We have demonstrated that memristors—novel nanoscale devices—can provide stable resistance values directly linked to fundamental constants of nature. This paves the way for electrical units such as electrical resistance to be traceable to the SI units far more simply and directly than it has been possible to date. By contrast, conventional, quantum-based measurement technology is so demanding that it can only be carried out in a few specialized laboratories worldwide.
Since 2019, all base units of the International System of Units (SI) – including the metre, second, and kilogram – have been based on fundamental constants of nature. For example, the kilogram, which was once based on the “prototype kilogram,” is now linked to Planck's constant h. A metre is defined by the speed of light, and a second by the oscillation of the cesium atom.
Until now, the quantum Hall effect has served as the standard for electrical resistance. While it provides accurate, reproducible values, it requires extreme laboratory conditions—temperatures close to absolute zero and magnetic fields stronger than those in clinical Magnetic Resonance Imaging systems. The measurements require sophisticated cryogenic systems and strictly controlled facilities, making measurements feasible only in a handful of National Metrology Institutes.
Memristors offer a radically different approach. Originally developed as building blocks for novel memory and computing architectures, they exhibit switching behaviour that directly follows universal constants. Functionally, they act as programmable resistors where functionalities rely on the formation of nanoscale conductive filaments. By applying electrical bias, these filaments can be adjusted with atomic precision so that their conductance changes not continuously, but in discrete quantum steps [1].
The foundation of this work is the quantized electrical conductance G0, derived from Planck’s constant h and the elementary charge e [2]. In the experiments, memristors were reproducibly programmed in air at room temperature into stable quantum conductance levels maintained over extended periods. The key lies in a process analogous to fine grinding: so-called “electrochemical polishing” here discussed for the first time. In this process, unstable atoms are removed from the conducting filament until only a stable quantized conduction channel remains.
This approach brings into reach a concept known as “NMI-on-a-chip”—the services of National Metrology Institutes condensed into a microchip. In the future, this could allow an electronic equipment to have its reference built directly into the chip. Lengthy calibration chains—from measurements in metrology institutes, through reference standards, down to the calibration of end-user devices—would no longer be necessary. Instead of repeatedly sending an electronic system to the calibration laboratory, it could check itself internally against the unchanging constants of nature – a built-in calibration standard.
Applications range from simplified calibration procedures in industry to mobile measuring systems and portable standards for research in the field or in space. A paradigm shift in metrology is underway—from reliance on complex, large-scale facilities to the development of intrinsic, quantum-based standards implementable on chips that are directly available to the end user.
Results have been obtained in the framework of the European MEMQuD project.
References
[1] Milano, Gianluca, et al. "Quantum conductance in memristive devices: fundamentals, developments, and applications." Advanced Materials 34.32 (2022): 2201248.
[2] Milano, Gianluca, et al. "Memristive devices for quantum metrology." Advanced Quantum Technologies 3.5 (2020): 2000009.