Proton-Radiation Tolerance of Silicon and SU-8 as Structural Materials for High-Reliability MEMS

The susceptibility of single-crystal silicon and SU-8 resonators to proton-radiation induced degradation was investigated. Both materials are in widespread use for microsystems structures, thus the stability of the mechanical properties must be ensured over the full device lifecycle. Effects of space-relevant proton doses were examined by monitoring minute changes in the Young's modulus and by structural investigations using high-resolution X-ray diffraction (HRXRD). Single crystal silicon resonators were exposed to 10 MeV and 60 MeV protons with doses up to 10¹³ cm⁻². Even at the highest doses neither a change of the Young's modulus was observed nor did X-ray diffraction indicate the formation of elevated concentrations of structural defects. The compatibility of SU-8 with in-orbit radiation environments was investigated at fluences of 10¹⁰-10¹² cm⁻² using protons with energies ranging from 10,MeV to 200,MeV. Its elastic modulus changed by less than 5.5% at the highest doses.