The space environment is one in which there is an abundance of high-energy particles. Consequently, electronics used in space are exposed to what’s called a total ionizing dose or TID.
The effects of total ionizing dose on electronic devices are critically important to technology manufacturers and any stakeholders that rely on their equipment. Malfunction or failure of equipment as a result of TID can not only jeopardize a mission, it can put lives at risk on manned missions.
Calculating Total Ionizing Dose
Calculating the total ionizing dose that electronic devices will be exposed to on a particular mission is challenging. This is because there are many sources of radiation in space. This includes the Van Allen radiation belt (protons and electrons trapped in orbit near Earth by its magnetic field) and galactic and extra-galactic cosmic rays.
Electronic devices can also be affected by solar events like solar flares and coronal mass ejections. In these events, protons, electrons and heavier ions reach Earth and the satellites and other technology orbiting it in just a few days. Solar flares in particular can cause radiation fluxes for several days.
Total Ionizing Dose Effects
The result of the high energies that electronic devices are exposed to depends on a number of factors. These include the type of radiation (proton, electron, photon, etc.), the types of materials in the device, the device structure and function (i.e., how it’s built and what it does) and the rate of the interaction.
In addition to TID, devices may be affected by single event effects (SEEs) and displacement damage. The potential consequences cover the spectrum from parametric drift and function loss to rupture.
More specifically, TID effects in materials can include things like the creation of dangling bonds in polymers that can result in cross-linking or chain scission, which manifests as the loss of elasticity or embrittlement. In optics, ionization creates color centers, a problem that manifests as absorption. Ionization can also produce a condition called luminescence.
The effects of total ionizing dose in electronics appear as a parametric degradation that leads to functional failure. This includes threshold voltage shifts, which are common and can occur in different locations and at different magnitudes. These shifts alter the way electronics function, such as how they are activated or deactivated.
Reduced gain, increased leakage, timing changes and decreased functionality can also occur. Plus, devices may exhibit enhanced low dose rate sensitivity (ELDRS).
Protecting Electronics from Radiation Effects
After radiation testing electronic devices and calculating total ionizing dose from different types of exposure, the next step is determining how to provide protection from these radiation effects. This involves radiation hardening, which is the process of making electronics more resistant to damage from total ionizing dose.
Ultimately, through potentially multiple rounds of design changes and retesting, manufacturers reach a point where the results show that an electronic device is adequately radiation hardened (or “rad hard”). The hardened device can then be incorporated into systems intended for use in the space radiation environment with confidence that it will operate as intended for the defined length of the mission.