U.S. patent application number 09/956341 was filed with the patent office on 2002-04-18 for busbars for electrically powered cells.
Invention is credited to Agrawal, Anoop, Cronin, John, Denesuk, Matthew, Kennedy, Steve, LeCompte, Robert, McCarthy, Kevin, Teowee, Gimtong, Tonazzi, Juan Carlos Lopez.
Application Number | 20020044331 09/956341 |
Document ID | / |
Family ID | 26784223 |
Filed Date | 2002-04-18 |
United States Patent
Application |
20020044331 |
Kind Code |
A1 |
Agrawal, Anoop ; et
al. |
April 18, 2002 |
Busbars for electrically powered cells
Abstract
Edge busbars on a substantial perimeter of an electrochromic
device are disclosed having electrical paths wrapping over the
perimeter edge. Internal busbars interior from the perimeter are
disclosed which lower the conductivity of the conductive layer of
an electrochromic device. Signals supplied to the busbars to
control the electrochromic device are controlled by a switching
power supply that allows the maintaining of the color of the
electrochromic device without application of continuous power.
Inventors: |
Agrawal, Anoop; (Tucson,
AZ) ; Tonazzi, Juan Carlos Lopez; (Tucson, AZ)
; LeCompte, Robert; (Tucson, AZ) ; Cronin,
John; (Tucson, AZ) ; Kennedy, Steve; (Tucson,
AZ) ; McCarthy, Kevin; (Tucson, AZ) ; Denesuk,
Matthew; (Tucson, AZ) ; Teowee, Gimtong;
(Tucson, AZ) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Family ID: |
26784223 |
Appl. No.: |
09/956341 |
Filed: |
September 20, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09956341 |
Sep 20, 2001 |
|
|
|
09347807 |
Jul 2, 1999 |
|
|
|
6317248 |
|
|
|
|
60091678 |
Jul 2, 1998 |
|
|
|
Current U.S.
Class: |
359/265 ;
359/251; 359/252; 359/254 |
Current CPC
Class: |
H01R 12/7076 20130101;
H01M 14/005 20130101; H05K 3/403 20130101; G02F 1/155 20130101 |
Class at
Publication: |
359/265 ;
359/254; 359/251; 359/252 |
International
Class: |
G02F 001/15; G02F
001/03; G02F 001/07 |
Claims
What is claimed is:
1. An edge busbar having a shape effective to be peripherally
disposed about a substantial perimeter of an edge, between a first
surface and an opposite second surface, of an electrical device,
wherein said edge busbar comprises: at least one electrically
conductive connector portion effective to form an electrically
conductive path from said first surface, wrapping transversely
around a portion of said edge, to said opposite second surface; and
an electrically conductive perimeter portion in electrical contact
with said connector portion, wherein said perimeter portion is
peripherally on said substantial perimeter.
2. An edge busbar according to claim 1, wherein said connector
portion includes a plurality of said electrically conductive paths;
and wherein said perimeter portion is in electrical contact with
said plurality of electrically conductive paths.
3. An edge busbar according to claim 1, further including a
conductive layer formed on said first surface; and wherein said
connector portion has at least one separating portion electrically
bridged by said conductive layer.
4. An edge busbar according to claim 1, wherein said connector
portion and said perimeter portion are composed of aluminum,
copper, gold, silver, tungsten, stainless steel, tin,
copper/beryllium alloy, indium, nickel, rhodium, nichrome, solder,
or a conductive metal oxide.
5. An edge busbar according to claim 1, wherein said edge busbar is
composed of a metal in substantially a sheet configuration, wherein
said sheet includes a ribbon having a plurality of first finger
portions extending from a side of said ribbon, said ribbon forming
said perimeter portion and said first finger portions forming said
connector portions.
6. An edge busbar according to claim 5, wherein said sheet further
includes a second plurality of finger portions extending from an
opposite second side of said ribbon, said ribbon forming said
perimeter portion and said first and second finger portions forming
said connector portions.
7. An edge busbar according to claim 1, wherein said at least one
connector portion is made from a cured metallic frit, conductive
ink, or conductive adhesive.
8. An edge busbar according to claim 1, wherein said at least one
connector portion is composed of indium tin oxide or doped tin
oxide.
9. An edge busbar pair comprising a first edge busbar and a second
edge busbar, each edge busbar of said pair having a shape to be
peripherally disposed about a respective substantial perimeter edge
of a first substrate and a second substrate respectively of an
electrical device, said edge busbar pair further including: said
first busbar comprising a first connector portion and a first
perimeter portion, said first connector portion effective to form
an electrically conductive first path from a first front surface of
said first substrate, wrapping around a portion of said edge of
said first substrate, to an opposite first back surface of said
first substrate, said first perimeter portion being in electrical
contact with said first connector portion, and wherein said first
perimeter portion is peripherally on said first substantial
perimeter of said first substrate; a second busbar comprising a
second connector portion and a second perimeter portion, said
second connector portion effective to form an electrically
conductive second path from a second front surface of said second
substrate, wrapping around a portion of an edge of said second
substrate, to an opposite second back surface of said second
substrate, said second perimeter portion being in electrical
contact with said second connector portion, and wherein said second
perimeter portion is peripherally on said second substantial
perimeter of said second substrate; and wherein said first front
surface and said second front surface proximately face each
other.
10. An edge busbar pair according to claim 9, wherein said first
substantial perimeter is correspondingly opposite said second
substantial perimeter.
11. An edge busbar pair according to claim 9, wherein said first
and second connector portions each includes a plurality of said
electrically conductive respective first and second paths; and
wherein said first and second perimeter portions are in electrical
contact with said respective plurality of electrically conductive
first and second paths.
12. An edge busbar pair according to claim 11, wherein said
plurality of first paths and said plurality of second paths are in
an alternating relation.
13. An edge busbar pair according to claim 12, wherein said first
and second connector portions have a thickness in the range of from
more than one half of a gap distance to less than said gap
distance; and wherein said gap distance is the distance separating
said first front surface and said second front surface.
14. An edge busbar pair according to claim 9 or 11, further
including an insulator disposed between said first substrate and
said second substrate effective to prevent electrical shorting of
said first connector portion to said second connector portion.
15. An edge busbar pair according to claim 9, wherein said first
and second connector portions and said first and second connector
perimeter portions are composed of aluminum, copper, gold, silver,
tungsten, stainless steel, tin, copper/beryllium alloy, indium,
nickel, rhodium, nichrome, solder, or a conductive metal oxide.
16. An electrochromic device comprising a first substrate; a second
substrate; and an edge busbar pair, wherein said edge busbar pair
comprising a first edge busbar and a second edge busbar, each edge
busbar of said pair peripherally disposed about a respective
substantial perimeter edge of said first substrate and said second
substrate respectively, said edge busbar pair further including:
said first busbar comprising a first connector portion and a first
perimeter portion, said first connector portion effective to form
an electrically conductive first path from a first front surface of
said first substrate, wrapping around a portion of said edge of
said first substrate, to an opposite first back surface of said
first substrate, said first perimeter portion being in electrical
contact with said first connector portion, and wherein said first
perimeter portion is peripherally on said first substantial
perimeter of said first substrate; a second busbar comprising a
second connector portion and a second perimeter portion, said
second connector portion effective to form an electrically
conductive second path from a second front surface of said second
substrate, wrapping around a portion of an edge of said second
substrate, to an opposite second back surface of said second
substrate, said second perimeter portion being in electrical
contact with said second connector portion, and wherein said second
perimeter portion is peripherally on said second substantial
perimeter of said second substrate; and wherein said first front
surface and said second front surface face each other.
17. An electrochromic device according to claim 16, wherein said
plurality of first paths and said plurality of second paths are in
an alternating relation.
18. An electrochromic device according to claim 16, wherein said
first and second connector portions have a thickness in the range
of from more than one half of a gap distance to less than said gap
distance; and wherein said gap distance is the distance separating
said first substrate and said second substrate.
19. An internal busbar for a substrate having a conductive layer
and a reactive layer on a first surface, said internal busbar
comprising: at least one conductive strip, isolated from chemical
reaction with said reactive layer; and at least one conductive
connecting portion, each connecting portion electrically connecting
a non-peripheral portion of said conductive layer to a segment of
said conductive strip.
20. An internal busbar according to claim 19, wherein said
conductive layer is isolated from chemical reaction with said
reactive layer by a passivation layer.
21. An internal busbar according to claim 19, wherein said at least
one conductive strip is substantially embedded in the
substrate.
22. An internal busbar according to claim 19, wherein said at least
one conductive strip is on an opposite second surface of said
substrate, and said at least one connecting portion extends through
said substrate from said first surface to said at least one
conductive strip.
23. An internal busbar for a substrate having a conductive layer on
a surface of the substrate, said internal busbar comprising: at
least one conductive strip having increased electrical conductance
per unit length from the conductive layer in a longitudinal
direction of said conductive strip, and said conductive strip
having a perimeter in contact with the conductive layer.
24. An internal busbar according to claim 23, wherein said
conductive strip is substantially embedded in the substrate.
25. An internal busbar according to claim 23, wherein said
conductive strip is embedded in the substrate, and wherein said
conductive strip has a longitudinal surface coextensive with a
surface of the conductive surface layer.
26. An internal busbar according to claim 23, comprising a
plurality of said conductive strips; and further comprising: at
least one sublayer conductive strip under the conductive layer,
said sublayer conductive strip having increased electrical
conductance per unit length from the conductive layer.
27. An internal busbar according to claim 23, wherein said at least
one conductive strip has a transverse axis at an angle to the axis
perpendicular to the surface of the substrate.
28. An internal busbar according to claim 27, wherein said
transverse axis is parallel to a viewing direction of the
substrate.
29. An internal busbar according to claim 28, wherein the substrate
is a part of a window, a windshield, a sunroof, a light filter, or
a mirror.
30. An internal busbar according to claim 23, wherein said at least
one conductive strip is composed of a cured metallic frit,
conductive ink, conductive epoxy, a metal rod, or a metal bar.
31. A transparent conducting sheet comprising: a transparent
substrate sheet; a transparent electrically conducting layer on a
substantial surface of said substrate sheet; and at least one
conductive strip interior to a perimeter edge of said conducting
layer; said at least on e conductive strip effective to lower an
effective conductivity of said conducting layer.
32. A transparent conducting sheet according to claim 31, further
including at least one edge conductor electrically connected to
said transparent conducting layer on a portion of a peripheral edge
of said substrate sheet.
33. A transparent conducting sheet according to claim 31, wherein
an end of said conductive strip is proximate to said edge
conductor, separated by a proximate distance from said edge
conductor, and wherein said proximate distance is electrically
bridged by said conducting layer.
34. An electrical device comprising: a conductive layer; an edge
conductor on a perimeter portion of said conductive layer; and at
least one conductive strip having increased electrical conductance
per unit length from said conductive layer, and said conductive
strip having a perimeter in contact with said conductive layer.
35. An electrical device according to claim 36, wherein said at
least one conductive strip has an end proximate to said edge
conductor.
36. An electrical device according to claim 37, wherein said end
and said edge conductor form a gap bridged by said conductive
layer.
37. A chromogenic device comprising: a plurality of layers
responsive to a first signal applied transversely effective to
cause a change in a first property of said chromogenic device, and
responsive to a second signal applied in a laminar direction
effective to cause a change in a second property of said
chromogenic device; at least one conductor strip arranged in said
laminar direction, said conductor strip interior of a perimeter of
said layers; a first edge conductor at a first perimeter portion of
a first layer of said layers; a second edge conductor at a second
perimeter portion of a second layer of said layers; wherein
application of said first signal transversely from said first edge
conductor to said second edge conductor, without application of a
potential difference longitudinally along said at least one
conductor strip, causes a responsive change in said first property
without a change in said second property; and wherein application
of said second signal as a longitudinal signal along said at least
one conductor strip, without a transverse potential difference
between said first and second edge conductors, causes a responsive
change in said second property without a change in said first
property.
38. A chromogenic device according to claim 37, wherein said first
property is optical transmittance.
39. A chromogenic device according to claim 37, wherein said second
property is temperature.
40. A method to form an interior busbar comprising the steps of:
forming at least one channel on a surface of a substrate interior
to the perimeter; applying a conductive material to said at least
one channel; applying a conductive layer over said surface
effective to completely cover said applied conductive material.
41. A method to control an electrochromic device having a light
transmission property that responds to a physical or chemical
effect, wherein the light transmission property changes in response
to an electrical signal, wherein said method comprises the step of:
intermittently applying the electrical signal by controlling the on
duration t.sub.1 and the off duration t.sub.2 of the electrical
signal individually, in response to the physical or chemical
effect, effective to maintain the light transmission property
within a range of about 1% to about 10% of a predetermined value of
said light transmission property.
42. A method according to claim 41, wherein said t.sub.1 and
t.sub.2 are controlled in response to the physical effect of
temperature.
43. A method according to claim 41, wherein at least one of (i) the
current, and (ii) the change of current with time, (iii) output
from photosensors, (iv) charge passed through the device, (v) cell
potential, to said electrochromic device is used to respond to the
change caused in the device by the change in temperature; by
changing said t.sub.1 and t.sub.2.
44. A method according to claim 41, wherein the temperature of the
electrochromic cell is used to influence the control circuit so as
to adjust t.sub.1 and t.sub.2.
45. An electrochromic device having a light transmission property
that responds to a physical or chemical property, wherein the light
transmission property changes in response to an electrical signal,
wherein said electrochromic device includes: a means to
intermittently apply the electrical signal by controlling the on
duration t.sub.1 and the off duration t.sub.2 of the electrical
signal individually, in response to the physical or chemical
property, effective to maintain the light transmission property
within a range of about 1% to about 10% of a predetermined value of
the light transmission property.
46. An electrochromic device according to claim 45, wherein the
means to intermittently apply the electrical signal is a control
circuit which includes: an astable timer that supplies an input to
a first RC timing circuit; and a monostable timer that supplies an
input to a second RC timing circuit; wherein a first output from
the first RC timing circuit and a second output from the second RC
timing circuit is applied to the electrochromic device.
47. An electrochromic device according to claim 46, wherein a
microcontroller provides t.sub.1 and t.sub.2.
48. An electrochromic device according to claim 45 or 46, wherein
the voltage of the electrical signal is supplied from a regulated
power supply that is regulated by a switching voltage
regulator.
49. A method to control an electrochromic device having a light
transmission property that responds to a physical or chemical
property, wherein the light transmission property changes in
response to an electrical signal, wherein said method comprises the
step of: intermittently applying the electrical signal by
controlling the on duration t.sub.1 and the off duration t.sub.2 of
the electrical signal individually, in response to the physical or
chemical property, effective to maintain the light transmission
property within a range of about 1% to about 10% of a predetermined
value of said light transmission property; wherein the voltage of
the applied electrical signal is supplied from a regulated power
supply that is regulated by a switching voltage regulator.
50. An electronic circuit to power a chromogenic device wherein the
voltage reduction is carried out using a switching voltage
regulator.
Description
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/091,678, filed Jul. 2, 1998.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to busbars utilized in electrically
powered cells. In particular, this invention relates to edge and
internal busbars utilized in electrochromic devices. This invention
also relates to edge and internal busbars that can be utilized in
other electrically powered cells such as electroluminescent and
photochromic devices, thin-film batteries, and other cells that use
geometries similar to the electrochromic devices described herein.
Further, this invention relates to control circuits and methods to
control the coloration of such electrochromic devices through an
intermittent application of power.
[0004] Electrochromic (EC) devices are devices in which a change in
an electrical signal applied to the EC device results in a change
in an optical property of the EC device. Typically, the optical
property is optical transmittance, although other properties can be
affected such as, for example, optical spectral distribution or
polarization. Electrochromic devices can be used for many
applications, such as rear view automotive mirrors, windows,
sunroofs, shades or visors for automotive and mass transportation
applications, architectural windows, skylights, displays, light
filters and screens for light pipes, displays, and other
electro-optical devices.
[0005] A variety of technologies exist for producing chromogenic
members. "Chromogenic devices", as used herein, is employed as
commonly known in the art. Examples of these chromogenic devices
include electrochromic devices, photochromic devices, liquid
crystal devices, user-controllable-photochromic devices,
polymer-dispersed-liquid-crystal devices, and suspended particle
devices.
[0006] For example, electrochromic devices are discussed by N. R.
Lynam and A. Agrawal in "Automotive Applications of Chromogenic
Materials", Large Area Chromogenics: Materials & Devices for
Transmittance Control, Optical Engineering Press, Bellingham, Wash.
(1989), incorporated herein by reference. Other pertinent
references include N. R. Lynam, "Electrochromic Automotive
Day/Night Mirrors", SAE Technical Paper Series, 87036 (1987); N. R.
Lynam, "Smart Windows for Automobiles", SAE Technical Paper Series,
900419 (1990); C. M. Lampert, "Electrochromic Devices and Devices
for Energy Efficient Windows", Solar Energy Materials, 11, 1-27
(1984); JP 58-20729; and U.S. Pat. Nos. 3,521,941, 3,807,832,
4,174,152, 4,338,000, 4,652,090, 4,671,619, 4,702,566, 4,712,879,
4,793,690, 4,799,768, Re. 30,835, 5,066,112, 5,073,012, 5,076,674,
5,122,647, 5,142,407, 5,148,014, 5,239,406, and 5,657,149 each
incorporated herein by reference.
[0007] Electrochromic panels are also discussed by Sapers, S. P.,
et al. in "Monolithic Solid-State Electrochromic Coatings for
Window Applications", Proceedings of the Society of Vacuum Coaters
Conference (1996), incorporated herein by reference, with regard to
devices of the type shown in FIG. 1E. Devices comparable to that
shown in FIG. 1E, and having photovoltaic layers for self-biasing
operation are also described in U.S. Pat. No. 5,377,037.
[0008] Other related references of interest include U.S. Patent No.
5,241,411, U.K. Patent No. 2,268,595, Japanese Laid-Open Patent No.
Appln. No. 63-106730, Japanese Laid-Open Patent No. Appln. No.
63-106731, and U.S. Pat. No. 5,472,643, each incorporated herein by
reference. Also pertinent is International Application No. PCT/US
97/05791, incorporated herein by reference, which pertains to
electrochromic devices that can vary the transmission or reflection
of electromagnetic radiation by applying an electrical stimulus to
an EC device. International Application No. PCT/US 97/05791 uses a
selective ion transport layer in combination with an electrolyte
having at least one redox active material to provide a
high-performance device.
[0009] Also suitable for use in this invention are liquid crystal
devices such as those described by N. Basturk and J. Grupp in
"Liquid Crystal Guest-Host Devices and Their Use as Light
Shutters", Large Area Chromogenics: Materials & Devices for
Transmittance Control, Optical Engineering Press, Bellingham, Wash.
(1989), incorporated herein by reference.
[0010] User-controllable-photochromic devices (UCPC) are discussed
in U.S. Pat. No. 5,604,626, entitled "Novel Photochromic Devices",
incorporated herein by reference.
[0011] Polymer-dispersed-liquid-crystal (PDLC) devices are
described by N. R. Lynam and A. Agrawal, "Automotive Applications
of Chromogenic Materials", Large Area Chromogenics: Materials &
Devices for Transmittance Control, Optical Engineering Press,
Bellingham, Wash. (1989), incorporated herein by reference.
[0012] Suspended particle devices are discussed in U.S. Pat. No.
4,164,365, incorporated herein by reference.
[0013] Examples of chromogenic devices that emit light are
described in Applied Physics Letters, Vol. 71, page 1293
(1997).
[0014] Examples of chromogenic devices that can store image
patterns due to a change in an optical property of a material are
described in U.S. Pat. No. 5,744,267, incorporated herein by
reference.
[0015] The general control of chromogenic devices is discussed in
U.S. Pat. Nos. 4,793,690, 4,799,768, 5,007,718, and 5,424,898,
incorporated herein by reference.
[0016] The phenomenon of prolonged coloration of chromogenic
devices is discussed in U.S. Pat. Nos. 5,076,673 and 5,220,317,
each incorporated herein by reference.
[0017] FIGS. 1A through 1E depict typical examples of known
electrochromic devices, while FIG. 1F shows another known type of
chromogenic device.
[0018] For example, FIG. 1A depicts a layered EC device which
includes a substrate 101, transparent conductor 103, electrochromic
(redox) medium 105, transparent conductor 103' and substrate
101'.
[0019] FIG. 1B illustrates a layered EC device which includes a
substrate 101, transparent conductor 103, EC layer 107, electrolyte
(redox medium) 109, transparent conductor 103' and substrate
101'.
[0020] FIG. 1C shows another layered EC device having a substrate
101, transparent conductor 103, EC layer 107, ion-selective
transport layer 111, electrolyte (redox medium) 109, transparent
conductor 103' and substrate
[0021] Still another such EC device is shown in FIG. 1D. This
device includes a substrate 101, transparent conductor 103, EC
layer 107, electrolyte 113, counterelectrode 115, transparent
conductor 103' and substrate 101'.
[0022] FIG. 1E shows an EC device having a substrate 101,
transparent conductor 103, EC layer 107, electrolyte
(ion-conductive layer) 117, counterelectrode 115 and transparent
conductor 103'.
[0023] A typical liquid crystal or PDLC device is shown in FIG. 1F.
This device includes a substrate 201, transparent conductor 203,
liquid crystal or PDLC medium 205, transparent conductor 203' and
substrate 201'.
[0024] Since the above chromogenic devices are known to those
skilled in the art, a detailed explanation of the manner of
construction and operation of such devices is not necessary.
[0025] In general, it is important to distribute the voltage to an
electrochromic (EC) device uniformly in order to (i) maintain the
uniformity of the coloration and bleaching of the EC device during
changes between such states of coloration and bleaching, (ii) to
improve uniformity in such colored and bleached states, and finally
(iii) to enhance the kinetics of coloration and bleaching. As the
size of an EC device increases, it becomes increasingly more
difficult to maintain the desirable voltage distribution uniformity
because increased size typically leads to increased resistance of
various components. Such increased resistance results in voltage
drops and current losses that adversely affects the uniformity of
voltage distribution.
[0026] In other electrical devices, a particular spatial voltage
distribution profile often is desired. As the size of such devices
increases, similar to the example of EC devices, it also becomes
increasingly more difficult to maintain the desired spatial voltage
distribution profile because of the increasing electrical
resistance of various components.
[0027] An applied voltage is commonly distributed at the periphery
of EC devices through the use of an edge busbar which distributes
an applied voltage to a surface conductor electrode. The applied
voltage causes a response in a particular responsive property of an
EC device. Consequently, spatial or temporal differences in the
applied voltage will cause spatial or temporal differences in the
responsive property. Ohmic losses along an edge busbar can
therefore critically affect the even distribution of voltage,
leading to undesirable non-uniformities in the coloration and
bleaching of an EC device.
[0028] Furthermore, EC devices often employ thin film transparent
conductors such as indium tin oxide (ITO) and doped tin oxides
(DTO) for the surface conductor electrode. Such thin film
transparent conductors are also used in a wide range of
applications in other areas such as displays, solar cells, and
liquid crystal devices. If the magnitude of the electrical currents
in such devices is large, there can be a considerable electrical
potential drop across the transparent conductor. Similar to the
effect of voltage variations along an edge busbar, variations of
voltage in thin film transparent conductors can also lead to
spatial inhomogeneities in the device behavior as well as to slower
overall device kinetics. Such effects become increasingly
noticeable and problematic with increasing device area.
[0029] Another related aspect of electrochromic devices is that
they are current consuming devices. Accordingly, it is advantageous
for the transparent conductors, i.e., the surface electrodes, to be
very conductive. For applications such as large area EC panels,
where current consumption is large, it is particularly important
that the transparent conductors possess high effective
conductivities. Present conventional large-area EC devices
fabricated from commercially available transparent conductors such
as, for example, ITO and DTO, generally possess slow kinetics and
often display nonuniform coloring. For example, large-area EC
devices presently are often darker at the edges than in the
center.
[0030] EC devices can be fabricated on one substrate as described
in U.S. Pat. No. 4,712,879; J. Gordon H. Matthew et. al., Proc. of
3d Svmposium on Electrochromic Materials, The Electrochemical
Society, Proc. Volume 96-24, Pennington, N.J., 1997, p. 311; and
Badding, M. E., et al., Proc. of 3d Symposium on Electrochromic
Materials, The Electrochemical Society, Proc. Volume 96-24,
Pennington, N.J., 1997, p. 369, each incorporated herein by
reference.
[0031] Electrochromic devices can also be made using two substrates
as described in U.S. Pat. Nos. 4,761,061, 4,768,865, 4,902,108,
5,142,407, 5,231,531, 5,472,643, and U.S. patent application Ser.
No. 09/155,601, filed Aug. 9, 1997, each incorporated herein by
reference.
[0032] Prior art EC devices are also described in Lynam N. R.,
Agrawal, A., Automotive Applications of Chromogenic materials, in
Large-Area Chromogenics: Materials and Devices for Transmittance
Control, SPIE Optical Engineering Press, Bellingham, Wash., 1990,
p. 46 and Lampert C. L., Selkowitz, S. E., Large-Area Chromogenics:
Materials and Devices for Transmittance Control, SPIE Optical
Engineering Press, Bellingham, Wash., 1990, p. 22, each
incorporated herein by reference.
[0033] U.S. Pat. Nos. 5,202,787 and 5,151,824, each incorporated
herein by reference, show the way busbars in an EC device are
typically put on the substrate edges in the prior art. As shown in
FIGS. 2, 3A, and 3B, taken from the referenced patents, in a
commercial EC automotive mirror which features two substrates 2223
and 2224, or 3333 and 3334, the substrates are staggered slightly
with respect to each other. Spring clips 2221 and 2222, or 3331 and
3332, of a conductive material such as a copper sheet or a
beryllium copper coated with tin are clipped to the two staggered
edges of substrates 2223 and 2224, or 3333 and 3334, in order to
provide an electrical connection to substrates 2223 and 2224, or
3333 and 3334. The two substrates must be offset, or staggered,
from each other in order to expose surfaces 2225 and 3335 for the
attachment of clips 2221 and 2222, or 3331 and 3332. The surfaces
2225 and 3335 are minimized in order to maximize the optical
throughput area of the device--that is, to maximize the overlapping
area of the two substrates. Accordingly, the prior art provides
electrical connections at less than one half of the perimeter of
each substrate.
[0034] When a potential is applied to the wire clips 2221 and 2222,
or 3331 and 3332, only a small potential drop occurs in these clips
because of their high conductivity. The small potential drop can be
neglected for small dimensions. However, as the dimensions of the
application increases, the potential drop can become significant.
Such potential drops can be a problem because the potential drop
comes at a cost to the potential available to the chromogenic
elements themselves. Further, significant current flow can occur at
the clips and clip junctions, thereby adversely adding to the
overall current load.
[0035] The resistance of a typical wire clip used in commercial
automotive mirrors that are about 12 inches (30 cm) in length is
about 0.29. The conductivity associated with the clip depends on
the intrinsic conductivity of the material, the geometric
parameters of the clip (such as thickness, width and the length of
the strip), and on the relevant contact resistance.
[0036] To demonstrate the current consumption in the EC devices, a
commercial EC automotive mirror was colored by applying a DC step
voltage of 1.4 V. The mirror initially consumed a current of 3
mA/cm.sup.2, decreasing to 0.9 mA/cm.sup.2 in the fully colored
state.
[0037] According to Hichwa, B.P1, "Large Area Electrochromics for
Architectural Applications", International Conference on Coatings
on Glass, Saarbrucken, Germany, October 1996, an EC window device
made from all thin films on a single substrate when powered at 1.8
V showed an initial current consumption of about 2 mA/cm.sup.2
which decreased to about 1 .mu.A/cm.sup.2 in the colored
steady-state. By assuming that such devices can be fabricated with
the above current values scaling with size while keeping similar
performance characteristics, the current consumption can be
calculated for an EC automotive mirror and a single substrate EC
window at different dimensions.
[0038] Table 1 shows the current consumption of the devices with
two different active areas: (1) 6 inches by 6 inches (15
cm.times.15 cm) and (2) 12 inches by 12 inches (30 cm.times.30
cm).
1 TABLE 1 Colored (steady Device Initial current state) current
type/Size consumption consumption Auto Mirror, 0.7 A 0.2 A 6 inch
(15 cm) Thin film 0.5 A 0.2 mA window, 6 inch (15 cm) Auto Mirror,
2.8 A 0.8 A 12 inch (30 cm) Thin film 1.9 A 0.9 mA window, 12 inch
(30 cm)
[0039] Therefore, as the size of the EC device increases, the
current loads that the electrodes must carry are substantially
increased.
[0040] Table 2 shows the resistance characteristics of several
materials and the resistance associated with a tape with a
dimension of 1 meter in length, 2 mm in width and 0.1 mm in
thickness. Table 2 also shows the resistance drop in these tapes
when they carry 0.1, 1 and 10 A of current.
2 TABLE 2 Data for one m long tape with a width of 2 mm and a
thickness of Resist- 0.1 mm ivity Resis- Voltage Voltage Voltage at
25.degree. C. tance drop at drop at Drop at Material
(10.sup.-8.OMEGA.m) (.OMEGA.) 0.1A (v) 1A (v) 10A (v) Aluminum 2.71
0.1355 0.01355 0.1355 1.355 Copper 1.71 0.0855 0.00855 0.0855 0.855
Gold 2.21 0.1105 0.01105 0.1105 1.105 Silver 1.62 0.081 0.0081
0.081 0.81 Tungsten 5.39 0.2695 0.02695 0.2695 2.695 ITO 200 10 1
10 100 Stainless 72 3.6 0.36 3.6 36 steel type 304 Tin 11.5 0.575
0.0575 0.575 5.75 Copper/ beryllium (98/2) Indium 8 0.4 0.04 0.4 4
Nickel 7.12 0.356 0.0356 0.356 3.56 Rhodium 4.3 0.215 0.0215 0.215
2.15 Nichrome 150 7.5 0.75 7.5 75 Solder 16 0.8 0.08 0.8 8 (Pb/Sn,
67/33) Solder 25 1.25 0.125 1.25 12.5 (Sn/Ag, 95/5) Conduct- 300 15
1.5 15 150 ive epoxy Ablebond .RTM. 8380 Silver 7 0.35 0.035 0.35
3.5 Frit (DuPont, 1991)
[0041] As seen in Table 2, several materials incur serious voltage
drops across their resistance runs (for a specific geometry) for
the amount of current that must be provided to the EC cell. Since
EC devices are typically powered at 1 to 3 volts, the voltage drop
can significantly affect the actual voltage applied to the EC
material, causing increases in coloration and bleach times, and in
certain devices, leading to nonuniform coloration in the steady
state condition. The problem of the voltage drop, resulting from
the electrode resistance, is compounded by the increase in current
when the size of the device gets larger as seen previously in Table
1. This invention is particularly useful for those EC devices where
the current consumption exceeds 0.1 A during either coloring or
bleaching processes.
[0042] When chromogenic devices are fabricated using two coated
substrates, the typical gap between the substrates is in the range
of from 10 to 1000 micrometers. As the size of the devices
increases, such as for a six inch by six inch (15 cm.times.15 cm)
device, in order to increase the charge throughput and to
distribute the charge uniformly, it is important that busbars be
applied to as much of the device perimeter as possible.
[0043] One prior art approach for a rectangular device as shown in
FIG. 4, is to offset substrates 3301 and 3302 simultaneously around
two edges of a corner to provide two exposed L-shaped surfaces
3304. Then, busbars 3303 are attached in a conventional way.
[0044] In another prior art approach, busbars 5503 are applied on
opposite edges of exposed surface pairs 5504 by employing the
geometry as shown in FIG. 5 where the rectangular substrates 5501
and 5502 are pivoted from each other so that the long dimension of
each rectangular substrate is parallel to the short dimension of
the other rectangular substrate.
[0045] Neither approach provides busbar coverage of a substantial
perimeter of a substrate. As used herein, "substantial perimeter"
means more than half of the perimeter of a substrate which is
covered by a continuous busbar. For larger devices such as those
bigger than about 6 inches (15 cm) in width and length, it is
especially desirable to put the busbars all around the device, in a
manner which covers a substantial perimeter of each substrate in
order to provide the applied signal to the entire chromogenic panel
evenly.
[0046] Nevertheless, as described above, as the length of the
busbar run increases, the resistance undesirably increases. As a
result, the prior art increases the thickness of the busbar
material for large devices in order to increase the
conductivity/unit length of the busbar in an attempt to maintain
the desirably low resistance of the busbar. However, a major
problem with the use of conventional busbars such as spring clips
and wires for such large chromogenic applications arises when the
thickness of the busbar exceeds the typical cell gaps. Even when
the thickness of the busbar does not exceed the cell gap, the
geometries of the prior art busbars and their placement limit the
allowable increases to conductivities. Further, there may also be a
problem around substrate corners when one continuous strip of the
prior art busbar clip is used.
[0047] Another method with substantial coverage is provided all
around the periphery, by using thin conductors, as shown in U.S.
Pat. No. 5,066,112. However, in this case, the conductor thickness
is limited by the gap between the substrates and its width.
[0048] Another approach is to make the two substrates dissimilar in
size so that the edges of one substrate extend from all around the
perimeter of the other substrate. In this configuration,
conventional wire clip busbars can be used on the larger substrate.
However, it is difficult to attach conventional wire clip busbars
to the smaller substrate due to the limited gap available between
the two substrates. The very close geometry could cause electrical
shorting of the two substrates at the conventional wire clip busbar
of the smaller substrate.
[0049] As noted above, in addition to the problem of voltage drops
from the edge busbar clips, if the magnitude of the electrical
currents in EC devices is large, there can be a considerable
electrical potential drop across the thin film transparent
conductor, leading to detrimentally slower overall device kinetics
and spatial inhomogeneities in the EC device behavior. Therefore,
for applications where current consumption is large, and especially
where the area of the EC devices is large (e.g., chromogenic
panels), it is particularly important that the transparent
conductors possess large effective conductivities. Large-area EC
devices fabricated from commercially available transparent
conductors such as, for example, indium tin oxide (ITO) and doped
tin oxide (DTO) generally possess slow kinetics and often display
nonuniform coloring (e.g., darker at the edges to which the busbars
are connected than in the center).
[0050] Values for the sheet resistance of commercially available
transparent conductors such as ITO and DTO are typically greater
than about 5 .OMEGA./sq (the units are also commonly written as
.OMEGA./.box-solid.) to about 15 .OMEGA./sq. Lower sheet
resistances may be obtained by increasing the thickness of the
transparent conductor, but this adversely affects the optical
properties (e.g., increased haziness and/or diminished
transmissivity) and also adds appreciably to the cost. It is
desirable to form substrates which possess appreciably lower
effective sheet resistance (can be less than 1 .OMEGA./sq) at a
cost that is attractive for applications such as those described
above.
[0051] U.S. Pat. No. 5,293,546, incorporated herein by reference,
describes a method for making a display device in which one of the
electrodes is preferably a metallic grid. Preferred line widths
were 20 micrometers with line spacings of 500 micrometers and line
heights of 0.2 to 3 micrometers. The grid is then coated by a metal
oxide (e.g., 1000 .ANG. of ITO). The invention relates to displays
in which high resolution processing equipment must be used for
depositing the grid pattern. Thus the cost is high, particularly if
large substrates such as 6 inch-6 inch (15 cm.times.15 cm) or
bigger are required because maintaining high precision in such a
fine grid pattern over increasing areas is costly. Further, since
these substrates must be over-coated with ITO, they are unable to
use more cost effective, mass produced transparent conductors, such
as mass produced ITO or inexpensive DTO deposited onto glass sheets
in a float line.
[0052] U.S. Pat. No. 4,768,865, incorporated herein by reference,
describes the use of a free-standing metallic grid as one of the
transparent conductors. In this invention, the metal grid
participates directly in the electrochemical reaction in the EC
cell. However, for most EC devices, it is not desirable for the
electron conductor also to participate in the reaction.
[0053] U.S. Pat. No. 5,724,176, incorporated herein by reference,
describes the use of a counterelectrode for a smart window that
contains a transparent substrate and a linear electrically
conductive material formed on a surface of the transparent
substrate. A layer of an electrochromic material is formed on the
window's surface, and a layer of an electrolyte is arranged between
the counterelectrode and the electrochromic electrode and in
contact with the layer of the electrochromic material. Various
patterns are described for the placement of the linear electrically
conductive material.
[0054] U.S. Pat. No. 5,066,111, incorporated herein by reference,
describes laminated EC devices. A metal grid on a glass substrate
is employed as one electrode and a longitudinal set of busbars,
preferably composed of a metal foil such as copper, or an
electroconductive ceramic frit deposited on glass or on the surface
of an electro-conductive film, is employed as the other electrode.
The electrochromic film is deposited over the second electrode.
Thus, the metal foil or frit conductors of the U.S. Pat. No.
5,066,111 invention are always in direct contact with either the
electrochromic coating or the electrolyte. However, such direct
contact can decrease the device lifetime because of reaction
between the coating and the electrolyte or electrochromic coating.
Moreover, if put on glass and then coated with the transparent
conductive coating (TCC), other problems can arise. Most
importantly, the TCC is usually deposited in a thickness of less
than 0.3 micrometers. In comparison, tapes or underlying frits,
etc., are typically in thicknesses of 10 to 1000 times the
thickness of TCC. Thus, vacuum methods that are typically used to
coat TCC have difficulty getting a conforming coating that
adequately covers the edges. The reference does not address the
relationship of the busbar thickness and width to the device
size.
[0055] POLYCHROMIC.TM. solid films are described in European Patent
Publication No. EP 0 612 826 A1, incorporated herein by reference.
The reference describes how polychromic solid films may be used in
electrochromic devices, particularly glazings and mirrors, whose
functional surface is substantially planar or flat or that are
curved with a convex curvature, a compound curvature, a
multi-radius curvature, a spherical curvature, an aspheric
curvature, or combinations of such curvature.
[0056] Often, a demarcation means, such as a silk-screened or
otherwise applied line of black epoxy, may be used to separate the
more curved, outboard blind-spot region from the less curved,
inboard region of such electrochromic mirrors. The demarcation
means may also include an etching of a deletion line or an
otherwise established break in the electrical continuity of the
transparent conductors used in such mirrors so that either one or
both regions may be individually or mutually addressed. Optionally,
this deletion line may itself be colored black. Thus, the outboard,
more curved region may operate independently from the inboard, less
curved region to provide an electrochromic mirror that operates in
a segmented arrangement. As described in European Patent
Publication No. EP 0 612 826 A1, upon the introduction of an
applied potential, either of such regions may color to a dimmed
intermediate reflectance level, independent of the other region,
or, if desired, both regions may operate together in tandem.
[0057] An insulating demarcation means, such as demarcation lines,
dots and/or spots, may be placed within electrochromic devices,
such as mirrors, glazings, optically attenuating contrast filters
and the like, to assist in setting out the interpane distance of
the device and to enhance overall performance, in particular the
uniformity of coloration across large area devices. Such insulating
demarcation means, constructed from, for example, epoxy coupled
with glass space beads, plastic tape or die cut from plastic tape,
may be placed onto the conductive surface of one or more substrates
by silk-screening or other suitable technique prior to assembling
the device. The insulating demarcation means may be geometrically
positioned across the panel, such as in a series of parallel,
uniformly spaced-apart lines, and may be clear, opaque, tinted, or
colorless, and appropriate combinations thereof, so as to appeal to
the automotive stylist.
[0058] As described in European Patent Publication No. EP 0 612 826
A1, a demarcation means may be used that is conductive as well,
provided that it is of a smaller thickness than the interpane
distance and/or a layer of an insulating material, such as a
non-conductive epoxy, urethane or acrylic, is applied thereover so
as to prevent conductive surfaces from contacting one another and
thus short-circuiting the electrochromic assembly. Such conductive
demarcation means include conductive frits, such as silver frits
like the #7713 silver conductive frit available commercially from
E.I. du Pont de Nemours and Co., Wilmington, Del., conductive paint
or ink and/or metal films. Use of conductive demarcation means,
such as a line of the #7713 silver conductive frit, having a width
of about 0.09375" (0.238 cm) and a thickness of about 50 .mu.m,
placed on the conductive surface of one of the substrates of the
electrochromic device may provide the added benefit of enhancing
electrochromic performance by reducing busbar-to-busbar overall
resistance and thus enhancing uniformity of coloration, as well as
rapidity of response, particularly over large area devices.
However, the non-conductive layers are applied in a way which does
not prevent the underlying frit lines from making contact with the
electrolyte or electrochromic layers. Thus, this frit may
potentially react, especially when coloring and bleaching
potentials are applied.
[0059] As described above, electrochromic (EC) devices are used to
reversibly vary the light transmission or reflection by application
of an electrical voltage. Applications of electrochromic devices
include windows for architectural use (windows, interior
partitions, skylights, light pipes), windows in transportation
(automobiles, trucks, planes, trains, boats, etc.), eye-wear, and
displays (including large area signage).
[0060] Electrochromic windows in buildings can provide higher
energy efficiency as compared to static transmission windows, while
increasing the user comfort by controlling illumination and
reducing glare. The same benefits can accrue for transportation
uses where the user comfort is enhanced by reducing solar heat and
glare during the day, while reducing the cooling load on the
air-conditioner. In many of these applications the EC device can be
required to be kept in a certain desired state of transmission for
long periods of time. For example, a window may be kept in a
darkened or bleached state for many hours of the day and may even
be kept in this state for many days.
[0061] Thus, it is desirable to enhance the durability of EC
devices that are used in this long single state mode, while
reducing energy consumption of the EC devices. Reducing energy
consumption is particularly useful in circumstances where solely a
battery is used to power such a device and thus, it is important to
ensure that the battery drain is minimized. Such circumstances
include use in a car, aircraft, watercraft, or eyeware. One aspect
of the present patent describes circuitry which addresses one or
more of these issues.
[0062] U.S. Pat. No. 5,148,014, incorporated herein by reference,
describes the use of a linear regulated power supply to power an EC
mirror.
[0063] U.S. Pat. No. 5,193,029, incorporated herein by reference,
describes the use of a Zener diode and transistor, which is
essentially a linear regulation, to provide voltage to an EC
mirror.
[0064] U.S. Pat. No. 5,220,317, incorporated herein by reference,
describes the use of a voltage divider consisting of series
resistors to scale down the voltage provided to EC elements.
[0065] Electrochromic devices which will benefit from this
invention are well known in the art. For example, these are
described in U.S. patent application Nos. 09/155,601 and
08/699,940, filed Apr. 9, 1997 and Aug. 20, 1996, respectively.
[0066] For those EC devices which are colored by applying a
voltage, it would be desirable not to require applying continuously
the coloring potential after the required coloration depth has been
reached. Such continued application of the coloring potential,
while promoting EC reactions, can also promote side reactions which
could have detrimental effect on the device longevity. This applies
for all EC devices which need to be maintained in a state of
coloration that is different from their natural transmission state.
The natural transmission state of an EC device is measured at
equilibrium with no applied potential and when the potential
difference between the opposing electrodes is zero.
[0067] Typically, the EC devices can be kept colored for a finite
period of time when the coloring potential is removed, i.e., the
color of the device will change towards its natural state over a
period of time. This change could occur over a wide range of time
intervals, from fast over several seconds or minutes, to as slow as
extending up to many days, depending on the device. A device where
this change is fast is said to have short "memory" and one where
the change is slow is said to possess long "memory". For example,
U.S. patent application No. 09/155,601 discloses devices with long
memories and compares them with devices that have short
memories.
[0068] It is clear that is would be advantageous to be able to
maintain a coloration setting without having to maintain an applied
voltage to electrochromic devices because circuitry that allows
intermittent adjustment of the voltage as needed to maintain a
coloration setting would lead to lower Dower consumption in the
device.
[0069] U.S. Pat. No. 5,384,578 (to Lynam et.al.), incorporated
herein by reference, describes the use of intermittent voltages for
continuously variable mirror and windows, but does not relate to
changing the voltage-on or voltage-off periods and voltage-time
shapes under different conditions as discussed in the present
invention.
[0070] U.S. Pat. No. 4,298,970 (to Saegusa), incorporated herein by
reference, describes a technique for utilizing an intermittent
technique to drive EC displays with memory. The patent only
describes bimodal displays which have only two states, i.e.,
colored and bleached states and does not discuss devices which need
continuously variable light transmission across a continuum of
transmissive states.
[0071] U.S. Pat. No. 5,007,718, incorporated herein by reference,
describes a method of driving electrochromic elements by using a
current stabilizing circuit and a voltage stabilizing circuit in
tandem with a power supply to form a stabilized power source, and
applying a gradually increased coloring voltage and a gradually
decreased discoloring voltage to keep the current flow within
predetermined amounts.
[0072] U.S. Pat. No. 5,365,365, incorporated herein by reference,
describes an electrochromic system for controlling the color state
by determining the charge needed to obtain a set color from the
discharge potential of the system and the coloration set-point. An
integrator measures the charge passing through the system and
compares it to the charge to be transferred, which is measured by a
differential amplifier which compares a discharge potential
measured by a capacitor with a selected color set-point.
[0073] U.S. Pat. No. 5,231,531, incorporated herein by reference,
describes an electrochromic system in which a voltage generator is
connected to electrically conductive films by an electrical control
circuit. The voltage generator receives a set-point from a control
unit and generates a potential differences as a function of the
temperature of the electrolyte.
SUMMARY OF THE INVENTION
[0074] This invention is related to edge and internal busbars that
lower the overall effective resistance of electrical devices,
particularly EC devices, thereby enabling large devices to maintain
desirable electrical properties. The present invention describes
the benefits of applying the busbars of the present invention to a
substantial perimeter of an EC device, as well as the materials and
processes to accomplish this.
[0075] As shown later, the contact points with the conductive
coatings constituting the EC devices may be less than half of the
perimeter, but the busbar of the present invention runs
continuously for more than half of the device perimeter. The term
"busbar" refers to a conducting medium that provides a
substantially uniform voltage to all those points on the device
perimeter that are connected to the busbar. The busbar should be
capable of carrying substantial current with a voltage drop of
preferably less than {fraction (1/10)}th of the applied voltage, or
a voltage drop less than that which causes a perceptible change in
the kinetics of the device (rate of coloration and bleach) or in
the depth of coloration.
[0076] The voltage drop should be less than that voltage drop which
would cause a perceptible change in the kinetics or coloration
properties of the device. Thus, for some particular devices, higher
voltage drops can be accommodated so long as such perceptible
changes do not occur. Generally, however, such voltage drops are
less than {fraction (1/10)}th of the applied voltage.
[0077] The conductance of the edge busbar conductor is dependent on
the cross-section, length and the intrinsic conductivity of the
busbar material. Since the gap between the two substrates for a EC
cell is limited, the thickness of the busbar conductors must be
within the limitations imposed by the cell's size. To maximize the
EC device viewing area, the width of the conductor in the prior art
is limited as shown in FIGS. 4 and 5, where the width is limited to
the exposed areas 3304 and 5504. Typically, this width is less than
25 mm, preferably less than 10 mm, in order to maximize effective
cell area. At times, this width can be on the order of less than 2
mm. Further, for a device made by substrates that are exactly
stacked on one another and separated by a gap of 100 micrometers,
the thickness of the conductor on each substrate located between
the two substrates is typically limited to less than 50
micrometers.
[0078] The present invention teaches the use of materials and
processes to deposit busbars on a substantial portion of the device
perimeter while overcoming the geometric constraints described
above. A copper conductor which is 35 micrometers thick and 3 mm
wide exhibits a resistance drop of 0.16.OMEGA. per meter.
Accordingly, for a device that is one meter square, a continuous
conductor around the device periphery will exhibit a drop of
0.32.OMEGA. from one diagonal edge to the other. For a device that
will carry a current as low as even one ampere, the drop of 0.32 V
at an applied potential of about 1.5 V is significant. This can
result in non-uniform coloration, slow kinetics, etc. In such
devices, it is preferable to maintain the potential drop below
{fraction (1/10)}th of the applied voltage or below any voltage
that will cause a perceptible change in the color uniformity of the
device or a decrease in the kinetics.
[0079] Since the current consumption of an EC device changes with
time, particularly when step potentials are used, it is preferable
that the potential drop in the busbar is kept within the limits
described above during both the switching period and also when the
steady state is reached. If other materials from Table 2 are used
instead of copper, except for silver, the resistance drop will be
even higher for the same busbar dimensions. Thus the geometry of
the busbar (such as thickness and width) of the tape will have to
be increased for best performance.
[0080] An object of the present invention is to overcome the prior
art constraints on edge busbar effective resistance arising from
the geometrical limitations of busbar length, width, and thickness.
The present invention uses specific geometry, materials and
processes to form the edge busbars.
[0081] This invention overcomes these geometrical limitations by
forming a conductive path from the electrode on a front side of a
substrate to the edges of the substrate and then extending this
conductive path on to the back of the substrate. On the edge of the
device, on the back, or on both the edge and the back, highly
conductive paths such as reinforcing conductors may be employed to
lower the busbar resistance. The conductive path from the front of
the substrates to the back could be the continuation of the same
material which is used for the transparent conductor, such as
indium tin oxide, or can be fabricated from a different material,
so long as dimension and conductivity requirements are met. That
is, the conductivity must be effective to prevent a potential drop
of 10% or a potential drop that would detrimentally affect the
performance of the EC panel, while the dimensions must be effective
to allow the substrates to maintain a close proximity to each
other. Once the conductive path is formed on the back of the
substrates, the geometrical limitations on the thickness and the
width of the busbar conductor are relieved substantially.
[0082] Accordingly, the present invention provides an edge busbar
for an electrical device, wherein the edge busbar comprises at
least one electrically conductive connector portion effective to
form an electrically conductive path from a surface of the
electrical device, wrapping around a portion of an edge, to an
opposite surface of the electrical device, and an electrically
conductive perimeter portion in electrical contact with the
connector portion, wherein the perimeter portion is peripherally on
a substantial perimeter of the electrical device.
[0083] The connector portion of the edge busbar of the present
invention can be continuous peripherally on a substantial perimeter
of the electrical device, can be continuous peripherally on an
entire perimeter of the electrical device, or can be composed of a
plurality of connector portions. That is, the connector portion can
wrap completely around an entire perimeter edge of the electrical
device, can wrap completely around a substantial perimeter portion
of the perimeter of the electrical device, or it can be a series of
smaller portions that each wrap around smaller portions of the
perimeter of the electrical device. Regardless, there is a
perimeter portion of the edge busbar of the present invention which
is peripherally on a substantial perimeter of the electrical device
and connects to the various connector portion(s) of the present
invention.
[0084] The front of a substrate is generally defined as the surface
having the conductive electrode layer thereon.
[0085] In the case of a two substrate device, the front of a
substrate is the surface facing the other substrate. In the case of
a single substrate EC device, the front of a substrate is the
surface facing the EC stack. In general, the layer of transparent
conductive material is on the front of a substrate.
[0086] Although other parameters such as the conductivity of the
transparent conductors (electron conductors), the ionic
conductivity of the electrolyte layer, and the intercalation rate
in the EC coating and other coatings if used, might also influence
the kinetic parameters of EC devices, as shown above, the
resistance of the edge busbar itself can have an important affect
on the performance of the EC device. Accordingly, it is an object
of the present invention to minimize the contribution of the edge
busbars towards slowing the EC device kinetics. The edge busbars of
the present invention may also assist in promoting a spatially
uniform rate of color change during coloring and bleaching
cycles.
[0087] In one embodiment of the present invention, an edge busbar
includes a connector portion that has a separation or separating
portion. However, the connector portion at each side of the
separation is electrically connected by the conductive electrode
coating layer of the electrical device. The separation is
relatively small between the connector portions on each side of the
separation, so that there is negligible resistance across the
break. In other words, the separation is electrically bridged by
the conductive electrode coating layer. This allows the connector
portion to be effectively continuous peripherally about the entire
perimeter of the electrical device even though separations exist in
the connector portion. Advantages to this configuration include
ease of manufacture and reduced complexity of design.
[0088] Busbars of the present invention can be advantageously used
in pairs. Another embodiment of the present invention provides an
edge busbar pair for an electrical device, each edge busbar
comprising a connector portion and a perimeter portion, wherein
each connector portion is effective to form an electrically
conductive path from a front surface of a substrate, wrapping
around a portion of an edge of the substrate, to an opposite back
surface of the substrate. The perimeter portions being in
electrical contact with its respective connector portion, and
wherein each perimeter portion is peripherally on a substantial
perimeter of each respective substrate, and wherein the front
surfaces of each substrate face each other with each substantial
perimeter proximate to and substantially opposite to the other
substantial perimeter.
[0089] As discussed previously, each edge busbar of an edge busbar
pair can be continuous peripherally on a substantial perimeter of
its substrate, can be continuous peripherally on an entire
perimeter of its substrate, or can be composed of a plurality of
connector portions. It is advantageous for each edge busbar to be
composed of a plurality of connector portions. It is particularly
advantageous for each connector portion of each edge busbar to be
in an alternating relation with connector portions of the other
edge busbar. As shown later, when the connector portions are in
such alternating relation, the thickness of the busbar material can
be thicker than one half of the total gap distance between the
substrates and yet still not cause an electrical short. Further, a
sealant and/or an insulator can be added to assure against any
shorting. Nonetheless, as explained earlier, thicker busbar
material is desirable in order to maximize conductivity.
[0090] The present invention can be implemented for single
substrate devices or dual substrate devices. The edge busbars of
the present invention can be used singly as needed advantageously
(as contrasted with the prior art). However, single substrate
devices can nonetheless require a pair of edge busbars because such
devices, as described earlier and as known in the art, often are
made by forming an EC stack onto a substrate. In such cases, the EC
stack requires a pair conductive electrodes as well as the
substrate. Accordingly, both conductive electrodes have electrical
signals applied to them which would benefit from the advantages of
the edge busbars of the present invention.
[0091] In the present invention, an edge busbar is used having a
portion that can be fabricated of any convenient material with an
effective maximum thickness that can be inserted in the cell gap
without shorting from touching with the other busbar or with the
opposing conductive substrate. At the same time, the edge busbar of
the present invention provides sufficient conductivity such that a
negligible voltage drop (preferably less than one tenth of the
applied voltage) occurs in the edge busbar. Further, the edge
busbar of the present invention covers a substantial portion of the
device perimeter and can include the internal busbars of the
present invention.
[0092] The present invention also relates to the construction of
substrates, especially transparent conducting substrates, which
possess relatively large effective conductivities by the inclusion
of internal busbars.
[0093] The present invention further relates to the use of the
aforementioned substrates to construct affordable large area EC
devices that can be used for architectural applications, (e.g.
windows, partitions, skylights, diffuser panels, light pipes,
etc.), automotive (windows, sunroofs, etc.) or other transportation
(windows for planes, trains, buses, boats, etc.) applications, or
signage applications (including large area displays such as those
used at stock exchanges, airports and other such facilities).
[0094] The present invention also provides substrates which possess
appreciably lower effective sheet resistances (can be less than 1
.OMEGA./sq or .OMEGA./.box-solid.) at a cost that is attractive for
applications such as those described above.
[0095] The present invention teaches means for lowering the sheet
resistance of thin film transparent electrically conducting
assemblies for use in chromogenic devices, particularly
electrochromic (EC) devices. The present invention permits the
manufacture of EC devices which possess significantly improved
kinetics with regard to coloration and/or bleaching, even for
devices which possess relatively large active areas. The present
invention also results in devices which possess considerably
improved coloration and bleaching uniformity.
[0096] Most practical EC devices, as shown in FIG. 6, are comprised
of an "EC Assembly" 6601 which is effectively bound on either side
by electronically conducting electrodes (ECE) 6602. Generally
speaking, electrodes 6602 may be comprised of any of a variety of
electronic conducting materials. Because EC devices are generally
used to modulate light, however, at least one of the ECE 6602
should possess reasonable transparency at the wavelengths of
interest (mirrors and many displays, e.g., typically possess only
one transparent ECE; and window-type devices typically possess two
transparent ECE's). The present invention provides improved
effective conductivity of transparent ECE's in a manner readily
integrated into the device structure.
[0097] The present invention forms internal busbars by providing
strips of highly conductive material electrically connected to
interior portions of a transparent ECE. The internal busbars add
regions of increased conductivity into a transparent ECE, thereby
lowering the overall effective resistance of the transparent ECE.
Such lowered overall resistance leads to large device
advantages.
[0098] The internal busbars of the present invention have increased
conductivity compared to the transparent ECE when measured along
the longitudinal direction of the conductive strips of the present
invention. That is, in a top view of the transparent ECE with an
internal busbar strip, when one compares a section of the
conductive strip having a length L and a width W with a section of
the transparent ECE also having the dimensions of W.times.L, the
conductivity of the W.times.L section of the internal busbar will
be higher than the conductance of the W.times.L section of the
transparent ECE, along either dimension L or W. Preferably the
conductivity of the conductive strip will be greater than about 2
times the conductivity of the transparent ECE, more preferably
greater than about 10 times.
[0099] The internal busbars of the present invention achieves such
higher conductance by several ways. According to one embodiment of
the present invention, materials having inherently higher
conductivities are used for the busbars. According to another
embodiment of the present invention, the busbar strips are made
thicker than the surrounding transparent ECE. Such thicker strips
can be embedded below the transparent ECE and/or into the
underlying substrate. It is important that these two--that is, the
internal busbars and the transparent ECE--are in electrical contact
with each other (continuous or spatially intermittent). One may
even use a material, to enhance or to tailor the electrical
characteristics of this electrical contact, different from that
material of the internal busbars or of the transparent ECE.
[0100] In another embodiment, the internal busbar strips are formed
on a different surface from that surface which has the transparent
ECE. Strip connecting portions connect interior portions of the
transparent ECE or device with segments of the internal busbar
strip. Such strip connecting portions can extend through the
substrate. The internal busbars of this embodiment are nonetheless
"internal" because they connect to regions of the transparent ECE
away from the periphery.
[0101] The present invention also is directed to circuitry which
uses low power. Another object of the present invention are
circuits which apply intermittent coloration power to EC devices in
order to maintain or control the EC devices' coloration while
compensating for the EC devices' inherent coloration decay without
needing a constant application of coloration power.
BRIEF DESCRIPTION OF THE DRAWINGS
[0102] FIGS. 1A, 1B, 1C, 1D, 1E, and 1F are side cross-sectional
views of a number of different prior art electrochromic, liquid
crystal, PDLC, and photochromic devices suitable for use in the
present invention.
[0103] FIG. 2 is a perspective view of a prior art arrangement of
edge busbars clips on two substrates.
[0104] FIG. 3A is an perspective exploded view of a prior art
arrangement of edge busbar clips on two substrates.
[0105] FIG. 3B is a sectional view of a prior art arrangement of
edge busbar clips on two substrates.
[0106] FIG. 4 is a perspective view of a prior art arrangement of
edge busbars clips on two substrates.
[0107] FIG. 5 is a perspective view of a prior art arrangement of
edge busbars clips on two substrates.
[0108] FIG. 6 is a schematic side view of an EC device.
[0109] FIG. 7A is a schematic sectional view of an EC device having
edge busbars of the present invention.
[0110] FIG. 7B is a schematic sectional view of an EC device having
edge busbars and conductive paths of the present invention.
[0111] FIG. 8A is a perspective view of an EC device with a
substrate having edge busbars of the present invention.
[0112] FIG. 8B is a schematic top plan view of a substrate having a
continuous conductive path of the present invention.
[0113] FIG. 8C is a schematic top plan view of a substrate having
strip conductive paths of the present invention.
[0114] FIG. 9A is a schematic side view of a pair of edge busbars
of the present invention.
[0115] FIG. 9B is a schematic side view of an adhesive multilayer
strip for the fabrication of an edge busbar of the present
invention.
[0116] FIG. 9C is a plan view of an adhesive multilayer strip for
the fabrication of an edge busbar of the present invention.
[0117] FIG. 9D is a perspective partial view of a pair of edge
busbars of the present invention at a corner.
[0118] FIG. 10 is a schematic cross sectional view of a pair of
edge busbars of the present invention.
[0119] FIG. 11A is a side view of a prior art stacked substrate
arrangement.
[0120] FIG. 11B is a top view of a prior art stacked substrate
arrangement.
[0121] FIG. 12 is a schematic side sectional partial view of a
prior art stacked substrate arrangement.
[0122] FIG. 13 is a perspective view of a single substrate with a
bottom conductor applied according to an embodiment of the present
invention.
[0123] FIG. 14 is top view of a single substrate with a top
conductor applied according to an embodiment of the present
invention.
[0124] FIG. 15A is a schematic sectional side view of a single
substrate with a top and bottom conductors applied according to an
embodiment of the present invention.
[0125] FIG. 15B is a schematic sectional side view of a single
substrate with a top and bottom conductors applied according to an
embodiment of the present invention.
[0126] FIG. 15C is a schematic sectional side detail view of a
substrate with a bottom conductor and signal connections according
to an embodiment of the present invention.
[0127] FIG. 16A is a schematic sectional side view of a single
substrate with embedded edge busbars according to an embodiment of
the present invention.
[0128] FIG. 16B is a schematic sectional side view of a single
substrate with embedded edge busbars according to an embodiment of
the present invention.
[0129] FIG. 17A is a top view of a substrate with a continuous
conductor busbar according to an embodiment of the present
invention.
[0130] FIG. 17B is a perspective view of a substrate with a
continuous conductor busbar according to an embodiment of the
present invention at an intermediate fabrication step.
[0131] FIG. 18 is a graph of the light transmittance vs. time for
different busbar configurations according to the present
invention.
[0132] FIG. 19A is a schematic sectional view of a stacked circular
substrate arrangement according to an embodiment of the present
invention.
[0133] FIG. 19B is a top view of a stacked circular substrate
arrangement according to an embodiment of the present
invention.
[0134] FIG. 20A is a schematic perspective view of a coated
substrate with internal busbars formed on the surface according to
an embodiment of the present invention.
[0135] FIG. 20B is a schematic perspective view of a coated
substrate with two sets of internal busbars formed on the surface
according to an embodiment of the present invention.
[0136] FIG. 21 is a schematic cross sectional view of a process to
form embedded internal busbars on a substrate according to an
embodiment of the present invention.
[0137] FIG. 22 is a schematic plan view of a device with internal
busbars having different widths according to an embodiment of the
present invention.
[0138] FIG. 23 is a schematic cross sectional side view of a device
with internal busbars having a transverse axis parallel to a sight
line that is at an angle to the surface normal according to an
embodiment of the present invention.
[0139] FIG. 24 is a schematic cross sectional diagram of a device
according to an embodiment of the present invention having internal
busbars that cause a property change when a signal is applied
between them, a different property change when a signal is applied
along each busbar equally, and changes in both properties when a
difference occurs in the signals applied to each busbar according
to an embodiment of the present invention.
[0140] FIG. 25A is a schematic plan view of a group of internal
busbars addressable as a group according to an embodiment of the
present invention.
[0141] FIG. 25B is a schematic plan view of a group of internal
busbars individually addressable according to an embodiment of the
present invention.
[0142] FIG. 26A is a schematic plan view of two groups of internal
busbars arranged at an angle to each other according to an
embodiment of the present invention.
[0143] FIG. 26B is a schematic plan view of a group of internal
busbars arranged substantially parallel to each other according to
an embodiment of the present invention.
[0144] FIG. 26C is a schematic plan view of a spiral internal
busbar according to an embodiment of the present invention.
[0145] FIG. 27A is a schematic plan view of a group of internal
busbars connected to the conductive layer by conductive posts
according to an embodiment of the present invention.
[0146] FIG. 27B is a schematic side sectional view of a group of
internal busbars connected to the conductive layer by conductive
posts according to an embodiment of the present invention.
[0147] FIG. 28 is a schematic perspective exploded view of a group
of internal busbars connected to the conductive layer by conductive
posts according to an embodiment of the present invention.
[0148] FIG. 29 is a schematic side sectional close up view of an
internal busbar connected to the conductive layer by a conductive
post according to an embodiment of the present invention.
[0149] FIG. 30 is a graph of the transmissivity v. elapsed time for
EC cells of different sizes without internal busbars or edge
busbars.
[0150] FIG. 31A is a schematic plan view of a set of internal
busbars disposed on a substrate according to an embodiment of the
present invention.
[0151] FIG. 31B is a schematic sectional view of a set of internal
busbars disposed between two substrates according to an embodiment
of the present invention.
[0152] FIG. 31C is a schematic sectional view of a set of internal
busbars disposed between two substrates according to an embodiment
of the present invention.
[0153] FIG. 32A is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
[0154] FIG. 32B is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
[0155] FIG. 32C is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
[0156] FIG. 32D is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
[0157] FIG. 32E is a schematic sectional view of an electrically
reinforced edge busbar according to an embodiment of the present
invention.
[0158] FIG. 33A is a plan view of an electrochromic cell according
to an embodiment of the present invention.
[0159] FIG. 33B is a cross-sectional side view of an electrochromic
cell according to an embodiment of the present invention.
[0160] FIG. 34A is a graph of the coloration kinetics of a 6" by 3"
(15 cm.times.7.5 cm) electrochromic window with internal busbars
according to an embodiment of the present invention, and of a
comparison electrochromic window without internal busbars.
[0161] FIG. 34B is a graph of the current/time behavior of a 6" by
3" (15 cm.times.7.5 cm) electrochromic window with internal busbars
according to an embodiment of the present invention, and of a
comparison electrochromic window without internal busbars.
[0162] FIG. 35 is a graph of light transmission (T) and applied
voltage (V) as a function of time (t) according to an embodiment of
the present invention.
[0163] FIG. 36A is a circuit diagram of an embodiment of the
present invention that includes a thermistor.
[0164] FIG. 36B is a circuit diagram of an embodiment of the
present invention that includes a micro-controller.
[0165] FIG. 37A is a circuit diagram of a switching regulator
circuit according to an embodiment of the present invention.
[0166] FIG. 37B is a circuit diagram of a switching regulator
circuit according to an embodiment of the present invention.
[0167] FIG. 37C is a circuit diagram of a switching regulator
circuit according to an embodiment of the present invention
yielding a very low quiescent current.
[0168] FIG. 38A is a circuit diagram of a switching regulator
circuit according to an embodiment of the present invention having
a resistor placed in series with the power supply output and EC
cell.
[0169] FIG. 38B describes the various shapes that the voltage vs.
time curve can follow depending on the parameters of the control
circuit of the present invention that controls an EC cell and
compared to the prior art continuous step shape and the prior art
linear ramp shape.
[0170] FIG. 38C describes the various shapes that the voltage vs.
time curves can follow depending on the circuit resistance
parameters.
[0171] FIG. 39 is a circuit diagram illustrating the incorporation
of an op amp and thermistor in a circuit for regulating the voltage
supplied to an EC cell.
[0172] FIG. 40 is a circuit diagram illustrating the use of a
thermistor in a circuit to vary the output voltage with
temperature.
[0173] FIG. 41 is a circuit diagram illustrating the use of a
thermistor in a comparator circuit.
[0174] FIG. 42 is a circuit diagram illustrating the use of a
thermistor in a comparator circuit.
[0175] FIG. 43 is a circuit diagram illustrating the use of an
adjustable voltage power supply with an EC device.
[0176] FIG. 44 is a circuit diagram illustrating the use of a
sensing resistor in series with the power output to limit the
maximum current flowing in the circuit.
[0177] FIG. 45 illustrates an electric circuit attached to an EC
cell having switches that may be used to determine t.sub.1 or
t.sub.1 by mesuring the voltage at the EC cell V.sub.cell and
comparing the value with V.sub.c or V.sub.B.
DETAILED DESCRIPTION OF THE INVENTION
[0178] Edge Busbars
[0179] In the present invention, a conductive path is formed from
the electrodes to the edges of the substrate. Preferably, this path
is extended on to the back of the substrate as shown in FIGS. 7A
and 7B (the details of other coatings employed in the device have
been omitted). Two substrates 701 and 702 are shown attached to
each other at close proximity by cell adhesive 703. On the edge of
the device, preferably including on the back, highly conductive
paths are employed to lower the busbar resistance. FIG. 7A shows an
edge busbar 704 of the present invention which wraps around the
edge of the substrate to provide highly conductive paths on three
sides of the edge. FIG. 7B shows a conductive path 706 of the
present invention to which is attached a highly conductive
perimeter portion 705.
[0180] The conductive path 706 from the front of the substrates to
the back could be the continuation of the same material which is
used for the transparent conductor on the substrate, such as indium
tin oxide, or can be fabricated from a different material. Once the
conductive path is formed on the back of the substrates, the
geometrical limitations on the thickness and the width of the
busbar conductor are relieved substantially because the perimeter
portion can cover a larger area without concerns about thickness.
The busbar of the present invention includes the conductive path
and the perimeter portion.
[0181] Conductive path 706 forms an electrical connection from the
front to the back. Therefore, the paths can be called connector
portions. These electrical connector portions can be made using
conductive adhesives, silver frits (e.g., available from Dupont
Electronic Materials, Research Triangle Park, N.C. or FX 33-246
available from Ferro Inc. of Santa Barbra, Calif.), solder
materials, physical vapor deposition, chemical vapor deposition,
electroless deposition of metals, metallo-organics (e.g., available
from Engelhard Electronic Materials, N.J.) and conductive tapes.
The conductivity of these connector portions need not be as high as
the perimeter portions that connect to these connector portions
because the connector portions only have to carry the current over
a short distance, hence their actual effective resistance is
low.
[0182] These connector portions could be continuous, thereby
merging with the perimeter portion, or in strips. Either connector
portion configuration, continuous or strips, encompasses a
substantial portion of the device perimeter. FIG. 8A shows two
substrates 801 and 802, separated for clarity. Substrate 802 is
shown with a continuous conductive path 803. FIG. 8B shows
substrate 802, continuous conductive path 803, and an adhesive 804.
FIG. 8C shows a substrate 802', strip conductive paths 803', and
adhesive 804. In FIG. 8C, perimeter portion 805 connects strip
conductive paths 803'. Perimeter portion 805 extends to a back
perimeter region (not shown).
[0183] According to the present invention, referring to FIGS. 8B
and 8C, it is not necessary to have a width of the substrate
exposed between the sealant or adhesive 804 and the connector
portion or conductive paths 803 and 803'. Depending on the nature
of the sealant and connector portion and their bonding
characteristics, a partial or a complete overlap may exist. If the
connector portion of the present invention is used in the strip
form as shown in FIG. 8C, the connector portion strips on the
bottom and on the top substrates may be offset from each other, may
be stacked on top of each other, or may have no particularly set
geometric relationship.
[0184] In a preferred configuration where the connector portion
strips are offset, the thicknesses may be increased almost to the
point where they occupy the entire gap between the substrates
without shorting. Such connector portion strips are offset
effective to allow an insulating distance between a particular
connector portion strip and any neighboring connector portion
strips connected to an opposite substrate, as well as between the
particular connector portion strip and the opposite substrate. The
insulating distance can include insulating material. The insulating
material can also be preformed on the conductive strips. In a
particularly preferred configuration, the connector portion strips
from one substrate are in an alternating relationship to the
connector portion strips of the other substrate.
[0185] The perimeter portion materials could be selected from the
same list of materials as the connector portions. However, to
enhance their conductance, materials with high conductivity could
be selected and/or the geometry (i.e., increased thickness, width,
perimeter portions etc.) may be different from the connector
portions.
[0186] Thick metallic strips and wires may also be used as
perimeter portions. The conductive path of the connector portions
of the present invention overcomes the prior art's dependence on
the busbars' specific conductivity because the present invention
provides a broad area of conductance to which the connector portion
is attached.
[0187] The devices are preferably assembled (e.g., by bonding
together two substrates) after the connector portion strips or
front to back connections are attached to each of the substrates.
If counterelectrode coatings are required in the EC device, such
strip connector portions can be formed or positioned before or
after these coatings are deposited. Further, the part of the
connector portion strips on the back of the substrates can be
joined or reinforced (such as with conductive copper tapes) with
highly conducting medium either before or after the device
assembly. The adhesive in the copper tapes may be pressure
sensitive adhesive (PSA), or may be curable later into a
thermosetting material by the application of pressure, heat,
radiation, moisture, or more than one of these methods.
[0188] As described above, and further below, the edge busbars of
this invention can be augmented ("reinforced") in conductivity.
That is, the electrical conductivity is augmented or reinforced in
order to increase the busbar electrical conductivity, by such
methods as (i) by wrapping a continuous connector from the front to
the back of the substrate, thus providing a wider conductor
resulting in higher electrical conductivity, (ii) by attaching the
connector to a conductive wire, foil, or tape positioned on the
back of the substrate so that the connector's conductivity can be
augmented by the conductance of the wire, foil, solder, frit, or
tape, and (iii) attaching a wire or conductor on the edge of the
substrate to electrically contact the connector in order to augment
the conductance of the connector.
[0189] A preferred method to form the edge busbar is to use a
conductive tape with a conductive adhesive layer that conducts
through the adhesive layer thickness. FIG. 9B shows a conductive
tape 909 having a conductor 911, a conducting adhesive layer 912
and an optional insulating layer 910. A continuous strip of such a
tape is shown in FIG. 9C. Tape 909 includes the continuous
conductor or perimeter portion 913, and fingers or connector
portions 914 that will form the contact with the transparent
conductor on the front side of the substrate. The front side, as
defined previously, refers to the substrate side that faces the
other substrate of an EC device, while the back of a substrate
refers to the side, opposite to the front side, that faces away or
is farther away from the other substrate. Tape 909 connects the
front of the substrate (facing inward) by way of connector portions
914 to perimeter portion 913 at the back of the substrate. An edge
portion 915 of connector portion 914 lies on the edge of the
substrate.
[0190] As shown in FIG. 9C, perimeter portion 913 and strip
connector portion 914 could be integrally connected, i.e., one
piece of tape of the perimeter portion is preferably aligned with
the bottom edge of the substrate, or is on the backside of the
substrate. The flat side is folded and adhered to the substrate
back. For a rectangular device with sharp corners, the tape in the
corner could be folded over the back side to form a crease without
effecting the connector portions at the front side. Since there is
effectively no limitation on the gap or tape thickness on the back
side (or the outside) of the device, the procedure of the present
invention can be used without affecting the separation distance of
the substrates. Instead of a crease on the back side, the tape can
be cut and the tape strips running at an angle to each other can be
folded on top of each other on the corners. The corners may also be
bridged by a piece of another tape, wire, solder, etc., to keep
preferably one continuous electrical path forming a perimeter
portion for each substrate. The tape or the strip on the back can
be made more conductive by reinforcing the tape with a more
conductive medium, e.g., more tape, wire, metallic strip, etc.
Accordingly, the perimeter portion can be multilayered or made from
a number of components.
[0191] In this description, the use of the above shape of the tape
(i.e. tape with connector portions or fingers extending from a
continuous perimeter portion) avoids any kinds of creases or kinks
on the front surface. Such kinks can develop as the tape traverses
over the corners of the substrate. It is readily understood that as
an edge bends to form a curve or to form a corner, an inner path
which is a certain distance from the outer edge will trace a
different distance from the outer edge. In the case of a convex
curve, the inner path will be shorter. Accordingly, a
non-stretching material will tend to crease or kink to try to
accommodate the excess material on such an inner path. The recesses
between each connector portion prevents accumulation of excess
material on the front side between the substrates.
[0192] The above description shows a tape that is easily and
advantageously used for applications where a pair of edge busbars
can be placed correspondingly opposite each other on two substrates
without physical interference or electrical shorting because of the
innovative geometry of the edge busbar pairs of the present
invention. Such geometry innovatively allows the pair of edge
busbars to nest together in an alternating relation. Such geometry
further innovatively allows each of the pair of edge busbars to be
thicker than half the gap separating the substrates on which they
cover, thereby increasing the edge busbar conductivity without
shorting to each other. Such geometry also allows edge busbars to
wrap around corners without interfering busbar material in between
the substrate separation gap.
[0193] For those EC panels that are rectangular in shape, it is
particularly at the corners that certain configurations of the
present invention are important. It is important to ensure that no
fingers are located on those areas of the tape which bend around
the sharp corners. Furthermore, the fingers are spaced such that
they do not overlap each other over the conductive substrates. Any
kinks, overlaps, or creases on the front (conductive) side can
interfere with the predetermined gap between the two substrates
and, depending on the materials employed, could also lead to
electrical shorting between the two substrates.
[0194] The tape shown in FIG. 9C can optionally have an additional
row of strip connector portions 914 (not shown) on the side of
perimeter portion 913 opposite the side with the row of strip
connector portions 914 shown. In this optional configuration,
perimeter portion 913 is affixed to the edge of the substrate and
the each opposite rows of strip connector portions 914 are affixed
to respective opposite surfaces of the substrate.
[0195] Besides for substrates with sharp corners, the geometry of
the tapes described above can be similarly employed for substrates
with circular, elliptical, or any other regular or irregular
shapes. For shapes that have a gradual change, such as a circle,
the width of the strip connector fingers and the spacing between
them should be such so that no noticeable kink is introduced on the
front side of the substrate for the reasons described above.
[0196] The electrical connections to the device are made from the
perimeter portion on the back of the substrate by using more
conductive tape, solder, adhesive, wires, etc., or preferably the
tape described above may be provided in a pre-cut size and shape
that has a connector or a connector attachment already
assembled.
[0197] As shown in FIG. 9A, it is preferable for connector portion
914 of each tape 909 to be in an alternating relationship with the
connector portions 914 of the other tape 909 to minimize the
chances of shorting or of overlapping of fingers. As shown in FIG.
9D, a corner of substrate 901 and a corner of substrate 902 meet
without any connector portions 914 at the corners. The connector
portions 914 remain in an alternating relationship to prevent any
overlap of tape conductive material
[0198] As shown in FIG. 9B, tape 909 employed for this purpose can
be coated or laminated with a nonconductive material insulating
layer 910 on the side that is non-adhering. This will reduce the
chances for shorting of the two substrates should the fingers
inadvertently overlap or if there is a malfunction, for example,
when one of the strip fingers lifts off the surface.
[0199] In another method, highly conductive busbars are made by
wrapping the connector from the substrate front to the substrate
edges and then reinforcing the edge portion with a highly
conductive material. This is shown in FIGS. 32A and 32D. The
connectors are shown as 3205 and 3205" and the reinforcements as
3203 and 3203'" forming the busbars 3202 and 3202'". The
reinforcement can be any convenient shape such as a cylindrical
wire, as shown for example. Another shape is a flattened wire. In
this example the conductor is shown significantly thicker at the
edges than its thickness on the front of the substrate. In FIG.
32D, the reinforcement is located in a precut groove on the edges
of the substrate.
[0200] FIG. 32E shows highly conductive reinforced busbars having
the reinforcement in a groove with the conductive connector
wrapping from the front of the substrate around the edge to the
opposite side of the substrate.
[0201] The busbars can be made by any convenient method such as,
for example, by feeding the reinforcing wire and solder (as
connector) so that both can be put in place simultaneously. Another
method could be where the wire is pre-attached, e.g., by wrapping
and then mechanically tightening around the perimeter of the
substrate. The solder is then deposited on the front and the edge
thus electrically attaching the reinforcement with the connector.
In this method it may be advantageous to have a precut groove on
the perimeter edge of the substrate in which the wire can be
placed, as shown in FIG. 32D.
[0202] The arrangement shown in FIG. 32A can be modified as shown
in FIGS. 32B and 32C where the connector wraps around from the
front to the back. Similarly, the conductor shown in FIG. 32D can
be extended by having a wrap around connector (as shown in FIG.
32E). Further, the wire may be placed in a groove on the edge (as
shown in FIG. 32D) or in a groove made in the back of the substrate
close to the perimeter edge (not shown).
[0203] The connector may be deposited by using a soldering iron,
with its tip shaped so that the solder can be melted and
simultaneously deposited on two adjacent surfaces (as shown in FIG.
32A) or on three adjacent edges (as shown in FIG. 32B). Instead of
using a solder, a conducting adhesive may also be applied. The
solder or adhesive may be applied from a bath of molten solder or
uncured liquid adhesive by dipping the substrate edge in the bath
and then moving the part (e.g., rotationally) effective to cover a
substantial perimeter of the substrate.
[0204] To improve the reliability of the connections, it is
preferred to seal the device using a non-conducting adhesive. As
shown in FIG. 10, it may even be desirable to allow the edge
sealant adhesive to fill in the remaining gap between the
substrates and preferably extend to the substrates edges for
improved reliability. Substrates 1001 and 1002 are separated and
attached to each other by cell adhesive 1003. Edge busbars 1005
including conductive paths that wrap around to the fronts of
substrates 1001 and 1002 have an edge sealant 1004 filling the
respective gaps between each opposite pairs of edge busbars. Any
convenient non-conducting material can be used such as, for
example, a curable formulation such as a caulking, a heat or
radiation curable material, or a hot melt adhesive that cures
later, or a non-curable formulation such as a hot-melt adhesive.
Some examples of materials used in sealants are silicones,
polysulfides, butyls, urethanes, epoxies, vinyls, polyolefins,
polyamides and acrylics, etc. Hot melt urethanes that cure later
due to the diffusion of moisture may be preferred as a sealant
because devices so made could be handled soon after fabrication and
a non-flowable, non-sagging bond is obtained after curing. One may
preferably employ the cell adhesive 1003 to be the same as edge
sealant 1004. This adhesive may have spacers so that the cell
spacing is governed by the size of these spaces and the thickness
of edge busbars 1005. This avoids electrical shorts between the two
substrates, due to busbar peel, moisture condensation or conductive
impurity.
[0205] Although the present invention has been discussed in terms
of electrochromic devices, it can also be useful in photochromic
devices (U.S. Pat. No. 5,604,626, incorporated herein by
reference), liquid crystal based devices as described in
Motogomery, G. P., in Large-Area Chromogenics: Materials and
Devices for Transmittance Control, SPIE Optical Engineering Press,
Bellingham, Wash., 1990, p. 577, suspended particle devices
(Research Frontiers Inc., Woodbury, N.Y.) and other devices.
[0206] Highly conductive busbars may be deposited on single
substrate devices in a number of ways to achieve substantial
perimeter contact. In the prior art, for example in U.S. Pat. No.
5,187,607, incorporated herein by reference, the busbars for an EC
device do not cover a substantial perimeter of the device. As shown
in FIG. 12 (taken from U.S. Pat. No. 5,187,607) a busbar is formed
on the edges of the substrate. The first transparent coating layer
(bottom conductor) is deposited so that it touches both the
busbars, but it is not continuous. This coating is either etched or
deposited in such a way (e.g., by masking) that there is no
electrical continuity between the two busbars. The coatings which
comprise the EC stack are substantially deposited on one of these
sections. However, the top conductor is deposited in such a way
that it touches the second part of the bottom conductor and is
electrically insulated from the first part of the bottom conductor
by the EC stack. Thus, in this design none of the two busbars
occupies a substantial perimeter of the device. Instead, the
busbars run along the two edges similar to the prior art discussed
previously.
[0207] As shown in FIGS. 11A, and 11B, the use of busbars according
to the present invention which are deposited on a substantial
perimeter of an electric cell can be effectively employed for those
devices that use thin coatings on one substrate. A substrate 1101
has a transparent electrode 1102 on its front surface. An EC stack
1104 is on the transparent conductor 1102. A bottom busbar 1103 is
formed on the perimeter of the transparent conductor 1102 while a
top busbar 1105 is formed on the perimeter of the top of the EC
stack. Electric leads are connected to each busbar.
[0208] As shown in FIG. 13, a bottom electrode 1402 is formed on
substrate 1405 in a pattern with recesses 1301 at the edges of
bottom electrode 1402. Bottom electrode 1402 can be formed by any
convenient method such as, for example, by depositing the bottom
electrode (e.g. made from ITO, doped tin oxide, doped zinc oxide,
etc.) over an appropriate mask, or by etching through an
appropriate mask after deposition. Preferably, the sheet resistance
of the transparent conductors is less than about 30
.OMEGA./.box-solid., more preferably less than about 15
.OMEGA./.box-solid., and most preferably less than about 10
.OMEGA./.box-solid..
[0209] The EC stack is then deposited along with the top electrode
only onto the device area, and recesses 1301 in the electrode
border area. Optionally, one can deposit the EC stack over the
device area and only the top electrode layer would extend into
recesses 1301 of the electrode border. It is important to keep the
top electrode layer and the bottom electrode layer from shorting,
thus it is desirable that the top electrode be deposited in such a
way that it covers only a portion of recesses 1301 in the border
region to avoid shorting. Optionally, an insulating layer can be
deposited.
[0210] As shown in FIGS. 14, 15A, and 15B, one embodiment includes
forming an EC stack 1406 on bottom electrode 1402. A top electrode
1401 is formed on EC stack 1406. An edge busbar 1404 connects to
top electrode 1401, while an edge busbar 1403 connects to bottom
electrode 1402. Edge busbar 1404 comprises a perimeter portion
1404C and a connector portion 1404D. Connector portion 1404D
includes a contacting portion 1404A and an edge portion 1404B.
Contacting portion 1404A electrically contacts a surface of top
electrode 1401. Edge busbar 1403 comprises a perimeter portion
1403C and a connector portion 1403D. Connector portion 1403D
includes a contacting portion 1403A and an edge portion 1403B.
Contacting portion 1403A electrically contacts a surface of bottom
electrode 1402. Connector portion 1404D and 1403D are in
alternating relationship on each side of EC device 1444.
[0211] One method to form the continuous busbar on this device is
to utilize a tape as shown in FIGS. 9B and 9C. As described
earlier, the first tape is placed around the periphery of the
device with its fingers touching the bottom electrode in the
connector border area. The continuous body of the tape is folded
and adhered to the back of the substrate. The fingers of the tapes
form the connector portions 1403D and 1404D. The fingers of the
second tape are then adhered on the top electrode (in the connector
border area) and folded and adhered to the back of the
substrate.
[0212] The tapes, after assembly, appear as shown in FIG. 15A and
15B in a cross-section view (two sections shown from FIG. 14). One
of the tapes is wider, in order to protrude out. Perimeter portion
1403C extends beyond perimeter portion 1404C to expose surface
1403E. This allows connection to be made to both edge busbars 1403
and 1404 directly to any convenient point or points on perimeter
portion 1404C and to any convenient point or points on exposed
perimeter portion 1403E.
[0213] Referring to FIG. 15C, the connection can be made by
removing the insulating layer locally, or the tape may come with a
connector-adapter and/or connector pre-attached as discussed
earlier. Connections 1408A and 1408B are shown connecting to
perimeter portions 1403C and 1404C, respectively while being
insulated from perimeter portions 1404C and 1403C, respectively.
Connections 1408A and 1408B can be, for example, a conductive wire
or tape connected to an exterior signal connector. Connections
1408A and 1408B can be attached at only one corner (a smaller
portion of the device perimeter), or at a longer portion of the
device perimeter such as, for example, a substantial perimeter.
[0214] In all cases, one must be careful that the two busbars 1403
and 1404 do not electrically short in the regions 1410 where an
edge of perimeter portion 1403C meets edge portion 1404B at the
edge of substrate 1405. Shorting can be avoided by ensuring that
the insulator layer of the tape extends out and covers the edges of
the conductor. Alternatively, after adhering the first tape, these
edges can be treated with an insulating material (tape, adhesive,
coating) before the second tape is applied.
[0215] Once all the edge busbars are in place, the edges of the EC
device 1444 can be encapsulated, for example, by injection molding
(e.g., using thermoplastic elastomers or plasticized polyvinyl
chloride) or reaction injection mold (e.g., using polyurethane)
with a resin that can be solidified to ensure the reliability of
the connections. It may even be desirable to cover the entire
device with another substrate (preferably a glass or a plastic
sheet) for mechanical and environmental protection before edge
encapsulation. This cover substrate may also incorporate UV
blocking characteristics. The edge encapsulation may be achieved
such that a connector plug (which is internally connected to the
busbars) is molded therein which can be easily disconnected from
the power supply. This will allow EC panels to be quickly serviced
and replaced in the field.
[0216] As shown in FIGS. 16A and 16B, busbars 1602 may be embedded
in the edge of a substrate 1601 or busbars 1603 may be embedded in
the edge regions of substrate 1601. The appropriate region of the
substrate is etched, ablated, or otherwise conveniently removed to
form a recess. A highly conductive material (e.g., a metal) is
deposited into the recess region. Planarization, to bring the
substrate surface and the busbars substantially to a plane, may be
necessary prior to the deposition of an additional layer or layers.
Such embedded busbars 1602 and 1603 can serve as perimeter portions
with connector portions formed (not shown) by any convenient method
such as, for example, wrapping tape around the edge to contact the
back surface and the embedded busbar, depositing conductive
material such as a frit or a coating around the edge from the
embedded busbar to the back surface, or attaching a multitude of
preformed conductive channels to the edge to contact the back
surface and the embedded busbar.
[0217] As described previously, the edge busbar of the present
invention provides sufficient conductivity such that a negligible
voltage drop (preferably less than one tenth of the applied
voltage) occurs in the edge busbar. The conductivity can be
optionally reinforced by the addition of a supplemental conductor
portion as part of the edge busbar of the present invention, as
shown in FIGS. 32A, 32B, and 32C. In a preferred embodiment, an
ultrasonic solder dispenses an appropriate soldering material on
the edge of the substrate. A highly conductive medium (e.g. a wire,
conductive tape or foil, etc.) is attached to reinforce the overall
conductance around a substantial perimeter of the substrate. It is
preferable that both the solder and Whe wire or strip are dispensed
simultaneously to form the edge busbar and the reinforcement at the
same time.
[0218] The reinforcement bar can also be in the form of a closed
loop with a perimeter slightly smaller than that of the substrate.
In this case, after applying the edge busbar, the reinforcement is
expanded by heating and positioned around the edge making contact
with the busbar. Of necessary, it can be soldered to further
improve electrical contact. This method is particularly appropriate
in the case of cells having circular or oval substrates where the
reinforcement can be made in the form of a ring and contracted, by
cooling, uniformly around the substrate. Finally, a lead can be
soldered to the reinforcement.
[0219] Referring to FIG. 32A, an edge busbar 3202 is formed on a
peripheral surface and a substantial perimeter edge of a substrate
3201. Edge busbar 3202 includes a reinforcement portion 3203 which
can be any convenient conductor such as, for example, wire, foil,
or bead of solder. Reinforcement portion 3203 is shown as a
circular cross-sectional wire attached to the side of the edge
portion 3205 of edge busbar 3202. A connection 3204 provides an
external electrical lead to edge busbar 3202.
[0220] Referring to FIG. 32B, an edge busbar 3202' is formed on
opposing peripheral surfaces and a substantial perimeter edge of a
substrate 3201. Edge busbar 3202' includes a reinforcement portion
3203' which is shown as a circular cross-sectional wire attached to
the side of the edge portion 3205' of edge busbar 3202'. A
connection 3204' provides an external electrical lead to edge
busbar 3202'.
[0221] Referring to FIG. 32C, an edge busbar 320211 is formed on
opposing peripheral surfaces and a substantial perimeter edge of a
substrate 3201. Edge busbar 3202" includes a reinforcement portion
3203" which is shown as a circular cross-sectional wire attached to
one peripheral edge portion 3206 of edge busbar 3202". A connection
3204" provides an external electrical lead to edge busbar
3202".
[0222] Referring to FIG. 33A, a substrate 3301 is shown having a
solder edge busbar 3302. Solder edge busbar 3302 is in electrical
contact with one segment of a silver frit layer 3303. Another
segment of silver frit layer 3303 forms an internal busbar 3304.
Internal busbar 3304 is interior to the perimeter formed by a main
epoxy seal 3305.
[0223] Referring to FIG. 33B, two substrates 3301' and 3301", each
has a solder edge busbar 3302' and 3302" respectively. Each solder
edge busbar 3302' and 3302" are in contact with segments of silver
frit layers 3303' and 3303". A common epoxy seal 3305' bounds
internal busbars 3304' and 330411 which are segments of silver frit
layers 3303' and 3303" respectively.
[0224] The Examples which follow are intended as an illustration of
certain preferred embodiments of the invention, and no limitation
of the invention is implied.
EXAMPLES
Example 1 and Comparative Examples 1C and 2C
[0225] EC devices were made having two substrates, one employing a
one half wave ITO (about 12 ohms/square) on glass substrate (from
Donnelly Applied Films, Boulder, CO) and the other being a TEC 15
glass (from Libby Owens Ford (LOF), Toledo, Ohio). The nominal size
of these was 6 inch by 6 inch (15 cm.times.15 cm). The gap between
the substrates was 210 micrometers. Busbars were formed using a
copper tape with conductive adhesive. Three different
configurations were made: (i) Comparative Example 1C was made in a
configuration as shown in FIG. 2, where the edge busbar was on one
edge of each substrate, (ii) Comparative Example 2C was made in a
configuration as shown in FIG. 4, where the edge busbars are on the
two edges of each substrate, and (iii) Example 1 was made in a
configuration as shown in FIG. 7A and constructed by a method as
shown in FIGS. 17A and 17B, where the edge busbars are on four
edges of each substrate. Copper tape (with conductive pressure
sensitive adhesive) was used to form the busbars. The thickness of
the copper tape was 50 micrometers and a width of 3 mm.
[0226] To form the busbar on all four edges, as shown in FIGS. 17A
and 17B, four strips of copper tape 1701 were attached to substrate
1702 and then folded on the back of the substrate. Care was taken
that these strips were close but not overlapping. On only one of
the substrates, the copper tape was covered with a 50 micrometer
thick polyimide tape, the latter was wider than the copper tape by
about {fraction (1/32)} of an inch (0.079 cm). This was done to
prevent shorting of the two substrates if the copper tape peeled
accidentally and touched the other substrate. Optionally, tabs 1703
can be formed by extending one portion of copper tape 1701. The two
substrates were then adhered to each other in a configuration shown
in FIG. 7A. The total gap between the two substrates was 210
micrometers (controlled by the adhesive) and the total thickness of
the tape was 150 micrometers.
[0227] The assembled cells were powered by connecting power to the
busbars. In the case of Example 1, power was connected to one of
the copper tabs 1703 sticking out from each of the substrates. In
this example the tabs were not joined by a wire or a tape on the
back. Since the distance between the adjacent copper strips was
small, the potential drop in the intervening ITO was negligible for
this device. Thus, the busbars of Example 1 effectively formed a
continuous electrical conductor around each substrate perimeter.
The continuous electrical conductor of Example 1 included the
connector portions being effectively electrically continuous as
well as the perimeter portions being effectively electrically
continuous.
[0228] FIG. 18 shows the kinetic traces of each of the three
devices when they were colored and bleached by applying identical
step potentials. Example 1, the cell with busbar on all four sides
colors, was the fastest to color and colored the deepest (during
the time shown in the graph), while Comparative Example 1C, the one
with busbar only on one edge, was the slowest to color and also
colored the least deep of the three devices.
Example 2
[0229] An EC device 1910 was made using two TEC 15 transparent
conductive substrates as shown in FIGS. 19A and 19B. Example 2 was
a circular EC device 1910 with a substrate 1902 being 13 inches
(33.02 cm) in diameter and a second smaller substrate 1901 being 12
inch (30 cm) in diameter. Before EC device 1910 was assembled, a
busbar 1904 on the smaller substrate 1901 was formed by screening
on a silver frit from Dupont Electronic Materials, Wilmington, Del.
(frit Type 7713). The frit forming was deposited in a perimeter
ring geometry to form busbar 1904, with the outer dimensions of the
ring being substantially the same as that of substrate 1901. The
width of the ring was 2 mm and the thickness was 5.5 micrometers.
In one part of the busbar 1904 ring the silver frit was painted on
the edge (while keeping it connected to the ring) and extended on
to the back of the substrate to form a conductive path 1908 of
busbar 1904 which is conductive from the front to the back. An
electrical conducting wire 1906 is connected to conductive path
1908 on the back.
[0230] Substrate 1901 was heated to 575.degree. C. for 6 minutes to
consolidate and cure the frit. The busbar 1905 on the larger
substrate 1902 was formed by attaching a copper beryllium spring
clip 1905 around the circumference. Spring clip 1905 comprises a
continuous perimeter portion 1911 which extends circumferentially
around the edge of substrate 1902, and finger connector portions
1912 which extends radially from continuous perimeter portion 1911
to substrate 1902. A conducting wire 1907 was soldered to clip 1905
to power substrate 1902. EC cell 1910 was assembled by gluing the
two substrates together with adhesive 1903, as shown in FIGS. 19A
and 19B. The smaller substrate 1901 was kept concentric with the
larger substrate 1902.
[0231] Internal Busbars
[0232] To produce the desired improvements in EC device behavior,
it is necessary to reduce appreciably the effective resistance of
the transparent electronic conductors (TC) in the devices or to
otherwise transport charge more efficiently laterally across the
device. In contrast to the case of a TC, when the transparency of a
particular electronically conducting electrode (ECE) is not
important, the ECE can generally be made thick enough in the prior
art so that its resistance does not adversely affect the device
behavior. For example, for a prior art mirror device with an
Aluminum (Al) ECE and an ITO ECE, the Al layer can be deposited
sufficiently thick. The result, however, is that the effective
resistance of the ITO (the transparent electronic conductor or TC)
usually is the primary limiting factor which must be overcome to
improve the device behavior.
[0233] In reducing the effective resistance of a TC, it is crucial
to ensure that the means employed does not adversely affect other
components of the device operation. This is especially problematic
when the TC acts as a substrate for an active EC layer or layers
(such as for devices which contain EC tungsten oxide deposited on
ITO-coated glass substrates). In addition, one must ensure that the
means employed do not too strongly diminish the transmissivity or
apparent transmissivity of the TC or otherwise adversely affect the
cosmetics of the device. For example, the resistance of the TC may
be decreased appreciably by increasing its thickness, but increased
thickness generally has a strongly negative impact on TC
transmissivity characteristics and cost.
[0234] Means for Decreasing the Effective Resistance of The
TC's
[0235] A desirable means of imparting a relatively high effective
conductivity to a TC comprises depositing a pattern of a highly
conductive material over, under, or within it (or some
combination). Commercially available TC's such as half-wave ITO or
doped tin oxide (DTO) can be used and modified by adding internal
busbars according to the present invention. As shown in FIGS. 20A
and 20B, e.g., the pattern can be formed as lines across the
substrate. These lines may or may not intersect. The lines or
patterns may be referred to as internal busbars (IB's). FIG. 20A
shows a substrate 2001 made of, for example, glass, coated with a
transparent conductive coating 2002. Internal busbars 2003 are
formed on conductive coating 2002, FIG. 20B shows additional
internal busbars 2004 transverse to internal busbars 2003.
[0236] It is important to ensure that the materials used for the
internal busbars (IB) of the present invention do not react with
the cell components. That is, the internal busbars should be
chemically and electrochemically isolated from the reactive layers
of the cell. Reactive layers are the electrolyte, the ion insertion
electrodes, and the electrochromic layers. In these layers,
chemical and physical reactions take place when the cell is colored
or bleached.
[0237] The chemical and electrochemical isolation can be by any
convenient means such as, for example, by interposing a barrier
layer between the IB and the reactive layer. The property of being
not ionically conductive is a requirement of the optical
passivation layer so that, when a voltage is applied to the
finished cell for coloring or bleaching, no ion transport takes
place from any of the cell components to the internal busbars and
vice versa.
[0238] As described below and in the figures, the isolated IB's of
this invention are connected to the conductive layers by connecting
portions that are electrically conductive. Accordingly, the IB's of
this invention can provide substantial improvement of the
electrical properties of the conductive layer while not being in
contact with the layer.
[0239] A calculation of the effective sheet resistance
corresponding to a pattern consisting of parallel lines on a
transparent conductor was performed. The physical dimensions of
these internal busbars (e.g., their thickness (or height), width,
length, resistivity) along with the underlying transparent
conductor characteristics, determine the overall effective sheet
resistance. Tables 1A, 1B, and 1C below show the calculated
effective sheet resistance of the substrates for various values of
the relevant parameters. The calculations were made for 5
cm.times.5 cm square substrates traversed by five (n=5, or
"N.sub.5") parallel internal busbars, each of width w.sub.s and
height h.sub.s. For these calculations, the strips were assumed to
be composed of Pt-metal
(.sigma.=0.96.times.10.sup.5(.OMEGA.cm).sup.-1). The effective
sheet resistance was taken as the resistance that would be measured
between an electrode connected on one full side of the square and
another connected to the opposite full side. It should be noted
that the calculations can be repeated for a grid pattern which may
consist of curved lines or non-uniformly dimensioned (e.g., in
width and thickness) conductive line patterns.
3 TABLE 1A h.sub.s.backslash.w.sub.s w.sub.s h.sub.s 0.01 mm 0.05
mm 0.1 mm 0.15 mm 100 nm 13.29 13.448 13.396 13.344 1 .mu.m 12.526
9.721 7.595 6.232 2 .mu.m 11.683 7.595 5.283 4.051 3 .mu.m 10.946
6.232 4.051 3.001 4 .mu.m 10.297 5.283 3.284 2.383 0.1 mm 1.538
0.339 0.171 0.115
[0240] Table 1A. Calculated effective sheet resistances
.OMEGA./.box-solid. for a system comprising 3 strips, where each
strip possesses the dimensions (h.sub.s, w.sub.s) given in the
Table.
4TABLE 1B h.sub.s.backslash.N.sub.s N.sub.s h.sub.s 1 2 3 4 5 100
nm 13.448 13.396 13.344 13.293 13.243 1 .mu.m 9.721 7.595 6.232
5.283 4.586 2 .mu.m 7.595 5.283 4.051 3.284 2.762 3 .mu.m 6.232
4.051 3.001 2.383 1.976 4 .mu.m 5.283 3.284 2.383 1.87 1.538 .sup.
0.1 mm 0.339 0.171 0.115 0.086 0.069
[0241] Table 1B. Calculated effective sheet resistances
.OMEGA./.box-solid. for a system comprising Ns strips, where each
strip possesses a width of 0.15 mm and a height, h.sub.s, as
indicated in the Table.
5 TABLE 10 w.sub.s.backslash.N.sub.s N.sub.s w.sub.s 1 2 3 4 5 0.01
mm 12.232 11.181 10.297 9.543 8.891 0.05 mm 8.891 6.628 5.283 4.392
3.758 0.1 mm 6.628 4.392 3.284 2.623 2.183 0.15 mm 5.283 3.284
2.383 1.87 1.538
[0242] Table 1C. Calculated effective sheet resistances
.OMEGA./.box-solid. for a system comprising N.sub.s strips, where
each strip possesses a height of 4 .mu.m and a width, w.sub.s, as
indicated in the Table.
[0243] The effect of size on the conductance of a 15
.OMEGA./.box-solid. (TEC 15) substrate with internal busbars is
shown in Tables 2A and 2B below.
[0244] Two different systems are considered:
[0245] System A: IB's comprise Pt-strips
(.sigma.=0.96.times.10.sup.5 (.OMEGA..multidot.cm).sup.31 1), each
0.15 mm wide and 41 .mu.m high; and
[0246] System B: IB's comprise strips of DuPont 7713 Frit with a
sheet resistance of R.sub.s=3 m .OMEGA./.box-solid. at 25 .mu.m
thickness. Each strip is 1.5 mm wide and 25 .mu.m high.
[0247] The number, N.sub.s, of IB's is such that there is a fixed
spacing of 1 cm between busbars. Edge busbars are not represented
in the calculations (so, e.g., for a L cm.times.L cm system, there
are (L-l) IB's). In all cases, the underlying conducting sheet
possesses a sheet resistance of 15 .OMEGA./.box-solid..
6TABLE 2A Calculated effective sheet resistance for Systems A and B
R.sub.Sheet for R.sub.sheet for Substrate Area System "A" System
"B" 5 cm .times. 5 cm 1.90 .OMEGA./.box-solid. 0.0250
.OMEGA./.box-solid. 10 cm .times. 10 cm 1.71 .OMEGA./.box-solid.
0.0222 .OMEGA./.box-solid. 30 cm .times. 30 cm 1.60
.OMEGA./.box-solid. 0.0207 .OMEGA./.box-solid. 100 cm .times. 100
cm 1.57 .OMEGA./.box-solid. 0.0202 .OMEGA./.box-solid.
[0248] The effective sheet resistance is useful for comparing
substrates of comparable size. However, an effective resistance
(R), defined as the effective sheet resistance multiplied by the
area of the substrate (thus possessing units of
.OMEGA..multidot.cm.sup.2/.box-solid.), is more useful for
comparing substrates of different sizes. Table 2B comprises the
data for the effective resistance (R), for each sheet, as a
function of substrate size.
7TABLE 2B Calculated effective resistances for Systems A and B.
Effective Effective Resistance Resistance for System for System
Substrate Area "A" "B" 5 cm .times. 5 cm 47.4 .OMEGA. .multidot.
cm.sup.2/.box-solid. 0.624 .OMEGA. .multidot. cm.sup.2/.box-solid.
10 cm .times. 10 cm 171 .OMEGA. .multidot. cm.sup.2/.box-solid.
2.22 .OMEGA. .multidot. cm.sup.2/.box-solid. 30 cm .times. 30 cm
1440 .OMEGA. .multidot. cm.sup.2/.box-solid. 18.6 .OMEGA.
.multidot. cm.sup.2/.box-solid. 100 cm .times. 100 cm 15700 .OMEGA.
.multidot. cm.sup.2/.box-solid. 202 .OMEGA. .multidot.
cm.sup.2/.box-solid.
[0249] It is desired that the width of the internal busbars should
be small so that the active area of the EC device can be maximized.
Further, such narrow widths also minimize optical interference to
viewing through EC devices to which such internal busbars are
incorporated. Thus, narrow widths are less obtrusive to vision.
[0250] As used herein, unless specified to the contrary, the
descriptors "narrow or wide" refer to a "width" dimension parallel
to the surface of the feature being described, while the
descriptors "thin or thick" refer to a "thickness" dimension
orthogonal to the surface of the feature being described.
[0251] A preferred geometry of the IB's include patterns which are
greater than about 1 .mu.m in thickness, and most preferably
greater than about 10 .mu.m in thickness. Although any convenient
material can be used and formed by any convenient technology,
materials and technologies that allow such thick IB's to be
deposited are preferred. Examples of materials which are easy to
deposit in these dimensions are typically conductive inks, pastes,
and frits. Examples of the methods are described below.
[0252] Generally, the overall conductivity of the substrate does
not depend appreciably on whether the conductive electrode coating
is over the grid, around the grid, under the grid, or in some such
combination. In the present invention, if the grid is deposited on
the surface of the transparent conductor, the grid should be
prevented from reacting or corroding in the device through the use
of a protective barrier or passivation coating. The construction
and materials of such a barrier coating depends upon the degree of
reactivity of the grid material at the potentials encountered
during device operation.
[0253] The internal busbars of the present invention may not be
directly connected to other busbars such as edge busbars or such
signal leads. The internal busbars of the present invention can be
termed "floating"busbars. The signals are generally conducted to
the internal busbars of the present invention by the conductive
layer that is in contact with them. By such contact, the conductive
layer's conductive is effectively lowered because the internal
busbars of the present invention have lower conductivity than the
conductive layer they are in contact with. The IB's of the present
invention can be optionally connected to other busbars described
above, to other IB's, or to electrical leads. However, as discussed
below, an IB of the present invention can nevertheless receive an
applied signal by the IB's being "bridged" to other voltage sources
through the conductivity of the conductive layer the IB is in
contact with. There are applications such as, for example, those
that call for specific signals being applied to specific internal
busbars where the internal busbars of the present invention can
optionally be directly connected to a signal source.
[0254] In addition to a variety of lateral geometries, the IB's can
occupy a variety of transverse locations in a device. For example,
a pattern may be deposited on top of the TC. In a device of the
form
Glass.vertline.TC1.vertline.electrolyte/redox
species.vertline.EC.vertline- .TC2.vertline.Glass
[0255] (where EC refers to an electrochromic film), for example,
one may deposit a grid pattern on TC1, on TC2, or on both TC's.
Naturally, the height of a grid on TC1 should be significantly less
than the cell gap (i.e., the thickness of the electrolyte/redox
species medium), preferably much less. For a grid deposited on TC2,
one must ensure that the thickness, morphology, and chemistry of
the grid do not adversely affect the EC film. Regarding thickness,
if the thickness of the grid is much less than that of the EC film,
then the grid has little effect on the shape of the EC film. If the
thickness of the grid is on the order of or greater than that of
the EC film, then the EC film may often form a noticeable "relief"
of the grid pattern (or it may even form in separate areas defined
by the grid pattern).
[0256] The durability of devices with the IB grid of the present
invention generally should be similar to devices without the IB
grid. Any durability test should yield the same result with or
without the grid. That is, the addition of the internal busbars of
the present invention should not affect the reliability and
durability of the devices. Accordingly, results of any durability
tests to qualify a device for a particular application are likely
transferable, or can be anticipated to be the same if such tests
are repeated with the devices having internal busbars. Because
durability is one of the key issues involved in developing a
commercially viable device, this is an important parameter. To
ensure durability of these devices, it has been discovered that it
is preferred to deposit a passivation layer on top of the internal
busbars, particularly if the IB's are deposited on top of the
transparent ECE's. Materials for passivation are described
below.
[0257] As shown in FIG. 21, the "effective height" of the grid may
be reduced by embedding the grid conductor partially in the TC and
substrate. Internal busbar conductors 2102 are embedded in
substrate 2101. The formation of internal busbar conductor 2102 may
be done by any convenient way such as, for example, by etching or
ablating away a desired pattern in the substrate and then
depositing the desired grid material. The effective height of the
grid may be reduced by embedding it partially in the glass as well
as the TC. One can etch or ablate away consecutively the TC coating
and the substrate, followed by depositing the desired grid
material. Alternatively, one can deposit the grid onto, or embed
the grid into, the glass before the TC is deposited. The portion of
busbar conductors 2102 that are above the surface plane of
substrate 2101 is removed until the surface and the busbar
conductors are at substantially the same plane 2103.
[0258] In one embodiment, the grid is partially embedded into the
glass and then the surface is planarized by, for example, polishing
to produce a structure as shown in the process in FIG. 21.
Planarizing may also be done by depositing additional material on
to the substrate so that the top surface of this added material is
coplanar with the grid. Although FIG. 21 shows conductors 2102
having circular cross section such as commonly found in a wire, it
could be of another convenient shape, such as rectangular.
Additionally material can be deposited, for example, from
solutions, or by physical vapor deposition, etc. Some examples of
such materials are polyimide, sol-gel deposited oxides and
organic/inorganic hybrids.
[0259] A TC is then deposited on the resulting planarized surface
and the resulting glass.vertline.TC substrates used in the same
manner as they are typically used. This process of the present
invention has the distinct advantage that the more chemically
active components of the device such as the EC film and the
electrolyte are not directly exposed to the IB grid material.
[0260] Except for the glass substrates, the layers in single
substrate devices (See, for example, FIG. 1E) are generally each
quite thin (typically in the 100's of nm). It is therefore
particularly preferred to use IB's which are fully embedded under
the TC in such devices. The IB on the outer TC (layer 103' of FIG.
1E) could consequentially be of any thickness since it will
protrude on the outside of the device.
[0261] Whether it is desirable to include IB's on one or both TC's
in a device depends on a variety of factors, including the required
response time and coloration uniformity characteristics and the
cost of manufacturing the devices. Devices generally display faster
response times and greater coloration uniformity with the IB's
implemented on both TC's.
[0262] IB Dimensions
[0263] The dimensions of the IB's width and depth can be varied
throughout a substrate. As shown in FIG. 22, EC device 2210 has
conductive transparent substrate 2201 transversed by narrower
internal busbars 2202 and wider internal busbars 2203. Narrower
internal busbars 2202 and wider internal busbars 2203 are separated
by gaps 2208 from edge busbar 2204. Gaps 2208 are bridged by
conductive transparent substrate 2201. Narrower internal busbars
2202 and wider internal busbars 2203 optionally connect directly to
edge busbar 2204.
[0264] By combining, for example, narrow and wide IB's one can
enhance the conductivity of the substrate while maximizing its
transmission. However, while incorporating the use of wider IB's
decreases their resistance (and thus advantageously decreases the
effective resistance of the TC), it also affects the apparent
transmission of the device. The transverse or primarily transverse
direction is usually the direction of most importance for the
optical properties of the devices. Accordingly, increasing the
depth (or height) of the IB's is advantageous when compared to
increasing the width of the IB because increasing the depth will
typically have a much smaller adverse effect on the cosmetic
appearance and/or the apparent transmission of the devices than
increasing the width.
[0265] Another component of the present invention is the use of
IB's which will be optically less prominent, by making the IB's
much deeper than they are wide. For example, defining the aspect
ratio, r.sub.1b, as the effective width of the internal busbar
structure divided by its effective height (thickness), it is
generally desirable to have r.sub.1b smaller than 1, for optical
transmission applications where a viewing path is through the
surface on which is deposited the busbar structure.
[0266] The reason is that, if one is viewing parallel to the height
(thickness) of the IB, then increasing the thickness while the
other dimensions of the IB remain constant does not substantially
affect the appearance of the device; but such increased thickness
does desirably reduce the resistance of the IB (and therefore
desirably reduces the effective resistance of the corresponding
TC). It is therefore generally desirable that the height direction
of the IB's be parallel to the primary viewing direction for such
applications.
[0267] Most commonly, this means that the height direction of the
IB's should be transverse to the plane of the substrates of the
device. But for some devices such as, for example, an automotive
windshield, the primary viewing direction might be at some angle to
the approximate plane of the windshield. In such applications it
would be preferable to implement the IB's such that their height
direction is parallel to such slanted viewing direction. As shown
in FIG. 23, device 2301 has internal busbars 2302 embedded in
substrate 2303 at an angle parallel to the viewing direction
2305.
[0268] Another consideration is the need to provide a contiguous
channel within the device that allows the electrolyte fluid to flow
throughout the gap during filling in order to minimize
manufacturing difficulties. Referring to FIG. 31A, a device 3101
has internal busbars 3102 disposed such that no internal busbar
blocks a contiguous channel. Internal busbars 3102 are in contact
with only one device edge and extend only to the other device edge,
thereby forming a contiguous channel 3103. If the device is filled
with the electrolyte after edge sealing (such as by vacuum
back-filling), only one fill hole is required to perform the
filling task.
[0269] Similarly, FIG. 31B shows a device 3110 where internal
busbars can extend from one device edge to the other device edge.
The internal busbars are arranged in a staggered configuration.
Consequently, although internal busbars 3102' might extend from one
device edge to the other device edge, and each internal busbar
3102' might be thicker than one half the gap distance, their
staggered arrangement forms a contiguous channel 3103' which allows
easy filling of device 3110, with electrolyte fluid, without
interruption.
[0270] FIG. 31C shows a device 3120 which has internal busbars
3102" that can extend from one device edge to the other device
edge, and that can be in an overlapping relation. Internal busbars
3102" are, however, in alternate ramped geometries which form a
contiguous channel 3102" which allows easy filling of device 3120,
with electrolyte fluid, without interruption.
[0271] FIGS. 31B and 31C show embodiments of the present invention
in which the sum of the thicknesses of the internal busbars is
larger than the cell gap distance. Yet, the innovative geometries
of the present invention allows such internal busbars' use without
any problems of electrical shorting or interrupted electrolyte
fluid continuity. As described above, the width of the internal
busbars should be small so that the active area of the overall EC
device can be maximized. The resistance of internal busbars with
narrow width can be nonetheless low because the height (thickness)
of the internal busbars can be made effectively thick. As described
above, geometries and patterns that form IB's having thicknesses
greater than about 1 .mu.m are preferred, and most preferred are
thicknesses greater than about 10 .mu.m. FIGS. 31B and 31C show how
such thicker dimensions can be used without causing the gap
distance to be disadvantageously thick.
[0272] Auxiliary Uses for IB's
[0273] The IB's included in devices under the present invention may
be used for additional purposes, and these may or may not require
modification of the IB design. For example, the IB's may be used as
Joule heating elements for purposes such as de-fogging. For this
purpose, it is desirable to pass current through the IB's
independently of current being used to color or bleach the
device.
[0274] One means for implementing this purpose according to the
present invention includes providing for separate addressing of the
two ends of a set of IB strips. FIG. 24 shows a device 2410 with an
EC assembly 2401 having two internal busbars 2402 over the layers
of TC 2403. Applying a voltage V1 and V2 of equal values across the
two ends will induce a current flow along each of the internal
busbars 2402 but will not result in EC activity in device 2410
because, with equal voltage potentials at each end, there is no
current path or potential drop transverse to the device. If it is
desired that EC activity and heating occur contemporaneously, the
signals can be adjusted accordingly to provide for a current path
and a potential drop transverse to the device by changing V1 and V2
to be unequal. For most EC devices the voltage difference needed
between V1 and V2 is less than 2 volts.
[0275] If IB's are implemented on both TC's of a window-type
device, separate heating of both TC's without inducing EC activity
requires balancing of the lateral voltage potentials so that there
is no transverse potential. If simultaneous coloring is desired,
the potentials can be adjusted accordingly.
[0276] The IB's may also be used as antennae for electromagnetic
signals. For example, one can use a strip IB as a monopole antenna,
letting one end float electrically and connecting the other end to
the appropriate signal processing electronics such as, for example,
a radio receiver. To obtain a larger signal, the signals from a set
of strip IB's forming well known antennae geometries may be
combined and the combined signal appropriately processed. Other
patterns of IB's forming well known antennae geometries may be used
to optimize the antenna functionality. If desired, IB's may also be
used as transmitters following well known transmitter grid
geometries.
[0277] IB's may also be used to provide or enhance the effective
shielding from unwanted electromagnetic waves or interference. The
penetration depth (or "skin depth") of electromagnetic waves into
the devices may be decreased by increasing the effective
conductivity of the TC layers. In addition, specific IB patterns
may be employed such as, for example, forming a part of a Faraday
cage to provide optimal shielding for a particular class of
electromagnetic waves.
[0278] Separately-Addressable IB's
[0279] In an embodiment of the present invention, IB's form a
single addressable array. FIG. 25A shows a device 2501 with
internal busbars 2505 arranged at an angle to and proximate to a
busbar 2507 with proximate gaps 2508 between busbar 2507 and each
internal busbar 2505. Proximate gaps 2508 are bridged by conductive
layer 2509 on substrate 2510. Busbar 2507 can be an internal busbar
or an edge busbar. Busbar 2507 and internal busbars 2505 form a
single addressable array 2503 powered by a conductor 2504.
Optionally, each internal busbar 2505 is directly connected to
busbar 2507.
[0280] In another embodiment of the present invention, the IB's are
made to be separately addressable. FIG. 25B shows a device 2502
with separately addressable internal busbars 2506, each separately
powered by separate conductors 2504.
[0281] One can use the separately addressable IB's to obtain an
added measure of control over the spatial distribution of the
coloring and/or bleaching of an EC device. Whether one needs to be
able to address separately the IB's on one of the TC's or on both
of the TC's depends upon the degree of control required.
[0282] One can utilize the separately addressable busbars (or
separately addressable busbar groups) to have an EC device (e.g., a
sunroof or windshield) that has differential coloration from one
side to the other, or from top to bottom, etc. Such individual
control can produce a number of effects such as, for example, a
gradient effect, a shade effect, or a geometric pattern effect.
[0283] One can employ light sensors and use the signals from the
sensors to determine the appropriate signals to apply to the
separately addressable IB's to obtain the desired spatial
distribution of coloring or bleaching. For example, for an
automotive sunroof, one can use light sensors to effectively track
the position and intensity of the sun and then color more deeply
the appropriate regions of the sunroof. In addition, information
(obtained either automatically or manually) regarding the presence
and positions of occupants of the automobile may be combined with
the signals from the light sensors to determine the appropriate
signals to apply to the separately addressable IB's to obtain an
appropriate coloring or bleaching pattern. The light sensors should
be situated such that they provide effective indications of the
light intensity from a variety of directions. The presence and
positions of occupants of the automobile may, for example, be
sensed via transducers in the seats and/or by detecting the status
of the seatbelts.
[0284] Under the present invention, a variety of "Smart Devices"
can be made by using the signals derived from a system of sensors
to determine the appropriate drive signals to be applied to the
individually-addressable IB's and edge busbars in EC devices.
[0285] Conductive frits are usually pastes and liquids (also termed
inks) of a conductive material in a carrier. The carrier typically
cures or typically is eliminated during a post-application process
such as subjecting to elevated temperatures. Conductive frits for
IB can be deposited by any convenient method such as, for example,
X-Y Motor Painting/Screening, Doctor Blading/Silk Screening/Circuit
Printing, Chemical Vapor Deposition and Physical Vapor Deposition
(CVD and PVD):
[0286] 1. X-Y Motor Painting/Screening: For certain conductive
materials, which are applied in the form of viscous liquids, a
programmable X-Y table with a fluid dispenser may be utilized to
apply the desired pattern to the substrate. The thickness and width
of the conductive line is determined by factors such as the size of
the dispenser tip opening, the viscosity of the fluid, the
dispenser line pressure and the lateral speed of the dispensing tip
relative to the substrate, and the distance between the dispensing
tip and the substrate. Low viscosity molten metals may also be used
for the busbars. These could be sprayed or processed by soldering
or welding. These methods could be assisted by ultrasound or other
energy imparting means to promote uniformity and/or better adhesion
to the substrate.
[0287] 2. Doctor Blading/Silk Screening/Circuit Printing: This
method involves the forcing of a viscous liquid through narrow
openings in an appropriate mask, to be deposited on a substrate in
a pattern determined by the mask design. This mask may consist of
any type of tape, film, or other mask material, such as a
silk-screen-like item, placed on top of the substrate, with
channels or isolated voids in a desired pattern. An excess of the
fluid is then placed at one end of the mask, then a uniform, flat
tool (such as a "squeegee" or similar implement) is dragged across
the mask, forcing the fluid through the pattern troughs onto the
substrate.
[0288] Another alternative is to silkscreen, or otherwise use a
doctor blade to deposit uniform layers of photoprintable thick film
compositions. The internal busbar pattern is then formed by
exposing the deposited film to certain wavelengths of light through
masks and followed by chemical processing. The passivation
materials for internal busbars such as certain dielectric materials
can be similarly processed. The advantage of this over conventional
silkscreening is to get finer resolution and/or higher densities of
conductive lines.
[0289] 3. Chemical Vapor Deposition and Physical Vapor Deposition
(CVD and PVD): CVD is a known process which deposits a coating by
decomposing a chemical vapor to provide the depositing material.
PVD is a known process which deposits a coating by vaporizing a
material and then redepositing this in a substrate in a vacuum
chamber. CVD and PVD may be assisted by energy imparting sources
such as plasma, ionized beams, microwave, etc.
[0290] In these methods, patterns are applied by placing either a
shadow mask over the substrate and coating directly onto the
surface, or by using photolithographic technology to apply a
photoresist mask to the substrate, coating that assembly with
metal, and then stripping the photoresist layer away, leaving the
metal pattern.
[0291] Some exemplary frit, inks and conductive adhesives that may
be employed in this invention include:
[0292] Frits
[0293] DuPont Electronic Materials, Wilmington, Del.,
Silver-Bearing Conductors: DuPont Silver Thick Film Composition,
Nos. 1991, 1992, 1993, 1997; DuPont Silver Thick Film Composition,
#7713; and DuPont Solamet Photovoltaic Compositions such as
#E64885-52A.
[0294] DuPont Gold-Bearing Conductors.
[0295] DuPont Fodel Photoprintable Conductors DC201 and DC010.
[0296] Ferro Silver Paste FX 33-246 available from Ferro Inc.,
Santa Barbra, Calif.
[0297] Metal Inks
[0298] Engelhard Electronic Materials, East Newark, N.J.,
Metallo-Organic Inks: Platinum Inks such as #05X, Gold Inks such as
#A3622, and Silver Inks such as #R2/321 and low temperature cured
flexible materials such as #M5860.
[0299] Conductive Epoxies, Silicones, etc.
[0300] Grace Specialty Polymers, Emerson & Cuming Inc. (Woburn,
Mass.), Minico M 4200 Flexible Silver Buss Bar; 4xxx series
materials; Eccocoat CT 5030 A/B Flexible/Rigid Buss Bar; Minico M
6xxx series silver/copper materials.
[0301] When devices are fabricated that use two substrates, such as
those described in U.S. Pat. Nos. 5,142,407, 5,241,411 and
4,761,061, one or both of the substrates may have added internal
busbars according to the present invention.
[0302] FIGS. 26A and 26B show two configurations of various grid
patterns according to the present invention that do not extend to
the edges. FIG. 26A shows a device 2608 having a perimeter busbar
2602 on substrate 2601. Substrate 2601 has a conductive layer 2615
on its surface. A series of internal busbars 2603 form a crosshatch
pattern. Internal busbars 2603 can be on, in, and/or below
conductive layer 2615. The perimeters of each internal busbar 2603
are in contact with conductive layer 2615.
[0303] FIG. 26B shows a device 2609 having a series of internal
busbars 2604 forming a parallel pattern. Neither series of internal
busbars 2603 or 2604 touch perimeter busbar 2602. As a result, when
an EC device is fabricated using two substrates, the grid pattern
can be completely enclosed in the device. The internal busbars
conduct a current that travels from the perimeter conductor through
the conductive layer 2615 to the internal busbar. This may be
advantageous, since the adhesive used to seal the edges of the two
substrates need not be modified in composition and no change in
processing parameters is needed for ensuring good adhesion to the
internal busbars and for accommodating the change in substrate
topography.
[0304] FIG. 26C shows a device 2610 having a coiling internal
busbar 2605 which is in contact with conductive layer 2615 at the
entire perimeter of internal busbar 2605. Coiling internal busbar
2605 has higher conductivity than conductive layer 2615, which
serves to lower the overall resistance of conductive layer 2615,
thereby making more homogeneous the applied signal to conductive
layer 2615. Coiling internal busbar 2605 can stand alone as shown.
Coiling internal busbar 2605 also can be formed in close proximity
at its outer coil to a perimeter busbar (not shown). Alternatively,
the coiling internal busbar can be attached directly to a signal
power by leaving a portion of the coiling internal busbar exposed
and attaching a signal wire to the exposed portion.
[0305] Since the current at the perimeter has to flow only through
gaps of a short distance through the transparent conductors to the
internal busbars of FIGS. 26A, 26B, and 26C, the resistance drop
will be negligibly small across such gaps. This use of the
transparent conductor to connect an internal busbar to the primary
busbar has not been discussed or disclosed in any prior art
described above.
[0306] A passivation layer may be deposited using similar
techniques described previously. If certain materials and methods
are used to deposit the grid pattern such as silk-screening of
metal frits, then post-treatment such as curing or hardening with
time, heat, radiation (UV, visible, IR, microwave) may be required.
The passivation layer is typically deposited after the above
post-treatment. Similar types of post-treatment procedures may be
required to harden the passivation layer.
[0307] The post-treatment for the grid pattern may also result in
an in-situ formation of a passivation layer on the surface. The
in-situ formed surface may consist of a phase separated inert
material, an oxidize portion, a nitride portion, etc. This will
also depend on the atmosphere and temperature conditions under
which such post-treatment is carried out. This passivation layer
may be sufficiently passivating to be incorporated in these
devices. Treatment where a part of the exposed grid pattern becomes
passivated could also be done when the grid patterns are deposited
by physical and chemical vapor deposition. The surface of these may
be passivated using oxidation, nitriding, heat, laser, plasma, or
ion bombardment assisted treatments. The passivation layer may
consist of organics, inorganics or hybrid materials. Adhesives such
as, for example, non-conducting epoxy adhesives, urethanes,
acrylates, or polyesters could be deposited for passivation. These
may be the same materials that are used for making device seals.
The materials may be cured by heat and/or radiation, such as UV, IR
or microwave. The viscosity and the application procedure can be
adjusted so that the desired thickness is obtained.
[0308] The materials can be applied by any convenient method such
as, for example, being screened, dispensed, sprayed, or painted.
Sol-gel methods could also be used to deposit oxides and
polyceramics as passivation layers. Examples of such materials are
alcoholic or non-alcoholic based solutions of metal alkoxides,
nitrides, halides, or mixtures thereof, or solutions of reactive
metallic precursors with organic complexing agents. Further, these
oxides may be inert such as silica or could be conducting such as
indium tin oxide and doped tin oxide. Preferably the passivating
materials should be non-conductive, both ionically and
electronically. Electronically conducting materials which may be
used as passivating materials are those which are used in making
transparent ECE's such as doped tin oxide and indium tin oxide.
They should not also be attacked, swelled, or interact with the
layers that come in contact with such as electrochromic layers, ion
storage layers, electrolytes, etc. Examples of some commercial
encapsulants/passivation layers that could be silk-screened include
#A3840, #A3560, and #A3563, made by Engelhard. An example of a
photoprintable passivation layer is Fodel DG211 from DuPont
Electronic Materials.
[0309] Electrochromic devices use several transparent conductors
that are not reactive while the other components such as
electrochromic layers, counterelectrodes, and redox materials in
the electrolyte necessarily participate in the electrochemical
activity required for electrochromic operation. Thus, non-reactive
materials are defined as those that lie outside the electrochemical
potential range that is utilized for operating the EC device. Also
materials that are insulators and/or do not transmit or get
intercalated with ions under the above operating conditions and
will not change their physical properties in the cell (such as
dissolution in the liquid electrolyte if used) can also be
considered as non-active. Materials such as many polymers such as
epoxies, polyimides, acrylics, urethanes, and inorganics such as
dense silica, alumina, several other oxides, silicates, and
organo-silicates can be also considered non-reactive. For some
devices, metals such as gold and platinum may also be considered
non-reactive. Thus these metals may be used for busbars without
additional passivation layers. There may even be thick layers of
transparent conductors such as ITO, in a thickness that is
conductive enough for the busbar, but not transmissive enough to be
called TC (transparent conductor).
[0310] For designs where the internal busbars extend to the
perimeter edge of the substrate, the passivation layer may extend
to the edge of the substrate, or stop short of the edge so as to
only be in the interior of the device. In the latter case, the
internal busbars can be electrically contacted with the edge
busbars (for example by using wires, tapes, conductive adhesives,
solders, or wire clips). The novel edge busbars of the present
invention may also be used in conjunction with the novel internal
busbars of the present invention.
[0311] The conductivity of the substrate can also be enhanced
through the use of a wire pattern embedded in a substrate (the
substrate may be constructed from glass, plastic, or some other
material). This wire pattern substitutes for the grid pattern
described above. If the substrate is essentially electrically
insulating, and if the conductive pattern is entirely embedded in
the insulating substrate, then it is generally necessary to connect
electrically the conductive pattern and the transparent conductor.
This may be done, for example, by drilling holes though the
substrate up to the metal grid and then filling the holes with a
conductive material. FIGS. 27A, 27B, 28, and 29 illustrate this
concept, including different methods of ensuring transparent
conductor/plug contact.
[0312] FIGS. 27A and 27B show a device 2710 with a substrate 2705
covered with a transparent conductor layer 2704. Internal busbar
conductors 2702 are embedded in substrate 2705. Conductive plugs
2703 lead from the surface of device 2710 to electrically contact
internal busbar conductors 2702. In this example, transparent
conductor layer 2704 was applied after the holes for plugs 2703
were made but before plugs 2703 were formed.
[0313] FIG. 28 shows a device 2801 formed by attaching internal
busbars 2802 to a surface 2807 of a substrate 2803. Holes 2805 are
formed effective to extend from an opposite surface 2808 of
substrate 2803 to internal busbars 2802. Conductive plugs 2804 are
formed effective to extend from internal busbars 2802 to opposite
surface 2808. Transparent conductive layer 2806 is then formed on
opposite surface 2808, contacting conductive plugs 2804, thereby
being in electrical contact with internal busbars 2802.
[0314] FIG. 29 shows a device 2901 where direct addressing of the
internal busbar conductor was not necessary. Device 2901 has an
internal busbar conductor 2902 embedded in substrate 2904. A
conductive layer 2903 provides electrical contact between
transparent layer 2905 and internal busbar conductor 2902. Inert
filler plug 2906 fills the hole. Transparent conductor 2905 is
applied after the hole that provide access to internal busbar
conductor 2902 is made. Then conductive layer 2903 is formed in the
hole. Finally, inert filler plug 2906 is formed.
[0315] If the conductive pattern is not entirely embedded in the
substrate (i.e., if it contacts the transparent conductor) or if
the substrate is sufficiently conductive, a separate conductor is
generally not necessary.
[0316] Internal busbars can also be used to make devices with those
substrates on which only low conductivity transparent ECE's can be
deposited. Typically, transparent ECE's such as indium tin oxide
and doped tin oxide are deposited at high temperatures (in excess
of 200.degree. C.) to get good conductivity. Most of those
materials, when deposited on plastics, at lower temperatures, are
less conductive. Thus, the use of EB's as described above in
conjunction with lower conductivity transparent ECE's would result
in high conductivity substrates which will be attractive for
electrochromic devices.
[0317] The Examples which follow are intended as an illustration of
certain preferred embodiments of the invention, and no limitation
of the invention is implied.
Example 3
[0318] Strips of silver frit paste (DuPont # 7713) were deposited
by silk-screening onto a 3 inch.times.3 inch (7.5 cm.times.7.5 cm)
TEC 15 substrate. The substrate was then heated under ambient
atmosphere according to the following four step procedure;
[0319] Step 1: Temperature raised from 25.degree. C. to 100.degree.
C. at 10.degree. C./min and held at 100.degree. C. for 15
minutes.
[0320] Step 2: Temperature raised from 100.degree. C. to
325.degree. C. at 10.degree. C./min and held at 325.degree. C. for
10 minutes.
[0321] Step 3: Temperature raised from 325.degree. C. to
600.degree. C. at 10.degree. C./min and held at 600.degree. C. for
10 minutes.
[0322] Step 4: Temperature lowered from 600.degree. C. to
25.degree. C. at 10.degree. C./min.
[0323] After firing the width and depth of the silver lines were
measured using surface profilometry and found to be 0.2" (5.1 mm)
wide and 15 .mu.m deep. The spacing between the lines was 1.0"
(25.4 mm).
Examples 4, 5, 6, 7, and Comparative Example 3C
[0324] The "TEC-Glass" products, commercially available from
Libby-Owens-Ford Co. (Toledo, Ohio), are manufactured by an on-line
chemical vapor deposition process. This process pyrolytically
deposits onto clear float glass a multi-layer thin film structure,
which includes a microscopically thin coating of fluorine-doped tin
oxide (having a fine grain uniform structure) with additional
undercoating thin film layers disposed between the fluorine-doped
tin oxide layer and the underlying glass substrate. This structure
inhibits reflected color and increases light transmittance. The
resulting "TEC-Glass"product is a non-iridescent glass structure
having a haze within the range of from about 0.1% to about 5%; a
sheet resistance within the range of from about 7 to about 1000
ohms per square or greater; a daylight transmission within the
range of from about 77% to about 87%; a solar transmission within
the range of from about 64% to about 80%; and an infrared
reflectance at a wavelength of about 10 .mu.m within the range of
from about 30% to about 87%.
[0325] A TEC 15 substrate (3 inch.times.3 inch; 7.5 cm.times.7.5
cm) was silk-screened with silver paste as described in Example 1,
where the length of the silver strip was incrementally varied in
such a manner as to leave an equal distance between edges, at right
angles to the strips, of the glass substrate as shown in FIG. 26B.
The distances of the silver strip from the edge for Examples 4, 5,
6, and 7 are 0.0 mm, 1.0 mm, 3.0 mm, and 7.0 mm respectively. The
resistance of the substrate was measured by soldering a metal strip
2 mm wide at both edges of the substrate which were at right angles
to the internal silver strips to serve as a representative portion
of a perimeter busbar. By applying a voltage across the soldered
strips the resistance was measured for different increments of
distance of the silver strip from the perimeter busbar. The results
are listed in the following Table 3.
8TABLE 3 Distance of Silver Strip Resistance of From Edge Substrate
Example (mm) (.OMEGA.) 4 0.0 0.1 5 1.0 1.2 6 3.0 1.9 7 7.0 3.2
[0326] The Comparative Example 3C, a TEC 15 substrate with no
internal silver busbars had a resistance of 15 .OMEGA.. By
comparison, as shown in the table, Example 4, the substrate with
internal silver strips extended fully to the perimeter busbars had
a resistance of 0.1.OMEGA.. Even in Example 7, with the silver
busbars as far as 7 mm from the perimeter busbar, the resistance is
decreased to 3.2 .OMEGA. from the Comparative Example's
15.OMEGA..
Example 8
[0327] Internal silver busbars were prepared as described in
example 3, except that after the four step firing procedure the
metal strips were over-coated with an epoxy based polymer for
passivation and cured at 120.degree. C. for one hour.
Comparative Example 4C
[0328] A 3".times.3" (7.5 cm.times.7.5 cm) TEC 15 substrate coated
with 380 nanometers of WO.sub.3 according to the method set forth
in U.S. Pat. Nos. 5,252,354, 5,457,218 and 5,277,986 and a counter
electrode of TEC 15 of similar size was made into a cell using an
epoxy seal containing 210.mu.m spacers. The two electrodes were
positioned so that they were slightly off-center exposing a region
at either end for application of a metallic busbar. Prior to
assembly the counter electrode had two holes drilled in it for
application of the electrolyte. The cell was filled with
electrolyte containing 0.01M LiClO.sub.4 and 0.05M ferrocene in a
60:40 volume % mixture of propylene carbonate and tetramethylene
sulfone and the fill holes plugged with epoxy. The conductive
surfaces which protruded from either side of the cell were
ultrasonically soldered with lead-tin-cadmium-based solder. Wires
were then attached to these contacts. The electrochromic
performance of the device was determined by placing the cell in a
spectrometer and following the color kinetics at 550 nm while
applying a coloring potential of 1.3 volts followed by a bleaching
potential of -0.3 volts. In the transmissive (bleached) state the
cell had a transmission of 77% and in the fully colored state a
transmission of 10% T. At a coloring potential of 1.3 volts the
cell took 46 seconds to color from 70% T to 10% T and 47 seconds to
bleach back to 70% T.
Examples 9, 10, 11 and Comparative Example 4C
[0329] Four electrochromic cells were prepared as described in
comparative Example 4C where the composition of the electrodes were
varied as follows;
[0330] Cell A, Comparative Example 4C, had conductive electrodes
with no internal busbars.
[0331] Cell B, Example 9, had internal busbars on the working
electrode (WO.sub.3) only.
[0332] Cell C, Example 10, had internal busbars on the counter
electrode only.
[0333] Cell D, Example 11, had internal busbars on the both
electrodes.
[0334] In all cases, Examples 9, 10, and 11, the internal busbars
were deposited as described in Example 8. The cells were colored at
1.3 volts for 90 seconds and bleached at -0.3 volts for 90 seconds.
The color kinetic data for the cells is shown in the following
Table 4:
9TABLE 4 Time to color from Time to bleach from 70% T to 10% T 10%
T to 70% T Cell Seconds Seconds Cell A 89 89 Cell B 74 65 Cell C 89
89 Cell D 56 58
Comparative Example 5C
[0335] An electrochromic cell was prepared as described in Example
8 with conductive electrodes which contained internal busbars
without a passivation layer. The cell was cycled at 70.degree. C.
at a color potential of 1.3 volts for 15 seconds, long enough to
colorize, followed by being bleached for 45 seconds at -0.3 volts.
After 5,000 such cycles the cell showed visible reaction of the
silver strips within the cell. This resulted in a degradation in
the cell's optical properties.
Example 12
[0336] An electrochromic cell was prepared as described in Example
8, containing internal silver busbars, on both electrodes, with a
protective epoxy overcoat. At a coloring potential of 1.3 volts the
cell colored from 70% T to 10% T in 8 seconds. The cell was cycled
at 70.degree. C. under a coloring potential of 1.3 volts for 15
seconds and a bleach potential of -0.3 volts for 45 seconds. After
5,000 cycles the cell showed no visible reaction of the internal
busbars in the cell nor degradation of the cell's electrochromic
performance.
Example 13
[0337] Silver strips were deposited onto TEC 15 as described in
example 3, and overcoated with a layer of indium tin oxide (ITO).
The ITO was deposited by electron beam (E-beam) evaporation and
deposited directly on top of the TEC 15 and the silver strip lines
through the use of a mask. The E-beam target was an indium tin
oxide composite and the thickness of the ITO layer thus formed was
500 nm. Two of these TEC 15 substrates having the described
electrodes were used to make an electrochromic cell as described in
example 9. Under a coloring potential of 1.3 volts the transmission
at 550 nm changed from 76% T to 8% T. It took 14 seconds to
modulate from 70% T to 10% T at 1.3 volts, while it took 23 seconds
to bleach back to 70% T at -0.3 volts.
Example 13B
[0338] Silver strips were deposited onto TEC 15 as described in
example 3, and overcoated with a layer of Sol-Gel derived antimony
doped tin oxide (ADT). The ADT precursor was prepared as described
in U.S. Pat. Nos. 5,525,624 and 5,457,218. The electrodes were made
into an electrochromic cell as described in example 9. At a
coloring potential of 1.3 volts the cell colored from 70% T to 10%
T in 19 seconds. At a potential of -0.3 volts it bleached back to
70% T in 20 seconds.
Example 14
[0339] Fodel materials and processes (from DuPont) and the like can
be used to deposit busbars which are less than 100 .mu.m in width.
These lines are practically invisible to the eye, depending on the
distance between the eye and the substrate on which the lines are
deposited. For example, a normal eye subtends a small enough angle
with lines of widths of 100 .mu.m from a distance of 19 inches that
the line is not discernible (about 0.01 degrees). Thus, any angle
equal to or smaller than 0.01 degrees can be considered as
invisible. Such busbar widths that form these angles, depending
upon the distance of the substrate from the observer, can be
utilized with little or no interference with vision. For example,
50 .mu.m wide lines (6 .mu.m thick) spaced at a distance of 0.75 cm
are expected to give the same overall conductivity to the
substrates as lines which are 100 .mu.m wide (6 .mu.m thick) and
spaced 1.5 cm. Both of these widths and line spacings are expected
to give photopic transmissions in excess of 70% when deposited on
conductive glass (such as TEC glass from LOF) with a resistance of
8 or more ohms/square.
[0340] Although the above description is for chromogenic windows,
these principles can also be utilized to develop non-chromogenic
windows which can be defrosted by applying an electrical voltage at
the edges but without any visible obstruction from conductors in
the center of the window. These windows can be used in various
applications where frost-free characteristics are desired. Examples
of such application are in aircraft and automotive windows and
mirrors. For an automotive windshield, these can be deposited on
glass before lamination. After lamination, preferably these lines
reside inside of the laminated area so that they are not scratched.
They can also be used for other windows and mirrors which are not
laminated, and to further enhance their scratch resistance they may
be coated with hard transparent materials (for example, see U.S.
patent application No. 09/099,035, filed Jun. 18, 1998, which is
incorporated herein by reference). Since high temperatures
(typically 500 to 800.degree. C.) are required to fire these lines,
this could be accomplished simultaneously while the glass is being
bent and/or strengthened (or tempered) which may be necessary for
these products. As described above, based on the angular
calculations, widths of these lines can be wider for rear
automotive windows as compared to the windshields, since the latter
are closer to the observer. Further, the material in these widths
can also be used to deposit antennas on glass (such as automotive
windows) which are invisible, i.e., the window appears transparent
although a patterned antenna is printed using these conductors and
processes.
Example 15 and Comparative Example 6C
[0341] Two 6".times.3" (15 cm.times.7.5 cm) sized electrochromic
cells were prepared. TEC 15 was used as the transparent conductor
in each cell. Example 15 had an internal busbar while Comparative
Example 6C did not. The cell without the busbar, Comparative
Example 6C, was assembled similarly to the assembly described in
Comparative Example 4C. The spacing between the substrates,
however, was 88 micrometers. The two electrodes were positioned
with an offset so that about 0.25 inch (0.63 cm) of each electrode
strip, at either of the 3" (7.5 cm) ends of the substrates, was
exposed. To these exposed edges, a solder was applied by a heated
ultrasonic soldering system (Sunbonder from Sanwa Components USA,
San Diego, Calif.). The solder used was Cerasolzer 186 (obtained
from Sanwa Components US), and had an average thickness of about 20
micrometers.
[0342] The second cell, Example 15, also had a gap 88 micrometers
thick and was made with both internal busbars and edge busbars as
taught in this invention. In Example 15, edge busbars and an
internal silver frit busbar were applied to three contiguous edges,
via an x-y dispensing technique, similar to that shown in FIG.
33A.
[0343] The frit layers were fired with the four-step procedure as
in Example 3 and then passivated as in Example 8 using a black
colored bisphenol A based epoxy adhesive. This frit/passivation
pattern was applied to both the substrates. The width of the frit
line was about 0.7 mm and thickness of the frit line was between 10
and 15 micrometers. The thickness of the passivation layer was
about 30 to 40 micrometers with a width of about 1.5 mm so as to
completely cover the frit to form an encapsulation around the frit.
One of the substrates was then coated with tungsten oxide,
assembled, and filled as described in the Comparative Example 4C.
The frit pattern was identical on both the substrates except that
the frit line pattern was lightly offset so that the frit lines on
the two substrates were next to each other rather than opposed or
on top of each other. This was done to ensure that any local bumps
would not lead to any electrical shorting and that the cell gap is
maintained at 88 micrometers.
[0344] Similar to that geometry shown in FIG. 33B, the internal
busbar was formed by one of the frit lines, while the other three
frits formed an edge busbar since they were outside the cell seal
area. Further, the soldered busbar which was applied in addition to
the frit busbar on the edge, reinforced the conductivity on that
edge, while providing a means to attach a soldered electrical lead.
The silver frit and the soldered busbar were touching each other in
this Example.
[0345] Example 15 and Comparative Example 6C were colored at 1.3
volts for 60 seconds and bleached at -0.3 volts for 60 seconds. The
plots of transmission versus time are shown in FIG. 34A, and the
concomitant current flow through the devices is shown in FIG. 34B.
In FIG. 33B, DuPont Frit type 7713 was used to form the frit
layers. It can be seen that in Comparative Example 6C, the cell
without the internal busbar, the coloring reaction is slow and the
depth of color is small. By contrast, in the cell with the internal
busbar, Example 15, the coloring and bleaching reactions are faster
and the depth of coloration is much higher because the internal
busbars are able to supply much higher levels of current when
needed during coloration and bleaching. Thus, devices that demand
high currents any time during coloration or bleaching will
particularly benefit from this invention. Typically, EC devices
requiring currents in excess of 0.1 mA during coloration or
bleaching will benefit most.
[0346] Intermittent Potential Circuitry
[0347] As described previously, the coloring voltage only needs to
be applied intermittently, depending on the length of the color
state memory, after sufficient coloration has been achieved. For
example, if the memory of the device was longer than the color
duration required for the particular application to be colored,
then the coloring potential effectively could be applied just once
and then turned off (i.e., the device is left in non-powered open
circuit mode). The potential can then be applied again when the
device's light transmission needs to change, e.g., while bleaching
or changing its transmission to a different desired level. However,
under certain circumstances, it might be necessary to keep the
device in a desired state of transmission for periods that are
longer than their color state memory.
[0348] In the present invention, consider for example the case
where a coloring potential is initially applied which is removed
after the device attains the desired color, i.e., the device is
kept in an open circuit. The device is thus allowed to gradually
bleach with time, for a period t.sub.1, as a result of its limited
color state memory. Before the device completely bleaches, the
coloration potential is reapplied for a duration of time t.sub.2.
This process can be continued indefinitely for as long as the
device needs to be kept in the particular colored state before a
different voltage is required to be applied to change the device's
light transmission (e.g. bleach potential).
[0349] The period t.sub.1, after which the coloration voltage is
re-applied, depends in part on the extent of color change that is
allowed before it might become obvious to the user that the device
light transmission is changing. This allowable change in photopic
transmission, all measured at 550 nm, for a window in a building or
a car (e.g., a sunroof) is preferably in the range of from about
(the difference (T.sub.c1%-T.sub.c2%), as in FIG. 35) 0.1% to about
20%, more preferably from about 1% to about 15%, and most
preferably from about 5% to about 10% from the desired colored
state. The above transmission criteria can also be used where the
devices only color in the near infrared region, about 0.7 .mu.m to
about 2.5 .mu.m. The change in light transmission can be solar
transmission instead of photopic transmission. Furthermore, the
light transmission wavelength can be selected in any conveniently
selected range.
[0350] The process of this invention is explained referring to FIG.
35, where transmission vs. time and applied voltage vs. time is
plotted for a typical EC device controlled by the present
invention. A voltage V.sub.c is first applied to colored the window
(as shown by the transmission T % falling, indicating that the
light transmission is low). The voltage is then removed, as shown
by a break in the voltage line, for a period of t.sub.1. During
this time t.sub.1, the cell starts to bleach, as shown by the
transmission T % rising. The time ti is related to the length of
the color state memory for a particular EC device. To keep a window
colored (after initial coloration), the coloring potential is
reapplied for a period of t.sub.2 followed by the removal of power
(holding period) for a period of t.sub.1. This alternating sequence
is continued indefinitely, for as long as it is desired to keep the
device in that desired state of transmission. The desired state is
a range of transmission defined by T.sub.c1% and T.sub.c2 %. In
this case, the total time t.sub.C is the overall time of
coloration.
[0351] FIG. 35 also shows that the initial coloring voltage can be
applied as an increasing linear ramp to a maximum potential
V.sub.c. Alternatively, a step potential V.sub.c can be applied.
Another way to apply the potential is by imposing a maximum curent
limitation. Either of these two modes, or a non-linear ramp, could
be conveniently used. With increasing device area, it may be
preferred to ramp the coloring and bleach potential so that the
current densities at the edges can be lower. This also promotes a
spatial uniformity in color change during coloration and bleaching.
This is particularly noticeable as the device area increases. Also
during the interval t.sub.2, the coloration potential (V.sub.c)
could be applied as a step potential (as shown), or it may be
ramped from the open circuit potential of the device to V.sub.c. It
must be noted that V.sub.c or V.sub.b referes to the potential
which the power supply attempts to apply to the EC cell and is also
the limiting potential on the EC cell. Hence the EC cell has
charateristics of an (RC) circuit, the potential of the cell
(V.sub.cell) only changes slowly as shown by the dashed line in
FIG. 35.
[0352] One of the more important variables that affects t.sub.1 and
t.sub.2 is the device temperature. As an example, depending on the
EC device and the components used, t.sub.1 at -20.degree. C. could
range from a few hours to several days or even months, while
t.sub.1 at 70.degree. C. could change to range from about 1 to
about 15 minutes. Similarly, t.sub.2 at -20.degree. C. could range
from about 1 to about 60 minutes, while changing to range at
70.degree. C. from a fraction of a minute to about 10 minutes.
Further, the change in these times might not be linear with
temperature.
[0353] It is understood that for certain situations, t.sub.1 and
t.sub.2 can be fixed as in the prior art; but in this invention
these time intervals can be allowed to change as discussed above,
unlike the prior art.
[0354] FIG. 35 also shows that even the bleach time (tB) could
depend on the device temperature or/and on the total time the
device was kept in the colored state (t.sub.c) prior to initiating
the bleach.
[0355] Typically both t.sub.1 and t.sub.2 decrease with increasing
temperature. Thus, incorporation of a temperature sensor which
provides a feedback into the control circuit could be used for this
purpose. The temperature sensor may be any convenient sensor such
as, for example, a thermistor, a RTD thermocouple, a transistor, or
a diode, the output from which can be used to determine t.sub.1 and
t.sub.2.
[0356] For example, referring to FIG. 36A, in the case where a
timer is used to provide the t.sub.1 and t.sub.2 circuit functions,
the thermistor would preferably be a negative thermal coefficient
(NTC) thermistor. When the temperature increases, the resistance of
the NTC thermistor would decrease and the resulting RC product (R
is resistance, and C is capacitance) connected to the LM 556
(National Semiconductor, Santa Barbra, Calif.) timer would also
decrease leading to smaller t.sub.1 and t.sub.2. The drop in
resistance in the NTC thermistor with temperature would be
correlated with the transmission changes during t.sub.1 and t.sub.2
periods of the EC device.
[0357] Preferably, the temperature coefficient of the thermistor
and the capacitor in the circuit should be chosen so that the
change in RC would naturally mimic the desired change trends needed
for t.sub.1 and t.sub.2. One may even employ two thermistors in
conjunction with two capacitors respectively, where the parameters
of one set of resistors/capacitors are tailored to correspond with
the changes in t.sub.1 and the other set of resistors/capacitors
corresponds with the changes in t.sub.2.
[0358] In a variable coloration device, t.sub.1 and t.sub.2 will
depend on the depth of coloration. For example, in the open circuit
mode the transmission change for a deeper colored state may be
faster (thus requiring a shorter t.sub.1) than for a shallower
colored state. Similarly, it may take more time to achieve a darker
state (thus requiring a longer t.sub.2) Since the depth of
coloration is typically related to the potential used for
coloration, one could define and store in the control circuit a
profile of t.sub.1 and t.sub.2 values that are calibrated with the
applied coloration voltage.
[0359] As the device ages, t.sub.1 and t.sub.2 may also shift.
Account could be kept of the number of cycles, time spent in a
particular state of transmission or any other convenient method
which keeps a track of the age and usage of the cell. An aging
profile with varying t.sub.1 and t.sub.2 could be used to drive the
cell and if needed, the potential can also be varied and controlled
to keep the initial level of coloration. Such control can be by any
convenient method such as, for example, the use of monitoring
sensors and feedback processes.
[0360] In another aspect of this invention, no prescribed periods
are used but rather the actual level of coloration is sensed
through the EC cell. In this case where one or more photosensors
are used, the degree of color change can be detected by the
photosensor and once the coloration has changed to a predetermined
level, the necessary voltage can be applied to recolor the EC cell
back to its original depth. Use of the photosensor can also
eliminate any need to pre-program values of or factors to calculate
t.sub.1 and t.sub.2 with aging, temperature or coloration
voltage.
[0361] Photosensors, e.g., CdS photoconductors on Si photodiodes,
can be used to provide feedback signals for controlling t.sub.1 and
t.sub.2 instead of presetting fixed values for t.sub.1 and t.sub.2.
In this case, the photosensor(s) would monitor the transmission of
the EC cell and actively signal the circuitry as to the appropriate
times to remove and to apply the voltage. As coloration rates and
bleach rates change with temperature, aging, and other factors,
t.sub.1 and t.sub.2 are adjusted accordingly. Preferably a pair of
photosensors are used. One photosensor is placed on top of the cell
to obtain the baseline for incoming light while another is placed
underneath the cell to collect the transmitted light. The
electrical signals from these two photosensors are then connected
to a differential amplifier, the output of which is proportional to
the relative transmission through the cell. Depending on the sensed
output, the cell will be subjected to open circuit (holding period
t.sub.1) or voltage application (period t.sub.2).
[0362] Further, as the cell ages thereby affecting its coloring and
bleaching kinetics, the depth of coloration can still be maintained
since t.sub.1 and t.sub.2 will change due to the feedback provided
by the photosensors. For example if the coloration rate of the cell
slows down, both t.sub.1 and t.sub.2 will increase to maintain a
pre-determined differential output from the photosensors for
identical illumination conditions. Also, if t.sub.1 and t.sub.2
become longer than pre-determined "acceptable periods", then the
circuit may be configured to increase the coloration potential
(subject to a maximum safe-potential for the devices) to increase
the coloration speed.
[0363] Another method monitors the current (I) or the rate of
change in current injected with time (t), i.e. dI/dt. Once dI/dt
reaches a prescribed low value, the coloring potential is
removed.
[0364] The transmission change during the holding period (t.sub.1)
can also be correlated to the open circuit potential change between
the two cell electrodes. During the holding period (tl), the
potential between the two opposing electrodes of the EC cell
(V.sub.cell) will also decrease. Once a predetermined change in
this voltage (.DELTA.V) is reached, a coloring voltage can be then
applied to recolor the EC device. The time period t.sub.2 can be
determined by checking the current being injected into the cell.
For example, as shown in FIG. 34B, for a constant voltage the rate
of change of the current decreases with time and reaches a limiting
value. Thus, when the change in the current with time becomes
smaller than a predetermined level, the coloring voltage can be
removed.
[0365] Alternatively instead of monitoring dI/dt, just the current
(I) could be measured. Once the absolute value of the current is
below a predetermined limit the coloring voltage is removed. As
described earlier, this method also self compensates for any
changes in cell kinetics, caused by aging, by increasing time
periods t.sub.1 and t.sub.2 during the coloration period. When
these time periods become longer than pre-determined "acceptable
periods", the circuit if desired may be configured to increase the
coloration potential (subject to a maximum safe potential for the
devices) in order to increase the coloration speed.
[0366] Alternatively, the charge injected during coloration can be
monitored by a charge integration circuit. Once a predetermined
charge has been injected, the coloration voltage can be removed.
For many EC devices, the charge passed into the device for a
desired level of coloration may depend on temperature. One method
to take into account where this charge will increase with
temperature is to have a comparator with a thermistor-containing
reference. All of the control parameters which determine t.sub.1
and t.sub.2 such as T.sub.c1%, (T.sub.c1%-T.sub.c2%), .DELTA.V, I,
and dI/dt may be fixed and/or varied with temperature and/or aging
of the device. One may also determined t.sub.1 or t.sub.1 by
measuring the voltage at the EC cell V.sub.cell and comparing this
with the V.sub.C or V.sub.B. During coloration V.sub.cell
asymptotically approaches V.sub.c. When V.sub.cell is within 5%
(preferable 1%) of V.sub.c, the coloring potential V.sub.c is
removed to let the cell rest in open circuit conditions.
Alternatively, V.sub.c could be continued to be applied for an
additional fixed time after the above condition is met to allow the
cell to reach equilibrium. The total coloration time (t.sub.1 or
t.sub.2) are obtained by adding the time for coloration during
which V.sub.cell approaches V.sub.c and the fixed duration
described above. During the open circuit mode (e.g., in coloration)
the potential of the cell (V.sub.cell) is measured and when it
drops to about 3 to 30% of V.sub.c (preferably 10 to 15% of
v.sub.c) the coloring voltage V.sub.c is re-applied. Schematically
an electric circuit showing V.sub.cell and V.sub.c (or V.sub.B) is
shown in FIG. 45.
[0367] In addition to varying t.sub.1 and t.sub.2 with temperature,
the coloring and bleaching voltages may also be varied with
temperature if desired. For example, depending on the devices,
higher voltages may be used at lower temperature or vice-versa.
Additionally, with temperature feedback to the control circuities,
both the duration (i.e., t.sub.1 and t.sub.2) and the voltage can
be varied simultaneously to further mitigate electrical or
electrochemical stress on the EC cell.
[0368] The voltage can be made temperature dependent by having a
thermistor-containing voltage reference in the power supply. This
thermistor can be a NTC (negative thermal coefficient) or a PTC
(positive thermal coefficient) type. As the temperature rises the
resistance will be lower in NTC thermistors. Consequently, when
incorporated with suitably-biased series resistors and an
operational amplifier (op amp), the reference voltage to the
error-sensing op amp will be lower as temperature increases,
resulting in a lower voltage applied to the EC cell at higher
temperatures.
[0369] An example of a circuit incorporating an NTC thermistor TM1
and an op amp OP1 is shown in FIG. 39. As the temperature
increases, the resistance of the TM1 will be lower, resulting in a
reference voltage from PS2 to OP1 to be lower. Thus, output voltage
V.sub.OUT will be lower. Accordingly, a properly designed resistor
stack with a combination of series and/or parallel resistors
incorporating such thermistors would cause the voltage needed
(V.sub.OUT) to track with operating temperature. In a particular
example, the values of each component were: PS1 was 12 VDC, R1 and
R2 were 10K .OMEGA. each, C1 was 10 .mu.F, PS2 was 2.5 VDC, OP1 was
a LM324 op amp available from National Semiconductor, Santa Clara,
Calif., TM1 was an NTC Thermistor having a resistance of 1.76 kg at
50.degree. C., and the output voltage was 1.35 V.
[0370] A PTC thermistor TM2 can also be used in a circuit to change
the output voltage with temperature, an example of which is shown
in FIG. 40. In a particular example, the values of each component
were similar to that example above, PS3 was 12 VDC, R3 and R4 were
10K .OMEGA. each, C2 was 10 .mu.F, PS4 was 2.5 VDC, OP2 was a LM324
op amp, TM1 was an PTC Thermistor having a resistance of 1.76k
.OMEGA. at 5.degree. C. , and the output voltage was 1.15
volts.
[0371] Additionally, the thermistor can also be used in a
comparator circuit to trigger the microprocessor to use different
t.sub.1, and t.sub.2 periods, for example, as shown in FIG. 41. In
the example, the thermistor TM3 used was a NTC Digikey part # PNT
117-ND available from Panasonic, Cupertino, Calif., with a
resistance of 1.76K .OMEGA. at 50.degree. C. The potentiometer
resistor R5 in series with the thermistor was adjusted to match the
thermistor's set value, i.e. 1.76K .OMEGA.. PS5 was 12 VDC, R6 and
R7 were each 15K .OMEGA., and the op amp was an LM324 op amp
available from National Semiconductor. As a result, the voltage
drop across R6 and R7 (Vcc) is 5.0 V. The positive input of the op
amp is fixed at 2.5 V by the two 15K .OMEGA. series resistors R6
and R7. At temperatures lower than 50.degree. C., the TM3
resistance is higher than 1.76K .OMEGA. resulting in a voltage of
higher than 1/2 of Vcc (that is, 2.5 V) to the negative input of
the LM324 op amp. Since the negative input is higher than the
positive input there is no output from the op amp at such lower
temperatures. When the temperature climbs to 50.degree. C. and
above, the resistance in the thermistor drops below 1.76K .OMEGA.,
thereby lowering the voltage below 2.5 V and resulting in a
positive output signal from the op amp that can be routed to a
microprocessor input port. The microprocessor can then change the
t.sub.1, and t.sub.2 periods in response to the positive output
signal.
[0372] Based on this circuit, the output of the op amp will be
turned on at the threshold temperature; however near the region of
this threshold there may be thermal fluctuations which may cause
the output to erratically turn on and off. In order to eliminate
such erratic behavior, a positive hysteresis can be added to the op
amp comparator using positive feedback. As shown in FIG. 42, a
feedback loop can be formed by resistor R12, resulting in a Schmitt
trigger. In the example, the values of the components were those of
the corresponding components in FIG. 41, with the added resistors
R11 being 10K .OMEGA. and R12 being 1K .OMEGA..
[0373] With such a Schmitt trigger in the circuit, the low trigger
threshold is different from the high trigger threshold (the
difference being the hysteresis intentionally induced in the
comparator, rather than a single threshold value as in a
conventional comparator). Such Schmitt triggers can also be used in
photosensors to detect daylight--it is well known that around the
region of daylight threshold, e.g., during dusk and dawn,
photocells can behave erratically. Having positive hysteresis in
the op amp comparator will aid in obtaining a smooth output.
Furthermore, Schmitt triggers can be used in EC skylight circuits
where both photosensors and temperature sensors are employed.
[0374] FIG. 43 shows an example of an implementation of an
adjustable voltage power supply where the output voltage supplied
to the electrochromic panel ECU1 can be tuned to give two different
output voltages depending on the transistor switch T4 which will be
activated when there is a predefined temperature change. In a
particular example, PS7 was 12 VDC, PS8 was 2.5 VDC, R14 and R13
were each 10K .OMEGA., R15 and R16 were each 1K .OMEGA., R17 was 4K
.OMEGA., and C3 was 10 .mu.F. The transistors T3 and T4, and the op
amp were those described above. The trigger to the base of T4 can
come from either a microprocessor port as shown in FIG. 43, or the
comparator output from a circuit as shown in FIG. 41 or 42. Upon
turning on of transistor T4, the resistor R15 will be in parallel
with the reference resistor R14 resulting in a lower overall
resistance and hence lower reference voltage to the error-sensing
op amp. The output voltage will also be lower. Alternatively, such
output voltage can change to vary the EC color voltage below full
coloration, e.g., during half color.
[0375] The EC power supply can also incorporate current limitation,
e.g., using simple transistor switching or current holdback
techniques. The addition of a sensing resistor in series with the
power output, together with another transistor as shown in FIG. 44,
can limit the maximum current flowing in the circuit by the
judicious choice of the sensing resistor R20 value. This sensing
resistor can be fixed for constant maximum current or made variable
for variable current limiting in the circuit. In a particular
example, PS9 was 12 VDC, PS10 was 2.5 VDC, R18 and R19 were 10K
.OMEGA., TM4 was an NTC thermistor having a resistance of 1.76K
.OMEGA. at 50.degree. C., Op Amp OP6 was an LM324, T5 and T6 were
2N3904 transistors described above, and C4 was 10 .mu.F. With
sensing resistor R20 having a resistance of 1K .OMEGA. (V.sub.BE of
T6 is 0.7 volts), the voltage output V.sub.OUT was 1.35 volts, and
was limited to a current I.sub.OUT of 0.7 mA.
[0376] A particular benefit of this current limiting is in the case
of an electrical short--the circuit will allow only the maximum
limited current to flow through rather than a potentially damaging
high current, thus offering protection.
[0377] In some devices, the variation in t.sub.1 may be much more
strongly dependent on temperature than t.sub.2 (e.g., see device #1
and 2 in Table 5 below). In such cases the powering circuit could
be simplified so that only t.sub.1 varies with temperature and
t.sub.2 is fixed in duration.
[0378] In all the examples above it is assumed that the coloration
and bleaching are controlled by applying a pre-specified maximum
potential and that this potential can be a step, ramp, non-linear,
etc. In another method the power supply can be configured so that
it applies a pre-specified current for coloring and bleaching,
subject to a maximum safe-potential. This means that the applied
potential from the power supply will vary with time (to compensate
for changes in impedance, for example).
[0379] In coloration, as an example, a controlled current source
could be used. The current is reduced, or the current source is
removed, as the maximum safe-potential is reached. Thus, when a
pre-specified potential between the cell electrodes is reached, the
power source is removed. A current limit for coloring (or
bleaching) for non-internal busbar cells is typically chosen
between 50 to 5000 .mu.A/cm.sup.2 of active area of the EC cell,
more preferably between 100 and 1000 .mu.A/cm.sup.2. For cells with
internal busbars current limit (if imposed) can exceed the upper
limit of this range to insure that time to color and bleach is
rapid.
[0380] In all cases where the temperature is being measured, it is
important that the temperature measuring or sensing elements such
as thermistors, ferroelectric capacitors, thermocouples, or other
such temperature measuring means, are mounted in such a way that
they sense or measure temperatures that are similar to the
temperature of the EC cells. That is, the measured temperature must
have a corresponding relation to the temperature of the EC cell.
For example, the measuring means could be mounted on a cell
surface, on a cell edge, or at a position proximate to the cell so
that the temperature of the cell and the temperature of the sensing
element are similar. In some cases it may be preferred to mount the
thermistor so that it is hidden from the direct view of the user.
Adhesives with high thermal conductivity may be used for mounting
so that the sensing elements are close in temperatures to the
substrates they are mounted on.
[0381] In other examples where the EC cell is large, or where the
sensing element controls multiple EC cells, it is apparent that the
sensing element should measure a temperature that is relevant to
the temperature of the large EC cell or of the multiple EC cells.
Such relevant temperature would be, for example, an average
temperature across the large EC cell or the multiple EC cells. In
other cases, the peak or low temperature might be relevant.
Accordingly, the sensing element should be positioned so that such
a relevant temperature is sensed or measured.
[0382] The above descriptions of determining t.sub.2 may also be
used for determining and/or controlling t.sub.1. The time period
t.sub.b may be fixed or could be varied.
[0383] The Examples which follow are intended as an illustration of
certain preferred embodiments of the invention, and no limitation
of the invention is implied.
Example 16
With Thermistor and/or Ferroelectric Capacitor
[0384] Referring to FIG. 36A, the EC control circuit was designed
to incorporate the intermittent powering of the EC cell E1, as
described above. In this example, the coloring and bleach
potentials were fixed at 1.2 V and -0.3 V respectively, while
t.sub.1 and t.sub.2 were allowed to vary with temperature.
[0385] The system can utilize any convenient voltage as would be
apparent to one of ordinary skill in the art. In this case, for
example, 12 V DC is used. The voltage can be supplied from any
convenient source such as, for example, from a car battery or from
a transformer that steps down 110 V AC to 12 V DC. The circuit uses
a LM 556 dual timer (National Semiconductor, Santa Clara, Calif.),
which includes an astable timer U1/A and a monostable single shot
timer U1/B, to control the timed cycles for the EC device.
[0386] Astable timer U1/A includes an RC circuit comprised of
resistors R2, R3, and capacitor C1. This astable timer provides the
holding and voltage application periods. The periods for t.sub.1
and t.sub.2 are obtained by using the formula
t.sub.1=0.693(R3+R2)C1 and t.sub.2=0.693(R2)C1. The output of timer
U1/A drives a transistor Q1 which then further drives a transistor
Q2. Transistor Q2 activates the relay K1:A which upon closing
applies the coloring potential from the 1.2 V voltage source.
[0387] A pair of diodes D1 and D2 isolate the outputs of U1/A and
U1/B from each other. Astable timer U1/A is cycling constantly but
its output is only applied to electrochromic cell E1 when switch S3
is in the color position after an initial time period, for example,
200 sec from U1/B.
[0388] Resistors R2 and R3 may each be replaced with a NTC
thermistors, e.g., model DC95-& 104Z available from
Thermometrics, Edison, N.J., to allow for t.sub.1 and t.sub.2
compensation at electrochromic cell E1. For example, the cycling
conditions of a particular EC device at 25.degree. C. are
t.sub.1=138 sec, t.sub.2=69 sec. These times are obtained with
thermistor R2 and R3 values of 100K .OMEGA. and C1 of 1 mF. Using
the thermistors described, the resistance increases to 1 M .OMEGA.
at -25.degree. C. and decreases to 23K .OMEGA. at 65.degree. C.,
resulting in t.sub.1=1444 sec and t.sub.2=722 sec at -25.degree.
C., and t.sub.1=32 sec and t.sub.2=16 sec at 65.degree. C.,
respectively.
[0389] Monostable single shot timer U1/B provides the initial
duration--in this case, for example, 200 sec, of coloring or
bleaching potential. The duration for the initial color (t.sub.1)
or bleach (t.sub.b) is calculated according to the formula t=R3*C4.
The values are calculated, in this example, to yield the 200 sec
duration to initially color or bleach the cell and is triggered by
switch S1. The output from switch S1 drives transistors Q2 and Q3.
Resistor R6 can be replaced with an NTC thermistor to obtain longer
and shorter initial bleaching (or coloring) periods,
respectively.
[0390] The potential which is applied to electrochromic cell E1
depends on the position of switch S3, which the user selects. If
switch S3 is in the coloring position, astable timer U1/A takes
over after the initial 200 sec coloring cycle and then
electrochromic cell E1 is cycled intermittently by astable timer
U1/A to maintain coloration. Astable timer U1/A is never applied
while switch S3 is in the bleaching position.
[0391] Alternatively, ferroelectric-capacitors having a Curie
point, T.sub.c, for example, below -45.degree. C., based on
SrTiO.sub.3-- containing compositions, can also be used in the
timer circuit to provide temperature sensitive capacitors. In these
capacitors, the capacitance declines with increasing temperature.
Accordingly, such capacitors can be used to cause the periods of
t.sub.1 and t.sub.2 to be changed along non-linearly with
temperature changes, such as to cause even longer periods at lower
temperatures and shorter periods at higher temperatures.
Furthermore, a combination of thermistors and ferroelectric
capacitors can be used simultaneously to obtain the RC product
necessary to change t.sub.1 and t.sub.2 according to
temperature.
[0392] A microcontroller can also be used to obtain t.sub.1 and
t.sub.2 functionalities in the control circuities using built-in
timer modes thus negating the use of any external timer chips such
as LM555 or LM556. Examples of such microcontrollers are PIC16F84
from Microchip (Chandler, Ariz.), MC68HC11E9 from Motorola (Tempe,
Ariz.), and Z-80 from Zilog (Campbell, Calif.). Temperature sensors
can be connected to the microcontroller to change t.sub.1 and
t.sub.2 accordingly. Flash memory or EEPROM can further be utilized
in conjunction with the microcontroller to store information on the
temperature dependence, electrical history and aging properties of
the EC cell. This information will then be used as feedback to
optimize the cell bleaching and coloring characteristics. These may
include changes to V.sub.c, V.sub.b, T.sub.cl%, T.sub.c2%, t.sub.1,
t.sub.1, t.sub.2 and t.sub.b.
[0393] In a particular example, a Microchip microcontroller
PIC16F84 as shown in FIG. 36B was used (in place of the LM556 dual
timers of FIG. 36A) in a circuit similar to that shown in FIG. 36A.
The EC cell was configured so that it could only be colored during
the day time by using a CdS photocell sensor to determine whether
it is daytime or nighttime. At night, the EC coloring function was
disabled. Upon coloring, a coloring potential of 1.2 V from the
power supply would be applied to the cell for 3 minutes. Following
this initial coloring potential, the specific t.sub.1 and t.sub.2
intermittence functionality (for example, 45 sec turn off and 15
sec turn on of the coloring potential) was also written into the
program. Upon bleaching, a -0.3 V would be applied to the cell for
3 minutes. During the coloring or bleaching process, the output pin
would be enabled turning on the relay or semiconductor switches to
power the EC cell directly from the coloring or bleaching power
supplies. The firmware was programmed into the microcontroller
using a PicStart Plus Programmer. A thermistor suitably mounted on
the EC cell can also be connected to one of the I/O ports in the
P1C16F84. The change in resistance of the thermistor is then
correlated to temperature of the EC cell. Depending on the
temperature measured, the coloring and bleaching potentials,
t.sub.1 and t.sub.2 characteristics can then be controlled.
Microcontrollers can also be used to control the powering method of
the EC cells during coloring and bleaching. This includes specific
potential ramps, constant current control, or potential increases
and decreases in multiple discrete steps.
Example 17
Change in t.sub.1 and t.sub.2 With Temperature of Electrochromic
Devices
[0394] Various electrochromic devices, 3 in.times.3 in, were
fabricated using 12 ohms/square ITO as the conductive substrates.
The tungsten oxide coating deposition methods and device
fabrication processes used in these EC devices were similar to the
methods and processes described in copending U.S. patent
application Ser. No. 09/155,601 (incorporated by reference herein)
which also describes the use of and methods to fabricate Selective
Ion Transport Layers (SITL). The EC devices were made both with
SITL layers and without SITL layers. The electrolyte consisted of
at least one solvent, one dissociable salt and at least one redox
promoter. Polymeric viscosity modifiers and UV stabilizers and
water were also added.
[0395] Although any of the solvents described in copending U.S.
patent application Ser. No. 09/155,601, could be used, although
carbonates, sulfolanes, glymes, and their mixtures are preferred.
Examples of suitable carbonates are propylene carbonate, ethylene
carbonate, ethyl propyl carbonate, isopropyl ethyl carbonate,
diethyl carbonate, methyl propyl carbonate, isopropyl methyl
carbonate, ethyl methyl carbonate, dimethyl carbonate, butylene
carbonate and other alkyl carbonates. Examples of some other
suitable solvents are alkyl sulfones, tetraglyme, toluene, xylene,
decaline and other aliphatic and aromatic alkyls with or without
substituted polar groups.
[0396] Dissociable salts were typically based on alkali metal
cations, such as lithium, sodium, and potassium. Some examples of
suitable anions are perchlorate, tetrafluoroborate, triflate, etc.,
as described in copending U.S. patent application Ser. No.
09/155,601, which lists other suitable salts.
[0397] When tungsten oxide, molybdenum oxide and other cathodic
oxides and their mixtures were used as chromogenic layers, the
redox promoters used in the devices were typically based on
ferrocene and its derivatives. Substituted ferrocenes with electron
donating groups attached on the cyclopentadiene rings of the
ferrocenes are a preferred sub-class in ferrocenes. These groups
can be substituted to any of the cyclopentadiene rings. Further,
the substituted groups may be the same or different on each of the
rings. Such groups include methyl, propyl, n-butyl, tertiary butyl,
etc. Examples of such ferrocenes include decamethyl ferrocene,
octamethyl ferrocene, tertiary butyl ferrocene, interannual
substituted ferrocenes such as 1-1'-(propane-1,3-diyl) ferrocene,
1,1':3,3'-bis(propane-1,3-diyl) ferrocene,
1,1':2,2':4,4'-tri(propane-1,3- -diyl) ferrocene. Another preferred
sub-class of ferrocenes are biferrocenes and bridge ferrocenes,
where in the latter, the cyclopentadiene rings of different
ferrocene molecules are chemically bonded to each other. Examples
of these include 2,2-bis(tert-butylferroce- nyl)propane,
2,2-bis(ethyl ferrocenyl)propane, etc. Further, the selection of
the ferrocene will also influence the extent of the back reaction
with other ingredients, components and device construction details
remaining the same.
[0398] Typically, inclusion of polymers that are soluble in the
electrolyte will result in increased viscosity and accordingly such
polymers can be used as viscosity modifiers.
[0399] The size of such crystals should typically be smaller than
about 0.5 .mu.m, preferably less than 0.2 .mu.m so that they do not
create haziness in optically clear systems. Some preferred polymers
are polymethyl methacrylate, polyvinyl chloride, polyvinyl chloride
and polyvinyl acetate copolymers, polyvinyl butyral,
polyacrylonitrile and its copolymers, polyvinylidene fluoride,
copolymers of polyvinylidene fluoride and hexafluoropropylene. The
last two are available from Elf Atochem North American
(Philadelphia, Pa.) under the trade names of Kynar and Kynar flex
respectively.
[0400] In one of the samples the electrolyte was processed using a
sol-gel technique to form a solid. The solid resulted from the
formation of "Si--O--Si" cross-linkages in-situ after filling the
EC cell with a electrolyte precursor. This is also described
below.
[0401] The selection and the concentration of the ingredients
described above will influence the extent of the back reaction
while other components and device construction details remain the
same. The back reaction will change with temperature and this will
cause change in t.sub.1 and t.sub.2.
[0402] As shown in Table 5 below, the presence and absence of a
SITL layer, the type of SITL layer, and any changes in the
electrolyte have considerable influence on t.sub.1 and t.sub.2.
Polyceram SITL layer formation by sol-gel processing is described
below. Polystyrene-sodium-sulfonate (PSSNa) SITL layer was
processed by dip-coating the tungsten oxide coated substrates with
a 540,000 mol. wt. PSSNa solution (5% by weight/vol) in a 50/50
mixture (by volume) of distilled water and reagent grade ethanol
and 0.01% of a surfactant, Triton X-100 available from Aldrich
Chemical Co. (Milwaukee, Wis.).
[0403] The devices were colored by applying 1.2 V. The values of
T.sub.c1% and T.sub.c2% (FIG. 35) were 10% and 15% respectively.
The leakage current was measured as the current consumed after
applying the coloring potential for 15 minutes. The table also
shows that when ferrocene has bulky constituents, such as in the
compound 2,2-bis(ethyl ferrocyl)propane, a lower leakage current is
obtained. For example, compare the leakage current of device 1 to
that of device 2, and the leakage current of device 5 to that of
device 6.
[0404] The various electrolyte compositions were:
[0405] electrolyte A: 85% Propylene carbonate, 0.8% 2,2-bis(ethyl
ferrocenyl)propane, 0.4% LiClO.sub.4, 9.4% PMMA, 3.6% UV400, and
0.1% water (all percenntages by weight).
[0406] Elecrolyte B: 85.2% Propylene carboate, 0.7% ferrocene, 0.4%
LiClO.sub.4, 9.5% PMMA, 3.6% UV400 and 0.7% water (all percentages
by weight).
[0407] Electrolyte C: 53.6% Propylene Carbonate, 35.7% Sulfolane,
8.4% Poly(methy methacrylate), 1.0% Deionized water, 0.8%
Ferrocene, 0.5% Lithium perchlorate (all percentages by
weight).
10TABLE 5 De- Type of Leakage vice Electrolyte SITL SITL Temp.
t.sub.2 current # composition Layer layer .degree. C. t.sub.1 (s)
(s) (.mu.A/cm.sup.2) 1 Electrolyte C No 25 30 20 210 50 20 20 370
70 15 20 530 2 Electrolyte A No 25 61 6 126 50 31 4 268 70 24 4 392
3 See forma- No 25.sup.a 7 31 29 tion of sol- gel electro- lyte
below this table 50.sup.b 5 15 87 70.sup.c 2 12 151 4 Electrolyte B
Yes Poly- 25 1079 14.4 6.4 ceram-2 50 431 7.2 31.5 70 184 5.8 90.0
5 Electrolyte B Yes Poly- 25 590 24 10 ceram-1 50 145 8 47 70 64 6
136 6 Electrolyte A Yes Poly- 25 2749 10.2 4.8 ceram-1 50 1272 6 13
70 785 4 26.7 7 Electrolyte C Yes PSSNa 25 3600 25 3.3 70 900 7
14.5 .sup.aT.sub.c1% and T.sub.c2% were 18.8% and 23.8%
respectively .sup.bT.sub.c1% and T.sub.c2% were 23.3% and 28.3%
respectively .sup.cT.sub.c1% and T.sub.c2% were 30% and 35%
respectively
[0408] Example: Formation and processing of Polyceram-1 SITL Layer
(CH.sub.3(OCH.sub.2CH.sub.2).sub.nOCONH(CH.sub.2).sub.3Si(OC.sub.2H.sub.5-
).sub.3/Si(OCH.sub.3).sub.4, overcoated on WO.sub.3 electrode)
[0409] Polyceram layer was processed as described in the examples
given below. Polyceram layer was made in the same way but the ratio
of ingredients was modified. The weight ratio of
(CH.sub.3(OCH.sub.2CH.sub.2-
).sub.nOCONH(CH.sub.2).sub.3Si(OC.sub.2H.sub.5).sub.3 to
Si(OCH.sub.3).sub.4 was 1:0.51 in the case of Polyceram-1 but
1:1.02 in the case of Polyceram-2.
[0410] 75.00 g of poly(ethylene glycol) methyl ether,
CH.sub.3(OCH.sub.2CH.sub.2).sub.nOH (number average MW=ca. 350,
obtained from Aldrich Chemical Co., Milwaukee, Wis.), 58.31 g of
3-(triethoxysilyl) propylisocyanate,
(C.sub.2H.sub.5O).sub.3Si(CH.sub.2).- sub.3NCO, and 0.15 ml of
dibutyltin dilaurate were heated at approximately 50.degree. C.
under nitrogen, with stirring, for 2 hrs to give a silylated
derivative with the nominal formula: CH.sub.3(OCH.sub.2CH.sub.2-
).sub.nOCONH(CH.sub.2).sub.3Si(OC.sub.2H.sub.5)3.
[0411] 24.30 g of
CH.sub.3(OCH.sub.2CH.sub.2).sub.nOCONH(CH.sub.2).sub.3Si-
(OC.sub.2H.sub.5).sub.3, 49.59 g of C.sub.2H.sub.5OH and 2.20 g of
H.sub.2O (acidified to 0.15 M HCl) were combined and refluxed for
30 mins. The solution was then cooled and 12.38 g of
Si(OCH.sub.3).sub.4 added and the resulting solution refluxed for
60 mins. The solution was then cooled and 5.86 g of H.sub.2O
(acidified to 0.15 M HCl) was added and the resulting solution
refluxed for 60 mins. The solution was then cooled and 3.00 g of
Amberlyst.RTM. A-21 ion-exchange resin (Rohm & Haas Co.) added,
followed by gentle stirring. After 30 mins the solution was
filtered through a fritted glass disc Buchner funnel. 45.00 g of
the filtrate was taken and 0.21 g of 3-aminopropyltriethoxysilane
was added. The resulting solution was diluted 1:1 (by weight) with
ethanol and filtered through a 1 .mu.m syringe filter. It was then
spin-coated on a transparent WO.sub.3 ITO coated glass substrate.
The coating was cured at 135.degree. C. for 1 hr under humid
atmosphere, after this treatment it has a thickness of about 0.6
.mu.m . A device was then assembled as described in Comparative
Example 1.
[0412] Example: Formation and processing of Polyceram-2 SITL layer
(CH.sub.3(OCH.sub.2CH.sub.2).sub.nOCONH(CH.sub.2).sub.3Si(OC.sub.2H.sub.5-
).sub.3/Si(OCH3).sub.4 overcoated on WO.sub.3 electrode)
[0413] 6.08 g of
(CH.sub.3(OCH.sub.2CH.sub.2).sub.nOCONH(CH.sub.2).sub.3Si-
(OC.sub.2H.sub.5).sub.3, 12.40 g of C.sub.2H.sub.5OH and 0.55 g of
H.sub.2O (acidified to 0.15 M HCl) were combined and refluxed for
30 mins. The solution was then cooled and 6.19 g of
Si(OCH.sub.3).sub.4 added and the resulting solution refluxed for
60 mins. The solution was then cooled and 2.93 g of H.sub.2O
(acidified to 0.15 M HCl) was added and the resulting solution
refluxed for 60 mins. the solution was then cooled and 1.30 g of
Amberlyst.RTM. A-21 ion-exchange resin (Rohm & Haas Co.) added,
followed by gentle stirring. After 30 mins the solution was
filtered through a fritted glass disc Buchner funnel. The filtrate
was diluted 1:2 (by weight) with ethanol and filtered through a 1
.mu.m syringe filter. It was then spin-coated on a transparent
WO.sub.3 ITO coated glass substrate. The coating was cured at
135.degree. C. for 1 hr under a humid atmosphere, after this
treatment it had a thickness of 0.3 .mu.m. A device was then
assembled as described in Comparative Example 1.
[0414] Example: Formation of sol-gel electrolyte
[0415] This describes a crosslinkable electrolyte which can be
substituted for the electrolyte in cells such as those given in
Comparative Example 1a or in other examples with SITL overlayers
described earlier. The electrolyte was prepared in the following
way: 12.00 g of poly(ethylene glycol).
HO(CH.sub.2CH.sub.2O).sub.nOH (number average molecular weight=ca.
400, obtained from Aldrich Chemical Company), 15.58 g of
3-(triethoxysilyl) propyl isocyanate, (C.sub.2H.sub.5O).sub.3Si
(CH.sub.2).sub.3NCO (obtained from Aldrich Chemical Company), and
0.03 g dibutyltin dilaurate,
(CH.sub.3(CH.sub.2).sub.3).sub.2Sn(O.sub.2C(CH.sub.-
2).sub.10CH.sub.3).sub.2, were heated to approximately 70.degree.
C. under nitrogen, with stirring, for 15 minutes to yield a
silylated derivative with the nominal formula:
(H.sub.5C.sub.2O).sub.3S1
(CH.sub.2).sub.3HNOC(OCH.sub.2CH.sub.2).sub.nOCONH(CH.sub.2).sub.3Si
(OC.sub.2H.sub.5).sub.3.
[0416] 2 g of CH.sub.3
(OCH.sub.2CH.sub.2).sub.nOCONH(CH.sub.2).sub.3Si
(OC.sub.2H.sub.5).sub.3, 1.50 g
(H.sub.5C.sub.2O).sub.3Si(CH.sub.2).sub.3- HNOC
(OCH.sub.2CH.sub.2).sub.nOCONH(CH.sub.2).sub.3Si(OC.sub.2H.sub.5).sub-
.3 (prepared as above), 1.75 g .gamma.-butyrolactone, 0.0326 g
ferrocene, and 0.4107 g LiClO.sub.4 are stirred until a clear
solution is formed. Then 0.3636 g H.sub.2O (acidified to 0.15 M
HCl) is added. The solution is stirred until homogeneous. A cell
fabricated as in comparative Example 1 utilizing an ITO electrode
and a transparent WO.sub.3 ITO coated glass substrate is then
filled with the solution obtained above. The cell thickness in this
example was 53 .mu.m rather than 210 .mu.m as given in the earlier
example. After filling the cell, the solution forms a rigid gel
(net work) within 10 hours. The gel time can be controlled, e.g.,
by changing the type and amount of catalyst (e.g., HCl is used
above) as known in the art, temperature of cell after filling and
using appropriate functionality of the ingredients. Functionalised
ferrocenes also could be used which will attached chemically to the
electrolyte network. Some exemplary ferrocenes are: 1
[0417] These ferrocenes could be used by themselves or in
conjunction with non-functionalized ferrocenes (the ones which will
not chemically attach to the network). Depending on the cell
characteristics if non-ferrocene redox materials are used, the same
can be implemented for non-ferrocene redox materials. The cell may
also consist of ferrocene and non-ferrocene based redox
materials.
[0418] Power consumption reduction in EC devices by using switching
power supplies:
[0419] The power consumption of these devices can be further
reduced by incorporating such elements in the circuit that would
efficiently step down the voltages from the incoming power supply
to the desired coloration or bleaching voltages. For example, a
typical car battery has an output of about 12 V, while an EC device
might only need 1 to 2 volts for coloration, for example 1.2 V.
Thus, if the EC device needs a current of 10 mA in the colored
state at a voltage of 1.2 V, then a power conserving circuit would
allow only a 1 mA drainage from the battery at 12 V assuming that
the power is converted at 100% efficiency.
[0420] Typical power supplies for powering EC devices in automotive
mirrors use linear regulators or linear regulation for the voltage
conversion process. Although widely used for such applications, the
power conversion efficiencies of linear regulators are usually very
low, typically 10-30%. The conversion efficiency, however, is
typically not a major concern. Since the EC mirror is normally
operated when the car in turned on, the current or power draw is
not a significant drain on the car's alternator and linear
regulation can be utilized. Examples of such circuits are described
in U.S. Pat. Nos. 5,148,014, 5,193,029, and 5,220,317, each
incorporated herein by reference.
[0421] However, the switching regulator can be used for EC devices
as taught in the present invention and can offer up to 95%
efficiency. In the prior art power supplies, the current draw is
usually maintained when the voltage is switched from high to low
potential. For example, for linear regulators, in going from 12 V
at 1 mA, to 1.2 volts, the output current will still be 1 mA, which
reflects a power conversion efficiency of only 10%. In this
invention, use of circuits that regulates the power supply voltage
by a switching function to control the electrochromic products
increases the power conversion efficiency by at least two fold over
linearly regulated power supplies.
[0422] In aircraft, boats, eyewear and automotive EC windows, such
as automotive EC sunroofs, where the coloration needs to be
maintained even when the vehicle is in a mode such as when parked,
where the engine is off, the current drain from the battery becomes
a critical issue. In cars, the current draw is usually preferably 2
mA or less at 12 V in order not to drain the battery excessively.
During this coloration state, the present invention subjects the
cell to an intermittent voltage rather than a continuous voltage,
thereby enhancing device durability. During initial coloration and
intermittent coloration periods (t.sub.2) the switching power
supply of the present invention is used to convert the power
efficiently to reduce the battery drain. During the holding period
when no current is flowing, the regulator should preferably have a
low or no quiescent current.
[0423] An example of a switching regulator circuit used in this
invention is shown in FIG. 37A. The circuit is able to regulate
even low voltages below about 1.2 V. As described earlier, the
switching regulator circuit of this invention has a low or no
quiescent current in order not to drain the battery excessively.
Switching regulators, as used here, have lower current drains than
linear regulators. The switching regulator of the present invention
preferably should have a quiescent current drain of lower than 100
mA. It is more preferred that the switching regulator of the
present invention have a quiescent current drain of lower than 25
mA and most preferably lower than 5 mA. Such low current drains
minimize drawdown of the battery in situations where the battery is
not being charged such as while the vehicle is parked with ignition
off.
[0424] Comparative Example: Linear Regulator
[0425] During operation of a prior art well known linear regulator
such as, for example, National LM317 (National Semiconductor, Santa
Clara, Calif.) series pass transistor is turned on continuously and
the output voltage is determined through a voltage divider and a
feedback circuit. There is a significant heat dissipation load for
the transistor. Furthermore, as a result of the continuous "on"
state of the transistor, there is a constant background current
draw regardless of the load. When a load is connected, the
conversion efficiency is typically not more than 30% for a ten fold
change in voltage down conversion.
[0426] Example of Switching Regulator
[0427] In a switching regulator (e.g. National LM78S40), pulse
width modulation (PWM) is used to switch the input voltage through
a high speed transistor at an adjustable duty cycle. In contrast to
a linear regulator where the series pass transistor is always on,
in a switching regulator the series pass transistor is turned on
and off at a convenient predetermined frequency (usually in the
range of about 25-250 kHz). The output voltage is the average of
the rectangular pulses resulting from such switching. Switching
regulation results in higher efficiency, such as over 30% and can
be as high as about 95%. In addition, the quiescent current draw is
also very low, typically less than imA thus keeping overall heat
dissipation low. Additionally in some switching regulators, e.g.,
Maxim MAX 1627 (Maxim Company, Sunnyvale, Calif.), the quiescent
current draw can be further lowered to 1 .mu.A.
[0428] As shown in FIG. 37A, a switching regulator circuit used in
this invention can be based on a National LM78S40 switching
regulator chip U1. It accepts a 12 V pre-regulated input voltage. A
peak current of 1.5 A is assumed for this regulator. A sense
resistor calculated as 0.33/peak current according to the
manufacturer, R4 detects the peak incoming current. Based on the
value of input and output voltage expected, a duty cycle of 23% is
obtained. Assuming a switching frequency of 25 kHz, a turn-on time
of 33 .mu.s is calculated. Based on the turn off time, the timing
capacitor C2 of 0.15 .mu.F is then used to set the switching
frequency to 25 kHz. An inductor, L1 was used to couple the
switching pulses while the capacitor C1 reduces the ripples in the
pulses to an average voltage output. The combination of peak
current and turn-on time results in an inductance of 50 .mu.H.
Voltage ripple of 1% is tolerated resulting in the capacitor C1 of
about 1mF. The chip contains a built-in PWM module, Darlington
series pass transistor and reference voltage. Trimmer resistor, R5,
in conjunction with series resistor R3, then sets the output
voltage. The built-in reference voltage is set at 1.3 V which is
the lower limit for the regulated voltage. In the circuit the
reference voltage is reduced by using a voltage divider via series
resistors, R1 and R2 of 1 M .OMEGA. each to further lower the
minimum voltage regulated to 0.65 V.
[0429] To change the applied potential to an EC device with
temperature, an NTC thermistor can also be used in place of trimmer
resistor R5. At higher temperatures, the resistance decreases,
leading to lower coloring and bleaching voltages while at lower
temperatures, the resistance is higher resulting in higher
voltages.
[0430] Switching regulator radiates EMI due to the switching
transistor. Adequate shielding, e.g. Faradaic shield, must be
provided to mitigate such EMI to reduce electromagnetic
interference with other subsystems including communications such as
a cellular phone. For example the shielding aspect could be useful
for powering of EC components in a car or any other transportation
vehicle. It is also novel to use switching and linear regulator
with the former working when the car is in a parked state while the
latter being used while the car is parked (ignition off), the
degree of interference to other electronic systems is lower.
[0431] Example of a Switching Regulator With Ultra Low Quiescent
Switching Current
[0432] A switching regulator used in this invention employing a
MAXIM Max 1627 yielding very low quiescent current of 0.001 mA is
shown in FIG. 37C. The switching efficiency is a high as 85% at 1 A
current draw. Without modification using the manufacturers'
specification, this chip outputs voltage at a lower limit of 1.27
V. In this particular example, the circuit is modified, to allow
output voltages lower than 1.27 V, by having feedback resistors R2
and R1 connected through a high speed comparator MAXIM Max 987. The
p-MOSFET used in the circuit was International Rectifier (El
Segundo, Calif.) IRF7416.
[0433] Example of Ramped Voltage Application
[0434] The voltage applied to the EC cell may consist of a
non-linear ramp. The ramp only refers to the time period when the
voltage is changing before the voltage settles at the hold
potential (e.g., V.sub.cis holding potential in FIG. 38B). Such
non-linearity can be obtained, e.g., by having some amount of
internal resistance in the power supply. This internal resistance
can be intentionally designed into the power supply itself or by
inserting an external resistor between the voltage terminal and the
EC cell. This is shown in FIG. 38A where resistor R7 is placed in
series with the power supply output and EC cell. FIG. 38C describes
the various shapes that the voltage vs. time curves can follow
depending on the circuit parameters. The applied voltage is across
the EC cell and the resistor. During bleaching or coloring times,
there will be a large initial surge of current resulting in a
sizable ohmic drop in R7 which then limits the voltage applied to
the EC cell. At saturation, only a very low amount of current
flows, and the voltage drop across R7 becomes negligible and hence
the EC cell sees the full potential again. The overall voltage
applied to the EC cell during coloring and bleaching processes
appears similar to a capacitor charging curve. The sharpness of the
curves depends on the value of resistor used; larger resistance
results in more gradual and slower saturation.
[0435] Switching Power Supply Where Output Voltage Varies With
Temperature
[0436] A switching regulator circuit was constructed similar to the
one described previously except that a thermistor was located in
place of fixed resistor R5-see FIG. 37B. An example of the
thermistor used is KE D331BZ from Thermometrics (Edison, N.J.). It
exhibits resistance values of 4000 .OMEGA. and 60 .OMEGA.at
-25.degree. C. and 65.degree. C. respectively. By having another
fixed resistor R6 with a value of 3.6 kg in series with thermistor
R5 and fixed resistor R3 with a value of 5.6 k .OMEGA., the voltage
was automatically tuned to 1.3 V and 1 V at -25.degree. C. and
65.degree. C. respectively.
[0437] Other variations and modifications of this invention will be
obvious to those skilled in the art. This invention is not limited
except as set forth in the following claims.
* * * * *