System Bits: Feb. 10

Mapping temperature for better chip design; tinkering ruins ferromagnetic topological insulator materials; one-atom-thin transistors.

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Mapping temperature
Given that overheating is a major problem for chips today a team of UCLA and USC scientists have made a breakthrough that they believe should enable engineers to design microprocessors that minimize that problem with a thermal imaging technique that can see how the temperature changes from point to point inside the smallest electronic circuits.

The technique is called plasmon energy expansion thermometry (PEET) and allows temperatures to be mapped in units as small as a nanometer, which shatters the previous record for thermal imaging resolution, and could eventually lead to faster and more capable electronics.

Artist’s conception of plasmon energy expansion thermometry showing a focused electron beam penetrating a 100 nanometer wide aluminum wire atop a thin glass window. The wire’s temperature is mapped by scanning the electron beam. (Source: UCLA, USC)

Artist’s conception of plasmon energy expansion thermometry showing a focused electron beam penetrating a 100 nanometer wide aluminum wire atop a thin glass window. The wire’s temperature is mapped by scanning the electron beam.
(Source: UCLA, USC)

To better understand precisely where the heat is being generated, engineers want to be able to map temperature in tiny electronic circuits. Currently, they use one of two thermal imaging techniques: capturing the infrared radiation the device emits or dragging a tiny thermometer back and forth across the device’s surface – but both standard techniques have fundamental limitations.

Without a way to measure the temperature of extremely small circuitry, manufacturers have worked blindly, relying on simulations to estimate the devices’ temperatures. Now, PEET mapping will enable them to heat a transistor and accurately map which parts of it heat up and track how the heat is transported away — knowledge that could help engineers revolutionize the design of the nanoscale electronics inside the next generation of computing devices.

Physics breakthrough stalled by magnetic disorder
Exotic new materials called “ferromagnetic topological insulators” were supposed to be the next big thing, offering potential breakthroughs in electronics and new insights into the physics of solids – but it hasn’t happened, as researchers at Cornell University and Brookhaven National Lab discovered, because tinkering with the materials to make the insulators work has actually introduced a disorder that spoils the desired effects.

Topological insulators are insulators in bulk, but an electric current flows smoothly on their surface. The team described them as ‘very weird compounds’ with a conducting sheen one electron thick, that for five or more years people have been trying to develop all the exotic potential, with very few results.

Theorists predicted that topological insulators might be used in new kinds of electronic devices, including quantum computers, and that they could display unusual physical phenomena, including simulations of magnetic monopoles or of axions – particles theorized to be associated with dark matter. To make these things happen, theory says, the conducting electrons would have to be exposed to a high magnetic field that would lock them into a particular quantum energy level – roughly, the amount of energy it would take to yank an electron out of the system – where they are “protected” from change. Materials scientists synthesized new versions of topological insulators “doped” with atoms of magnetic elements, such as chromium, making them “ferromagnetic.” Still, none of the expected phenomena appeared.

Scanning tunneling microscope image of a 47-nanometer square area of the surface of a topological insulator showing variations in the Dirac-mass gap - a measure of conductance - from high (yellow) to low (blue). Red triangles are chromium atoms, concentrated in the high gap areas. The inset plots the correlation between Dirac-mass gap and chromium atom density. (Source: Cornell/Brookhaven)

Scanning tunneling microscope image of a 47-nanometer square area of the surface of a topological insulator showing variations in the Dirac-mass gap – a measure of conductance – from high (yellow) to low (blue). Red triangles are chromium atoms, concentrated in the high gap areas. The inset plots the correlation between Dirac-mass gap and chromium atom density.
(Source: Cornell/Brookhaven)

They realized they needed to find those magnetic atoms and look at their relationship with the electrons. In the end, they believe their discovery will likely result in revisions of the basic research directions in this field.

One-atom-thin transistors
In researcher that could hold the promise of building faster, smaller and more efficient chips, scientists at The University of Texas at Austin’s Cockrell School of Engineering have created the first transistors made of silicene, the world’s thinnest silicon material.

Made of a one-atom-thick layer of silicon atoms, silicene has outstanding electrical properties but has until now proved difficult to produce and work with, they said.

Buckled honeycomb lattice structure of silicene. (Source: University of Texas at Austin)

Buckled honeycomb lattice structure of silicene.
(Source: University of Texas at Austin)