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Good vibes: New technology could result in smaller, more efficient wireless devices

What if your earbuds could do everything your smartphone already does, except better? What sounds a bit like science fiction may not be so far off after all. A new class of synthetic materials could herald the next revolution in wireless technologies, making devices smaller, requiring less signal strength and consuming less energy.

The key to these advances lies in what experts call phonics, or photonics-like. Both use similar physical laws and offer new ways of developing technology. While photonics uses photons – or light – phonics does the same with phonons, which are physical particles that transmit mechanical vibrations through a material, similar to sound but at frequencies much too high to be heard.

In a paper published in Nature Materials, researchers from the University of Arizona’s Wyant College of Optical Sciences and Sandia National Laboratories report that they have achieved an important milestone toward real-world applications based on phononics. By combining highly specialized semiconductor materials and piezoelectric materials that are not usually used together, scientists managed to generate giant nonlinear interactions between phonons. Together with previous innovations demonstrating phonon amplifiers using the same materials, this opens up the possibility of making wireless devices such as smartphones or other data transmitters smaller, more efficient and more powerful.

“Most people would probably be surprised to hear that there are about 30 filters on their cell phone whose sole purpose is to convert radio waves into sound waves and vice versa,” said study senior author Matt Eichenfield, who has a joint appointment at the UArizona College of Optical Sciences and Sandia National Laboratories in Albuquerque, New Mexico.

These piezoelectric filters, made on special microchips and part of so-called front-end processors, are necessary to repeatedly transform sound and electronic waves every time a smartphone receives or sends data, he said. Because they cannot be made of the same materials, such as silicon, as the other all-important chips in the front-end processor, the physical size of your device is much larger than necessary, and along the way “there are losses due to the flow of radio waves and sound waves , which add up and degrade performance,” Eichenfield said.

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“Typically, phonons behave completely linearly, which means they do not interact with each other,” he said. “It’s a bit like shining one beam of a laser pointer through another; they just pass through each other.”

Nonlinear phonics refers to what happens in special materials when phonons can and do interact with each other, Eichenfield said. In the paper, the researchers demonstrated what they call “giant phonon nonlinearities.” The synthetic materials produced by the research team caused the phonons to interact with each other much more strongly than with any conventional material.

“In a laser pointer analogy, it could be compared to the change in the frequency of photons in the first laser pointer when the second one is turned on,” he said. “As a result, you will see the beam from the first one change color.”

With new phononic materials, scientists have shown that one beam of phonons can actually change the frequency of another beam. Moreover, they showed that phonons can be manipulated in ways that were previously only possible using transistor-based electronics.

The group has been working towards the goal of producing all the components needed for radio frequency signal processors using acoustic wave technology rather than transistor-based electronics on a single chip, in a manner consistent with standard microprocessor manufacturing, and the latest publication demonstrates that it can be done to do. Previously, scientists have managed to produce acoustic components, including amplifiers, switches and others. Thanks to the acoustic mixers described in the latest publication, they have added the last piece of the puzzle.

“Now you can point to every element in a schematic of a front-end RF processor and say, ‘Yes, I can do all this on one chip using acoustic waves,’” Eichenfield said. “We are ready to move on to creating all the chaos in the acoustic domain.”

According to Eichenfield, putting all the components needed to make an air interface on a single chip could shrink devices such as cell phones and other wireless gadgets by up to a hundredfold.

The team achieved proof of principle by combining highly specialized materials into microelectronics-sized devices through which they sent acoustic waves. Specifically, they used a silicon wafer with a thin layer of lithium niobate – a synthetic material widely used in piezoelectronic devices and cell phones – and added an ultrathin layer (less than 100 atoms thick) of a semiconductor containing indium gallium arsenide.

“When we combined these materials in the right way, we were able to experimentally access a new regime of phonon nonlinearity,” said Sandia engineer Lisa Hackett, lead author of the paper. “This means we have a long way to go to develop high-efficiency technology for sending and receiving radio waves that will be smaller than ever before.”

In this configuration, acoustic waves traveling through the system behave in a nonlinear manner as they travel through materials. This effect can be used to change the frequency and encode information. Nonlinear effects, the basis of photonics, have long been used to transform things like invisible laser light into visible laser pointers, but the use of nonlinear effects in phononics has been difficult due to technological and material limitations. For example, although lithium niobate is one of the most nonlinear phonon materials known, its usefulness in technical applications is hampered by the fact that these nonlinearities are very weak when used alone.

By adding an indium gallium arsenide semiconductor, Eichenfield’s group created an environment in which acoustic waves traveling through the material affect the distribution of electrical charges in the indium gallium arsenide semiconductor layer, causing the acoustic waves to mix in a specific way that can be controlled by opening the system for various applications.

“The effective nonlinearity that can be generated with these materials is hundreds or even thousands of times greater than was possible before, which is crazy,” Eichenfield said. “If you could do the same with nonlinear optics, you would revolutionize the field.”

According to the authors, because physical size is one of the primary limitations of current state-of-the-art radio frequency processing equipment, the new technology could open the door to electronic devices that are even more efficient than their current counterparts. Communication devices that take up virtually no space, have better signal range and longer battery life are emerging on the horizon.

Reference: Hackett L, Koppa M, Smith B et al. Enormous electron-mediated phonon nonlinearity in semiconductor-piezoelectric heterostructures. Nat Mater. 2024. doi: 10.1038/s41563-024-01882-4

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