<< Chapter < Page Chapter >> Page >
Chapter 7_Part 3_Conclusion module concludes the basic electrical properties of MOSFET by discussing the latch-up problem and its remedies.

SSPD_Chapter 7_Part 3_Basic Electrical Properties of MOSFET_concluded.

7.3.16. Latch-Up problem in CMOS and its remedy.

[This part is adapted from the lecture series of Steve McGarry,Department of Electronics, University of Carleton, Ottawa. e-mail:smcgarry@doe.carleton.ca]

CMOS logic is fabricated either by P-Well or N-Well Process or by Twin-Well Process. In any of these processes we have a large number of junctions as . In Figure 7.3.16.1. we give the cross-sectional view of CMOS fabricated by N-Well process. These multiple junctions give rise to three-junction four-layer device which behaves like a SCR. This we call parasitic SCR.

This arises due to cross coupling of P+NP and N+PN transistors. How these parasitic transistors action arise is shown in Figure 7.3.16.2.

If this parasitic SCR is turned ON by the glitches on the power bus or by irradiation, then a low resistance conducting path is created between Positive Voltage Bus (V DD ) and GND Bus (V SS ). This causes irreversible damage to the IC chip. This precisely is SCR Latch-Up problem in CMOS. By careful control during fabrication, the parasitic SCR can be prevented from latching up under all conditions.

In MOS structures the source is always shorted to the body. As seen in the above Figures, Source of NMOS i.e. N+S is connected to P+body by a metal interconnect and P+body makes an ohmic contact to P-substrate. Similarly Source of PMOS i.e. P+S is connected to N+body by a metal interconnect and N+body makes an ohmic contact to N-Well. This ensures that Source-Body bias is zero which leads to zero BODY EFFECT hence threshold voltage of the MOS is held constant.

The equivalent circuit model is given in Figure 7.3.16.3.

As seen in the Figure, the positive voltage bus acts as the Anode of the parasitic SCR and the GND bus i.e. V SS bus acts as the Cathode of the parasitic SCR. For discussion purpose we assume that R substrate and R well are infinite . Under normal condtions voltage between the two buses is 5V or less hence SCR doesnot fire and there is no latching.

7.3.16.1. Why does SCR fire above break-over voltage ?

By inspection of the Circuit Model of SCR in Figure 7.3.16.3 we get the following equations:

We further see that:

Where I CBO = Collector-Base Junction reverse leakage current with Emitter open.

Adding the two above equations, we get:

By rearranging the terms we get:

We know that I E1 = I E2 = I E by Kirchoff’s Current Law;

Also I C1 + I C2 = I E2 = I E ;

Therefore rearranging the terms we get:

Forward Current Transfer Ratio of BJT is α F = γ×β*×M

Where γ = injection efficiency. It falls at low currents due to recombination in depletion layer and it also falls at high current due to conductivity modulation. It is at the maximum value at moderate currents.

Also β* = base transport factor. This improves as Base Width becomes narrower which it will at higher voltages of V CE (forward active mode).

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
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
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
Got questions? Join the online conversation and get instant answers!
Jobilize.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