Modelling of the Initial Deformation of TriPleX Based Bimorph Actuators Used in Alignment of Optical Waveguides

A lot of research is being done in the field of Photonic Integrated Circuits (PICs) for use in telecom, datacom, optical sensing and visible light applications. Optical packaging of these PICs is still a challenge; increasing complexity leads to a higher number of interconnects and, combined with the need for sub-micrometer accuracy, this places a significant burden on the overall packaging costs. One proposed method of optical packaging of multichannel PICs focusses on the alignment of waveguides using an actuator integrated into the waveguide beam. The waveguide itself consists of a small silicon nitride core surrounded by a thick silicon oxide cladding (TriPleX). Typical dimensions for these waveguide beams are 16 ?m in thickness and width and 250 to 1000 ?m in length. By depositing of a layer of polysilicon on top of the waveguide beam, it is effectively turned into a bimorph actuator. Heating the polysilicon, and subsequently the TriPleX beam below, causes a deflection of the endpoint of the waveguide in vertical direction. This deflection can be varied to find the optimal alignment between waveguides. Due to the characteristics of the deposition process, mainly the high temperature, layered structures are subject to residual stress when cooled down to room temperature. This residual stress consists of a thermal part, caused by the difference in thermal expansion coefficient between the two layers, and an intrinsic part, which is related to, among others, impurities introduced during deposition and structural mismatch at the interface between layers. This residual stress causes an initial deformation of the bimorph waveguide beam, in the form of curvature and elongation. In order to accurately align the waveguides the initial deformation of the bimorph beam needs to be known. Predicting this deformation is the subject of this thesis.Micro and Nano EngineeringPrecision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin