ADVANCING MEMS GYROSCOPES: DESIGN, ANALYSIS AND THERMAL MANAGEMENT FOR ENHANCED FIGURE OF MERIT

Abstract

Microelectromechanical systems (MEMS) have become a cornerstone of modern sensing technologies owing to their unique combination of miniaturization, low power consumption, batch fabrication capability, and high sensitivity. This thesis presents a comprehensive investigation of MEMS-based sensors, with a particular emphasis on MEMS gyroscopes as inertial sensors for navigation, intelligent systems, and defence-related applications. The work begins with a broad overview of MEMS sensors, covering pressure, acceleration, and angular rate sensors; bolometers; magnetic sensors; humidity and flow sensors; optical sensors; biosensors; and microphones. The historical evolution of MEMS technology, its biological inspiration, fabrication techniques, and material considerations are discussed in detail. In addition, the emerging role of MEMS in quantum technologies is explored, highlighting their increasing use in quantum sensing, communication, and atomic-scale devices. Building on this foundation, the thesis focuses on MEMS gyroscopes operating on the Coriolis principle and develops a detailed theoretical framework to describe their dynamic behaviour and performance. Key performance parameters, including sensitivity, bandwidth, noise, and quality factor, are systematically analysed. Rather than optimizing these parameters individually, the work emphasizes the importance of maximizing an integrated performance measure. To this end, a unified design methodology is proposed to enhance an amended Figure of Merit (FOM) that simultaneously accounts for sensitivity, bandwidth, and noise. Analytical vi models are validated using CoventorWare and MATLAB/Simulink simulations, demonstrating close agreement with theoretical predictions within 5%. Under identical operating conditions, the optimized thick sense mass configuration achieves a 52-fold improvement in FOM, expressed in units of m Hz/dps²·mm². Furthermore, a new empirical relationship between sensitivity and bandwidth is proposed, offering additional insight into design trade-offs. The effect of temperature on thermomechanical noise is also incorporated to improve the realism of performance prediction. To further enhance miniaturization without sacrificing performance, a novel Vertical Sense Mass (VSM) MEMS gyroscope architecture is introduced. The proposed VSM design employs deep reactive ion etching (DRIE) to realize thick proof masses in the out-of-plane direction. This approach enables a 30% reduction in sense mass area and a corresponding 36% reduction in overall sensor footprint compared to conventional planar sense mass designs. Despite this reduction in size, the VSM architecture delivers a substantial performance enhancement, with the overall Performance Metric (PM) increasing from 70.7 mHz/dps²·µm² for the planar design to 1090 mHz/dps²·µm² for the VSM design. Detailed fabrication process flows are presented, and the successful experimental realization of thick proof mass structures using DRIE confirms the practical feasibility of the proposed architecture. Recognizing damping as a fundamental limitation in miniaturized MEMS gyroscopes, this thesis presents a comprehensive comparative analysis of energy dissipation mechanisms in both PSM and VSM architectures under identical sense mass areas. The study systematically examines air damping, thermoelastic damping, material damping, anchor loss, viscous damping, and acoustic damping. The results indicate that residual air damping remains a dominant loss mechanism even under vacuum packaging. While the overall trends of individual damping mechanisms are similar for both architectures, the net quality factor (QTotal) of the VSM design is approximately eight times higher than that of the planar design. Temperature dependent analysis further shows that the VSM architecture maintains a 2.7-times higher quality factor across the operating temperature range. In addition, the VSM design exhibits higher sense displacement up to a quality factor of 100, approximately 20 times the bandwidth across all Q values, and a noise reduction factor of 3.3 compared to the planar counterpart. Sensitivity analysis accounting for fabrication imperfections reveals a maximum variation in QTotal of ±12.8%, indicating acceptable robustness. The proposed VSM design is further vii validated through comparison with state-of-the-art reported designs and available experimental results. Finally, the thesis addresses thermal robustness, a major challenge that affects the reliability and accuracy of MEMS gyroscopes in real-world operating environments. A novel packaging level thermal management strategy is proposed through the integration of a thermally optimized substrate that establishes a controlled temperature offset between the sensor and the package base. When combined with a thermally engineered structural design that minimizes heat flow into the sense mass, this approach achieves a device temperature reduction of approximately 25 °C, as confirmed by transient thermal analysis. The improved thermal isolation leads to significant reductions in temperature-dependent variations of sense deflection and scale factor. Specifically, sense deflection variation is reduced from 2.7 × 10⁻⁶ µm/°C to 8.6 × 10⁻⁸ µm/°C, while scale factor temperature sensitivity decreases from 232 ppm/°C to 6 ppm/°C. Additional improvements are observed in noise reduction and bandwidth stabilization. Stress analysis confirms enhanced structural integrity, and etching experiments validate the feasibility of the thermally optimized substrate. Overall, this thesis presents a holistic, fabrication-aware, and quantitatively validated approach to MEMS gyroscope development, integrating architectural innovation, performance optimization, damping mitigation, and thermal management. The outcomes of this work significantly advance the state of MEMS gyroscope technology and provide robust design guidelines for the development of compact, high-performance, and thermally stable inertial sensors suitable for next-generation navigation, autonomous, and defence systems.