Design of a test structure based on chevron-shaped thermal actuator for in-situ measurement of the fracture strength of MEMS thin films

A novel test structure to characterize the fracture strength of MEMS (Micro-electro-Mechanical Systems) thin films is presented. The test structure is comprised of a micro fabricated chevron-shaped thermal actuator and test specimen. The test structure is capable of producing large displacement and stress while keeping a relatively low temperature gradient across the test specimen. A voltage is applied across the beams of the chevron-shaped actuator, producing thermal expansion force to fracture the test specimen. Actuator deflection is computed based on elastic analysis of structures. To verify the test structure, simulations have been implemented using COMSOL Multiphysics. A 620 μm long, 410 μm wide, 10 μm thick test structure produced stress of 7.1 GPa while the applied voltage is 5 V. The results indicate that the test structure is suitable for in-situ measurement of the fracture strength of MEMS thin films. Keywords: MEMS thin films, Fracture strength, Chevron-shaped thermal actuator