As can be seen from Figure 1, both the energy and
density of high-energy particles vary by many orders
of magnitude. Galactic cosmic radiation, the most
destructive, is thought to originate from supernovas.
Although relatively uncommon, they pose the greatest
risk to long-term space installations and interstellar
movie stars. The atmosphere protects terrestrial
lifeforms, although incoming cosmic rays do collide
with atoms and molecules, resulting in showers
of secondary radiation including alpha particles,
electrons, neutrons, and X-rays.
Radiation-hardened design is not only applicable to
space, of course. Nuclear reactors produce gamma
radiation and neutron radiation which can affect sensor
and control circuits in nuclear power plants. And
doomsday planners are concerned about the effects of
an electromagnetic pulse (EMP) and neutron radiation
in case of a nuclear explosion.
Radiation’s Effect On Electronic Circuits
When radiation collides with electronic circuits, it can
change the contents of memory cells, cause spurious
current flow, or even burn out devices completely.
Ionizing radiation can damage devices via two
Protons, neutrons, alpha particles, heavy ions, and
very-high-energy gamma rays change the arrangement
of atoms in the crystal lattice, a phenomenon known as
lattice displacement. The result is permanent damage:
increasing the number of recombination centers,
depleting the minority carriers, and altering the analog
properties of the affected semiconductor junctions.
Charged particles, including those with energy below
the threshold for lattice displacement, can also cause
transient ionization effects. Although they typically
only result in glitches and soft errors, ionization effects
can trigger other damage mechanisms, such as latchup,
that can destroy the device.
There are several ways to describe this damage:
Total Ionizing Dose (TID) effects occur when
electrons and protons create excess charge in dielectric
insulating layers. TID effects accumulate over time
and degrade device performance until it becomes
For example, a power MOSFET must be able to
switch reliably and predictably from on to off and
back when the gate voltage passes through a defined
threshold. Over time, TID radiation can shift the
MOSFET’s threshold voltage, making it easier or
harder to switch. Radiation may also increase the
MOSFET’s leakage current, causing the on and off
states to become less distinguishable. Either effect can
ultimately cause device failure.
Single-event effects (SEE) are caused by the
passage of a single high-energy particle through a
device. The severity of a single-event effect can range
from minor and unnoticeable to catastrophic. Newer
semiconductor technologies such as high-speed or low-power CMOS, or fiber optics, are more susceptible to
Figure 2: An SEU generates electron-hole pairs as a function of
time, distance from the particle entry point, and distance from the
particle track center. (Source: Silvaco)
Classes of SEEs include the Single Event Transient
(SET), the Single Event Upset (SEU), the Single
Event Functional Interrupt (SEFI), and the Single
Event Latch-up (SEL), which is often a destructive
failure. Figure 2 shows the results of an SEU strike.
Power devices are susceptible to hard failure modes
such as Single Event Burn-Out (SEB) and Single Event
Gate Rupture (SEGR), but they can also suffer from
soft mechanisms like SET or SEFI.
Mitigating Radiation Damage
How do designers reduce or prevent radiation damage?
Shielding is the first option. Lead shielding can protect
against X-rays, gamma radiation, and lower-energy
particles, but it’s ineffective against high-energy
cosmic rays, which can cause secondary radiation in
the shield that is more damaging than the original
Researchers are looking at active shields that make
use of magnetic or electric fields to deflect particles.
Without such devices, NASA estimates that a human
crew will exceed their lifetime radiation exposure even
during the relatively short six-month trip to Mars and
back. They’ll also increase their lifetime risk of cancer
by about 5 percent. With current shield technology,
Jim, Aurora, and everyone else in Passengers would
have absorbed a lethal dose of radiation long before
they reached their intended destination.
At the system level, designers can build in
redundancy and backup systems. Such systems
reduce but don’t eliminate the radiation effects; they