Breaking point

The quest for faster and smaller silicon chips has reached a stage where critical breakdown is not far away, says Christine Evans-Pughe

Software bugs may crash our PCs and mobiles, viruses may corrupt our data, but at least we can trust the basic hardware behind all this technology: the silicon chip. Well, that's been the assumption so far. But it may be time for a re-think.

Software bugs may crash our PCs and mobiles, viruses may corrupt our data, but at least we can trust the basic hardware behind all this technology: the silicon chip. Well, that's been the assumption so far. But it may be time for a re-think.

About two years ago Lloyd Condra, a scientist at Boeing, and Joe Chapman, from the United States Department of Defence, started warning people about the risk of chips wearing out in essential electronic systems such as air traffic control, national security, telecommunications, banking, avionics, military and medical equipment. "This challenge is as grave as any since the beginning of the solid-state revolution 50 years ago," Dr Condra said at one military and aerospace conference.

His concern was about chips being built using nanometre-scale semiconductor processes. One nanometre (nm) is a billionth of a metre; present cutting-edge chips have 90nm processes. The heat produced by the electrical current passing through such circuitry could, he suggested, erode their essential metal connections or oxide insulation layers, and cause transistors to break down.

The plausible result: chips that don't calculate correctly and, at the larger level, computers that don't behave, or malfunction silently - and perhaps catastrophically. And because every major form of transport, from cars to airliners, relies on chips, such questions are increasingly important.

Today, nano-scale semiconductor processes are becoming mainstream. "The challenges are greater in avionics because we tend to use devices in more harsh environments. And we have longer lifetime requirements because our systems operate for longer times," explains Dr Condra. "It's hard to say how big the problem is or will become. We may start to notice some problems in some of these newer designs. Until now, there hasn't been an obvious issue," he adds.

But frequent flyers will be glad to hear that Boeing says it is being very careful about using these new chips for its production systems.

Silicon chip circuit elements are now one-fiftieth the size they were in the Seventies, when lifetime estimates were hundreds of years, and computers occupied entire rooms rather than your lap. Since then the semiconductor industry has followed Moore's Law - doubling the amount of circuitry it fits into an area every 18 months by scaling down the transistors and the wires that link them. Scaling cuts costs and means chips can run faster, but also makes them more fragile.

Until now, chip lifetimes have been in the decades but the latest scaling step down to 130nm and more recently 90nm has been tricky. The silicon dioxide layers that make up vital transistor structures are now just a few atoms across. And at the same time, all the linking wires have been changed from aluminium to copper, a material with very different failure characteristics.

Semiconductor firms really don't want to discuss chip wear-out. Only by oblique questioning do you get close to the truth: 130nm chips designed for mobile phones might have minimum expected lifetimes of three years, and those manufactured for PC chips five years.

Calculating a chip's lifetime has in the past been done by putting them under extremes of temperature and voltage to accelerate the ageing process - in which heat generated by the currents can move atoms around, thinning or thickening the vital transistor "gates". But there are doubts as to whether this method still reflects what is likely to occur in real operating conditions.

"You are no longer looking at bulk materials, you are looking at a collection of 'individuals' [atoms or molecules]," suggests Tim Saxe, the vice-president of engineering at QuickLogic, an American firm that makes general-purpose chips called programmable logic devices. "If one of those individuals is a little strange, the properties [of the device] are going to be determined by him and not the average. If his statistics are different from the average, then the rules for accelerating are no longer correct.

"If you increase the temperature by a factor of two, is that the equivalent of running it four times as long or 10 times as long or what?" he asks.

So far, no one has the answer. QuickLogic has held off from using 130nm technology, and is unusual in its readiness to talk openly about wear-out. Saxe has been working in the industry for more than 20 years and points out that the history of semiconductors has always been about overcoming problems and there are always new problems. "Typically, the commercial side of the business has its head in the sand on these things, and so it really takes a big disaster before someone will say, 'we need to change the way we do things'," he says. "We do care about reliability, but Condra is making an excellent point in that we only care about relatively short-term reliability. How much electronic equipment have you kept for more than five years?"

High-reliability systems such as those in aeroplanes represent only 1 per cent of chip sales, so the only incentive for semiconductor manufacturers to extend chip lifetimes is fear of lawyers should things break down and people get hurt. Semiconductor firms are now working with Boeing and others to devise strategies that guarantee the reliability of certain commercial chips.

"I guess they believe it is in their interest to keep us informed as to what's going on," comments Condra. "If there is a problem with some of our systems, they can be highly visible problems."

The companies who make chip-design software are also working on the problem. Guillaume d'Eyssautier, the european general manager of the firm Cadence, says: "If you're designing a water reservoir, you can design very thick walls everywhere to be sure it is safe, but it's really expensive to do this. You know where you need thicker walls and where you can put thinner walls. Similarly, we're looking at areas of the chip where you have to reinforce the transistors or re-route some of the power lines, according to what the chip's function is."

The good news is that chip wear-out is probably a gradual process, according to Guido Groeseneken, an expert in chip reliability at the IMEC research institute in Belgium. "People have done work on this and proved that some circuits can survive the odd breakdown. If a transistor stops working, it's not always catastrophic to the circuit operation. It depends on where it is located and how sensitive the circuit is to that transistor."

The odd bit of metal erosion isn't instantly catastrophic. The signal will usually be able to take another path. The bad news is that things may get worse before they get better. Production of chips built on the new 90nm nanometre process is underway, and requires a range of new materials to improve on and replace structures such as the now perilously thin silicon dioxide layers. "The long-term performance and the wear-out [of these new materials] is unexplored," says Groeseneken. With silicon and silicon dioxide we had a learning curve of 40 years. But for copper and all these new materials, it's in its infancy."

He suggests that in the meantime, for chips in cars, telecoms infrastructure and definitely aeroplanes we should stick to less advanced chips. "As industry builds up confidence in the new materials from failures in the field, they will learn from those what are the weak points. Then the materials will go into high reliability applications."

Start your day with The Independent, sign up for daily news emails
ebookA unique anthology of reporting and analysis of a crucial period of history
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Digital Designer - Award Winning Agency

£30000 - £40000 per annum: Recruitment Genius: A fantastic opportunity for a t...

Recruitment Genius: Project Manager

£35000 - £50000 per annum: Recruitment Genius: This global provider of call ce...

Recruitment Genius: Customer Service and Business Support Assistant

Negotiable: Recruitment Genius: By developing intimate relationships with inte...

Recruitment Genius: Application Support Engineer - Software

£18000 - £22000 per annum: Recruitment Genius: A small rapidly expanding IT So...

Day In a Page

Blundering Tony Blair quits as Middle East peace envoy – only Israel will miss him

Blundering Blair quits as Middle East peace envoy – only Israel will miss him

For Arabs – and for Britons who lost their loved ones in his shambolic war in Iraq – his appointment was an insult, says Robert Fisk
Fifa corruption arrests: All hail the Feds for riding to football's rescue

Fifa corruption arrests

All hail the Feds for riding to football's rescue, says Ian Herbert
Isis in Syria: The Kurdish enclave still resisting the tyranny of President Assad and militant fighters

The Kurdish enclave still resisting the tyranny of Assad and Isis

In Syrian Kurdish cantons along the Turkish border, the progressive aims of the 2011 uprising are being enacted despite the war. Patrick Cockburn returns to Amuda
How I survived Cambodia's Killing Fields: Acclaimed surgeon SreyRam Kuy celebrates her mother's determination to escape the US

How I survived Cambodia's Killing Fields

Acclaimed surgeon SreyRam Kuy celebrates her mother's determination to escape to the US
Stephen Mangan interview: From posh buffoon to pregnant dad, the actor has quite a range

How Stephen Mangan got his range

Posh buffoon, hapless writer, pregnant dad - Mangan is certainly a versatile actor
The ZX Spectrum has been crowd-funded back into play - with some 21st-century tweaks

The ZX Spectrum is back

The ZX Spectrum was the original - and for some players, still the best. David Crookes meets the fans who've kept the games' flames lit
Grace of Monaco film panned: even the screenwriter pours scorn on biopic starring Nicole Kidman

Even the screenwriter pours scorn on Grace of Monaco biopic

The critics had a field day after last year's premiere, but the savaging goes on
Menstrual Hygiene Day: The strange ideas people used to believe about periods

Menstrual Hygiene Day: The strange ideas people once had about periods

If one was missed, vomiting blood was seen as a viable alternative
The best work perks: From free travel cards to making dreams come true (really)

The quirks of work perks

From free travel cards to making dreams come true (really)
Is bridge the latest twee pastime to get hip?

Is bridge becoming hip?

The number of young players has trebled in the past year. Gillian Orr discovers if this old game has new tricks
Long author-lists on research papers are threatening the academic work system

The rise of 'hyperauthorship'

Now that academic papers are written by thousands (yes, thousands) of contributors, it's getting hard to tell workers from shirkers
The rise of Lego Clubs: How toys are helping children struggling with social interaction to build better relationships

The rise of Lego Clubs

How toys are helping children struggling with social interaction to build better relationships
5 best running glasses

On your marks: 5 best running glasses

Whether you’re pounding pavements, parks or hill passes, keep your eyes protected in all weathers
Joe Root: 'Ben Stokes gives everything – he’s rubbing off on us all'

'Ben Stokes gives everything – he’s rubbing off on us all'

Joe Root says the England dressing room is a happy place again – and Stokes is the catalyst
Raif Badawi: Wife pleads for fresh EU help as Saudi blogger's health worsens

Please save my husband

As the health of blogger Raif Badawi worsens in prison, his wife urges EU governments to put pressure on the Saudi Arabian royal family to allow her husband to join his family in Canada