SUPACT - 7334
Keywords superconductivity, Josephson junctions, active devices
Start Date: 15-SEP-92 / Duration: 36 months
[ contact / participants ]
Objectives and Approach
The objective of SUPACT is to develop high-frequency active superconducting components that operate at liquid nitrogen temperatures and make use of the special properties of superconducting circuits (very high magnetic field sensitivity, inherent quantisation and counting mechanisms, low dispersion and loss in high-frequency operation).
The fundamental building-block of these components is the Josephson Junction (JJ), and the first part of the project will concentrate on the fabrication and characterisation of reproducible and reliable JJs, using HTS materials from the YBCO family and step, step edge and bi-epitaxial designs. The junctions will be used as the basis for three demonstrators; a broad-band SQUID, and infrared detector, and ADC demonstration circuits.
Progress and Results
The main achievements during the first year have been:
- Establishment of common test structures and procedures by specifying and defining the important parameters of films, junctions and SQUIDs. A common mask for patterning of test structures has been designed and circulated to all participants.
- Development of complete simulation and modelling programmes to allow circuit parameters to be calculated from device geometries, individual junction characteristics to be understood, and device performance to be simulated as a function of frequency and device parameters. A careful treatment of noise has been included to provide an accurate description of realistic structures.
- Fabrication of reproducible bicrystal and N-YBCO SNS junctions, although further development is needed in order to obtain a manufacturable process. It is likely that different junction technologies will be appropriate in different applications.
- Detailed modelling of electron-beam irradiated (EBI) junctions to show the almost ideal uniform behaviour of these junctions. These EBI junctions allow considerable flexibility in device fabrication.
- A survey of ADC technologies has been carried out, comparing silicon, GaAs, Nb and high-Tec technologies. The survey indicates clear advantages for a superconducting technology in a number of applications.
- A prototype ADC test structure has been designed and simulated to show the limitations of the frequency response. Preliminary microwave measurements have been made on a closely related structure.
- Coupling schemes for the input and output of a board-band SQUID have been designed and simulated. The input coils can operate up to several hundred megahertz, and the output is designed to give broad-band coupling to semiconductor electronics.
- The photoresponse of a range of ramp and trilayer junctions, and a superconducting FET has been measured, and shown to be sufficiently large for array applications.
Dr A. Philips
GEC Hirst Research Centre
UK - Borehamwood WD6 1RX
tel: + 44/ 953-2030
fax: + 44/ 817-320-200
GEC MARCONI LTD - UK - C
SIEMENS AG - D - P
LETI CEA-DTA - F - P
TECHNISCHE HOCHSCHULE ILMENAN - D - A
UNIVERSITY OF CAMBRIDGE - UK - A
SUPACT - 7334, December 1993
please address enquiries to the ESPRIT Information Desk
html version of synopsis by Nick Cook