Page 947 - Basic Electrical Engineering

The transistor, most commonly used in electronic circuits, was invented in
1948. The first integrated circuit (IC) came in the market in the mid 1960s.
Through continuous research and development, very large scale integrated

(VLSI) circuits have been brought in use, resulting in gradual miniaturization
of electronic circuits and devices. The sizes of calculators, computers,

communication satellite, and all such electronic gadgets and systems have
become smaller but powerful. It is predicted that nano-technology will further

revolutionize the industry in general in the years to come.
Electronics deals with the flow of electrons through vacuum, gas or

semiconductors. Electronic devices like diodes, transistors, field effect
transistors (FETs), silicon controlled rectifiers (SCRs), optoelectronic
devices, and resistors, inductors, capacitors, etc. form circuits of electronic

gadgets, equipment, and control systems.
An electronic device consists of integrated circuits which have several

diodes, transistors, resistors, capacitors, etc. mounted on a single chip.
Electronic components like diodes, transistors, SCRs, etc. are made of

semiconductor materials.
As we know, all materials are classified into three categories, namely

conductors, semiconductors, and insulators. Gold, silver, copper, aluminium,
etc., are conducting materials. Conducting materials have a large number of
free electrons in their atomic structure which allow flow of current.

Rubber, ceramic, glass, wood, paper, bakelite, mica, etc. are insulating
materials. In these materials no free electrons are available and as such no

current should flow through them.
Substances like germanium, silicon, carbon, etc. are called semiconducting
materials. Atoms of these materials binds themselves through sharing of

electrons in their outermost shell or orbit. Such bonds are called covalent
bonds. At absolute zero degree temperature, semiconducting materials behave

like insulators as no free electrons are available for conduction. However,
with increase of temperature or on application of voltage, some electrons

become free electrons by breaking away from their covalent bonds and create
a current flow. That is why these materials are called semiconductors. To