Effects of Gamma Ray Radiation on the Performance of Microelectromechanical Resonators

While much radiation test data are available for metal-oxide-semiconductor (MOS) devices, research into the effects of radiation on microelectromechanical systems (MEMS) is in its relative infancy. Piezoelectrically transduced MEMS resonators have broad applications in signal processing, environmental monitoring, and navigation. Aluminum nitride (AlN), in particular, is an attractive piezoelectric because of its favorable fabrication characteristics and ease of integration into the complementary MOS (CMOS) manufacturing process. The utility of these devices in space and nuclear systems necessitates research into their performance in radiation environments. Resiliency and an established relationship between radiation dose and device behavior provide a critical tool for engineers in their design process. Multiple AlN-based MEMS resonator designs are created and exposed the devices to 1 Mrad(Si) gamma irradiation from a Cobalt-60 source while measuring scattering (S-) parameters in situ. The experimental data are matched to a theoretical model to describe the change in frequency as a function of radiation-induced displacement damage. It is demonstrated that the AlN-based resonators are resilient against radiation-induced charge-trapping effects. Furthermore, a new method is presented of permanent frequency trimming MEMS resonators up to 30% of their bandwidth without modifying quality factor or motional resistance.