Logo PTB

JRP “e-SI-Amp” finalized successfully


The definition of the ampere, the unit of electric current, in the just revised International System of Units (SI) is based on a fixed value for the elementary charge e. The Joint Research Project (JRP) “e-SI-Amp: quantum realisation of the SI ampere” was launched in the frame of the European metrology research programme EMPIR to develop ways for generating and disseminating electrical current standards within the revised SI. Coordinated by the National Physical Laboratory (UK), the three-years project comprised ten partners from Europe and Asia and was finalized in April 2019. PTB was able to substantially contribute to the success of the JRP in the fields of single-electron current sources and small-current measurement capabilities.




Single-electron current sources, generating currents by transferring an exact number of electrons per cycle, are the most direct methods for the realisation of the revised ampere. Being suited to generate small currents below 1 nA, these nano-structured circuits could enhance metrological capabilities for small-current applications. The project developed semiconductor single-electron devices and novel instrumentation technologies required to implement practical methods for the realisation of the new ampere. The results comprise numerous peer-reviewed journal publications plus conference presentations and training activities, which created considerable impact on the metrology, scientific and industrial communities.

In the field of single-electron current sources, the quantization of the current I generated by the device in terms of I = e.f (f = 600 MHz being the driving frequency of the device) was verified by PTB with a relative uncertainty of only 1.6 parts in 107, i.e. with highest accuracy so far at a current level of 100 pA.

In the field of high-precision measurement capabilities for ultra-small currents down to 1 fA, PTB developed two special versions of the Ultrastable Low-Noise Current Amplifier (ULCA). These instruments were distributed within the consortium for on-site comparison and calibration experiments and commercialized via an instrumentation manufacturer. This activity has contributed to the improvement of small-current and high-resistance measurement capabilities of the partners and enabled the consortium to engage with stakeholders. The improved capabilities already were exploited in various areas of metrology and industrial applications, such as nuclear and gas-particle metrology, semiconductor characterisation, and lighting industry.

Further detailed information on the content and outcomes including success stories are available on the project web site: www.e-si-amp.eu