U.S. patent application number 10/359786 was filed with the patent office on 2003-07-31 for printable electronic display.
Invention is credited to Comiskey, Barrett, Jacobson, Joseph M., Turner, Christopher.
Application Number | 20030142062 10/359786 |
Document ID | / |
Family ID | 25229776 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030142062 |
Kind Code |
A1 |
Turner, Christopher ; et
al. |
July 31, 2003 |
Printable electronic display
Abstract
A display system includes an electronic display, a power supply
physically separate from the display, and a means for electrically
coupling the display with the power supply. The display may include
nonlinear devices such as printed, particulate Schottky diodes,
particulate PN diodes, particulate varistor material, silicon films
formed by chemical reduction, or polymer semiconductor films.
Elements of the display system may be deposited using a printing
process.
Inventors: |
Turner, Christopher;
(Somerville, MA) ; Jacobson, Joseph M.;
(Cambridge, MA) ; Comiskey, Barrett; (Cambridge,
MA) |
Correspondence
Address: |
TESTA, HURWITZ & THIBEAULT, LLP
HIGH STREET TOWER
125 HIGH STREET
BOSTON
MA
02110
US
|
Family ID: |
25229776 |
Appl. No.: |
10/359786 |
Filed: |
February 7, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10359786 |
Feb 7, 2003 |
|
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08820057 |
Mar 18, 1997 |
|
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Current U.S.
Class: |
345/107 |
Current CPC
Class: |
G02F 1/167 20130101;
G02F 1/1365 20130101; G02F 1/172 20130101; G02F 1/16757 20190101;
G02F 1/16766 20190101; G02F 1/1679 20190101 |
Class at
Publication: |
345/107 |
International
Class: |
G09G 003/34 |
Claims
What is claimed is:
1. An electronic display system comprising: a. an electronic
display; b. a power supply physically separate from the display;
and c. means for electrically coupling the display with the power
supply.
2. The system of claim 1 wherein the coupling means comprises a
first pair of conductive plates associated with the display and a
second pair of conductive plates associated with the power supply,
the first and second pairs of plates capacitively coupling in
physical proximity to each other.
3. The system of claim 1 wherein the coupling means comprises at
least one antenna associated with the display and at least one
antenna associated with the power supply, the antennas inductively
coupling to each other.
4. The system of claim 1 wherein the electronic display comprises
at least one printed element.
5. The system of claim 1 wherein the electronic display comprises a
printed electrophoretic ink.
6. The display system of claim 1 wherein the coupling means
transmits information to the display.
7. The display system of claim 1 wherein the electronic display is
a particle-based, nonemissive display.
8. The display system of claim 1 wherein the electronic display is
an electrophoretic display.
9. The display system of claim 1 wherein the electronic display is
a rotating-ball display.
10. The display system of claim 1 wherein the electronic display is
an electrostatic display.
11. The display system of claim 1 wherein the electronic display
further comprises a plurality of nonlinear elements.
12. The display system of claim 11 wherein at least one of the
nonlinear elements is a transistor.
13. The display system of claim 11 wherein at least one of the
nonlinear elements is a diode.
14. The display system of claim 11 wherein at least one of the
nonlinear elements is a varistor.
15. The display system of claim 11 wherein at least one of the
nonlinear elements is a particulate varistor device.
16. The display system of claim 11 wherein at least one of the
nonlinear elements is a particulate Schottky diode.
17. The display system of claim 11 wherein the electronic display
further comprises: a. a first set of display electrodes associated
with a first layer; and b. a second set of display electrodes
associated with a second layer distinct from the first layer and
disposed in an intersecting pattern with respect to the first set
of electrodes, the first and second sets of electrodes not
contacting one another, the display and the nonlinear elements
being sandwiched between the first and second display electrode
layers so as to electrically couple at least some electrodes of the
first layer with corresponding electrodes of the second layer at
regions of intersection and thereby facilitate actuation of the
display by the electrodes at said regions.
18. A graduated display comprising: a. a plurality of display units
arranged in parallel, each display unit comprising a
particle-based, nonemissive display device and a nonlinear element
connected thereto, each of the nonlinear elements having a
different breakdown voltage; and b. a power source, having a source
voltage, connected across the display units, the power source
activating any of the display units whose nonlinear-element
breakdown voltages does not exceed the source voltage.
19. The graduated display of claim 18 wherein the non-linear
elements have progressively higher breakdown voltages and are
sequentially arranged according to those voltages.
20. The graduated display of claim 18 further comprising a switch
which reverses the connection to the source voltage causing it to
generate a potential exceeding the breakdown voltages of the
nonlinear devices.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a division of U.S. Ser. No. 08/820,057, filed Mar.
18, 1997, the disclosure of which is incorporated by reference
herein.
FIELD OF THE INVENTION
[0002] The present invention relates to electronic displays, and in
particular to non-emissive, flat-panel displays.
BACKGROUND OF THE INVENTION
[0003] Electrooptic display systems typically include an
electrooptic element (e.g., the display material itself) and
electrodes (either opaque or transparent) for applying control
voltages to the electrooptic element. Such a system may also
include a nonlinear element to allow for multiplexing of the
address lines to the electrodes, and an insulating material between
various layers of the display system. These components have been
fabricated by a multitude of conventional processes. For
versatility and convenience of manufacture, many recent efforts
have focused on producing all components of such displays by
deposition printing using, for example, screen or ink-jet printing
apparatus. The use of printing techniques allows displays to be
fabricated on a variety of substrates at low cost.
[0004] The conducting materials used for electrodes in display
devices have traditionally been manufactured by commercial
deposition processes such as etching, evaporation, and sputtering
onto a substrate. In electronic displays it is often necessary to
utilize a transparent electrode to ensure that the display material
can be viewed. Indium tin oxide (ITO), deposited by means of a
vacuum-deposition or sputtering process, has found widespread
acceptance for this purpose. More recently, ITO inks have been
deposited using a printing process (see, e.g., U.S. Pat. No.
5,421,926).
[0005] For rear electrodes (i.e., the electrodes other than those
through which the display is viewed) it is often not necessary to
utilize transparent conductors. Such electrodes can therefore be
formed from a material such as a silver ink. Again, these materials
have traditionally been applied using costly sputtering or vacuum
deposition methods.
[0006] Nonlinear elements, which facilitate matrix addressing, are
an essential part of many display systems. For a display of
M.times.N pixels, it is desirable to use a multiplexed addressing
scheme whereby M column electrodes and N row electrodes are
patterned orthogonally with respect to each other. Such a scheme
requires only M+N address lines (as opposed to M.times.N lines for
a direct-address system requiring a separate address line for each
pixel). The use of matrix addressing results in significant savings
in terms of power consumption and cost of manufacture. As a
practical matter, its feasibility usually hinges upon the presence
of a nonlinearity in an associated device. The nonlinearity
eliminates crosstalk between electrodes and provides a thresholding
function. A traditional way of introducing nonlinearity into
displays has been to use a backplane having components that exhibit
a nonlinear current/voltage relationship. Examples of such devices
used in displays include thin-film transistors (TFT) and
metal-insulator-metal (MIM) diodes. While these types of devices
achieve the desired result, both involve thin-film processes. Thus
they suffer from high production cost as well as relatively poor
manufacturing yields.
[0007] Another nonlinear system, which has been used in conjunction
with liquid crystal displays, a printed varistor backplane (see,
e.g., U.S. Pat. Nos. 5,070,326; 5,066,105; 5,250,932; and
5,128,785, hereafter the "Yoshimoto patents," the entire
disclosures of which are hereby incorporated by reference). A
varistor is a device having a nonlinear current/voltage
relationship. Ordinarily, varistors are produced by pressing
various metal-oxide powders followed by sintering. The resulting
material can be pulverized into particulate matter, which can then
be dispersed in a binder.
[0008] Additionally, the prior art mentions the use of a varistor
backplane to provide thresholding for a nonemissive electrophoretic
display device; see Chiang, "A High Speed Electrophoretic Matrix
Display," SID 1980 Technical Digest. The disclosed approach
requires the deposition of the display material into an evacuated
cavity on a substrate-borne, nonprinted varistor wafer. Thus,
fabrication is relatively complex and costly.
[0009] Some success has been achieved in fabricating electronic
displays using printing processes exclusively. These displays,
however, have for the most part been emissive in nature (such as
electroluminescent displays). As is well known, emissive displays
exhibit high power-consumption levels. Efforts devoted to
nonemissive displays generally have not provided for thresholding
to facilitate matrix addressing.
DESCRIPTION OF THE INVENTION
[0010] Brief Summary of the Invention
[0011] The present invention facilitates fabrication of an entire
nonemissive (reflective), electronically addressable display using
printing techniques. In particular, printing processes can be used
to deposit the electrodes, insulating material, the display itself,
and an array of nonlinear devices to facilitate addressing.
Accordingly, fabrication of the displays of the present invention
may be accomplished at significantly lower cost and with far less
complexity than would obtain using coventional fabrication
technologies. Furthermore, the approach of the present invention
affords greater versatility in fabrication, allowing the displays
to be applied to substrates of arbitrary flexibility and thickness
(ranging, for example, from polymeric materials to paper). For
example, static screen-printed displays may be used in signs or
lettering on consumer products; the invention can also be used to
form dynamic, electronically alterable displays. Moreover, the
invention can be employed to produce flat-panel displays at
manufacturing costs well below those associated with traditional
devices (e.g., liquid crystal displays).
[0012] As used herein, the term "printing" connotes a non-vacuum
deposition process capable of creating a pattern. Examples include
screen printing, ink-jet printing, and contact processes such as
lithographic and gravure printing.
[0013] For the display element, the present invention utilizes
certain particle-based nonemissive systems such as encapsulated
electrophoretic displays (in which particles migrate within a
dielectric fluid under the influence of an electric field),
electrically or magnetically driven rotating-ball displays (see,
e.g., U.S. Pat. Nos. 5,604,027 and 4,419,383), and encapsulated
displays based on micromagnetic or electrostatic particles (see,
e.g., U.S. Pat. Nos. 4,211,668; 5,057,363 and 3,683,382). A
preferred approach is based on discrete, microencapsulated
electrophoretic elements, suitable examples of which are disclosed
in U.S. application Ser. No. 08/738,260 and PCT application serial
no. US96/13469. The entire disclosures of the '027, '383, '668,
'363, and '382 patents, as well as the '260 and '469 applications,
are hereby incorporated by reference.
[0014] Electrophoretic displays in accordance with the '260
application are based on microcapsules each having therein an
electrophoretic composition of a dielectric fluid and a suspension
of particles that visually contrast with the dielectric liquid and
also exhibit surface charges. A pair of electrodes, at least one of
which is visually transparent, covers opposite sides of a
two-dimensional arrangement of such microcapsules. A potential
difference between the two electrodes causes the particles to
migrate toward one of the electrodes, thereby altering what is seen
through the transparent electrode. When attracted to this
electrode, the particles are visible and their color predominates;
when they are attracted to the opposite electrode, however, the
particles are obscured by the dielectric liquid.
[0015] In accordance with the present invention, the
electrophoretic microcapsules are suspended in a carrier material
that may be deposited using a printing process. The suspension
thereby functions as a printable electrophoretic ink. Preferably,
the electrodes are also applied using a printing process. For
example, the transparent electrode(s) may be a print-deposited ITO
composition, as described in the above-mentioned '926 patent, and
the rear electrodes may also be an ITO composition or,
alternatively, a silver ink. The electrophoretic ink is deposited
between the electrode arrays, forming a sandwich structure.
[0016] Preferably, the invention also includes a series of
nonlinear devices that facilitate matrix addressing, whereby
M.times.N pixels are address with M+N electrodes; again, these
devices (which may include diodes, transistors, varistors or some
combination) are desirably applied by printing. In one approach, a
varistor backplane is deposited in accordance with, for example,
the Yoshimoto patents described above. Alternatively, a backplane
of nonlinear devices may utilize printed particulate silicon diodes
as taught, for example, in U.S. Pat. No. 4,947,219 (the entire
disclosure of which is hereby incorporated by reference). With this
approach, a particulate doped silicon is dispersed in a binder and
applied in layers to produce diode structures.
[0017] Thus, a display system in accordance with the invention may
include a substrate upon which the display system is fabricated; a
printable electrooptic display material, such as a
microencapsulated electrophoretic suspension; printable electrodes
(typically based on a transparent, conductive ink) arranged in an
intersecting pattern to allow specific elements or regions of the
display material to be addressed; insulating layers, as necessary,
deposited by printing; and an array of nonlinear elements that
facilitate matrix addressing. The nonlinear devices may include
printed, particulate Schottky diodes, particulate PN diodes,
particulate varistor material, silicon films formed by chemical
reduction, or polymer semiconductor films.
[0018] The displays of the present invention exhibit low power
consumption, and are economically fabricated. If a bistable display
material is used, refreshing of the display is not required and
further power consumption is achieved. Because all of the
components of the display are printed, it is possible to create
flat-panel displays on very thin and flexible substrates.
[0019] In another aspect, the invention comprises means for
remotely powering a nonemissive display, and in still another
aspect, the invention comprises a graduated scale comprising a
series of nonemissive displays each associated with a nonlinear
element having a different breakdown voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The foregoing discussion will be understood more readily
from the following detailed description of the invention, when
taken in conjunction with the accompanying drawings, in which:
[0021] FIG. 1 schematically represents a display in accordance with
the present invention, including row and column electrodes, an
electrooptic display material, and an array of nonlinear
elements;
[0022] FIG. 2 is a graph of the current/voltage characteristic of a
printable nonlinear element in accordance with the invention;
[0023] FIG. 3A is an enlarged sectional view of a varistor device
in accordance with the invention;
[0024] FIG. 3B is an enlarged sectional view of a semiconductor
Schottky diode in accordance with the invention;
[0025] FIG. 3C is an enlarged sectional view of a particulate
semiconductor diode in accordance with the invention;
[0026] FIGS. 4A and 4C are enlarged sectional views of display
systems in accordance with the invention each including row and
column electrodes, a microencapsulated electrophoretic display
material, an insulator material, and a nonlinear backplane;
[0027] FIGS. 4B and 4D are partially cutaway plan views of the
display systems shown in FIGS. 4A and 4C, respectively;
[0028] FIG. 5 is an isometric view of a display device in
accordance with the invention, and which has been fabricated into
the form of the letter M; and
[0029] FIG. 6A is a partially exploded, schematic illustration of
an address configuration with one electrode floating;
[0030] FIG. 6B is an elevation of an alternative embodiment of the
floating-electrode address configuration shown in FIG. 6A;
[0031] FIGS. 7A and 7B schematically illustrate remotely powered
displays; and
[0032] FIGS. 8A and 8B illustrate application of the invention to
produce a graduated scale.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] Refer first to FIG. 1, which schematically illustrates a
display system in accordance with the invention. The depicted
system includes an electrophoretic display, and the various
components are deposited by a printing process as permitted by the
present invention. It should be understood, however, that the
invention may be practiced using other particle-based displays, and
with components deposited by conventional (e.g., vacuum-type)
processes.
[0034] The illustrated embodiment includes a series of row and
column electrodes indicated generally at 100 and 102, respectively,
and preferably formed using a printed conductive ink. Assuming the
column electrodes 100 are the ones through which the display is
viewed, these are transparent. The row electrodes 102, which serve
as the rear electrodes, may or may not be transparent, depending
upon the application. The electrophoretic display material 104 and
the nonlinear elements 106 are sandwiched between column electrodes
100 and row electrodes 102, forming a series circuit at each
topological point of overlap (intersection) between the two
electrode arrays. The display element 104 is shown as a capacitor
because, for most display applications, the display material acts
as a dielectric between two conductive plates (the electrodes),
essentially forming a capacitor. The nonlinear element 106 is
depicted as two back-to-back diodes because the I-V characteristic
of element 106 is preferably similar thereto.
[0035] The display shown in FIG. 1 may be addressed by any of a
variety of schemes. Assume, for purposes of discussion, that the
voltage across a display pixel 104 and the associated nonlinear
element 106 is defined as the row voltage (V.sub.r) minus the
column voltage (V.sub.c). Assume further that the display material
is configured to "switch" or change state if a certain voltage
V.sub.on or greater is applied to it, and to reassume the original
state when a voltage of -V.sub.on is applied across it. The voltage
V.sub.on is a function of the display material and the desired
switching speed.
[0036] In a matrix addressing scheme it possible to selectively
apply voltage of V.sub.on or -V.sub.on to certain pixels using
row-at-a-time addressing, but unselected pixels may experience a
voltage of up to V.sub.on/2 in magnitude. This half-select voltage
V.sub.h is the reason that a threshold is required. By placing a
nonlinear element 106 in series with the display material,
interference (e.g., slow but nonetheless perceptible switching) due
to V.sub.h is eliminated. The nonlinear element 106 is chosen such
that for voltages of less than V.sub.h across it, very little
current flows. When the voltage across nonlinear element 106 rises
to V.sub.on, however, the device effectively acts as a smaller
resistance, allowing more current to flow. This prevents
"half-selected" pixels from switching while ensuring that fully
selected ones do switch. It is thus necessary to have a nonlinear
device with symmetrical characteristics such that V.sub.b, the
breakdown voltage of the device, is greater than V.sub.h, but less
than V.sub.on. The amount of current that the device passes at
V.sub.on determines the switching speed of the display; that is,
the amount of current passed at V.sub.h determines how long it will
take an unselected pixel to switch, and thus in non-bistable
systems effectively determines how many pixels can be multiplexed
(by dictating how often the display must be refreshed for a given
switching speed).
[0037] A preferred current/voltage characteristic of the nonlinear
element 106 is depicted at 200 in FIG. 2. The characteristic is
preferably symmetric as shown, with high impedance between some
breakdown voltages -V.sub.b and V.sub.b. For voltages greater in
magnitude than V.sub.b the device exhibits a lower impedance,
allowing exponentially more current to flow as the magnitude of the
voltage across the device increases. The device whose response is
depicted in FIG. 2 is essentially equivalent to two back-to-back
Zener diodes. (Two diodes are necessary to ensure that the device
is symmetric.) However, the response profile 200 can be obtained
using devices other than back-to-back Zener diodes. The voltage
V.sub.b is equal to the forward voltage drop V.sub.f of one diode
plus the reverse breakdown voltage V.sub.br of the second diode.
V.sub.br is usually larger in magnitude than V.sub.f and thus
accounts for most of the breakdown voltage. Above V.sub.b, current
flow is exponentially proportional to the applied voltage.
[0038] This is similar to a varistor. A varistor has an inherently
symmetrical I-V curve, given by the relation
I.sub.v=(V/K).sup..alpha. where V is the applied voltage, K is a
constant and a is determined by device structure. Thus, the
varistor also offers an exponential rise in current for voltages
above some breakdown voltage, and while the actual IV curves of
back-to-back diodes and varistors may be slightly different, they
have the same general properties and are both suitable for use as
nonlinear elements in the display system of the present
invention.
[0039] Methods for creating nonlinear elements 106 vary depending
upon the desired implementation. FIGS. 3A-3C show cross-sections of
three different nonlinear elements suitable for use herewith: a
particulate varistor device, a particulate Schottky diode, and a
particulate PN diode.
[0040] The varistor of FIG. 3A can be prepared in the following
manner (in rough accordance with the Yoshimoto patents). ZnO
particles are first pressed under high pressure (greater than 100
kg/cm). After pressing, the resulting ZnO pellets are sintered at a
temperature between 800.degree. C. and 1400.degree. C. After the
initial sintering the ZnO is pulverized and sintered again. In
order to fabricate a good varistor, the resulting particles are
doped with one or more compounds selected from the group consisting
of Sb.sub.2O.sub.3, MnO, MnO.sub.2, Co.sub.2O.sub.3, CoO,
Bi.sub.2O.sub.3, and Cr.sub.2O.sub.3. The amount of these dopants
is up to 15% by weight of the ZnO particles. This mixture is then
sintered again at temperatures greater than 800.degree. C. The
final particles are depicted at 300 in FIG. 3A.
[0041] The particles 300 are mixed with a suitable binder for
screen printing. Binders based on either ethyl cellulose or
polyvinyl alcohol with suitable solvents, as are well known to
those of skill in the art, may be used. For ethyl cellulose-based
binders, butyl carbitol acetate is the preferred solvent. The
binder is typically almost completely burned off after curing, but
is represented schematically (pre-cure) at 302.
[0042] In addition to the aforementioned binder it is desirable to
add a glass frit to the mixture to provide for adhesion of the
varistor paste to the substrate onto which it is to be printed.
Typically, a glass frit having a low-temperature (e.g., 400.degree.
C.) melting point is used. An alternative to the binder/glass-frit
mixture is to disperse the varistor particles in a photohardening
resin or epoxy. This provides adhesion the particles at a lower
temperature than is required by the glass frit, and is cured
through exposure to actinic radiation.
[0043] The exact composition of the mixture may vary. In a typical
application, the composition may consist of 70% varistor material,
20% glass frit and 10% binder. Different ratios may be used, for
example, depending on whether the binder is ethyl cellulose-based,
polyvinyl alcohol-based, resin-based, or epoxy-based.
[0044] This slurry or paste formed by dispersion of the particles
in the binder is then deposited by means of standard printing
techniques onto the bottom electrode 304. The deposited mixture is
cured at temperatures up to 400.degree. C. and/or exposed to
actinic radiation, depending on the nature of the binder. Binders
including a glass frit typically require curing temperatures of
400.degree. C. and higher, while the systems not including glass
may be cured at lower temperatures (e.g., less than 200.degree.
C.). After curing of the varistor, a top electrode 306 is printed,
thus completing the device.
[0045] The Schottky diode structure shown in FIG. 3B is prepared in
the following manner, in rough accordance with the '219 patent.
Silicon particles derived from either amorphous or single-crystal
silicon are first obtained. In an exemplary embodiment, P-type
(boron-doped) silicon is employed. A suitable material is chosen
for the rear electrode such that an ohmic contact can be formed
with the semiconductor. Aluminum is especially suitable, although
other metals with appropriate electron work functions may be used
instead.
[0046] A rear or bottom electrode 320 is first printed and cured.
The silicon particles 322 are mixed in a suitable binder 324 to
produce a paste having desired properties for the particular
application. For example, ethyl cellulose with butyl carbitol
actetate as a solvent can serve as a suitable binder. For adhesion
purposes, a glass frit may be mixed in with the binder and the
silicon particles. The mixture is first printed (e.g., screened)
onto the rear electrode. It is desirable to limit the thickness of
this printed layer so that it is comparable to the diameter of the
silicon particles. This produces a monolayer of particles, which
ensures good current flow between the electrodes.
[0047] The applied mixture is then exposed to a multiphase
temperature cycle. Initially a low temperature of 200.degree. C. is
used to burn off the organic binder. The sample is then raised to a
temperature of approximately 660.degree. C. This temperature, which
is the eutectic point of silicon and aluminum, allows the silicon
particles to form a good ohmic contact to the electrode. (Of
course, the temperature may be altered if a material other than
aluminum is used for rear electrode 320.) At this temperature the
glass fit also becomes molten, helping to adhere the silicon to
electrode 320 as well as providing an insulating layer so that the
top electrode 326 does not short to bottom electrode 320. The
temperature is then slowly lowered, allowing the silicon to
recrystallize. After the sample has been cooled, top electrode 326
is printed on the device. Silver inks provide rectifying contacts
to P-type materials and are preferred for electrode 326 in the
context of this example. Different materials may be utilized if
desired, or if N-type particles are used. After the electrode 326
is printed, the sample is fired to cure the ink and complete the
device.
[0048] The device depicted in FIG. 3B forms only one half of the
necessary back-to-back structure. A second device is therefore
created and attached in the appropriate configuration to the first
device to produce a symmetric nonlinear element.
[0049] The PN diode structure shown in FIG. 3C may be prepared as
follows. Silicon particles derived from either amorphous or
single-crystal silicon are first obtained. In a representative
example, P-type and N-type silicon are used. A suitable material is
chosen for both the rear and front electrodes such that ohmic
contacts can be formed with the two types of semiconductor. The
bottom electrode 330 is first printed and cured. The P-type silicon
particles 332 are once again mixed in a suitable binder 334. Once
again, a variety of pastes may be obtained, depending on the binder
chosen. Ethyl cellulose with butyl carbitol acetate as the solvent
can serve as a suitable binder. For adhesion purposes, a glass frit
may be mixed in with the binder and silicon. The mixture is printed
(e.g., by screening) onto electrode 330, which serves as the rear
electrode.
[0050] The N-type particles 336 are also dispersed in a binder.
After the P-type particles are exposed to a 200.degree. C.
temperature cycyle to burn off their binder, the N-type particles
are printed (again, for example, by screening) on top of the layer
of P-type particles 332. Once again, a 200.degree. C. temperature
cycle is used to burn off the binder. A top electrode 338 is then
printed on the N particles.
[0051] This construction is then exposed to a multiphase
temperature cycle. Initially a low temperature of 200.degree. C. is
used to eliminate any remaining organic binder. The sample is then
raised to a higher temperature, which is chosen to alloy the
silicon particles to their respective contacts. At this temperature
the glass frit also becomes molten, helping to adhere the silicon
to the contact as well as providing an insulating layer so that the
eletrodes do not short to each other. The temperature is then
slowly lowered, allowing the silicon to recrystallize and thereby
form the PN diode structure.
[0052] Once again, this device only forms one half of the necessary
back-to-back structure. A second device is therefore created and
attached in the appropriate configuration to the first device to
produce a symmetric nonlinear element.
[0053] It is also possible to utilize for creating printable
nonlinear elements that do not involve particulate systems. For
example, the printable nonlinear element may be a silicon film
formed by chemically reducing a molecularly dissolved silicide
salt, as described in the '469 PCT application and in Anderson et
al., "Solution Grown Polysilicon for Flat Panel Displays," Mat.
Res. Soc. Meet., Spring 1996 (paper H8.1) (incorporated by
reference herein); or may instead be a printable polymer conductor,
as described in the '469 PCT application and in Torsi et al.,
"Organic Thin-Film Trasnsistors with High On/Off Ratios," Mat. Res.
Soc. Symp. Proc. 377:695 (1995) (incorporated by reference
herein).
[0054] The electrooptic display element of the present invention is
preferably an electrophoretic display in accordance with the '260
application, and is based on an arrangement of microscopic
containers or microcapsules, each microcapsule having therein an
electrophoretic composition of a dielectric fluid and a suspension
of particles that visually contrast with the dielectric liquid and
also exhibit surface charges. Electrodes disposed on and covering
opposite sides of the microcapsule arrangement, provide means for
creating a potential difference that causes the particles to
migrate toward one of the electrodes.
[0055] As discussed in the '260 application, the display
microcapsules preferably have dimensions ranging from 5 to 500
.mu.m, and ideally from 25 to 250 .mu.m. The walls of the
microcapsules preferably exhibit a resistivity similar to that of
the dielectric liquid therein. It may also be useful to match the
refractive index of the microcapsules with that of the
electrophoretic composition. Ordinarily, the dielectric liquid is
hydrophobic, and techniques for encapsulating a hydrophobic
internal phase are well characterized in the art. The process
selected may impose limitations on the identity and properties of
the dielectric liquid; for example, certain condensation processes
may require dielectric liquids with relatively high boiling points
and low vapor pressures.
[0056] FIGS. 4A and 4B illustrate a complete printed display system
with a continuous nonlinear-element backplane. The device includes
a substrate 400, which is typically a thin, flexible material such
as KAPTON film. The row electrodes 402 have preferably been
deposited on substrate 400 by means of a printing process. In the
illustrated embodiment, the nonlinear backplane 404 is a continuous
layer of either particulate varistor material or particulate diode
material. The structure represented at 404 may also be a layer of
particulate silicon, a printed metal contact and then another layer
of particulate silicon. Alternatively, the structure 404 may
comprise layers of P- and N-doped particulate semiconductor inks,
printed in an ascending pattern such as PNPNPNNPNPNP. An
arbitrarily large number of layers may be printed, the optimal
number depending primarily upon the desired breakdown voltage.
[0057] An optional second set of printed row electrodes 406 (shown
only in FIG. 4A), aligned with the first set 402, provide a contact
to the other side of the nonlinear material 404. An insulator
material, such as Acheson ML25208, is print-deposited in the lanes
408 defining the space between electrodes 402, so that a smooth
surface is formed. An electrooptic display 410, such as a layer of
electrophoretic display microcapsules, is print-deposited onto
electrodes 406 or, if these are omitted, onto nonlinear backplane
404. A set of transparent column electrodes 412 is print-deposited
onto display 410 in a pattern orthogonal to row electrodes 402
(and, if included, 406). An insulator material is print-deposited
in lanes 414 between electrodes 412. Active picture elements are
defined in the regions of display 410 where these orthogonal sets
of electrodes overlap. Thus, a display with M row electrodes and N
column electrodes has M.times.N picture elements.
[0058] The material of nonlinear backplane 404 can be continuous or
deposited as a discrete array, e.g., in a matrix pattern with
nonlinear material printed only in the areas of active picture
elements (i.e., where row and column electrodes overlap). Such an
arrangement is depicted in FIGS. 4C and 4D. A substrate 430,
typically composed of a thin, flexible material such as KAPTON
film, underlies a set of row electrodes 432 which preferably have
been deposited on the substrate by means of a printing process. The
nonlinear backplane 434, which may comprise printed back-to-back
diodes or printed varistor material, is deposited in a pattern
corresponding to the active picture elements-that is, where the row
and column electrodes cross. An insulator material 435 is deposited
so as to surround elements 434 and thereby create a uniform planar
surface. Once again, the structure represented at 434 may also be a
layer of particulate silicon, a printed metal contact and then
another layer of particulate silicon. Alternatively, the structure
434 may comprise layers of P- and N-doped particulate semiconductor
inks, printed in an ascending pattern such as PNPNPNNPNPNP. An
arbitrarily large number of layers may be printed, the optimal
number depending primarily upon the desired breakdown voltage.
[0059] An optional second set of printed row electrodes 436,
aligned with the first set 432, provide a contact to the other side
of the nonlinear material 434. An insulator material, such as
Acheson ML25208, is print-deposited in the lanes 438 defining the
space between electrodes 432. An electrooptic display 440 is
print-deposited onto electrodes 436 or, if these are omitted, onto
nonlinear backplane 434. A set of transparent column electrodes 444
is print-deposited onto display 440 in a pattern orthogonal to row
electrodes 432 (and, if included, 436). Active picture elements are
defined in the regions of display 440 where these orthogonal sets
of electrodes overlap. An insulator material is print-deposited in
lanes 4446 between electrodes 444.
[0060] FIG. 5 depicts a screen-printed display 500 in the form of
the letter `M`. The display 500 is a layered structure, the layers
corresponding to those shown sectionally in FIGS. 4A and 4B. The
result is a nonemissive, screen-printed, microencapsulated
electrophoretic display, printed on an arbitrary substrate in an
arbitrary shape.
[0061] FIGS. 6A and 6B show a scheme for addressing a display where
the top electrode is "floating," i.e., not electrically connected.
This greatly simplifies the layout, although at the cost of
increasing the required supply voltage; the depicted arrangement
also envisions pixelwise addressing. With reference to FIG. 6A, a
series of display elements 602 each overlie an associated electrode
604, all of which are carried as a pixel array on a substrate 606.
A single floating plate electrode 608 overlies the displays 602.
Alternatively, as shown in FIG. 6B, the display may be a continuous
element substantially coextensive with substrate 606; discrete
regions of such a display, which lie above and are separately
addressed by each of the electrodes 604, act as individual
pixels.
[0062] Electrodes 604 are spaced apart from one another by a
distance s, and with the components in place, are separated from
electrode 608 by a distance r. So long as r<<s, placing two
adjacent electrodes 604 at V.sub.1 and V.sub.2 induces a potential
of (V.sub.1+V.sub.2)/2 at electrode 608; accordingly, as a result
of the arrangement, the field across display medium 602 will be
half that which would be achieved were V.sub.1 and V.sub.2 applied
directly. More specifically, suppose, as shown in FIG. 6B, that a
first electrode 604.sub.1 is grounded and a second electrode
604.sub.2 connected to a battery 620 of voltage V. In this case the
induced voltage in electrode 608 is V/2, but the electric field F
traverses the display 605 in opposite directions above electrodes
604.sub.1, 604.sub.2. As a result, assuming that the voltage V/2 is
sufficient to cause switching of display 625 within an acceptable
switching time, the regions of display 625 above the two electrodes
will be driven into opposite states.
[0063] This arrangement cannot sustain a condition where every
display element (or region) is in the same state. To provide for
this possibility, a separate electrode 650 (and, if the display is
organized discretely, a corresponding display element 652) are
located outside the visual area of the display-that is, the area of
the display visible to the viewer. In this way, electrode 650 may
be biased oppositely with respect to all other pixels in the device
without visual effect.
[0064] Refer now to FIGS. 7A and 7B, which illustrate remote
powering of displays. With particular reference to FIG. 7A, a
capacitive arrangement comprises a logic/control unit 700 and a
pair of transmitting electrodes 710 connected thereto. A display
unit or "tag" 720, which may have a nonlinear backplane, is
connected to a complementary pair of receiving electrodes 730. Upon
application of an AC signal to transmitting electrodes 710, an AC
field is induced in receiving electrodes 720 as they physically
approach the transmitting electrodes. The current produced by this
field can be used to directly power display unit 720 (e.g., after
being passed through a rectifier), or it can instead be filtered or
otherwise processed by on-board logic in display 720. For example,
the AC signal can convey information to such display logic to
determine the appearance of the display. For example, one or more
notch filters can be employed so that upon detection of a first AC
frequency, the display 720 is placed into a certain state, and upon
detection of a second AC frequency, is changed into a different
state. With the addition of nonlinear elements, more sophistical
signal processing can be effected while retaining the simple
circuit design of FIG. 7A. All electronic elements associated with
logic unit 700 and display unit 720 may be generated by a printing
process.
[0065] FIG. 7B shows an inductive approach to remote powering and
signalling. The illustrated inductive arrangement includes a
logic/control unit 740 and one or more transmitting coils 750. A
display unit or tag 770, which may have a nonlinear backplane, is
connected to a complementary pair of receiving coils 760. Upon
application of an AC signal to transmitting coils 750, the
resulting magnetic field induces an AC current in receiving coils
760. The induced current can be used to directly power display unit
770 or convey information in the manner described above. Once
again, the arrangment may include notch filters or additional
nonlinear elements for more sophistical signal processing. All
electronic elements associated with logic unit 740 and display unit
770 may be generated by a printing process.
[0066] Refer now to FIGS. 8A and 8B, which illustrate application
of the invention to create a voltage scale (which may serve, for
example, as a battery indicator). The display system 800 includes a
series of individual particle-based (preferably electrophoretic)
display devices 810 mounted on a substrate 820. Each display device
810 includes a rear electrode, a nonlinear device, a display
element (which may be discrete or shared among all devices 810),
and a transparent electrode; these components are preferably
printed in a stack structure in the manner illustrated in FIG.
6A.
[0067] As shown in FIG. 8B, each display can be represented as a
nonlinear device 830.sub.1 . . . 830.sub.n and a capacitor
840.sub.1 . . . . 840n. The nonlinear devices 830 have
progressively higher breakdown voltages. Accordingly, the number of
such displays "turned on" (or "turned off") at any time reflects
the voltage (e.g., from a battery 850) across the displays. In
operation, all of the displays 810 are initially in the same state.
Each of the displays 810 changes state only when the potential
exceeds the breakdown voltage of the associated nonlinear device.
To reset the device, the user activates a switch (not shown) which
reverses the connection of battery 850 and causes it to generate a
potential exceeding the breakdown voltages of all nonlinear devices
830.
[0068] It will therefore be seen that the foregoing represents a
versatile and convenient approach to the design and manufacture of
particle-based display systems. The terms and expressions employed
herein 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, but it is recognized that various modifications
are possible within the scope of the invention claimed.
* * * * *