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Driving toward millivolt electronics

Article posted at EDN: Information, News, & Business Strategy for Electronics Design Engineers

http://www.edn.com/article/520180-Driving_toward_millivolt_electronics.php

Pallab Chatterjee, Contributing Technical Editor at EDN

Thanks to new behaviors and the characteristics of materials at small geometries, nanotechnology has the potential to introduce great change to the electronics arena. The University of California—Berkeley’s Center for E3S (Energy Efficient Electronics Science) is working to develop fundamental devices that will result in a millionfold reduction in power for future generations of electronic systems.

The overall goal of the center, which receives its funding from the National Science Foundation, is to develop high-performance devices and circuits that require low power to run. Current electronics nominally operate at 1.25 to 5V. The E3S Center is researching devices that can operate at millivolts. The more-than-1000-mV reduction in required power would result in a power-reduction factor of 1 million, assuming that power is proportional to voltage squared.

Driving toward millivolt electronics figure 1Eli Yablonovitch, PhD, leads the research group, which focuses on nanoelectronics, nanomechanics, nanophotonics, nanomagnetics, and system integration (Figure 1). The nanoelectronics program focuses on eliminating the voltage mismatch between devices, allowing circuits to operate on just a few millivolts of supply power and still have a large enough noise margin. The group is investigating switches—from the level of modulating thermionic-emission current over a barrier to the level of modulating the tunneling current through a barrier. The challenges include modeling and tuning tunneling probability and identifying and manufacturing materials exhibiting the desired band-edge-energy alignment.

Tsu-Jae King Liu, PhD, leads the nanomechanics research team in addressing the off-state leakage in CMOS switches, which sets a lower limit in energy per operation. Mechanical switches have zero off-state current. The mechanical switches have a speed limitation of reaching saturation at the speed of sound at approximately 340m/sec in air. When the switches use a diamond-substrate architecture, they have a saturation point close to that of an electron, which is comparable to that of a CMOS switch. The researchers are addressing the complexity of manufacturing the devices and creating higher-density circuits.

Ming C Wu, PhD, is leading the nanophotonics research group, which focuses on circuit and data communication using light rather than electrons. Photons can consume less energy for longer links, and recent demonstrations have shown optical interconnects achieving 10−12J of energy per bit. The challenge includes the creation and identification of fundamentally new approaches for transmitters and detectors to get the operating energy to the goal of communicating with one optical bit using 10−17J of energy.

Jeff Bokor, PhD, leads the nanomagnetics researchers, who are investigating nanomagnetics devices for logic functions rather than memories. Nanomagnetic logic allows a spin degree of freedom with low energy dissipation—even less than the Landauer Limit—on each transition. (The Landauer Limit is the minimum possible amount of energy necessary to change 1 bit of information.) Theoretically, a room-temperature circuit or memory operating at the Landauer Limit could change at a rate of 1 Gbps and expend only 2.85 trillionths of 1W of power. Scientists have recently challenged this principle, and the circuits in this research program are using energy below this threshold.

The last area of focus is the development of systems that use these devices and techniques to allow for the realization of known common circuit functions. These circuits would use models that only nanotechnology can realize.