The first ever semiconductor-free, optically-controlled microelectronic device has been developed by engineers at the University of California San Diego. The team used metamaterials to build a microscale device that has a 1,000 percent increase in conductivity when activated by low voltage and a low power laser.
The breakthrough basically amounts to a modern-day vacuum tube in nanoscale, paves the way for microelectronic devices that are faster and capable of handling more power, and could lead to more efficient solar panels.
UC San Diego Applied Electromagnetics Group
Most of today’s technology, like computers and mobile phones, would not exist without semiconductors. But these devices are actually limited by the properties of their constituent materials.
For example, semiconductors impose limits on a device’s conductivity, or electron flow. Semiconductors have what’s called a band gap, meaning they require a boost of external energy to get electrons to flow through them.
And electron velocity is limited, since electrons are constantly colliding with atoms as they flow through the semiconductor.
Free Electrons At Microscale
The researchers in the Applied Electromagnetics Group led by electrical engineering professor Dan Sievenpiper at UC San Diego set out to remove these roadblocks to conductivity by replacing semiconductors with free electrons in space, said Ebrahim Forati, a former postdoctoral researcher in Sievenpiper’s lab and first author of the study:
“And we wanted to do this at the microscale.”
But freeing up electrons from materials is challenging. It either requires applying high voltages (at least 100 Volts), high power lasers or extremely high temperatures (more than 1,000 degrees Fahrenheit), which aren’t practical in micro- and nanoscale electronic devices.
So the team fabricated a microscale device that can release electrons from a material without such extreme requirements.
The device consists of an engineered surface, called a metasurface, on top of a silicon wafer, with a layer of silicon dioxide in between. The metasurface consists of an array of gold mushroom-like nanostructures on an array of parallel gold strips.
The gold metasurface is designed such that when a low DC voltage (under 10 Volts) and a low power infrared laser are both applied, the metasurface generates “hot spots”—spots with a high intensity electric field—that provide enough energy to pull electrons out from the metal and liberate them into space.
Tests on the device showed a 1,000 percent change in conductivity.
“This certainly won’t replace all semiconductor devices, but it may be the best approach for certain specialty applications, such as very high frequencies or high power devices,” Sievenpiper said.
According to researchers, this particular metasurface was designed as a proof-of-concept. Different metasurfaces will need to be designed and optimized for different types of microelectronic devices.
Top Image: Scanning electron micrograph of the gold metasurface. Credit: UC San Diego Applied Electromagnetics Group