Q.C. Zhao

An Electrically Decoupled Lateral-Axis Tuning Fork Gyroscope Operating at Atmospheric Pressure

In this paper, a bulk micromachined lateral axis TFG (tuning fork gyroscope) with torsional sensing comb capacitors is presented. Both driving and sensing modes of the gyroscope are dominated by slide film air damping, then it can work even at atmosphere. Novel driving comb capacitors are used to electrically decouple the mechanical coupling from sensing mode to driving mode. The process for this gyroscope is also compatible with z-axis gyroscope, which makes it potentially to realize low coast monolithic MIMU (miniature inertial measurement unit) without vacuum packaging. The TFG was fabricated and tested at atmosphere. The sensitivity is 17.8mV/°/s while the nonlinearity is 0.6%. The bias stability is 0.05°/s (1¿) and the noise floor is 0.02°/s/Hz1/2

Decoupled Comb Capacitors for Microelectromechanical Tuning-Fork Gyroscopes

This letter presents a novel comb capacitor which can decouple the mechanical crosstalk between the sensing and driving modes of gyroscopes. The capacitance and electrostatic force of the comb capacitor are simulated and analyzed to verify the decoupling principle. A lateral-axis tuning-fork gyroscope is used successfully to demonstrate the decoupling capability of the comb capacitor, resulting in a nonlinearity of 0.6% with full scale of 1000 °/s and a bias stability of 0.05 °/s (1¿) for 30 min.

A Latching Acceleration Switch with Multi-Contacts Independent to the Proof-Mass

An acceleration latching switch with independent multi-contacts is presented in this paper. All the contacts and their beams are independent to the proof-mass so as to prevent the contacts from the impact resulting from the rebound or vibration of the proof mass once the switch is latched. Moreover, multiple contacts are used in order to get high reliable contact, to lower the contact resistance and to increase the maximum allowable current. The switch was fabricated by low-cost process and tested. The latching shock is 4500G and the response time is less than 0.1ms. The contact resistance is no more than 5 ohms while the isolation resistance is more than 200M ohms and the maximum allowable current is up to 100mA.

Electrostatic isolation structure for linearity improvement of a lateral-axis tuning fork gyroscope

The electrostatic negative-stiffness behavior of vertical structures under out-of-plane motion decreases the resonant frequency and deteriorates the linearity of a lateral-axis tuning-fork gyroscope (TFG). An electrostatically isolated silicon island is proposed to suppress this behavior. The negative-stiffness behavior is observed and the effectiveness of the electrostatic isolation is experimentally verified. The nonlinearity of the TFG is reduced to 0.34% with a full range of 1,000°/s. This is a 5× improvement.

A doubly decoupled micromachined vibrating wheel gyroscope

In this paper, a doubly decoupled vibrating wheel gyroscope with novel torsional sensing comb capacitors is presented. The doubly decoupled design and symmetrical structure can efficiently suppress the mechanical coupling of the gyroscope. Moreover, the symmetrically distributed proof masses make it immune from the linear accelerations. Both driving and sensing modes of the gyroscope are dominated by slide film air damping, so it can work even at atmospheric environment. The process for this gyroscope is also compatible with z-axis gyroscope, which makes it potential to realize low cost monolithic MIMU (miniature inertial measurement unit) without vacuum packaging. The gyroscope was fabricated and tested at atmosphere. The sensitivity is 3.1mV/º/s while the nonlinearity is 7.68‰ with the full scale of 900º/s. The noise floor is 0.45º/s/Hz1/2.

Design of a digital closed control loop for the sense mode of a mode-matching MEMS vibratory gyroscope

This paper presents a digital closed loop control method for the sense mode of a mode-matching MEMS vibratory gyroscope. The sense closed loop system reported in our previous work is relatively complex and unreliable due to the existence of notch filter. In this work, a more simple and robust control system is realized with the help of mode-matching control. With a tuning voltage automatically applied on the tuning combs of the gyroscope, a frequency split of less than 0.3 Hz is achieved. Experimental results show that the mode-matched gyroscope achieves a scale factor of 18.5mV/deg/s with a nonlinearity of 0.088% and a bias instability of 2.7deg/h.

A lateral-axis micromachined tuning fork gyroscope with novel driving and sensing combs

A decoupled lateral-axis TFG (tuning fork gyroscope) with novel driving and sensing combs is presented. The EFBD (electrostatic force balanced comb driver) adopted in the TFG can efficiently suppress the mechanical coupling in a simple manner. The structure of the gyroscope is also optimized to suppress the coupling further. Moreover, torsional sensing combs are adopted to detect the out-of-plane movement, so it can work at atmospheric pressure. The TFG was fabricated and tested at atmosphere. The measured CFDTS (coupling from driving mode to sensing mode) and CFSTD (coupling from sensing mode to driving mode) are −45dB and −51dB respectively. The sensitivity is 2.9mV/°/s while the nonlinearity is 0.9% with the full scale of 800°/s. The noise floor is 0.035°/s/Hzx8d.

Research on the packaging reliability and degradation models of quality factors for a high vacuum sealed MEMS gyroscope

This paper proposes a novel evaluation method for MEMS gyroscopes packaging reliability. Based on the principles of thermodynamics and hydromechanics, the relationships among quality factors, air pressure, and gas number, as well as degradation models of them, are deducted for the first time. Experimental tests demonstrate that the relationships between the reciprocals of the two-mode quality factors and air pressure are approximately piecewise linear. Besides, the relationships between the reciprocals of quality factors and accelerated aging time are exponential, which accord with the theoretical analysis.

A novel 0–3 kPa piezoresistive pressure sensor based on a shuriken-structured diaphragm

This paper reported a novel high sensitivity and linearity 0-3 kPa piezoresistive pressure sensor by carefully trading off the stress on the beam edge and the deflection of the sensing diaphragm. A shuriken-structured diaphragm (SSD) was proposed for the first time to improve both sensitivity and linearity for the piezoresistive pressure sensor. The fabricated sensor showed a sensitivity of 4.72 mV/kPa/V and a nonlinearity of 0.18% FSO (full scale output) in the pressure range of 0-3 kPa. Compared with our previous work, the sensitivity was increased by 28.3%, while the nonlinearity was reduced by 50%.

A lateral-axis tuning fork gyroscope with combined sensing capacitors and decoupled comb drive

In this paper, a bulk micromachined lateral-axis TFG (tuning fork gyroscope) with improved architecture and combined mechanism sensing capacitors is reported. The combined sensing capacitors make the TFG have high sensitivity and good linearity even under wide input range and fabrication imperfection. Moreover, the decoupled comb drive, together with the improved architecture, can efficiently decouple the mode coupling. At atmospheric pressure, the TFG has a sensitivity of 0.1126mV/°/s even with unity gain. The nonlinearity is 0.7% with an input range of up to 1000°/s.