WP1: Graphene devices for AC-QHE application
The aim of this work package is to advance the development of graphene QHE devices beyond the current state of the art in order to obtain a reliable supply of QHR standards that are stable for a long time. Graphene based quantum devices that are suitable for metrological applications need to have stable electrical and mechanical properties after many cooling cycles in order to compete with conventional GaAs/AlGaAs heterostructures which are stable for decades. This will require high quality epitaxial graphene layers to be grown and specific doping techniques to be used to adjust the electron density to values which will allow metrological measurements at low magnetic fields (below 6 T). Although several doping techniques (i.e. ultraviolet (UV) treatment, corona discharge, organic doping layers, ambient air annealing) have been published so far, the goal of long-term stability (for years) has not been satisfactorily solved. This will be the first systematic study of the fabrication of graphene quantum Hall (QH) devices with the aim of establishing a fabrication process and verifying the optimal parameters which will allow the use of the graphene-based devices as resistance and impedance standards, which are stable in the long term.
WP2: Digital- and Josephson impedance bridges for the realisation of capacitanc
The aim of this work package is to improve the accuracy of digital bridges to between 10-5 and 10-7. The accuracy achieved will depend on the frequency and the specific device. The aim is also to push their operating frequency range up to 100 kHz.
With the redefinition of the SI in May 2019, the QHE will be the realisation of the resistance unit. To fully take advantage of this redefinition, the various impedance scales need to be realised directly from the QHR using fully automated bridges that will be able to cover the entire complex plan up to frequencies of at least 50 kHz. Traditional transformer-based bridges are not suitable for automation and are limited in frequency. Therefore, digital bridges, based on state-of-the-art ADC and DAC, and Dual Josephson Impedance Bridges (DJIB) have been developed recently. This new class of bridges are already fully automated. However, they are not as accurate, by at least an order of magnitude, as traditional bridges and their working frequency range needs to be expanded.
WP3: Graphene AC-QHR with digital- and Josephson impedance bridges
The aim of this work package is to simplify and enhance the realisation of the impedance units based on the quantum Hall effect. The combination of graphene-based AC-QHR devices (WP1) with digital impedance bridges (WP2) (based on digital-to-analogue converters or Josephson voltage standards) will result in the universal implementation of a traceability chain for capacitances. Furthermore, the scaling of the impedance magnitude is possible without significantly deteriorating the intrinsic quantum accuracy of the QHR even for non-decadic values. Simplification of this new traceability chain will be realised using the impedance bridges developed in WP2, as these offer an automated operation over an extended frequency range.
Another aim in this WP is to combine QHR and a Josephson voltage standard (JVS) into one single cryocooler to realise a compact and universal system. This proof of principle will be a first step towards a compact and highly precise quantum device that can be used to obtain traceability for voltage, current and impedance from a single cryogenic system. This will be of use in other National Metrology Institutes (NMIs) and especially for calibration laboratories and industry.
WP4: Creating impact
The aim of this work package is to maximise the impact of the project by ensuring a wide dissemination of the knowledge generated – mostly by creating and utilising links to stakeholders from metrology organisations, calibration service companies, industry and academia. It is also important to gather information and on-going feedback regarding the needs of the end users and other stakeholders both in terms of those providing input to the project and the European end-user community. A close interaction with the Stakeholder Committee, which includes representatives from leading calibration laboratories, will ensure that the activities will also consider the requirements of non-NMI laboratories, and that the stakeholders have an early opportunity to familiarise themselves with new methods and equipment that can make use of graphene standards. The involvement of academia and non-European NMIs with the project will further contribute to creating impact on the worldwide metrology system and on science.
WP5: Management and coordination
The aim of this work package is to manage internal and external affairs regarding the GIQS project and to coordinate the interaction of the partners and the work packages.