Transistor BJT – the most basic element
The bipolar blade transistor was invented in December 1947 at Bell Telephone Laboratories by John Bardeen and Walter Brattain, working under William Shockley. The next iteration of this design, the bipolar junction transistor (BJT), was invented by Shockley a year later. This opened up enormous possibilities in electronics. Transistors replaced vacuum tubes. They are better, smaller and more energy-efficient, but the technology for producing these types of elements has changed dramatically from the time of their invention to today. However, they are still an indispensable part of every electronic circuit. Transistors not only made it possible to reduce the size of radios and televisions, but also enabled the creation of integrated circuits which often contain millions of transistors in their structure.
How are bipolar transistors made?
A bipolar transistor consists of three differently doped semiconductor regions - emitter, base and collector. These regions are P- or N-type doped and arranged alternately. Each semiconductor region is connected to a terminal, labelled accordingly - emitter (E), base (B) and collector (C). The base is located between the emitter and collector and is made of a lightly doped high resistance material. The collector surrounds the emitter region, making it almost impossible for electrons injected into the base region to escape without being collected, and the resulting common base gain value is very close to unity, thus giving the transistor a large common collector gain value.
The bipolar transistor Elements NPN and PNP differences in the structure and action
The order in which the P and N layers are arranged determines its type and operation of a bipolar transistor. BJTs are available in two types or polarities, known as PNP and NPN. An NPN transistor contains two semiconductor junctions that share a thin P doped region, while a PNP transistor contains two semiconductor junctions that share a thin N doped region. NPN is one of the two types of bipolar transistors. It consists of a P-doped semiconductor layer between two N-doped layers. The small current entering the base is amplified to produce a large collector and emitter current. When there is a positive potential difference, measured from the base to the emitter, the transistor is active. PNP transistors are built in exactly the opposite way. They also have the opposite action. They are active when there is no voltage at the base.