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Field effect transistors

Arguably the most important invention of modern times, the transistor was invented in 1947 at Bell Labs by John Bardeen, William Shockley, and Walter Brattain. The result of efforts to replace inefficient and bulky vacuum tubes in current regulation and switching functions. Further advances in transistor technology led to the field effect transistors (FETs), the bedrock of modern electronics. FETs operate by utilizing an electric field to control the flow of charge carriers along a channel, analogous to a water valve to control the flow of water in your kitchen sink. The FET consists of 3 terminals, a source (S), drain (D), and gate (G). The region between the source and drain is called the channel. The conduction in the channel depends on the availability of charge carriers controlled by the gate voltage. [link] depicts a typical schematic and [link] the associated cross-section of a FET with the source, drain, and gate terminals labeled. FETs come in a variety of flavors depending on their channel doping (leading to enhancement and depletion modes) and gate types, as seen in [link] . The two FET types are junction field effect transistors (JFETs) and metal oxide semiconductor field effect transistors (MOSFETs).

The n-channel enhancement mode MOSFET symbol.
A typical cross-section of a n-channel enhancement mode MOSFET.
Field effect transistor family tree. Adapted from P. Horowitz and W. Hill, in Art of Electronics , Cambridge University Press, New York, 2nd Edn., 1994.

Jfet fundamentals

Junction field effect transistors (JFETs) as their name implies utilize a PN-junction to control the flow of charge carriers. The PN-junction is formed when opposing doping schemes are broght together on both sides of the channel. The doping schemes can be made to be either n-type (electrons) or p-type (holes) by doping with boron/gallium or phosphorus/arsenic respectively. The n-channel JFETs consists of pnp junctions where the source and drain are n-doped and the gate is p-doped. [link] shows the cross section of a n-channel JFET in the “ON” state obtained by applying a positive drain-source voltage in the absence of a gate-source voltage. Alternatively the p-channel JFET consists of npn junctions where the source and drain are p-doped and the gate is n-doped. For p-channel a negative drain-source voltage is applied in the absence of a gate voltage to turn “ON” the npn device, as seen in [link] . Since JFETs are “ON” when no gate-source voltage is applied they are called depletion mode devices. Meaning that a depletion region is required to turn “OFF” the device. This is where the PN-junction comes into play. The PN-junction works by enabling a depletion region to form where electrons and holes combine leaving behind positive and negative ions which inhibit further charge transfer as well as depleting the availability of charge carriers at the interface. This depletion region is pushed further into the channel by applying a gate-source voltage. If the voltage is sufficient the depletion region on either side of the channel will “pinch off” the flow through the channel and the device will be “OFF”. This voltage is called the pinch off voltage, V P . The n-channel V P is obtained by increasing the gate-source voltage in the negative direction, while the p-channel V P is obtained by increasing the gate-source voltage in the positive direction.

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Good
how to find Rutherford scattering parameters angles
saksham Reply
advantages of NAA
Sai Reply
how I can reaction of mercury?
Sham Reply

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Source:  OpenStax, Physical methods in chemistry and nano science. OpenStax CNX. May 05, 2015 Download for free at http://legacy.cnx.org/content/col10699/1.21
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