The great bulk of CVD effort on superconducting oxide materials has concerned MOCVD of the 93 K superconductor YBa2Cu3O7−δ. Most current work involves growth of triaxially oriented YBa2Cu3O7−δ films a few hundred nanometers in thickness on monocrystalline metal oxide substrates at 650–8500C. Optimized MOCVD processes now produce YBa2Cu3O7−δ films with crystallographic quality and electrical properties comparable to the best films prepared by physical vapor deposition techniques, and offer especially attractive opportunities for large-area growth. Nevertheless, the metal δ-diketonate precursors used in YBa2Cu3O7−δ MOCVD have limited volatility and other drawbacks, which have motivated extensive background research on barium sources in particular. Non-traditional methods for delivering precursors to the deposition zone of a reactor, such as aerosol injection and flash vaporization techniques, have also been developed in response to these problems. A diverse range of YBa2Cu3O7−δ MOCVD processes, some involving plasma- or photo-assisted deposition, are in current use. These have been optimized by largely empirical means, although thermodynamic analyses and mechanistic studies offer the prospect of controlling film deposition on a more scientific basis. Unique features of MOCVD in comparison with physical vapor deposition methods include the possibility of controlling film orientation through photochemical effects, and exploitation of the high surface mobility of adsorbed molecular precursors to grow YBa2Cu3O7−δ below 600°C. With reference to potential uses for MOCVD films, near-term applications in passive microwave devices are considered in greatest detail.

Metal‐organic CVD of the high‐Tc superconductor YBa2Cu3O7−δ

Channel-spark pulsed electron beam deposition (CS), a new deposition method based on a simple and inexpensive system, has been used for preparation of high-quality GdBa2Cu3O7-x, Gd1-xEuxBa2Cu3O7-x and YBa2Cu3O7-x thin films epitaxially grown on NdGaO3 and SrTiO3 substrates. Typical critical temperatures for zero DC resistance lie in the intervals 87-89 K for Y-based films and 91.0-92.6 K for Gd- and GdEu-based ones. The transition widths for the best films are less than 0.5 K. The critical current densities reach the values of 3*106 A cm-2 at 77 K, zero field.

Deposition of MBa2Cu3O7−x thin films by channel-spark method

High-quality YBCO thin films have been grown by Inverted Cylindrical Magnetron Sputtering (ICMS) on LaAlO3(100), SrTiO3(100), SrTiO3(110), and MgO(100) substrates. Transition temperatures of c-axis films exceed 90 K, and transition widths are within 1 K. Critical currents range up to 5 × 106 A/cm2 at 77 K. Structural and morphological features analyzed by x-ray diffraction and scanning electron microscopy, respectively, are found to be strongly dependent on film orientation and deposition temperature. In order to understand such dependence, a simple interpretation is proposed in terms of Gibbs energies and growth dynamics of the nucleation process.

Morphological and structural properties of high quality YBCO thin films

Properties of YBCO superconductors prepared by ammonium nitrate melt and solid-state reaction methods

This paper deals with YBCO Josephson junctions based on artificially generated in-plane bi-epitaxial grain boundaries fabricated on SrTiO 3 and buffered R-plane sapphire. The grain boundary was obtained by partly interposing a MgO seed layer between a bare or even-buffered substrate and a CeO 2 layer [1]. The devices were produced by patterning the overhanging YBCO film in a form of stripes across the grain boundary occurring at the interface between the two regions. The samples were structurally and electrically characterized. As shown by X-ray diffraction analyses and high resolution electron microscopy, the structural perfection of the YBCO film decreases as the complexity of the stacking sequence increases. The fabricated junctions behave according to the Resistively Shunted Junction model for both the samples on SrTiO 3 and on Al 2 O 3 . Under microwave irradiation, the devices displayed several Shapiro steps while their critical currents were deeply modulated under magnetic field. By comparing the transport properties of the devices with the structural properties of the YBCO film on the different stacking sequences, we found a strong correlation between the normalized resistance R N A and the degree of structural disorder in the superconducting film.

Bi-epitaxial YBCO grain boundary Josephson junctions on SrTiO3 and sapphire substrates

In situ direct deposition at approximately 700 degrees C of thin YBa/sub 2/Cu/sub 3/O/sub 7-x/ superconductive films and multilayers has been done by three techniques using stoichiometric YBa/sub 2/Cu/sub 3/O/sub 7-x/ sintered targets. Excimer laser ablation in a DC magnetron system with hollow and planar targets leads to 0.5-, 1.2-, and 2.5-in diameter uniformly superconductive layers under static conditions. High critical current densities (>10/sup 6/ A cm/sup 2/ at 77 K) associated with low resistivity and good epitaxial behavior are achieved on top of MgO, SrTiO/sub 3/, LaAlO/sub 3/, and YSZ single-crystal wafers. High-quality c-oriented films (T/sub c/>80 K) are routinely obtained by means of a DC magnetron on large sapphire (>2 in) substrates covered by a YSZ RF sputtered buffer layer. The infrared properties of such films have been checked at 1.15- mu m wavelength. In order to achieve active devices (such as optical detectors and high-frequency mixers), small (<10- mu m/sup 2/) YBa/sub 2/Cu/sub 3/O/sub 7/-YSZ-Ag tunnel junctions and arrays have been successfully patterned in the superconductor/insulator/normal-metal trilayers using SNOP (selective niobium overlap process).

In-situ deposition and processing of YBa/sub 2/Cu/sub 3/O/sub 7-x/ films and multilayers for optoelectronic devices

This paper reports on in-situ direct deposition at {approximately} 700{degrees}C of thin YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} superconductive films and multilayers done by three techniques using stoichiometric YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} sintered targets. Excimer laser ablation, DC-Magnetron with hollow and with planar targets lead respectively to 0.5, 1.2 and 2.5 inches diameter uniformly superconductive layers. under static conditions. High critical current densities ({gt}10{sup 6} Acm{sub {minus}2} at 77K) associated with low resistivity and good epitaxial behaviors are achieved on top of MgO, SrTiO{sub 3}, LaAlO{sub 3}, YSZ single crystal wafers. High quality c-oriented films (Tc {gt} 80K) ae routinely obtained by DC magnetron on large sapphire ({gt}Z inches) substrates covered by the YSZ RF sputtered buffer layer. IR properties of such films have been checked at 1.15 {mu}m wavelength. In order to achieve active devices (such as optical detectors, high frequency mixers...), small ({lt}10 {mu}m{sup 2}) YBa{sub 2}Cu{sub 3}O{sub 7}-YSZ-Ag (SIN) tunnel junctions and arrays have been successfully patterned in the (SIN) trilayers using the SNOP process.

In-situ deposition and processing of YBa sub 2 Cu sub 3 O sub 7 minus x films and multilayers for optoelectronic devices

The critical current density (Jc) for zero magnetic field has been measured as a function of temperature in c-oriented thin layers of YBa2CU3O7-x prepared by different synthesis methods. One direct and two indirect Jc(T) methods were employed for each film: transport measurements on patterned film constrictions, DC remanent magnetization studies using the Bean model and non-linear AC screening analysis. Results from the indirect methods were calibrated against transport data. Possible origins of observed dependences are suggested and calibration procedures are discussed. The investigation demonstrated the feasibility of using AC screening analysis in rapid determinations of Jc(T) close to Tc.

https://iopscience.iop.org/article/10.1088/0953-2048/7/4/003/pdf

Measurements of critical currents as a function of temperature in YBa2Cu3O7-x thin films: a comparative study

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In-situ deposition and processing of YBa/sub 2/Cu/sub 3/O/sub 7-x/ films and multilayers for optoelectronic devices

In-situ deposition and processing of YBa sub 2 Cu sub 3 O sub 7 minus x films and multilayers for optoelectronic devices

Measurements of critical currents as a function of temperature in YBa2Cu3O7-x thin films: a comparative study