Sapphire In The Growth Of Large Area Ybco Thin Films Of Ceo <sub> 2 </ Sub> Buffer Layer Study

Owing to its excellent electrical properties, superconducting YBa₂Cu₃O_7-δ(YBCO)thin films make the devices smaller, lighter, and with higher quality factor and lower insertion loss. Furthermore, the microwave surface resistance, Rs, of YBCO thin films is several orders of magnitude lower than that of metals at microwave frequencies. Hence, YBCO thin has been researched intensively. The fabrication of large-area double-sided YBCO thin films is a convenient way to realize large scale production and multi-component integration. In this paper, we primarily research deposition parameters of CeO₂ thin films and YBCO films in order to gain excellent properties on 3-inch R-plane sapphire. Among the substrate commonly used for YBCO thin films, sapphire is the best candidate. But a buffer layer must be used to prevent the interdiffusion between YBCO and sapphire, and to provide good lattice matching for YBCO. For these purposes, YSZ,STO,MgO,CeO₂ had been attempted as a buffer layer. After many experiments, it is proved that CeO₂ is an excellent material for a buffer layer. With a four-target sputtering system, a series of CeO₂ thin films is prepared by modification growth parameters such as substrate temperature, sputtering pressure, deposition rate, and CeO₂ film thickness. By analyzing microstructure, orientation and surface roughness, optimum processing parameters are gained as following: Substrate temperature ranging from 700 to 750℃, sputtering power ranging from 100 to 150(×2)w, sputtering pressure being 14Pa, Po2:PAr being about 1:2, CeO2 thin film thickness ranging from 10 to 40Pa. With a speed-modulated biaxial substrate rotation YBCO thin films were in-situ deposited on R-plane sapphire buffered with CeO₂ layers. The basic properties are measured : the samples are strictly out-of-plane and in-plane epitaxial orientation, The thickness deviation of the YBCO thin films is less than ±5%, Tc is about 89K, ΔTc is less than 1K, Jc(77K,0T) is more than 1×106A/cm,, Rs(10GHz,77K) is 0.53mΩand 0.56 mΩfor both sides, respectively. The 3-inch samples obtained by optimizing the deposition parameters had been used by different users in small scale which can meet the microwave device...