Engineers have taken a major step toward producing the smallest earthquakes ever created, shrinking seismic-style vibrations down to the scale of a microchip.

The breakthrough centers on a device called a surface acoustic wave phonon laser. The technology could eventually enable more advanced chips for smartphones and other wireless electronics, helping make them smaller, faster, and more energy efficient.

The research was led by Matt Eichenfield, an incoming faculty member at the University of Colorado Boulder, along with scientists from the University of Arizona and Sandia National Laboratories. Their findings were published Jan. 14 in the journal Nature.

What Are Surface Acoustic Waves?

The new device relies on surface acoustic waves, commonly known as SAWs. These waves behave somewhat like sound waves, but instead of traveling through the air or deep inside a material, they move only along its surface.

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“SAWs devices are critical to the many of the world’s most important technologies,” said Eichenfield, senior author of the new study and Gustafson Endowed Chair in Quantum Engineering at CU Boulder. “They’re in all modern cell phones, key fobs, garage door openers, most GPS receivers, many radar systems and more.”

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Most existing SAW systems require two separate chips and an external power source. The new design combines everything into a single chip and could operate using just a battery while reaching much higher frequencies

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the team built a bar-shaped device about half a millimeter long.

A Stack of Specialized Materials

The device consists of several layered materials. At its base is silicon, the same material used in most computer chips. Above that sits a thin layer of lithium niobate, a piezoelectric material. When lithium niobate vibrates, it produces oscillating electric fields, and those electric fields can also trigger vibrations.

The final layer is an extremely thin sheet of indium gallium arsenide. This material has unusual electronic properties and can accelerate electrons to very high speeds even under weak electric fields.

Together, these layers allow vibrations traveling along the lithium niobate surface to interact directly with fast-moving electrons in the indium gallium arsenide.

Making Waves Build Like a Laser

The researchers describe the device as working similarly to a wave pool.

When electric current flows through the indium gallium arsenide, surface waves form in the lithium niobate layer. These waves travel forward, strike a reflector, and then move backward, much like light reflecting between mirrors in a laser. Each forward pass strengthens the wave, while each backward pass weakens it.

“It loses almost 99% of its power when it’s moving backward, so we designed it to get a substantial amount of gain moving forward to beat that,” Wendt said.

After repeated passes, the vibrations grow strong enough that a portion escapes from one side of the device, similar to how laser light eventually exits its cavity.

Faster Waves, Smaller Devices

Using this approach, the team generated surface acoustic waves vibrating at about 1 gigahertz, meaning billions of oscillations per second. The researchers believe the same design could be pushed into tens or even hundreds of gigahertz.

Traditional SAW devices typically max out at around 4 gigahertz, making the new system far faster.

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Source: Engineers just created a “phonon laser” that could shrink your next smartphone | ScienceDaily

To find out what SAWS are used for and how they work, check out: Trends and Applications of Surface and Bulk Acoustic Wave Devices: A Review

A lot of the applications are in MEMS (Micro-Electro-Mechanical Systems) chips and signal filtering.

It seems to me that the biggest innovation must be that they reduced the spacial periodicity, allowing for a much higher frequency (see formula 1 in the above link)

[…] acoustic devices, especially FBARs, represent a broad market as RF filters, compared with conventional electromagnetic devices, thanks to much slower propagation velocity allowing for shorter wavelength and, thus, easy miniaturization and integration into circuits. We then presented another important field of applications of SAW and BAW/FBARs, namely as sensors and actuators. A section was dedicated for their application as physical sensors. Examples of their use for magnetic field, pressure, and temperature monitoring and detection were illustrated. In addition, their application in other fields such as mechanical (in automotive) and orientation measurements were presented. Some examples of SAW-based motors and actuators were also introduced. We then focused on SAW/BAW-based biochemical sensors, which are receiving increasing attention in the research field. Indeed, because of their performances, among them a high sensitivity, a versatile feature that makes them easily functionalized for selectivity, and low cost, they are widely used for gas, liquid, bio-sensing, etc. The sensing applications are still under development, with a rising demand especially for biosensors, since health concerns are more than ever a major topic. As of now, SAW and FBAR devices show a very good capacity for sensing DNA, RNA, proteins, and a wide variety of other bio-compounds. With the COVID-19 pandemic, several biosensors based on SAW and FBAR devices are also reported for the detection of SARS-CoV-2 virus and application for living-matter monitoring is under development, which could be helpful for fast screening of therapeutic nanodrugs, for example. Lastly, we presented current trends related to quantum acoustics, which studies the behavior of phonons and their interactions, as opportunities for new schemes to control quantum information and explore atomic physics beyond photonic systems[…]