This paper reports on a symmetrical z-axis gyroscope, whose stiffness of sensing and driving mode is identical in spite of the fabrication and design errors. There is no need of the electrical tuning of frequencies for a high sensitivity because the effective masses of the driving and sensing directions are hardly changed. Furthermore, it is very simple to fabricate the gyroscope with a total chip size of 3x3.5x1mm2 using only one mask. The gyroscope structure is fabricated on an anodic bonded 4Oum-thick silicon on glass. After the top silicon is etched using a deep RE, a part of the glass under the silicon structure is etched by HF for releasing the top silicon structure. Since the depth of the etched glass under the silicon structure is about 20-30pm, the damping and the stiction between the structure and the glass substrate are minimized. The minimum gap and the aspect ratio of this structure is 2pm and 20, respectively. Without an additional frequency tuning method, it is demonstrated that the difference between the two frequencies is about 85Hz, and the noise equivalent rate is O.Oldeg/sec at 5OmTorr pressure.

A surface micromachined accelerometer, which senses an inertial motion with an area variation, has been developed. The accelerometer is designed as an interdigital rib structure that has a differential capacitor arrangement. The movable electrodes are mounted on a mass of 7 µm thick polysilicon and a pair of stationary electrodes is formed under the mass with a 1.5 µm gap. Both sides of the movable electrodes are fixed on the mass, and the stationary electrode is formed on the substrate without being suspended. As a result, the mechanical stress and the electrical pulling effects can be reduced in comparison to the comb-type capacitor arrangement. In order to improve the dynamic range and the linearity, a pair of comb-shaped force-balancing electrodes is placed on both sides of the mass. The force-balancing electrodes are fabricated on the same layer as the mass and anchored on a silicon substrate. In particular, differential feedback electrodes enable linear control of mass repositioning.

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