breaking the wall to a new age of
electronics
our micro and optoelectronics lead to
transparent and paper transistors
universitat nova de lisboa portugal
on november the 9th 1989 i was working
at the new
university of lisbon as a teaching
assistant
good afternoon ladies and gentlemen
first of all i would like
to thank you the falling walls
association
foundation sorry to invite me and to
allow me to share with you
some of our results the last results
that we have done in our
laboratory so
i will start with the title that was
already presented
and maybe i will i will i need to start
with the question
what is transparent electronics maybe we
need to learn a little bit about
what it is and in fact
this is quite simple so we just need to
combine
optical transparency with electrical
conductivity
in fact it's easy but maybe it's not so
easy
let's let's see so this is for an
example of
conducting materials this is metals
but as you can see they are not
transparent
so if we are looking for transparent
electronics we need to have
something else so we need to have
maybe the optical properties of
our window glasses by combining
optical properties of insulators and
electrical properties
of metals maybe we reach transparent
electronics
and this is what we have done but maybe
we can say that
the inventor or the inventor of
transparent electronics
was stephen spielberg and in fact in
2004
with this nice movie called minority
report where tom cruise manipulates
all this information at that time this
was
science fiction really but now we can
say that
became reality and also in some way like
if you remember the work of julio vernes
maybe for science science fiction is
quite
important because we can think in huge
things and we scientists we are able
after some some work to to realize
and to make the dreams reality so this
is one of the first prototypes using
transparent electronics
this is a as you can see this is a
laptop
where the screen is fully transparent
but the picture is not quite nice
because it's quite difficult
for the camera to take a picture for
something that is transparent
so here the next one it's a movie that
it's available
at youtube also this is a prototype from
samsung
where the develop windows are displays
that are fully transparent and besides
having transparency
they are for example like that one is a
touch screen so
simultaneously you have a huge window
glass that works like
a display but simultaneously has a
touch screen capabilities
or even a window or maybe in the near
future we will have something like that
a fully transparent mobile phone
so this is not yet done so how can we
make
these things possible how
very easy by using metal oxide
semiconductors so we can use
new materials or new semiconductors in
order to realize
these devices and to be able to make
this technology
really real so in fact
we are today in the presence of a new
hero of
electronic materials and for example
like in a classroom
if we choose the good students
and for example peroxide zinc oxide
and we try to avoid the bad ones by
using these
metal oxide materials we are able to
make
transparent electronics and in fact we
substitute
in some way silicon which is the
conventional
semiconductor used for making integrated
circuits
we use copper oxide zinc oxide gallium
oxide
indium oxide tin oxide for making
semiconductors and why
why these materials are so attractive
because
they present a low cost they are
biocompatible
they are recyclable the technology for
producing these materials is green is
not is not
polluting like the one used for
used for conventional silicon and also
they present
superior electrical performance for
example if we compare
to what we are using today in our
displays
as you know a display needs to have a
liquid crystal this
film or some oleds but we need to have
pixels and for each pixel we need to
have a transistor
and the semiconductor used for that
transistor is based on amorphous silicon
but they have this material has some
disadvantages
and in that case these oxides
they present superior electrical
properties
so in terms of the applications for this
new technology
or for transparent electronics of course
the first one
is related to the display industry but
we are not limited to the displays we
can use these
this technology are these new materials
for a wide variety of
other applications and since
when we are dealing with something that
is disruptive or
it is completely new even for us is a
little bit
difficult to imagine or to realize where
we can use
all these uh capabilities but as you can
see here
we are not limited to this place we have
a huge
number of other possible possibilities
so we have also some work with samsung
we got
the international patent on that
and now i will switch to paper
electronics so i thought
the first part was on transplant
electronics now i will
explain you and i will try to convince
you what is
paper electronics and it's also very
simple is the possibility to use
conventional
versatile cellulose conventional paper
for electronic applications
and why we choose cellulose because
as you know is the earth's major
biopolymer so we have
a resource available in the world
it's a material that is flexible and for
some applications flexibility is a
huge advantage is a cheap material
the technology is already available we
don't need to invent
nothing the paper was already invented
by the chinese
uh when 1000 years ago it's a good
as a good good dialectic property so
it's an
issue later and also is
recyclable so paper is quite interesting
not only for packaging or writing
and when we are talking about
electronics maybe this type of images or
even in my
the previous speaker these images are
very familiar to you
electronics okay we associate
electronics to this type
of images but also we are facing some
problems with the conventional
electronics
we are producing what we call the
high tech trash because in some cases
it's not
possible to recycle all these
all these things and also not only the
electronics but if we are think uh
thinking about the packaging industry
also we are polluting
especially especially the oceans with
all these
plastics around
and of course for example this is just
for you for
for you to give you an idea about the
international
electronic waste shipments where
we are not solving the problem but we
are reallocating
this problem for other countries
especially for this part
of the earth
and today we are used to ebooks
journals papers read ereaders
so the idea of a paper is to substitute
journals or cellulars for from
an electronic device in our case
is exactly the opposite we are trying to
use
again cellulose paper for electronic
applications
and that's why we shift the e from left
to right because instead of working with
e paper we are we are working with paper
e
and what it is peppery paper electronics
is very easy paper works like the
physical support
and also as an active function in the
device
because we are now using paper for
writing so we need to have a physical
support for the ink
here paper works like a physical support
for
our transistors for our integrated
circuits but simultaneously has an
active function
on the device so this is what we have
done
in 2008 so we have a cellulose
a sheet of paper which is dialectic as
is an insulator and on both faces of the
paper we print
a conductive material and on the other
hand the semiconductor
and we build a transistor this is the
easiest way
to build a field effect transistor
and it works so a transistor is like a
switch on off so here for example you
can see
this is a logarithmic scale where you
have the current
as a function of the gate voltage but
what you saw
you can see here we have a logarithmic
scale
so it means that in the off region the
current available supplied by the device
must be
very very low and during the on
switch the current must be very high so
this is just
what how it works the transistor is a
switch on
off in the off state the current is very
low
on the on state the current must be very
high and this value
the ratio must be as high as possible
so this is how they look like it's still
papers
even we can functionalize the paper with
some materials
and turn on piper
an insulator paper on conducting paper
and also this is our last streams since
we are working with transparent
electronics
in in a way on the other way we are
working with pepper electronics
why not combine and have a transparent
paper and taking profit of
nanotechnology for example we can
develop
some nanocellulose by this is an example
from
cellulose fibers from cotton and here
you can see
a piece of transparent paper
what it's called nanopaper is still
cellulose but simultaneously is
transparent because we are
playing the the fibers are much smaller
and also following the trend in the
paper work also we are
working on microfluidic on paper in fact
this work
was started in harvard by professor
george
whitesides where the main idea is to use
low-cost safe disposable rapid and
self-sustainable paper-based
platforms for a diagnostic testing so
our idea is to use very simple
colorimetric devices like pregnant tests
and to try to democratize all these
diagnosis stats
tests for regions where nothing is
available
unless the diseases so
these paper transistors got
a huge interest around the world even i
gave a lot of interviews for all these
things
but of course i would like just to
finalize that this is not a
self woman work this is a team work
as we are doing and i would like to
thank of course the team that is
supporting all
these activity as well as okay persons
are quite important
but even without the defending of
projects we cannot realize or we cannot
materialize our dreams and finally i
would like
to thank you for your kind of attention
and to stay until the last session