Metamaterials Enable Faster, More Powerful Semiconductor-Free Microelectronics

Researchers have developed the first semiconductor-free optically controlled microelectronic device.

Researchers at the University of California San Diego (UCSD) have developed the first optically controlled microelectronic device that doesn’t use a semiconductor. The research allows for the design of microelectronic devices that work faster and can handle higher power loads, as well as paves the way for more efficient efficient solar panels, researchers said.

Current microelectronic devices, such as transistors, are limited in capability by the properties of components such as semiconductors, which can impose limits on a device’s conductivity, or electron flow. That’s because semiconductors have what’s called a band gap, meaning they require a boost of external energy to get electrons to flow through them. This limits electron velocity, as electrons are constantly colliding with atoms as they flow through the semiconductor.

To help overcome these limitations, a team in the Applied Electromagnetics Group at UCSD—led by electrical engineering professor Dan Sievenpiper—aimed to remove these roadblocks in conductivity at a microscale by using free electrons in space, said Ebrahim Forati, a former postdoctoral researcher in Sievenpiper’s lab and first author of a paper on the work published in the journal Nature Communications.

However, allowing electrons to roam free without being linked to materials is easier said than done, researchers found. To liberate them from materials typically requires applying high voltages of at least 100 volts, high-power lasers, or extremely high temperatures of more than 1,000 degrees Fahrenheit, Forati said. These methods just aren’t practical in electronic devices at the micro- and nanoscale, however.

To solve the problem, the UCSD team turned to metamaterials—in this case, a metasurface comprised of an array of gold mushroom-like nanostructures on an array of parallel gold strips. Researchers fabricated a microscale device comprised of this metasurface on top of a silicon wafer with a layer of silicon dioxide in between.

Activated by low voltage and a low-power laser, the device in tests showed a 1,000% increase in conductivity
Activated by low voltage and a low-power laser, the device in tests showed a 1,000% increase in conductivity. (Source: UC San Diego Applied Electromagnetics G

The design of the gold metasurface is such that when a low DC voltage—under 10 volts—and a low power-infrared laser are both applied, it generates so-called “hot spots,” or spots with a high intensity electric field. These spots provide enough energy to pull electrons out from the metal and free them into space, according to the team.

This method also showed a 1,000 percent improvement in conductivity, meaning more electrons are available for manipulation, Sievenpiper said. The microelectronic device designed may not be well-suited to all semiconductor-dependent applications, he said, “but it may be the best approach for certain specialty applications, such as very high frequencies or high power devices.”

The team designed the metasurface as a proof of concept, but aims to develop and optimize different metasurfaces for different types of microelectronic devices, Sievenpiper said. Researchers also are exploring other applications beyond electronics for the technology, including photochemistry, photocatalysis, new kinds of photovoltaic devices, and environmental applications.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years.

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