Mechanical trimming with focused ion beam for permanent tuning of MEMS dual-mass gyroscope.

• Structural asymmetries of the vibratory gyroscope are induced mainly by fabrication errors. • Structural imperfections limit the sensor performance by affecting the signal-to-noise ratio, resolution, zero rate output and bias stability. • Mechanical ablation of interconnecting spokes in concentric ring suspension of a gyroscope enabled coarse (>50 Hz) tuning and fine-tuning (<1 Hz) of resonant frequencies. • Mechanical trimming allows for permanent tuning of the gyroscope's vibratory modes without introducing additional noise. • Electrostatic tuning allows for gyroscope frequency split reduction to the level of mHz after packaging of the device. This paper reports mechanical ablation techniques for permanent frequency tuning of the primary wineglass modes in planar gyroscopes with concentric ring suspension. Three different approaches for frequency tuning are discussed: (1) selective mass removal, (2) stiffness reduction via thinning of suspension elements, and (3) stiffness reduction by removal of interconnecting spoke elements between concentric rings. A predictive tuning algorithm is developed for identification of ablation locations to guide the trimming process. A dual-mass Dynamically Amplified Gyroscope (DAG) design is used to demonstrate the tuning approach. It is shown that introduction of "side-spokes" to the concentric ring system of DAG enables coarse (> 50 Hz) tuning, as well as fine-tuning (< 1 Hz) of resonant frequencies, which is performed by means of mechanical ablation with focused ion beam (FIB). Finally, a comparison of the sensor noise characteristics using active electrostatic tuning and mechanical ablation is presented. [ABSTRACT FROM AUTHOR]