Thin films of the Tl-based high-temperature superconducting (HTS) phases are beginning to find application in a number of practical devices, especially in the field of microwave communication systems. This review describes the issues surrounding the fabrication of thin films of the thallium-based HTS materials. The influence of thermodynamics and kinetics, the various potential thalliation techniques and the selection of an appropriate substrate material are all important considerations when designing a process for the fabrication of thin films of these highly reactive materials. The properties of the resulting films are critically dependent on the microstructures developed during thalliation. Microstructural evolution during thalliation, the effect of structural defects on the properties of such films and the importance of achieving biaxial grain alignment in optimizing the properties of the films are all discussed.

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Tl2Ba2Ca1Cu2Ox thin films have been grown on highly textured CeO2 layers deposited onto R-plane sapphire substrates. The Tl2Ba2Ca1Cu2Ox films have critical temperature (Tc) values around 95 K and current density (Jc) values up to 8×104 A/cm2. The films are c-axis oriented even though we have identified the formation of a polycrystalline BaCe(Tl)O3 layer by reaction between the buffer layer and the superconducting precursor during the thalliation process.

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TI-Ba-Ca-Cu-0 thin films have been grown on a variety of substrates, both with and without the use of buffer layers. Differences in processing routes required for the various film-substrate combinations are highlighted and the effect of the buffering layers on the microstructure, transport and microwave properties of the films are discussed.