Optimizing the fabrication processes of reliable polymer planar lightwave circuit devices

Abstract

Polymers are increasingly becoming attractive for planar lightwave circuit (PLC) devices due to their structural flexibility, ease of processing and fabrication capabilities. However, the application possibilities of polymer integrated optics in real-world devices are only beginning to be appreciated. Excellent optical, mechanical and physical properties are only achievable through the use of proper materials and process parameters. Any material or processing-induced defects will either result in excessive optical loss and joint fatigue failure or totally ruin the whole PLC device. This research aims to establish a good fundamental understanding of optimizing the process parameters for the reliable fabrication of polymer-based PLC devices. As a reliability factor, high adhesion strength is a critical parameter of the multi-layer interconnections that are fragile to shocks encountered during fabrication, handling and lifetime of the device. The adhesion strength depends on the substrate materials. It also depends on the processing condition of the subsequent fabrication steps and environmental operating condition. Both the process and environmental conditions greatly affect the optical performance of the devices. The optical performance would most probably be degraded in the subsequent fabrication process or when they are used in an adverse situation such as a high temperature or high humidity environments. First, this study focuses on the interfacial adhesion of polymeric adhesive film on different possible substrate surfaces, such as pure silicon wafer, silica on silicon wafer and thin Chromium (Cr) metal layer on silicon wafer. Different process conditions (heat treatment and damp heat test) are also applied on the polymer film or fabricated shear button to identify the reliability on different substrates. The impacts of adverse environmental situations are then studied in terms of optical performances. The correlation is made between the optical performances with the changes in the two main design parameters of the waveguide structures: film thickness and refractive index. Finally, the impact of high temperature curing for achieving the high refractive index is also studied. The viscosity of the polymer is modified to avoid the process-induced cracking or delamination. The results generated in this study should provide useful information in fabricating reliable polymer PLC devices. The information can help manufacturers in selecting the suitable substrate material and proper process parameter, as well as in choosing the information which can dictate the suitable operational environment for polymer PLC devices. The information is also important for the optical engineer designing a polymer PLC device which can protect itself from process and environment related deviations. The method of achieving the improved characteristics during high temperature processing for high index contrast devices is demonstrated.

Date of Award	15 Jul 2009
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Kim Fung MAN (Supervisor) & Hau Ping Andy CHAN (Supervisor)