A polysilicon test structure for fatigue and fracture testing in micro electro mechanical devices

Fatigue test results on 15 mum thick polysilicon specimens are presented and compared in this work, both on a quantity and on a quality level, to existing literature results. The experimental results have been obtained by means of a newly designed, electrostatically actuated, MEMS test device, produced with the STMicroelectronics THELMAcopy process. The new device allows for the execution of on-chip fatigue and fracture tests on polysilicon specimens and is interfaced with an analog, low-noise and low-perturbing electrostatic position measurement system for capacitive MEMS sensors. The setup allows for a real time monitoring of the MEMS position, from which the elastic stiffness of the specimen can be evaluated at any time, provided that the applied force is known. Elastic stiffness variations can be related to resonance frequency variations found in the literature. System resolutions of 30 ppm and good long-term stability have been obtained.