Accurately measuring small electrical currents is important in many areas of science and technology from photovoltaics, nano-scale electronics and semiconductor fabrication, to dosimetry, and environmental analysis. The redefined ampere requires a new traceability chain based on single electron transport devices and highly accurate current amplification methods, but generating and counting electrons one by one is difficult. New and advanced concepts for single-electron error accounting using micro-chip detection require characterisation to enable labs outside the NMI community to accurately realise the ampere.
The EMRP project Quantum ampere: realisation of the new SI ampere (Qu-Ampere), developed measurement devices and techniques to support the realisation of the proposed 2018 ampere redefinition.
- Developed and characterised the three best existing single-electron transferal pumps for generating currents at the 100 pA level, achieving measurement uncertainties that match the requirements of the ampere redefinition.
- Demonstrated the first proof-of-principle of a ‘self-referenced’ single electron transport pump with in situ detection of electron transfer errors, and established that this technique can significantly enhance the accuracy of current generating pumps.
- Developed an innovative ultrastable low-noise current amplifier (patents pending) with unparalleled performance and stability which can be used for the realisation of ampere traceability by calibration laboratories.
This EMRP collaboration has identified a basic characteristic of single-electron transferal devices, essential components for the realisation of the redefined ampere. The project team found that there is no ‘rapid characterisation’ procedure based on a series of quick measurements that can predict the accuracy of single electron transport pumps. Instead, better on-chip error accounting strategies, will have to be applied to achieve the required uncertainties of 0.1 ppm.
The ultrastable low-noise current amplifier instrument, developed in the project, is giving Europe a world leading capability in the field of ultra-accurate small current measurement instrumentation. Validated within the project as a travelling standard for small direct currents, it was commercialised by a German SME and is available for use by calibration laboratories requiring the realisation of the redefined ampere for measurements of small currents and high-value resistors.