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Semiconductors, transistors, integrated circuits in 2013 Print
February 2013

What is Semiconductors?

o The context here is conduction of electricity.  Some materials such as wood and stone do not conduct electricity and some materials such as copper and steel conduct electricity.  There are also some materials that conduct electricity but not efficiently. They are called semiconductors.  Is sand or silicon a semiconductor?  Pure sand or silicon is not a conductor, but impure silicon is a semi-conductor.  Why is it?

o Silicon has an atomic number of 14 and this means it has 14 electrons.  These electrons are arranged in 3 layers: 2 of them are close to the nucleus, 8 next, and 4 in the outer layer.  This is a pure Silicon atom. When more pure Silicon atoms are present, the outer 2 electrons of each atom will join force with 3 other atoms to form a stable configuration of 8.  This group of Silicon atoms will not conduct electricity.  However, if Silicon is mixed with Aluminium (atomic number 13), the mixture will have 7 electrons in the outer layer and there is a hole for another electron from somewhere.  This is a Positive charge situation.  Similarly, if Silicon is mixed with Phosphorus (atomic number 15), the mixture will have 9 electrons in the outer layer and there is an excessive electron.  This is a Negative charge situation. When these 2 mixtures are placed together, they conduct electricity when the excess electrons from one mixture fill the holes of the other mixture.  Either PN or NP arrangement allows electricity flow in one direction and both are called diodes.  Both are semiconductors.

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o We can construct a circuit for executing the Boolean ADD with 2 diodes linked in series, and a circuit for Boolean OR with 2 diodes linked in parallel.  We can also produce LED for lighting or various purposes.

Why is Semiconductor so well known?

o When a semiconductor is further configured to PNP or NPN arrangement, we can control the amount of electricity flowing through the diode by controlling one of the junctions of the arrangement.  This device becomes a triode and is called a transistor. 

o We can construct circuits for executing the Boolean NOT with 1 triode and 2 resistors.  Combining NOT and AND is NAND.  It is the basic element of USB drive and Solid State Disk as both use NAND memory for storage and is non-volatile. 

o A group of transistors that is manufactured together in a compact arrangement is an integrated circuit. 

o Semiconductors, transistors, and integrated circuits are the basic elements that make up a lot of electronic devices such as computers, camera lens sensors, CPU, memory, and a large number of electronic control devices.

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