Dual-axis microgyroscope with closed-loop detection

Abstract

A novel dual-axis microgyroscope fabricated by a surface micromachining process is developed. A 7.0-mu m thick polysilicon layer deposited by LPCVD (Low Pressure Chemical Vapor Deposition) is used for the vibrating structure. The microgyroscope is based on the angular vibration of the four plates with closed-loop rate detection. The comb-driven rotational body tilts to each input-axis parallel to the substrate and the tilting motion is sensed with capacitance change between the bottom electrode and the structure. The two tilting modes enable the sensor to detect two-input axis angular rate simultaneously within a single-chip. In particular, the structure utilizes a simple force-balancing torsional torque which does not need another top electrode layer to reduce the intrinsic non-linearity of a capacitance-type sensor. The vibrating structure is strongly damped by air, so the gyroscope is tested in a high vacuum chamber for a high quality factor with hybrid signal-conditioning integrated circuit. The experiment resulted in a noise equivalent signal of 0.1 degrees/s. (C) 1999 Elsevier Science S.A. All rights reserved.