<p> Lithium niobate is an important photonic material that has potential applications in MEMS. Unfortunately, it is difficult to process using conventional methods. This thesis is an exploratory study to determine the viability of using a femtosecond laser as a fabrication tool for lithium niobate. Unexpectedly, a rich range of behaviour, likely arising from the complex material structure and composition, was discovered. Depending on the processing conditions, it was demonstrated that machining can either result in deep, high-aspect ratio grooves with minimal surrounding damage or dramatic modification of the lithium niobate to great depths with very little material removal.</p> <p> When machining grooves, increasing the effective number of pulses Neff (i.e. decreasing cutting speed) gave rapidly increasing ablation depths until a threshold was reached, after which the grooves were nearly filled with amorphous material. The depth of these amorphous channels rapidly saturates and becomes nearly independent of Neff. The ablation depth dependence on fluence showed gentle and strong ablation regimes. The amorphous channel depth depended almost linearly on fluence. Subsequent laser passes over amorphous channels eventually removed the amorphous material from the groove, indicating a dependence on the time between laser pulses. Crystal orientation was not a factor.</p> <p> The results are understood in terms of incubation and wave guiding. The first pulses ablate some material and incubate a channel of material below the surface. With further pulses, increasing incubation accelerates ablation. At the threshold Neff, the absorption coefficient has increased enough that the next pulse is able to melt a significant amount of material, which expands to fill the groove. It is suggested that, initially, the amorphous material is able to guide subsequent pulses to the bottom of the channel, resulting in a very slowly increasing depth with Neff. Subsequent passes cause ablation once again since compositional changes in the amorphous material have relaxed. Irradiated samples appear thermally reduced, which would create colour centres leading to increased absorption and thus incubation.</p> <p> Femtosecond lasers are indeed able to create MEMS structures. Multiple passes in the ablation regime yielded deep grooves, with laser polarization perpendicular to the groove giving the best results. Fabrication of micro-cantilevers and bridges was demonstrated.<p> / Thesis / Master of Applied Science (MASc)

An investigation into the responses of microbeams to electric actuations is presented. Attention is focused mainly on the use of microbeams in two important MEMS-based devices: capacitive microswitches and resonant microsensors. Nonlinear models are developed to simulate the behavior of the microbeams in each device. The models account for mid-plane stretching, an applied axial load, a DC electrostatic force, and, for the case of resonant sensors, an AC harmonic force. Further, a novel method that uses a reduced-order model is introduced for simulating the behavior of microbeams under a DC electrostatic force. The presented method shows attractive features, like for example, a high stability near the pull-in and a low computational cost. Thus, it can be of significant benefit to the development of MEMS design software. The static behavior of microbeams under electrostatic forces is studied using two methods. One method employs a shooting technique for solving the boundary-value problem that governs the static behavior. The second method is based on solving an algebraic system of equations obtained from the reduced-order model. Further, the eigenvalue problem describing the vibrations of a microbeam around its statically deflected position is solved using a shooting method to obtain the microbeam mode shapes and natural frequencies. The dynamic behavior of resonant microbeams is also investigated. A perturbation method, the method of multiple scales, is used to obtain two first-order nonlinear ordinary-differential equations that describe the amplitude and phase of the response and its stability. The results show that an inaccurate representation of the system nonlinearities may lead to an erroneous prediction of the nonlinear resonance frequency of a microbeam. The case of three-to-one internal resonance between the lowest two modes is treated. Finally, the reduced-order model is used to study the dynamic behavior of the electrostatically actuated microbeams. The proposed models are validated by comparing their results with experimental results available in the literature. / Master of Science

A growing industry demand for smart pressure sensors that can be quickly calibrated to compensate for sensor drift, nonlinearity effects, and hysteresis without the need for expensive equipment has led to the development of a self-calibrating pressure sensor. Pressure sensor inaccuracies are often resolved with sensor calibration, which typically requires the use of laboratory equipment that can produce a known, standard pressure to actuate the sensor. The developed MEMS-based, self-calibrating pressure sensor is a piezoresistive-type sensor with a sensing element made from a silicon on insulator (SOI) wafer using deep reactive-ion etching to create a hollow reference cavity. Using a micro-heater to heat the small, air-filled reference cavity of the sensing element, a standard pressure is generated to actuate the sensor's pressure-sensitive membrane, creating a self-calibration effect. Previous work focused on modeling and improving the thermal performance of the sensor identified potential solutions to extend the sensor's calibration and operating range without increasing the micro-heater's power consumption. This report focuses on using a water liquid-to-vapor phase change inside the sensor's reference cavity to increase the sensor's effective range and response time without increasing power demands. A combination of Ansys Fluent CFD modeling and benchtop experiments were used to guide the development of the two-phase, self-calibrating pressure sensor. A two-phase benchtop testing rig was built to demonstrate the anticipated effects of a liquid-to-vapor phase change in a closed domain and to provide experimental data to anchor CFD models. Due to the complexity of modeling a phase-change within a closed domain with Ansys Fluent R21.1, the CFD modeling was performed in two stages. First, the two-phase benchtop rig was modeled, and validated using benchtop test data to verify the Volume of Fluid multiphase model setup in Ansys Fluent. Then, a 2D Ansys Fluent model of the self-calibrating pressure sensor's reference cavity using the validated multiphase model was made, demonstrating the potential temperature, pressure, and density gradients inside the reference cavity at steady state. Using the guidance from the benchtop testing and CFD modeling, a prototype two-phase, self-calibrating pressure sensor was fabricated with a water volume fraction of at least 0.1 in the reference cavity. Testing the prototype two-phase sensor showed that the addition of a water liquid-to-vapor phase change inside the sensor's reference cavity can nearly triple the sensor's effective range of operation and self-calibration without increasing the power consumption of the cavity micro-heater. / Master of Science / Highly sensitive pressure sensors are essential to many modern engineering applications. For a pressure sensor to be accurate and functional, it must be properly calibrated with a known, standard pressure range that overlaps with the sensor's intended operating range. Mechanical wear, material aging, and thermal effects all reduce a pressure sensor's accuracy over time, requiring recalibration which often involves expensive equipment and long downtimes. To eliminate the need for additional equipment and the removal of the pressure sensor from its use-site for calibration, the authors have developed a pressure sensor capable of self-calibration. The self-calibrating sensor uses a MEMS sensing element with an integrated micro-actuator in the form of a small heating element to create the standard pressure range necessary for calibration. Previous work focused on modeling the thermal performance of the sensor identified potential solutions to extend the sensor's calibration and operating range without increasing the micro-heater's power consumption. This report focuses on using a water liquid-to-vapor phase change inside the sensor's reference cavity to increase the sensor's effective range and response time without increasing power demands. To help guide the development of the two-phase, self-calibrating sensor, a benchtop testing rig and CFD model were used to examine the effects of heating a liquid inside of a closed domain. A 2D CFD model of the sensor's reference cavity was also used to provide insight into the expected temperature and pressure gradients inside the sensing element after heating with the micro-actuator. Using the guidance from the CFD models, a prototype two-phase, self-calibrating pressure sensor was fabricated. Testing the prototype two-phase sensor showed that the addition of a water liquid-to-vapor phase change inside the sensor's reference cavity can nearly triple the sensor's effective range of operation and self-calibration without increasing the power consumption of the cavity micro-heater.

This work addresses issues in energy harvesting that have plagued the potential use of harvesting through the piezoelectric effect at the MEMS scale. Effective energy harvesting devices typically consist of a cantilever beam substrate coated with a thin layer of piezoceramic material and fixed with a tip mass tuned to resonant at the dominant frequency of the ambient vibration. The fundamental natural frequency of a beam increases as its length decreases, so that at the MEMS scale the resonance condition occurs orders of magnitude higher than ambient vibration frequencies rendering the harvester ineffective. Here we study two new geometries for MEMS scale cantilever harvesters. The zigzag and spiral geometries have low fundamental frequencies which can be tuned to the ambient vibrations. The second issue in energy harvesting is the frequency sensitivity of the linear vibration harvesters. A nonlinear hybrid energy harvester is presented that has a wide frequency bandwidth and large power output. Finally, linear and nonlinear energy harvesting devices are designed for powering the cardiovascular pacemakers using the vibrations in the chest area induced by the heartbeats. The mechanical and electromechanical vibrations of the zigzag structure are analytically modeled, verified with Rayleigh's method, and validated with experiments. An analytical model of coupled bending torsional vibrations of spiral structure is presented. A novel approximation method is developed for analyzing the electromechanical vibrations of energy harvesting devices. The unified approximation method is effective for linear, nonlinear mono-stable, and nonlinear bi-stable energy harvesting. It can also be utilized for piezoelectric, electromagnetic or hybrid energy harvesters. The approximation method accurately approximates the effect of energy harvesting on vibrations of energy harvester with changes in damping ratio and excitation frequency. Experimental investigations are performed to verify the analytical model of the nonlinear hybrid energy harvester. A detailed experimental parametric study of the nonlinear hybrid design is also performed. Linear and nonlinear energy harvesting devices have been designed that can generate sufficient amounts of power from the heartbeat induced vibrations. The nonlinear devices are effective over a wide range of heart rate. / Ph. D.

This thesis investigates the design and the performance of low-power microsensors that communicate directly to a satellite or a constellation of satellites. Information is spread using pseudo noise (PN) or Barker codes. The sensors use a single circular microstrip patch element with a wide beamwidth or a miniature phased array antenna that continuously scans to access the satellite(s). The array beam is controlled with a beam-forming network (BFN), which contains 3 or 4-bit phase shifters, which can be made in micro-electro-mechanical systems (MEMS) or in monolithic microwave integrated circuits (MMIC). The antennas are designed using array simulation program called 'ARRAY' and the results are used in another simulation program called Advanced Design System (ADS) to simulate the whole sensor package that uses one of the antennas. The simulation results show that a sensor as small as 2.35 cm in diameter is able to send information with data rate of 1 kbps at bit error rate less than 10?? to low-earth orbit (LEO) satellites with a transmitted power of 27.5 microwatts (-15.6 dBm). / Master of Science

In this thesis, MEMS switches actuated using electrostatic actuation is explored. MEMS switches that are lateral switches and clamped-clamped switches are designed, fabricated, and tested in this thesis. This thesis extensively explains the process by which the MEMS Switches were designed and fabricated. In addition, it explains the changes in the switches when issues called for a modification to devices. Contact resistances were extensively studied, in this thesis. There has been a trade-off between the reliability of switches and their contact resistances. Many actions were taken to mitigate this trade-off and to allow both reliable devices with low contact resistances. The efforts to do so ranged from thermal oxidation to reduce the scalloping on the sidewalls, to modifying the dry etching recipe, to modifying the sputtering recipe, to electroplating, and many more. However, reliability of the MEMS Lateral switches was accomplished independent to the contact resistances. In addition, low contact resistances were accomplished independent to reliability. A novel approach to designing clamped-clamped MEMS switches is also showcased in this thesis. These devices experienced unique challenges compared to those faced with lateral switches. Both lateral and clamped-clamped switches are discussed in-depth in this thesis. / Master of Science

The rapid advancement in complimentary metal-oxide-semiconductor (CMOS) electronics has led to a reduction in the sizes of wireless sensor networks (WSN) and a subsequent decrease in their power requirements. To meet these power requirements for long time of operation, energy harvesters have been developed at the micro scale which can convert vibration energy into electrical energy. Recent studies have shown that for mechanical-to-electrical conversion at the mm-scale (or micro scale), piezoelectric mechanism provides the best output power density at low frequencies as compared to the other possible mechanisms for vibration energy harvesting (VEH). However, piezoelectric-based VEH presents a fundamental challenge at the micro scale since the resonance frequency of the structure increases as the dimension decreases. Electromagnetic induction is another voltage generation mechanism that has been utilized for VEH. However, the electromagnetic induction based VEH is limited by the magnet and coil size and the decrease in power density at the micro scale. Hybrid energy harvesting is a novel concept that allows for increased power response and increased optimization of the generated voltage. The work in this field is currently limited due to integration challenges at small dimensions. An effective design for low frequency piezoelectric VEH is presented in this work. A unique cantilever design called arc-based cantilever (ABC) is presented which exhibits low natural frequencies as compared to traditional cantilevers. A general out-of-plane vibration model for ABCs was developed that incorporated the effects of bending, torsion, transverse shear deformation and rotary inertia. Different configurations of micro ABCs were investigated through analytical modeling and validation experiments. ABC structures were fabricated for dual-phase energy harvesting from vibrations and magnetic fields. Next, a levitation-induced electromagnetic VEH concept based on double-repulsion configuration in the moving magnet composite was studied. Computational modeling clearly illustrated the advantages of the double-repulsion configuration over the single-repulsion and no-repulsion configurations. Based on the modeling results, an AA battery-sized harvester with the double-repulsion configuration was fabricated, experimentally characterized and demonstrated to charge a cell phone. The scaling analysis of electromagnetic energy harvesters was conducted to understand the performance across different length scales. A micro electromagnetic harvester was developed that exhibited softening nonlinear spring behavior, thus leading to the finding of nonlinear inflection in magnetically-levitated electromagnetic harvesters. The nonlinear inflection theory was developed to show its causal parameters. Lastly, a coupled harvester is presented that combines the piezoelectric and electromagnetic voltage mechanisms. The advantages of each mechanism were shown to positively contribute to the performance of hybrid harvester. The cantilever provided low stiffness, low frequency, and pure bending, while the magnetic system provided nonlinearity, broadband response, and increased strain (and thus voltage). / Ph. D.

Separation of complex gaseous mixtures using gas chromatography (GC) is an important step in analytical systems for environmental monitoring, medical diagnosis, and forensic science. Due to its high resolving power, analysis speed, and small sample size, GC, has become the premier technique for separation and analysis of volatile and semi-volatile organic compounds. Miniaturization of analytical systems has become a major trend which is mainly driven by advancements in microfabrication techniques and a need for portable lab-on-a-chip systems for onsite monitoring. Microfabricated columns have been explored for applications in analytical processes like GC in several research studies. These microGC columns typically have open rectangular or open circular cross sections which is a result of the etching process utilized in the fabrication. This work reports the fabrication and performance of a new generation of silicon-on-glass micro-electro-mechanical systems (MEMS) based GC columns with microposts namely "semi-packed." These columns can be fabricated on a 2 cm2-die for a 1 m-long channel or a 1 cm2-die for a 25 cm-long channel. The semi-packed columns have a higher sample capacity as the overall surface area is larger than that of open rectangular columns of the same dimensions. The separation efficiency of these columns is also superior to that of open columns due to the presence of the microposts. As compared to conventional packed columns, the semi-packed columns show lower pressure drops and a more uniform flow profile, both of which contribute to, performance in terms of separation efficiency. / Master of Science

Advances in micro-electro-mechanical-systems (MEMS) along with nanotechnology based methods have enabled the miniaturization of analytical chemistry instrumentation. The broader aim is to provide a portable, low-cost, and low-power platform for the real-time detection and identification of organic compounds in a wide variety of applications. A benchtop gas chromatography (GC) system is considered a gold standard for chemical analysis by analytical chemists. Similarly, miniaturization of key GC components (preconcentrator, separation column, detector, and pumps) using micro- and nanotechnology based techniques is an on-going research field. This dissertation specifically deals with the design, fabrication, coating, and chromatographic testing of microfabricated separation columns for GC. This work can be broadly categorized into three research areas: design and development of new column designs, introduction of new stationary phases and the development of novel fabrication methodologies for integrating functionalized thin-film into microchannels for chromatographic separations. As a part of this research, two high performance new micro column designs namely width-modulated and high-density semi-packed columns are introduced for the first time. Similarly, two new types of functionalized stationary phases are also demonstrated i.e. a highly stable and homogenous silica nanoparticles coating deposited using a layer-by-layer self-assembly scheme and a highly conformal functionalized thin aluminum oxide film deposited using atomic layer deposition. Moreover, novel thin-film patterning methods using different microfabrication technologies are also demonstrated for high-aspect ratio multicapillary and semi-packed columns. / Ph. D.

MEMS devices are finding application in diverse fields that include energy harvesting, microelectronics and sensors. In energy harvesting, MEMS scale devices are employed due to its efficiencies of scale. The miniaturization of energy harvesters permit them to be integrated as the power supply for sensors often in the same package and also extends their use to remote and extreme ambient applications. Unlike inductive harvesting, piezoelectric and magnetoelectric devices lend easily to MEMS scaling. The processing of such Piezo-MEMS devices often requires special fabrication, characterization and testing techniques. Our research work has focused on the development of the various technologies for a) the better characterization of the constituent materials that make up these devices, b) the conceptualization and structural design of unique MEMS energy harvesters and finally c) the development of the unit operations (many novel) for fabrication and the mechanical and electrical testing of these devices. In this research work, we have pioneered some new approaches to the characterization of thin films utilized in Piezo-MEMS devices: (1) Temperature-Time Transformation (TTT) diagrams are used to document texture evolution during thermal treatment of ceramics. Multinomial and multivariate regression techniques were utilized to create the predictor models for TTT data of Pb(Zr0.60Ti0.40 O3) sol-gel thin films. (2) We correlated the composition (measured using Energy Dispersive X-ray analysis (EDX) and Electron Probe Micro Analysis (EPMA)) of Pb(Zr0.52Ti0.48 O3) RF sputtered thin films to its optical dispersion properties measured using Variable Angle Spectroscopic Ellipsometry (VASE). Wemple-DiDomenico, Jackson-Amer, Tauc and Urbach optical dispersion factors and Lorentz Lorenz polarizability relationships were combined to realize a model for predicting the elemental content of any thin film system. (3) We developed in house capability for strain analysis of magnetostrictive thin films using laser Doppler Vibrometry (LDV). We determined a methodology to convert the displacements measurements of AC magnetic field induced vibrations of thin film samples into magnetostriction values. (4) Finally, we report the novel use of a thermo-optic technique, Time Domain Thermoreflectance (TDTR) in the study of Pb(Zr,Ti)O3 (PZT) thin film texturing. Time Domain Thermoreflectance (TDTR) has been proved to be capable of measuring thermal properties of atomic layers and interfaces. Therefore, we utilized TDTR to analyze and model the heat transport at the nano scale and correlate with different PZT crystalline orientations. To harvest energy at the low frequency (<100Hz) of ambient vibrations, MEMS energy harvesters require special structures. Extensive research has led us to the development of Circular Zigzag structure that permits inertial mass free attainment of such low frequencies. In addition to Si micromachining, we have fabricated such structures using a new Micro water jet micromachining of thin piezo sheets, unimorphs and bimorphs. For low frequency magnetic energy harvesting, we also fabricated the first magnetoelectric macro fiber composite. This device also employs a novel low temperature metallic bonding technique to fuse the magnetostrictive layer to the piezoelectric layers. A special low viscosity epoxy enabled the joining of the flexible circuit to the magnetoelectric fibers. Lastly, we developed a nondimensional tunable Piezo harvester, called PiezoCap, which decouples the energy harvesting component of the device from the resonant vibration component. We do so by using magnets loaded on piezo harvester strips, thereby making them piezomagnetoelastic and vary the spacing between 2 magnet+piezoelectric pairs to eliminate dimensionality and permit active tunability of the harvester's resonant frequency. / Ph. D.