Title: Photoluminescent electrophoretic display
Abstract: Electrophoretic displays (100, 400) comprise suspensions in one or more bodies of liquid (116, 418, 426) of reflective particles (118, 420), and photoluminescent particles (120, 422). The one or more bodies of liquid are located between a front wall (104, 402) and a back wall (102, 404). Electrodes (128, 129, 410, 412) and optionally a transparent ground plane layer (124) are provided for applying electric fields to the suspensions according to image information. The reflective particles and the photoluminescent particles are characterized by the electrophoretic mobilities of the same sign, and therefore move in the same direction in response to applied fields. A source of radiation (140, 428) capable of exciting photoluminescence of the photoluminescent particles is optically coupled to the liquid suspensions. An optical filter layer is optionally located at the front of the displays. The display is capable of operating under a wide range of ambient light conditions.
Patent Number: 7,015,893 Issued on 03/21/2006 to Li, et al.
| Inventors:
|
Li; Zili (Barrington, IL);
Coleman; Zane (Chicago, IL)
|
| Assignee:
|
Motorola, Inc. (Schaumburg, IL)
|
| Appl. No.:
|
356003 |
| Filed:
|
January 31, 2003 |
| Current U.S. Class: |
345/107; 430/32 |
| Current Intern'l Class: |
G09G 3/34 (20060101); G03G 17/04 (20060101) |
| Field of Search: |
345/107
359/296
250/458.1,461.1
430/32
|
References Cited [Referenced By]
U.S. Patent Documents
| 3668106 | Jun., 1972 | Ota.
| |
| 3756693 | Sep., 1973 | Ota.
| |
| 6067185 | May., 2000 | Albert et al.
| |
| 6262833 | Jul., 2001 | Loxley et al.
| |
| 6323989 | Nov., 2001 | Jacobson et al.
| |
| 6327072 | Dec., 2001 | Comiskey et al.
| |
| 6392786 | May., 2002 | Albert.
| |
| 6721083 | Apr., 2004 | Jacobson et al.
| |
| 6822782 | Nov., 2004 | Honeyman et al.
| |
| 6842279 | Jan., 2005 | Amundson.
| |
| 2002/0180687 | Dec., 2002 | Webber.
| |
| 2002/0185378 | Dec., 2002 | Honeyman et al.
| |
| 2003/0011560 | Jan., 2003 | Albert et al.
| |
| 2003/0112491 | Jun., 2003 | Albert et al.
| |
| 2003/0132908 | Jul., 2003 | Herb et al.
| |
| 2003/0137717 | Jul., 2003 | Albert et al.
| |
| 2005/0035941 | Feb., 2005 | Albert et al.
| |
Primary Examiner: Yang; Ryan
Claims
What is claimed is:
1. An electrophoretic display comprising:
a first wall; and
a second light transmissive wall spaced from the first wall;
one or more bodies of liquid located between the first wall and the second wall;
a plurality of first cohesive bodies that are light reflective and are characterized
by electrophoretic mobility of a particular sign suspended In at least a subset
of the one or more bodies of liquid;
a plurality of second cohesive bodies that are photoluminescent and are characterized
by electrophoretic mobility of the particular sign suspended in at least a subset
of the one or more bodies of liquid;
one or more electrodes located proximate the one or more bodies of liquid for
imagewise application of electric fields to the one or more bodies of liquid; and
a source of radiation capable of exciting photoluminescence of the plurality
of second cohesive bodies optically coupled to the plurality of second cohesive bodies,
wherein the liquid is transmissive of radiation capable of exciting photoluminescence
of the second cohesive bodies, and blocks radiation emitted by photoluminescence
of the second cohesive bodies, and
wherein the liquid comprises nigrosin.
2. An electrophoretic display comprising:
a first wall; and
a second light transmissive wall spaced from the first wall;
one or more bodies of liquid located between the first wall and the second wall;
a plurality of first cohesive bodies that are light reflective and are characterized
by electrophoretic mobility of a particular sign suspended in at least a subset
of the one or more bodies of liquid;
a plurality of second cohesive bodies that are photoluminescent and are characterized
by electrophoretic mobility of the particular sign suspended in at least a subset
of the one or more bodies of liquid;
one or more electrodes located proximate the one or more bodies of liquid for
imagewise application of electric fields to the one or more bodies of liquid; and
a source of radiation capable of exciting photoluminescence of the plurality
of second cohesive bodies optically coupled to the plurality of second cohesive bodies,
wherein the one or more electrodes comprise an array of electrodes that are transmissive
of radiation capable of exciting photoluminescence of the second cohesive bodies, and
wherein the source of radiation is optically coupled to the second plurality
of cohesive bodies through the array of electrodes.
3. The electrophoretic display according to claim 2 wherein:
the array of electrodes comprise indium tin oxide.
4. The electrophoretic display according to claim 2 wherein:
the array of electrodes comprises a transparent conductive polymer.
5. The electrophoretic display according to claim 2 wherein:
the source of radiation comprises an emitting diode that emits radiation in the
range of 370 to 405 nanometers;
and the second cohesive bodies comprise one or more phosphors selected from the
group consisting of:
(Ba
1-x-y-z,Ca
X,Sr
Y,Eu
Z)
2(Mg
1-w,Zn
W)Si
2O
7,
wherein
X+Y+Z<=1;
Z>0; and
0.05<=W<=0.50;
(Sr
X,Ba
Y,Ca
Z)
5(PO
4)
3Cl:Eu
2+;
wherein:
X+Y+Z=1; and
Y
2O
3:Eu
3+,Bi
3+.
6. The electrophoretic display according to claim 2 further wherein:
the army of electrodes is located proximate the first wall; and
the electrophoretic display further comprises:
an optical filter layer that transmits light in the visible portion of the spectrum;
and blocks radiation capable of exciting photoluminescence of the second cohesive
bodies said optical filter layer located proximate the second light transmissive wall.
7. An electrophoretic display comprising:
a first wall; and
a second light transmissive wall spaced from the first wall;
one or more bodies of liquid located between the first wall and the second wall;
a plurality of visible light reflecting, photoluminescent cohesive bodies suspended
in the one or more bodies of liquid, said reflecting, photoluminescent cohesive
bodies comprising reflective phosphor particles;
one or more electrodes located proximate the one or more bodies of liquid for
imagewise application of electric fields to the one or more bodies of liquid; and
a source of radiation capable of exciting photoluminescence of the plurality
of visible light reflecting, photoluminescent cohesive bodies optically coupled
to the plurality of visible light reflecting, photoluminescent cohesive bodies; and
an optical filter layer that transmits light in the visible portion of the spectrum;
and blocks radiation capable of exciting photoluminescence of the light reflecting,
photoluminescent cohesive bodies said optical filter layer located proximate the
second light transmissive wall.
8. An electrophoretic display comprising:
a first wall; and
a second light transmissive wall spaced from the first wall;
one or more bodies of liquid located between the first wall and the second wall;
plurality of visible light reflecting, photoluminescent cohesive bodies suspended
in the one or more bodies of liquid, said reflecting, photoluminescent cohesive
bodies comprising reflective phosphor particles;
one or more electrodes located proximate the one or more bodies of liquid for
imagewise application of electric fields to the one or more bodies of liquid; and
a source of radiation capable of exciting photoluminescence of the plurality
of visible light reflecting, photoluminescent cohesive bodies optically coupled
to the plurality of visible light reflecting, photoluminescent cohesive bodies,
wherein the liquid is transmissive of radiation capable of exciting photoluminescence
of the light reflecting, photoluminescent cohesive bodies, and blocks radiation
emitted by photoluminescence of the light reflecting, photoluminescent cohesive
bodies, and
wherein the liquid comprises nigrosin.
9. An electrophoretic display comprising:
a first wall; and
a second light transmissive wall spaced from the first wall;
one or more bodies of liquid located between the first wall and the second wall;
a plurality of visible light reflecting, photoluminescent cohesive bodies suspended
in the one or more bodies of liquid, said reflecting, photoluminescent cohesive
bodies comprising reflective phosphor particles;
one or more electrodes located proximate the one or more bodies of liquid for
imagewise application of electric fields to the one or more bodies of liquid; and
a source of radiation capable of exciting photoluminescence of the plurality
of visible light reflecting, photoluminescent cohesive bodies optically coupled
to the plurality of visible light reflecting, photoluminescent cohesive bodies,
wherein the one or more electrodes comprise an array of electrodes that are transmissive
of radiation capable of exciting photoluminescence of the light reflecting, photoluminescent
cohesive bodies; and
the source of radiation is optically coupled to the light reflecting, photoluminescent
cohesive bodies through the array of electrodes.
10. The electrophoretic display according to claim 9 wherein:
the array of electrodes comprise indium tin oxide.
11. The electrophoretic display according to claim 9 wherein:
the array of electrodes comprises a transparent conductive polymer.
12. The electrophoretic display according to claim 2, wherein the plurality of
second cohesive bodies comprise core particles that are coated with photoluminescent material.
13. The electrophoretic display according to claim 2, wherein a ratio of the
surface area of the plurality of first cohesive bodies to the surface area of the
plurality of second cohesive bodies is at least one to one.
14. The electrophoretic display according to claim 2, wherein the source of radiation
comprises an electroluminescent lamp.
15. The electrophoretic display according to claim 2, wherein the liquid is transmissive
of radiation capable of exciting photoluminescence of the second cohesive bodies,
and blocks radiation emitted by photoluminescence of the second cohesive bodies.
16. The electrophoretic display according to claim 2, wherein the source of radiation
comprises an emitting diode that emits radiation in the range of 320 to 405 nanometers.
17. The electrophoretic display according to claim 2, wherein the first wall
transmits ultraviolet light.
18. The electrophoretic display according to claim 2, wherein the second wall
substantially blocks ultraviolet light.
19. The electrophoretic display according to claim 2, wherein the plurality of
second cohesive particles comprise core particles that are reflective in the visible spectrum.
20. The electrophoretic display according to claim 19, wherein the first cohesive
particles and the core particles comprise titanium oxide.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to displays. More particularly, the
present invention relates to electrophoretic displays.
2. Description of Related Art
Proliferation of computers, and other electronic devices, such as for
example advanced wireless telephones, personal digital assistants (PDA), electronic
games, and new types of television monitors have increased the importance of display technologies.
Cathode Ray Tubes (CRT) and Liquid Crystal Displays (LCD) are the two most
common types of displays. CRT displays are presently dominant. LCD displays have
the advantage that they are essentially 'flat', having a small depth compared to
the dimensions of the viewable area. The flatness of LCD displays compared to traditional
CRT displays makes them especially suitable for use in small size portable devices,
such as notebook computers, PDAs, and wireless telephones, and is also attractive
for larger home entertainment, and commercial displays.
Flatness is a generally regarded as a positive attribute in display technology,
and there are other types of displays, aside from LCD displays, that are flat.
One other type of flat display technology is electrophoretic. Electrophoretic displays
comprise a suspension of particles in a liquid. The suspension is held between
two flat walls, one of which is transparent and serves as a viewable display surface.
Optionally the suspension is encapsulated in many small capsules that are held
between the two flat walls, or emulsified in a polymeric matrix. The particles
have optical properties that are different from the liquid in which they are suspended.
For example electrophoretic displays in which the particles are more reflective
of light than the liquid have been proposed and electrophoretic displays in which
the particles are luminescent have also been proposed. Each type is suited to use
under particular ambient light conditions. Due to the electrochemical properties
of the particles, and of the liquid, the particles spontaneously acquire a net
charge when placed in the liquid. Having a charge, the particles can be caused
to translate by an externally applied electric field. Electrodes are provided for
imagewise application of electric fields to the suspension. Selectively causing
the particles to translate to the viewable display surface, according to an image
pattern, causes an image to appear at the viewable display surface. In as much
as electrophoretic displays work by application of electric fields, they are potentially
very efficient in terms of current consumption, which is a significant attribute
for battery operated portable electronic devices.
Certain display applications, such as portable electronic devices, typically
require that a display be able to operate in a wide range of ambient light conditions,
i.e., in conditions ranging from mid day sun, to complete darkness.
It would be desirable to have an electrophoretic display that is capable of operating
in wide range of ambient light conditions.
BRIEF DESCRIPTION OF THE FIGURES
The present invention will be described by way of exemplary embodiments, but
not limitations, illustrated in the accompanying drawings in which like references
denote similar elements, and in which:
FIG. 1 is a sectional elevation view of an electrophoretic display according
to the preferred embodiment of the invention;
FIG. 2 is a cross section of a photoluminescent particle used in the display
according to an alternative embodiment of the invention;
FIG. 3 is a flow chart of a method of forming an image according to the preferred
embodiment of the invention; and
FIG. 4 is a sectional elevation view of an electrophoretic display according
to an alternative embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As required, detailed embodiments of the present invention are disclosed herein;
however, it is to be understood that the disclosed embodiments are merely exemplary
of the invention, which can be embodied in various forms. Therefore, specific structural
and functional details disclosed herein are not to be interpreted as limiting,
but merely as a basis for the claims and as a representative basis for teaching
one skilled in the art to variously employ the present invention in virtually any
appropriately detailed structure. Further, the terms and phrases used herein are
not intended to be limiting; but rather, to provide an understandable description
of the invention.
FIG. 1 is a sectional elevation view of an electrophoretic display
100
according to the preferred embodiment of the invention. The electrophoretic display
100 comprises a back wall
102, and a light transmissive front wall
104 that is spaced from the back wall
102. A sealant
106 bonds,
and seals the perimeters of the walls
102,
104 forming a chamber
108 between the walls
102,
104.
A plurality of capsules
110,
112 are located in the chamber
108.
Each of the capsules
110,
112, encloses a liquid
116, a first
plurality of reflective particles
118 that are reflective of at least a
portion of the visible spectrum, and are preferably white i.e., reflective across
the visible spectrum, and a second plurality of photoluminescent particles
120.
The particles
118,
120 are suspended in the liquid
116. The
photoluminescent particles
120 preferably comprise phosphors. The reflective
particles
118 and the photoluminescent particles
120 are characterized
by electrophoretic mobility of the same sign, so that under the influence of a
given field, the reflective particles
118, and the photoluminescent particles
120 move in the same general direction. The liquid
116 is transmissive
of radiation capable of exciting photoluminescence of the photoluminescent particles
120, and preferably blocks light that is emitted by the photoluminescent
particles
120. The liquid
116 preferably absorbs visible light. The
liquid
116 preferably comprises a nigrosin solution. Alternatively, instead
of using capsules
110,
112, the liquid
116, and particles
118,
120 are emulsified in a polymeric matrix.
The back wall
102 is transmissive of at least radiation capable of exciting
the photoluminescent particles
120, and the front wall
104 is transmissive
of at least a portion of a spectrum emitted by the photoluminescent particles
120.
The front wall is also transmissive of at least a portion of a spectrum reflected
by the reflective particles
118.
An optical filter layer
122 is supported on the front wall
104.
The optical filter is transmissive of at least a portion of the visible spectrum.
In particular, the optical filter layer
122 is transmissive of at least
a portion of the spectrum emitted by the photoluminescent particles
120,
and at least a portion of the spectrum reflected by the reflective particles
118.
The optical filter layer
122 blocks (either by reflection or absorption)
radiation capable of exciting the photoluminescent particles
120. Alternatively,
the optical filter
122 is eliminated and a front wall
104 is made
from a material that has the optical properties of the optical filter layer
122.
Alternatively, optical filter
122 is eliminated and the front wall made
of a material that is transmissive of optical radiation capable of exciting the
photoluminescent particles
120.
A transparent ground plane layer
124 is also supported on the front wall
104, opposite the optical filter
122, facing chamber
108.
The transparent ground plane layer
124 is transmissive of at least a portion
of the spectrum emitted by the photoluminescent particles
120 and at least
a portion of the spectrum reflected by the reflective particles
118. The
transparent ground plane layer
124 can for example comprise indium tin oxide
(ITO), or a conductive transparent polymer such as poly (3,4) ethylenedioxythiophene/polystyrenesulfone
acid (PEDOT/PSS) sold under the trade name ORGACON™ by Agfa of Ridgefield
Park, N.J. Alternatively, the functions of the transparent ground plane layer
124,
and the optical filter layer
122 are combined in a single layer. The relative
positions of the transparent ground plane layer
124, the optical filter
layer
122, and the front wall
104 are alternatively altered from
what is shown in FIG. 1.
An active matrix
126 is supported on the back wall
102 opposite
the chamber
108. Alternatively, the active matrix
126 is supported
on the back wall
102 facing the chamber
108. The active matrix
126
comprises a rectangular array of pixel electrodes
128,
129 row conductors
130, column conductors (not shown), and thin film transistors (not shown).
By application of signals to the individual row conductors
130, and individual
column conductors voltages on the pixel electrodes
128,
129 (relative
to the transparent ground plane layer
124) are controlled. The pixel electrodes
128,
129 are transmissive of radiation capable of exciting photoluminescence
of the photoluminescent particles
120. The pixel electrodes
128,
129 preferably comprise ITO or PEDOT/PSS.
An optical coupling element
132 in the form of a wedge of transmissive
material is located at the back of the electrophoretic display
100. An output
surface
134 of the optical coupling element
132 abuts the active
matrix
126. In the alternative case that the active matrix faces the chamber
108, the output surface
134 abuts the back wall
102. A reflective
layer
136 is located on a canted surface
138 of the optical coupling
element
132 that is opposite the output surface
134. One or more
sources of radiation
140 (one shown) capable of exciting photoluminescence
of the photoluminescent particles
120 faces an input surface
142
of the optical coupling element
132. The source of radiation
140
preferably comprises an ultraviolet emitting diode that emits radiation including
radiation in the range of 370 to 405 nanometers. Ultraviolet emitting diodes are
efficient low power sources of ultraviolet radiation. Radiation emitted by the
source of radiation
140 transmits through the input surface
142,
is reflected by the canted surface
138, and propagates through the output
surface
134, through the pixel electrodes
128,
129 through
the back wall
102, through the liquid
116 to the photoluminescent
particles
120. Thus, the photoluminescent particles
120 are optically
coupled to the source of radiation
142 through the pixel electrodes
128,
129 which are transmissive of radiation capable of exciting photoluminescence
of the photoluminescent particles
120. Alternatively, other types of optical
coupling elements or more elaborate optical coupling arrangements that include
multiple optical coupling elements are used in lieu of the optical coupling element
132 shown in FIG. 1.
The photoluminescent particles
120 preferably comprise a phosphor that
is efficiently excited by radiation that is efficiently produced by a diode. In
particular, the photoluminescent particles
120 preferably comprise one or
more of the following phosphors: (Ba
1-X-Y-Z,Ca
X,Sr
Y,Eu
Z)
2(Mg
1-W,Zn
W)Si
2O
7,
where X+Y+Z<=1,Z>0; and 0.05<=W<=0.50; (Sr
X,Ba
Y,Ca
Z)
5(PO
4)
3Cl:Eu
2+
where X+Y+Z=1; and/or Y
2O
3:Eu
3+,Bi
3+.
The foregoing phosphors are excited efficiently by radiation in the range of 370
to 405 nanometers which can be efficiently produced by diodes such as ultraviolet
diode
140.
The optical filter layer
122 protects users from radiation emitted by
the ultraviolet diode
140. The optical filter layer
122 also serves
to shield the photoluminescent particles
120 from solar ultraviolet radiation.
In operation, ultraviolet diode
140 is powered causing the ultraviolet
diode
140 to emit radiation that impinges on the photoluminescent particles
120, causing the photoluminescent particles
120 to emit visible light.
Optionally the ultraviolet diode is powered, in response to a signal from a photodetector
(not shown), only under low ambient light conditions. Electrical signals are applied
to the row conductors
130 and column conductors (not shown) in order to
selectively apply potentials to the pixel electrodes
128,
129 in
order to cause the reflective
118, and photoluminescent
120 particles
to move toward or away from the front wall
104.
At least two extreme states are useful in displaying information with the display
100. In a first state corresponding to a first group of capsules
110,
and pixel electrodes
128 in FIG. 1, the reflective particles
118,
and the photoluminescent particles
120 are located at the front wall
104.
In the first state ambient light that is transmitted through the front wall
104
is reflected by the reflective particles
118 back through the front wall
104. Also, in the first state the photoluminescent particles
120
photoluminesce and emit visible light which is transmitted through the front wall
104.
In a second state corresponding to a second group of capsules
112 and
pixel
electrodes
129 in FIG. 1, the reflective particles
118, and the photoluminescent
particles
120 are located near the back wall
102. In the second state
ambient light transmitted through the front wall
104 will be absorbed by
the liquid
116, and consequently will not be reflected by the reflective
particles
118. Also, in the second state light emitted by the photoluminescent
particles
120 will be absorbed by the liquid
116 and will not be
transmitted through the front wall
104.
By controlling the voltages applied to the pixel electrodes
128 129
according to image information, images are caused to appear on the display
100
which is viewed by looking toward the front wall
104. Having reflective
particles
118, and photoluminescent particles
120 that move in the
same direction in response to applied fields allows the display
100 to display
information under high ambient light conditions, in total darkness and under intermediate
ambient light conditions. In conditions of lower intensity ambient light, photoluminescence
of the photoluminescent particles
120 makes a dominant contribution to displaying
of information, and in high ambient light conditions, the reflective particles
118 make a dominant contribution to displaying image information. The display
100 is operable under a wide range of ambient light conditions, and does
not require drive signals applied to the pixel electrodes
128,
129
to be changed according to the ambient light conditions. The display
100
does not suffer from contrast reversal when operated under different lighting conditions.
Preferably, the ratio by surface area of the reflective particles
118
to the photoluminescent particles
120 is at least one-to-one.
The display
100 is alternatively made into a color display by adding color
filters adjacent the front wall
104, and driving the pixel electrodes
128,
129 according to color image signals. Alternatively, the display
100
is made into a color display by locating reflective particles
118 that reflect
different colors (e.g., red, blue and green), and photoluminescent particles
120
that emit different colors over specific pixel electrodes
128,
129.
FIG. 2 is a cross section of a photoluminescent particle
200 used in
the display
100 according to an alternative embodiment of the invention.
The photoluminescent particle
200 comprises a core
202, and a coating
of photoluminescent material
204 on the core
202. In this embodiment
the core
202 preferably comprises the same material e.g., titanium oxide,
that is included in reflective particles, e.g.,
118 with which the photoluminescent
particle
200 is used.
FIG. 3 is a flow chart of a method
300 of forming an image according
to the preferred embodiment of the invention. In step
302 a liquid suspension
of reflective particles e.g.,
118 and photoluminescent particles e.g.,
120
having electrophoretic mobility of the same sign is irradiated with radiation capable
of exciting photoluminescence of the photoluminescent particles e.g.,
120.
The liquid of the suspension irradiated in step
302 is preferably transmissive
of the radiation with which the suspension is irradiated, and preferably blocks
light emitted by the photoluminescent particles e.g.,
120, and light that
the reflective particles e.g.,
118 can reflect. In step
304 electrical
fields having directions as a function of position that are determined by image
information are applied to the suspension irradiated in step
302. Although
shown in sequence, steps
302, and
304 preferably occur concurrently.
FIG. 4 is a sectional elevation view of an electrophoretic display
400
according to an alternative embodiment of the invention. The electrophoretic display
400 comprises a top wall
402, and a bottom wall
404 that are
bonded near their peripheries by a sealant
406 forming a chamber
408.
A first plurality of capsules of a first type
414, and a second plurality
of capsules of a second type
416 are located in the chamber
408.
The capsules of the first type
414 enclose a first type fluid
418
in which a plurality of reflective particles
420 are suspended. The capsules
of the second type
416 enclose a second type fluid
426 in which a
plurality of photoluminescent particles
422 are suspended. The reflective
particles
420 and the photoluminescent particles
422 are characterized
by electrophoretic mobility of the same sign. Using separate capsules
414,
416 enclosing the different type fluids
418,
426 allows the
fluids
418,
426 to be optimized (e.g., optically, as to specific
gravity, and electrochemically) for each type of particle
420,
422.
A plurality of parallel elongated row electrodes
410 (only one of which
is visible in FIG. 4) are formed on the top wall
402 facing the chamber
408. Similarly, a plurality of parallel elongated column electrodes
412
are formed on the bottom wall
404 facing the chamber
408. The row
electrodes
410 extend to an edge portion
424 of the top wall
402
where a connection is made to an external driver circuit (not shown). A similar
extension of bottom wall (out of the plane of FIG. 4) is provided.
Pixel areas are defined by the overlap of crossing row electrodes
410,
and column electrodes
412. The row electrodes
410 and the column
electrodes
412 are conductive. The row electrodes
410 and the column
electrodes
412 are used to apply electric fields to the pixel areas in order
to induce electrophoresis of the reflective
420, and photoluminescent particles
422 within the first type
418, and second type
426 fluids
respectively. Although as shown in FIG. 4 the size of the capsules
414,
416 is such that about two capsule diameters span the width of each of the
column electrodes
412, the capsules
414,
416 are preferably
substantially smaller than the widths of the row
410, column electrodes
412, so that in the case of a random mix of capsules of the first
414,
and second
416 types there will be approximately proportionate numbers of
capsules of both types in each pixel area. The scale of the capsules
414,
416 shown in FIG. 4 is used in the interest of clearly illustrating the
capsules
414,
416 their contents.
An ultraviolet electroluminescent lamp
428 is located adjacent the back
wall
404, opposite the chamber
408. The ultraviolet lamp
428
emits radiation that is capable of exciting photoluminesce of the photoluminescent
particles
422. The ultraviolet electroluminescent lamp
428 offers
the advantage, especially for use in the electrophoretic display
400, of flatness.
An optical filter layer
430 is located on the front wall
402 opposite
the chamber
408. The optical filter layer
430 serves a function analogous
to the optical filter layer
122 shown in FIG. 1.
The column electrodes
412 and the second type fluid
426 is transmissive
of radiation capable of exciting photoluminescence of the photoluminescent particles
422. The first type fluid
418 absorbs light that the reflective particles
420 are capable of reflecting. The second type fluid
426 absorbs
light emitted by the photoluminescent particles
422. The row electrodes
410 are transmissive of at least a portion of the spectrum emitted by the
photoluminescent particles
422, and at least a portion of the spectrum reflected
by the reflective particles
420.
An active matrix driving scheme is illustrated in FIG. 1, and a passive matrix
driving scheme (using row
410, and column
412 electrodes) is illustrated
in FIG. 4. Alternatively, a direct drive driving scheme is used. A direct drive
driving scheme is especially suitable for activating predetermined pattern indicia,
such as for example a seven segment display and/or a display including predetermined
graphical icons. A direct drive display preferably includes one or more electrodes
shaped according to indicia to be displayed.
Alternatively, in lieu of the reflective particles
118, shown
in FIG. 1, and the reflective particles
420, shown in FIG. 4, smaller capsules
that enclose reflective particles and move within the capsules
110,
112
shown in FIG. 1 or the capsules
414 shown in FIG. 4 are used. Also alternatively,
in lieu of the photoluminescent particles
120 shown in FIG. 1, and the photoluminescent
particles
422 shown in FIG. 4, smaller capsules that enclose photoluminescent
particles, or photoluminescent dye, and move within the capsules
110,
112
shown in FIG. 1, or the capsules
414,
416 shown in FIG. 4 are used.
Particles or such aforementioned smaller capsules are cohesive bodies. Such cohesive
bodies are cohesive in as much as they are chemically, and physically stable in
a liquid in which they are suspended, which implies that they do not break down.
Whether particle or small capsule, in any particular embodiment the reflective
cohesive bodies, and the photoluminescent cohesive bodies are characterized by
electrophoretic mobility of the same sign.
According to another alternative particles, rather than using separate
reflective and photoluminescent particles, cohesive bodies that comprise phosphor
particles that are both photoluminescent and reflective are used. For example particles
such as shown in FIG. 2 that are both photoluminescent and reflective can be used.
While the preferred and other embodiments of the invention have been illustrated
and described, it will be clear that the invention is not so limited. Numerous
modifications, changes, variations, substitutions, and equivalents will occur to
those of ordinary skill in the art without departing from the spirit and scope
of the present invention as defined by the following claims.
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