Preparation and characterisation of an epoxy-functional inorganic–organic hybrid material system with phenyl side group for waveguiding applications Shane O'Brien a , Mehmet Çopuroğlu a , Gabriel M. Crean a,b, ⁎ a Tyndall National Institute, Cork, Ireland b Department of Microelectronic Engineering, University College Cork, Ireland Received 13 February 2006; received in revised form 8 November 2006; accepted 29 November 2006 Available online 6 February 2007 Abstract An epoxy-functional inorganic–organic hybrid material system for use in photonic waveguiding applications was synthesised by the sol–gel method. The influence of preparation process parameters such as composition and UV irradiation, on the properties of the deposited thin films was studied. Crack-free films with thickness up to 37 μm were obtained from a single-step deposition process. A tunable refractive index, at 633 nm, which ranged between 1.480 and 1.515 was observed by modifying the concentration of the refractive index modifier. It was also demonstrated that UV irradiation resulted in an increase in the refractive index of the system by 0.49%. Planar waveguiding structures were demonstrated. A high thermal stability, up to 275 °C, was achieved compatible with post-processing integration processes. © 2006 Elsevier B.V. All rights reserved. Keywords: Sol–gel method; Refractive index; Waveguiding; Thermal stability 1. Introduction In the context of material development for optical waveguiding applications, inorganic–organic hybrid materials offer significant opportunities [1–8]. In terms of their optical properties, polymers have certain features, which make them useful for waveguide fabrication, in particular they can be processed using a wide range of techniques such as lithography and embossing. However, in applications in which polymer waveguides are utilised in harsh environments, deterioration in optical propagation can be encoun- tered. On the other hand, glasses have excellent optical trans- mission and thermal stability in the order of hundreds of degrees Celsius. However, glass waveguide production techniques are expensive and complex. Consequently, a hybrid system, which would produce a material with advanced optical and physical properties, combined with enhanced thermal and mechanical sta- bility in a convenient process, is of interest. The development of multi-functional organically modified silanes, such as alkoxysi- lanes, which contain acrylate or methacrylate crosslinkable groups, has enabled increased control over chemical composition, crosslinking and phase stability [9]. This has resulted in the pro- duction of materials that have the optical transparency of poly- mers, but also have inorganic characteristics, such as the thermal and mechanical properties of a glass or ceramic [10,11]. Such tunability of properties is of particular interest in the area of optical waveguide materials. Nonetheless, these hybrid material systems cannot be easily produced by conventional material processing methods, such as chemical vapour deposition or sputtering and therefore alternative processing routes, such as sol–gel, are required. Using this latter process, it is possible to carefully control the microstructure and hence material properties. In this present work, a preparation method for an epoxy- functional inorganic–organic hybrid material thin film system, via the sol–gel method, is described. Epoxy functionality potentially imparts the required thermal stability to the system to survive subsequent high temperature post-processing e.g. solder reflow (typically 230 °C for 10 s). The optical properties of the films were studied by means of refractive index measurements at 633 nm. Fourier transform-IR (FT-IR) spectrometry was performed in order to exhibit the chemical structure of the resultant films and also to follow the influence of UVexposure time on it. Thermogravimetric Thin Solid Films 515 (2007) 5439 – 5443 www.elsevier.com/locate/tsf ⁎ Corresponding author. Department of Microelectronic Engineering, Uni- versity College Cork, Ireland. Tel.: +353 21 4904256. E-mail address: gcrean@tyndall.ie (G.M. Crean). 0040-6090/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2006.11.154