What are the effects of cosmic rays on consumer electronics?

Question

When electronics/computer companies design a new chip, processor/ memory card/ or a solar cell, do they study the effect of cosmic rays on such electronically sensitive materials? If not, why not?

Answer 1

For the most part cosmic rays do nothing to consumer electronics.

This is not to say that they can't flip bits or even damage elements, but the rate for such effects is very, very low.

Radiation effects are routinely observed in electronics placed in accelerator experimental halls (where the radiation levels are at lethal-dose-in-minutes levels when the beam is on). Ones that I have observed include

• darkening of plastic scintillator and acrylic light guides
• killing pixels on consumer closed circuit cameras used to allow operators to monitor activities in the hall and visually clear the area before allowing the beam to resume
• circa weekly random crashes on DAQ boards that would run for months at a time while the beam was off. (No way to certainly rule of data loads as the cause of this, but the rate seemed to correlate with the beam current)

Note that the beam dump radiation monitors were calibrated to 1 Mrad/hr and often registered sustained rates around 10 krad/hr. Intensities in the other parts of the hall fell off to very reasonable levels like 100 rad/hr.

Note that the beam cutoff circuitry connected to the beam-dump radiation monitors worked reliably in a intense radiation environment for years.

Answer 2

Cosmic rays do have noticeable affect on electronics. The most prevalent effect is from memory bit flips (known as "soft errors").

The degree of significance of the effect depends on the application. A typical soft error rate for static RAM is in the region of 400 FITs/Mbit [1]. (Failures in time=failures per billion device hours) So if you have 1 Gb of memory per chip and 1000 chips, then expect 0.4 flips every hour. This is precisely the reason that a lot of applications require ECC on their memories.

[1] footnotes: Part of the rate is from alpha particles from decay of materials of or near the chip (this is the smaller of the two major components). Also, the rate is quite a lot higher for DRAMs, which is why DIMMs with ECC exist.

Soft error rates are quoted at sea-level because the effect of being closer to space is non-trivial; which is pretty much proof right there that the effect is from cosmic rays.

There are effects on logic gates too, but this is usually not worked around for two reasons. (1) It is very difficult and/or expensive to do, however there is much research into redundant/fault tolerance circuits (2) when a bit flip occurs on a combinational path, it would have to coincide with exactly when the output of the path is observed (e.g. at a flipflop) which reduces the observability of the effect.

Finally, there is an effect known as single event latchup (SEL). I'm not certain my conception of the mechanism is correct, but as I understand is, a cosmic ray can ionize the path from source to drain of a transistor which will then conduct current regardless of voltage on the gate until the current goes away. I.e. it remains in that state until the power rail is powered down; hence "latchup". This is obviously much more rare, but real.