Reliability Assessment of MEMS Structure of Su-8 Thin Film

This paper describes new test method for obtaining static and dynamic characteristics of thin film and reliability evaluation method on MEMS device with thin film. The Su-8 is often used in micro-electro-mechanical systems devices. Durability should be ensured for such devices under cycling load. Therefore, with the proposed specimen and test procedure, tensile test was performed to obtain mechanical properties. The specimen was made with dimensions of 1000μm long, 9 and 11 μm thickness, and 3 kinds of width, 50, 100 and 150μm. Behaviors of Su-8 have the 3 kinds of stress-strain curves. The mechanical characteristics of Su-8 were multiple, showing characteristics of brittle and ductile material and polymer. It was found that the mechanical properties of Su-8 did not have any effect on thickness. High cycle fatigue test was performed to obtain probability of failure at a given stress. We found that fatigue life of Su-8 was very susceptible to stress level and then strength-stress model was suitable for the assessment of durability of MEMS structure under cycling load.