A simple and inexpensive technique for PDMS/silicon chip alignment with sub-μm precision

This paper describes a novel simple and inexpensive assembly technique with highly accurate alignment of a polydimethylsiloxane (PDMS) layer on a silicon chip for hybrid microfluidic/electronic applications. It is based on strong electrostatic adhesion of a 200 mm thick and dense layer of PDMS onto a metallic cylindrical tool mechanically fixed to an optical microscope. A 2 mm hole in the tool allows precise alignment of the PDMS layer, 10 mu m from the surface, without the usage of any lubricant. The same tool is used for PDMS bonding in a well-controlled manner. This technique is compatible with wafer scale alignment. A very precise consideration of the PDMS shrinkage ratio, reduced by 50% for thin layers, enables a misalignment range of less than 1 mu m in the experiments.