Integration of Amorphous Low Refractive Index Active Materials in Silicon Photonics

Abstract

Rapid progress of Silicon photonics circuits this last decade makes it as a key enabling technology for data communications. In order to increase optical functionalities of such circuits, monolithic integration of new materials [1]-[3] having different physical properties is challenging. This study is focused on a generic waveguide configuration called "Half Etch Waveguide" (HEW) allowing integration of a stack of 2 layers composed of a High Band Gap (HBG) and low refractive index materials as HFO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , AlN, and SiC and amorphous silicon on top of a Silicon on Insulator (SOI) substrate (see Fig. 1a). Advantages HEW are that:-Interaction of light with HBG active material is maximized for both polarizations (TE and TM) of light because HBG is located in the central part of the waveguide where the overlap with the TE-like mode is optimum. This effect is increased with the slot effect occurring for the TM-like mode.--Light confinement in the waveguide is provided by etching only the amorphous silicon (a-Si) upper layer that preserves HBG material. Also lateral electrodes can be placed directly on the HBG material that overcomes capacitance parasitic effects responsible of high speed limitations. Figure 1:(a) Cross section of the guiding structure (a-Si/LR/SOI); (b) MMI splitter;(c) Asymmetric Mach-Zehnder; (d) Racetrack resonator. Fabrication of the devices starts with deposition of HBG and a-Si by Low-cost techniques: RF magnetron sputtering and/or sol-gel deposition. Waveguides and basic building blocks for optical routings shown in Figs. 1b, 1c and 1d are realized by e-beam lithography and transferred in the a-Si layer by Reactive Ionic Etching (RIE). Finally, devices are encapsulated in a 1 micron PECVD SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> cap layer.Optical characterizations of a set of test devices allow the determination of propagation losses and dispersion laws of both straight and bend parts of the waveguides. First measurements show that propagation losses are in the range of 5, 8 and 12 dB/cm, respectively, for SiC, AlN and HfO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Modellings are performed with home-made mode solvers [4]. Mode solvers are used to calculate propagation losses originated by the punctual defects induced by the stitching of the e-beam lithography (~1.3 dB/cm), in HBG layer involved by the deposition of the a -Si layer (~3 dB/cm) and also to compare experimental dispersion laws with theory. In order to overcome defects induced by the fabrication process, a next run with a new recipe of a low loss a-Si layer deposition and laser lithography are in progress. Optical non-linear characterizations will be performed on the different samples.