Need answers (10 points) What are the FET sensors and what are t

need answers . (10 points) What are the FET sensors and
what are the types and advantages?
Solution
Ans: Field-effect transistor (FET) is a transistor that uses
an electric field to control the electrical behaviour of the
device. First prepared as the metal oxide semiconductor
and later recognised as the transistor. Display very high
input impedance at low frequencies. The conductivity
between the drain and source terminals is controlled by an
electric field in the device, which is gener ated by the
voltage difference between the body and the gate of the
device. FET’s can be fabricated using various
semiconductors or with silicon. FET doped with different
metal ions either named as n-type or p-type
semiconductors.
Types of FET’s
JFET: (junction field-effect transistor) uses a reverse
biased p–n junction to separate the gate from the body. It
is the simplest unipolar type of field -effect transistor. They
are three-terminal semiconductor devices that can be used
as electronically-controlled switches, amplifiers, or
voltage-controlled resistors. The JFET is a long channel of
semiconductor material, doped to contain an abundance of
positive charge carriers or holes (p -type), or of negative
carriers or electrons (n-type). Ohmic contacts at each end
form the source and the drain. A pn -junction is formed on
one or both sides of the channel, or surrounding it, using a
region with doping opposite to that of the channel, and
biased using an ohmic gate contact.
MOSFET: (metal–oxide–semiconductor field-effect
transistor) utilizes an insulator (typically SiO2) between
the gate and the body. fabricated by the controlled
oxidation of silicon. It has an insulated gate, whose
voltage determines the conductivity of the device. This
ability to change conductivit y with the amount of applied
voltage can be used for amplifying or switching electronic
signals. A metal-insulator-semiconductor field-effect
transistor or MISFET is a term almost synonymous with
MOSFET. Another synonym is IGFET for insulated -gate
field-effect transistor. Material used is highly doped
polycrystalline silicon
MNOS: metal–nitride–oxide–semiconductor transistor
utilizes an nitride-oxide layer insulator between the gate
and the body. It is used in non -volatile computer memories
DGMOSFET: (dual-gate MOSFET), a FET with two insulated
gates. The multiple gates may be controlled by a single
gate electrode, wherein the multiple gate surfaces act
electrically as a single gate, or by independent gate
electrodes. A multigate device employing independent gate
electrodes is sometimes called a multiple -independent-gate
field-effect transistor (MIGFET)
FREDFET: (fast-reverse or fast-recovery epitaxial diode
FET) is a specialized FET designed to provide a very fast
recovery (turn-off) of the body diode. This specialised
field-effect transistor is designed to provide a very fast
recovery (turn-off) of the body diode, making it convenient
for driving inductive loads such as electric motors,
especially medium-powered brushless DC motors.
TFET: (tunnel field-effect transistor) is based on band -toband tunneling. experimental type of transistor. Even
though its structure is very similar to a metal -oxidesemiconductor field-effect (MOSFET), the fundamental
switching mechanism differs, making this device a
promising candidate for low power electronics. TFETs
switch by modulating quantum tunneling through a barrier
instead of modulating thermionic emission over a barrier
as in traditional MOSFETs. Because of this, TFETs are not
limited by the thermal Maxwell –Boltzmann tail of carriers
IGBT: (insulated-gate bipolar transistor) is a device for
power control. It has a structure akin to a MOSFET coupled
with a bipolar-like main conduction channel. These are
commonly used for the 200–3000 V drain-to-source voltage
range of operation. Power MOSFETs are still the device of
choice for drain-to-source voltages of 1 to 200 V.
HEMT: (high-electron-mobility transistor), also called a
HFET (heterostructure FET), can be made using
bandgapengineering in a ternary semiconductor such as
AlGaAs. The fully depleted wide -band-gap material forms
the isolation between gate and body.
ISFET: (ion-sensitive field-effect transistor) can be used to
measure ion concentrations in a solution; when the ion
concentration (such as H+, pH electrode) change s, the
current through the transistor will change accordingly.
BioFET: (Biologically sensitive field -effect transistor) is a
class of sensors/biosensors based on ISFET technology
which are utilized to detect charged molecules; when a
charged molecule is present, changes in the electrostatic
field at the BioFET surface result in a measurable change
in current through the transistor. These include EnFETs,
ImmunoFETs, GenFETs, DNAFETs, CPFETs, BeetleFETs,
and FETs based on ion-channels/protein binding.
MESFET: (metal–semiconductor field-effect transistor)
substitutes the p–n junction of the JFET with a Schottky
barrier; and is used in GaAs and other III -V
semiconductormaterials.
NOMFET: is a nanoparticle organic memory field -effect
transistor. The transistor is designed to mimic the feature
of the human synapse known as plasticity, or the variation
of the speed and strength of the signal going from neuron
to neuron. The device uses gold nano -particles of about 520 nm set with pentacene to emulate the change in
voltages and speed within the signal. This device uses
charge trapping/detrapping in an array of gold
nanoparticules (NPs) at the SiO2/pentacene interface to
design a SYNAPSTOR (synapse transistor) mimicking the
dynamic plasticity of a biological synapse. This device
(memristor-like) mimics short-term plasticity (STP) and
temporal correlation plasticity (STDP, spike -timing
dependent plasticity),[2] two \”functions\” at the basis of
learning processes. A compact model was developed and
these organic synapstors were used to demonstrate an
associative memory, which can be trained to present a
pavlovian response. A recent report showed that these
organic synapse-transistors (synapstor) are working at 1
volt and with a plasticity typical response time in the
range 100-200 ms. The device also works in contact with
an electrolyte (EGOS : electrolyte gated organic synapstor)
and can be interfaced with biologic neurons. The recent
creation of this novel transistor gives prospects to better
recreation of certain types of human cognitive processes,
such as recognition and image processing. When the
NOMFET is used in a neuromorphic circuit it is able to
replicate the functionality of plasticity that previously
required groups of several transistors to emulate and thus
continue to decrease the size of the processor that would
be attempting to utilize the computational advantages of a
pseudo-synaptic operation. (See Moore\’s Law).
CNTFET: (carbon nanotube field-effect transistor). a fieldeffect transistor that utilizes a si ngle carbon nanotube or
an array of carbon nanotubes as the channel material
instead of bulk silicon in the traditional MOSFET structure.
First demonstrated in 1998, there have been major
developments in CNTFETs since
OFET: (organic field-effect transistor) uses an organic
semiconductor in its channel. is a field -effect transistor
using an organic semiconductor in its channel. OFETs can
be prepared either by vacuum evaporation of small
molecules, by solutioncasting of polymers or small
molecules, or by mechanical transfer of a peeled single crystalline organic layer onto a substrate. These devices
have been developed to realize low -cost, large-area
electronic products and biodegradable electronics. OFETs
have been fabricated with various device geometries. T he
most commonly used device geometry is bottom gate with
top drain and source electrodes, because this geometry is
similar to the thin-film silicon transistor (TFT) using
thermally grown SiO2 as gate dielectric. Organic polymers,
such as poly(methyl-methacrylate) (PMMA), can also be
used as dielectric
DNAFET: (DNA field-effect transistor) is a specialized FET
that acts as a biosensor, by using a gate made of single strand DNA molecules to detect matching DNA strands. is a
field-effect transistor which uses the field-effect due to the
partial charges of DNA molecules to function as a
biosensor. The structure of DNAFETs is similar to that of
MOSFETs with the exception of the gate structure which,
in DNAFETs, is replaced by a layer of immobilized ssDNA
(single-stranded DNA) molecules which act as surface
receptors. When complementary DNA strands hybridize to
the receptors, the charge distribution near the surface
changes, which in turn modulates current transport
through the semiconductor transducer. Arrays of DNAFETs
can be used for detecting single nucleotide polymorphisms
(causing many hereditary diseases) and for DNA
sequencing. Their main advantage compared to optical
detection methods in common use today is that they do
not require labeling of molecules. F urthermore, they work
continuously and (near) real-time. DNAFETs are highly
selective since only specific binding modulates charge
transport.
QFET: (quantum field effect transistor) takes advantage of
quantum tunneling to greatly increase the speed of
transistor operation by eliminating the traditional
transistor\’s area of electron conduction.
Advantages:
One advantage of the FET is its high gate to main current
resistance, on the order of 100 M? or more, thus providing
a high degree of isolation between c ontrol and flow.
Because base current noise will increase with shaping
time, a FET typically produces less noise than a bipolar
junction transistor (BJT), and is thus found in noise
sensitive electronics such as tuners and low -noise
amplifiers for VHF and satellite receivers. It is relatively
immune to radiation. It exhibits no offset voltage at zero
drain current and hence makes an excellent signal
chopper. It typically has better thermal stability than a
BJT. Because they are controlled by gate charge, on ce the
gate is closed or opened, there is no additional power
draw, as there would be with a bipolar junction transistor
or with non-latching relays in some states. This allows
extremely low-power switching, which in turn allows
greater miniaturization of circuits because heat dissipation
needs are reduced compared to other types of switches.
For example MOSFET is that it requires almost no input
current to control the load current, when compared with
bipolar transistors. In an enhancement mode MOSFET,
voltage applied to the gate terminal increases the
conductivity of the device. In depletion mode transistors,
voltage applied at the gate reduces the conductivity.
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