Subatomic particles from deep space can flip bits inside your computer memory

The Physics of an Ionizing Strike

A single-event upset occurs when an energetic ionizing particle travels through a semiconductor device and deposits an electrical charge within a sensitive node. In digital electronics, information is represented by tiny packets of electrical charge held within transistors and memory cells, corresponding to binary states of ones and zeros. When an external particle penetrates the silicon substrate, it leaves behind a wake of electron-hole pairs along its trajectory. If this accumulated electric charge exceeds the minimum threshold required to maintain the current state—known as the critical charge—the node can be forced to switch values.

Because subatomic particles interact with matter through different mechanisms, the path to a bit flip depends on the particle type. Heavy charged ions, common in extraterrestrial environments, cause direct ionization by stripping electrons from atoms as they pass through. Energetic neutrons, which dominate the particle flux at terrestrial altitudes, carry no electrical charge and cannot ionize silicon directly. Instead, a fast neutron collides with a silicon nucleus, triggering an inelastic nuclear reaction that ejects secondary charged fragments. These recoil fragments then ionize the surrounding silicon, generating the localized charge burst that flips the stored bit.

Unlike destructive radiation phenomena—such as single-event latchup or gate rupture, which physically burn out or permanently short-circuit silicon components—a single-event upset is classified as a soft error. The physical hardware remains undamaged. The memory cell continues to operate normally as soon as the flipped state is overwritten with new data or cleared during a system reset.