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<p>This thesis presents investigations on ultrafast laser irradiation of silicon towards the goal of hybridizing ultrafast laser processing and conventional semiconductor fabrication techniques to improve device applications. The fundamental sub-threshold damage accumulation mechanisms for potential defect engineering applications were studied through the use of positron annihilation spectroscopy, in situ sample heating during laser irradiation, varying the laser repetition rate, and samples implanted with various ion species at different conditions. Positron annihilation spectroscopy results suggest an increase in the divacancy density at the surface region of silicon following near- and slightly sub-threshold ultrafast laser irradiations. Laser irradiations at increasing sample temperature up to 600°C show a general decreasing trend of single-shot thresholds, and an increase in the suppression of sub-threshold damage accumulation. There is also a temperature dependence on the surface morphology resulting from ultrafast laser irradiation. Ion implantation modified the ablation threshold fluence, and a dependence on the ion implantation conditions was observed. Surface microstructuring of silicon was shown to improve absorption of light with a sub-bandgap wavelength of 1550 nm. An initial attempt with sulfur implantation did not exhibit further improvement in the optical absorption, and first attempts in device fabrication did not provide photoresponsivity at sub-bandgap wavelengths. Ultrafast laser irradiation of SiO₂-on-Si structures yielded different modification thresholds for different thicknesses of the oxide layer. Surface morphologies obtained in the irradiation of these structures can affect potential applications. Selected studies of ultrafast laser irradiation of GaP, metal-SiO₂-Si structures, quartz, diamond, and porcine bone demonstrated similarities in ablation behavior and morphologies, and the potential for a broad range of applications. The results in combination with the proposed future work in this thesis can contribute to potential device applications while providing valuable insights into the ultrafast laser ablation mechanisms.</p> / Doctor of Philosophy (PhD)

<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)

This dissertation presents the exploration of two fiber optics techniques involving high power pulse laser delivery. The first research topic is "Embedded Active Fiber Optic Sensing Network for Structural Health Monitoring in Harsh Environments", which uses the fiber delivered pulse laser for acoustic generation. The second research topic is "Fiber Optics Guided Laser Micromachining", which uses the fiber delivered pulse laser for material ablation. The objective of the first research topic is to develop a first-of-a-kind technology for remote fiber optic generation and detection of acoustic waves for structural health monitoring in harsh environments. Three different acoustic generation mechanisms were studied in detail, including laser induced plasma breakdown (LIB), Erbium-doped fiber laser absorption, and metal laser absorption. By comparing the performance of the acoustic generation units built based on these three mechanisms, the metal laser absorption method was selected to build a complete fiber optic structure health monitoring (FO-SHM) system. Based on the simulation results of elastic wave propagation and fiber Bragg grating acoustic pulse detection, an FO-SHM sensing system was designed and built. This system was first tested on an aluminum piece in the room temperature range and successfully demonstrated its capability of multi-parameter monitoring and multi-point sensing. With additional studies, the upgraded FO-SHM element was successfully demonstrated at high temperatures up to 600oC on P-91 high temperature steels. During the studies of high power pulse laser delivery, it was discovered that with proper laser-to-fiber coupling, the output laser from a multimode fiber can directly ablate materials around the fiber tip. Therefore, it is possible to use a fiber-guided laser beam instead of free space laser beams for micromachining, and this solves the aspect ratio limitation rooted in a traditional laser beam micromachining method. In this dissertation, this Guided Laser MicroMachining (GLMM) concept was developed and experimentally demonstrated by applying it to high aspect ratio micro-drilling. It was achieved that an aspect ratio of 40 on aluminum and an aspect ratio of 100 on PET, with a hole diameter less than 200 um. / PHD / This dissertation presents two research topics both related to high power laser and fiber optic. The first topic studies the application of using optical fiber and high power laser for ultrasonic non-destructive evaluation. The general idea is to use fiber optic to remotely generate and monitor ultrasonic waves on a workpiece. Due to the fact that there are no electronic components involved in the sensing part of the system, this system can work at high temperature and is unsusceptible to EMI. The second topic studies the usage of optical fiber in high aspect ratio micromachining. The key concept is to use a fiber tip and the output high power laser as a "drilling tip", which eliminate the aspect ratio limitation rooted in the traditional free-space laser micromachining method. With this concept and a demonstrative micromachining system, we achieved record-breaking aspect ratio on both aluminum and plastic.

This dissertation presents an investigation of miniaturized magnetic induction and permanent magnet (PM) machines, intended for use in a microengine. Similar to a macroscale turbogenerator, a microengine comprises a small, gas-fueled turbine engine for converting chemical fuel energy into mechanical power and an integrated electrical generator for converting mechanical power to electrical power. The microengine system is proposed as a revolutionary, high power-density source for portable electronics. In this research, miniaturized magnetic induction machines and PM machines were designed, fabricated, and characterized. Both types of machines used axially directed magnetic fields and were nominally 10 mm in diameter and 1.5-2.3 mm in thickness. Innovative microfabrication techniques were developed to demonstrate the feasibility of integrating magnetic machines within a bulk-micromachined, silicon-based microengine system. Two-phase, eight-pole induction machines were constructed within silicon substrates using Cu coils in a laminated, slotted ferromagnetic NiFe or CoFeNi stator core. Silicon etching, wafer bonding, and electrodeposition were used to form all of the magnetic machine components. The induction machines were characterized in motoring mode using tethered rotors and demonstrated motoring torques of up to 2.5 uN-m. Also, three-phase, eight-pole, surface wound PM machines were built using a hybrid microfabrication/assembly approach. The stators were fabricated by electroplating Cu coils on ferromagnetic NiFeMo (Moly Permalloy) substrates. The rotors were formed by assembling a magnetically patterned SmCo PM with a FeCoV (Hiperco 50) back iron. The PM machines were tested as generators with free-spinning rotors, powered by an air-driven spindle, and demonstrated 2.6 W of mechanical-to-electrical power conversion with continuous DC power generation of 1.1 W at 120 krpm rotor speed. The primary contributions of this work are (1) the demonstration of microfabricated magnetic machines integrated within bulk-micromachined silicon and (2) the demonstration of multi-watt power conversion from a microfabricated PM generator. These achievements represent progress in the ongoing development of silicon-based microengines, but in addition, the fabrication technologies and device structures may find application in other microsystems.

This dissertation deals with the development of RF MEMS switches with novel materials and micromachining techniques for the RF and microwave applications. To enable the integration of RF and microwave components on CMOS grade silicon, finite ground coplanar waveguide transmission line on CMOS grade silicon wafer were first studied using micromachining techniques. In addition, several RF MEMS capacitive switches were developed with novel materials. A novel approach for fabricating low cost capacitive RF MEMS switches using directly photo-definable high dielectric constant metal oxides was developed, these switches exhibited significantly higher isolation and load capacitances as compared to comparable switches fabricated using a simple silicon nitride dielectric. The second RF MEMS switch developed is on a low cost, flexible liquid crystal polymer (LCP) substrate. Its very low water absorption (0.04%), low dielectric loss and multi-layer circuit capability make it very appealing for RF Systems-On-a-Package (SOP). Also, a tunable RF MEMS switch on a sapphire substrate with BST as dielectric material was developed, the BST has a very high dielectric constant (>300) making it very appealing for RF MEMS capacitive switches. The tunable dielectric constant of BST provides a possibility of making linearly tunable MEMS capacitor-switches. For the first time a capacitive tunable RF MEMS switch with a BST dielectric and its characterization and properties up to 40 GHz was presented. Dielectric charging is the main reliability issue for MEMS switch, temperature study of dielectric polarization effect of RF MEMS was investigated in this dissertation. Finally, integration of two reconfigurable RF circuits with RF MEMS switches were discussed, the first one is a reconfigurable dual frequency (14GHz and 35 GHz) antenna with double polarization using RF MEMS switches on a multi-layer LCP substrate; and the second one is a center frequency and bandwidth tunable filter with BST capacitors and RF MEMS switches on sapphire substrate.

<p>This thesis addresses assembly issues encountered in optical and fluidic microsystem applications.</p><p>In optics, the first subject concerns the active alignment of components in optical fibersystems. A solution for reducing the cost of optical component assembly while retaining submicron accuracy is to integrate the alignment mechanism onto the optical substrate. A polymer V-shaped actuator is presented that can carry the weight of the large components - on a micromechanical scale - and that can generate movement with six degrees of freedom.</p><p>The second subject in optics is the CMOS-compatible fabrication of monocrystalline silicon micromirror arrays that are intended to serve as CMOS-controlled high-quality spatial light modulators in maskless microlithography systems. A wafer-level assembly method is presented that is based on adhesive wafer bonding whereby a monocrystalline layer is transferred onto a substrate wafer in a CMOS-compatible process without needing bond alignment.</p><p>In fluidics, a hybrid assembly method is introduced that combines two separately micromachined structures to create hotwire anemometers that protrude from a surface with minimum interference with the air flow. The assembled sensor enables one to make accurate time-resolved measurements of the wall shear stress, a quantity that has previously been hard to measure with high time resolution. Also in the field of hotwire anemometers, a method using a hotwire anemometer array is presented for measuring the mass flow, temperature and composition of a gas in a duct.</p><p>In biochemistry, a bio-analysis chip is presented. Single nucleotide polymorphism scoring is performed using dynamic allele-specific hybridization (DASH). Using monolayers of beads, multiplexing based on single-bead analysis is achieved at heating rates more than 20 times faster than conventional DASH provides.</p><p>Space and material e±ciency in packaging are the focus of the other two projects in fluidics. The first introduces an assembly based on layering conductive adhesives for the fabrication of miniature polymer electrolyte membrane fuel cells. The fuel cells made with this low-cost approach perform among the best of their type to date. The second project concerns a new cross-flow microvalve concept. Intended as a step towards the mass production of large-flow I/P converters, the silicon footprint area is minimized by an out-of-plane moving gate and in-plane, half-open pneumatic channels.</p>