Methodology for low- and high-cycle fatigue characterization with kHz-frequency resonators

Micromachined resonators are now routinely employed to evaluate the mechanical properties of structural films used in microelectromechanical systems. However, the behavior of kHz-frequency resonators is highly sensitive to temperature, humidity, and other environmental factors. Additionally, the rapid cycle accumulation rate makes it difficult to characterize fatigue lives less than ∼1 × 106 cycles. This work presents a general testing methodology based on empirical measurements and numerical modeling that allows accurate stress amplitude and fatigue lifetime measurements in both air and vacuum environments. Additionally, this strategy enables the characterization of very short fatigue lives (i.e., a few hundred cycles) for structures resonating at high frequencies (∼40 kHz). This testing methodology can be used to generate accurate stress-life (S–N) fatigue curves for a larger range of accumulated cycles than previously possible.