Single Event Latchup

How Latchup Occurs

Circuits are manually made in silicon by combining adjacent p-type and n-type regions (i.e., over-seeded, or "doped," with appropriate impurities) into transistors. Paths other than those chosen to form the desired transistor can sometimes result in so-called parasitic transistors, which, under normal conditions, cannot be activated. Latchup occurs when a spurious current spike, such as that produced by a heavy cosmic ray, activates one of a pair of these parasitic transistors, which combine into a circuit with large positive feedback. The result is that the circuit turns fully on and causes a short across the device until the latter burns up or the power to it is cycled. This condition, when caused by a charged particle, is called Single Event Latchup.