On May 18 2003, officials overseeing an election in Schaerbeek, a suburb of Brussels, got a shock. An electronic vote-counting machine declared that 4 096 more people had cast their vote than the ballot slips testified.
The machine had been thoroughly tested and deemed perfect. So what went wrong? The answer was, literally, a strike from the heavens.
Technicians pointed the finger of blame at cosmic rays — particles that zip across the cosmos at huge speed and, while rightly ignored by humans as a health concern, can wreak havoc with highly sensitive microelectronic circuits.
”The phenomenon has been known for a long time by aerospace experts but, as components become more and more miniaturised, almost any electronic equipment these days is at risk,” says French scientist Jean-Luc Autran.
When cosmic particles reach the Earth, they usually collide with molecules in the upper atmosphere, and the debris then whacks into other atoms until it is safely smashed.
Only a tiny fraction of the original particles that perpetually bombard our planet ever reaches the Earth’s surface. Even so, a whizzing neutron can be lethal to information technology. When it hits an electronic component, it unleashes a parasitic electrical discharge.
”In the past, when circuits were big and clunky, this was no big deal,” says Autran, of the L2MP laboratory at the University of Provence, Marseille. ”But now, more and more circuits are being crammed into chips. As a result, the electrical discharge can be as powerful or even greater than the charge used to store the binary code on the chip.
”If the zero or one which is knocked out by the discharge is part of a logic code, the consequences can be disastrous,” says Autran.
Altitude
Altitude adds to vulnerability. At sea level, one square centimetre is hit by 10 neutrons every hour; for an airliner cruising at high altitude, the tally is a thousand times higher.
”Take a laptop which runs perfectly and hop on a transatlantic flight,” says Autran. ”There is a high risk that it will jam up once during the trip and you have to reboot it.”
Some particles are especially invasive, such as high-energy neutrons, which can pass through a shield of armour plate or reinforced concrete.
For years, airliner and spacecraft engineers have tackled the problem by installing back-up circuitry. But this costly solution is hardly feasible in small, cheap consumer gadgets.
This is where Autran comes in. His lab, and STMicroelectronics, a Franco-Italian semiconductor maker, have set up the first high-altitude test bench for accurately assessing the problem.
Set up in July at 2 252m at a cost of €1,1-million at the Plateau de Bure astronomical observatory in the French alps, the platform is testing nearly 1 300 embedded memory circuits.
Each circuit houses four million memory points, which means it can store a sequence of four million zeroes and ones — a total of nearly five billion memory cells in all.
Checks
The work entails checking whether any rogue galactic particle has corrupted the data — the memories are periodically checked to see whether a zero has been transformed into a one or vice-versa.
To get a comparison of exposures, a similar lab has been set up near sea level in Marseille and a third 550m underground at the former headquarters of France’s nuclear strike force on the Plateau d’Albion, about 120km north of that southern French city.
The underground HQ, swathed in concrete and protected by rock, is deemed to be impenetrable even to high-energy neutrons.
The chips being studied have a circuit size of 130 nanometres (130-billionths of a metre). This size is already being surpassed in state-of-the-art circuits of 65 nanometres, where as many as four bits of information could be corrupted by a particle strike.
Autran points out that the problem goes beyond mundane gadgets such as laptop computers, cellphones and high-definition TVs. Cars, high-speed trains, hospital equipment, ”even pacemakers”, could be vulnerable to the risk from space from their dependence on high-performance chips, he says. — Sapa-AFP