Localized Eutectic Trimming of Polysilicon Microhemispherical Resonating Gyroscopes

This paper describes a novel technique to permanently tune a frequency mismatch between degenerate modes of a polysilicon microhemispherical resonating gyroscope ( $\mu $ HRG) caused by fabrication imperfections with the potential to be implemented postpackaging. A systematic trimming algorithm is introduced to compensate for frequency mismatch and mode misalignment based on laser-induced silicon-metal eutectic formation. The stiffness changes are applied to the vicinity of the supporting post at the base of a hemispherical resonator, a region, which has not been previously studied for this purpose. Our numerical studies show the four-nodal point elliptical wineglass modes are highly sensitive to strain modifications around the post. The algorithm is developed and proven effective through finite element method simulations in COMSOL, where a significant reduction ( $> 10\times $ ) of the frequency split of the wineglass modes in an imperfect $\mu $ HRG has been achieved.