Metal-organic CVD of the high-T-c superconductor YBa2Cu3O7-delta

The great bulk of CVD effort on superconducting oxide materials has concerned MOCVD of the 93 K superconductor YBa2Cu3O7-delta. Most current work involves growth of triaxially oriented YBa2Cu3O7-delta films a few hundred nanometers in thickness on monocrystalline metal oxide substrates at 650-850 degrees C. Optimized MOCVD processes now produce YBa2Cu3 O-7-delta 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 beta-diketonate precursors used in YBa2Cu3O7-delta 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-delta 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 stu dies 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-delta below 600 degrees C. With reference to potential uses for MOCVD films, near-term applications in passive microwave devices are considered in greatest detail.