Sound waves tapped to unleash hidden power of 2D materials for revolutionary electronics & brain chips

Sound Waves Unlock New Dimension for Next-Generation Memory and Brain-Inspired Chips

A team of electronics scientists led by Jing Liu from Tianjin University in Tianjin, China have pioneered a groundbreaking approach that merges sound wave technology with the extraordinary properties of atomically-thin materials, overcoming a fundamental limitation in electronics and opening doors to revolutionary memory and computing devices. By ingeniously leveraging the unique tunability of 2D materials combined with surface acoustic waves (SAW), the team has demonstrated that SAWs can produce opposite electrical currents within the same physical device channel, depending solely on whether electrons or holes are the dominant charge carriers. They then took the crucial step of transforming this novel physical effect into the first functional prototypes of multi-bit memory elements and neuromorphic synaptic devices, proving its exceptional potential for boosting performance in these critical technologies.

2D materials offer unparalleled control over electronic properties. A key feature is the ability to dynamically tune the dominant carrier type (polarity) – electrons (negative) or holes (positive) – within a single device channel through external means. This tunable polarity adds a powerful extra dimension ("degree of freedom") for designing sophisticated devices. However, traditional voltage control hides this dimension: electrons and holes move oppositely but, because they carry opposite charges, they produce an external current in the same direction. This "degeneracy" masks the carrier type, preventing its exploitation for enhanced functionality.

Harnessing Tunability to Break the Degeneracy

While sound waves' ability to move both electrons and holes directionally on surfaces was previously known, this team uniquely exploited the tunable polarity of 2D materials to achieve a critical breakthrough in the same channel.

"We didn't just observe carrier transport; we actively controlled the majority carrier type within one device and measured the result," explained Jing Liu. "When we tuned the 2D channel to be electron-dominated, the SAW generated a measurable current flowing one way. Crucially, when we tuned the same device to become hole-dominated, the current generated by the SAW reversed direction completely. This current reversal, driven by the wave transporting the opposite charge type, directly signals the dominant carrier polarity. It's a clean break from the degeneracy that plagued voltage control."

Pioneering Devices Validating Performance Potential

The key significance lies in translating this effect into devices that unlock new performance levels:

1. Multi-State Memory Prototypes: The team built the first memory elements exploiting the SAW-polarity effect. "A single memory cell, using the direction of the SAW-induced current as a readout, can now represent multiple distinct states for electron-dominant and hole-dominant current," explained the researcher. This proves the concept for significantly boosting memory density beyond traditional limits.
2. SAW-Controlled Neuromorphic Synapses: The team also created the first artificial synapses where the strength (weight) of the connection isn't just adjusted in magnitude, but also fundamentally shaped by the polarity state tunable via SAW. "This isn't just ‘more’ tuning; it's richer, multi-factor tuning," the researcher stated, highlighting its potential for more powerful, efficient, and biologically plausible neuromorphic systems. The prototype validates the pathway towards synapses with a vastly expanded dynamic range and functional complexity.

The Proven Path Forward

"Our work is distinct because it's the first to combine SAW transport with the inherent tunability of 2D materials in a single device to create a usable, polarity-dependent electrical signal – the current reversal," emphasized the lead researcher. "More importantly, we are the first to demonstrate how this effect can be harnessed to develop memory devices with fundamentally higher information density and synaptic devices with unprecedented tunability. This isn't just theory; we built functional prototypes proving the performance potential."

Immediate goals focus on optimizing these prototypes for higher speed, lower power, and greater stability. The team is also refining SAW generation for precise and efficient carrier manipulation. "Having validated this powerful approach, our ultimate vision is to develop a new generation of ultra-compact, ultra-efficient electronic and brain-inspired computing hardware that fully exploits the 'polarity' knob provided by 2D materials, perfectly controlled by sound waves."

This work was supported by the National Natural Science Foundation of China (No. 62431018, No. 12034001) the National Key R&D Program of China (No. 2024YFA1200125).

About the Authors

Dr. Jing Liu is a full professor at School of Precision Instruments and Opto-electronics Engineering, Tianjin University, Tianjin, China. Her research interests focus on the property modulation of two-dimensional materials, and novel information devices, including reconfigurable devices, multi-bit memory, and neuromorphic devices. She has published more than 100 research articles, served as principal investigator (PI) and co-PI for more than 10 projects funded by the National Natural Science Foundation of China and the National Key R&D Program of China.

About Nano Research

Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 7,000 articles. In 2024 InCites Journal Citation Reports, its 2024 IF is 9.0 (8.7, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.