Fabrication, Testing and Characterization of MEMS Gyroscope

This thesis presents the design, fabrication and characterization of two Micro-Electro-Mechanical Systems (MEMS) vibratory gyroscopes fabricated using the Silicon-On-Insulator-Multi-User-MEMS Process (SOIMUMPs) and Polysilicon Multi-User-MEMS-Process (Poly-MUMPs). Firstly, relevant literature and background on static and dynamic analysis of MEMS gyroscopes are described. Secondly, the gyroscope analytical model is presented and numerically solved using Mathematica software. The lumped mass model was used to analytically design the gyroscope and predict their performance. Finite element analysis was carried out on the gyroscopes to verify the proposed designs. Thirdly, gyroscope fabrication using MEMSCAP's SOIMUMPs and PolyMUMPs processes is described. For the former, post-processing was carried out at the Quantum Nanofab Center (QNC) on a die-level in order to create the vibratory structural elements (cantilever beam). Following this, the PolyMUMPs gyroscopes are characterized optically by measuring their resonance frequencies and quality factor using a Laser Doppler Vibrometer (LDV). The drive resonance frequency was measured at 40 kHz and the quality factor as Q = 1. For the sense mode, the resonance frequency was measured at 55 kHz and the unity quality factor as Q = 1. The characterization results show large drive direction motions of 100 um/s in response to a voltage pulse of 10 V. The drive pull-in voltage was measured at 19 V. Finally, the ratio of the measured drive to sense mode velocities in response to a voltage pulse of 10 V was calculated at 1.375

Design, Fabrication and Characterization of MEMS Gyroscopes Based on Frequency Modulation

Conventional amplitude modulated (AM) open loop MEMS gyroscopes experience a significant performance trade-off between having a large bandwidth or high sensitivity. It is impossible to improve both metrics at the same time without increasing the mass of the gyroscope or introducing a closed loop (force feedback) system into the device design. Introducing a closed loop system or increasing the proof mass on the other hand will surge power consumption. Consequently, it is difficult to maintain consistently high performance while scaling down the device size. Furthermore, bias stability, bias repeatability, reliability, nonlinearity and other performance metrics remain primary concerns as designers look to expand MEMS gyroscopes into areas like space, military and navigation applications. Industries and academics carried out extensive research to address these limitations in conventional AM MEMS gyroscope design. This research primarily aims to improve MEMS gyroscope performance by integrating a frequency modulated (FM) readout system into the design using a cantilever beam and microplate design. The FM resonance sensing approach has been demonstrated to provide better performance than the traditional AM sensing method in similar applications (e.g., Atomic Force Microscope). The cantilever beam MEMS gyroscope is specifically designed to minimize error sources that corrupt the Coriolis signal such as operating temperature, vibration and packaging stress. Operating temperature imposes enormous challenges to gyroscope design, introducing a thermal noise and drift that degrades device performance. The cantilever beam mass gyroscope system is free on one side and can therefore minimize noise caused by both thermal effects and packaging stress. The cantilever beam design is also robust to vibrations (it can reject vibrations by sensing the orthogonally arranged secondary gyroscope) and minimizes cross-axis sensitivity. By alleviating the negative impacts of operating environment in MEMS gyroscope design, reliable, robust and high-performance angular rate measurements can be realized, leading to a wide range of applications including dynamic vehicle control, navigation/guidance systems, and IOT applications. The FM sensing approach was also investigated using a traditional crab-leg design. Tested under the same conditions, the crab-leg design provided a direct point of comparison for assessing the performance of the cantilever beam gyroscope. To verify the feasibility of the FM detection method, these gyroscopes were fabricated using commercially available MIDIS™ process (Teledyne Dalsa Inc.), which provides 2 μm capacitive gaps and 30 μm structural layer thickness. The process employs 12 masks and hermetically sealed (10mTorr) packaging to ensure a higher quality factor. The cantilever beam gyroscope is designed such that the driving and sensing mode resonant frequency is 40.8 KHz with 0.01% mismatch. Experimental results demonstrated that the natural frequency of the first two modes shift linearly with the angular speed and demonstrate high transducer sensitivity. Both the cantilever beam and crab-leg gyroscopes showed a linear dynamic range up to 1500 deg/s, which was limited by the experimental test setup. However, we also noted that the cantilever beam design has several advantages over traditional crab-leg devices, including simpler dynamics and control, bias stability and bias repeatability. Furthermore, the single-port sensing method implemented in this research improves the electronic performance and therefore enhances sensitivity by eliminating the need to measure vibrations via a secondary mode. The single-port detection mechanism could also simplify the IC architecture. Rate table characterization at both high (110 oC) and low (22 oC) temperatures showed minimal changes in sensitivity performance even in the absence of temperature compensation mechanism and active control, verifying the improved robustness of the design concept. Due to significant die area reduction, the cantilever design can feasibly address high-volume consumer market demand for low cost, and high-volume production using a silicon wafer for the structural part. The results of this work introduce and demonstrate a new paradigm in MEMS gyroscope design, where thermal and vibration rejection capability is achieved solely by the mechanical system, negating the need for active control and compensation strategies

High-Q Fused Silica Micro-Shell Resonators for Navigation-Grade MEMS Gyroscopes

This research aims to develop the resonator for a navigation-grade microelectromechanical system (MEMS) Coriolis vibratory gyroscope (CVG) that will bring inertial navigation capabilities to a wider range of applications by reducing gyroscope size and cost. To achieve the desired gyroscope performance, the gyroscope resonator must have low energy dissipation and a highly symmetric structure. Several challenges arise at the micro-scale due to the increased sensitivity to imperfections and increased susceptibility to energy loss mechanisms. This work investigates the lower limit on energy dissipation in a micro-shell resonator known as the birdbath (BB) resonator. The BB resonator is designed to mitigate the energy loss mechanisms that commonly limit MEMS resonators, including anchor loss and thermoelastic dissipation, through a unique shape and fabrication process and through the use of fused silica as the structural material. A blowtorch molding process is used to form high aspect ratio fused silica shells with a range of wall profiles, providing a high level of control in three dimensions that is not possible with conventional micromachining techniques. Prototype BB resonators were developed prior to this dissertation work but they achieved low quality factors (Q) and low ring-down time constants (T) on the order of 100 thousand and 1 s, respectively. The goal of this work is to drastically increase performance above these initial results. Each relevant energy loss mechanism is considered in order to identify the dominant loss mechanism for a given device. Process improvements are implemented to mitigate each loss mechanism, including improved thermal management during blowtorch molding, cleaner lapping and polishing, reduced upfront surface contamination, and methods to remove contaminants after fabrication. Following optimization, Qs up to 10 million and Ts up to 500 s are measured, representing a marked improvement over the prototype resonators. It is found that BB resonators are now limited by surface loss, as indicated by the observed inverse relationship between Q and surface-to-volume ratio. The surface-loss-limited regime results in a high sensitivity to added surface layers. The addition of a conductive layer to enable electrostatic transduction is found to have a large impact, decreasing Q by 50% with the addition of only 30 angstroms of metal. It is suggested that the origin of this loss may be interfacial slippage due to a large increase in stress that occurs at the interface during oscillation. Experimental investigation into the dependence of Q on conductive layer composition, thickness, deposition conditions, and post-deposition treatments is carried out. Following treatments to removed adsorbed contaminants from the surface, resonators with a 15/50 angstrom Ti/Pt layer are found to maintain 60% of their initial Qs. Indium tin oxide (ITO) is identified as a promising conductive layer candidate, with initial experiments producing shells that maintain 70% of their initial Q. The values of Q and T produced in this work are unprecedented for MEMS resonators. Even accounting for the losses that accompany conductive layer deposition, birdbath resonator gyroscopes are expected to achieve navigation-grade performance.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/146096/1/taln_1.pd

Micro-Resonators: The Quest for Superior Performance

Microelectromechanical resonators are no longer solely a subject of research in university and government labs; they have found a variety of applications at industrial scale, where their market is predicted to grow steadily. Nevertheless, many barriers to enhance their performance and further spread their application remain to be overcome. In this Special Issue, we will focus our attention to some of the persistent challenges of micro-/nano-resonators such as nonlinearity, temperature stability, acceleration sensitivity, limits of quality factor, and failure modes that require a more in-depth understanding of the physics of vibration at small scale. The goal is to seek innovative solutions that take advantage of unique material properties and original designs to push the performance of micro-resonators beyond what is conventionally achievable. Contributions from academia discussing less-known characteristics of micro-resonators and from industry depicting the challenges of large-scale implementation of resonators are encouraged with the hopes of further stimulating the growth of this field, which is rich with fascinating physics and challenging problems

Development of an integrated robotic polishing system

This thesis presents research carried out as part of a project undertaken in fulfilment of the requirements of Loughborough University for the award of Philosophical Doctorate. The main focus of this research is to investigate and develop an appropriate level of automation to the existing manual finishing operations of small metallic components to achieve required surface quality and to remove superficial defects. In the manufacturing industries, polishing processes play a vital role in the development of high precision products, to give a desired surface finish, remove defects, break sharp edges, extend the working life cycle, and meet mechanical specification. The polishing operation is generally done at the final stage of the manufacturing process and can represent up to a third of the production time. Despite the growth automated technology in industry, polishing processes are still mainly carried out manually, due to the complexity and constraints of the process. Manual polishing involves a highly qualified worker polishing the workpiece by hand. These processes are very labour intensive, highly skill dependent, costly, error-prone, environmentally hazardous due to abrasive dust, and - in some cases - inefficient with long process times. In addition, the quality of the finishing is dependent on the training, experience, fatigue, physical ability, and expertise of the operator. Therefore, industries are seeking alternative solutions to be implemented within their current processes. These solutions are mainly aimed at replacing the human operator to improve the health and safety of their workforce and improve their competitiveness. Some automated solutions have already been proposed to assist or replace manual polishing processes. These solutions provide limited capabilities for specific processes or components, and a lack of flexibility and dexterity. One of the reasons for their lack of success is identified as neglecting the study and implementing the manual operations. This research initially hypothesised that for an effective development, an automated polishing system should be designed based on the manual polishing operations. Therefore, a successful implementation of an automated polishing system requires a thorough understanding of the polishing process and their operational parameters. This study began by collaborating with an industrial polishing company. The research was focused on polishing complex small components, similar to the parts typically used in the aerospace industry. The high level business processes of the polishing company were capture through several visits to the site. The low level operational parameters and the understanding of the manual operations were also captured through development of a devices that was used by the expert operators. A number of sensors were embedded to the device to facilitate recording the manual operations. For instance, the device captured the force applied by the operator (avg. 10 N) and the cycle time (e.g. 1 pass every 5 sec.). The capture data was then interpreted to manual techniques and polishing approaches that were used in developing a proof-of-concept Integrated Robotic Polishing System (IRPS). The IRPS was tested successfully through several laboratory based experiments by expert operators. The experiment results proved the capability of the proposed system in polishing a variety of part profiles, without pre-existing geometrical information about the parts. One of the main contributions made by this research is to propose a novel approach for automated polishing operations. The development of an integrated robotic polishing system, based on the research findings, uses a set of smart sensors and a force-position-by-increment control algorithm, and transpose the way that skilled workers carry out polishing processes

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

Design and fabrication of novel microfluidic systems for microsphere generation

In this thesis, a study of the rational design and fabrication of microfluidic systems for microsphere generation is presented. The required function of microfluidic systems is to produce microspheres with the following attributes: (i) the microsphere size being around one micron or less, (ii) the size uniformity (in particular coefficient of variation (CV)) being less than 5%, and (iii) the size range being adjustable as widely as possible. Micro-electro-mechanical system (MEMS) technology, largely referring to various micro-fabrication techniques in the context of this thesis, has been applied for decades to develop microfluidic systems that can fulfill the foregoing required function of microsphere generation; however, this goal has yet to be achieved. To change this situation was a motivation of the study presented in this thesis. The philosophy behind this study stands on combining an effective design theory and methodology called Axiomatic Design Theory (ADT) with advanced micro-fabrication techniques for the microfluidic systems development. Both theoretical developments and experimental validations were carried out in this study. Consequently, the study has led to the following conclusions: (i) Existing micro-fluidic systems are coupled designs according to ADT, which is responsible for a limited achievement of the required function; (ii) Existing micro-fabrication techniques, especially for pattern transfer, have difficulty in producing a typical feature of micro-fluidic systems - that is, a large overall size (~ mm) of the device but a small channel size (~nm); and (iii) Contemporary micro-fabrication techniques to the silicon-based microfluidic system may have reached a size limit for microspheres, i.e., ~1 micron. Through this study, the following contributions to the field of the microfluidic system technology have been made: (i) Producing three rational designs of microfluidic systems, device 1 (perforated silicon membrane), device 2 (integration of hydrodynamic flow focusing and crossflow principles), and device 3 (liquid chopper using a piezoelectric actuator), with each having a distinct advantage over the others and together having achieved the requirements, size uniformity (CV ≤ 5%) and size controllability (1-186 µm); (ii) Proposing a new pattern transfer technique which combines a photolithography process with a direct writing lithography process (e.g., focused ion beam process); (iii) Proposing a decoupled design principle for micro-fluidic systems, which is effective in improving microfluidic systems for microsphere generation and is likely applicable to microfluidic systems for other applications; and (iv) Developing the mathematical models for the foregoing three devices, which can be used to further optimize the design and the microsphere generation process

Mikro-Nano-Integration für metallische Mikrosysteme mit vertikal integrierten Federelementen

Mikro-Nano-Integration (MNI) ist ein skalenübergreifender Ansatz, um Nanomaterialien in Mikrosystemen zur Anwendung zu bringen. Die Nanotechnologie bietet vielfältige, vollständig neuartige Effekte sowie wesentlich verstärkt auftretende Effekte und stellt so eine Bereicherung für die Funktionalität von Mikrosystemen dar. Gleichzeitig liefert die Mikrotechnik eine sehr gezielte Anbindung der Nanomaterialien an die Systemtechnik, sodass sich aus geringen Mengen Nanomaterial große Effekte im MNI-System erzielen lassen. Daher ist zu erwarten, dass der Einsatz von Nanomaterialien in Mikrosystemen zukünftig stark anwachsen wird. Das Anwendungsspektrum der MNI-Systeme erstreckt sich bereits heute von einem sehr starken Sektor der Mikrosensorik, über Mikroaktorik, Mikroelektronik und Optik bis hin zu Chemie, Energie und biotechnischen Systemen. Eine umfangreiche Analyse zum Stand der Technik und zum Stand der Standardisierung verdeutlicht die Relevanz des Themenfelds. Die Technologie zur Integration von Nanomaterialien weist eine Reihe an Herausforderungen auf, da die Integrationsschritte erheblichen Einfluss auf die Nanomaterialeigenschaften haben. In dieser Arbeit werden Verfahren zur Vor-Ort-Synthese hochgeordneter 1-D Nanomaterialien betrachtet, insbesondere galvanisch abgeschiedener metallischer Nanodrähte. Sind diese Nanodrähte senkrecht stehend auf einem Trägersubstrat verankert, können sie als einseitig eingespannte Biegestäbe betrachtet und in alle lateralen Richtungen flexibel federnd gebogen werden. Diese Eigenschaft macht sich der hier untersuchte Ansatz zum Aufbau eines Inertialsensors zunutze. Fixiert man eine Inertialmasse am freien Ende des Biegestabs, ist diese in erster Näherung mit zwei lateralen translatorischen und zwei lateralen rotatorischen Freiheitsgraden aufgehängt. Somit lässt sich mit einer einzigen Inertialmasse die Beschleunigung in zwei lateralen Raumrichtungen bzw. die Drehrate aus der Ebene hinaus in Richtung der Biegestab-Hauptachse messen. Die Besonderheit dieses Ansatzes liegt in den geringen Abmessungen sowie der Skalierbarkeit des Konzepts. Im Gegensatz zum Stand der Technik bei Silizium-Inertialsensoren wird für Federelement und Masseelement deutlich weniger Chipfläche benötigt. Die Arbeit beschreibt die statische und dynamische Auslegung des Beschleunigungs- und des Drehratensensors einschließlich Stabilitätsbetrachtung des Biegestabs, der Übertragungsfunktionen und der Dimensionierung von der Mikroaktorik. Ein weiterer Schwerpunkt liegt auf der Fertigung des Technologie-Demonstrators basierend auf den Verfahren UV-Lithographie mit anschließender Galvanoformung (UV LIGA) und Röntgen-Synchrotron-Lithographie mit anschließender Galvanoformung (Röntgen LIGA). Diese ermöglichen die Fertigung senkrecht stehender dünner Stäbe aus Metall, die als Federelemente dienen, in direkter Umgebung von Metallquadern, die als Inertialmassen fungieren. Mit Hilfe tiefenlithographischer Verfahren auf Basis von UV-Strahlung bzw. von Röntgen-Synchrotron-Strahlung lassen sich Photoresiste so mikrostrukturieren, dass Öffnungen mit Länge-zu-Durchmesser-Verhältnissen (Aspektverhältnissen) von bis zu 14,5 für UV-Strahlung und von bis zu 70 für Röntgen-Synchrotron-Strahlung entstehen. Die Kombination von Lithographieschritten in mehreren aufeinander folgenden Ebenen mit Metallabscheideschritten erlaubt die Vor-Ort-Synthese der Inertialsensor-Funktionselemente. Im Rahmen dieser Arbeit entstehen so Technologie-Demonstatoren für einachsige, differentiell kapazitiv auswertbaren Beschleunigungssensoren mit Federelementen und Inertialmassen aus galvanisch abgeschiedenem Kupfer. Ihr Aufbau zu Sensor-Demonstratoren mündet in der Charakterisierung des statischen und dynamischen Übertragungsverhaltens. Der Übertragungsfaktor eines Sensor-Demonstrators beträgt 26,46 fF/g. Die Durchmesser der als Federelemente eingesetzten Stäbe lassen sich entsprechend der Auslegung gezielt zwischen 1,5 µm und 75 µm bei Längen zwischen 94 µm und 409 µm einstellen. Die Skalierbarkeit des Konzepts stellt jedoch in Aussicht, auch Submikro- und Nanodrähte mit Durchmessern kleiner als 1 µm einzusetzen. Diese Arbeit stellt den internationalen Stand der Technik zur Mikro-Nano-Integration in einem neuen Umfang dar. Beispielhaft geht sie intensiv auf die Auslegung eines Multi-Inertialsensor-Technologie-Demonstrators mit nur einer Probemasse und nur einem Federelement ein und stellt so einen wegweisenden Ansatz für neuartige hochminiaturisierte Inertialsensoren vor. Auf technologischer Ebene geht die Arbeit auf neuartige Ansätze zur Optimierung der galvanischen Multiskalenfertigung ein und gibt detaillierte Parameter zur Reproduktion der gesamten Prozesskette an. Erstmals wird die Funktion eines Inertialsensors mit nur einem vor Ort synthetisierten Biegestab aus Metall als Federelement experimentell nachgewiesen