<< Chapter < Page Chapter >> Page >
SSPD_Chapter 7_Part 3 is the continuation of the Electrical Properties of MOS. In this module theoretical formulation of threshold voltage, transconductance, unity gain BW, output incremental conductance and figure of merit of NMOS is derived.

SSPD_Chapter 7_Part3_Electrical properties of MOS continued2

7.3.4. Theoretical Formulation of Threshold Voltage in (E)NMOS.

In SSPD_Chapter 6_Part 4_concluded_MOS and its Physics we have dealt with the theoretical formulation of the Threshold Voltage. The expression comes as follows:

7.3.18

Where The Flat Band Voltage is = V FB = ϕm – ϕs = ϕm – [χ + E g /(2q) + ψ B ]

χ = electron affinity in semi-conductor, E g = energy band-gap of Silicon and ψ B = potemtial diiference between Fermi-level(Ef) and intrinsic level(Ei) in Si-Bulk.

Therefore qV FB = qϕm – qϕs = qϕm – [qχ + E g /(2) + qψ B ];

If source to bulk voltage (V SB ) is not zero then this also has to be accounted. This is called Body Effect.

Q SS = Q it (interface trapped charges) + Q ot (oxide trapped charges) + Q m (mobile charges in the oxide) + Q f (fixed oxide charges).

Generally substrate and source are connected together and threshold voltage is at the minimum.

But in certain applications, substrate is kept at reverse bias with respect to source. NMOS is built in P tub and PMOS is built in N tub.

Hence in NMOS, substrate is at negative bias with respect to source and in PMOS, substrate is at positive bias with respect to source.

Substrate bias gives rise to increase in threshold voltage. Hence Body-effect is represented by the following empirical expression:

7.3.17

V TO = Threshold voltage with zero substrate bias;

And γ = body effect parameter (√V);

B = surface potential parameter.

Lower is the substrate doping, lower will be body effect.

The Typical values of Body effect is given in Table 7.3.1.

Table 7.3.1. Body effect in (E)NMOS and (D)NMOS

Device Substrate biasV SB ThresholdV Th
(E)NMOS 0V 0.2V DD 1V for V DD = +5V
5V 0.3V DD 1.5V for V DD = +5V
(D)NMOS 0V -0.7V DD -3.5V for V DD = +5V
5V -0.6V DD -3V for V DD = +5V

7.3.5. Theoretical formulation of Transconductance (g m )

Transconductance is the partial derivative of output current (I ds ) with respect to input voltage (V gs ) with output voltage constant i.e. V DS is held constant.

7.3.18

From Eq.7.3.3,

And Transit Time is given by equation 7.3.7,

Using these two equations incremental change in output current:

7.3.19

But channel charge induced depends on gate capacitance and gate voltage:

Therefore

Hence

7.3.21

In saturation from Eq.7.3.15,

.

is the actual drop across the conical channel no matter what V ds is.

Hence in saturatin region:

(
7.3.22

From Eq.7.3.13 ,

Substituting this in Eq.7.3.22:

(
=
(

Or

Or

7.3.23

Where

From Eq.7.3.23 it is evident that transconductance can be improved by reducing Channel Length.

Transconductance can be improved by increasing Channel Width. But both these methods have their drawbacks.

7.3.6. Theoretical Formulation of unity current gain band-width.

In BJT unity current gain band-width is defined as transit frequency ω T . It is derived by determining the Current Gain Band Width Product.

Questions & Answers

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
Maciej
Do somebody tell me a best nano engineering book for beginners?
s. Reply
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
s.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
SUYASH Reply
for screen printed electrodes ?
SUYASH
What is lattice structure?
s. Reply
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
Sanket Reply
what's the easiest and fastest way to the synthesize AgNP?
Damian Reply
China
Cied
types of nano material
abeetha Reply
I start with an easy one. carbon nanotubes woven into a long filament like a string
Porter
many many of nanotubes
Porter
what is the k.e before it land
Yasmin
what is the function of carbon nanotubes?
Cesar
I'm interested in nanotube
Uday
what is nanomaterials​ and their applications of sensors.
Ramkumar Reply
what is nano technology
Sravani Reply
what is system testing?
AMJAD
preparation of nanomaterial
Victor Reply
Yes, Nanotechnology has a very fast field of applications and their is always something new to do with it...
Himanshu Reply
good afternoon madam
AMJAD
what is system testing
AMJAD
what is the application of nanotechnology?
Stotaw
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
Azam
anybody can imagine what will be happen after 100 years from now in nano tech world
Prasenjit
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
Azam
name doesn't matter , whatever it will be change... I'm taking about effect on circumstances of the microscopic world
Prasenjit
how hard could it be to apply nanotechnology against viral infections such HIV or Ebola?
Damian
silver nanoparticles could handle the job?
Damian
not now but maybe in future only AgNP maybe any other nanomaterials
Azam
Hello
Uday
I'm interested in Nanotube
Uday
this technology will not going on for the long time , so I'm thinking about femtotechnology 10^-15
Prasenjit
can nanotechnology change the direction of the face of the world
Prasenjit Reply
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
Privacy Information Security Software Version 1.1a
Good
Berger describes sociologists as concerned with
Mueller Reply
Got questions? Join the online conversation and get instant answers!
QuizOver.com Reply

Get the best Algebra and trigonometry course in your pocket!





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
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Solid state physics and devices-the harbinger of third wave of civilization' conversation and receive update notifications?

Ask