Symmetrical and decoupled nickel microgyroscope on insulating substrate

This paper presents a symmetrical and decoupled surface micromachined gyroscope fabricated by electroforming thick nickel on a glass substrate. The symmetric structure allows matched resonant frequencies for the drive and sense vibration modes for improved sensitivity, while the decoupled drive and sense oscillation modes prevents unstable operation due to mechanical coupling, resulting in a low zero-rate output drift. The use of a glass substrate instead of a silicon substrate reduces noise due to the parasitic signal coupling by two orders of magnitude, according to both simulation results in CoventorWare and measured results on fabricated devices. A capacitive interface circuit which is fabricated in a 0.8 mum CMOS process is hybrid connected to the gyroscope, where the circuit has an input capacitance lower than 50 fF and a sensitivity of 33 mV/fF, which are currently limited by the parasitic capacitances due to hybrid wirebonding. It has been identified that the amount of parasitic capacitances must be lower than or at least in the same order with the electrical equivalent capacitance of the gyroscope for clear mechanical resonance characteristics to be obtained. Fabricated gyroscopes have close resonant frequencies for the drive and sense modes, as 37.2 and 38.3 kHz, respectively. Calculations on measured resonance values suggest that the fabricated gyroscope with 16 mum-thick structural layer provides a Brownian noise floor of 7.3degrees/h/Hz(1/2) at vacuum. Currently, the overall rate sensitivity of the gyroscope is limited to 96degrees/h in 50 Hz bandwidth for matched-frequency operation, and it can be decreased down to 56degrees/h in 50 Hz bandwidth, by improving the quality of the electrodeposited nickel. (C) 2004 Elsevier B.V. All rights reserved.