Saints or sinners

Chips could play a major role in cutting carbon emissions but simply making them incurs a big burden.

The consumer lifestyle seems to fly in the face of a more frugal energy-using world as people flock to buy the latest electricity-guzzling gadget. But the situation is not that black and white.

Steven Nadel, director of the American Council for an Energy-Efficient Economy (ACEEE), was keen to set the record straight. He wrote in his foreword to the group's report on semiconductor technologies: "While the emergence and widespread adoption of advanced semiconductor devices and related technology systems have been identified as principal drivers of the growth in economic productivity, their effect on energy productivity has received much less attention. This lack of recognition is likely due to what we previously have called 'the high-tech energy paradox' whereby analysts tend to pay more attention to the energy-consuming characteristics of semiconductor devices than to their broader, economy-wide, energy-saving capacity."

The UK's Energy Saving Trust pointed to the increasing energy consumption of home technology in its 2007 report 'The Ampere Strikes Back'.

The report claimed, by 2020, a staggering 45 per cent of domestic electricity consumption would be down to gadgets in the home. To reach its estimate, the trust took heating out of the equation, which dominates domestic energy consumption, but included the contribution from electric cookers and kettles, as well as fridges and washing machines.

The basis for the trust's calculation came from a report by the UK government's Market Transformation Programme (MTP), an agency funded by Defra that estimates the environmental impact of products.

The most pessimistic estimate produced by the MTP report claimed consumer electronics energy consumption could rise more than 50 per cent from 17.4TWh in 2005 to 27.3TWh in 2010. By 2020, that total could climb to 37.5TWh, more than double today's energy consumption, with 40 per cent of that total just coming from TVs. Factor in computers and other IT equipment for the home, the total energy consumption could climb to more than 50TWh by 2020 - around 750kWh per person and just under 10 per cent of total domestic energy consumption once heating is included.

However, the MTP's 'earliest best practice' scenario - which takes into account potential savings from better design and improved components - projected a dramatic fall in computer power consumption, to just 2.9TWh from 12.6TWh, with a much more modest rise in overall consumer electronics power consumption to 19.6TWh in 2020.

The Energy Saving Trust drew attention to the rise in electricity consumption from large plasma and LCD TVs. However by 2020, more efficient designs that use organic light emitting diodes (OLEDs) should be in widespread use in homes. Shifts in technology such as this could make a large difference to the estimated energy demand of the typical home.

The ACEEE report on US consumption has taken a more bullish tone on the role of electronics and semiconductors in the energy economy. The authors claimed, since 1976, the use of semiconductors has led to a massive reduction in energy usage. They estimated, compared to the situation if 1976-class equipment was used, the semiconductor technology employed in 2006 saved the US some 776TWh of electricity - roughly 2.6MWh per person. Had the US economy relied on 1976 technology and expanded in the way it had done in the 30 years since, John Laitner and colleagues estimated the country would need 20 per cent more generating capacity, demanding the construction of close to 200 large power stations.

An earlier study by Laitner and Karen Ehrhardt-Martinez claimed for every 1kWh of electricity consumed by IT equipment in the 60 years from 1949 to 2006, an estimated 8.6kWh were saved economy-wide.

Semiconductors and heavy equipment

A less obvious beneficiary of improved semiconductors is heavy equipment. Better control techniques can improve the efficiency of AC motors to the degree that, with the right digital signal processor (DSP) algorithms, they become cheaper to run than more complex DC motors.

The ACEEE report estimated some 20 per cent of motors saved energy thanks to semiconductors, for a saving relative to 1976 of 40TWh in 2006 - about 2 per cent of the electricity consumed by motors. By 2030, the ACEEE report estimates the savings will exceed 100TWh.

Overall, the ACEEE concluded that by 2030, the US economy could have grown by 70 per cent but consume 22 per cent more electricity.

Although the ACEEE claimed semiconductors could provide big savings in terms of energy during the use phase, the team did not take into account the energy and resources needed to manufacture the devices themselves. An appendix at the back of the report claims the industry used a mere 0.3 per cent of the total energy consumed in the US using data from the Census Bureau's 2006 Annual Survey of Manufacturers and that, based on reports from the Bureau of Economic Analysis, energy use declined in the ten years from 1997 to 2007 against an overall increase of 13 per cent in the same period. However, a large proportion of semiconductor production is conducted outside the US and manufacture has gradually shifted offshore since the 1990s.

Although energy consumption per square millimetre of silicon has dropped over time - largely thanks to increases in wafer size - the increased complexity of processing coupled with the need for increasingly pure materials has helped keep energy usage in the semiconductor industry high.

The amount of energy needed to make a square centimetre of silicon is surprisingly high. In a presentation to the Tokyo International Symposium on Information Technology and the Environment, Eric Williams, then of the United Nations University, argued that the total fossil fuel and chemical resources needed to produce a 2g chip was some 1.7kg. Of that, 1.2kg was down to fossil fuel use alone.

Short product-life

For a desktop computer, Williams concluded 83 per cent of the total life-cycle energy usage was down to the production phase, partly because semiconductor production itself is energy intensive but also because of the relatively short life-span of the typical PC which, at the time was assumed to be three years.

It's a similar story for mobile phones, which often have an even shorter lifetime in the hands of consumers. A study by ESU-Services, Deutsche Telecom, Motorola and Swisscom found that the bulk of the environmental cost associated with a mobile was from its production.

"This is mostly due to its short service life," Mireille Faist Emmenegger and colleagues wrote in the International Journal of Life-Cycle Analysis. "The use of the phone is responsible only for approximately 5 per cent (UMTS) to 15 per cent (GSM) of the impacts. The impact of the UMTS mobile phone is about 35 per cent higher as compared to a GSM mobile phone."

Producing the electronic components for the phone accounts for the lion's share of environmental impact. "The production of printed wiring boards and integrated circuits make up about 40 to 50 per cent of the environmental impacts."

Transport was also a major contributor the team found: moving electronic components contributes 18 to 25 per cent to the energy of production caused largely by the air transport of components. Because they are relatively light and take weeks to make, manufacturers prefer to air-freight components to cut down the time it takes to get parts into the hands of customers.

The high energy cost of semiconductor production comes down to two factors. One is the amount of electricity used in the processing itself as, over a six week period, a single wafer will be subjected to numerous heating and cooling cycles.

The second factor in wafer energy cost comes down to purity of chemicals and the surrounding environment. The fans employed to keep cleanrooms clean also consume a lot of energy, and this figure rises as the cleanroom class heads towards higher levels of quality. According to a study conducted by Williams and Nikhil Krishnan and Sarah Boyd from Columbia University and the University of California at Berkeley, respectively, a Class 1 cleanroom demands three times as much electricity for air conditioning as a Class 100 chamber.

Similarly purifying water for use in wafer production - it frequently needs to be deionised to avoid poisoning the semiconductor layers - calls for a significant energy input.

Some processes generate more greenhouse gases than others. The shift to LCDs for screens has pushed up emissions of sulphur hexafluoride, which is a strong greenhouse gas. However, this is an area where the chipmaking industry is responding. Taiwan, the home of much of the world's LCD production, embarked on a programme to eliminate SF6 from factories several years ago.

Foundries such as TSMC and UMC have in recent years documented the environmental cost of their processes and they have shown steady declines in energy use as they focus on making equipment more efficient. In the US, Sematech has set up the ESH Technology Center to focus on reducing energy usage in fabs, following on from targets set by the International Technol--ogy Roadmap for Semiconductors (ITRS) to improve efficiency by 10 to 15 per cent for each successive generation of silicon processes. For example, the chips that control fans are making an impact in fabs - pushing up efficiencies and turning them off when not needed. Until recently, many fabs kept air conditioning running at full power whether it was needed or not.

Despite regular improvements, energy consumption is likely to remain high in silicon production - the biggest changes in lifecycle cost come from extending the lifetime of electronic systems and, longer term, by shifting lower-performance components to alternative technologies. For example, one of the benefits of polymer semiconductors lies in the much lower temperatures needed for manufacture. A move to self-assembly techniques may also yield benefits. But, in the meantime, if you want to lower carbon dioxide emissions, it's worth hanging on to that digital TV or PC a little while longer.

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