Lateral-axis Gyroscope Research Articles

A Lateral-Axis Microelectromechanical Tuning-Fork Gyroscope With Decoupled Comb Drive Operating at Atmospheric Pressure

In this paper, a silicon bulk micromachined lateral-axis tuning-fork gyroscope (TFG) with a decoupled comb drive and torsional sensing comb capacitors is presented. The novel driving comb capacitors are used to suppress the parasitic out-of-plane electrostatic force and, hence, can decouple the mechanical crosstalk from the sensing mode to the driving mode in a simple manner. The torsional sensing combs are designed to differentially sense the out-of-plane rotational moment and are arranged centroidally to be immune to fabrication imperfections for good linearity and electrostatic force balancing. The torsional sensing combs adopted in the TFG help to lower the air damping of the sensing mode while the driving mode of the gyroscope is dominated by slide-film air damping; hence, it can work even at atmospheric pressure. The process for this lateral-axis gyroscope can also be used to fabricate z-axis gyroscopes; therefore, low-cost miniature monolithic inertial measurement units can be realized without vacuum packaging. The TFG is tested at atmospheric pressure with a sensitivity of 17.8 mV/°/s and a nonlinearity of 0.6% in a full-scale range of 1000°/s. The bias stability is measured to be 0.05°/s (1 ?) in 30 min with an equivalent noise angular rate of 0.02°/s/Hz1/2.

Vertical comb-finger capacitive actuation and sensing for CMOS-MEMS

Abstract A new method for out-of-plane (vertical) electrostatic actuation and capacitive displacement-sensing that utilizes sidewall capacitance change of multiconductor comb fingers is analyzed and experimentally verified. Combining the inherited in-plane (lateral) actuation and sensing capacities of comb fingers, three-dimensional actuation/sensing can be realized. A maskless post-CMOS micromachining process is employed and the fabrication is compatible with standard CMOS processes. Applications include an three-axis microstage, a z -axis accelerometer and a lateral-axis gyroscope that use the proposed vertical comb-finger actuation/sensing method. The measured maximum vertical displacement of the microstage is 3.5 μm with a resonant frequency of 6.17 kHz. Measured sensitivity of the z -axis accelerometer is 0.5 mV/g with less than −40 dB cross-axis sensitivity, noise floor 6 mg/√Hz, and linear range from −27 to 27 g. The lateral-axis gyroscope design uses integrated comb drives for out-of-plane actuation, and is motivated by the desire to integrate three-axis gyroscopes on a single chip. The packaged gyroscope operates at atmospheric pressure with a sensitivity of 0.12 mV/ o /s and the resonant frequency of the drive mode is thermomechanically tuned between 4.2–5.1 kHz. Resonant frequency matching between the drive and sense modes is realized by integrating a polysilicon heater inside the spring beams.