Overview

According to the International Energy Agency (IEA), electronic devices currently account for 15 percent of household electricity consumption, and energy consumed by information and communications technologies as well as consumer electronics will double by 2022 and triple by 2030 to 1,700 Terawatt hours -- this is equal to the total residential electricity consumption of the United States and Japan in 20091.

Particularly wasteful is the enormous amount of standby consumption. In the European Union it is estimated that standby power already accounts for about 10 percent of the electricity use in homes and offices of the member States2. By 2020 it is expected that electricity consumption in standby/off-mode will rise to 49 terrawatt hours per year - nearly equivalent to the annual electricity consumption for Austria, Czech Republic and Portugal combined3.
The vision of STEEPER was to help manufacturers to build the Holy Grail in electronics, a computer that utilizes negligible energy when it's in sleep mode, also known as the zero-watt PC. With the support of the European Commission's 7th Framework Program (FP7), STEEPER explored novel nanoscale building blocks for computer chips that aim to reduce the operating voltage to less than 0.5 Volt, thus reducing their power consumption by one order of magnitude.

The development of novel devices, such as the steep slope transistors, from which the project gets its name, can provide a much more abrupt transition between the off and on states when compared with the current 60mV/decade limit of metal–oxide–semiconductor field-effect transistor (MOSFET) at room temperature.
This simultaneously allows for reducing the sub-threshold leakage and lowering the voltage operation. The development of energy-efficient steep sub-threshold slope transistors that can operate at sub-0.5V operation domain will be a critical factor in the success of the project.
To move towards this goal, scientists studied the development of so-called TFETs based on silicon (Si), silicon-germanium (SiGe) and III-V semiconducting nanowires. Nanowires are cylindrical structures measuring only a few nanometers (nm) in diameter, which allow optimum electrostatic control of the transistor channel. In a TFET, quantum mechanical band-to-band tunneling is exploited to switch on the device and thus achieve a steeper turn-on characteristics compared to conventional MOSFETs.
STEEPER evaluated the physical and practical limits of boosting the performance of TFETs with III-V nanowires, and the resulting advantages for future energy efficient digital circuits.

(1) Gadgets and Gigawatts, International Energy Agency (IEA), Policies for Energy Efficient Electronics, 424 pages, ISBN 978-92-64-05953-5

(2) European Commission Joint Research Center, Institute for Energy, European Codes of Conduct for ICT

(3) Electricity Consumption and Efficiency Trends in European Union, Status Report 2009, JRC-IE