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Quantum realisation of the SI ampere

Short Name: e-SI-Amp, Project Number: 15SIB08
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Development of single electron sources as candidates for primary standards to realise the SI unit of electrical current


Numerous electrical measurements are performed each year, including in medical devices, manufacturing, environmental monitoring, and security. To ensure consistent and standardised performance, all measurements must be accurate and traceable to the ampere, the International System (SI) unit for electrical current.

In 2019 the ampere was redefined, linking its value to the charge carried by a single electron (e). However, the ampere still lacked a direct method for its realisation. ‘Single-electron-pumps’, devices that periodically emit a single electron, offered one solution and could serve as a primary standard for electric current. However, a number of challenges existed before these could be adopted.

Methodology was required to reliably count single electrons flowing through the device. Additionally, single-electron sources generate extremely small currents – less than a billionth of the charge used by an electrical household device. Thus, current levels from such devices required scaling up to levels usable in real-world applications.

 

Building on the work of EMRP project Qu-Ampere, this project developed the semiconductor devices and instrumentation technologies required to implement methods to realise the new ampere. The consortium fabricated over 10,000 semiconductor-based single-electron sources and more than 100 single-electron devices were characterised at low temperatures (below 4.2 K).

Over 20 of these devices were selected and, for the first time, detailed current quantisation and comparison tests between devices of different materials were performed to assess their universality, robustness, and reproducibility. Together, these devices cover a wide measurement range from 10-15 to 10-3 amps. As a result, new, accurate sources have become available as candidates for primary standards for the new SI ampere.

Additionally, 3 instruments were developed to enhance the capability of small current measurements: an Ultra-Low Current Amplifier (ULCA), a Programmable Quantum Current Generator (PQCG) and an Ultra-Low DC Current Source (ULCS).
 For the ULCA, 4 variants were produced, differing in stability, gain, noise, and range, which are now commercially available.

The project’s results have also improved small-current measurement capability at European National Metrology Institutes, with resolution at the level of 10-18 amps.

Up to one order of magnitude measurement improvement in the range of 10-12 to 10-10 amps has also been achieved, and the uncertainties of electrical units through the calibration chains have been improved.

 

More accurate electrical units have become available to end users, and manufacturers of instruments such as particle counters or radiation dose meters have benefited from the availability of high-accuracy portable current measurement and source systems.

 

Project website
Publications
Electrometer Calibration With Sub-Part-Per-Million Uncertainty
2019

IEEE Transactions on Instrumentation and Measurement

Noise-optimized ultrastable low-noise current amplifier
2019

Review of Scientific Instruments

Interlaboratory Nanoamp Current Comparison With Subpart-Per-Million Uncertainty
2019

IEEE Transactions on Instrumentation and Measurement

Reference Ultralow DC Current Source Between 1 fA and 100 pA at TÜBİTAK UME
2019

IEEE Transactions on Instrumentation and Measurement

Random-telegraph-noise by resonant tunnelling at low temperatures
2017

2017 IEEE Electron Devices Technology and Manufacturing Conference (EDTM)

Transport properties in silicon nanowire transistors with atomically flat interfaces
2017

2017 IEEE Electron Devices Technology and Manufacturing Conference (EDTM)

Ultrastable Low-Noise Current Amplifiers With Extended Range and Improved Accuracy
2016

IEEE Transactions on Instrumentation and Measurement

Other Participants
Aalto-korkeakoulusäätiö sr (Finland)
Commissariat à l'énergie atomique et aux énergies alternatives (France)
Korea Research Institute of Standards and Science (Korea, Republic of)
The Chancellor, Masters and Scholars of the University of Cambridge (United Kingdom)
University of Southampton (United Kingdom)

Information

Programme
EMPIR
Field
SI Broader Scope
Status
completed
Call
2015
Duration
2016 - 2019