PRESENTATION ON
ELECTRIC-DOUBLE-LAYER TRANSISTORS
FOR BIO-CHEMICAL SENSING APPLICATIONS
ANDUKURI DINAKAR
Roll no:194503
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1. Introduction
2. Physics of EDLTs: The Basics for Sensing
2.1 EDL Capacitance and EDLTs
2.2 Materials in EDLTs
2.3 Ion-Modulation in EDLTs
2.4 Sensing Principle of EDLTs
3. EDLT Based Biochemical Sensors
3.1 Organic-Based EDLT Sensors
3.2 Oxide-Based EDLT Sensors
3.3 Nanomaterial-Based EDLT Sensors
4.Conclusion
Introduction:
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Biochemical species detection techniques have important
applications in the area of homeland security, medical..etc
Energy transduction principles have been employed for chemical
and biologica lsensing based either on optical ,electrochemical.
Electrochemical sensors analyze the content of target species due to
the direct conversion of a biochemical event into an electronic signal.
ISFETs are used widely in the growing field of biochemical sensing
applications due to their advantages of label-free detection, easy
miniaturization, integratability, robustness.
Introduction(contd)
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The variation of surface potential on the sensing membrane arising
from the adsorption of charged target species can be sensed by
ISFETs.
FIG ISFET
2. Physics of EDLTs: The Basics for Sensing
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The key feature of an EDLT is the formation of EDLs at the gate
electrode/electrolyte and electrolyte/semiconductor channel
interfaces.
The strong ion-induced EDL capacitive effect endows the EDLTs with
high carrier density, low operating voltage.
2.1 EDL Capacitance and EDLTs
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A double layer (DL, also called an electrical double layer, EDL) is a
structure that appears on the surface of an object when it is exposed
to a fluid. The object might be a solid particle, a gas bubble, a
liquid droplet, or a porous body.
Schematic of double layer in a liquid at contact with
a negatively-charged solid. Depending on the nature
of the solids, there may be another double layer
(unmarked on the drawing) inside the solid
2.1(contnd)
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The electrical double layer (EDL) is the result of the variation
of electric potential near a surface.
It has a significant influence on the behaviour of colloids and other
surfaces in contact with solutions or solid-state fast ion conductors.
The primary difference between a double layer on an electrode and
one on an interface is the mechanisms of surface charge formation.
EDLs are analogous to the double layer in plasma.
2.2 Materials in EDLTs
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Various semiconductor materials have been used as active channel
layers in EDLTs, including
organic semiconductors
oxide semiconductors
semiconducting nanomaterials
Organic-based EDLTs have significant advantages in low-cost
fabrications
But their low carrier mobility and poor stability are unfavorable for
ultrasensitive biospecies monitoring applications.
2.2 CONTD
Oxide-based EDLTs show relatively higher carrier mobility and better
stability.
 Nanomaterial-based EDLTs exhibit highest
sensitivity due to their small geometry
and special electrical properties.
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2.2CONTD
2.3 Ion-Modulation in EDLTs
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The operation mechanism of EDLTs is mainly based on the ion/electron
(hole) electrostatic coupling effect
The induced charge density Q = CDLVG
(a)The charge process in EDL formation
under an external voltage.
(b) The formation of EDL capacitors at the
electrode/electrolyte interfaces.
(c) The discharge process of EDL capacitors.
2.4 Sensing Principle of EDLTs
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Due to high EDL capacitance, EDLTs have been widely used to develop
biochemical sensors.
They have low operation voltage and high sensitivity.
During the sensing process, the target species adsorbed at the
electrolyte interfaces.
Gives rise to a change in the channel current of EDLTs, and as a result
a sensing signal is observed.
3.1 Organic-Based EDLT Sensors
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They are electrical insulators, but become semiconducting when
charges are either injected from appropriate electrodes,
upon doping or by photoexcitation.
Organic semiconductors have received growing interests in flexible
electronics and bioelectronics.
Features of organic semi are synthetic freedom, solution
processability, mechanical flexibility, biocompatibility, etc.
Advantages and Disad of organic electronics
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Organic electronics are lighter, more flexible
Low-Cost Electronics
No vacuum processing
No lithography (printing)
Low-cost substrates (plastic, paper, even cloth…)
Conductive polymers have high resistance and therefore are not good
conductors of electricity.
3.2 Oxide-Based EDLT Sensors
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A variety of semiconducting oxides have been used as channel layers
in EDLTs, including zinc oxide (ZnO), indium oxide (In2O3).
EDLTs based oxide semiconductor permit stable detection under harsh
environments due to their electrical and thermal robustness.
Metal oxides are superior sensing materials for biochemical
detections.
IGZO
Chae et al presented an
amorphous
IGZO-based solutiongated EDLT
as a biological sensing
platform.
3.3 Nanomaterial-Based EDLT Sensors
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carbon nanotubes (CNTs), graphene, molybdenum disulfide (MoS2)
nanosheet, various inorganic nanowires, etc. nanostructure EDLTs
As early as 2002, Rosenblatt et al. fabricated aSWNT-based
transistor gated by a NaCl solution.
3.3CONTD
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graphene devices used for biosensors due to their extremely high
carrier mobility, low intrinsic electrical noise.
solution-gated graphene transistor exhibit ultrahigh sensitivity
high mobilities and ambipolar field-effect characteristics, solutiongated graphene transistor shows unique radio-frequency properties
Conclusion
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The operation of EDLTs is based on the ion-induced capacitive coupling
effect at the electrolyte/semiconductor interfaces.
Due to the strong EDL capacitance, the electrical properties of EDLTs
depend deeply on the charged species at the interface, making EDLTs
more sensitive than common ISFET devices for biochemical sensing
applications
possibilities of processing EDLT sensors by printing technologies could
make their fabrication particularly cost effective for mass production.
contd
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EDLT-based sensors exhibit huge potential in the field of Internet of
Things applications, such as wearable medical devices, implantable
sensor chips, real-time environment analyzing, etc
More importantly, based on the inherent properties of dynamic ion
modulation, novel architectures and innovative test methods could be
exploited on EDLT-based sensors, making it feasible for multiplex
sensing and high-resolution temporal-spatial detection.