HIGH PERFORMANCE MATCHED-MODE TUNING FORK GYROSCOPE M.F. Zaman, A. Sharma, and F. Ayazi Integrated MEMS Laboratory Georgia Institute of Technology, Atlanta, Georgia, USA ABSTRACT This paper presents the perfect matched-mode operation of a type I non-degenerate z-axis tuning-fork gyroscope (i.e., 0 Hz frequency split between high-Q drive and sense modes). The matched-mode tuning fork gyroscope (M 2 -TFG) is fabricated on 50-µm thick SOI substrate and displays an overall rate sensitivity of 24.2 mV/º/s. Allan Variance analysis of the mode-matched device demonstrates an angle random walk (ARW) of 0.045 º/ hr and a measured bias instability of 0.96 º/hr. Temperature characterization of the M 2 -TFG verifies that mode matching is maintained over a temperature range of 20-100 ˚C. 1. INTRODUCTION The automotive and consumer electronics industries have embraced MEMS gyroscopes as attractive replacements to conventional macro-mechanical and optical gyroscopes, owing to their small size, low power and relatively inexpensive mass production potential. The most popular class of MEMS gyroscopes are the Coriolis vibratory gyroscopes (CVG) which are based on transfer of energy between two vibration modes of the microstructure in response to a rotation signal. Vibratory microgyros operate under matched-mode or split-mode condition as explained in [1]. The resulting quality factor amplification increases sensitivity and resolution and lowers bias drift in devices that are operated under matched-mode conditions. Current commercial vibratory MEMS gyros are employed in applications where extreme resolution and precision are not critical. MEMS gyros have yet to break into the high-precision market such as the defense, navigation and space industries where rate resolutions and bias stabilities of 0.1-1º/hr are required. The lack of mass, restricted drive amplitude, low quality factors or a combination of the above have been the limiting factors in the past. In [2] the authors introduced a novel type-I vibratory gyroscope, the M 2 -TFG design, which incorporated all the necessary features required to achieve inertial grade performance – large drive amplitude (employing comb-drives), maximum mass/unit area (made possible by an innovative fabrication process that facilitates proof-mass release without perforations), and high-Q resonant operating modes (through efficient flexural designs). However, excessive quadrature error prevented matched-mode operation of the device. Mode-matching enables unprecedented improvement in sensitivity and noise floor of vibratory gyros at the expense of reduced bandwidth. This paper presents experimental results under matched- mode and split-mode operation of the TFG, and examines the temperature and drift characterization data of the device. 2. THE MATCHED-MODE TFG Figure 1 shows an SEM image of the M 2 -TFG fabricated on a low resistivity 50 m thick SOI substrate using the fabrication process outlined in [2]. The M 2 -TFG is comprised of two proof-masses anchored at a central post and supported by flexural springs. The flexural designs ensure minimal support loss and thermoelastic damping in flexures to result in high-Q in-plane drive and sense resonant modes, as well as minimal coupling and frequency separation between the two modes (Fig. 2). Figure 1: SEM image of a M2-TFG on SOI substrate Figure 2: Resonant in-plane operating modes of the M2-TFG: (Left) Drive mode and (Right) Sense mode. The operating principle of the device is based upon a standard tuning fork’s response to rotation. The proof-masses are driven at resonance along the x-axis using comb-drive electrodes, and the Coriolis acceleration induced by rotation about the z-axis is sensed capacitively along the y-axis. The in-plane drive and sense resonant modes are illustrated in Fig. 2. Central Post Comb-Drive Electrode Proof Mass 66  