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Content archived on 2024-04-19



The progress in precursor chemistry has provided new solid and liquid precursors. Vaporisation of the new materials can be carried out at lower temperatures compared to the traditional ones, reducing the possibility of thermal degradation.

Liquid delivery systems using precursor solutions have been tested for the growth of YBCO thin films as well as buffer layers like YSZ and CeO2. The low storage temperature of the precursor solution and the fast evaporation step, both reduce the possibility of precursor decomposition and improve the reliability of the deposition process.

The design of MOCVD reaction chambers is very flexible and equipment for the continuous deposition of YBCO thin films on moving stainless steel tapes has been developed. For example, superconducting YBCO layers with a thickness up to 1.0 um and Jc ~ IE5A/cm{2} were fabricated at a speed of 20-40 cm/h.

MOCVD of YBCO thin films on singlecrystalline substrates and polycrystalline stainless-steel tapes resulted in Tc's around 90K and Jc well above IE6A/cm{2} (for single crystals) and above IE5A/cm{2} on technical metallic tapes. These results are promising values for future tape applications. Biaxially aligned buffer layers are required on stainless-steel substrates to prevent interdiffusion and to reduce interface reactions. Buffer layers deposited by an ion-beam-assisted growth process suffer from very low growth rates. The use of recently developed biaxially aligned Ni tapes will allow an all-MOCVD process for the deposition of both, the buffer layer and the YBCO thin film with faster growth rates.

The growth rates of YBCO deposited by a thermally activated MOCVD process are at present around 0.5um/h. The processes, developed in this Project show impressive growth rates of up to 10um/h. These data show, that a further optimisation of growth rates is still possible.

The present status of the fabrication of YBCO thin films on tapes by MOCVD has been summarised in this project. The high potential of the superconducting YBCO material as well as of MOCVD has been demonstrated. Furthermore, optimisation of the MOCVD process is not at its end and improved superconducting properties film properties can be expected.
The aim of this project i to develop a reliable MOCVD process for high Tc super conducting thick film elaboration in order to realise super conducting tapes carrying high critical currents.

To achieve this goal specific purposes are addressed such as :

(i) Elaboration, characterisation and selection of suitable precursors for MOCVD, in order to improve the reliability of the deposition process.
(ii) Improvement of the precursor injection system by modelisation and experimental studies of potential alternative methods : low pressure ultrasonic aerosol transport, modified spray or modified solid source injection systems.
(iii) Control of the MOCVD process for super conducting thick film deposition : either on single crystalline substrates or on more conventional ones with buffer layers;
MOCVD of "In-plane" oriented films by the use of e.g. textured substrates, graphoepitaxy and deposition on interlayers which increase the crystallite mobility on the substrate.
Evaluation of the developed process for deposition on metallic substrates.
(iv) Structural, chemical, electrical and magnetic interacting characterisations of YBaCuO (Bi based compounds) films realised using the aforementioned MOCVD techniques. Optimisation of layers able to carry large super conducting currents.
(v) Assembly of a basic CVD equipment for deposition on tapes planned with the help of hydrodynamic calculations in order to increase the effectively of the process.

An evaluation of the reliability of the MOCVD process and of the quality of the films will end this project through the elaboration of a demonstrator, which will be a high current carrying YBaCuO (Bi-based thick film on a metallic tape with buffer layer.

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Domaine Universitaire
38402 Saint-Martin-d'Hères

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