Mechanical characterization of SU-8 thin films through varying effective aspect ratios for microelectromechanical systems application

This work presents the mechanical characterization of SU-8 photoresists studied in the form of microscaled free-standing thin films with various effective length/width (aspect) ratios, achieved by a tensile testing method. Specimens were designed with gauge segments measuring 240 to 540 mu m long and 40 to 80 mu m wide with thickness fixed at 20 mu m, all fabricated in the same processing conditions. The experiments were carried out on a microtensile testing system which had a load and displacement resolution of 0.25 mN and 10 nm, respectively. With a tensile loading speed of 0.02 mu m/s, the average fracture strength of SU-8 photoresist was measured to be 66.34 MPa, and the calculated Young's modulus ranged from 0.86 to 2.33 GPa and the maximum strain from 1.02% to 9.70%, with variation dependent on the effective aspect ratio of the tested films. As a result, effective aspect ratio is concluded to be a significant factor mechanically charactering the size effect of SU-8 photoresist in microscale. (C) 2012 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI: 10.1117/1.JMM.11.2.023006]