Engineers have developed a device that generates small earthquake-like vibrations on the surface of the chip. They say it could one day be used for signal processing inside everyday electronic devices, paving the way for smaller, faster and more efficient wireless devices.
In a new study published in the journal Nature on January 14, the scientists described their device as a surface acoustic wave (SAW) phonon laser that generates very small, rapid oscillations.
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In nature, SAWs are generated on a large scale when plates slide against each other, causing earthquakes.
SAW is also used as a filter in smartphones to clean up wireless signals. Cell phone radios receive radio waves from cell phone base stations and convert them into small mechanical vibrations, which helps the chip filter out unwanted noise.
Every time you send a text, make a phone call, or access the Internet, multiple chips convert radio waves into SAW and back again.
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Although conceptually similar to seismic surface waves emitted by earthquakes, SAWs are too small to be measured on scales such as the moment magnitude scale used to estimate the energy released by movement of the earth’s crust.
SAW devices are essential to many of the world’s most important technologies, Matt Eikenfield, professor of quantum engineering at the University of Colorado Boulder and lead study author, said in a statement. This includes cell phones, key fobs, garage door openers, most GPS receivers, and radar systems.
The scientists said a completely solid-state single chip that produces coherent SAW at very high frequencies without the need for an external radio frequency source has never been achieved before.
Traditional SAW components typically require two separate chips and a power supply. The team’s design aims to provide similar functionality using a single chip, potentially capable of driving much higher frequencies with a typical smartphone battery.
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The researchers constructed the device by stacking ultrathin layers of various chip materials into tiny “bars” about 0.02 inches (0.5 millimeters) long.
This included a silicone base. A thin layer of lithium niobate, a type of piezoelectric crystal that converts electrical signals into mechanical vibrations. And the final layer is indium gallium arsenide, a semiconductor material that can accelerate electrons extremely fast when exposed to an electric field.
The system works by repeatedly amplifying vibrations as they travel back and forth within the structure, similar to how light is intensified in a diode laser between two mirrors. The surface vibrations of the lithium niobate interact with the electrons of the indium gallium arsenide, increasing the energy of the wave as it travels forward.
“Almost 99% of power is lost in reverse, so we designed it to have a significant amount of gain in forward motion to overcome that,” Wendt said in a statement.
The research team generates surface waves at about 1 gigahertz (equivalent to billions of oscillations per second) and believes the design can scale to tens or even hundreds of gigahertz. This far exceeds the capabilities of typical SAW devices, which often reach up to around 4 GHz, the researchers said.
The long-term goal is to simplify the way phones process wireless signals. That means using surface waves for much of the signal processing, and designing a single chip that can convert radio waves to SAW and back to SAW. Doing so could allow future wireless devices to filter and route signals on smaller chips using less power.
“This phonon laser was the last domino we needed to fall,” Wendt added. “We can now use the same type of technology to literally create all the components needed for a radio on one chip.”
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