J. Denul

Yttria-stabilized zirconia thin films grown by reactive r.f. magnetron sputtering

Abstract Zirconia thin films were deposited on different substrates by reactive r.f. magnetron sputtering. It was found that zirconia layers grew preferentially in the (200) direction with a columnar microstructure that is independent of the oxygen flow, argon to oxygen flow ratios and sputtering pressure. On the other hand the substrate roughness clearly affects the orientation of zirconia. Distinct changes were observed in the case of heated substrates. The heating of the substrates does not change the form of the zirconia, but strongly influences its orientation. When the substrate temperature increases, the crystallographic orientation gets more and more random, typically for the polycrystalline state. A decrease in the optical transmittance and an increase in the colour intensity of the layers with an increase in the substrate temperature was also found. As is shown, the oxygen non-stoichiometry of the zirconia is responsible for these changes.

Yttria-stabilized zirconia thin films grown by r.f. magnetron sputtering from an oxide target

Abstract Yttria-stabilized zirconia thin films with cubic crystallographic structure were deposited onto glass substrates by r.f. magnetron sputtering from an oxide target. It was found that zirconia growth is strongly dependent on the sputtering power and pressure. At low power and high pressure, zirconia grows preferentially in the (200) direction with columnar microstructurc. In contrast, high power and low sputtering pressures promote the growth of randomly oriented polycrystallinc zirconia. Increasing the argon flow at constant power and sputtering pressure again favours preferential growth of zirconia layers, however, not in the (200) direction as before, but in the (111) direction.

Deposition of biaxially aligned yttria stabilized zirconia layers on metal tape by modified magnetron sputtering

Biaxially aligned thin films of yttria stabilized zirconia (YSZ) are frequently used as buffer layers for the development of high current carrying YBa/sub 2/Cu/sub 3/O/sub 7-x/ coated conductor. In this research, biaxially aligned YSZ has been deposited on different substrate materials (glass, metal, polymer) using a modified magnetron as a source of both the particles to be deposited and a directed flux of energetic particles normal to the sputter target to induce biaxial alignment. By varying different deposition parameters, an ion assisted deposition process was developed and optimized which resulted in the deposition of in-plane textured layers of YSZ on metal tape with a FWHM of 11/spl deg/-13/spl deg/, which was measured with XRD (x-ray diffraction) pole figures. The deposition rate was as high as 43.3 nm/min. It was demonstrated that the developed deposition process is suitable for continuous deposition of biaxially aligned YSZ layers on a moving metal tape.

Unbalanced magnetron sputter deposition of biaxially aligned yttria stabilized zirconia and indium tin oxide thin films

Developing a fast and flexible deposition process for biaxially aligned buffer layers on polycrystalline or amorphous substrates is still an important step toward the development of a scalable process for REBa/sub 2/Cu/sub 3/O/sub 7-x/ (REBCO, RE(RareEarth) = Y, Nd,...) coated conductor. Biaxially aligned Yttria Stabilized Zirconia (YSZ) and Indium Tin Oxide (ITO) thin films were deposited using a specifically modified sputter magnetron. ITO could be an interesting alternative for YSZ as a buffer layer for REBCO, since it is an oxide materials with good electrical conductivity, the lattice matches with REBCO and it has more or less the same thermal expansion coefficient as REBCO. Conducting buffer layers are interesting for some applications. Some publications indicate that there is very little interaction between ITO and YBCO thin films. The layers were deposited in reactive DC sputter mode on glass and nonpolished Hastelloy substrates, at low pressure, with excellent adhesion and high deposition rate : deposition rates up to 75 nm/min were obtained for YSZ and up to 40 nm/min for ITO. The influence of some sputter parameters (e.g., pressure, target-to-substrate distance, ...) on the degree of biaxial alignment was investigated.

Ion assisted deposition of biaxially aligned YSZ layers on metal tape

Abstract Biaxially aligned Yttria Stabilized Zirconia (YSZ) on amorphous or polycrystalline substrates is very interesting for the development of YBCO coated conductors. Most of the techniques that have been used for the deposition of biaxially aligned YSZ are not suited for continuous deposition on a moving substrate (e.g. metal tape). Using a specifically modified sputter source, which generates a beam of ions directed towards the substrate under a controllable angle of incidence, a deposition process for biaxially aligned YSZ has been developed. XRD pole figures demonstrate that biaxial alignment can be achieved on different substrate materials (glass, metal, polymer). The deposition process was optimized resulting in a high degree of biaxial alignment (pole figure FWHM ∼12°) on Hastelloy tape. It was also determined that the heat load during deposition was very high and that further optimization could be achieved by controlling the substrate temperature. Finally, the use of this deposition process for depositing biaxially aligned YSZ on a moving tape was demonstrated.

Comparison of plasma sprayed and flame sprayed YBa2Cu3O7-x targets for rotatable magnetron sputtering

Rotatable magnetron sputter sources are standard equipment in large scale sputter industry for the deposition of metals and metal oxides. The power input in a rotatable magnetron can be much higher compared to a planar magnetron, resulting in improved discharge characteristics and increased deposition speed. In order to develop rotatable magnetron deposition of YBa 2 Cu 3 O 7-x (YBCO) on an industrial scale, the construction of large cylindrical YBCO targets using plasma and flame spraying was explored. Large cylindrical targets (O 13 cm x 30 cm length) consisting of a stainless steel substrate coated with a 5 mm YBCO coating were fabricated. This paper describes the microstructure, mechanical, structural, thermal and electrical characterisation of the obtained coatings and the characteristics of the targets during magnetron sputtering.

Rotatable magnetron sputtering of YBa2Cu3O7−x thin films on single crystal substrates

Abstract The development of sputter deposition of YBa 2 Cu 3 O 7− x (YBCO) from rotatable targets is an important step in the realisation of a large scale deposition process for YBCO coated conductor. Rotatable magnetron sputter sources are standard equipment in large scale sputter industry and the power input in a rotatable magnetron can be much higher compared to a planar magnetron with the same race track area. This result in improved discharge characteristics and increased deposition speed. For this work a flame sprayed and a plasma sprayed cylindrical YBCO target was used to deposit YBCO thin films on single crystal MgO. c -Axis oriented YBCO thin films were obtained at lower pressure than is normally used for YBCO sputter deposition, resulting in a higher deposition speed. The influence of deposition parameters (such as sputter pressure, oxygen partial pressure, substrate temperature, etc.) on the properties of the YBCO layer was investigated and the possibilities for large scale deposition were explored.

Superconducting thick films based on Bi-Pb-Sr-Ca-Cu nitrate pastes, screen printed on alumina and ZrO2 buffered alumina

Abstract This study demonstrates the preparation of screen printed Bi-(Pb)-Sr-Ca-Cu-oxide superconducting films starting from a paste, based on spray dried nitrate solutions. The spray dried precursor powder was studied using TGA-DTA and XRD. It is shown that decomposition to oxides occurs at temperatures more than 200°C lower than those in the respective oxide/carbonate mixture. The thick film properties were studied using XRD, SEM-EDAX and electrical resisitivity measurements. The films, coated on alumina substrates, showed clear superconducting transition below 60K, but did not reach zero resistivity. Films coated on alumina with a ZrO 2 buffer layer and sintered at 835°C showed T c , 0 up to 77 K.

The effect of composition and oxygen pressure on the superconducting properties of NdBa/sub 2/Cu/sub 3/O/sub 7-x/ thin films, deposited by rotatable magnetron sputtering

Rotatable magnetron sputtering is still a promising technique for scaling up of large area deposition of high temperature superconducting thin films. Furthermore, it represents a standard equipment for very large area web coating and glass coating in industrial environment. We have already demonstrated that with rotatable magnetron sputtering epitaxial c-axis oriented NdBa/sub 2/Cu/sub 3/O/sub 7-x/ (NBCO) thin films could be obtained on MgO and YSZ single crystals and buffered tapes. The superconducting properties, like T/sub c/ and J/sub c/, of these films are still reduced due to low pressure sputtering. The c-axis lattice parameter is expanded or the sputtered NBCO thin film exists of 2 phases, one with the correct c-axis parameter and the other phase shows an elongated c-axis parameter, which influences the superconducting properties. In this work we will investigate the properties of thin films, sputtered with a nonstoichiometric target at low pressure (classical sputter regime). Especially, the influence of the oxygen partial pressure is very important and will be studied.

Influence of deposition parameters on the biaxial alignment of YSZ buffer layers using an unbalanced magnetron

Abstract The development of a cost-effective deposition technique for depositing biaxially aligned buffer layers on polycrystalline and amorphous substrates would be a significant progress in developing YBa 2 Cu 3 O 7− x coated conductor. With this goal, biaxially aligned thin films of yttria stabilised zirconia (YSZ) have been deposited on several amorphous and polycrystalline substrates using a specifically modified sputter magnetron. The use of this unbalanced magnetron to deposit YSZ on tilted substrates resulted in highly textured layers on glass, metal and polymer substrates, the best in-plane full width at half maximum being 13° in a layer deposited at 43.3 nm/min. The same technique was also demonstrated on a moving metal tape, however with worse results. For the scaling up of this quite simple technique, a higher efficiency, an even higher deposition speed and no degradation of in-plane texture when depositing on moving substrates has to be established. Therefore some more fundamental aspects of the process were investigated.