Single Event Upset (SEU)

How an SEU (bit-flip) Occurs

The image below shows a simple 1-bit storage device illustrating the effect of an SEU, or "bit-flip." The circuit is designed so that it has two stable states, one that represents a stored '0' and one that represents a stored '1.' In each state, two transistors are turned on and two are turned off. A bit-flip occurs when an energetic particle causes the state of the transistors in the circuit to reverse. This phenomenon occurs in many microcircuits, including memory chips and microprocessors.

In a spaceborne computer, for example, a bit-flip could randomly change critical data, randomly change the program, or confuse the processor to the point that it crashes.

Interaction of a Cosmic Ray with Silicon

The figure below illustrates how an energetic particle can produce a spurious electrical signal. The particle produces charges along its path, in the form of electrons and holes. These are collected at the source and drain, and a current pulse appears. This can be large enough to produce an effect like that of a normal signal applied to the transistor.