Frozen phone? Cosmic rays could be to blame

Next time your smartphone freezes, think twice before cursing the shoddy workmanship of the phone manufacturer under your breath. The culprit might actually be the cosmic rays that are constantly raining down on us from outer space and can mess with the integrated circuits in electronic devices. A new study by Vanderbilt University has examined how modern consumer electronics are becoming more vulnerable to cosmic interference, and suggested ways for manufacturers to build better chips.

Thought to be produced by supernovae, cosmic rays are particles that travel through space at close to the speed of light, and they can be dangerous to humans and electronics alike. While the Earth's electromagnetic field shields us from the worst of the damage, astronauts in orbit or, eventually, journeying to Mars, can soak up unhealthy amounts of radiation fairly quickly. Likewise, satellites and probes need to carry proper shielding to protect their delicate electronics from failure.

Here on Earth, oxygen and nitrogen in the atmosphere break these cosmic rays down into other secondary particles, like neutrons, pions, positrons and muons. We're being showered in these lighter particles every second of the day, and although they're harmless to living organisms, they can interfere with electronic systems. Granted, a quick reboot can usually fix the problem, but unfortunately, the more advanced a computer system is, the more susceptible it is to failure by cosmic rays.

"The semiconductor manufacturers are very concerned about this problem because it is getting more serious as the size of the transistors in computer chips shrink and the power and capacity of our digital systems increase," says Bharat Bhuva, a professor and member of Vanderbilt University's Radiation Effects Research Group. "In addition, microelectronic circuits are everywhere and our society is becoming increasingly dependent on them."

Some of these particles have enough energy to actually alter individual bits of data in an electronic system, switching it from a zero to a one (or vice versa) in a process called a "bit flip." While it might sound too small to be a problem, the effects can be catastrophic: Bhuva illustrated the point with the example of a Belgian voting machine in 2003, where a bit flip resulted in over 4,000 erroneous votes. In 2008, the autopilot system in a Qantas A330 failed, causing the plane to buck and dive, injuring 119 people on board. Although it's hard to determine exactly what caused a given bit flip, cosmic rays were suspected in both incidents.

"When you have a single bit flip, it could have any number of causes," says Bhuva. "It could be a software bug or a hardware flaw, for example. The only way you can determine that it is a single-event upset is by eliminating all the other possible causes."

So the Vanderbilt team tested the rate that several generations of transistors would fail as a result of a single-event upset (SEU), or a bit flip caused by cosmic rays. By blasting samples of these chips with a neutron beam, the researchers measured how many failures occurred, and found that overall, that number is growing with each generation.

First, the "good" news: individual transistors are much less likely to experience an SEU now than ever. That's probably because they're shrinking with each generation, making them smaller physical targets for particles to strike. And since they're now made in a three dimensional architecture, the chips are also much hardier against SEUs.

But the problem is that modern devices contain billions of transistors, and each one also requires a smaller electrical charge to make up each bit of information. All factors considered, devices at the system level are increasingly vulnerable to cosmic ray-induced failures.

"Our study confirms that this is a serious and growing problem," says Bhuva."This did not come as a surprise. Through our research on radiation effects on electronic circuits developed for military and space applications, we have been anticipating such effects on electronic systems operating in the terrestrial environment."

Bhuva pointed out that industries like aviation, IT, transportation, spacecraft, communications, power and medical technology are addressing the problem in their devices, but so far consumer electronics have been lagging behind. Shielding isn't practical in everyday devices, but steps can be taken at the design level, by building in redundancy measures.

"The probability that SEUs will occur in two of the circuits at the same time is vanishingly small," says Bhuva. "So if two circuits produce the same result it should be correct."

Bhuva presented the Vanderbilt team's findings at the annual American Association for the Advancement of Science meeting last week.

Source: Vanderbilt University