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SSPD_Chapter 7_Part 3 gives the basic elecrical properties of MOS devices.

SSPD_Chapter 7_Part 3_Basic Electrical Properties of MOS and MOS circuits.

7.3 The Output Characteristics of (Depletion)n-channel MOSFET.

Field Effect Transistors cover JFET and MOSFET. The underlying principle of FET is that there is a conducting channel which obeys Ohm’s Law:


L = lemgth of the channel and A = cross-sectional area as shown in Figure 7.3.1.

And ρ = resistivity = 1/σ = 1/conductivity = 1/(qµ n n);

Here q = charge of an electron, µ n = mobility of an electron in the channel and n = conducting electron density in the n-channel.

Generally the n-channel is like a 2-D sheet hence its mobility is much lower than that in 3-D bulk. Typically µ n = 1450 cm 2 /(V-sec) in Bulk Semiconductor and 650 cm 2 /(V-sec) in the channel in FET.


As can be seen in the Figure 7.3.1 in n-channel FET electrons are being sourced from the source end and being drained out from the drain end. By corollary in p-channel FET holes will be sourced and holes will be drained out. This is the reason why the symbols are shown with the arrow of the conventional current flow. In nMOSFET conventional current is shown to come out of the Source and in pMOSFET conventional current is shown to enter into the Source as shown in Figure 7.3.2.

Equation 7.3.1 is a linear equation with I-V characterisyics as shown in Figure 7.3.3.

As seen in the Figure 7.3.3, I-V is linear for the whole range of voltage applied and is anti-symmetrical about the y-axis. Hence n-channel is a bilateral device where for positive voltage positive current flows and for negative voltage negative current flows with equal ease.

7.3.1. FET as a 3-terminal Device in Ohmic Region/Triode Region

Now by applying GATE voltage V GS transverse to the channel as shown in Figure 7.3.4 the channel thickness can be controlled and thereby the I-V slope can be controlled as shown in Figure 7.3.5.

In this OHMIC REGION of operation, we have two cases. First case is when V DS is kept less than 0.1V. In this case channel remains a parrallaelopied with a reduced thickness ‘t’. In this case if we continue to apply more and more negative voltage, the channel will be eventually be completed depleted and we say that the channel has pinched off. The negative gate voltage at which this occurs is known as Pinch-Off voltage (V P ).

There is a second case where V DS is greater than 0.1V and it continues to be increased. In this case the difference voltage between Gate and Drain>the difference between Gate and Source. Hence n-channel is trapezoidal and it does not give a linear I-V characteristics. This is also OHMIC REGION but non-linear. Linear and non-linear I-V curve is clearly indicated in Figure 7.3.5.

As seen in Figure 7.3.4 and Figure 7.3.5 we have achieved Voltage –Controlled Resistance (VCR) but this VCR is not quite linear. At V DS <0.1V, VCR is perfectly linear but at large V DS voltages the channel resistance deviates from the linear behavior.

In this kind of device at zero gate voltage, channel is present. Hence it is known as Normally-On . As the negative gate voltage is made more negative, the channel depletes until it finally completely pinches off . Hence it is known as .Depletion Type Device. As the gate voltage is made positive, channel becomes more conductive as it has a copious supply of electrons. Theefore we say that n-channel has enhanced.

Questions & Answers

what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
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
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
How can I make nanorobot?
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
how can I make nanorobot?
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
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Source:  OpenStax, Solid state physics and devices-the harbinger of third wave of civilization. OpenStax CNX. Sep 15, 2014 Download for free at http://legacy.cnx.org/content/col11170/1.89
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