Beating the heat: Cooler chips

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  • Published: Jun 15, 2015
  • Author: David Bradley
  • Channels: X-ray Spectrometry
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Correlated materials

Newly Discovered Property Could Help Beat the Heat Problem in Computer Chips Credit: SLAC

For the first time, X-ray studies undertaken at the US Department of Energy's SLAC National Accelerator Laboratory have revealed an exotic material property that could allow the electronic structure to be warped so that excessive and damaging heat build up in ever-smaller computer components might be avoided.

An international collaboration with researchers from Boston College, Northeastern University, SLAC’s SSRL and Stanford Institute for Materials and Energy Sciences (SIMES), Lawrence Berkeley National Laboratory, the University of California, Santa Barbara, in the USA, Peking University in China and the Hiroshima Synchrotron Radiation Center in Japan has turned its attention to the heat that builds up because of the endless high-speed shuttling of electrons our electronic gadgets and computers. Heat is important as in excess it will destroy the device. As circuit designers manage to cram ever more features on to a chip, so the heat problem becomes more troublesome.

The team has studied a form of iridium oxide, Sr3Ir2O7, that is one of a group of compounds known as "correlated materials" in which the electrons can be made to move in synchrony. This iridium oxide is therefore a candidate for reducing the heat generated by the billions of transistors on the chip's that drive modern computers. The rationale lies in the team's confirmation of the existence of a long-theorized property of these materials, previously only demonstrated in two-dimensional materials, known as 3D negative electronic compressibility.

Electronic deformation

A material's electronic structure is usually considered to be typically quite rigid, energy levels, bands, fill up with electrons in order and are effectively set by the atomic structure and chemical composition of the material in question. However, the team has demonstrated, using data from angle-resolved photoemission spectroscopy (ARPES) and theoretical calculations, that the bands in iridium oxide can be deformed in a fluid-like manner as electrons are added without distorting the physical structure significantly.

"Imagine pouring water into a cup and watching the water level in the cup appear to dip as the cup deforms," suggests study leader Junfeng He. "That's how 3D negative electronic compressibility appears to operate." But in this case, it is the material’s electronic structure - which defines how it can store or flow electric current - rather than its physical structure that substantially warps as electrons are added.

Gated communication

The work was guided by theoretical calculations carried out by Northeastern's Arun Bansil and his team in which they found that a gap between different groupings of energy bands in the sample material actually shrank as electrons were added, reducing the material's stored energy level - like the water level appearing to fall in that cup.

Such a material used as the conducting electrodes for microscopic gates on a chip could help regulate the flow of electrons and substantially improve overall efficiency, thus reducing heat accumulation. Project leader Rui-Hua He adds that, "Replacing normal metals in transistors with materials like this that have negative electronic compressibility presents an intriguing alternative to current approaches, with a goal of continuing device miniaturization.” The team is now working on the first demonstration of their potential application to transistors. 3D materials are more compatible with current microelectronic manufacturing technology and the CMOS architecture of modern microcircuitry, than 2D materials.

"This work informs us of the importance to continually look for other new materials with novel physical properties for use in transistors and for other applications," adds UCSB's Stephen Wilson, who prepared the sample materials. Potentially, the work could lead to room-temperature (field independent) and variable-frequency device operation with significantly reduced power consumption.

"Our next step (ongoing) is to build a capacitor with this NEC material as a top gate," He told SpectroscopyNOW. "We expect a substantial capacitance enhancement compared to capacitors made with normal metal gates. This enhancement is expected to lead to a notable decrease in power consumption of the transistor made with a NEC top gate. The latter effect is ultimately what we hope to demonstrate experimentally."

Related Links

Nature Mater 2015, online: "Spectroscopic evidence for negative electronic compressibility in a quasi-three-dimensional spin–orbit correlated metal"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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