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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