Design and Development of a MEMS Vibrating Gyroscope with Novel Inner Support Springs

Microelectromechanical Systems (MEMS) based resonating structures are used as the main sensing element in micro gyroscopes, accelerometers, and timing devices. The resonating microstructure needs to vibrate at its resonance frequency to maximize the sensitivity and signal output. Despite that numerous microstructure geometries have been explored in the literature, the technology still suffers from frequency stability and sensitivity issues. To address this challenge, this thesis presents two novel MEMS-based ring resonator microstructure designs inspired by nature for frequency symmetry and stability. The first design was inspired by the rose petal shaped structure, and the second design was motivated by cauliflower shape. The resonating ring structure is supported by inner springs attached to a central stem. Both proposed designs have four springs supporting the ring structure surrounded by sense electrodes, with a stem in the middle offering simplicity in fabrication and easy control of movement in the driving and sensing modes. Mathematical equations were developed to calculate the stiffnesses, natural frequencies, and sensitivities of the proposed designs. These values were compared and discussed based on their applications. The parameters of key geometric elements, such as the springs and the ring dimensions of the proposed designs, were selected using finite element modeling techniques to enhance the sensitivity for gyroscope applications. The resonance frequencies for the desired mode shapes were optimized by changing the geometric parameters of the proposed structures. The simulation results showed that the resonance frequencies of the rose petal and cauliflower designs were 64.89 kHz and 248.4 kHz for the mode shape at n=2 and 87.00 kHz and 305.2 kHz for the mode shape at n=3, respectively.

The rose petal prototype was fabricated using the standard surface micromachining process in a clean room, while the cauliflower prototype was developed using a commercial silicon-based foundry process. Scaled-down prototypes of both designs were also fabricated to verify that the characteristics are independent of the sizes. The experimental results show that the resonance frequencies of rose petal and cauliflower are 64.91 kHz and 300.5 kHz, respectively, corroborating the results obtained from the computational models (rose petal - 64.89 kHz at n=2 and cauliflower – 305.2 kHz at n=3).

Good agreement between the simulation and experimental models showed the proof of concept of the design and successful fabrication process. The Cauliflower design resonator was then implemented as a vibrating gyroscope to sense the rotational motion and tested on a rotating table at different speeds. The scale factor plot of the device showed a maximum linear change in output voltage and frequency shift of ±7.310 mV and ±5.920 kHz, respectively. The sensitivity was measured as 0.02030 mV/◦/sec. These novel resonators (rose petal and cauliflower) designs with better frequency symmetry can aid in furthering MEMS inertial sensors.