We report on the susceptibility of structural MEMS materials to proton radiation damage. Radiation tests at space relevant doses were conducted on MEMS resonators. The two materials examined were single crystal silicon and SU-8, which are both in widespread use in microsystems. The resonance frequency was monitored for measuring minute changes of the Young’s modulus. No radiation-induced changes of the elasticity were observed in the silicon devices up to fluences of 1013 cm-2, corresponding to a total ionizing dose (TID) of over 5.5 MRad for 10 MeV protons. The SU-8 resonators showed a variation of less than ±5.5% at doses of up to 1.4 Mrad (TID). Chemical and structural analyses of the polymer were performed using infrared absorption spectroscopy and x-ray diffraction methods. We discuss possible mechanisms for the observed changes of the elasticity of SU-8.
We report on a study of the sensitivity of silicon MEMS to proton radiation and mitigation strategies. MEMS can
degrade due to ionizing radiation (electron-hole pair creation) and non-ionizing radiation (displacement damage), such as
electrons, trapped and solar protons, or cosmic rays, typically found in a space environment. Over the past few years
there has been several reports on the effects of ionizing radiation in silicon MEMS, with failure generally linked to
trapped charge in dielectrics. However there is near complete lack of studies on displacement damage effects in silicon-
MEMS: how does silicon change mechanically due to proton irradiation? We report on an investigation on the
susceptibility of 50 μm thick SOI-based MEMS resonators to displacement damages due to proton beams, with energies
from 1 to 60 MeV, and annealing of this damage. We measure ppm changes on the Young's modulus and Poisson ratio
by means of accurately monitoring the resonant frequency of devices in vacuum using a Laser Doppler Vibrometer. We
observed for the first time an increase (up to 0.05%) of the Young's modulus of single-crystal silicon
electromagnetically-actuated micromirrors after exposure to low energy protons (1-4 MeV) at high absorbed doses ~ 100
Mrad (Si). This investigation will contribute to a better understanding of the susceptibility of silicon-based MEMS to
displacement damages frequently encountered in a space radiation environment, and allow appropriated design margin
and shielding to be implemented.
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