FIB-Based Fatigue Testing of Silicon Nitride Thin Films for Space Applications

Abstract

A novel micro-scale electrostatic actuator has been designed and fabricated to study fatigue properties of low-stress LPCVD silicon nitride thin films, which are the structural materials of microshutter arrays to be used in NASA’s James Webb Space Telescope (JWST). To obtain different stress levels without high applied voltages, the electrostatic actuator was designed based on a resonant technique to achieve mechanical amplification. All fabricated devices were tested inside a focused-ion-beam (FIB) system with pressure of 10⁻⁶ torr at room temperature (23 ± 1 °C) and with the test duration ranging from 5 seconds to 8.5 hours, 10⁵ to 10⁹ cycles, respectively. From the experiment, no fatigue failure of low-stress LPCVD silicon nitride thin films has been observed up to 10⁹ testing cycles, four orders of magnitude higher than the expected lifetime of the microshutter arrays. The presented test device and experimental technique can be extended to characterize fatigue properties for other thin film materials.