AVS 50th International Symposium
    Microelectromechanical Systems (MEMS) Tuesday Sessions
       Session MM-TuM

Paper MM-TuM10
Measurement of Mechanical Properties of Silicon Nitride Thin Film at Cryogenic Temperatures

Tuesday, November 4, 2003, 11:20 am, Room 320

Session: Development and Characterization of MEMS and NEMS Materials
Presenter: W. Chuang, University of Maryland, College Park
Authors: W. Chuang, University of Maryland, College Park
T. Luger, University of Maryland, College Park
R. Fettig, NASA Goddard Space Flight Center
R. Ghodssi, University of Maryland, College Park
Correspondent: Click to Email
Mechanical properties of MEMS materials at cryogenic temperatures are investigated to extend MEMS sensors and actuators into space and low temperature applications. Two-dimensional micro-shutter arrays, made in silicon nitride thin film, are being developed at NASA Goddard Space Flight Center (GSFC) for use in the James Webb Space Telescope (JWST). Reliability and exact mechanical properties of silicon nitride thin film at cryogenic temperatures are crucial in the development of the JWST. We have developed and installed a measurement setup inside a focused ion beam (FIB) system, which can provide scanning electron microscopy (SEM) and mask-less ion milling, to measure the mechanical properties of MEMS materials from room to cryogenic temperatures. A variety of low-stress silicon nitride T-shape cantilevers suspended on silicon micromachined v-grooves are fabricated as test devices. The resonant frequency method is used in experiments to minimize the required calibration in the measurement setup at different temperature ranges. A lead-zirconate-titanate (PZT) translator and a silicon diode are utilized as the actuator and temperature sensor in the measurement setup, respectively. Experiments are performed to measure resonant frequency, damping, coefficient of thermal expansion, Young's modulus, fracture strength and fatigue properties of the test devices from room to cryogenic temperatures. The measured resonant frequencies are varied from 15.81 kHz at 25.5 K to 14.61 kHz at 298 K (room temperature). The higher resonant frequency is consistent with the expected increased Young's modulus of silicon nitride thin film at cryogenic temperatures. The preliminary measurement results, detailed fabrication process and configuration of the measurement setup will be presented.