A Compact Angular Rate Sensor System Using a Fully Decoupled Silicon-on-Glass MEMS Gyroscope

This paper presents the development of a compact single-axis angular rate sensor system employing a 100- mum-thick single-crystal silicon microelectromechanical systems gyroscope with an improved decoupling arrangement between the drive and sense modes. The improved decoupling arrangement of the gyroscope enhances the robustness of sensing frame against drive-mode oscillations and therefore minimizes mechanical crosstalk between the drive and sense modes, yielding a small bias instability. The gyroscope core element is fabricated by through-etching a 100-mum -thick silicon substrate which is anodically bonded to a recessed glass handling substrate. A patterned metal layer is included at the bottom of the silicon substrate, both as an etch-stop layer and a heat sink to prevent heating- and notching-based structural deformations encountered in deep dry etching in the silicon-on-glass process. The fabricated-gyroscope core element has capacitive actuation/sensing gaps of about 5 mum yielding an aspect ratio close to 20, providing a large differential sense capacitance of 18.2 pF in a relatively small footprint of 4.6 mm times 4.2 mm. Excitation and sensing electronics of the gyroscope are constructed using off-the-shelf integrated circuits and fit in a compact printed circuit board of size 54 mm times 24 mm. The complete angular rate sensor system is characterized in a vacuum ambient at a pressure of 5 mtorr and demonstrates a turn-on bias of less than 0.1 deg/s, bias instability of 14.3 deg/h, angle random walk better than 0.115 deg/radic(h), and a scale-factor nonlinearity of plusmn0.6% in full-scale range of plusmn50 deg/s. [2007-0158].