WORLD’S 1ST:SPRAY ON SILICON INKJET

Spray-on silicon makes its debut
April 2006
Researchers
in Japan have unveiled a new way to make silicon-based microelectronic
devices. The method involves depositing silicon directly onto a
substrate from solution and overcomes some of the problems associated
with traditional silicon-processing lithographic techniques, such as
using sophisticated clean rooms and expensive vacuum equipment. The
researchers say the technique could lead to a way of making large,
flexible displays using “ink-jet” technology .
Silicon
microelectronic devices are currently made by heating highly purified
silicon in a vacuum and allowing the resulting “mist” of free silicon
atoms to coat a surface such as a plastic. Once deposited, the solid
film is etched and patterned using photolithography techniques to
produce circuit elements. However, this method is expensive and
complicated because it has to be carried out in an ultra-clean
environment to ensure that impurities do not contaminate the silicon
and ruin its electronic properties.
The new technique, developed by
a team led by Masahiro Furusawa of the Seiko Epson Corporation in
Nagano-ken, avoids these complications. It uses a liquid form of
silicon that can be made at room temperature and pressure and can then
be sprayed onto a surface using an ink-jet printer.
Furusawa and
co-workers start with a molecule called cyclopentasilane, which
contains five silicon atoms joined in a ring. When this liquid is
exposed to ultraviolet light, some of the rings break open to form
linear chains. These link up end-to-end to form even longer chains,
producing a highly viscous fluid.
The team dilute the liquid with an
organic solvent, which they then deposit on a surface either by
spin-coating or ink-jet printing. The resulting liquid film is finally
heated at around 500°C, which converts it into hard, polycrystalline
silicon. The team claims to have been able to make transistors from the
films.
According to the scientists, the electronic properties of
their films are as good as those of ultra-pure films made by
conventional processing techniques. Although the properties of the
ink-jetted films were not quite as good as those that were
spray-coated, the former were still much better than solution-processed
films of organic carbon-containing materials.
The new process is not
perfect, however, as air and water have to be carefully excluded.
Furthermore, the current ink-jetting method does not have the
resolution necessary to pattern high-density integrated circuits needed
to make computer chips. Nevertheless, the technique could be a novel,
inexpensive and easy way of making devices for a range of everyday
electronic equipment, including circuits for large-area displays, solar
cells and sensors.

        
Silicon film, TFTs use micro-liquid processes
Apr
2006Seiko Epson Corp. and JSR Corp. claims to have succeeded in
creating the world’s first silicon film with liquid coating and inkjet
patterning processes. The performance of low-temperature polysilicon
thin-film transistors (LTPS TFTs) produced with silicon film formed by
the spin coat method is said to be comparable to that achieved when
using silicon film formed using the conventional CVD method.
The new
material jointly announced by Epson and JSR is a high order silane
compound of hydrogen and silicon dissolved in an organic solvent. It
forms a silicon film when spin coated on the substrate and baked in an
inert atmosphere. When fabricating a TFT prototype using a silicon film
formed by spin coating (other than the formation of the silicon coat,
the production process is the same as for conventional LTPS TFTs), the
electrons achieved mobility of 108cm2/Vs.
Epson used its proprietary
micro liquid processes to demonstrate the possibilities of printed
TFTs, forming a silicon film pattern onto a substrate by firing the
materials onto a substrate using the inkjet method. As a result, part
of the pattern formation associated with traditional photolithography
is unnecessary, said the company. Forming a TFT prototype using a
silicon film pattern using the inkjet method, the electrons achieved
mobility of 6.5cm2/Vs, a figure that is said to be lower than that
achieved with spin coating. Although improvements need to be made to
the inkjet process, Epson believes that printed TFTs show sufficient
potential.|
This research was commissioned by Japan’s New Energy and
Industrial Technology Development Organization, an incorporated
administrative agency.