Inertial navigation, which may in future replace the Global Positioning System (GPS) in critical fields such as aerospace and defense, re-quires the development of high-performance gyroscopes. Currently, MicroElectroMechanical Systems (MEMS) gyroscopes are widely used in consumer applications due to their low cost, well-established fabrication process, suitability for large-scale production and integrability. Research efforts in both academia and industry are focused on improving the performance of MEMS gyroscopes to meet the requirements for inertial navigation. In this work, MEMS whole-angle gyroscopes, which measure the external rotation angle, are investigated. This type of gyroscopes offers higher measurement precision compared to devices that measure the external rotation rate, such as the Coriolis vibrating MEMS gyroscopes currently available on the market. Although whole-angle gyroscopes based on other technologies have been already developed, existing solutions are costly and bulky compared to MEMS. Nevertheless, whole-angle gyroscopes require a very high quality factor and a very high linearity, conditions that are challenging to achieve in MEMS gyroscopes. An already proposed structure, known as Dual-Foucault Pendulum (DFP) gyroscope, is redesigned in this work to meet these requirements. The device, fabricated through the THELMA® (Thick Epitaxial Layer for Micro-gyroscopes and Accelerometers) fabrication process of STMicroelectronics, is then characterized and operated as a whole-angle gyroscope, demonstrating the effectiveness of the proposed design, i.e a scale factor of 0.8, quality factor up to 300k and low nonlinearity. To explore alternative strategies to achieve very high quality factors, devices made of fused silica are also investigated. A Toroidal Ring Gyroscope (TRG) made of fused silica is designed to maximize the quality factor. A special attention is addressed to the minimization of thermoelastic losses that are dominating the quality factor. The device is subsequently fabricated through FLICE (Femtosecond Laser Induced Chemical Etching) at at University of California, Irvine and characterized, demonstrating a very high quality factor for a MEMS device, i.e a Q of approximately 1 to 1.2 M. Finally, a Single Ring Resonator (SRR), which can operate also as a gyroscope, is designed to further exploit a reliable mechanical design strategy for linear MEMS gyroscopes. The device is then fabricated and characterized at PoliFAB, the cleanroom of Politecnico di Milano, demonstrating the effectiveness of the adopted strategy for enhancing linearity, i.e. peak shift less than 10^−5% of the resonant frequency at the maximum admissible displacement. While TRG and SRR are not operated as whole-angle gyroscopes, their study provides insights into the optimization of quality factor and linearity. Future work will be addressed to the re-design of a DFP gyroscope with a higher Q and lower nonlinearities.
La navigazione inerziale, nell’ottica di sostituire il sistema di posizionamento globale (GPS) in settori critici come quello aerospaziale e quello della difesa, richiede lo sviluppo di giroscopi ad alte prestazioni. Attualmente, i giroscopi MEMS (MicroElectroMechanical Systems) sono ampiamente utilizzati in elettronica di consumo grazie al loro basso costo, al processo di fabbricazione consolidato, all’implementazione di produzione su larga scala e alla loro integrabilità. Allo stato dell’arte, sia in ambito accademico che industriale, numerose ricerche sono in corso al fine di ottenere giroscopi MEMS con prestazioni tali da permettere la navigazione inerziale. Questo lavoro si focalizza sui giroscopi MEMS whole-angle, i quali misurano direttamente l’angolo di rotazione esterno. Utilizzare giroscopi whole-angle aumenta la precisione della misura rispetto ai giroscopi che rilevano la velocità di rotazione esterna. Ad oggi, i giroscopi MEMS disponibili sul mercato fanno parte di questa seconda categoria. Solo alcuni giroscopi whole-angle, basati su tecnologie decisamente più costose ed ingombranti rispetto ai giroscopi MEMS, sono infatti commercialmente disponibili oggi. Il motivo dell’assenza dei giroscopi MEMS whole-angle sul mercato è che essi richiedendo un fattore di qualità molto elevato e una linearità altrettanto elevata, caratteristiche difficili da ottenere utilizzando tecnologia MEMS. In questo lavoro, una struttura già proposta, nota come giroscopio Dual-Foucault Pendulum (DFP), è stata riprogettata al fine di soddisfare questi requisiti. Il dispositivo, realizzato mediante il processo di fabbricazione THELMA® (Thick Epitaxial Layer for Micro-gyroscopes and Accelerometers) di STMicroelectronics, è stato poi caratterizzato ed infine utilizzato come giroscopio whole-angle, dimostrando l’efficacia del design proposto, ovvero uno scale factor di 0.8, un fattore di qualità fino a 300k ed una bassa nonlinearità. Per ottenere fattori di qualità molto elevati, diverse strategie possono essere esplorate: in questo lavoro, sono stati studiati dispositivi realizzati in silice fusa. Un Toroidal Ring Gyroscope (TRG) in silice fusa è stato progettato per massimizzare il fattore di qualità, prestando particolare attenzione alla minimizzazione delle perdite termoelastiche, che dominano il valore di Q. Il dispositivo è stato successivamente realizzato presso l’Università della California, Irvine, tramite il processo FLICE (Femtosecond Laser Induced Chemical Etching), e caratterizzato, dimostrando un fattore di qualità molto elevato per un dispositivo MEMS, ovvero Q compreso tra 1 e 1.2 M. Infine, è stato progettato un Single Ring Resonator (SRR), che può essere utilizzato anche come giroscopio, con l’obiettivo di validare ulteriormente una strategia di progettazione affidabile per giroscopi MEMS lineari. Il dispositivo è stato poi fabbricato e caratterizzato presso il PoliFAB, la cleanroom del Politecnico di Milano, dimostrando l’efficacia della strategia adottata per l’aumento della linearità, come dimostra lo spostamento della frequenza di risonanza di un valore inferiore a 10^−5% in corrispondenza del massimo spostamento possibile. Sebbene il TRG e il SRR non siano stati utilizzati in questo lavoro come giroscopi whole-angle, il loro studio fornisce indicazioni utili per l’ottimizzazione del fattore di qualità e della linearità di strutture MEMS utilizzabili come giroscopi whole-angle. I futuri sviluppi saranno orientati alla riprogettazione del giroscopio DFP con un maggiore Q e una minore nonlinearità.
Design and multi-physics simulation of innovative high-performance mems gyroscopes
Pavesi, Davide
2024/2025
Abstract
Inertial navigation, which may in future replace the Global Positioning System (GPS) in critical fields such as aerospace and defense, re-quires the development of high-performance gyroscopes. Currently, MicroElectroMechanical Systems (MEMS) gyroscopes are widely used in consumer applications due to their low cost, well-established fabrication process, suitability for large-scale production and integrability. Research efforts in both academia and industry are focused on improving the performance of MEMS gyroscopes to meet the requirements for inertial navigation. In this work, MEMS whole-angle gyroscopes, which measure the external rotation angle, are investigated. This type of gyroscopes offers higher measurement precision compared to devices that measure the external rotation rate, such as the Coriolis vibrating MEMS gyroscopes currently available on the market. Although whole-angle gyroscopes based on other technologies have been already developed, existing solutions are costly and bulky compared to MEMS. Nevertheless, whole-angle gyroscopes require a very high quality factor and a very high linearity, conditions that are challenging to achieve in MEMS gyroscopes. An already proposed structure, known as Dual-Foucault Pendulum (DFP) gyroscope, is redesigned in this work to meet these requirements. The device, fabricated through the THELMA® (Thick Epitaxial Layer for Micro-gyroscopes and Accelerometers) fabrication process of STMicroelectronics, is then characterized and operated as a whole-angle gyroscope, demonstrating the effectiveness of the proposed design, i.e a scale factor of 0.8, quality factor up to 300k and low nonlinearity. To explore alternative strategies to achieve very high quality factors, devices made of fused silica are also investigated. A Toroidal Ring Gyroscope (TRG) made of fused silica is designed to maximize the quality factor. A special attention is addressed to the minimization of thermoelastic losses that are dominating the quality factor. The device is subsequently fabricated through FLICE (Femtosecond Laser Induced Chemical Etching) at at University of California, Irvine and characterized, demonstrating a very high quality factor for a MEMS device, i.e a Q of approximately 1 to 1.2 M. Finally, a Single Ring Resonator (SRR), which can operate also as a gyroscope, is designed to further exploit a reliable mechanical design strategy for linear MEMS gyroscopes. The device is then fabricated and characterized at PoliFAB, the cleanroom of Politecnico di Milano, demonstrating the effectiveness of the adopted strategy for enhancing linearity, i.e. peak shift less than 10^−5% of the resonant frequency at the maximum admissible displacement. While TRG and SRR are not operated as whole-angle gyroscopes, their study provides insights into the optimization of quality factor and linearity. Future work will be addressed to the re-design of a DFP gyroscope with a higher Q and lower nonlinearities.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/242218