How Alpha Particles Can Break Computer Chips

In 1978, Intel engineers encountered mysterious and unexplained errors in their 16-kilobit dynamic random access memory (DRAM) chips, where stored ones would spontaneously flip to zeros. The investigation traced the root cause to the ceramic packaging surrounding the chips. The problem originated from a manufacturing plant built on Colorado's Green River, which was located downstream from a former uranium mill. Radioactive atoms from the mill had contaminated the river and, subsequently, the ceramic materials used in chip packaging.

Intel's scientists discovered that even trace amounts of uranium and thorium in the ceramic packaging were enough to cause these errors. In DRAM, data is stored as the presence or absence of electrons in semiconductor wells. The alpha particles emitted by uranium and thorium were energetic and ionizing enough to generate electron-hole pairs in the silicon. When an alpha particle struck in a critical location, it could produce a large number of free charge carriers, causing electrons to accumulate in a memory well and flipping a one to a zero — a phenomenon now known as a 'single event upset,' or soft error. Importantly, this type of error does not physically damage the chip; the bit can simply be erased and rewritten.

Experimental exposure of chips to alpha emitters at varying activity levels confirmed that the number of bit flips correlated directly with alpha particle exposure. The issue became detectable in the 1970s specifically because chip components had been miniaturized to the point where a single alpha particle could generate sufficient charge to flip a bit. The findings were widely circulated throughout the semiconductor industry even before formal publication, prompting manufacturers to adopt much stricter controls over radioactive materials in chip production.