A symmetric surface micromachined gyroscope with decoupled oscillation modes

Abstract

This paper reports a new symmetric gyroscope structure that allows not only matched resonant frequencies for the drive and sense vibration modes for better resolution, but also decoupled drive and sense oscillation modes for preventing unstable operation due to mechanical coupling. The symmetry and decoupling features are achieved at the same time with a new suspension beam design. The gyroscope structure is designed using a standard three-layer polysilicon surface micromachining process (MUMPs) and simulated using the MEMCAD software. Measured results show that the drive and sense mode resonant frequencies are 28,535Hz and 30,306Hz, respectively, which are in agreement with the finite element simulations. The small mismatch can be reduced further by applying different DC bias voltages to the drive and sense electrodes, improving the performance. The performance of the fabricated sensor is limited due to large parasitic capacitance between the proof mass and the substrate, nevertheless, measurements and calculations show that the sensor can sense angular rates as small as 0.37 deg/sec even in atmospheric pressure. A capacitive readout circuit for the sensor was also developed in a 0.8µm CMOS process, and the fabricated circuit detects capacitance changes smaller than 0.1fF with a sensitivity of 45mV/fF.