• Using the niobium nitride Josephson device, we have succeeded in developing the first 1V voltage standard chip in the world that does not require the cooling by liquid helium.
• Produced a prototype desktop Josephson voltage standard system with a small refrigerator, and succeeded in generating a highly accurate voltage of 1V.

The Nanoelectronics Research Institute of the National Institute of Advanced Industrial Science and Technology (AIST), has developed a 1V voltage standard chip integrating 32,768 niobium nitride Josephson devices (NbN/TiN/NbN elements), that does not require cooling by liquid helium. Moreover, by adapting this chip to a refrigeration system, AIST has succeeded in making a prototype of the first desktop Josephson voltage standard system in the world that can generate a highly accurate voltage of 1V. These results represent a significant advance towards the production of a low cost, portable Josephson voltage standard system, and paves the way towards the establishment of a global remote calibrating voltage standard network based on GPS and the internet.

Success in producing the first 1V voltage standard chip in the world composed of NbN Josephson devices that does not require cooling by liquid helium

AIST has made advances in the development of integration technology using NbN Josephson device (critical temperature, Tc, exceeding 15K) for the next-generation voltage standard. A successful operation of NbN Josephson devices at a small scale integration was announced by the former Electrotechnical Laboratory on March 6, 2001. This time AIST has achieved a high degree of integration of NbN Josephson devices (32,768 pieces) on a silicon chip, generating a highly accurate voltage of 1V. The breakthrough that led to the development of the large-scale integration was the use of chemical mechanical polishing (CMP) to process the surface of the substrate. The CMP made it possible to overcome the main problem related to the integration of Josephson devices, namely the decrease in the superconducting critical current in the wiring caused by unevenness of the substrate surface.

Success in producing the first desktop Josephson voltage standard system with a small freezing machine, which can generate a highly accurate voltage of 1V

In addition, AIST has also developed the technology for mounting the developed chip onto the cooling head of the small refrigerator, producing the first desktop type Josephson voltage standard system for trial purposes that does not require the cooling by liquid helium, which can generate a 1V voltage. This technology will make it possible to produce a low cost, portable Josephson voltage standard system, and, as a result, highly accurate standard voltage will be easily generated and supplied even at such places as laboratories or factories where the supply of liquid helium is difficult.

In the near future, this technology is expected to lead to the establishment of a global remote calibrating voltage standard network based on GPS and the internet.

This research has been conducted as a part of a contracted research “Remote calibration system based on information technologies” of the New Energy and Industrial Technology Development Organization (NEDO).