Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02345939 2001-05-03
APPLICATION OF DE L'TERIUM OXIDE IN PRODUCING SILICON
CONTAINING AND METAL CONTAINING MATERIALS
BACkGROUND OF THE INVENTION
Field of the Invention
This invention relates to the application of deuterium oxide, D20, in
producing O-H free materials or
chemicals for optical communication. 'the processes involved include,
hydrolysis and
polycondensation of silanes and metal compounds, such as the sol-gel process,
and the optical
deposition of silica and metal oxides. ~~tre resulting materials could be used
as optical waveguides,
adhesion promoters, coatings, adhesives and other materials where low optical
loss is essential in the
wavelength range of 1.55 lun or 1.3 pm.
Prior Art of the Invention
Low optical loss at working optical wamelengths, i.e. i .3 acrd particularly
1.55 Irm, is a key parameter
for applying a material as light transmission medium in fiber optical
communication. In silicon based
materials, such as sol-gel based silica, O-H plays an undesirable role in
building up high optical loss
at the wavelengths of 1.3 and 1.55 p.m, which are the regular wavelengths used
for optical
communication, because O-H has a strong absorption peak in this wavelength
region. Reducing O-H
content in the materials is, therefore, e:~ctrernely important in decreasing
optical loss. However, it is
very difficult to eliminate O-H in silica and metal oxidized materials. High
temperature baking is the
typical present way used to reduce (J-H in processing the materials. For
instance, high temperature
baking at around 1200 °C is usually used to eliminate O-H when
producing silica. This process does
not experience technical prablems in producing bulk components such as optical
fibers, but it does
cause some problems in coating deposition when the substrate is a different
material. For example,
the thermal expansion mismatch between a silicon substrate and the silica
coating might introduce a
significant stress in the silica coatings in a Flame Hydrolysis Deposition
(FHD) process, and the
capillary force-driven shrinkage can e~~sily crack sol-gel deposited coatings
at 600°C or above. As for
sol-gel based organic-inorganic hybrid materials, high temperature processes
are completely
unacceptable, because the organic p~urt can only withstand a temperature below
300°C.
CA 02345939 2001-05-03
Recently, sol-gel based organic-inorganic hybrid materials were developed for
fabricating optical
waveguiding components. The materials contain two parts: an organic one with
double bonds and an
inorganic one with Si-O-Si network. They can be 11V-patterned by using
traditional photolithography
technology and have good thermal stability. Various optical waveguide
components, such as hybrid
sputters, optical switches and waveguide gratings, were produced by using the
hybrid materials. The
materials are synthesized by hydrolyzing mufti-functional methoxyl or ethoxyl
silanes, followed by
proper polycondensation.
U.S. Patent 6,054,253 issued April 25, 20(10 to Fardad et al provided a method
in producing
waveguides by using methacryloxypropyl trirnethoxysilarre based on sol-gel
process. High
performance sol-gel waveguides were achieved with the technology. U.S. Patent
5,973,176 issued
October 26, 1999 to Rocscher et al teaches us to use synthesize fluorinated
silanes for sol-gel process
in fabricating low optical loss waveguides.
However, polycondensation is never completed in the system, leaving a
significant amount of residual
O-H in the materials. Many approaches were used to reduce the O-H content,
including, choosing
proper silanes, proper sol-gel conditions (catalyst concentration, solvent,
temperature), and using a
special monomer to react the O-H groups. It was reported that by eliminating O-
H, the materials'
optical loss can be reduced from several dB/cm to 0.5 dB/cm. Fundamentally,
however, choosing
proper silanes and reacrion conditions cannot complete the condensation and
thus eliminate the O-H
in such a reactive system with mufti-functional groups, because the
condensation of mufti-functional
monomers can never be completed.. 'lfiis has been well recognized in polymer
theory and experiment.
By reacting residual O-H with a special monomer it is possible to eliminate
all O-H, but the reaction
may affect the network built up and thus deteriorate the material's thermal
and mechanical properties.
An innovative prior art method to produce low O-H materials is to avoid the
use of Hz0 for
hydrolysis. For instance, diphenysilandiols were used to react with
methoxysilanes directly. However,
residual methoxy groups are inevitable in the materials due to the problem
mentioned above, i.e.
mufti-functional groups polycondensation can never be completed. Since GH also
has a strong
absorption peak in the region of I .3 to 1.55 um, the residual methoxy itself,
which contains three C-H
bonds, could negate the benefit achieved by reducing the O-H content. As a
result, real gain in
reducing optical loss in the wavelength region by such approach is limited.
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CA 02345939 2001-05-03
Indeed, it is a challenge to significantla- reduce the O-H content without
deteriorating material
properties, or to eliminate O-H without introducing other chemical groups
which have similar effects
to O-H on building optical loss.
SUM1MARY OF THE LNVENTION
The present invention provides an optical compound material for use in optical
devices in the
wavelength range between 1.0 and 1.8 micrometers, wherein substantially most O-
H bonds are
substituted by O-D bonds; H being protium and D being deuterium.
In a widely used compound material processes, is the sol-gel material a D20-
hydrolyzed silane, or a
Dz0-hydrolyzed metal compound.
The present invention also provides a method of producing optical compound
materials substantially
free from O-H bonds, comprises the steps of hydrolyzing and condensing of at
least one of silanes
and metal compounds using deuterium oxide (Dz0).
A sol-gel process for producing optical compound materials substantially free
from O-H bonds,
comprises the step of using deuterium oxide (DZO) to provide compound
materials containing Si-O-Si
bonds M-O-M bonds, wherein M is a metal atom suitable for use in the sol-gel
process, M is often
one of the group of Aluminum (Al,), Zirconium (Zr), Titanium (Ti), Erbium (Er)
and Germanium
(Ge).
An optical compound material made: by the process, will have low optical loss
in the optical
wavelength range between 1.0 and 1.8 micrometers.
A preferred application is a sol-gel process for making optical gratings and
optical index matching
coatings providing low optical loss in the wavelength range between l .(1 and
1.8 micrometers.
Further, a process for producing optic:rl compound materials substantially
free from O-H bonds,
comprises the step of using deuterium oxide (D2(I) in hydrolysis and
condensation of silanes and
metal compounds, for use as adhesives and surface treatments agents for
promoting adhesion between
silicon, silica, glass, metal oxide, or metal substrates with materials
containing organic groups.
CA 02345939 2001-05-03
The process is applicable for producin;~ optical compound materials wherein
the material is one of the
group of sol-gel materials, organic/inorganic hybrids, and polymer resins such
as polysiloxane.
The method enhances hydrolysis and condensation of silanes and metal compounds
in sol-gel
processes and is characterized by the step of substituting deuterium oxide
(D20) for protium oxide
(H20).
The method of depositing silica and metal oxides on a substrate is
characterized by use of deuterium
oxide (D20) as hydrolysis agent.
The method of depositing silica and metal oxides on a substrate by flame
hydrolysis depositian
(FHD) is characterized by use of deutea-ium oxide (DZO) as hydrolysis agent.
The method for reducing optical loss i n the range between 1.0 and 1.8
micrometers in optical
materials, wherein O-t~ bonds are replaced by O-D bonds, O being oxygen, H
being protium and D
being deuterium.
BRIEF DESCRIPTION OF THE DRAWING
The preferred exemplary embodiments of the present invention will now be
described in detail in
connection with the annexed drawing vfigures, in which:
Figure 1 shows the absorption of HAG and DZO in the near infrared region,
measured by using
Nicloet 470 FTIR/N1R spectrometer with transmission model and a 1 mm thick
quart sealed liquid
fell was used for the measurement; amd
Figure 2 shows the absorption of DZO and H z0 based sol-gel materials in the
near infrared region,
measured by using Nicloet 470 FTIWIdIR spectrometer with transmission model
and a sample
thickness of 2 mm.
DETAILED DESCRIPTION OF THE INVENTION
It is well known that any protium H in materials will increase optical loss in
the range of 1.3 to 1.55
pm, a typical wavelength range for optical communication. The strategy to
eliminate H is to replace
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CA 02345939 2001-05-03
H with fluorine F and deuterium D. 'This approach has received great success
in replacing C."-H bonds
with C-F or C-D bonds. The reason is that the C-H bond's vibrational overtones
occur near 1.3 and
1.55 Vim, and the related energy is irxvc~rsely related to the reduced mass.
Due to the highly reduced
mass of F and D, the fundamental bond vibrational overtones of C'-F and C-D
can be lowered, shifting
the related absorption peak to longer vravelength range. Fluorinated and
deuterated acrylate resins and
fluorinated sol-gel materials are examples of successful systems. It should be
noted, however, that
while the replacement of C-H with t:.'-I~ can reduce the optical loss at both
1.3 and 1.55 pm, the
replacement of C-H with C-D can only reduce the loss at 1.3 pm because C-D has
an absorption at
1.55 pm. C-D technology is definitely not suitable for the application at 1.55
pm. This excludes the
application possibility of C-D technology because 1.55 pm is the wavelength
used most in fiber
optical communication.
The method of the present invenrion is, to replace H20 with Dz0 for hydrolysis
of silanes, followed by
proper polycondensation. D and H are both isotopes of hydrogen. H is t:he most
common isotope of
hydrogen. It has a mass number of 1 and an atomic mass of 1.007822. Its
nucleus is a proton. D, also
called heavy hydrogen, has a mass number of 2 and an atomic mass of 2.0140.
Its nucleus consists of
a proton plus a neutron. DSO, so-called heavy water. has a melting point of
3.79°C, boiling point of
101.4°C, and density of 1.107 g/cm ' at 25°C.", in comparison to
H20 with 0°, 100°C, and 1.000 g/cm;,
respectively. Dz0 is not radioactive and is widely used as a moderator in
nuclear reactors. The
chemical properties of DZO are generally considered same as H20 because both D
and H have one
proton. The absorption behavior of O-D in comparison with O-H, is the reason
for the present D20-
based hydrolysis of silanes and other nnetal compounds, especially in sol-gel
processes.
FIG. 1 shows the absorption spectrum of D20 with HZO in the near infrared
region. The measurement
was conducted by using Nicloet 470 FT1R/N1R spectrometer with transmission
model. A 1 mm thick
quart sealed liquid cell was used for the measurement. 1'he first and second
overtones of O-H are
shown at 1.94 pm and 1.45 lun respectively with strong intensity. The
absorption of Hz0 at 1.55Nrn is
greatly enhanced especially by the second overtone, peak of O-H. On the other
hand, the second
overtone peak of O-D occurs at 1.98 N,m with intensity lower than that of the
second overtone peak of
O-H at 1.45 pm, and the first overtone of O-D occurs at above 2.61 pm (not
shown in the figure).
There is no absorption peak for O-D within the range of ( .0 to I .8 wtn. As a
result, the absorption of
D20 at 1.55~m is 1/10 ofthe absorption of HZO at the same wavelength. The
above result .fits well in
our theoretical calculation based on inlFrared theory.
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Although the absorption peaks of O-D> in a material, such as polysiloxane
resin, will not be the same
with those in D20 due to the changed chemical environment, the difference is
generally quite small. It
implies that for the same concentration of O-H and O-D in certain materials,
the O-D containing
system should have much lower chemical related absorption at 1.55 p.m than O-H
containing system.
The D20 based hydrolysis and condensation of silanes based on the present
invention have been
tested in the laboratory and can be expressed as:
Si-O-R + D20 --.-,. Si-(,)-D (1 )
Si-O-D + D-O-Si ~Si-O-Si (2)
Si-O-D + RO-Si ~ Si-O-Si + RO-D (3)
Where R is an organic group, such as CH3> CZH,, C~H~, . . .,etc.
The D20-based hydrolysis and condensation of metal compounds can be expressed
as:
M-OR + D20 --r M-O-l.) (4)
M-O-D + D-O-M -'' M-O'-M (5)
M-O-D + RO-M ~ M-O-M + RO-D (6)
Where R is the same as above, and M is a metal atom, such as AI, Ti, Zr, Er,
Pb, ..., etc.
As seen in the reaction equations, O-D~ is the only chemical residual in the
materials. The obtained
materials or chemicals are 100°% O-r-1 free.
The hydrolysis and condensation of silanes and metal compounds under DZO, can
be conducted under
the same condition as those under HZC). 'These reactions occur in acid or
basic catalyzed environment.
The difference between acid-catalyzed. amd basic catalyzed reaction is that
acid is in favor of
hydrolysis while basic is in favor of condensation. Chemicals, such as
methanol, ethanol,
isopropyanol, and acetone can be all used as the solvent for the reactions
based on D20. Bulk reaction
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CA 02345939 2001-05-03
without any solvent can be also conducted in a controlled way. Reaction
temperature can be kept at a
wide range from room temperature to 80°C. The advantage of applying D20
is that the technology
based on HZO, which was started a hundred year ago, cm be copied and
transferred to D20 system
with minor modification.
Very importantly, DZO involved hydrolysis and condensation were found very
easily in comparison
with H20 involved one. For instance, when H20 and DSO were respectively
applied in the hydrolysis
and condensation of methac~yloxypropyl tniethoxysilane in acid-catalyzed bulk
system, the DZO-
based reaction is faster than HBO-based one. The viscosity of the resulted
resin from DZO is 100%
higher than that of the HBO-resulted resin. Also, for a typical sol-gel
process based on
tetraethoxysilane in isopropyanol at acrid condition, DZO was found to be
impossible to generate a
transparent sol-gel solution because th.e condensation was too fast to produce
and precipitate gel
particles. On the other hand, transparent sol-gel solution was easily prepared
under the identical
condition with H20.
The easy hydrolysis and condensation is a real advantage for D20-based
reactions. It means that less
O-R will be le$ and more Si-O-Si will be formed in DSO based system than H20's
system, and the
residual O-D in Dz0 based system will be lower than the residual O-H in H20's
system. In other
words, even if O-D bond had the same; absorption behavior as O-H in the region
of 1 to 1.8 um, D20
based system will still have lower absorption, thus optical loss, than HZO
based system in the region.
It can be expected that, in comparison with HZO based system, D20 based system
should have even
lower O-D bond-caused optical loss at l .55pm than that obtained from FIG. 1.
FIG. 2 shows the absorption of DZO and HZO based sol-gel materials in the near
infrared region. The
measurement was conducted by using Nicloet 470 FT1R/NIR spectrometer with
transmission model
and sample thickness was 2 m for both materials. The materials were
synthesized from
methacryloxypropyl trimethoxysilane and diphenyldiethoxysilane by sol-gel
process, one with D20
and another one with H20 as hydrolysis agent. The peak at around I .4 um is
due to C-H bond for
D20 based material, and C-H bond and O-H bond for HBO based material.
Consequently, the
materials based on DZO does not have an absorption shoulder at 1.55 pm, while
the materials based
on HZO has a stronger O-H bond related shoulder at 1.55 pm. The waveguide
propagation loss of
Dz0 based materials is 30% to 50% lower than that of HZO based materials.
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Since the hydrolysis and condensation can develop easily in D20-based
reactions during the materials
synthesis stage, less post reaction will be required for the materials
processing stage for the system.
The benefit is that lower baking temperature would be required for processing
the materials reacted
from Dz0 and the achieved materials have less shrinkage during the processing,
and have better
thermal and mechanical properties tlmn HZO based materials. Also, it should be
noted that the acid-
catalyzed hydrolysis and condensation under DZC) is a problem for the
hydrolysis and condensation of
fluorinated silanes which are unstable under basic environment.
The D20 technology has resulted in various O-H free materials in our lab. Sol-
gel based silicon
containing materials and metal containing materials, which can be used as
waveguiding photonic
device, surface treatment agent, coating, index matcher, and adhesives, are
the representative
examples. Such technology can be easily extended to other application for
producing silica and metal
oxides for optical communication. Manufacturing of waveguiding photonic
devices by such as flame
hydrolysis deposition (FHD), for instance, is the area where Dz0 technology
can be applied because
H20 is used in these processes and the elimination of residual O-H is big
problem.
EXAMPLE 1
25g methacryloxypropyl trimethoxysilane was reacted with 4.4 g D20 with acid
HCL as catalyst at
room temperature. The mixture was opaque at beginning, and turned backed to
transparent within 3
minutes. Reaction heat resulted temperature increase was detected to start at
2 minutes. The mixture
was stirred for 16 hrs with aluminum foil covering the baker's top. Viscous
resin was obtained from
the reaction and the viscosity of the solution which contains D20 and ethanol
resulted from the
reaction was measured at room temperature as 63.4 cp by using Brookfield
viscometer. The solurion
was coated on silicon and glasses and baked at 110 to 1 30°C for 24 hr.
to produce flat, hard and
transparent coatings. No O-H absorption was detected in the materials in the
range of 1 to 1.8 N,m by
using Nicloet 470 FTIR/N1R spectrc»neter.
A parallel reaction with the replacetrrent of 4.4g DZO with 4.2g Hz0 was also
conducted. The reaction
phenomenon was basically t:he same ass the reaction with DZO. The resulted
resin after the svne
reaction time as above was measured as 31.6 cp of viscosity at room
temperature.
CA 02345939 2001-05-03
EXAMPLE 2
20 tetraethoxysilanes (TEOS) was reacted with 4.10 g DSO with 4.8g isopropanol
in presence and
HCL acid as catalyst. The mixture was opaque at the beginning, but turned
backed to transparent
within 3 minutes, and then turned into opaque. Reaction resulted temperature
increase was detected to
start within 2 minutes. After stirred fo~~ I .S hrs, opaque solution with fine
suspended particles was
obtained. These particles are visible when the solution was cast on glasses
and the solvent was
evaporated. Flat and hard coatings were obtained after the solution was
filtered with 0.451un sized
filter, and then coated by spinning coating. followed by baking at
110°('.
A parallel reaction with the replacement of 4. Ig DSO with 3.9g Hz0 was also
conducted. 1fie reaction
time was basically the same as the reaction with D ZO, however the solution
only experienced
transparent-to-opaque and opaque-to-transparent process and the final solution
was transparent one
with no suspended particles. Flat and lard coatings were obtained without
filtering the solution.
The particles generated from D20-based system during the reaction were silica
gels. They were
produced due to the fast condensation process. The solubility of silica gels
in the solution is limited
and the gel precipitate from the soluticm instantly when the gel particles
reach certain size. Similar
particles were reported in basic-eataly::ed H20-based system because
condensation under basic is
very fast.
EXAMPLE 3
25g methacryloxypropyl triethoxysilane and 3.0 g DZO was reacted under acid
condition for 2 hr. and
then mixed with the mixture of methac:rylic acid and zirconium n-propoxide
(18g), and then 1.5 g
D20 for 2 hr. The resulted solution was viscous with a viscosity at room
temperature as 142 cp when
the measurement was done 48hr after the reaction was completed. In the case
that H20 was used in
the reaction, the resulted solution viscosity was measured as 52.6 cp under
the same conditions. 2%
mol photosensitive initiator (Irgacure) was added into the system to yield a
free-flowing solution,
which was passed through 0.2 pm filter.
Films were deposited on polished silicon by dip coating with the filtered
solution and then prebaked
at 100 for 30 min to stabilize the coating. They were then exposed to UV light
through mask with
desired opening to polymerize the mavrvlates component. After rinsing with a
proper chemical and
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dried, desired waveguides were formed on the substrates. Channel waveguides
with proper buffer and
upper cladding, which were also based DZO resulted materials, were prepared
and tested. Their
propagation loss at 1.5 pm is 30 % less than that of the waveguides based on
HZO.
EXAMPLE 4
15g methacryloxypropyl triethoxysilane and 12g diphenyldiethoxysilane were
reacted with 5g D20.
A very viscous resin was obtained after the reaction. 2°ro mol
photosensitive initiator (Irgacure) and a
proper solvent was added into the system to yield a free-flowing solution. The
solution was filtered
through a 0.45 lun sized fili:er and deposited on silicon for preparing
channel waveguides and casting
cylinder/rectangular blocks with proper U V exposure and themal treatment.
Similar reaction based
on H20 was also conducted and the ot~tained material was used for comparison.
FIG. 2 shows the absorption of the materials in the near infrared range. 'Ifie
peak at around 1.4 pm is
due to C-H bond for D20 based materials, and C-H bond and O-H bond for H20
based materials.
Consequently, the materials based on DSO does not have an absorption shoulder
at 1.55 pm, while the
materials based on Hz0 has a stronger C>-H bond related shoulder at 1.55 p,m.
The waveguide
propagation loss of Dz0 based materials is 30% to 50% lower than that of H20
based materials.
EXAMPLE 5
15 g phenyltriethoxysilane and 2.5 g diphenyldiethoxysilane were reacted with
5.$ g D20 under basic
condition at 60°C. A very viscous resing was ontaied after the reaction
was proceed for 7 hrs. After
being cured at 130°C, the resin was measured to have a refractive index
of 1.501 at I .5 um
wavelength. The material was applied between two optical fibers and fiber to
waveguide as low
optical loss index matching materials.
EXAMPLE 6
15 g methacryloxypropyl trimethoxysilane and 12g diphenyldiethoxysilane were
reacted with 6.3 g
D20 under acid condition. After reacting for 7 hrs at 70"C:, 70 ml acetone was
added into the
solution at room temperature, followed by adding 2 g tetraethoxysilane. 4 hrs
later, 1 g of D20 was
gradually added into the solution and tlhe solution was kept stirring at room
temperature for 24 hrs.
CA 02345939 2001-05-03
The obtained solution was used as surFace promoter of silicon wager and silica
for producing
waveguides when using the materials as defined in EXAMPLE 4 as waveguide
materials.
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