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Content archived on 2024-04-30

Tunable htsc microwave devices - investigation of the tunability of cuprate / ferroelectric heterostructures

Objective



Research objectives and content
Modern radar and mobile phone systems have a great need of high quality tunable filters with very low response time. Unfortunately, the situation in this field has remained unchanged since the discovery of YIG ball tunable filters in the60's. In this technology, a change in the resonant frequency is obtained by variation of the magnetic field applied to the YIG. These devices can achieve good quality factors (of order 10,000) but their response time is poor (several microseconds). Moreover, as the limiting factor is the stabilisation time of the magnetic field, further reductions are not possible.
One solution to reduce the response time is to use an electric effect instead of a magnetic one. Ferroelectric materials are good candidates for this task, allowing a variation of the resonant frequency of the filter as a result of a controlled change i in their dielectric constant. BaxSrl-xTiO3 in association with the superconductor YBa2Cu3O7 shows great promise for such systems as these materials exhibit a small lattice mismatch (02%) which is required for the optimal growth of the superconducting layer and hence for devices exhibiting the lowest losses. The feasibility of this type of device has been demonstrated but the filter characteristics, especially the quality factor, have to be improved. The aim of this project is the epitaxial growth of ferroelectric / superconductor heterostructures by pulsed laser deposition (PLD). The first step will be to optimise the dielectric properties of the ferroelectric and the surface resistance of the superconductor. The structural quality of the materials will be analysed both in situ by RHEED and ex situ by X-Ray diffraction, electron microscopy (TEM, SEM) and atomic force microscopy (AFM). The tunable devices will be prepared by photolithography and tested on standard microwave equipment (network analyser).
Training content (objective, benefit and expected impact)
This project will mainly give the applicant experience in two domains: first. the structural analysis, especially the in situ RHEED monitoring of growth and ex situ X-Ray diffraction second, device fabrication by lithography, ion beam milling and wet etching.
Links with industry / industrial relevance (22)
The host laboratory is a contractual structure between CNRS and Thomson-CSF which connects fundamental and applied research in the field of low temperature HTSC electronics. The laboratory is a node of the SCENET-NOE 22804 and is involved in two European ESPRIT-LTR projects: JOVIAL (n0 21114) and RSFQ-HTS (n0 23429). The project will be carried out in connection with the << laboratoire des dispositifs supraconducteurs >> of Thomson-CSF which is also involved in two European projects: BRITE/EURAM (DIHIMICO n0 BRPR-CT95-0084) and ACTS (SUCOMS n0 AC115).

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Coordinator

CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE
EU contribution
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Address
Domaine de Corbeville UMR CNRS/Thales
91404 ORSAY
France

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Total cost

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Participants (1)

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