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7/28/2019 Transparent Final
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GOVT. WOMEN ENGINEERING
COLLEGE AJMER
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1. Introduction
2. Combining transparency with electrical conductivity
3. Carrier generation in TCO
4. Transparent electronic devices
5. Strengths and weaknesses
6. Application
7. Future Scope
8. Conclusion
9. References
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What is transparent electronics?
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Transparent electronics is an emerging science andtechnology focused on producing invisible electroniccircuitry and opto-electronic devices.
In transparent electronics the usual opaque
semiconductor materials forming the basis for electronicdevice fabrication is replaced with transparent materials.
Dramatical change in the look and use of electronic
devices
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A transparent material is an insulator which possesses completely
filled valence and empty conduction bands.
Hence their is a need to combine transparency with electrical
conductivity.
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For this we use-
DEGENERATE Doping
Certain oxides like In2O3,SnO2,Zn0,CdO consist of sufficient
transmission within the visible spectral range and moderate electrical
conductivity.
In a undoped state these are insulators with a band gap of 3eV.
To become a TCO host these are degenerately doped which results
in the displacement of Fermi-level into the conduction band. It
provides high mobility of extra carriers and low optical absorption.
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The high energy dispersion of conduction band also ensures apronounced Fermi level displacement above the conduction band
is known as BM shift (Burstein-Mass Shift).
This shift helps to broaden the optical transparency window
and keep the intense optical transition from the valence band out
of visible spectrum
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Burstein Mass (BM) Shift
http://en.wikipedia.org/wiki/File:MBshift_for_wiki.jpg7/28/2019 Transparent Final
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The optical and transport properties of a conventional TCO are
governed by the efficiency and the specifics of the carrier generation
mechanism employed. Even in the most favorable situation, i.e. when
the effects of dopant solubility, clustering ,secondary phase formation
and charge compensation can be avoided. Large concentrations of
electron donors (substitutional dopants and/or native point defects) not
only promote the charge scattering but also may significantly alter the
electronic band structure of the host oxide, leading to a non-rigid band
shift of the Fermi level.TWO METHODS:-
SUBSTITUTIONAL DOPING
OXYGEN REDUCTION
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Substitutional Doping
Substitutional doping with aliovalent ions is the most widely
used approach to generate free carriers in TCO hosts.Compared with native point defects, it allows a better control
over the resulting optical and transport properties as well as
better environmental stability of the TCO films.
For example ZnO films have been prepared by doping with
group III , IV and VII elements giving rise to a wide range of
electrical conductivities.
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Oxygen Reduction
Removal of an oxygen atom from a metal oxide leaves twoextra electrons in the crystal.
Whether one or both of these electrons become free carriers
or remain localized at the vacancy site correlates with the
oxide free energy of formation.
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Transparent electronicdevices
Transparent Passive devices
Transparent Active devices
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Transparent Passive Devices:-
Transparent Thin Film Resistors
Transparent Thin Film Capacitors
Transparent Thin Film Inductors
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Transparent Thin Film Resistors
Resistive material used is indium tinoxide
Fig (a) consist of sixteen path squares
Fig(b) consist of sixteen path squares
Greater the no of squares more is the
resistance
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Transparent Thin Film Capacitor
Dielectric are insulators and
hence transparent
So in case of capacitor the main
concern is contact layer
This layer is made with the help
of highly conducting oxide - ITO
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Transparent Thin Film Inductor
These are quite hard to design becauselarge inductance value require large no
turns which results in parasatic
resistance that is undesirable.
In this case also ITO is used due to
higher conductivity.
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Transparent Active Devices-Transparent Thin Film Transistor(TTFT)
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Transparent thin film transistor constitute the heart of
transparent electronics
The first transparent thin film transistor was made in 2003which uses zinc oxide as conductor
Channel is formed from highly insulating, wide band gap
transparent semiconductor(ZnO).
Source, drain and gate contacts are made from highly
conductive TCO (ITO).
N-type TFT are widely used as there are certain problems associated
with the doping of p-type TFT.
Efforts are being made to improve the performance of p-type TFT.
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Strengths
Weaknesses
Visible transparency High resistance of TCOsLarge area Lack of complementary devicesLow cost (solution based deposition
and printing)Technological immaturity
Low temperature processingFree real estateSafe, nontoxic materialsRobust stable inorganic materials
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1.Transparent Smart Window
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2.Transparent Cell-phones
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3.Transparent Laptops
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4.Transparent Oled
5.Transparent Batteries
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Transparent Smart Cards
Windowpanes with Transparent Solar Cell
Can be used for energy harvesting
Heads-Up Displays (HUD) showing driver support
information directly on a vehicle's windshield
Head-Mount Displays" where the lenses of goggles or
eyeglasses serve as displays
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Oxides a new class of material can be used for manufacturing
of transparent devices
These see-through devices can prove a boon to the to
technology
This will also help in development on flexible, non-breakable
electronics
It will be helpful in development of human machine
interaction in near future
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ZnO: From Transparent Conducting Oxide to
Transparent Electronics Fortunato E, Barquinha P, PimentelA, Pereira L, Goncalves G, Martins R 2007 Amorphous IZO
TTFTs with saturation mobilities exceeding 100cm2/Vs. Phys.
Stat. Sol. (RRL) 1 (1), R346.
Transparent Electronics , Springer publications, J.F.Wager,
D. A. Keszler, R. E.Presley.
Transparent electronics: from synthesis to applications,
Wiley publications: Antonio Facchetti, Tobin J. Marks.
www.sciencemag.org
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Queries?
Recommended