Towards realization of invariant resistance standard at mega-ohm level

- National competitiveness in metrology demonstrated through Korea-Japan collaboration -

The Korea Research Institute of Standards and Science (KRISS, President Sang-Ryoul Park) has played a pivotal role in the realization of invariant high resistance, which may serve as a standard at MΩ-level.

A team led by principal research scientist, Dong-Hun Chae of the Center for Electromagnetic Metrology at KRISS has contributed significantly through precision measurements of quantum Hall resistance array to the realization of 1 MΩ quantum resistance. The study, conducted jointly with Japanese researchers at the National Metrology Institute of Japan (NMIJ), verified for the first time that high resistance values derived from a quantum Hall resistance array remain unchanged over time.

* 1 MΩ: 1,000,000 ohm (Ω). Ohm (Ω) is the unit of electrical resistance.

Resistance, the basic element of any electronic circuit, is required for the operation of electronic devices. Resistance standards ensure that resistance values are accurate and reliable. Many industries have adopted resistance standards because deviation from required resistance affects both current and voltage, leading to fatal functional problems in products.

The standard of resistance is based on the quantum Hall effect* discovered by German scientist, Klaus von Klitzing in 1980.

* Quantum Hall effect :

A phenomenon in which the Hall resistance is quantized with respect to the magnetic field arising from the quantum mechanical wave nature of electron. This effect is distinctly different from the linear magnetic field dependance of the classical Hall resistance stemming from the Lorentz force. Quantized Hall resistance is used as the resistance standard because it is reproducible and can be calculated with only the electron charge and the Planck constant.

Advances in science and technology, however, presented another challenge. Despite the increased demand for MΩ-level resistance, the quantum Hall resistance at 12.9 kΩ was inadequate as a standard for high resistance. For this reason, artifactual metal resistors are used for high resistance standards.

To realize an invariant high resistance, NMIJ fabricated a 1 MΩ quantum Hall resistance array by connecting about 90 resistors in series and parallel. They faced challenges in the precise validation of the 1 MΩ array resistance due to the 100 times smaller applied current for precision measurements compared with the quantum Hall resistance standard. NMIJ requested KRISS, which is capable of the resistance metrology in the top flight, to participate in a joint study to overcome this issue.

Chae and his team succeeded in experimental demonstration that the array resistance is invariant with time within the relative measurement uncertainty of 10-8 using a Cryogenic Current Comparator. Similar to the act of placing two loads on a weighing scale, the team directly compared the proposed quantized Hall array resistance with the quantum Hall resistance standard.

The MΩ-level invariant quantum-mechanical resistance opens up new possibilities in science and across industries. This is because a quantum mechanical high resistance is needed for the precision measurement of a small current source and its stable generation. It is expected to drive technological innovation in precision measurements over various areas including, for instance, the determination of density of particulate matter and the radiometry in cancer treatment.

Chae said, “Quantum Hall array resistance can be utilized in various industries and research areas directly related to the lives of citizens. It can be also applied to the precision evaluation of single electron current sources, which may play an important role in a realization of the new SI ampere (A).”

The study was published in the October issue of Metrologia, the leading international journal on metrology published by the International Bureau of Weights and Measures in Paris.

▲ Professor Klaus von Klitzing mentioning the precision measurement data acquired at KRISS in the Conference on Precision Electromagnetic Measurements (CPEM) held in Paris, France last July.

▲ Principal research scientist, Chae preparing the precision measurements of the quantized Hall array resistance.