In Matt Eichenfield’s lab at Sandia National Laboratories, he and his team use a variety of microwave frequencies to analyze a nonlinear phononic mixing device they constructed on a silicon wafer. [Bret Latter/Sandia National Laboratories]
The paper, titled “Giant electron-mediated phononic nonlinearity in semiconductor–piezoelectric heterostructures,” describes the most efficient three-wave and four-wave phononic mixing to date. A team of researchers at Sandia National Laboratories and University of Arizona, including lead author Lisa Hackett and Matt Eichenfield, achieved up to 16% phononic power conversion efficiency for sum-frequency generation and 1% for difference-frequency generation.
New method could enable miniaturized RF front-end modules with enhanced performance
The scientists developed a method to use electricity to precisely control and manipulate sound waves in solid materials by integrating high-mobility semiconductors (indium gallium arsenide, InGaAs) with piezoelectric materials (lithium niobate, LiNbO3).
The strong coupling between the piezoelectric sound waves (phonons) and the charge carriers in the semiconductor enables the electronic nonlinearities to mediate efficient phononic frequency mixing, allowing them to create or remove specific sound frequencies.
In addition, the researchers demonstrated the ability to further bolster the nonlinear conversion efficiency by more than 200 times by applying electrical bias fields to the semiconductor, thus amplifying the sound waves. Already in 2021, the researchers demonstrated a novel acoustic circulator, which could be more than 1 million times smaller by volume than current circulators, featured in a IEEE Spectrum article. In 2023, they published an article in Nature Electronics demonstrating amplifiers for sound waves that work almost as well as microwave amplifiers work for microwaves, a decades-old technology, titled “Non-reciprocal acoustoelectric microwave amplifiers with net gain and low noise in continuous operation.”
Matt Eichenfield, Ph.D.
This emerging field could replace complex transistor-based circuitry with engineered sound waves, potentially leading to a new generation of miniaturized, high-performance smartphones and wireless devices — and even pointing to potential breakthroughs in quantum computing, where phonons, the quantum mechanical description of sound waves, could be used as qubits to process quantum information. The Nature Materials paper, published in May 2024, notes that “three-wave mixing processes such as sum-frequency generation are known to be quantum-state preserving.” It notes that this could thus enable connecting different microwave-frequency qubits on chips or up-converting phonons that carry quantum information to more easily detectable or transducible frequencies.
Phonon interactions point toward smaller, more efficient wireless devices
One challenge in phononic technology lies in the nature of phonons themselves. “Normally, phonons behave in a completely linear fashion, meaning they don’t interact with each other,” said Matt Eichenfield, a professor at the University of Arizona’s Wyant College of Optical Sciences and researcher at Sandia National Laboratories in Albuquerque, New Mexico. “It’s a bit like shining one laser pointer beam through another; they just go through each other.” This “unwillingness” of phonons to interact has limited their applications to exclusively filtering functions, especially in signal processing.
The historical challenges of getting phonons to interact directly have led to the need for additional transistor-based microchips, resulting in bulkier phones and shorter battery life. “Most people would probably be surprised to hear that there are something like 30 filters inside their cell phone whose sole job it is to transform radio waves into sound waves and back,” Eichenfield said. These filters, made from piezoelectric materials, translate into added complexity. “The filters aren’t bulky themselves. But because you can’t do everything on one chip, you end up having to have a whole bunch of chips and every chip has extra area for electrical feedthroughs and extra area around it for handling and packaging,” he said.
In addition, in a smartphone, the signal conversion process is repeated multiple times. “It comes in on the antenna, here it’s a sound wave, here it’s an electrical wave, over and over again,” he said. “Every time you do that, it adds loss because you can never perfectly convert between radio waves and sound waves.”
Consequences of current technology limitations
The inefficiency of current approaches is evident in the design of smartphone RF front-end modules. Teardowns of recent iPhone models, for example, reveal a jumble of separate chips for filtering, amplification, and mixing, all crammed together on a “multi-chip module.” This complex assembly requires extra space to accommodate the connections between these different components, and the back-and-forth conversion between sound waves and electrical signals degrades the signal, reducing performance. While newer smartphones have adopted somewhat more integrated designs, the fundamental challenges remain.
The solution lies in integrating semiconductor materials with piezoelectric materials, unlocking functions typically handled by transistors, such as amplification and nonlinear frequency conversion. This integration, as the Nature Materials paper describes, enables efficient phononic frequency mixing, allowing the creation or removal of specific sound frequencies. Eichenfield and his team have demonstrated these capabilities with significant improvements in nonlinear conversion efficiency and acoustic amplification, generating a minimum acoustic noise figure of 2.8 ± 0.5 dB at 28.0 dB of acoustic gain.
Beyond smartphone applications
While smartphones might spring to mind as a prime beneficiary, Eichenfield emphasizes that this technology’s potential extends far beyond our pockets: “Technically,” he explains, “it’s really any device that communicates by radio waves because wireless communications basically work the same way.” Eichenfield elaborates further, “You have to take either digital or analog data, encode it on a radio wave, and send it out.” This data could be destined for anything from a computer to an IoT-connected refrigerator, toaster or “whatever it is,” Eichenfield said.
As Eichenfield points out, many current IoT devices are relatively crude in terms of processing power and connectivity. “A lot of IoT sensors need to be small and power efficient to be useful. Doing those things and being able to handle a lot of data is what the technology could enable,” he said.
This increased bandwidth could unlock new possibilities for small, deployable sensors: “If you’re trying to make some really small, deployable sensor that goes on a whole bunch of things in your house, or you want to make somebody deploy out a bunch of micro-drones so they can fly over a farm and assess whether the crops are ready to harvest or if there’s bugs infesting them or something, the more RF communication bandwidth you have in a small package, the more you can do with all that stuff.”
“But in all cases,” Eichenfield continued, “you’re sending out encoded information from your own local processing and receiving information that somehow gets used by your processing.” All those devices use a radiofrequency front end processor to handle the encoding and decoding of radio frequency (RF) data. And it’s precisely this fundamental process — encoding, transmitting, receiving, and decoding information—that acoustoelectronics aims to reinvent.”
Inverting the traditional approach to sound wave manipulation
“We’re kind of flipping this thing on its head,” Eichenfield said. “Rather than taking these transistors, which are powerful but complex, and trying to make a filter with them, the question is, can we take the sound waves and do something to them that allows them to reproduce the functions that are done in the transistors?”
Eichenfield has secured a DARPA grant to investigate the development of a complete phononic radio frequency front end. “DARPA basically gave me up to a million dollars over three years to try to investigate making an actual radiofrequency front end processor using this technology,” he said.
“We’ve demonstrated these components individually, not all together working as a radiofrequency front-end processor,” he said. “We have now fundamentally demonstrated the individual components at a high performance level that should enable us to work towards actually building a whole system.”
things are finally entering an era of near breakthroughs.
Next thing you know people will learn to cooperate!?! Examine their own motives as a precursor to taking action, learn to negotiate from a position of honest neutrality?
Leading by good example will become the new norm.
Interesting article. I would imagine any predictable emission/twist in expression of an event related to the interaction(s) would be useful.
Real quantum events are difficult to interpret as “discrete events” as they are truly an expression of shared field expression….rather than “events.”
Wanna talk?
Hi William,
Sure, care to elaborate more on the quantum angle?
good play….
How’s New Orleans?