Radiation Effects on Electronics

Among the types of radiation damage suffered by microelectronics are:

• Total Dose Effects : Total radiation dose is the factor that usually limits the operational lifetime of spacecraft electronics. The electrical properties of solid-state components change upon exposure to radiation. As the dose accumulates, these changes drive the component parameters outside of the design range for the circuits in which they are used. Ultimately, these changes cause the circuit to cease proper functioning.
• Displacement Damage : Displacement damage is another cumulative effect, brought about by prolonged exposure to the radiation environment. Displacement damage is caused by relatively low-energy atomic particles, as they slow and nearly come to rest. These low-energy particles may be either directly present in the environment or produced indirectly by nuclear interactions in the device material or shielding. These stopping particles knock silicon atoms out of their proper crystal lattice locations, creating defects in the crystal structure which appear as low points (wells) in the electrical potential. These wells trap conduction electrons, increasing the resistance of the device. This problem is especially important for solar cells, where the accumulated displacement damage and increased resistance gradually reduce power output. Solar panel degradation is another factor which limits spacecraft lifetimes.
• Single Event Effects : Single Event Effects are changes in a microelectronic device caused by being hit by a single energetic particle. Types of single event effects include:
  • Single Event Upsets (SEUs): An energetic particle passing through a digital electronic device causes an unplanned change in its logic state. Afterward, the device may be re-written into the intended state.
  • Single Event Latchups (SELs): In this case, the device is latched into one logic state and will not change states in response to a logic signal. This occurs when the SEU activates a parasitic circuit in the device which connects its power supply to ground. If the current is externally limited, no permanent damage occurs and the operability of the device can be recovered by cycling the power.
  • Single Event Burnouts (SEBs): In this case, the current is not limited and the device is destroyed. SEBs occur in power MOSFETs.
  • Other single event effects, which are not yet well understood, include Single Event Gate Ruptures (SEGRs), Single Event Functionality Interrupts (SEFIs), and Single Event Dielectric Ruptures (SEDRs).

For further information on space radiation effects, see http://flick.gsfc.nasa.gov/radhome.htm .

CREME96 focuses primarily on Single Event Effects and contains routines for calculating SEU rates. These same routines can be used to calculate SEL, at least to the extent that these effects can be accurately characterized in terms of LET-dependent cross-sections. However, at present there do not appear to be any generally accepted techniques for calculating SEB and other SEE rates. It is believed that applying standard SEU techniques to SEBs probably leads to systematic overestimates to SEB rates.