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Epitaxial Templates for HTS and Silicon Devices

Applied Thin Films, Inc. recently developed a new process entitled “Epitaxial Conversion to Oxide via Nitride Oxidation” (ECONO™), under SBIR funding from the Missile Defense Agency (MDA), formerly BMDO, which allows the growth of high quality epitaxial oxide thin films needed for a broad range of applications including defense, semiconductor, telecommunications, and energy. The power of this new and exciting technology is in its generic nature and adaptability to various templates used in growth of oxide thin films. The technology was specifically developed for next generation high temperature superconductor (HTS) wire to be used in a wide range of military and commercial applications including lightweight power generation units for airborne lasers and reliable power generation and transmission for utility grids across the US. However, the discovery has significance much beyond these applications and hence the need to accelerate its development toward commercialization and for military use.

High-performance HTS tapes are intended to replace copper as a conductor for power generation, power transmission, transformers, and motors. For MDA and Air Force needs, HTS conductors provide avenue for fabricating lightweight generators which is critical for airborne missions (Airborne Lasers/ABL) with directed energy capability. HTS-based electronic devices for use in microwave filters used in communication systems, bolometers, high speed computing, and others are also useful for MDA missions where the proposed buffer layer technology is applicable. The ECONO™ process provides a distinct cost and performance advantage for fabrication of buffer layers needed for the HTS coated conductor tapes. The technology has been transitioned to OEM through a non-exclusive license who has demonstrated fabricating over one meter length of tape with the ECONO™ process with excellent epitaxy.

Current density of 1 MA/cm² has been demonstrated on a 0.3 μm thick YBCO layer deposited on the YSZ buffer using PLD with an intermediate ~20nm ceria layer. The buffer process essentially involves depositing a ~200nm thick epitaxial yttrium zirconium nitride directly on RABiTS which is subsequently converted to a ~300nm thick epitaxial yttria stabilized zirconia film via a simple oxidation step. The key advantage of this approach is it avoids interference from substrate oxidation during epitaxial growth, thus eliminating the need for an oxide seed layer and/or the need for a sulfur superstructure. In addition, nitrides can be deposited at much higher rates relative to oxides and the resulting YSZ films are dense and relatively defect-free.