In a

semiconductor device A semiconductor device is an electronic component that relies on the electronic properties of a semiconductor material (primarily silicon, germanium, and gallium arsenide, as well as organic semiconductors) for its function. Its conductivity li ...

, a parasitic structure is a portion of the device that resembles in structure some other, simpler semiconductor device, and causes the device to enter an unintended mode of operation when subjected to conditions outside of its normal range. For example, the internal structure of an NPN bipolar transistor resembles two PN junction

diode A diode is a two-terminal electronic component that conducts current primarily in one direction (asymmetric conductance); it has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other. A diode ...

s connected together by a common anode. In normal operation the base-emitter junction does indeed form a diode, but in most cases it is undesirable for the base-collector junction to behave as a diode. If a sufficient forward bias is placed on this junction it will form a parasitic diode structure, and current will flow from base to collector. A common parasitic structure is that of an SCR. Once triggered, an SCR conducts for as long as there is a current, necessitating a complete power-down to reset the behavior of the device. This condition is known as latchup.

References

Further reading