Experimental study of PDMS membranes fabricated either by spin coating or transfer bonding to a silicon chip with etched cavity

Abstract

Nowadays, with no doubt, PDMS, poly(dimethylsiloxane) elastomer is material of choice for microfluidic fabrication because of its unique chemical, optical and mechanical properties. Unfortunately, it is not photo-definable (i.e. not a photoresist) and fabrication of PDMS MEM (micro-electro-mechanical) devices is typically done using soft lithography. Some steps of the process are difficult to perform without manually handling PDMS layers. Next problem to be considered in patterning PDMS membranes is bond strength between membrane and silicon substrate. To investigate this, we fabricated PDMS membranes on silicon either by spin coating Si wafer or transferring previously fabricated PDMS membrane to Si chip with bonding layer on it. PDMS network samples for this research were synthesized with the same composition, which are Sylgard 184 (Dow Corning, USA) silicone elastomer base and silicone elastomer curing agent, volume ratio 10:1. Fabrication of test structures is based on bulk micromachining on ⟨100⟩ oriented Si wafers to fabricate square cavities on which PDMS membranes were realized by one of mentioned procedures. Mechanical testing of PDMS membranes, elastic properties and adhesion strength of membranes with different thicknesses were investigated applying pressurized bulge testing. Pressure was applied to the PDMS membrane via nitrogen gas and the resulting load-deflection curves were monitoring.