A new 100 picosecond time-resolved technique images surface acoustic wave devices

A Surface Acoustic Wave (SAW) device is an electronic device that uses sound waves traveling along the surface of a material (usually a piezoelectric crystal) to process, filter or transmit signals. Their applications are wide, and include mobile phones, Wi-Fi, GPS, and 5G networks to filter and separate different frequency bands, touchscreens, sensors in the automotive and aviation industry, biosensors. They are also promising devices in nanoscale applications, such as quantum communication.

Because they are highly sensitive, durable, compact and cheap, there is a lot of ongoing research into understanding how to optimise their structure. This needs a deep understanding of energy conversion and loss mechanisms taking place in the device.

In SAW devices, electrical energy is converted into sound waves using interdigital transducers. These are tiny comb-shaped metal electrodes placed on a piezoelectric crystal. One set of electrodes is grounded, while the other receives an alternating voltage, causing the crystal's surface to strain or deform. This vibration creates an acoustic wave that travels at several kilometers per second. These waves have extremely high frequencies (hundreds of MHz to GHz), far too fast for even the best high-speed cameras to capture.

However, now a team led by ESRF scientists has developed a technique called stroboscopic full-field diffraction x-ray microscopy on beamline ID01, which allows them to study the dynamic strain in SAW devices. “Today the spatial resolution at the ESRF’s ID01 is about 100nm and we have a time resolution in the storage ring of 100 picoseconds: this is practically the speed of sound . This means that we can image sound unblurred”, explains Tobias Schulli, scientist in charge of ID01 and co-corresponding author of the publication.

The experiments showed that there was an unexpected acoustic loss in a resonator device tested. It proved that propagating modes leak elastic energy away from the resonator. The high sensitivity of X-ray diffraction for changes in atomic distances by 1/100 000 together with the high time and spatial resolution available on ID01 represent the only available technique to detect and quantify such phenomena.

The next step for the team is to extend these measurements to more complex SAW devices and to win a larger device community such as high power transistors or fully functional CPUs, where either thermal or piezoelectric effects affect device operation and require observation on the sub nanosecond scale, the sweet-spot for storage-ring based time-resolved diffraction experiments.

Reference:

Zhou, T., et al. Nat Commun 16, 2822 (2025). https://doi.org/10.1038/s41467-025-57814-6

Text by Montserrat Capellas Espuny

Top image: 150 picosecond snapshot of a surface acoustic wave imaged with the ID01 full field diffraction microscope.