World’s smallest acoustic amplifier holds promise for wireless communications
Sandia claims the amplifier architecture, which operates at 276MHz, has opened up a novel route to the miniaturization of radio frequency circuits.
A paper on the technique – Towards single-chip radiofrequency signal processing via acoustoelectric electron–phonon interactions – was published May 13 in Nature Communications, reports that the device is more than 10 times more effective than the earlier versions.
Sandia’s acoustic, 276MHz amplifier occupies 0.5 square millimeters, demonstrating the potential of making radios smaller by using acoustic waves in silicon rather electronic signals. The technique is based on creating thin layers of active material to transport phonons.
An acousto-electric chip, top, produced at Sandia National Laboratories includes a radio-frequency amplifier, circulator and filter. An image taken by scanning electron microscopy shows details of the amplifier. Source: Sandia National Laboratories.
The acoustoelectric platform consists of a 50nm epitaxial indium gallium arsenide (In0.53Ga0.47As) semiconductor layer on a LiNbO3 substrate that supports a shear-horizontal surface acoustic wave (SH-SAW) with an electromechanical coupling of 17 percent and minimal propagation losses. Sandia’s authors reckon this 50nm platform can support acoustoelectric interactions to at least 5GHz.
“Acoustic wave devices are inherently compact because the wavelengths of sound at these frequencies are so small – smaller than the diameter of human hair,” said Lisa Hackett, lead author on the paper, in a statement.
For 2GHz signals, closer to that part of the electromagnetic spectrum used for cellular communications and Wi-FI, an amplifier would be even smaller, requiring 0.02 square millimeters, an order of magnitude smaller than conventional RF circuits.
Much of the work conducted by Sandia was related to process of growing crystals on top of other crystals and then removing material to produce a smooth contact surface. The Sandia team also created an acoustic circulator for separating transmitted and received signals and filters.
Scientists tried making acoustic radio-frequency amplifiers decades ago, but the last major academic papers from these efforts were published in the 1970s.
With the microfabrication technologies available at that time such acoustic amplifiers occupied large areas of the order of a square centimetre, 2,000V and consumed 500mW of power due to heat generation, Sandia reported.
Sandia’s amplifier can boost signal strength by a factor of 100 with 36V and 20mW.
Sandia said that the use of acousto-electric amplification in mobile phones would probably not come as quickly as it would for specialized RF devices where one vendor controls the whole of the transmit-receive chain.
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