At the present time only a few of the full compliment of transistors on a chip can be used at once, because of their limited energy capacity. For example, on a chip with three billion transistors, only 1.8% of them can be used at once. This is know as the "dark silicon" effect, since a large number of the components of an electronic chip are always switched off. In order to combat this phenomenon, a research project directed by Prof. Adrian Ionescu of EPFL has been set in motion. Known as Steeper, this project aims to develop a tunnel effect tranistor (TEFT) with very low consumption, which will allow a large number of components to work more efficiently than with current CMOS technology (Complementary Metal Oxide Semiconductor). The consumption of electronic appliances can be reduced by a factor of 10 when powered on, and reduced to practically zero in stand by. Steeper could well represent a major advance in terms of energy efficiency, since electronic appliances currently account for 15% of houselhold electrical consumption – a figure which, according to the IEA (International Energy Agency) should double by 2022, and triple by 2030.
In conversation with Prof. Adrian Ionescu
What does the project consist of?
Up until now the improvement of energy efficiency in electronic appliances has essentially been based on the reduction in size of the basic components. The Steeper project certainly involves nanotechnology, but is founded on the new physical principal called the "steep slope". The aim is to develop a tunnel effect transistor (TFET) to achieve an abrupt transition between powering on and switching off an electric circuit or component. In this way, the comsumption in dynamic mode can be reduced a factor of 10 when using an electrical supply of less than 0.5 volts for a portable computer (which is impossible with current technology), for example, and be practically erased in standby.
Why do you think the European Union has chosen EPFL to lead the Steeper project?
No doubt because EPFL is heavily involved in other international projects, in which I am also involved. Switzerland is also known as a centre of excellence as a result of its watch circuits, which have the lowest power consumption in the world. But I would also say IBM and the CEA-LETI of Grenoble are very much involved in the project with their research teams and their silicon foundries. We are also working with Infineon, Global Foundries, the Jülich research center as well as SCIPROM and the Universities of Bologne, Dortmund, Udine and Pisa.
How will future tunnel effect transistors be put to use?
In about five years time we estimate that they will allow us to divide by ten the energy comsumption of electronic appliances in use, and to reduce it almost zero in standy. This represents a substantial saving in energy, because the European union estimates that standby currently counts for about 10% of electrical household consumption. This technology will allow mobile telephones to function for a few weeks or even months without having to have their batteries recharged. This technology could allow for the creation of totally autonomous systems. In other words, appliances could power themselves from the sun, or other sources of energy such as vibrations or electromagnetic waves, thereby replacing batteries.
What is the greatest barrier that confronts you?
In this type of project the costs of industrialisation generally represent the greatest barrier. Modern transistors are among the cheapest components in the world. It will therefore be difficult to convince industry, straight off the bat, to replace field effect transistors (MOSFETs) with tunnel effect ones (TFETs). However I am optimistic because IBM’s involvement in Steeper shows a genuine interest from industry, particularly since TFETs can be produced without semiconductor manufacturers having to invest in new equipment. In order to offer the lowest possible manufacturing costs, we propose to replace only the greediest components of semiconductors with TFETs. In other words this is a hybrid solution, providing the best possible improvement in energy efficiency on a grand scale.