Researchers attack transistors to slay vampire power

The European Union is sponsoring a multimillion-dollar research project to boost the efficiency of everyday electronics and choke the constant flow of wasted energy from their chips.

The three-year effort, called Project Steeper, promises to result in gadgets that operate 10 times longer on a battery charge and don't lose energy to standby--or vampire--power, researchers say. Although there are many different ways to improve efficiency in computing, the focus of this work is on the basic building block of all electronics, the transistor.

Everything from TVs to cell phone chargers draws a small current even when they are not in use. Called standby or vampire power, this little trickle results in a huge amount of unused energy.

Lawrence Berkeley National Laboratory in the U.S. estimates that standby power alone is upwards of 10 percent of U.S. consumers' electricity bills. In Europe, standby power in one year is equal to the electricity consumption of Austria, the Czech Republic, and Portugal in one year, according to IBM Research, which is involved in the project.

At the same time, power consumption from electronic gadgets is becoming a bigger and bigger share of all electricity use, to the point where they can represent 15 percent of utility bills, according to the International Energy Agency.

The problem is that transistors, which control the flow of electricity through microprocessor circuits, "leak" electric charge, much the way that a leaky faucet drips water, explained Heike Riel, a researcher at IBM in Zurich. The problem is getting worse as chip designers cram more and more transistors into tighter packages, since transistor gates have less control over that flow, she explained.

Project Steeper researchers plan to design less "leaky" transistors that can be manufactured by the chip industry within 6 to 10 years, said Riel. The project, which will be funded with $5.5 million from the EU and an undisclosed investment from corporations involved, will be led by the Ecole Polytechnique Federale de Lausanne and IBM and will involve a number of other European academic and commercial research organizations.

"We are really optimizing the individual transistor, the building block of the processor," she said. "We are working on an existing technology platform, which is very important so we can stick to using (silicon) wafers."

Tunnel field-effect transistors
The EU-sponsored project, like a number of other research efforts like it, aims to create semiconductors that have a more abrupt switch between the on and off state than the metal oxide semiconductor field effect transistor (MOSFET) design, which has been used since the 1970s, according to IBM. These devices would have a steep slope between on/off transitions, which gives the project its name, and would lower the leakage of charge in transistors.

To get there, researchers will pursue new materials for so-called tunnel field-effect transistors, which have been studied for several years but no working devices have been shown, said Riel.

One group of researchers will seek to make these transistors from silicon and silicon germanium, and another group will work with semiconducting nanowires. These cylinder-shaped nanowires, which are only a few nanometers in diameter, allow better electrostatic control.

"Because they are cylindrical, we can now wrap the gate around the cylinder, which gives us much better gate control and leads to the fact that there is less leakage," explained Riel.

These devices would operate at under 0.5 volts, which means that electronics would use significantly less power, allowing for a reduction on the order of 10 times compared to today's products.

In three years, researchers hope to show a demonstrating nanowire semiconductor device. A second phase of research would adapt manufacturing techniques to make them. The nanowires would be made from indium arsenide grown on top of a silicon wafer, Riel said.

Low-power transistors not only translate into longer battery life for mobile phones or digital music players, but they also pave the way for new forms of power generation. For example, energy harvesting technologies, where motion is converted into usable energy, today are gated by the amount of power electronics need to operate.

But more efficient transistors have implications for large-scale computing as well. "Right now for supercomputers, it's less a technology challenge as it is power consumption that limits the increase in performance," said Riel.