Effect of Moisture and Anisotropy in Multilayer SU-8 Thin Films

Abstract

Biocompatible polymers, like SU-8, have become a vital part of Microelectromechanical System (MEMS) devices, especially as a structural layer in biosensors and micro-fluidics. In the present study, effect of moisture and anisotropy on the mechanical response of 2 micron thick SU-8 polymer films was investigated using optical in-situ microtensile experiments. The tensile specimens were fabricated using soft lithography, which consisted of deposition, patterning and release of the film from the silicon wafer. A novel methodology was followed to capture optical images of the patterned SU-8 surface during the experiment, for strain calculations using Digital Image Correlation (DIC). Tensile properties were derived from the uniaxial stress–strain curves. The tensile strength and fracture strain of the multilayer films increased by more than 10 and 5 %, respectively, as compared to the single layer film. Some experimental results along with Fourier Transform Infrared (FTIR) spectroscopy data is shown to support the observations from our experiments.