Loss Increase of (LuNdBi)3(FeAl)5O12 Films Caused by Sputter Etching

Abstract
Rib waveguides, which are made of magnetic garnet films of composition (LuNdBi)3(FeAl)5O12 (LNB), fabricated by Ar sputter etching have large propagation loss in comparison with LNB slab waveguides. X-ray photoelectron spectroscopy (XPS) is used to investigate chemical states of constituent elements existing in the surface layer where a Ti mask has been deposited during the etching process. The analysis shows that Fe chemical shift due to Ar+ ion bombardment can cause increase in the optical absorption loss, and hence the propagation loss. It is effective for suppressing the loss increase to employ a SiO2 mask deposited onto LNB film instead of a Ti mask.