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Transistor Construction

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Bipolar transistors comprise N-P-N or P-N-P junctions of semiconductor material. The junctions are, in fact, produced in a single slice of silicon by diffusing impurities through a photographically reduced mask. The diagram shows a cross-section through the silicon slice of an NPN transistor.

The name 'transistor' is, in fact, short for transfer resistor. This term provides a clue as to how the device operates; the current flowing in the output circuit is determined by the current flowing in the input circuit.

Transistors fall into two main categories (bipolar and field-effect) and are also classified according to the semiconductor material employed (silicon or germanium) and to their field of application.

<^< Transistors | Course index | Transistor Symbols and Connections >^>