substrate and the display
elements. Instead the lenses are formed directly on the substrate
corresponding to the geometric shapes and positions of the cavities
on the substrate. Because the display elements are contained in the
cavities, each lens is "custom-formed" based on the location of the
display element or display elements in the associated cavity, and
no indexing is required. That is, in contrast to the pre-formed
fly's eye lens structure, the inventive assisting lenses are
directly formed on the underlying substrate resulting in automatic
indexing or registration between the lenses and the corresponding
display units.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The present invention will be further explained with
reference to the drawing figures listed below, wherein like
structure is referred to by like numerals throughout the several
views.
[0024] FIG. 1A is a side sectional view of a monolayer black and
white gyricon display according to the present invention where the
display comprises a pluralist of similar or identical display
units.
[0025] FIG. 1B is a partial top view of the display in FIG. 1.
[0026] FIG. 2 is a side sectional view of a single display unit in
an embodiment according to the present invention where the
assisting optical element includes a converging lens.
[0027] FIG. 3 illustrates a first step used to form the lenses in
the embodiment of FIG. 2.
[0028] FIG. 4 illustrates a second step used to form the lenses in
the embodiment of FIG. 2, While the above-identified drawing
figures set forth several preferred embodiments of the invention,
other embodiments are also contemplated, as noted in the
discussion. In all cases, this disclosure presents the present
invention by way of representation and not limitation. It should be
understood that numerous other modifications and embodiments can be
devised by those skilled in the art which fall within the scope and
spirit of the principles of this invention.
DETAILED DESCRIPTION
1. General Aspects of the Invention
[0029] The invention will now be described with reference to the
drawings. For convenience, the drawing figures depict a reflective
gyricon display with each optical element being associated with one
spheroidal gyricon particle. The inventive structure in accordance
with the present invention, however, may also be used to enhance or
create certain optical effects in other types of microstructures.
Generally, any microstructure that contains an element having a
certain optical aspect by modulating or interacting with an
incident electromagnetic wave and giving rise to an identifiable
optical effect may use the assisting optical element of the present
invention to improve or enhance the optical effect. For example,
where elements having optical aspects pertaining to electromagnetic
waves other than a visible light are used, the inventive
microstructure may be used as a device for optical purposes other
than visual displays. Examples for such applications include but
are not limited to microwave reflectors and absorbers. IR
reflectors and absorbers, and configurable radio wave antennas and
reflectors. In the case where the electromagnetic wave is a visible
light., applications of the present invention include but not
limited to visual displays using microstructures containing a
display element. A display element can be anything that carries
certain visual information.
[0030] Particularly, the element having an optical aspect may be
optically anisotropic ( ie, having two or more optical aspects) and
capable of switching among the optical aspects in response to
external signal. The twisting particles or rotating balls used in
gyricon displays are examples of such responsive elements having an
optical anisotropy,
[0031] Visual displays that may use the inventive lens structure
typically contain multiple display units, each display unit
including one or more responsive elements as display elements.
Besides gyricon displays, examples of such visual displays include
but not be limited to displays based on the electrophoretic
principle such as electronic ink made by E Ink Corp.
[0032] Furthermore, when used with a gyricon display, the inventive
lens structure is not limited to uses with reflective gyricon
displays but may also be used with a transmissive gyricon display
or a retroreflective garrison display. In addition, each assisting
optical element may be associated with a display unit that consists
of multiple gyricon particles, and the particles may be of
geomtietric shapes other than balls. As described in U.S. Pat. Nos.
4,126,854; 5,389,945; 6,055,091; and 6,128,124 and European Patent
No, EP0902410, which patents are hereby incorporated herein by
reference, when a gyricon display is addressed using electrodes,
the display consists of multiple pixels of certain desired density,
each pixel being distinguished from other pixels by its addressing.
In the case of a color display, each pixel further consists of
multiple subpixels (generally three subpixels, each representing an
elemental color). Each pixel or subpixel may consist of a single
gyricon particle, or multiple gyricon particles. Unless specified
otherwise in the context, the present application uses the term
"display unit" to present a unit on the display substrate
containing a single particle or a group of particles in which group
the displays of the particles are addressed in an additive mode
(i.e., the display of each particle is designed to be mixed with
the displays of the rest of the particles in the same group). Such
a group may be a pixel in a black-and-white display, or either a
pixel or a subpixel in a color display.
[0033] With reference to FIG. 1A, a gyricon display 2 comprises a
plurality of repetitive display units 4. Each display unit
comprises a gyricon particle 6 (a spherical ball as shown), an
optical lens 38 and a portion of substrate 9. Each particle 6 has
two optically distinct sides 6a, 6b, one facing the viewer (not
shown) above and the other facing away from the viewer.
[0034] With reference to FIG. 1B, a viewer from above (not shown)
sees an top image of each display unit 4. When an optically
anisotropic particle 6 is selectively rotated, the side facing the
viewer has a dominant color. This is often true even if the
rotation is imperfect to a certain extent. Without assistance of
the optical lens 38, each display unit 6 has an effective display
area A which is typically the projection area or image size of the
ball. Due to the unfilled spaces between the particles, each
particle is surrounded by a peripheral area B. Without assistance
of an assisting optical element, the peripheral area B does not
carry any color information of the particle selectively rotated,
instead it reflects the optical characteristic of the substrate
which is typically dark. Where the peripheral area B is substantial
as compared to display area A, contrast of the display decreases.
In addition, incomplete or over rotation also lowers contrast by
contributing to area B due to showting portions of contrasting
colors instead of a single dominant color.
[0035] The optical lens 38 helps to enhance the contrast. With the
optical lens 38, the dominant color of the particle side facing the
viewer is spread or diffused into the peripheral area through
refraction. As a result, when viewed through the assisting optical
element, the viewer sees an image of the display unit larger than
the actual size of the particle. The enlarged image has the same
dominant color as that of top side 6a of the corresponding particle
and diminishes the image-derogating effect caused by the peripheral
area B.
[0036] In addition to contrast enhancement, other display qualities
such as a wider viewing angle or a wider incident light receiving
angle may be achieved by engineering various proper optics.
[0037] Description of preferred embodiments according to the spirit
of the invention follows.
2. Preferred Embodiments
[0038] With reference to FIG. 2, a single display unit 4 in an
embodiment according to the present invention includes a converging
lens 38 disposed at the top perimeter edge 37 of the cavity 33. The
converging lens 38 forms an enlarged image of the upper portion
(white hemisphere 6a as shown) of the ball 6 as explained
below.
[0039] When placed properly in relation to an object, a converging
lens may form an enlarged image of the object. When the object is
placed within the focus length of the converging lens, for example,
the viewer from the other side of the lens will see an enlarged
image of the object formed on the same side as the object relative
to the lens. With reference to FIG. 2, light 35 from a top portion
14 is refracted through the converging lens 38 before reaches the
viewer from above (not shown). If, for example, the top hemisphere
6a of the ball 6 is located within the focal length of the
converging lens 38, an enlarged image of the top hemisphere 6a will
be formed on the same side as the ball 6 (i.e., the opposite side
to the viewing side) relative to the lens to the viewer from
above.
[0040] If the enlargement is sufficient to cover a substantial
amount of the peripheral area around the ball 6, the contrast of
the display will be enhanced. The amount of enlargement, however,
should not be excessive. An over-enlarged image starts to blur with
the images of adjacent balls 6 and will lead to decreased
resolution of the display.
[0041] The degree of enlargement is determined by the focal length
of the converging lenses 38 and the distance between the top
hemisphere 6a and the lens 38. The maximum amount of enlargement
without blurring the display is determined by the size of the
peripheral area around each ball 6. To optimize the display, it is
therefore important to be able to control the focal length of the
lenses 38 and the sizes of the cavities 3 in the process of
manufacturing the display in FIG. 7, the converging lens 38 is
spaced from the rotating ball 6 and the space therebetween is
filled with entrapped air (not shown), Alternatively, a transparent
filler material 12 may be used. Besides being an optional support
for the lens 38, the filler material 12, when properly selected and
applied, helps to create bistability of the gyricon particles
6.
[0042] The cavity 33 has a smooth and continuous conical shape.
Alternatively, other geometric shapes of the cavity 33, such as the
two-portion design in FIG. 2 and FIG. 3 of the commonly-owned U.S.
patent application titled "Microstructures with Assisting Optical
Elements to Enhance an Optical Effect" and filed concurrently
(Attorney Docket Number M507.12-16) may be used. The disclosure of
the above-identified patent application is hereby incorporated
herein by, reference. Conversely, the assisting optical elements
illustrated in that application may also be combined with the
converging lens 38 this application. Additionally, the partial
enclosing design illustrated in FIG. 3 of that application may also
be used in the converging lens model as shown in FIG. 2 in this
application.
[0043] FIG. 2 and FIG. 3 both illustrate a single display unit. The
actual visual display comprises a two-dimensional array of such
single display units. FIG. 1A, for example, illustrates a partial
sectional view of a monolayer black and white gyricon display
according to the present invention where the gyricon display 2
comprises a plurality of display units 4. Each display unit 4 has
an optical lens 38 on top of a particle 6.
3. Method of Manufacture
[0044] To make a display in accordance with the present invention,
a substrate 9 containing cavities that have surfaced openings must
first be made. The display in the Crowley patent does not have a
substrate 9 containing cavities and is therefore not suitable for
implementing the improvement according the present invention. In
addition, the display in the Crowley patent has two other potential
problems. First, the display package is environmentally and
mechanically sealed only around the perimeter of the display. This
results in the package being susceptible to cracking as may result
from wear and tears in this instance, a single crack would be
adequate to enable all of the dielectric oil to drain or evaporate
away, thereby disabling the function of the display. Additionally,
the package is susceptible to buckling, and the elastomer-particle
film can sag or slide out of position because of gravity
(especially when held vertically for long periods of time, such as
for display signs). This is because the mechanical support for the
package is primarily the thin polymer films on the front and back
sides, and because the reinforcement of these films occurs only
where they are bonded together along the periphery.
[0045] Elastomer matrix structures in prior art may be used for the
purpose of the present invention if the elastomer, with or without
the combination of particles, has a surface structure that
facilitates lens forming. In most conventional elastomeric
structures, however, the cavities and particles are largely
enclosed and located inside the elastomer and therefore have no
surface openings, making it difficult to fabricate the lens
structure of this application. In addition, these elastomer matrix
structures have cavities that are randomly formed with irregular
shapes and locations. Where each cavity represents a pixel or
subpixel, there must be proper indexing or registration in the
alignment between the addressing electrodes and each cavity, making
the process of adding the auxiliary optical elements difficult and
consequently resulting in high costs for making a display. U.S.
Pat. No. 5,777,782 to Sheridon is an example for a structure with
such limitations.
[0046] An exemplary preferred method of making a preformed
substrate 9 containing cavities 33 is described in details in the
commonly-owned U.S. patent application titled "Post and Pocket
Microstructures for Movable Particles Having an Optical Effect" and
filed concurrently (Attorney Docket Number M507.12-14). The
disclosure of the above-identified patent application is hereby
incorporated herein by reference.
[0047] The concepts and the methods of manufacture disclosed in
that application may be used to preform a substrate 9 containing
cavities 33 that have proper geometric shapes and pattern to
accommodate both optically anisotropic particles 6 such as gyricon
particles and assisting optical lens 38. As described in that
application, the post and pocket microstructures have many other
advantages. Particularly, the pocket and post structure has a
surface structure such as the cavities which are open from the top
during manufacturing. Such a structure accommodates the process of
adding or directly forming an optical lens 38 on the substrate.
Additionally, where a dielectric fluid is used such as in a gyricon
display using rotatable particles the dielectric fluid does not
need to diffuse through an elastomer. This allows a much greater
variety of dielectric fluids to be used than in the case for the
swollen elastomer sheets.
[0048] With an above preferred preformed substrate 9, assisting
optical lens 38 may be included in the following two different
ways: 1) preforming the assisting optical lens 38 separately (e.g.,
formed on a top plate that also has the addressing electrodes) and
then placing them over the substrate 9, and, 2) forming the
assisting optical lens 38 directly or integrally on the elastomer
substrate 9. As used in the present application, a process of
"directly forming in assisting optical element on the substrate"
means a process that involves more than simple placement of a
pre-formed assisting optical element on the substrate or making
necessary physical connections between an assisting optical element
and the substrate. However, directly forming the lenses 38 on the
substrate 9 is preferred for the following reasons: 1) when the
preformed substrate disclosed in the above identified patent
application is used, fabrication of the substrate and fabrication
of the assisting optical elements (e.g., lens 38) may be made one
single integrated manufacturing process to improve efficiency and
lower the cost; and 2) integrated manufacturing process
additionally provides an intrinsic solution to the difficult
problem of exact indexing or registration between each lens 38 and
its corresponding display unit 4.
[0049] Assisting optical elements other than lenses 38 may also be
used to enhanced the contract of a display. For example, as
described in details in the commonly owned U.S. patent application
titled "Microstructures with Assisting Optical Elements to Enhance
an Optical Effect" and filed concurrently (Attorney Docket Number
M507.12-16), a reflective corona shouldering a particle, creates an
appearance of the surface of the particle larger than the actual
size of the surface through reflection of the light from surface,
given that the reflective corona is larger than the particle. A
reflective corona may simply be made of metalized reflective
surfaces, or alternatively formed by using the principle of total
internal reflection in which a total reflection is created at an
interface of two different materials at certain incident angles of
the light, even though the interface is not made of a material
which is highly reflective in ordinary sense.
[0050] The optical lens structure in accordance with the present
invention offers an alternative to the above assisting optical
elements. Besides being optically distinctive, the optical lens
structure also offers an alternative way of fabricating assisting
optical elements on a display. For example because the lenses 38
are formed subsequent to the placement of the display elements 6
(such as gyricon particles) into the substrate, the lenses 38 may
be formed directly on top of the display particles 6, resulting in
a lens structure automatically conforming to the geometric shape of
the particles, a benefit in addition to the above-discussed
automatic indexing.
[0051] Converging lenses 38 can be made by conventional methods,
such as compression molding. Conventional methods, if used to
preform the lenses separately, will be less preferable due to the
difficulties to register each lens 38 with a corresponding cavity
33.
[0052] With reference to FIG. 3 and FIG. 4, there is described
herein a preferable method of making converging lenses 38 using a
self-forming micro-lens array by self-forming micro-lens film 46.
An array of micro-lenslets 38 can be manufactured from transparent
thermoplastic polymer which is pressed onto an array of holes
(cavities 33 as applied in the present invention).
[0053] In FIG. 3, a plate assembly 42 comprises a high temperature
backing plate 44, a low temperature lens forming layer 46 and a
thin high temperature membrane 48. The backing plate 44 is a rigid
material which has a high melting temperature. The low temperature
lens forming layer 46 is a polymer which has a low melting
temperature such as an ethylene-vinyl acetate copolymer resin
(EVA). The thin high temperature membrane 48 is an elastic material
which has a high melting temperature such as a polyvinylidene
chloride type resin (PVDC). The plate assembly 42 is placed over a
two-dimensional array of display units 4.
[0054] FIG. 3 and FIG. 4 illustrate how a two-dimensional array of
micro-lenses 38 is formed from the lens-forming layer 46. In FIG.
3, the plate assembly 42 is placed over a two-dimensional array of
display units 4. Heat and pressure are then applied to the plate
assembly 42. While the high temperature backing plate 44 and the
high temperature membrane 48 withstand the temperature, essentially
all of the lower melt temperature lens-forming material 46 is
melted. The pressure deforms the membrane 48 (but does not
substantially deform the backing plate 44 as the plate 44 is rigid)
and pushes the membrane 48 into the cavities 33. Since the membrane
48 is withheld at top perimeter edges 37 of the cavities 33 but
pushed into each cavity 33 in the middle, the membrane 48 is
contoured into a spherical surface (lens 38) in each cavity 33. At
the same time, the melt lens-forming material 46 flows in response
to both gravity and the pressure exerted by the topplate 44. The
flow of melt lens-forming material 46, however, is constrained at
the bottom by the contoured and strained membrane 48 due to surface
tension. The final result is a steady equilibrium state of
pressure, forming a spherical lens 38.
[0055] Only a minimum pressure and temperature is preferred. As the
pressure increases, all lens-forming material 46 flows into the
cavities 33 and the backing plate 44 will eventually come in
contact with the top perimeter 37 of the cavities 33. This
condition will prevent further flow of the lens-forming material
46. As a result, further pressure only results strain on the
structure and contributes nothing in the lens making.
[0056] The temperature should higher than the melting temperature
of the lens-forming material 46 but less than the melting
temperature of the top-plate 44, membrane 48 and the substrate 4. A
temperature higher than the minimum melting temperature of the
lens-forming material 46 will only result in a faster process of
equilibrium to a limited degree, and is usually unnecessary or even
harmful because too high a temperature may lead to difficulties in
operation.
[0057] In the above process, the focal length of the lenses
F=(H.sup.2+A.sup.2)/2H, where H is the thickness of the lens 38 at
the center as shown in FIG. 4, while A is the diameter of the top
perimeter opening 37 (full view not shown) of the cavity 33. H
itself is determined by the total volume of each lens V according
to the equation V=1/6B H(3A.sup.2+H.sup.2). That is, for a given V
and A, the value of H can be readily determined by solving the
above equation. If the lens-forming layer 46 has a uniform
thickness r, each unit cell of the array will have a precise volume
V of lens-forming material associated with it. For example, if the
top opening of each cavity has an area of A.sup.2 (full view not
shown), each unit cell will have the volume V=TA.sup.2 of
lens-forming material associated with it. Therefore, focal length F
of the lenses 38 is ultimately determined by T and A and hence
easily controlled,
[0058] As applied to the present invention, the uniformity of the
focal length is not crucial as long as each lens has a sufficient
enlarging effect. The actual range of focal length of the lenses
38, however, is significant and must be controllable in the process
of manufacturing because a proper range is determined according to
the size of the cavities 33 so that the converging lenses 38 have
enough enlarging effect to increase the contrast yet do not
over-enlarge to cause blurring and hence decrease the
resolution.
[0059] Once the lens array 38 is formed, the backing plate 44 may
be separated from array of cavities 4 or may remain adhered. The
lens array 38 may also be separated form the array of cavities 4
and used for other purposes. In the present invention, however, the
lens array 38 and the array of cavities 4 are kept together,
resulting in intrinsic registration.
[0060] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of invention. All U.S. patents
referred in this disclosure are incorporated by reference
herein.
* * * * *