Energy dissipation and transport in nanoscale devices

microelectronicsUnderstanding energy dissipation and transport in nanoscale structures is of great importance for the design of energy-efficient circuits and energy-conversion systems. This is also a rich domain for fundamental discoveries at the intersection of electron, lattice (phonon), and optical (photon) interactions. A review article published in NanoResearch presents the recent progress in understanding and manipulation of energy dissipation and transport in nanoscale solid-state structures.

Some of the greatest challenges of modern society are related to energy consumption, dissipation, and waste. Among these, present and future technologies based on nanoscale materials and devices hold great potential for improved energy conservation, conversion, or harvesting. A prominent example is that of integrated electronics, where power dissipation issues have recently become one of its greatest challenges. Power dissipation limits the performance of electronics from handheld devices (~10–3 W) to massive data centres (~109 W), all primarily based on silicon micro/nanotechnology.

Importantly, the figures for data centre energy consumption have doubled in five recent years, with waste heat requiring drastic cooling solutions. Such challenges are also evident at the individual micro-processor (CPU) level, where the race to increase operating frequency beyond a few GHz recently stopped when typical dissipated power reached 100 W/cm² (see figure below). Such electronic power and thermal challenges have negative impacts in areas from massive database servers to new applications like wearable devices, medical instrumentation, or portable electronics. In the latter situations, there is a basic trade-off between the available functionality and the need to carry heavy batteries to power it.

CPU power density

Despite tremendous progress over the past three decades, modern silicon transistors are still over three orders of magnitude (>1000×) more energy inefficient than fundamental physical limits. These limits have been estimated as approximately 3kBT ≈ 10–20 J at room temperature for a binary switch with a single electron and energy level separation kBT, where kB is the Boltzmann constant and T is the absolute temperature. In the average modern microprocessor, the dissipated power is due, in approximately equal parts, to both leakage (or sleep) power and active (dynamic) switching power.

switching energy

Power dissipation is compounded at the system level, where each CPU Watt demands approximately 1.5× more for the supply, PC board, and case cooling. Such power misuse is even more evident in systems built on otherwise power-efficient processors, e.g., in the case of the Intel Atom N270 (2.5 W power use) which is typically paired up with the Intel 945GSE chipset (11.8 W power use). At the other extreme, data centres require 50%–100% additional energy for cooling, which is now the most important factor limiting their performance, not the hardware itself.

Such energy challenges for the electronics infrastructure stem not only from the power supply side which calls for new energy sources, efficient batteries, or thermoelectrics, but also from the demand side, i.e., the need for more energy-efficient computing devices. Breakthroughs in our understanding and improvement of energy efficiency in nanoelectronics will have a global effect, impacting our energy supplies, budgets, and the environment.

On a broader scale, just over half the man-made energy in the world is wasted as heat (1013 W), from power plants and factories to car engines and the power bricks on our laptops. Efficiently reclaiming even a small percentage of such wasted heat would itself nearly satisfy the electricity needs of our planet. The fundamental issues at hand are, in fact, a two-sided problem: on one side, there is a significant need for low-energy computing devices, which is perhaps the biggest challenge in micro/nanoelectronics today. On the other side there is the challenge of waste heat dissipation, guiding, or conversion into useful electricity. On a large scale, a transistor twice as energy-efficient could lower power use by a significant percentage of the planet power budget. Such progress is crucial to maintaining progress in a post-CMOS world, and has great environmental implications as well.

Original article: Eric Pop, Energy Dissipation and Transport in Nanoscale Devices

1 Comment to “Energy dissipation and transport in nanoscale devices”

  • P. Simps Wednesday April 28th, 2010 at 11:47 PM

    nice post. thanks.

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