04-10-2016, 11:26 AM
1457618709-17te.pdf (Size: 730.78 KB / Downloads: 31)
Abstract – Transparent electronics is an emerging science
and technology field concentrates on producing ‘invisible’
electronics circuit and optoelectronics devices. The
application contains consumer electronics such as
automobile windshield, transparent solar panel,
transparent display and real time wearable display. In the
conventional Si/III-V based electronics, the structure is
based on semiconductor junction & transistor. However,
the basic building material for transparent electronic
devices which is to be transparent and in visible range is a
true challenge! .Therefore to understand and implement
such technology there are two scientific goals, to have a
material which are optically transparent and electrically
conductive and to implement an invisible circuitry.
Development of such invisible transparent electronic
devices needs expertise together from pure and applied
science, material science, chemistry, physics &electronic
science.
I. INTRODUCTION
The classes of material available for transparent
electronics have grown dramatically in the last decade.
The TCO is widely used as oxide material as it is both
electrically conductive and optically transparent.
Transparent conductors are neither 100% optically
transparent nor metallically conductive. From the band
structure point of view, the combination of the two
properties in the same material is a contradictory.
A transparent material is an insulator which posses
completely field valance & empty conduction band
while conductive material has Fermi level of completely
field conduction and valance band.
The most commonly used TCO in transparent
electronics are In2O3, SnO2, ZnO and CdO.
Transparent conducting oxide such as Sn doped In2O3;
Al doped ZnO & Sb doped SnO2 are widely used as
transparent LCD, Organic light emitting diode & solar
cell. In addition TCO are applied to transparent
optoelectronics because it has unique feature of optically
transparent in visible region
FABRICATION
Generally, epitaxial films of semiconductors are
fabricated by conventional vapor phase epitaxy (VPE)
techniques such as RF sputtering, vacuum evaporation,
chemical vapor deposition (CVD), molecular beam
epitaxy (MBE), and pulsed-laser deposition (PLD).
However, such VPE methods cannot be applied directly
to the growth of TOSs because it becomes dominant at
temperatures higher than nearly 60% of the melting
point of the compound. Therefore such a hightemperature
deposition process in turn induces an
intrinsic problem for the growth of complex oxides
[1][4].
To overcome this difficulty in conventional VPE,
new technique is developed called reactive solid-phase
epitaxy (R-SPE). The solid-state reaction at high
temperature leads to the formation of a thin, single
crystalline layer on the substrate InGaO3 (ZnO) with a
layered natural super lattice structure which would have
been impossible by conventional VPE [1][4].
Several types of transparent optoelectronic devices
have been demonstrated, such as p-type SrCu2O2 and ntype
ZnO, UV-detectors composed of single crystalline
p-type NiO and n-type ZnO, and transparent thin-film
transistors (TTFTs) fabricated from single-crystalline
InGaO3(ZnO).
TRANSPARENT OPTOELECTRONICS
DEVICES
A. Transparent thin film transistor:
It is a special kind of field-effect transistor made by
depositing thin films of a semiconductor active layer as
well as the dielectric layer and metallic contacts over a
supporting substrate. A common substrate is glass, since
the primary application of TFTs is in liquid crystal
displays. This differs from the conventional transistor
where the semiconductor material typically is the
substrate, such as a silicon wafer[1][4].
TTFTs using TOSs as the channel layer have
several merits compared with conventional Si-TFTs
when applied to flat panel displays. These include the
efficient use of backlight in LCDs or emitted light in
OLEDs and insensitivity of device performance to
visible light illumination. In addition, oxide TFTs has
potential advantages over semiconductor-based TFTs in
terms of their high voltage gain, heat dissipation, and
radiation tolerances. The TTFTs fabricated to date using
conventional TOSs are SnO2 and ZnO [1][4][6].
A single-crystalline film of the TOS InGaO3(ZnO)
is used for the active channel layer to realize highperformance
TTFT devices. This material has
advantages over conventional TOSs, including the
efficient growth of high quality, single-crystalline films
and good control of carrier concentration. The crystal
structure of InGaO3(ZnO)m consists of an alternating
stack of InO2- layers and GaO+(ZnO) m blocks make
up a super lattice structure. For fabricating TTFT the RSPE
method is used and producing high quality single
crystalline films of InGaO3 (ZNO)5 and R-SPE is a
unique and practical growth method for this compound Indinium tin oxide &ZnO are used as interconnection. In
traansparent displays, the device exhibits an on-to-off
current ratio of nearly 106
and a field-effect mobility of
nearly 80 square centimeters per volt per second at room
temperature [1][4][6].
Transparent UV detector
The UV radiation that reaches the surface of the
Earth has a Wavelength of 280-400 nm (UV-A and UVB),
and plays an important role in skin aging and cancer.
Portable UV-detectors, which contain a pn-junction of a
wide band gap semiconductor, would be useful for
monitoring UV radiation intensity. Although several
UV-detectors have recently been developed using pn- or
Schottky-junction diodes of wide band gap
semiconductors such as GaN, ZnSe, ZnS, and diamond,
TOSs are preferable because they are optically
transparent in visible and near-UV regions,
environmentally friendly, and thermally and chemically
stable[1][4].
A transparent UV-detector was fabricated using a
high quality pn-heterojunction diode composed of ptype
NiO: Li and n-type ZnO and its UV response
measured at room temperature[4][1].A p-type NiO ntype
ZnO heterojunction diode measured in dark (UVOFF)
and UV (300-400 nm wavelength) illumination
(UV-ON, total power density ~0.33 W/cm2) at room
temperature [1][4].
IV. APPLICATIONS
Now days there is vast used of transparent
electronics application such as OLED display
&transparent solar panel
A. OLED Display
Types of OLED
A. Transparent OLED
Transparent OLEDs have only transparent
components (substrate, cathode and anode) and, when
turned off, are up to 85 percent as transparent as their
substrate. When a transparent OLED display is turned
on, it allows light to pass in both directions. A
transparent OLED display can be either active- or
passive-matrix. This technology can be used for headsup
displays [5].
CONCLUSION
Transparent electronics are relatively new class of
material which is applied to active devices such as TFT
and UV detector. Combining of two properties that are
optically transparent and electrically conductive gives
lots of advantages such as high mobility, low processing
temperature, high performance and flexibility. The use
of OLED as a display gives a high advantage such as
more brightness and less power consumption.
Transparent solar cell gives a tremendous advantage
over conventional solar cell as it required less space,
produces more energy, eco-friendly and replaces the
ordinary window glass and become a domestic
electricity generator. so this new class of electronic is
more advantageous than conventional electronics