Application of Pulsed Injection MOCVD to the Deposition of Dielectric and Ferroelectric Oxide Layers and Superlattices
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ABSTRACT The technique used for the control of the injection of fuel in thermal motors has been applied to the generation of active gases for MOCVD layers deposition. A wide variety of compounds and multilayers have already been grown using this new CVD source (from simple cxides, nitrides or metals to complex ternary oxides). Using two injection sources working sequentially, stackings like YBa2Cu307!CeO2 or SrTiO3/YBa2Cu3O7 double layers, Ta205/SiO2 amorphous or crystallized multilayers and SrTiO3/BaTiO3 or YBa2Cu307/PrBa2Cu3O7 epitaxial superlattices have been synthesized. The injection MOCVD seems to be a very promising technique for the stacking of multicomponents oxides having different electronic properties. This opens the way for the synthesis of a wide set of artificial materials, exhibiting completely new properties that cover a very large range of potential applications. After a description of the technique, we will demonstrate its performances on some results obtained on the synthesis of dielectric and ferroelectric layers and multilayers. INTRODUCTION The discovery of very exciting new properties in advanced oxides (high temperature superconductivity, colossal magnetoresistance, very high dielectric constants...) has aroused during the last ten years a considerable interest for the synthesis of thin layers of these materials. Electronic devices like microwave components obtained by the association of HTS and insulating, ferroelectric or magnetic oxides can now be realized (Josephson effect devices, spin-polarized quasi-particle injection devices, tunable filters..). New protective, thermal barriers or very efficient buffer layers can be obtained with the stacking of different oxides. Transparent thin layers or multilayers with different refractive index have numerous applications for optical amplifiers, narrow or large band filters, supermirrors or glass art. The recent development of MOCVD for the deposition of these complex materials is strongly related to the discovery of high temperature superconductivity. Twelve years ago, the high temperature superconductivity observed in compounds like REBa2Cu307, (where RE = Y or a rare earth), has impulsed a fantastic research effort, in relation with their potential applications. These materials being very hard and brittle, it is evident that the best route for many industrial use is to realize thin layers deposited on a convenient substrate (single crystal for electronics, flexible metallic tape for high power 33 Mat. Res. Soc. Symp. Proc. Vol. 606 ©2000 Materials Research Society
applications). A wide number of experiments have been done by physicists, who have generally no experience within chemical techniques : this explain why most of the results already reported are related to layers obtained by physical deposition techniques (sputtering, MBE or coevaporation, laser ablation). The research effort developed for chemical deposition techniques, like sol-gel, pyrosol gel or chemical vapor deposition (CVD) was lower by some orders of magnitude : in Europ for
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