Semiconductor device used to amplify.

Amplify:
Increasing the signal.

Semiconductor:
Exploit the electronic properties.

Who invented Transistor?
At Bell laboratories in New Jersey. John Bardeen, Walter Brattain, William Shockley.

Why they invented Transistor?
Developing a new kind of amplifier.

How does Transistor made of?
Silicon, element found in sand.
It doesn't normally allow electrons to flow through it.

How can we say Transistor is a semiconductor device because silicon doesn't allow electricity?
Silicon is doped with some impurities for positive and negative type.

Positive impurities:
Boron, gallium and aluminum.

Negative impurities:
Arsenic, phosphorous or antimony.

Does Transistor consists of only three terminal?
Four terminal and five terminal.

Why five terminals is not using?
Allows electrical signals like vacuum tubes.
No amplification.

Advantage of four terminal:
Increase the conductivity of current.

Conductivity:
Measurement of electrical conductance per unit distance.

Electrical conductance:
Material ability to conduct an electric current.

Does emitter, base and collector are of same size?
No. Collector is large in size.

Why collector is of large size?
Current flows here due to minority carriers, large heat is produced by majority carriers.
For cooling purpose it made larger.

How electrons are doped in emitter, collector and base?
Emitter  heavily doped.
Base lightly doped and thin.
Collector injected electrons by base.

Why base is thin?
For example in NPN if base is thick then electrons leaving in the emitter for base would combine holes with base making more holes to be created.

Why Emitter is heavily doped?
To emit or inject electrons into base.

How can we know base, emitter and collector in PNP and NPN?
By using multi-meter.

Why Transistors work as a Switch?
Off when there is no bias voltage or less than 0.7v.
On when bias is saturated so that collector current can flow without restriction.

What is Biasing of Transistor?
Process of setting transistors DC so that any AC signal can be amplified correctly.

How does Transistor acts as Switch?
Amplifier or as well as switch.
When there is no current to base, little or no current flow between emitter to collector.
 If base current on big current flows.

How does Transistor acts as Amplifier?
Acts as regulator or switch.
Acts regulator is called amplifier.

How does Transistor acts as Gate?
Transistor acts as switch called Gate.

What is power Transistor?
Used in high power amplifier and power supplies.
Here collector is connected to metal base that acts as heat sink dissipate excess power.

Why a Transistor known by its name?
Combination of transfer and resistor.

What is Transistor effect?
Uses electric field to control electrical behaviour of device.

How data is stored? 
Each bit of binary data stored in a tiny circuit called memory cell consisting of one to several transistor.


How many Transistor are required to store one bit of data?
Based on the memory.
For Register : 23 Transistor.
For SRAM   : 6 Transistor.
For DRAM  :  1 Transistor.

Register: 
Can store binary bit either zero or one.
Very fast storage.

SRAM:
Faster and requires less power.
Expensive.

DRAM:
Loses data when power is removed.
Needs constant refresh.