05-02-2013, 01:00 PM
Transistors
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What is a transistor?
A transistor is a 3 terminal electronic device made of semiconductor material.
Transistors have many uses, including amplification, switching, voltage regulation, and the modulation of signals
History
Before transistors were invented, circuits used vacuum tubes:
Fragile, large in size, heavy, generate large quantities of heat, require a large amount of power
The first transistors were created at Bell Telephone Laboratories in 1947
William Shockley, John Bardeen, and Walter Brattain created the transistors in and effort to develop a technology that would overcome the problems of tubes
The first patents for the principle of a field effect transistor were registered in 1928 by Julius Lillenfield.
Shockley, Bardeen, and Brattain had referenced this material in their work
The word “transistor” is a combination of the terms “transconductance” and “variable resistor”
Semiconductors
Semiconductors are more like insulators in their pure form but have smaller atomic band gaps
Adding dopants allows them to gain conductive properties
Semiconductors are two types
P-type semiconductor
N-type semiconductor
Doping
Foreign elements are added to the semiconductor to make it electropositive or electronegative
P-type semiconductor (postive type)
Dopants include Boron, Aluminum, Gallium, Indium, and Thallium
Ex: Silicon doped with Boron
The boron atom will be involved in covalent bonds with three of the four neighboring Si atoms. The fourth bond will be missing and electron, giving the atom a “hole” that can accept an electron
How Transistors Work
Doping: adding small amounts of other elements to create additional protons or electrons
P-Type: dopants lack a fourth valence electron (Boron, Aluminum)
N-Type: dopants have an additional (5th) valence electron (Phosphorus, Arsenic)
Importance: Current only flows from P to N