How Alpha Particles Can Break Computer Chips
In 1978, Intel discovered that radioactive contamination in ceramic chip packaging was causing spontaneous bit flips in their DRAM chips. Trace amounts of uranium and thorium emitted alpha particles that created free charge carriers in silicon, flipping stored data. The findings prompted the semiconductor industry to significantly tighten controls over radioactive materials in chip manufacturing.
Summary
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.
Key Insights
- Intel's 1978 DRAM errors were traced to radioactive uranium and thorium contaminating ceramic chip packaging, sourced from a plant downstream of an old uranium mill on Colorado's Green River.
- Even trace amounts of uranium and thorium in ceramic packaging were sufficient to cause bit flips, demonstrating how sensitive miniaturized chips had become to ionizing radiation.
- Alpha particles from radioactive decay create electron-hole pairs in silicon, and if they strike in the right location, can accumulate enough free charge carriers to flip a memory bit from one to zero.
- Investigators confirmed the mechanism experimentally, finding a direct correlation between the number of alpha particles a chip was exposed to and the number of resulting bit flips.
- The Intel findings were circulated widely across the semiconductor industry before formal publication, directly prompting manufacturers to avoid radioactive materials in chip and packaging production.
Topics
Transcript
[0:00] In 1978, Intel reported some strange errors popping up in their 16 kilobit dynamic random access memory or DRAM. Ones would spontaneously flip to zeros with no apparent cause. The problem turned out to be the ceramic packaging the chip was encased in. With the demand for semiconductor packaging skyrocketing in the 1970s, a new manufacturing plant was constructed on the Green River in Colorado. Unfortunately, this site happened to be just downstream of an old [0:31] uranium mill. Radioactive atoms made their way into the river and then into the ceramic packaging for Intel's microchips. Intel's scientists investigating the problem found that even trace amounts of uranium and thorium in the ceramic were sufficient to cause problems. In…
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