Tag Archives: International System of Units (SI)

Memristors as the new standard for electrical resistance

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An October 27, 2025 Polytechnic University of Turin (Politecnico di Torino [PoliTo]) press release announced research into the science of measurement (metrology), Note: Links have been removed,

Tracking electrical resistance is essential to ensure the accuracy and reliability of electrical measurements worldwide. Since 2019, the units of measurement in the International System (SI) are no longer based on standard samples (kilogram, metre, etc.), but are derived from universal constants such as the speed of light. For electrical resistance, reference is therefore made to electrical conductance – which measures the ability of a material to conduct electricity – quantised (G₀) – a combination of Planck’s constant (h) and the elementary charge (e) – typically measured using the quantum Hall effect, a technique that provides accurate and reproducible values but requires expensive cryogenic systems and high-intensity magnetic fields available in only a few national metrology institutes (NMIs).

The study ‘Quantum resistance memristor for International System of Units intrinsically traceable standard’, co-authored by a group of researchers from Politecnico di Torino together with leading European metrology centres and published today in the prestigious journal Nature Nanotechnology, introduces a new standard for the traceability of electrical resistance: memristors, nanometric devices capable of modifying their conductivity in response to external stimuli. This is an innovative discovery: memristors can provide stable resistance values that are intrinsically correlated with the fundamental constants of nature, with the possibility of programming the resistance by modifying the silver nanofilaments that characterise them.

These changes can be adjusted at the atomic level even at room temperature, thus generating quantum leaps – fundamental concepts of quantum mechanics referring to the phenomenon whereby a quantum system passes from one energy level to another in a discontinuous manner, i.e. without passing through intermediate states, as happens with an electron in an atom – discrete, corresponding to G0 (or multiples) that can be measured with conventional reading systems. This approach paves the way for the concept of “NMI-on-a-chip”, i.e. the possibility of integrating the functions of an entire national metrology institute at the microchip level.

In the future, electrical measuring devices such as multimeters – among the most widely used instruments in the industry for measuring electrical quantities – could thus have a memristor as a reference for self-calibration, i.e. to automatically adjust their measurement or operating parameters so as to maintain the accuracy and correctness of results without external human intervention. This will enable the use of simplified calibration procedures in industry and in sectors where the portability of calibrated measurements is a necessity.

“The results obtained and published in the prestigious journal Nature Nanotechnology are the fruit of the European MEMQuD project, where fundamental research by academic institutions such as Politecnico di Torino and the Forschungszentrum Jülich on the phenomenon of “electrochemical polishing” (thanks to which nanofilaments can be “filed” at the atomic level) was coupled with the methodological rigour of the national metrology institutes of Italy, Turkey, Spain, Portugal and Germany”, comment the co-authors of the study Carlo Ricciardi and Fabio Michieletti, respectively professor and post-doctoral researcher at the Department of Applied Science and Technology-DISAT and members of the NaMeS group at Politecnico di Torino.

An October 28, 2025 Universitat Autonoma de Barcelona press release (also on EurekAlert but published November 3, 2025) provides additional insight,

Microchips with a memristor could replace an entire electrical resistance calibration laboratory

An international research collaboration with the involvement of the UAB demonstrates for the first time that memristors, electronic devices at the nanoscale,  can easily calibrate electrical resistance for certain applications without requiring large and complex laboratories working at extreme temperatures and very high magnetic fields. The work, published in Nature Nanotechnology, explores for the first time the metrological applications of these devices in calibration procedures of electronic systems.

Measuring electrical resistance with maximum precision to be used as a standard in metrology requires complex laboratories at temperatures close to the absolute zero and magnetic fields that are more intense than those used in clinical magnetic resonance imaging.

International research under the framework of the European project MEMQuD, which included the involvement of UAB Department of Electronic Engineering professors Enrique Miranda and Jordi Suñé, demonstrates that memristors can provide stable resistance values directly linked to fundamental constants of nature. Thus, they can become a new much simpler standard than current systems for calibrations of this magnitude.

Measurement standards based on constants of nature

Since 2019, all base units of the International System of Units (SI)—including the metre, second, and kilogram—have been based on fundamental natural constants. For example, the kilogram, which was once based on the “prototype kilogram,” is now linked to Planck’s constant h. A metre is defined with respect to the speed of light, and a second by the oscillation of the cesium atom.

Thanks to laser interferometers and atomic clocks, units of length and time can be verified relatively easily worldwide. The situation is quite different for physical quantities such as mass and electrical units. Their metrological traceability is so complex that the measurements are feasible only in a handful of national metrology institutes.

Until now, the quantum Hall effect has served as the standard for electrical resistance. While it provides highly precise and reproducible values, it requires extreme laboratory conditions, i.e. temperatures close to absolute zero and high magnetic fields. The measurements require sophisticated cryogenic systems and strictly controlled facilities.

Memristors as standard resistance measurement systems

Memristors offer a radically different approach. Originally developed as building blocks for novel computing architectures, such as non-volatile memories and neuromorphic circuits emulating computations in the brain, they exhibit a switching behavior that directly follows universal constants.

Functionally, they act as programmable resistors—essentially resistors with memory. This resistance can be changed by applying external voltages or currents. Conductive nanofilaments of individual silver atoms forms inside them. By applying electrical bias, these filaments can be adjusted with atomic precision so that their conductance changes not continuously, but in discrete quantum steps.

“We have confirmed that memristors can reliably generate discrete resistance states that are directly related to universal constants of nature. In 1998, our group already revealed these quantum effects for the first time in the dielectric breakdown of thin insulators. For certain applications, these devices can be used for calibration without the need of complex cooling systems or high magnetic fields”, says UAB professor Enrique Miranda.

A national metrology institute condensed into one microchip

This approach makes it possible to talk about a concept known as “NMI-in-a-chip”: the service of a national metrology institute condensed into a microchip. In the future, this could mean that a measuring device has its resistance reference built-in directly into the chip. Lengthy calibration chains—from measurements in metrology institutes, reference resistors and precision calibrators, to the calibration of end-user devices—would no longer be necessary. Instead of repeatedly sending a multimeter to the calibration laboratory, it could check itself internally, i.e. a built-in calibration standard.

Applications in research and industries

Applications range from simplified calibration procedures in industry to mobile measuring systems and portable standards for research in the field or in space. “We are at the beginning of a paradigm shift—moving away from complex large-scale facilities towards intrinsic, quantum-accurate standards that can be integrated into any chip”, says UAB professor Jordi Suñé.

Quantified electrical conductance

The foundation of this work is the quantized electrical conductance G₀, derived from Planck’s constant h and the elementary charge e. In the experiments, memristors were reproducibly programmed in air at room temperature into stable conductance states of exactly 1·G₀ and 2·G₀, maintained over extended periods of time. Measurements taken at participating research institutes in Italy, Germany, Spain, Turkey, and Portugal revealed a deviation of 3.8 percent for 1·G₀ and 0.6 percent for 2·G₀. The key lies in a process known as “electrochemical polishing”. In this process, unstable atoms are removed from the conducting filament until only a stable quantized conduction channel remains.

The European project MEMQuD, funded by the European Metrology Programme for Innovation and Research (EMPIR) of the EURAMET alliance of metrology organisations, is an international collaboration with the involvement of the UAB, the INRiM (Italy), the Forschungszentrum Jülich, Peter Grünberg Institute (Germany), the Politecnico di Torino (Italy), the IMDEA Nanociencia (Spain), the TUBITAK National Metrology Institute (Turkey), the TOBB University of Economics and Technology (Turkey), the Instituto Português da Qualidade (Portugal), and the Bulgarian Academy of Sciences (Bulgaria).

Here’s a link to and a citation for the paper,

A quantum resistance memristor for an intrinsically traceable International System of Units standard by Gianluca Milano, Xin Zheng, Fabio Michieletti, Giuseppe Leonetti, Gabriel Caballero, Ilker Oztoprak, Luca Boarino, Özgür Bozat, Luca Callegaro, Natascia De Leo, Isabel Godinho, Daniel Granados, Itir Koymen, Mariela Menghini, Enrique Miranda, Luís Ribeiro, Carlo Ricciardi, Jordi Suñe, Vitor Cabral & Ilia Valov. Nature Nanotechnology volume 20, pages 1884–1890 (2025) Published: 27 October 2025 Version of record: 27 October 2025 Issue date: December 2025 DOI: https://doi.org/10.1038/s41565-025-02037-5

This paper is open access.

Monsieur Kilogram; an SI (international system of units) Superhero

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I wouldn’t have thought that measurement was such a crucial issue that it would require a superhero team but I have to admit the folks at the US National Institute of Standards and Technology (NIST) make a compelling case in a Feb. 2, 2016 NIST news release (also on EurekAlert but dated Feb. 4, 2016),

The nefarious Major Uncertainty has kidnapped Monsieur Kilogram, putting the world’s measurements of mass in jeopardy. As the world spirals into “Mass Hysteria,” the remaining SI Superheroes, champions of the metric system, leap into action to save the day, and hopefully Monsieur Kilogram as well.

This crisis kicks off the third and latest adventure from the League of SI Superheroes, the animated online series from the National Institute of Standards and Technology (NIST). “Mass Hysteria” touches upon a topic—how to redefine the basic unit of mass known as the kilogram—that represents a cutting-edge undertaking for researchers working to modernize the worldwide metric measurement system known as the International System of Units (SI).

From the very big to the very small, accurately measuring mass is important in the world around us. For example, many of the products you buy at the grocery store and other places are sold by mass or the related quantity of weight. Roughly speaking, mass is the amount and type of “stuff” there is in something, and weight is the force pulling on the mass by gravity. The masses of every ingredient in medications from aspirin tablets to cancer drugs are carefully measured to ensure that they are both safe and effective. In many cases, medical doctors consider the mass of the patient to determine the dosage of the medications they prescribe as well. And both the fuel and the amount of thrust produced by the huge engines that power airplanes and rockets depend on mass.

Small errors of even a few milligrams per kilogram may not sound like much, but they can be costly when measuring huge quantities of something like a tanker ship full of grain or oil. With medicines, slightly too little of a chemical could make it ineffective and slightly too much could be toxic.

Here’s a peek at Monsieur Kilogram who seems like a pretty tough customer,

Monsieur Kilogram, a character in NIST’s League of SI Superheroes animated online series, is able to determine the mass of any object simply by holding it. ©NIST

Monsieur Kilogram, a character in NIST’s League of SI Superheroes animated online series, is able to determine the mass of any object simply by holding it. ©NIST

Getting back to the news release and the importance of accurate measurement,

Being the last standard unit of measure still based on an actual physical object, in this case a golf-ball-sized cylinder of platinum and iridium, the kilogram is vulnerable to damage, as well as being lost or even stolen. While the international prototype kilogram itself cannot change because it is the kilogram by definition, copies of the international prototype that many countries use as their standard of mass have been gaining or losing mass relative to it.

The SI Superheroes’ latest episode briefly explores one of the efforts to redefine the kilogram in terms of natural forces called the watt balance, a complex machine that uses electric and magnetic forces to balance a 1-kilogram mass against the Earth’s gravity. Precise measurements related to these forces can then be used to provide a consistent definition of the amount of mass in the kilogram.

While the superheroes’ antics are not exactly representative of the efforts of actual researchers, super scientists at NIST and elsewhere have been working for years to reduce the errors in their measurement of this quantity to the point where the watt balance can take over for the international prototype kilogram.

They are closing in on their goal, and it is widely anticipated that the kilogram will be redefined in 2018.

Once this process is complete, the kilogram will have been freed from its dependence on a physical object, and anyone with the right technical expertise and equipment will be able to determine the mass of a kilogram for themselves.

Will the SI Superheroes finish the watt balance in time? Watch the next episode and find out! Modeled on the seven base units of the International System of Units, or SI, the League of SI Superheroes are:

Meter Man: With his laser interferometer eyes, graduated arms and extendable body, no dimension is too big or too small for Meter Man to measure.

The Mole: Able to sniff out and count the atoms of every element, the Mole is a master of chemistry.

Professor Second: By reading the vibrations of her laser-cooled cesium atoms, Professor Second can measure any frequency and calibrate any clock.

Monsieur Kilogram: Monsieur Kilogram loves lifting weights, and it shows. He is able to determine the mass of any object simply by holding it.

Ms. Ampere: Ms. Ampere rules the flow of electrons—electrical current—and makes sure that the right amount gets where it needs to go.

Dr. Kelvin: Dr. Kelvin heats up or cools down objects by speeding up or slowing down particles inside them. He can also measure the temperature of anything in the universe with his trusty thermometer.

Candela: Don’t let her small size fool you. Candela’s power over light helps to brighten the whole world.

Catch up on their adventures at The League of SI Superheroes kids’ page. Teachers can also request a classroom set of SI educational materials by submitting their contact information and grade level to TheSI@nist.gov.

Here’s the latest adventure,

Enjoy!