Process development of Ta2O5-SiO2 quantized nanolaminates for the use of complex optical filter systems

Manuel Bärtschi¹, Stephan Waldner², Fabian Steger¹, Thomas Frei², Silvia Schwyn Thöny², Xavier Maeder³, Daniel Schachtler¹ and Christoph Sturzenegger¹

Quantized nanolaminates (QNL) are a material system that was developed, produced and characterized by the LZH in 2016 as an alternative optical material. The idea behind it is that, like a normal mixed material, QNLs have a refractive index that is determined by the ratio of the two materials used. However, the electron mobility is severely restricted by the very thin high refractive index material. This results in a higher band gap and a lower absorption edge of the system. Their properties have been demonstrated on ALD and IBS systems. But the complex and slow coating processes meant that only a few iterations could be produced. We have now developed a process on a magnetron sputtering system with a rotating substrate table that makes it possible to produce QNL layers of SiO₂ and Ta₂O₅ at a very high rate of up to 0.8nm/s. This makes it possible to use these nanolaminates economically as a stand-alone material, even in thick and high layer count designs. Because of the process we were able to produce a variety of QNL with different layer thickness and ratio combinations and perform a variety of measurements such as atomic force microscopy (AFM), total scattering (TIS), transmission electron microscopy (TEM) and Laser induced damage threshold (fs-LIDT) to determine their properties. We were able to use the knowledge gained to coat more complex multilayer systems in a range that would otherwise not have been possible with normal Ta₂O₅-SiO₂ coating systems.

¹ RhySearch, Institute for Optical Coatings and Characterization, Werdenbergstrasse 4, 9470 Buchs, Switzerland
² Evatec Ltd, Hauptstrasse 1a, 9477 Trübbach, Switzerland
³ EMPA, Laboratory for Mechanics of Materials & Nanostructures, Feuerwerkerstrasse 39, 3602 Thun, Switzerland

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