U.S. patent application number 09/751123 was filed with the patent office on 2001-09-13 for dual titanium nitride layers for solar control.
Invention is credited to Dai, Yisheng, Woodard, Floyd Eugene.
Application Number | 20010021540 09/751123 |
Document ID | / |
Family ID | 22676770 |
Filed Date | 2001-09-13 |
United States Patent
Application |
20010021540 |
Kind Code |
A1 |
Woodard, Floyd Eugene ; et
al. |
September 13, 2001 |
Dual titanium nitride layers for solar control
Abstract
A solar control member utilizes a combination of layers that
include spaced apart titanium nitride layers to selectively
transmit a higher percentage of visible light than near infrared
energy, with a low visible light reflection. The titanium nitride
layers are spaced apart by a distance that promotes optical
decoupling with respect to occurrence of constructive and
destructive interference of visible light propagating between the
two titanium nitride layers. In one embodiment, the titanium
nitride layers are spaced apart by a laminating adhesive layer. In
another embodiment, the titanium nitride layers are formed on
opposite sides of a substrate. The ratio of transmission at the
wavelength of 550 nm to transmission at the wavelength of 1500 is
at least 1.25. Each titanium nitride layer is sputter deposited.
Care is taken to ensure that each layer does not become too
metallic and to ensure that excessive oxygen is not incorporated
into the layer. Thus, the nitrogen flow rate and the linespeed are
controlled. Sputtering occurs at a fast rate using high powers and
a minimum acceptable nitrogen flow, while minimizing background
contamination.
Inventors: |
Woodard, Floyd Eugene; (San
Jose, CA) ; Dai, Yisheng; (Singapore, SG) |
Correspondence
Address: |
Terry McHugh
Law Offices of Terry McHugh
101 First Street
PMB 560
Los Altos
CA
94022
US
|
Family ID: |
22676770 |
Appl. No.: |
09/751123 |
Filed: |
December 27, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09751123 |
Dec 27, 2000 |
|
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09184416 |
Nov 2, 1998 |
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6188512 |
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Current U.S.
Class: |
438/98 ; 359/584;
359/601; 438/455 |
Current CPC
Class: |
G02B 5/208 20130101;
B32B 17/10018 20130101 |
Class at
Publication: |
438/98 ; 438/455;
359/601; 359/584 |
International
Class: |
H01L 021/00; H01L
021/30; H01L 021/46 |
Claims
What is claimed is:
1. A method of fabricating a solar control member comprising steps
of: sputtering a first titanium nitride layer on a first
transparent substrate such that said first titanium nitride layer
maintains a transmission of at least thirty percent with respect to
visible light; sputtering a second titanium nitride layer on a
second transparent substrate such that said second titanium nitride
layer maintains a transmissivity of at least thirty percent with
respect to visible light; and bonding said first titanium nitride
layer to said second titanium nitride layer, including spacing said
first titanium nitride layer from said second titanium nitride
layer by a distance that is sufficient to promote optical
decoupling therebetween.
2. The method of claim 1 wherein said steps of sputtering include
maintaining a sputtering environment in which a ratio of oxygen to
nitrogen partial pressures is less than 0.5.
3. The solar control member of claim 1 wherein said steps of
sputtering include forming said first and second titanium nitride
layers to contain less than 20 atomic percent of oxygen.
4. The solar control member of claim 3 wherein said steps of
sputtering include forming said first and second titanium nitride
layers to contain less than 10 atomic percent of oxygen.
5. The method of claim 1 wherein said steps of sputtering include
using a mask on which a portion of titanium nitride plasma
collects.
6. The method of claim 1 wherein said bonding step includes
applying a laminating adhesive between said first and second
titanium layers, said laminating adhesive having a thickness of at
least 700 nm, thereby promoting said optical decoupling with
respect to constructive and destructive interference of visible
light propagating therebetween.
7. The method of claim 6 wherein said bonding step includes
applying said laminating adhesive to a thickness of at least 3000
nm, said laminating adhesive being in contact with both of said
first and second titanium nitride layers.
8. The method of claim 1 further comprising a step of forming at
least one layer of a transparent oxide or a transparent nitride
between said first titanium layer and said first transparent
substrate, said at least one layer having a refractive index that
is at least as great as a refractive index of said first
transparent substrate.
9. The method of claim 8 wherein said step of forming said at least
one layer includes forming a silicon nitride layer having a
thickness in the range of 10 nm to 60 nm.
10. The method of claim 1 further comprising forming a hardcoat
layer and a lubricating layer on an exterior surface.
11. A method of fabricating a solar control member comprising steps
of: providing a substantially transparent substrate; forming a
first titanium nitride layer at a fixed position relative to a
first surface of said transparent substrate; and forming a second
titanium nitride layer at a fixed position from said first titanium
nitride layer, said first and second titanium nitride layers being
on a same side of said transparent substrate and being spaced apart
by a distance of at least 700 nm to provide optical decoupling with
respect to constructive and destructive interference of visible
light propagating between said first and second titanium nitride
layers, wherein said first and second titanium nitride layers
cooperate to provide a higher transmission of visible light than
infrared light.
12. The method of claim 11 further comprising a step of forming an
optically massive layer which contacts each of said first and
second titanium nitride layers, said optically massive layer having
a thickness of at least 1000 nm, thereby providing said optical
decoupling.
13. The method of claim 12 wherein said step of forming said
optically massive layer includes providing a laminating
adhesive.
14. The method of claim 11 wherein said steps of forming said first
and second titanium nitride layers include using sputter deposition
techniques.
15. The method of claim 14 wherein said steps that include using
sputter deposition techniques employ sputtering through a mask.
16. The method of claim 11 further comprising steps of forming a
hardcoat layer and a lubricating layer to provide protection to an
exterior surface.
17. The method of claim 11 further comprising a step of forming a
layer of silicon nitride between said transparent substrate and
said first titanium nitride layer, said silicon nitride having a
thickness in the range of 10 nm to 60 nm.
18. The method of claim 11 further comprising a step of forming a
thin layer of transparent oxide or transparent nitride on a side of
said second titanium nitride layer opposite to said first titanium
nitride layer, said thin layer having a thickness in the range of
10 nm to 60 nm.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a divisional of copending application Ser. No.
09/184,416, filed on Nov. 2, 1998.
TECHNICAL FIELD
[0002] The invention relates generally to solar control members for
coating windows and the like, and relates more specifically to
applied window film members which provide solar rejection and low
visible reflection.
BACKGROUND ART
[0003] Various films have been applied to windows to reduce glare
and to obtain solar screening for an interior of a structure, such
as a home, building or car. For example, a plastic film may be dyed
to provide desired optical properties or may be coated with a
number of layers to acquire the optical properties. A film that
provides solar screening is one that has a low transmission in both
the visible range (400 to 700 nm) and the near infrared range (700
to 2100 nm). To reduce glare, the transmission of visible light
(T.sub.VIS) must be controlled.
[0004] Primarily through absorption, dyed films can be fabricated
to provide a wide range of T.sub.VIS values. However, dyed films
generally do not block near infrared solar energy and,
consequently, are not completely effective as solar control films.
Another shortcoming of dyed films is that they often fade with
solar exposure. When the films are colored with multiple dyes, the
dyes often fade at different rates, causing unwanted color changes
over the life of the film.
[0005] Other known window films are fabricated using
vacuum-deposited grey metals, such as stainless steel, inconel,
monel, chrome or nichrome alloys. The deposited grey metal films
offer about the same degrees of transmission in the visible and
near infrared portions of the solar spectrum. As a result, the grey
metal films are an improvement over dyed films with regard to solar
control. The grey metal films are relatively stable when exposed to
light, oxygen and moisture, and in those cases in which the
transmission of the coatings increases due to oxidation, color
changes are generally not detectable. After application to clear
float glass, grey metals block light transmission by approximately
equal amounts of solar reflection and solar absorption.
[0006] Vacuum-deposited layers such as silver, aluminum and copper
control solar radiation primarily by reflection. Because of the
high reflection in the visible spectrum (i.e., high R.sub.VIS),
films having these vacuum-deposited layers are useful in only a
limited number of applications. A modest degree of selectivity of
transmission in the visible spectrum over transmission in the near
infrared spectrum is afforded by certain reflective materials, such
as copper and silver.
[0007] Traditionally, the best glare reducing coatings have been
sputtered grey metals, such as stainless steel, chrome and nickel.
The graph of FIG. 1 is a transmission spectrum 10 for a sputtered
nichrome coating that is designed to transmit approximately 50% of
the light at the center of the visible light spectrum (i.e.,
T.sub.VIS=50%). The nichrome is affixed to a 3.2 mm-thick plate of
float glass. As can be seen, the transmission of energy is
controlled in both the visible and near infrared portions of the
solar spectrum. A slight degree of wavelength selectivity is
observed due to the iron oxide in the glass.
[0008] In the graph of FIG. 2, the visible reflectivities of single
and double layer nichrome films of various thicknesses are shown as
a function of the corresponding visible light transmissions. (Here,
double nichrome films refer to a construct in which two optically
isolated sputtered coatings are employed, with the films being
separated from each other by a relatively thick (22 micrometers)
layer, such as a laminating adhesive.) While not shown in FIG. 2,
the nichrome layer thicknesses decrease from left to right. As can
be seen, the R.sub.VIS value decreases and the T.sub.VIS value
increases as the nichrome layers become thinner. The comparison
between the single and double layer nichrome films evidences that
the double layer of nichrome has a substantially reduced R.sub.VIS
value for the same T.sub.VIS value. For example, at a T.sub.VIS
value of 20%, the single nichrome coating has an R.sub.VIS value of
24%, while the double nichrome coating has an R.sub.VIS value of
13%. As the nichrome layers become thinner, the R.sub.VIS values of
the two films converge.
[0009] The percentages of solar rejection achieved by films with
single and double layers of nichrome are compared in the graph of
FIG. 3. Solar rejection is defined as:
solar rejection=solar reflection+(0.73.times.solar absorption).
[0010] Within the art, solar rejection is often calculated using
solar energy distributions as given in the ASTM E 891 method. The
slightly better solar rejection noted for the low transmission
single nichrome coatings relative to the twin nichrome equivalents
is due to solar reflection differences.
[0011] A low visible light transmission and low visible light
reflection film utilizing double layers of nichrome is disclosed in
U.S. Pat. No. 5,513,040 to Yang. The patent discloses a solar
control film having two or more transparent substrates, each
bearing a thin, transparent and discontinuous film of metal having
low R.sub.VIS and a degree of visible light blocking capacity. The
substrates are arranged and laminated into a composite, such that
the visible light blocking capacities of the metal films are
effectively combined to provide a composite having low visible
light transmittance, i.e., a low T.sub.VIS. The discontinuous films
of nichrome are attached using an adhesive layer.
[0012] The possibility of using metal nitride films in
window-energy applications was discussed by C. Ribbing and A. Roos
in an article entitled, "Transition Metal Nitride Films for Optical
Applications," which was presented at SPIE's International
Symposium on Optical Science, Engineering and Instrumentation, San
Diego, July/August 1997. Single layers of TiN, ZrN and HfN were
specifically identified. The article discusses the use of the
materials in low emissivity coatings to replace noble metals, such
as silver and gold. It is noted that the low emissivity coatings
will not reach as high a selectivity as the current noble
metal-based multi-layers, but may find use in aggressive
environments, because of their excellent stability.
[0013] What is needed is a solar control member for application to
a window or the like in order to achieve a high selectivity of
visible transmission to near infrared transmission, with a
controlled visible reflection and with age stability. What is
further needed is a repeatable method of fabricating such a solar
control member.
SUMMARY OF THE INVENTION
[0014] A solar control member utilizes a combination of layers that
include spaced apart titanium nitride layers in order to achieve a
desired combination of optical characteristics, including
characteristics relating to visible transmission (T.sub.VIS), near
infrared transmission (T.sub.NIR) and visible reflection
(R.sub.VIS). Adjacent titanium nitride layers are spaced apart by a
distance that promotes optical decoupling with respect to
constructive and destructive interference of visible light
propagating between the two titanium nitride layers. In the
preferred embodiment, each titanium nitride layer is formed on a
separate substrate, such as a PET substrate, with first and second
titanium nitride layers then being joined by a laminating adhesive
having a thickness greater than the wavelengths associated with
visible light (i.e., greater than 700 nm). It is recommended that
the distance between the titanium nitride layers be at least 1000
nm, with 3000 nm being more preferred. In another embodiment, the
first and second titanium nitride layers are formed on opposite
sides of a substrate, such as PET, so that the substrate provides
the recommended spacing between the two layers.
[0015] The thickness of each titanium nitride layer depends upon
the desired optical properties. Preferably, the titanium nitride
layers are sputter deposited in a manner that facilitates
reproducibility, but allows an adaptation for varying the T.sub.VIS
value within a range of 20 to 70% and more preferably within the
range of 30 to 60%. The T.sub.VIS value is achieved while the
R.sub.VIS value remains below 20%. Moreover, the ratio of
transmission at the wavelength of 550 nm (T.sub.550) to
transmission at the wavelength of 1500 nm (T.sub.1500) is at least
1.25. That is, the selectivity as defined by T.sub.550/T.sub.1500
exceeds 1.25.
[0016] In most applications, two sputtered titanium nitride layers
are sufficient. Individual T.sub.VIS values for the films should be
within the range of 45 to 70%, so that the dual film laminate
structure has an R.sub.VIS close to 10%. However, to obtain a
composite visible transmission of less than 40% while maintaining
the individual film visible transmissions within the range of 45 to
70%, a third sputtered titanium nitride layer may be necessary.
More than three sputtered layers may be required to obtain a
composite visible transmission of 20%.
[0017] Greater wavelength selectivity is obtained if the titanium
nitride layers are combined with transparent oxides (e.g., oxides
of tin, indium, zinc, titanium, niobium, bismuth, zirconium, or
hafnium) or nitrides (e.g., silicon or aluminum nitride) having a
refractive index at least as great as that of the substrate
material (the refractive index of PET is 1.7). The transparent
oxides or nitrides can be placed on one or both sides of the
titanium nitride. The thickness would range between 10 and 60 nm,
depending upon color, reflectivity, or cost requirements. A
transparent nitride, such as silicon nitride, is preferred over an
oxide, since during the deposition process "crosstalk" between the
titanium and silicon processes is less likely to introduce
excessive oxygen into the titanium nitride layer.
[0018] In all practical vacuum web coaters, some incorporation of
oxygen will occur, so that in practice what is deposited is
actually titanium oxynitride. However, if excessive oxygen is
incorporated into the titanium nitride coating, the wavelength
selectivity and electrical conductivity will be lost. It is
believed that the oxygen-to-nitrogen partial pressure ratio during
the sputtering process should be less than 0.5. To ensure that
wavelength selectivity and electrical conductivity are achieved,
the stoichiometry of each titanium nitride layer must be
controlled. Two of the concerns with regard to adversely affecting
the titanium nitride performance are (1) ensuring that each layer
does not become too metallic and (2) ensuring that excessive oxygen
is not incorporated into the layers. In either case, the wavelength
selectivity will be lost if the sputtering process is not properly
performed. A titanium nitride layer will become too metallic if it
is nitrogen depleted, as will occur if nitrogen flow during the
process is inadequate. The exact nitrogen flow to achieve a
suitable titanium nitride layer varies from coater to coater.
However, the most preferred flow generally corresponds to minima in
sheet resistance and absorption at 1500 nm. As the nitrogen flow is
being adjusted, if a T.sub.1500 value is to be maintained with an
increase in nitrogen flow, the linespeed of the deposition process
should be reduced. This is largely due to a decrease in the
deposition rate of the titanium nitride.
[0019] Regarding excessive oxygen, the extra oxygen typically comes
from background water and oxygen contaminants present in the
sputtering system. The problem is enhanced if other
oxygen-requiring processes (e.g., plasma pretreatments or reactive
sputtering) are conducted in the vacuum chamber while the titanium
nitride deposition process is being conducted. To reduce the
likelihood that contamination will occur, the following steps may
be taken (1) sputter as fast as possible using high powers and the
minimum acceptable nitrogen flow, since excessive nitrogen
"poisons" the titanium target and reduces the deposition rate; (2)
minimize background contamination by controlling "crosstalk"
between neighboring processes, by minimizing the water content in
the substrate (for example by preheating or separate outgassing
steps), by eliminating any water leaks in the vacuum chamber, and
by adequately pumping down the vacuum system prior to beginning the
deposition; and (3) sputter through a mask, so that the outer
perimeter of the titanium nitride plasma (which deposits on a mask,
rather than the substrate) acts as an "oxygen getter."
[0020] Optionally, the surface that is exposed when the solar
control member is attached to a window is protected by a hardcoat
layer. Hardcoat layers are known to provide resistance against
abrasion. Another optional layer is a low surface energy layer on
the hardcoat. The low surface energy layer acts as an antisoiling
layer for resisting smudges and the like and as a lubrication layer
for improving the resistance to mechanical abrasion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a graph of a transmission spectrum for a single
layer nichrome film that is designed to transmit approximately 50%
of the light at the center of the visible light spectrum.
[0022] FIG. 2 is a graph of visible reflection versus visible light
transmission as a function of film thickness for a single layer
nichrome film and a double layer nichrome film on 3.2 mm glass.
[0023] FIG. 3 is a graph of the percentage of solar rejection
versus visible light transmission as a function of film thickness
of a single layer nichrome film and a double layer nichrome film on
3.2 mm glass.
[0024] FIG. 4 is a side sectional view of a portion of a solar
control member in accordance with the invention.
[0025] FIG. 5 is a side sectional view of the solar control member
of FIG. 4 shown in a window energy application.
[0026] FIG. 6 is a side sectional view of another embodiment of a
window energy application in accordance with the invention.
[0027] FIG. 7 is a side sectional view of a third embodiment of a
solar control member in accordance with the invention.
[0028] FIGS. 8-11 are plots of values from Table 1 that is to
follow.
[0029] FIG. 12 is a comparison of performances of three laminates
having single and double layer titanium nitride film and a double
layer nichrome film.
BEST MODE FOR CARRYING OUT THE INVENTION
[0030] With reference to FIG. 4, a solar control member 11 is shown
as including first and second substrates 12 and 14, with each
substrate having a layer of titanium nitride 16 and 18,
respectively. The titanium nitride layers are bonded together using
a laminating adhesive layer 20.
[0031] Preferably, the substrates 12 and 14 are flexible members
that allow the titanium nitride layers 16 and 18 to be sputter
deposited using web processing techniques. The substrates may be
PET films, but other materials may be substituted. The substrates
must be substantially transparent, since the objectives in forming
the solar control member 11 include providing an R.sub.VIS value in
the range of 5 to 20%, a T.sub.VIS value in the range of 20 to 70%
(and more preferably within the range of 30 to 60%), and an NIR
transmission (i.e., from 700 to 2100 nm) that is lower than the
T.sub.VIS value. With regard to the wavelength selectivity, the
ratio of transmission at the wavelength of 550 nm to transmission
at the wavelength of 1500 nm should be at least 1.25 (i.e.,
T.sub.550/T.sub.1500.gtoreq.1.25).
[0032] A standard thickness of the substrates 12 and 14 is between
1 and 2 mils, but the thickness is not critical to the invention.
The thicknesses of the titanium nitride layers 16 and 18 are
selected based upon the desired optical properties of the solar
control member 11. A thicker titanium nitride layer will block a
greater percentage of energy, but will also increase reflection and
decrease transmission within the visible range. Preferably, the
individual film transmissions are within the range of 45 to 70% at
the visible range. This is the preferred range of individual film
transmissions, even if more than two layers of titanium nitride are
used. While the layers 16 and 18 are described as titanium nitride
layers, in practice it is difficult to avoid some incorporation of
oxygen into the layers, so that the titanium nitride layers are
actually titanium oxynitride layers (TiN.sub.xO.sub.y). However, if
the amount of oxygen in the layers becomes excessive, wavelength
selectivity and electrical conductivity are lost. It is believed
that the ratio of oxygen to nitrogen partial pressures during the
sputtering process should be less than 0.5. Measurements of various
TiN.sub.x samples indicate the highest wavelength selectivity is
obtained when the oxygen content of TiN.sub.xO.sub.y coatings is
less than 20 atomic percent or most preferably less than 10 atomic
percent. The sheet resistance of each titanium nitride layer should
be less than 500 ohms/square.
[0033] The laminating adhesive layer 20 is an optically massive
layer. That is, the thickness of the adhesive layer should be such
that the two titanium nitride layers 16 and 18 are sufficiently
spaced apart to avoid constructive and destructive interference of
visible light propagating between the two titanium nitride layers.
To ensure that the spacing between the two layers is greater than
the wavelengths associated with visible light, the adhesive layer
should have a thickness of at least 700 nm. In a more preferred
embodiment, the thickness is at least 1 micron (i.e., 1000 nm),
with at least three microns being most preferred.
[0034] In another embodiment, the spacing between the two titanium
nitride layers 16 and 18 is achieved by forming the two layers on
opposite sides of a single substrate, such as a PET film. Thus, the
laminating adhesive layer 20 would not be required. In other
embodiments, the spacing between the two titanium nitride layers 16
and 18 may be provided by more than one layer. However, the layers
should not adversely affect the above-identified optical objectives
of the solar control member 11. While not shown in FIG. 4, there is
often a hardcoat layer on one PET surface opposite to the titanium
nitride coated side. Hardcoat layers improve the durability of the
flexible substrate during processing and particularly during use of
the end product. The hardcoat layers can be any one of a variety of
known hardcoat materials, such as silica-based hardcoats, siloxane
hardcoats, melamine hardcoats, and acrylic hardcoats. An acceptable
thickness range is 1 .mu.m to 20 .mu.m. The use of hardcoat layers
is not critical to the invention.
[0035] Other optional layers include primer layers between the
adhesive layer 20 or the substrate layers 12 and 14 and each of the
titanium layers 16 and 18. The primer layers may be used to improve
adhesion between the titanium nitride layers and the adhesive or
substrate. The primer layer may be a metal that undergoes oxidation
or nitridation in situ during processing, so as to yield a
substantially transparent, substantially colorless inorganic metal
oxide. Examples of useful primer materials include silicon,
titanium, chromium, nickel and alloys. The primer layer should be
sufficiently thin to minimize disruption of the desired optical
properties of the solar control member 11. Preferably, the primer
layer has a thickness of less than 30 angstroms.
[0036] The laminating adhesive layer 20 may be an adhesive such as
Morton's Adcote 1130 adhesive. This and other such adhesives are
well known in the industry. For fabricating prototype samples,
MacTac transfer adhesive #IP2704 may be used.
[0037] Typically, the two substrates 12 and 14 will be from
separate webs, since it is more practical. However, the substrates
may be different portions from a single web. That is, following the
web processing operation of depositing titanium nitride onto a
continuous web of PET, the PET film is divided into sections that
may be combined as shown in FIG. 4. This is possible when the two
titanium nitride layers 16 and 18 are to have the same thickness.
However, in some applications, there may be advantages to having
titanium layers of different thicknesses. In such applications, it
is typically more economical to sputter the titanium nitride layers
on different substrates.
[0038] Referring now to FIG. 5, the solar control member of FIG. 4
is shown attached to float glass 22 by means of a second adhesive
layer 24. The float glass may be a windshield of a vehicle or may
be a window of a home or building. The solar control member
provides solar screening to the interior of the vehicle, home or
building. It should be noted that the titanium nitride layers 16
and 18 are not specifically designed to provide low heat
emissivity. Although titanium nitride layers are electrically
conductive, and therefore have relatively low heat emissivity and
relatively high heat reflection, in the construct of FIG. 5, the
titanium nitride layers do not directly contact air and are
"buried" within infrared opaque wet coatings and substrates. This
renders them relatively ineffective at blocking long wave (IR) heat
transfer. As noted above, PET films typically are provided with a
hardcoat layer. Thus, the exposed surface of the substrate 14 will
be protected by the hardcoat layer. As will be explained more fully
with reference to FIG. 6, another optional layer is a low surface
energy (anti smudge) layer that resists mechanical damage and
soiling to the solar control member.
[0039] With reference to FIG. 6, a second embodiment of a solar
control member is shown. For simplicity, reference numerals of FIG.
5 are used for comparable elements of FIG. 6. Thus, the solar
control member is attached to float glass 22 by means of adhesive
layer 24. The solar control member includes first and second
titanium nitride layers 16 and 18 that were previously sputter
deposited onto substrates 12 and 14 and adhered to one another by
means of a laminating adhesive layer 20. The solar control member
includes a third titanium nitride layer 26 on the side of the
substrate 14 opposite to the second titanium nitride layer 18.
While not critical, the third titanium nitride layer may have a
thickness identical to the thicknesses of the first and second
titanium nitride layers. As previously noted, the individual film
transmission should be within the range of 45 to 70% with respect
to visible light. In many applications, a third titanium nitride
layer is not necessary in order to achieve the target T.sub.VIS
value for the composite solar control member. However, if the
target T.sub.VIS value is in the range of 20 to 40%, the third
layer may be required in order to keep the R.sub.VIS value within
the targeted range (e.g., approximately 10%). In fact, there may be
applications in which more than three sputtered titanium nitride
layers are necessary.
[0040] The solar control member of FIG. 6 is shown as including the
hardcoat layer 28 described above. The hardcoat layer is an
abrasion-resistant coating that enhances durability of the solar
control member. An acceptable thickness is within the range of 1
.mu.m to 20 .mu.m.
[0041] An anti smudge layer 30 coats the hardcoat layer 28. The
anti smudge layer reduces the susceptibility of the solar control
member to scratches and other damage caused by contact with the
outermost surface of the member. A desirable anti smudge layer is
achieved by providing an adhesion promotion lower film of silane
material and an upper film of a fluorocarbon with a low surface
energy and with anti friction properties that facilitate cleaning
and provide scratch resistance. The low surface energy layer may be
a fluorocarbon sold by 3M Company under the federally registered
trademark FLUORAD. In a more preferred embodiment, the material is
FLUORAD FC722, which is sold diluted in 2% solution of a
fluorinated solvent. The silane that is used as the adhesion
promotion film may be N-(2-aminoethyl)-3-propyltrimethoxysilane in
isopropyl alcohol (2-propanol). However, other silanes may be used,
and in fact a silane may not be required in some applications.
[0042] Referring now to FIG. 7, a third embodiment of a solar
control member 32 includes first and second substrates 34 and 36,
first and second titanium nitride layers 38 and 40, an adhesive
layer 42, and first and second silicon nitride layers 44 and 46.
The only significant difference between the embodiments of FIGS. 4
and 7 is the inclusion of the silicon nitride layers 44 and 46.
Greater wavelength selectivity can be obtained if the titanium
nitride layers are combined with transparent oxides or nitrides
with a refractive index that exceeds the refractive index of the
substrates 34 and 36. Thus, if a PET film is used to form the
substrates, the additional layers 44 and 46 should have a
refractive index of 1.7 or greater. An acceptable transparent oxide
is an oxide of tin, indium, zinc, titanium, niobium, bismuth,
zirconium, or hafnium. Acceptable nitrides are silicon and aluminum
nitride. However, the silicon nitride is preferred, since the
nitride layers are likely to introduce excessive oxygen into the
titanium nitride layers 38 and 40. While each titanium nitride
layer is shown as having only one adjacent silicon nitride layer,
silicon nitride may be formed on both sides of each titanium
nitride layer. The thickness of the silicon nitride layers should
be within the range of 10 and 60 nm, depending upon color,
reflectivity, or cost requirements. While greater wavelength
selectivity is achieved by including the silicon nitride layers,
the solar control member 32 of FIG. 7 is less cost-effective than
the member 11 of FIG. 4.
Deposition Conditions For TiN.sub.x
[0043] Each of the solar control members of FIGS. 4-7 includes at
least two layers of titanium nitride that cooperate to provide the
desired wavelength selectivity with the low R.sub.VIS value. In
particular, the transmission of visible wavelengths is
significantly higher than the transmission of wavelengths in the
near infrared. The ratio of T.sub.550 to T.sub.1500 should be at
least 1.25. To ensure that the target selectivity is achieved, the
stoichiometry of the titanium nitride must be controlled during the
sputtering process. Two concerns regarding adversely affecting the
titanium nitride performance are (1) ensuring that the titanium
nitride does not become too metallic and (2) ensuring that
excessive oxygen is not incorporated into the titanium nitride. If
a titanium nitride layer becomes too metallic (i.e., nitrogen is
depleted, as would happen if the nitrogen flow to the process were
inadequate), wavelength selectivity will be less desirable. If
excessive oxygen is incorporated into a titanium nitride layer
(i.e., more than 10 to 20 percent), the selectivity will be
adversely affected. Sources of extra oxygen are background water
and oxygen contaminants present within the sputtering system. The
difficulties are enhanced if other oxygen-requiring processes are
conducted in the vacuum chamber while the titanium nitride
deposition process is being conducted. For this reason, the silicon
or aluminum nitride layers 44 and 46 of FIG. 7 are preferred over
the formation of oxide layers.
[0044] To minimize contamination from oxygen sources, several steps
can be taken. The sputtering process for depositing the titanium
nitride should be performed as quickly as possible using high
powers and a minimal amount of nitrogen, while still retaining the
desired stoichiometry. Excessive nitrogen "poisons" the titanium
target and reduces the deposition rate. A second step is to
minimize background contamination. This can be accomplished by
controlling "crosstalk" between neighboring processes, by
minimizing the water content in the substrates (e.g., by preheating
or outgassing), by ensuring that there are no water leaks in the
vacuum chamber, and by adequately pumping down the vacuum system
prior to the start of the deposition process. As a third step, the
sputtering may occur through a mask, so that the outer perimeter of
the titanium nitride plasma deposits on the mask, rather than on
the substrate. Thus, the mask acts as an "oxygen getter."
[0045] A number of experiments were conducted in view of these
concerns and corrective steps. Results are shown in Table 1. The
legends are defined as follows:
[0046] "Linespeed"--Rate at which the film is moved through the
coating zone of the system;
[0047] "N.sub.2 flow"--Gas flow to the titanium source;
[0048] "R.sub.SHEET"--Sheet resistance of TiN.sub.x coated film
measured in the vacuum coater (i.e., in situ);
[0049] "T.sub.1550"--Transmission of coated film at a wavelength of
1550 nm, measured in situ;
[0050] "T.sub.max"--The transmission at the wavelength in the range
400 to 700 nm at which a maxima is observed;
[0051] "T.sub.max/T.sub.1550"--A first wavelength selectivity
ratio;
[0052] "R.sub.1550"--The reflectivity at 1550 nm;
[0053] "T.sub.VIS"--The integrated visible transmission weighted
for wavelength variations in illuminant (i.e., C) intensity and eye
sensitivity (assuming a standard 2.degree. observer);
[0054] "T.sub.VIS/T.sub.1550"--A second wavelength selectivity
ratio.
1TABLE 1 OPTIMIZATION OF THE TiN.sub.x PROCESS OPTICAL PARAMETERS
ARE FOR FILMS ONLY Experiment No. 1 No. 2 No. 3 No. 4 No. 5 No. 6
Units Linespeed 7.90 10.15 13.27 15.76 18.05 20.0 mm/s N.sub.2 Flow
45.0 40.0 35.0 32.5 30.0 27.5 sccm R.sub.SHEET 103 86 75 75 80 115
.omega./.quadrature. T.sub.1550 15.3 14.9 14.8 15.1 15.0 14.9 % at
1550 nm T.sub.max 38.9 40.4 42.4 43.4 42.5 -- %
T.sub.max/T.sub.1550 2.54 2.71 2.86 2.87 2.83 -- -- R.sub.1550 50.6
52.4 53.6 53.7 53.3 49.6 % T.sub.VIS 37.6 38.5 39.4 39.5 37.4 26.7
% T.sub.VIS/T.sub.1550 2.46 2.58 2.66 2.62 2.49 1.79 --
[0055] In these experiments, the titanium power was maintained at
5.7 kW and an argon flow was set at 110 sccms, as required to
obtain a 3 milliTorr pressure. As the nitrogen flow was varied
between 27.5 and 45 sccms, the linespeed was adjusted as required
to maintain a T.sub.1550 value of approximately 15%. The dimensions
of the titanium target were 397.88 mm by 82.55 mm. As can be seen
in Table 1, as the nitrogen flow varied, so did the spectral
properties of the titanium nitride layers that were formed during
the experiments.
[0056] In order to obtain a simple measure of the selectivity at
various nitrogen flow rates, two factors were considered, (1)
T.sub.max/T.sub.1550 and (2) T.sub.VIS/T.sub.1550. T.sub.max is the
maximum transmission at any wavelength in the visible spectrum and
T.sub.VIS is the weighted visible light transmission. These two
factors from Table 1 are shown as being plotted in FIG. 8. Clearly,
the preferred coatings were formed with a nitrogen flow rate of
32.5 to 35 sccms. However, acceptable values were achieved with a
nitrogen flow rate within the range of 30 to 35 sccms. It is
interesting, as shown in the plots of FIGS. 9 and 10, that these
preferred flows correspond to the minima and sheet resistance and
absorption at 1550 nm (because the transmission was held relatively
constant at 1550 nm, a minimum absorption at that wavelength
corresponds to a maximum reflection). The "poisoning" effect of
nitrogen on the titanium deposition rate is shown in FIG. 11. As
the nitrogen flow increased, the linespeed had to be reduced
substantially in order to maintain the same value of T.sub.1500.
This is largely due to the decrease in the deposition rate of the
titanium nitride as the nitrogen flow rate was increased.
[0057] Table 2 shows the details of the measured deposition
parameters for forming seven samples of titanium nitride on a PET
substrate. In each case, the titanium nitride layers were
electrically conductive (i.e., less than 300 ohms per square). Of
course, as the films were made thinner in order to achieve higher
visible light transmission, the electrical resistance increased. In
Table 2, the sheet resistivity was measured in the vacuum chamber
immediately after the coating was deposited. These samples (as
distinguished by the sample numbers given in Table 2) were used to
fabricate various window laminate structures (as given in Tables 4
and 5) for performance comparisons.
2TABLE 2 DETAILS OF DEPOSITION PARAMETERS FOR TiN.sub.x SAMPLES
Measured Units 82-2 83-1 83-2 83-3 83-4 84-1 84-2 Glow Amps 100 100
100 100 100 50 50 Current Glow Volts 1500 1500 1500 1500 1500 1500
1500 Voltage Glow sccm 13.3 13.6 14.1 14.0 13.9 11.5 11.5 O2 Flow
Glow microns 10 10 10 9 10 7 8 Pressure Titanium kWatt 4.5 5.7 5.7
5.7 5.7 5.7 5.7 Power Titanium Volts 460 465 457 454 458 446 446
Volts Titanium Amps 9.8 12.26 12.4 12.5 12.4 12.76 12.78 Current
Titanium sccm 105.5 105.5 105.5 104 104 105 105 Ar Flow Titanium
sccm 26.2 33.5 32.5 32.5 32.5 32.5 32.5 N.sub.2 Flow Titanium
microns 3.61 3.71 3.72 3.67 3.7 3.67 3.65 Pressure Linespeed mm/sec
10.1 8.8 16.7 12.45 7.45 6.05 4.18 Resistance ohm/sq 185 109 278
194 123 68 43.5 (in situ) T.sub.VIS % 55 47 63 60 47 36 26 (in
situ)
Benefits of Using Double TiN.sub.x Layers
[0058] In order to determine whether window structures with double
titanium nitride layers provided better results than those
containing a single titanium nitride layer and/or double nichrome
layers, a number of samples were fabricated, with the results being
shown in Tables 3-5. The samples listed in Table 3 were dual
TiN.sub.x laminates. The laminates listed in Table 4 had a single
layer of titanium nitride. The laminates listed in Table 5 included
dual layers of a nonselective metal alloy, nichrome. In each table,
when a reflection measurement is listed, it is followed by (PET) or
(GLASS). This refers to the side on which the laminated window
structure reflection measurement was made.
3TABLE 3 TiN.sub.X DATA SUMMARY OPTICAL PROPERTIES FOR WINDOW FILM
LAMINATES CONTAINING TWO (I.E., DUAL) SPUTTERED TIN.sub.X FILMS
Sample No 82-2 83-1 83-2 Lamination Type Dual Dual Dual T.sub.VIS:
in situ - film only 55 47 63 T.sub.VIS: film only 59.47 51.34 67.35
T.sub.VIS 43.55 33.49 53.98 R.sub.VIS (Glass) 10.64 12.29 9.93
R.sub.VIS (PET) 10.97 12.8 10.21 T.sub.SOL 30.85 21.55 41.7
R.sub.SOL (Glass) 12.14 15.67 10.01 R.sub.SOL (PET) 13.74 18.76
11.1 Ta* -3.32 -3.98 -2.73 Tb* 1.55 0.23 3.92 Ra* (Glass) 1.2 2.13
0.15 Rb* (Glass) -0.35 1.9 -2.05 Ra* (PET) 1.64 2.88 0.6 Rb* (PET)
-0.23 2.47 -1.9 Sol Rej (Glass) 53.8 61.5 45.3
[0059]
4TABLE 4 TiN.sub.X DATA SUMMARY OPTICAL PROPERTIES FOR WINDOW FILM
LAMINATES CONTAINING A SINGLE SPUTTERED TIN.sub.X COATED FILM
Sample No. 83-3 83-4 84-1 84-2 Lamination Type Single Single Single
Single T.sub.VIS: in situ - film only 67 47 36 26 T.sub.VIS: film
only 61.25 51.1 39.51 28.82 T.sub.VIS 62.74 54.9 42.88 33.41
R.sub.VIS (Glass) 10.04 10.8 14.81 19.38 R.sub.VIS (PET) 12.15 13.4
18.26 22.86 T.sub.SOL 50.41 41.42 29.79 21.79 R.sub.SOL (Glass)
10.7 13.5 20.28 26.54 R.sub.SOL (PET) 14.47 18.55 27.45 34.78 Ta*
-2.32 -2.8 -3.2 -3.43 Tb* 1.75 0.81 -2.34 -4.62 Ra* (Glass) 0.54
1.55 2.52 2.98 Rb* (Glass) -1.04 0.94 6.78 11.05 Ra* (PET) 1.04
2.23 3.16 3.71 Rb* (PET) -1.7 -0.46 5.58 9.27 Sol Rej (Glass) 39.1
46.4 56.7 64.3
[0060]
5TABLE 5 NiCr DATA SUMMARY OPTICAL PARAMETERS FOR WINDOW FILM
LAMINATES CONTAINING TWO (I.E., DUAL) SPUTTERED NiCr FILMS Sample
No. R1-Q1 R1-Q2 R1-Q3 Lamination Type Dual Dual Dual T.sub.VIS:
film only 40.06 52.39 65.43 T.sub.VIS 22.03 35.2 51.49 R.sub.VIS
(Glass) 14.61 11.39 9.84 R.sub.VIS (PET) 15.35 11.51 9.8 T.sub.SOL
18.18 30.25 46.75 R.sub.SOL (Glass) 13.98 10.59 8.87 R.sub.SOL
(PET) 15.96 12.02 9.54 Ta* -0.95 -1.14 -1.12 Tb* -2.99 -0.97 1.4
Ra* (Glass) -0.85 -0.48 -0.56 Rb* (Glass) 1.36 -0.18 -1.14 Ra*
(PET) -0.084 -0.015 -0.17 Rb* (PET) 1.9 0.43 -0.42 Sol Rej (Glass)
63.5 53.8 41.3
[0061] Within the single sputtered films of titanium nitride of
Table 4, thicker titanium nitride layers were required in order to
obtain lower transmissions. After lamination to glass, the
resulting composites had visible transmissions ranging from
approximately 33% to approximately 63%. The dual titanium nitride
layers provided a visible transmission range of 33% to 54%.
Regarding visible reflection from the glass side of applied window
film laminates containing various single and double titanium
nitride films, at lower transmissions (e.g., approximately 55%),
significantly lower reflections are obtained if two separate
sputtered titanium nitride layers are used instead of one thicker
titanium nitride layer. The same trend applies with regard to
reflection from the PET side.
[0062] One concern with using dual layers is that for a given
visible transmission, the solar rejection might be significantly
lower than that observed for coatings containing a single sputtered
layer. Measurements of solar rejection are obtained using the
following equation for monolithic glazing:
solar rejection=solar reflection+(0.73.times.solar absorption)
where
solar absorption=100%-solar reflection-solar transmission.
[0063] Here, integrated solar properties are determined using
wavelength specific weighting factors as specified in ASTM E 891.
From Tables 3-5 and FIG. 12, it can be seen that the solar
rejection for single titanium nitride layers is only two or three
percentage points greater than the double layers. This is a
relatively small sacrifice in order to receive the benefit of the
large decrease in visible reflection.
[0064] FIG. 12 also illustrates the benefits of the present
invention over the prior art of dual nonselective metals. Clearly,
for a given visible transmission the dual TiN.sub.x window
construct provides significantly higher solar rejection than the
dual nichrome constructs.
[0065] In Tables 3-5, transmitted and reflected a* b* colors (from
both sides of the glass/film composite) are indicated. It is noted
that +a* means red, -a* means green, while +b* means yellow and -b*
means blue. The primary difference between the two structures is in
Rb*. The single film structures become more yellowish (gold or
brass-like) at lower transmissions when viewed from either side of
the composite. The dual film structures remain more color
neutral.
* * * * *