Fabrication and characterization of aluminum nitride pedestal-type optical waveguide

In this paper we present the fabrication and characterization of pedestal-type optical waveguides using aluminum nitride (AlN) as core layer. To the best knowledge of the authors, the utilization of AlN as core layer in pedestal-type waveguides has not been studied. The AlN thin films were obtained by radio frequency reactive magnetron sputtering from a pure aluminum target. The AlN refractive index was determined by ellipsometry. The optical waveguides were fabricated by the pedestal technique, which consists in etching the silicon oxide lower cladding layer before depositing the core layer. Thus, the waveguide geometrical definition is simplified because etching the AlN core is not necessary. AlN thin films of 0.6, 1, and 1.2 μm thick were deposited on thermally grown silicon dioxide using crystalline silicon (100) as substrate. The pedestal profile was defined using conventional photolithography, followed by plasma etching of the cladding layer. Optical propagation losses were measured for pedestal heights of 1 μm and widths from 1 to 100 μm.