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.
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The authors would like to thank the microshutter group at NASA Goddard Space Flight Center for their support and help of this project. The staff of the Institute for Research in Electronics and Applied Physics (IREAP) at University of Maryland, especially Nolan Ballew and John Barry, are also acknowledged for their help in using the cleanroom facility and the FIB system.
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Chuang, WH., Fettig, R.K. & Ghodssi, R. FIB-Based Fatigue Testing of Silicon Nitride Thin Films for Space Applications. MRS Online Proceedings Library 851, 310–315 (2004). https://doi.org/10.1557/PROC-851-NN5.16