PDMS surface modification in the application of waveguide claddings for evanescent field sensing

Wang Meng, Sanna Uusitalo, R. Myllylä, Leena Hakalahti, Markku Känsäkoski

    Research output: Chapter in Book/Report/Conference proceedingConference article in proceedingsScientificpeer-review


    We fabricated SU-8 based slab waveguides on surface-modified poly(dimethyl siloxane) PDMS lower claddings for application in evanescent field sensing. In this application, higher sensitivity is obtained by generating stronger penetrating power above the waveguide into the analyte. This can be achieved by reducing the refractive index of the substrate. Compared with glass substrates that have a refractive index of 1.5, PDMS has a refractive index of 1.42 at 633 nm, thus serving as a better lower cladding material for high-sensitivity sensing with an evanescent field or as claddings in multilayer waveguide applications. In order to increase the adhesion of PDMS surfaces for successful SU-8 application we treated PDMS thin films in low-frequency (40 kHz) oxygen plasma for varied length of exposure time. The treatment process made PDMS hydrophilic and created nano-structures on the surfaces. The resultant surface topography with different exposure time was studied by an interferometric profiler on PDMS lower claddings and the later spin-coated SU-8 waveguides. Measurement results showed that longer plasma treatment on PDMS claddings significantly improved the uniformity and waviness of the waveguides. Light propagation tests performed with a prism coupler and an end-butt coupling setup proved that PDMS can be used as a proper material for SU-8 waveguides.
    Original languageEnglish
    Title of host publicationMicrofluidics, BioMEMS, and Medical Microsystems VIII
    Place of PublicationUSA
    PublisherInternational Society for Optics and Photonics SPIE
    Publication statusPublished - 2010
    MoE publication typeNot Eligible
    EventMicrofluidics, BioMEMS, and Medical Microsystems VIII, SPIE MOEMS-MEMS, 2010 - San Francisco, United States
    Duration: 25 Jan 201027 Jan 2010

    Publication series

    SeriesProceedings of SPIE


    ConferenceMicrofluidics, BioMEMS, and Medical Microsystems VIII, SPIE MOEMS-MEMS, 2010
    Abbreviated titleSPIE MOEMS-MEMS, 2010
    Country/TerritoryUnited States
    CitySan Francisco


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