MOS-FET operation:
Both JFETs and MOSFETs are conductivity modulated devices, utilizing only one type of charge carrier that signifies they are unipolar devices as distinct from Bipolar Transistors that use both electrons and holes.
In the MOS-FET, P-N junction is replaced with the metal-oxide layer that is much simpler to mass produce; mainly in microchips involving thousands integrated MOSFET devices.
Unlike the JFET in which the conducting channel is formed by doping and its geometry modulated by applied voltages, MOSFETs change the carrier concentration in their channel that in turn changes conductivity of channel.
In illustration of the p - type MOSFET above, source and drain are n+ regions in the p-substrate while gate is capacitive coupled to channel region through insulating layer; this insulating layer is generally the thin layer of Silicon dioxide (SiO2).
When the positive voltage is applied to gate, electron concentration at silicon surface beneath gate increases and just as in JFET the combination of gate and drain voltages control conductivity of channel.
In absence of any special surface preparation surface of silicon is n-type that is p-type silicon inverts at surface. The n-channel MOSFET uses the n-channel in the p-substrate, so application of the positive potential to gate forms inversion layer required for channel.
As in JFET, combination of current flow in channel and applied potentials forms the depletion region which is greatest near drain. At a sufficiently large drain potential channel pinches off.
Illustrations below show relationship between Drain voltage and saturation in MOSFET. In illustration drain voltage is less than saturation voltage which can be defined as VD < Vsat. In this region MOSFET presents resistive channel. When VD = Vsat as illustrated in (b) saturation starts to set in and when VD > Vsat as illustration (c) depicts, output current of the MOFET is saturated.
MOSFET output curves:
Output curves of the MOSFET are like Junction Field Effect Transistor and similarly, drain voltage needed to get saturation increases with operating current.
When MOSFET is in saturation region
ID = (W/L)(μCi/2)(VG - VT)2
Where Ci is gate capacitance per unit area eox /dox and VT is gate threshold voltage that corresponds to commencement of strong inversion.
From above, transconductance is:
gm = (W/L)Ciμ(VG - VT) = (W/L)(εox/dox)μ(VG - VT) = √(W/L)(εox/dox)μ.ID
And with the given width W and drain current ID transconductance is increased by decreasing channel length L and thickness of gate oxide dox
MOSFET device types:
MOSFETs can be executed with either n or p-channels depending on substrate doping while the thin surface layer can be implanted to adjust threshold voltage. This determines whether device is usually on at zero gate voltage (depletion mode device) or usually off at zero gate voltage whereby gate needs increased voltage to form the inversion layer (enhancement mode device)
P-Channel Enhancement Mode: P-Channel Enhancement mode MOSFET is usually off and applied gate voltage decreases channel resistance.
N-Channel Enhancement Mode: N-Channel Enhancement mode MOSFET is usually off and applied gate voltage decreases channel resistance.
P-Channel Depletion Mode: P-Channel Depletion mode MOSFET is usually off and applied gate voltage decreases channel resistance.
N-Channel Depletion Mode: N-Channel Depletion mode MOSFET is usually off and applied gate voltage decreases channel resistance.
Tutorsglobe: A way to secure high grade in your curriculum (Online Tutoring)
Expand your confidence, grow study skills and improve your grades.
Since 2009, Tutorsglobe has proactively helped millions of students to get better grades in school, college or university and score well in competitive tests with live, one-on-one online tutoring.
Using an advanced developed tutoring system providing little or no wait time, the students are connected on-demand with a tutor at www.tutorsglobe.com. Students work one-on-one, in real-time with a tutor, communicating and studying using a virtual whiteboard technology. Scientific and mathematical notation, symbols, geometric figures, graphing and freehand drawing can be rendered quickly and easily in the advanced whiteboard.
Free to know our price and packages for online physics tutoring. Chat with us or submit request at [email protected]
tutorsglobe.com significance of abscission assignment help-homework help by online abscission and senescence tutors
Theory and lecture notes of Sticky-Price Equilibrium all along with the key concepts of Equilibrium on the Income-Expenditure figure, Economy Move to Equilibrium, Inventories as the Balancing Item. Tutorsglobe offers homework help, assignment help and tutor’s assistance on Sticky-Price Equilibrium.
tutorsglobe.com methods of controlling monopoly assignment help-homework help by online monopoly tutors
www.tutorsglobe.com offers quantity variances homework help, quantity variances assignment help, answering questions to accounting for quantity variances, online tutoring by accounting tutors.
the major thing which sets a home theatre distant from an ordinary television setup is the surround sound.
Reptiles tutorial all along with the key concepts of Features of Reptiles, Lizard, Ecological Adaptation, Different kinds of Lizards and adaptive characteristics of lizard
Introduction to Microbiology tutorial all along with the key concepts of Microorganisms, Microorganisms are Cells, Classification Systems for Microorganisms, Domain Bacteria, Domain Archaea and Domain Eucarya
Modern Art Assignment Help is an effectual means to score your desired grades without putting your hands in complex tasks.
Energy Metabolism tutorial all along with the key concepts of Metabolism-Energy for Life's Work, Free Energy, Oxidation, Reduction and Energy Content, Compounds Involved in Energy Metabolism, Nucleoside Triphosphates
We offer the most sought-after Astrophysics Assignment Help at the most apt price range to score A++ in academics.
tutorsglobe.com evolution of parasitic association assignment help-homework help by online helminthology tutors
tutorsglobe.com types of ligands assignment help-homework help by online terminologies tutors
Characteristics of the mollusca tutorial all along with the key concepts of Class Scaphopoda, Class Bivalvia, Class Gastropoda, Torsion, Coiling and Class Cephalopoda
mechanical degree, ?md is employed for accounting the angle among two points on a circle or round object based upon the mechanical or physical placement of there.
tutorsglobe.com programming in web-development assignment help-homework help by online computer programming tutors
1942863
Questions Asked
3689
Tutors
1485563
Questions Answered
Start Excelling in your courses, Ask an Expert and get answers for your homework and assignments!!