A low-cost rate-grade nickel microgyroscope

This paper presents a low-cost microgyroscope with a resolution in the rate-grade at atmospheric pressure, which is fabricated using a CMOS-compatible nickel electroforming process. Angular rate resolution of the gyroscope is increased by matching the resonance frequencies of the drive and sense modes close to each other using symmetric suspensions and electrostatic frequency tuning; whereas, undesired mechanical coupling between the two modes during matched mode operation is reduced by the fully decoupled gyro flexures. Reduced mechanical coupling results in a stable zero-rate output bias, i.e., providing excellent bias stability. The fabricated gyroscope has 18 μm-thick nickel structural layer with 2.5 μm capacitive gaps providing an aspect ratio above 7, which results in sensor capacitances about 0.5 pF. The resonance frequencies of the fabricated gyroscope are measured to be 4.09 kHz for the drive-mode and 4.33 kHz for the sense-mode, which are then matched by a tuning voltage less than 12 V dc. The gyroscope is hybrid connected to a CMOS capacitive interface circuit, and the hybrid system operation is controlled by external electronics, constructing an angular rate sensor. The gyroscope is oscillated along the drive-mode to vibration amplitude above 10 μm. The rate sensor demonstrates a noise-equivalent rate of 0.095 (°/s)/Hz 1/2 and short-term bias stability better than 0.1 °/s. The nominal scale factor of the sensor is 17.7 mV/(°/s) in a measurement range of ±100 °/s, with a full-scale nonlinearity of only 0.12%. The measurement bandwidth of the gyroscope is currently set to 30 Hz, while it can be extended beyond 100 Hz depending on the application requirements. The quality factor of the sense-mode improves by an order of magnitude at vacuum, which yields an estimated noise-equivalent rate better than 0.05 (°/s)/Hz 1/2 in a narrowed response bandwidth of 10 Hz.