Polymer based thick film fabrication technologies for flexible and standalone multifunctional devices

In this thesis, different polymer based thick film fabrication technologies are presented. The primary focus for such fabrication technology is to develop standalone multifunctional devices especially for bio-medical and microfluidics applications. The proposed thick film fabrication technologies are developed using PDMS and SU-8, two prominent polymers for microfabrication. First, a new fabrication process utilizing polydimethylesiloxane (PDMS) as a sacrificial substrate layer for fabricating free-standing SU-8 based biomedical and microfluidic devices is described. The PDMS-on-glass substrate permits SU-8 photopatterning and layer-to-layer bonding. The novel process allows the SU-8 structures to be easily peeled-off from the substrate after complete fabrication. As an example, a fully enclosed microfluidic chip has been successfully fabricated. The enclosed microfluidic chip uses the adhesive bonding technology and the SU-8 layers from 10 µm to 450 µm thick and as large as the glass substrate are successfully fabricated and peeled from the PDMS layer as single continuous sheets. Secondly, a fabrication technology utilizing SU-8 as a sacrificial mask for metallization of the PDMS surface is presented. Sacrificial SU-8 masks from 45 µm to 250 µm thickness are successfully fabricated for patterning gold on the PDMS surface. The sacrificial SU-8 layers are successfully peeled from the PDMS surface after the metal deposition step. Metal lines from 10 µm to 500 µm wide and 1 mm to 50 mm long are successfully patterned and tested. Thirdly, a hybrid fabrication technology is presented that uses covalently bonded a flexible polymer (polydimethylsiloxane - PDMS) and a rigid polymer (SU-8). A covalent bond between the flexible and rigid polymer layers is achieved using an oxygen plasma treatment during a layer-by-layer direct spin-on process. As a proof-of-concept, PDMS-based flexible microfluidic devices with SU-8-based rigid world-to-chip/chip-to-world interconnects are successfully fabricated. Finally, fully flexible 3-D electrodes are realized on PDMS utilizing ordered arrays of pillars with different shapes and heights. Square and cylindrical pillars with different height (50 µm, 100 µm and 200 µm) and uniform metal coverage are successfully fabricated. These electrodes are utilized to fabricate electro-enzymatic glucose sensors with increased surface area and hence sensitivity.