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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

Leo Robinson's definition
Adejimi Reply
how is equilibrium defined in financial markets?
Babakura Reply
the concept of it
Country A has export sales 20 billion, government purchases 1000billion, business investment is 50 billion, imports are 40billion, and consumption spending is 2000billin. What is the dollar value of GDP ?
Habtamu Reply
what is determination of national income?
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economic growth
stock of capital
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Y =C+l
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what is quantity2
Deji Reply
An indefinite amount of something.
what is demand
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in ordinary sense demand means desire
demand in economics means both willingness as well as the ability to purchase a commodity by paying a price an also its actuall purchase
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demand refers to the various quantity of goods and services that consumers are willing and able to purchase at a particular period of time all other things been equal
The amount of a good or service that consumers are willing to buy at a particular price.
what is cost pull inflation?
what is utility
what is cost pull inflation?
demand is economic principle referring to a consumer's desire and willingness to pay a price for a specific or service..
utility is the among of certisfaction driving from using a comundity
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state the law of diminishing marginal utility
dt know WATS the answer
mention and explain two Bank I financial institutions and two non baking financial institutions
Onah Reply
wat is demand pull inflation
Tony Reply
Demand-pull inflation is asserted to arise when aggregate demandin an economy outpaces aggregate supply. It involvesinflation rising as real gross domestic product rises and unemployment falls, as the economy moves along the Phillips curve.
Perfectly elastic demand
Abubakar Reply
this is a form of demand where goods are demanded at a constant price
what inelastic demanding
demand of any good demanded more after a certain period. if a commodity prices may high and scarcity of that resources.
cannot demand more
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Miles Reply
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Rukundo Reply
conditions of perfect market
NdzAlama Reply
CONDITIONS OF PERFECT MARKET: 1. Perfect competition(PC): no increasing returns, many buyers and sellers, all are price takers, not prices makers. 2. Perfect Information (PI): buyers and sellers know all they need to know about what they are buying and selling to make the right decisions.
3. Complete Markets(CM): no externalities or public goods, no transactions costs, "thick" markets.
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A numerous downsized market that does not meet standards.
A Perfect Market is a numerous downsized market that does not meet standards.
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is place where buyers and sellers met together for the purpose of buying and selling of good and services
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Damian Reply
types of nano material
abeetha Reply
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what is system testing?
preparation of nanomaterial
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Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
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what is system testing
what is the application of nanotechnology?
In this morden time nanotechnology used in many field . 1-Electronics-manufacturad IC ,RAM,MRAM,solar panel etc 2-Helth and Medical-Nanomedicine,Drug Dilivery for cancer treatment etc 3- Atomobile -MEMS, Coating on car etc. and may other field for details you can check at Google
anybody can imagine what will be happen after 100 years from now in nano tech world
after 100 year this will be not nanotechnology maybe this technology name will be change . maybe aftet 100 year . we work on electron lable practically about its properties and behaviour by the different instruments
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how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
silver nanoparticles could handle the job?
not now but maybe in future only AgNP maybe any other nanomaterials
can nanotechnology change the direction of the face of the world
Prasenjit Reply
At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
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the Beer law works very well for dilute solutions but fails for very high concentrations. why?
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