capacitor basic

Capacitor: A capacitor is a passive two terminal electronic component that stores electrical energy in an electric field.

E = k*Q/r^2
V = k*Q/r
& Q is directly proportional to V
Q = C*V
Q/V = C (capacitance is measured in Farad,F)

So,a capacitance is the charge required to increase the voltage of 1volt.
For Ex> If capacitance  of a material is 50 F it means that it needs 50 coulomb of charge to increase 1 volt.

Have you ever thought that how much charge can be given to a conductor??
> A conductor can store charge until the surrounding mediam  does not get ionised.

 V = k*Q/R &  C =Q/V
so C = k*R
from above equation  it's clear that  capacitance  depends on size of sphere.

*

Semiconductor basics part (a)

An isolated or a single atom has some energy level which become different when combine with any other atom.

Note: When two charges are near to each other they experience a force of attraction/repulsion.
i.e, F=k*q1q2/r^2 and U=k*q1*q2/r.

so during formation of crystal, electrons of two atoms will repel each other and their corresponding +ve charge will attract their electrons but the distance between the electrons are not the same so every electron of an atom will experience some different energy and hence, energy will not be the same what it was earlier.

 As we know one silicon atom has 4 electrons in outermost orbit each having different energy level. Now, after forming crystal each atom has 4 level of energy.  when N number of atoms comes closer to form a crystal. So, N atoms would have 4N energy level.(i.e,  one atom>4energy level

Si atomic configuration is:
1s2 2s2 2p6 3s2 3p2
so, probable energy level is 8N (two energy level of 3s which is completely filled and six energy level of 3p  where  2N is filled and 4N is unfilled). so, we can say that out of 8N, 4N is filled and 4N is vacant and if electron get that possible energy then they may excite to vacant 4N.

 After actual formation of crystal it was observed that  there remains only two energy levels.Some electrons occupy  higher energy level(4N) and some electrons occupy lower energy level (4N) forming a high band and low band energy level. It was observed that between high band and low band there is no electron(vacant space was observed between high and low energy band).

Valance band: The lower energy band occupied by electrons after formation of crystal is called valance band.

Conduction band: The higher energy band occupied by the electrons after formation of crystal is called conduction band. Electrons in conduction band are free electrons.

NOTE: After formation of crystal  one electron revolves around its own orbit and  also around its neighboring orbit.

          Formation of free electrons:
Nucleus attract the electron towards  its center with a force of attraction  and an electron has some energy but that is not sufficient to come out from its respective orbit so they keep on revolving around its respective nucleus.
If electron gain the enough energy from external applied source  then that electron will escape the orbit and becomes free.

Types of semiconductor:
a) Intrinsic semiconductor
b) extrinsic semiconductor

a) Intrinsic semiconductor:
 --> At 0 k all electrons are in valance band and conduction band is empty so there is no free electron.
Hence, it is said that at 0 k semiconductor behaves like an insulator.

-->At room temperature,  some electrons (few electrons)  gain energy equal to or more than Eg and become conduction or free  electrons.

Semicondutor behaviour at room temp.

  

Semiconductor Basics (outline of the course and some basic terminologies)

Here, I will give the detailed information about semiconductor from very basic to a advanced level.

I will try to provide some interview questions that has been asked in different semiconductor companies.









ok, so here we go,

So, What you  need to know if you want to go into a semiconductor industries (here, my focus is on VLSI)

You should have  clear concepts of some subjects as I have disscussed below. (You can skip the advanced part if  you are a fresher).

1. Analog electronics

:  Capacitor, Diode,  BJT, FET , MOSFET, Oscillator, Op-amp, 555 Timer

2. Digital electronics

:logic minimization, k-map,Sop,Pos,AOI, Adder, Subtractor, combinational, and sequential circuits, state machine, counters, registers and its types, conversion of flip-flops  etc....

3. Physics of semiconductor

: Good understanding of semiconductor and its types

:Good understanding of mos capacitor with band diagram

4.  Basic VLSI

mosfet, cmos, voltage and transfer characteristics of cmos, Different regions of operation of cmos, stick diagram etc.

5. Advance VLSI

a. static time analysis

: Setup time and hold time

: time exceptions

:false path, multi-cycle path etc.

b. About different  physical cells

c. latch-up issue and its solution

d. Antenna effect and its  solution

e. PnR flow

f. Different updated technologies used by the semiconductor companies.

So, here we go one by one:

Before starting semiconductor we should have some basic knowledge about signal , voltage, current etc.

signal contain information about a variety of things and activities in our physical world.like Information about the weather is contained in signals that contains the air temp. , pressure, wind speed etc. 

Now the question is  how to extract the information from that particular signal?

> extract the information from the signal one needs to process the signal(means signal will go through some process) in some  predetermined manner.

For this to be possible signal must be converted into electrical signal, e.g voltage and current

This process accomplished by a device known  as Transducer.

>> Don't confused with the term signal processing its just like, if you need oil from coconut then to extract the oil, coconut must go through some process . 

Types of signal

1. Analog

2. Digital

1. Analog signal: It derived from the fact that such signal is analogous to the physical signal that it represent.

It can take any value at any time within the given limit.

e.g, The amplitude of an analog signal exhibits a continuous variation over its range of activity.

* An analog signal may be continuous or discrete in nature

--> All continuous signal is analog in nature but not all analog signal is continuous in nature.

>> If time is discretized (i.e the independent variable is discretized) but not  the amplitude (i.e dependent variable is not discretize) it's still an analog signal.

To get the clear view just see the fig1.1b and fig1.1c given below.

>>Now you may have doubt that how amplitude is dependent and time is independent?

 See the fig carefully, the amplitude is changing w.r.t time so, it's depends on time.

at time t1 temprature is 1c at t2 temprature is 2c and so on. so, here the temp. is increasing with increase of time. hence, we can say that amplitude (here Temp.) depends on time. while we can clearly obseve that time is independent variable.

>> Guys do not get confuse with the term discretize, it's just a specific value of signal at a specific time instant. It can be obtained by sampling a continuous signal. in fig1.1a and fig1.1b and  the samples are taken at various time instant these instant may be regular or irregular.

fig1.1a

fig1.1b

When I will discuss about digital signal in detail then you will get more clear idea.

2. Digital signal: It's a representation of signal as sequence of numbers, each numbers represents the signal magnitude at an instant of time, the resulting signal is called as Digital signal