Effects of Fast Neutrons on the Electromechanical Properties of Materials Used in Microsystems

Microelectromechanical systems (MEMS) technology is expected to play a significant role in avionics and in future space missions provided that the effect of radiation on the reliability of MEMS devices is well understood. Most tests, to date, have been performed on MEMS that operate based on electrostatic principles, and radiation-induced dielectric charging has been identified as a mechanism which can potentially limit the reliability of such devices. Experiments with piezoresistive and piezoelectrically actuated MEMS have also revealed changes in the operation of devices after exposure to different types of ionizing radiation. However, not many reports on the damage effects in MEMS due to fast neutrons exist. In this paper, we present results from mechanical and electrical tests on different materials which are typically used in microsystems, before and after exposure to fast neutrons. Changes were detected in the residual stress and in the resonant frequencies of silicon nitride microbeams. There was also evidence of radiation-induced charge trapping in metal-insulator-semiconductor capacitors fabricated from thermal oxide, silicon nitride, and aluminum oxide deposited by atomic layer deposition. Finally, we observed that the electrical properties of ferroelectric capacitors fabricated from lead zirconate titanate and lead strontium titanate thin films do not degrade after exposure to fast neutrons.