SPI Supplies® Brand Indium-Tin-Oxide (ITO) Coated Substrates
Choose from a variety of resistivities for a range of applications for ITO coated substrates
Introduction:
The concept behind the use of indium-tin-oxide (ITO) coated microscope
slides is surprisingly simple: Take a microscope slide, be it made of glass,
or quartz, or even plastic, coat it with ITO, apply a suitable conductor
strip at the ends, connect electrical leads (to put a voltage potential
across the slide) and the slide will be uniformly heated, higher even than
the boiling point of water (if desired). High transparency (from UV to NIR)
ITO coatings have applications not only for microscopy but any time planar,
electrically conductive surfaces are required that have the just indicated
transparency. Our coatings are also used by researchers in the areas of
liquid crystal display technology, polymer light emitting diode technology
and related applications. Our ITO coatings in general, provide good
transparency, good conductivity with reduced charging of the substrate
surface.
Anti Reflective Coatings:
The ITO coating itself is reflective, the antithesis of being
"anti-reflective". SPI Supplies is now able to offer our ITO coated
substrates with high quality anti-reflective as well as index matching
coatings.
Increased transmittance:
For those doing microscopy with ITO coated slides, there are times when no
matter how much transmittance there is, just a bit more is needed. Up until
now there was nothing anyone could do about that. But using the latest
technology in the thin film coatings industry, SPI can now offer two
additional coatings for slides.
1. Index matching coating (IMC) involves the application of a thin quartz
layer on top of the already applied ITO layer. The miracle of the IMC
quartz layer is that the transmittance is boosted up considerably.
2. Antireflective (AR) coating which is a quartz coating on the side of the
substrate opposite to the side with the ITO coating.
Do all users need an index matching coating or an AR coating, remembering
that we are talking about coatings to increase transmittance?
The answer is probably not everyone but for many of our customers, since
transmittance is one of those things in life that we say "never enough", the
possibility of getting these additional coatings is highly attractive for
their work.
No SiO2 passivation layers present under the ITO coating!
While certain products used in research are seen by the typical user as
being "generic", that all brands are "the same", let us assure you that this
is not the case for ITO coatings. The SPI Supplies Brand of ITO coated
substrates are most certainly not like any other. While we surely do want to
protect our proprietary technology and know how, we do want to cite one
important difference: The SPI Supplies ITO coatings are not applied over
an SiO2 passivation layer and the absence of such
a passivation layer can have important advantages to many users.
How can we get away with no passivation layer?
Because of the uniqueness of our process, one absolutely need not worry
about the leaching of alkali oxides into liquid crystal systems, and
therefore there is no need for a passivation layer. Our ability to avoid
this costly step results in a
lower cost production process and at the same time, results in an
incremental increase in transmittance. SPI Supplies can of course, provide
ITO coatings over an SiO2 layer, but it will also add to the final
price and would be treated as a special order.
Refractive index of the ITO coatings:
For those who need it, we can provide estimates of the refractive index of the ITO coatings
products by SPI Supplies.
Cleaning your ITO-coated slides:
Each SPI Supplies Brand ITO coated slide arrives individually wrapped in a special protective
paper selected to keep the slide clean and damage free during shipment and storage. However,
there could be times when the user would feel more comfortable giving the slide a cleaning
treatment prior to use, and the recommended cleaning solvent is isopropyl alcohol. This
solvent should not injure the ITO coating but with prolonged contact, it could start to
dissolve a bus-bar if present. Under no circumstances should you try cleaning with alkali solutions.
Dilute sodium hydroxide solutions are commonly used for patterning ITO.
We would also recommend a high quality lint-free cotton wiper such as our
own SPI-Wipes™ Lint-Free Cotton Wipers.
In any case, whatever you do, do not use any acid for cleaning, even a weakly acid agent, because it will
definitely damage the ITO coating irreparably.
If you are a "new-bie" to this field, we have attempted to "walk you
through" the product selection process. We realize that out of our desire
to create off-the-shelf products that can be manufactured in quantity,
thereby lowering both production and selling prices for both ourselves and
our customers, we do not want to create the appearance that we are closed to
the idea of making something "custom". We are happy to quote and
manufacture such custom products for our customers. However, for research
applications, where the numbers tend to be smaller, keep in mind that the
tooling and other set up costs to make the first one can be considerable,
and these are costs over which we have little control.
Custom ITO coating of customer supplied substrates:
We are very happy to receive customer supplied substrates for ITO coating.
Included in our pricing quotes for such a service is the proper cleaning and
preparation of the substrates prior to coating. This includes a special
proprietary solvent cleaning followed by a plasma cleaning to promote
adhesion of the coating to the substrate.
Let us know your requirements being sure to tell us the outside dimensions of the
items to be coated and also the resistivity wanted, remembering that using
one of our standard resistivities
will result in the lowest cost to you. This also means that we can apply over the ITO coating an index
matching layer designed to increase the transmittance. And
additionally, we can apply a proprietary antireflective (AR) coating on the
opposite face to increase the transmittance even further.
Use of busbars:
When the ITO coated substrate is to be connected electrically, some facility
must be made for the electrical contacts. In former days, early workers
used a piece of copper tape that was carefully wrapped around the edge of
the substrate but in later years, we developed an efficient process of
screen printing onto the substrates a silver paint (e.g. ink) that once
cured, exhibits a resistivity of better than 0.2 ohms per square. All SPI
supplied busbars are silver lines applied this way with this resistivity.
What we can not do.......
Our unique coating facility is set up to coat only ITO and quartz
and nothing else. We are not able to coat indium oxide or tin oxide, only ITO and quartz.
The quartz that we coat is
hard, durable and with a refractive index of ~ 1.47.
Cutting down larger coated pieces to smaller sizes:
Some of our customers are at times tempted to purchase a large piece of ITO-coated glass,
with the idea of scribing and then breaking down the glass to smaller sizes. Life should
only be that simple! Unfortunately, when this is done, there is sufficient disruption to
the ITO coating at the edges that it is never a good result. We always advise cutting the
glass down to the desired size and then coat the cut pieces. This does result in additional
handling, and higher costs but one is assured of a much higher quality result.
We segment our customers for these unique products as being either
Microscopy
- Cover slips
- Slides
- Large glass plates
- Other applications and custom coating
Select your area of interest and let us lead you through the selection
process which hopefully will lead to the optimum product for your
applications.
A Note on Terminology:
The electrical properties of the ITO coating are given as surface resistivity,
measured in ohms per square. In some disciplines,
people refer to this as sheet resistance. For reasons perhaps of laziness,
or other reasons, most people just call this number "resistivity". But we
should also point out that this is definitely not what is called "bulk resistivity.
To determine the actual resistance of a slide,
it is necessary to do a short calculation. For example, if the resistivity
is 30 to 60 ohms per square, then the resistance of the coating on a slide 1
x 3 inches (25 x 75 mm), measured along the length, is 90 to 180 ohms. This
is determined by dividing the length of the slide by the width of the slide,
in our example dividing 3 by 1, or 75 by 25, and multiplying that result (3
in our example) by the resistivity. No matter what units you use to measure
the dimensions, the resistance of the coating is the same.
Caution:
Electrical resistance heating can expose you to potentially lethal voltages.
We recommend that you use only low voltage power supplies for this application.
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Wednesday May 14, 2008
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