Imaging electrical switching of ultraefficient memory devices
28.03.2026A recent study from the Paul Scherrer Institute PSI has improved understanding of how electrical switching in ultrathin cryogenic memory devices works. Using spatially resolved X-ray diffraction at the Swiss Light Source SLS, scientists tracked how atomic layers of a van der Waals crystal reorganize during device operation. The research provides insights into a new class of ultraefficient memory elements.
Large-scale facilities like the Swiss Light Source SLS synchrotron at PSI are essential for characterizing quantum materials and next-generation electronics. In a recent example, scientists from PSI and the Jožef Stefan Institute in Slovenia peeked inside ultrathin layered flakes of a crystal using the SLS to better understand their unusual properties.
"Their electronic properties can be flipped with high efficiency and speed between insulating off and conducting on states," says Corinna Burri, first author of the study. At low temperature, the ground state is insulating, but light or current pulses can make the crystal flakes electrically conducting. By tracking how atom layers rearrange during this process, the team has now learned how to control the switching more effectively. “This behaviour is promising for future devices, such as the cryogenic memory needed for the classical control electronics of solid-state quantum computers," Burri adds.
A layered material with remarkable properties
As traditional silicon electronics approach their physical limits, researchers are increasingly exploring alternative materials with tuneable electronic properties that require minimal energy to change.
"Van der Waals materials – composed of weakly bound atomic layers – are especially promising," explains Simon Gerber, whose group in the PSI Center for Photon Science led the study. Some of these materials host a variety of correlated electronic phases that can be switched with short electrical or optical pulses, making them candidates for highly efficient memory devices.
The compound 1T-TaS₂ is one such layered van der Waals material. At low temperatures, it forms an electrically insulating state that is governed by a collective reordering of electrons. During the last decade, the research team of Dragan Mihailovic at the Jožef Stefan Institute discovered that the material possesses some remarkable features: the insulating ground state can be transformed into a long-lived metallic “hidden” state by applying an ultrashort light or current pulse.
"This switchable behaviour has been demonstrated in transport measurements, but a central question has remained unanswered: Where and how does the switching actually occur inside the material?" notes Mihailovic.
How does the switching occur?
In many conventional memory devices, switching is driven by the formation of narrow, filament-like conduction paths that concentrate current in small regions. Whether a similar mechanism is at work in 1T-TaS₂ cryomemory devices, or whether switching instead involves a collective reorganization of the crystal, has important implications for device reliability, scalability, and efficiency. But addressing this question requires a way to look inside a functioning device without destroying it.
To tackle this challenge, Corinna Burri fabricated ultrathin 1T-TaS₂ flakes into microscopic devices in the PICO clean room of PSI. The devices were then cooled to cryogenic temperatures, and a combination of electrical transport measurements with spatially resolved X-ray diffraction and fluorescence was performed at the microXAS beamline of the SLS. While short current pulses were applied to switch the device, a tightly focused X-ray beam scanned across the samples, enabling the team to map both the electronic state and the atomic structure in three dimensions.
A fundamentally different basis of switching
The study reveals that electrical switching of 1T-TaS₂ differs fundamentally from the filamentary process of conventional memories. Rather than forming localized conductive paths, the metallic hidden state appears as an extended, well-ordered region that spans a significant volume of the device. This region penetrates deeply into the material and even extends beneath the metal electrodes, showing that switching is a bulk, collective process involving many atomic layers.
By reconstructing the stacking of the van der Waals layers before and after switching, the team showed that electrical pulses change how the layers are arranged on top of each other. This structural rearrangement stabilizes the metallic state and explains its non-volatile character at low temperatures.
Simon Gerber adds: "Beyond the insights into the non-thermal switching process of the material 1T-TaS2, this work highlights the power of non-destructive X-ray imaging for the development of next-generation electronic devices." Being able to visualize where and how switching occurs inside an operating device provides a new level of feedback for device design and optimization.
Text: Paul Scherrer Institute PSI
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