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DEVELOPMENT OF CVD, METALORGANIC PRECURSORS AND PATTERNING TECHNIQUES FOR HIGH TC APPLICATIONS

Objective

The overall objective of the project is to demonstrate the capability of producing patterned, high Tc, layered, superconducting materials.
Precursor Synthesis and Characterisation

- [Ba(TDFND)2.tetraglyme] has been developed and is the first Ba precursor to sublime at ambient pressure without decomposition. It is molten and indefinitely thermally stable at temperatures of use in a conventional low pressure MOCVD bubbler. Practical routes have been developed for commercialisation of the three YBCO precursors showing optimum properties: [Ba(TDFND)2.tetraglyme], Cu(TDFND)2 and [Y(TMHD)3.4tBuPyNO]
- Ten Y compounds have been shown to be suitable CVD precursors. They are more stable than [Y(TMHD)3]. Four have higher volatility compared to [Y(TMHD)3] and three have melting points below 100°C and can therefore be used as liquid precursors.

MOCVD and Characterisation of Thin Films

- A pre-prototype MOCVD reactor has been successfully developed for the growth of HTS thin films. It is capable of handling low volatile precursors without precondensation or premature reactions. The implementation of a Gas Foil Rotation Susceptor has demonstrated the feasibility of the technology for large scale production of YBCO thin films.
- Vapour pressure and stability as a function of temperature has been determined for 12 novel Y, Ba and Sr precursors to confirm their suitability as MOCVD precursors. The novel precursors [Ba(HFA)2.tetraglyme], [Y(TMHD)3.-4tBuPyNO], [Zr(NEt2)4] and [Sr(HFA)2.tetraglyme] have been used in the TNO test reactor to deposit YBCO , YSZ, Y2O3 and SrTiO3. The results have been successfully transferred to the AIXTRON pre-prototype reactor. Epitaxial pin-hole free SrTiO3 has been deposited by MOCVD on YBCO.
- An impinging jet reactor has been modified for laboratory scale deposition of high Tc thin films by MOCVD and a greatly improved precursor container has been designed and built. It has enabled corrected kinetic parameters to be determined for deposition from individual precursors by allowing for mass transport contributions to the deposition rate
- A system has been designed to allow mass spectroscopic analysis of the decomposition of precursors for MOCVD of high Tc materials and new information has been obtained about the decomposition chemistry of traditional and new precursors
- An FTIR system for in situ analysis of the vapour phase in the reactor has been constructed and results obtained for copper, yttrium and barium precursors for the variation of decomposition characteristics for each of the complexes as a function of temperature have been related to molecular structures
- Deposition of superconducting YBCO films in the pre-prototype reactor using novel, fluorinated Ba precursor [Ba(TDFND)2.tetraglyme] by in situ MOCVD has yielded films with Tc = 90-93 K; Jc = 5 MA/cm{2}. The layers are single phase, XRD showed only (00l) peaks, and epitaxial (Rocking Curve FWHM (005) = 0.2°)
- The first YBCO films deposited using 3 liquid precursors with Tc=91 K and Jc=5 MA/cm{2} have been deposited. The precursors [Y(TMHD)3.4tBuPyNO], [Ba(TDFND)2.tetraglyme] and [Cu(TDFND)2] synthesised in this project were employed. Residual fluorine levels of 10-4 F atoms per YBCO were detected by SIMS. The films were deposited with good uniformity over large surface area (40 mm diameter) using Gas Foil Rotation Susceptor
- SEM, EDX and ICP have been applied for film characterisation and to aid optimisation of the deposition processes.
- Temperature dependence of ac-susceptibility and resistance have been applied for characterisation of YBCO films deposited by MOCVD. Excellent quality have been observed on the optimised MOCVD YBCO films.

Film Patterning

- The laser writing process has been optimised. Stable and reproducible patterns with resolution down to 2um can be formed on YBCO thin films. The most unique property of this technique is the reversibility which enables tuning of the properties of superconducting YBCO thin film devices.
- Ion milling has been successfully applied for thinning, polishing and submicron patterning of YBCO thin films and for YBCO/SrTiO3/YBCO multilayer patterning. The process has been successfully combined with the HTS SQUID technique for fabricating highly sensitive integrated magnetometers. The sensitivity of one of the magnetometers is the best that has ever been observed on integrated HTS magnetometers. The multilayer patterning process has been applied for characterising YBCO/SrTiO3/YBCO structures where the SrTiO3 dielectric layer was deposited by MOCVD. The results show that highly epitaxial and insulating SrTiO3 layers can been deposited on YBCO by MOCVD.
This will be achieved through the development of :
-novel, volatile precursors suitable for high Tc, mixed metal oxides;
-a prototype, metal-organic chemical vapour deposition (MOCVD) reactor designed to suit the novel precursors;
-a fundamental understanding of the effect of deposition parameters on layer characteristics and properties and
-novel patterning techniques suitable for both thin and thick films.

Coordinator

Associated Octel Company Ltd
Address
Oil Sites Road
L65 4HF Ellesmere Port
United Kingdom

Participants (4)

Aixtron GmbH
Germany
Address
Kackerstrasse 15
5100 Aachen
NKT Research Center a/s
Denmark
Address
Sognevej 11
2605 Broendby
Nederlandse Organisatie voor Toegepast Natuurwetenschappelijk Onderzoek
Netherlands
Address
Utrechtseweg 48 108
3700 Zeist
UNIVERSITY OF STRATHCLYDE
United Kingdom
Address
16 Richmond Street
Glasgow