2. Ever you wondered that you are
travelling in a car and you want to
watch a movie or play video and the
glass shields i.e. window panels will
turn into a television screen or working
on a computer that simply looks like a
glass sheet just like the future computer
in movie “Krrish” or holding a
transparent iPhone…!!!
It is possible with the help of
transparent electronics.
2
4. INTRODUCTION
Transparent electronics (also called as invisible
electronics) is an emerging technology.
It employs wide band-gap semiconductors for the
realization of invisible circuits and opto-electronic
devices.
The first scientific goal of this technology must be to
discover, understand, and implement transparent high-
performance electronic materials.
The second goal is their implementation and
evaluation in transistor and circuit structures.
The third goal relates to achieving application-
specific properties since transistor performance and
materials property requirements vary, depending on the
final product device specifications. 4
5. 5
PRE-HISTORY
The two technologies which preceded and
underlie transparent electronics are Transparent
Conductive Oxides (TCOs) and Thin- Film
Transistors (TFTs).
TCOs constitute an unusual class of materials
possessing two contradictory physical properties-
high optical transparency and high electrical
conductivity. The three most common TCOs are
indium oxide In2O3, tin oxide SnO2 and zinc
oxide ZnO2.
The thin-film transistor (TFTs) is another
technology underlying transparent electronics,
since it is a bridge between passive electrical and
active electronic applications. But it does not
evolve a fully transparent transistor.
Material
Bandgap
(eV)
Conductivity
(Scm-1)
(siemen/cm)
Electron
Concentration
(cm-3)
Mobility
(cm2V-1s-1)
In2O3 3.75 10,000 >1021 35
ZnO2 3.35 8,000 >1021 20
SnO2 3.6 5,000 >1020 15
Electrical properties of
common TCOs
6. Transparent conductive oxides
Transparent conductive oxides (TCO) are doped metal oxides used in optoelectronic
devices such as flat panel displays and photovoltaic. Most of these films are fabricated
with polycrystalline or amorphous microstructures.
Thin-film transistor (TFT)
A thin-film transistor (TFT) is a special kind of field-effect transistor made by
depositing thin films of an active semiconductor layer as well as the dielectric layer
and metallic contacts over a supporting (but non-conducting) substrate. A common
substrate is glass , because the primary application of TFTs is in liquid-crystal displays.
6
7. HOW TRANSPARENT ELECTRONIC
DEVICES WORK?
7
The challenge for producing "invisible"
electronic circuitry and opto-electronic devices
is that the transistor materials must be
transparent to visible light yet have good carrier
mobilities which requires a special class of
materials having "contra-indicated properties".
Oxide semiconductors are very interesting
materials because they combine simultaneously
high/low conductivity with high visual
transparency.
Transparent oxide semiconductor based
transistors have recently been proposed using
as active channel intrinsic zinc oxide (ZnO).
8. The main advantages of using ZnO are:
1. The fact that it is possible to growth at/near
room temperature high quality polycrystalline
ZnO, which is a particular advantage for
electronic drivers, where the response speed is
of major importance.
2. Since ZnO is a wide band gap material (3.4
eV), it is transparent in the visible region of the
spectra and therefore, also less light sensitive.
The second is amorphous oxides with heavy metal
content, such as amorphous InGaZnO4 (a-IGZO)
also used in this application.
A comparison of ZnO and a-IGZO(indium gallium
zinc oxide)shows that ZnO has the lead when it
comes to carrier mobility. At present, though, a-
IGZO is the material of choice for large-area
displays, electronic paper utilizing low-temperature
processing, etc.
Oxides play key role:
Oxides
ZnO InGaZnO4
The major substrate
used for this
purpose is Glass.
Diamon
d
Glass
9. ADVANCEMENTS MADE IN
TRANSPARENT ELECTRONICS
Researchers at Oregon State University and Hewlett Packard have reported their
first example of an entirely new class of materials which could be used to make
transparent transistors that are inexpensive, stable, and environmentally begin.
9
Significant advances in the emerging
science of transparent electronics, creating
transparent "p-type" semiconductors that
have more than 200 times the conductivity
of the best materials available for that
purpose a few years ago.
This basic research is opening the door to
new types of electronic circuits that, when
deposited onto glass, are literally invisible.
10. 10
Characteristics other than Transparency.
Transparent semiconductors, in addition to being transparent, have a
number of useful characteristics, including a wide band gap, relatively
high carrier mobility, low-temperature manufacturability, and low
manufacturing costs thanks to the low-temperature process and
inexpensive materials. As a result, R&D into properties other than
transparency is also active.
Lets consider the properties of materials
other than transparency and their
applications…
11. 11
APPLICATIONS OF TRANSPARENT
ELECTRONICS
Transparent circuits will have
unprecedented applications in flat panel
displays and other electronic devices,
such as see through display or novel
display structures.
They have been widely used in a
variety of applications like:
1. Antistatic coatings
2. Touch display panels
3. Solar cells,
4. Flat panel displays
5. Heaters
6. Defrosters
7. Optical coatings.
and many more….
12. 12
MARKET OF TRANSPARENT ELECTRONICS
There are four critical aspects of “transparency” that the design and marketing of transparent
electronics products needs to focus on for it to become a serious revenue earner. These
factors are:
• Integration
• Improved economics
• Aspects of transparent materials that are not directly related to transparency.
The transparent electronic devices in the
market have many challenges to overcome in
order to capture the market like current apps
for transparent electronics are quite primitive.
This is the major distraction in the path of
these invisible devices…!!!
13. 13
Future Scope
In the field of solar cells, although much
progress has been made in developing new
materials and devices for high performance
transparent solar cells, there is still plenty of
opportunity to study and improve device
performance and fabrication techniques
compared with the nontransparent solar cell
devices.
It is likely that new scientific discoveries
and technological advances will continue to
cross fertilize each other for the foreseeable
future.
14. 14
CONCLUSION
Oxides represent a relatively new class of
semiconductor materials applied to active
devices, such as TFTs.
The combination of high field effect
mobility and low processing temperature for
oxide semiconductors makes them attractive
for high performance electronics on flexible
plastic substrates.
