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Surface micromachining of micro-electro-mechanical systems (MEMS), like all other fabrication processes, has inherent variation that leads to uncertain material and dimensional parameters. To obtain accurate and reliable predictions of mechanism behavior, the effects of these variations need to be analyzed. This thesis expands already existing tolerance and uncertainty analysis methods to apply to micro compliant mechanisms. For simple compliant members, explicit equations can be used in uncertainty analysis. However, for a nonlinear implicit system of equations, the direct linearization method may be used to obtain sensitivities of output parameters to small changes in known variables. This is done by including static equilibrium equations and pseudo-rigid-body model relationships with the kinematic vector loop equations. Examples are used to show a comparison of this method to other deterministic and probabilistic methods and finite element analysis.

Proper positioning of Microelectromechanical Systems (MEMS) components influences the functionality of the device, especially in devices where the motion is in the range of hundreds of micrometers. There are two main obstacles to positioning: off-axis displacement, and position determination. This work studies four large-displacement devices, their axial and transverse stiffness, and piezoresistive response. Methods for improving the device characteristics are described. The folded-beam suspension, small X-Bob, large X-Bob and double X-Bob were characterized using non-dimensional metrics that measure the displacement with regard to the size of the device, and transverse stiffness with regard to axial stiffness. The stiffness in each direction was determined using microprobes to induce displacement, and microfabricated force gauges to determine the applied force. The large X-Bob was optimized, increasing the transverse stiffness metric by 67%. Four-point resistance testing and microprobes were used to determine the piezoresistive response of the devices. The piezoresistive response of the X-Bob was maximized using an optimization routine. The resulting piezoresistive response was over seven times larger than that of the initial design. Piezoresistive encoders for ratcheting actuation of large-displacement MEMS are introduced. Four encoders were studied and were found to provide information on the performance of the ratcheting actuation system at frequencies up to 920 Hz. The PMT encoder produced unique signals corresponding to distinct ideal and non-ideal operation of the ratchet wheel actuation system. Encoders may be useful for future applications which require position determination.

The purpose of this research is to examine the effect of iron catalyst thickness on the straightness of growth of carbon nanotube microelectromechanical systems (CNT-MEMS). One of the key benefits of CNT-MEMS is that they can potentially have very high aspect ratios. One of the challenges in attaining these high aspect ratios is maintaining device straightness; as these devices get taller, the edges tend to curve rather than grow straight vertically. Scanning electron mi- croscope images of samples grown using various iron catalyst thicknesses show that both straight growth and relatively good edge definition can be achieved using iron thicknesses between 7 and 8 nm. Below this thickness, individual CNT are well-aligned, but CNT forests are not necessarily straight. Above this thickness, the CNT forests are relatively straight, but individual CNT are not well-aligned and edge definition is very poor. Iron availability for CNT growth is also affected by a device's or feature's proximity to other regions of iron. By using an iron catalyst thickness ap- propriate for straight growth, and by adding borders of iron around features or devices, a designer can greatly improve straightness of growth for CNT-MEMS.

This work presents the modeling, design, and testing of an underwater microactuation system. It is composed of several thermomechanical in-plane microactuators (TIM) integrated with a ratchet system to provide long displacements and high forces to underwater microelectromechanical systems (MEMS). It is capable of actuating a 200µN load 110µm. It is a two-layer silicon MEMS device fabricated with a MEMS fabrication process, PolyMUMPS. This work also shows the development of an elliptic integral model to analyze the compliant fixed-guided beams in the TIM and gives new insight into the buckling behavior, reaction forces, and displacement of the beams. The derivation, verification, and practical use of the model are shown in detail. It compares the reaction force predictions from the elliptic integral model with finite element modeling results over a wide range of non-dimensional displacements and slenderness ratios. The elliptic integral model was used to design a TIM that can operate in an aqueous environment. It was designed to achieve 9µm of displacement to drive a linear ratcheting mechanism. The thermal analysis was done in ANSYS using a 3D conduction model to predict the temperature of the heated beams. The TIM was designed to operate with a peak beam temperature of 100 ° C to prevent damage to the device due to vapor bubble formation. The main actuator showed significant electrolysis due to the high voltages used to drive the system, but otherwise functioned as predicted. Through the development and testing of the actuation system, quantitative voltage limits were discovered for underwater actuation systems under which electrolysis and boiling can be eliminated using alternating current.

Nowadays, integrated circuits (IC) are mostly implemented using Complementary Metal Oxide Semiconductor (CMOS) transistor technology. This technology has allowed the chip industry to shrink transistors and thus increase the device density, circuit complexity, operation speed, and computation power of the ICs. However, in recent years, the scaling of transistor has faced multiple roadblocks, which will eventually lead the scaling to an end as it approaches physical and economic limits. The dominance of sub-threshold leakage, which slows down the scaling of threshold voltage VTH and the supply voltage VDD, has resulted in high power density on chips. Furthermore, even widely popular solutions such as parallel and multi-core computing have not been able to fully address that problem. These drawbacks have overshadowed the benefits of transistor scaling. With the dawn of Internet of Things (IoT) era, the chip industry needs adjustments towards ultra-low-power circuits and systems. In this thesis, energy-efficient Micro-/Nano-electromechanical (M/NEM) relays are introduced, their non-leaking property and abrupt switch ON/OFF characteristics are studied, and designs and applications in the implementation of ultra-low-power integrated circuits and systems are explored. The proposed designs compose of core building blocks for any functional microprocessor, for instance, fundamental logic gates; arithmetic adder circuits; sequential latch and flip-flop circuits; input/output (I/O) interface data converters, including an analog-to-digital converter (ADC), and a digital-to-analog converter (DAC); system-level power management DC-DC converters and energy management power gating scheme. Another contribution of this thesis is the study of device non-ideality and variations in terms of functionality of circuits. We have thoroughly investigated energy-efficient approximate computing with non-ideal transistors and relays for the next generation of ultra-low-power VLSI systems.

<p>Over the years, research and development of micro-force sensing techniques has gained a lot of traction, especially for microrobotic applications, such as micromanipulation and biomedical material characterization studies. Moreover, in recent years, new microfabrication techniques have been developed, such as two-photon polymerization (TPP), which enables fast prototyping, high resolution features, and the utilization of a wide range of materials. In general, the main goals of this work are to improve the resolution and range of novel vision-based force sensors, create microrobotic and micromanipulation systems capable of tackling a multitude of applications, and ensuring these systems are flexible and provide a sold foundation to the advancement of the field as a whole.</p> <p><br></p> <p>The current work can be divided into three main parts: (i) a wireless magnetic microrobot with 2D vision-based force sensing, (ii) a 3D vision-based force sensing probe for tethered micromanipulators, and (iii) a micromanipulation system capable of accurately controlling and performing advanced tasks. The vision-based force sensors developed here have resolutions ranging from the mN range to even sub-$\mu$N range, depending on the material used, geometry, and overall footprint. </p> <p><br></p> <p>In part (i), the microrobot has been developed mainly for biomedical applications \textit{in vitro}, with the ability to perform mechanical characterization and microassembly tasks of different rigid and biomedical materials. In part (ii), a similar sensor mechanic is used, but now adapted to a micromanipulation probe, which is able to detect forces in three dimensions and work in dry environments. In conjunction with the micromanipulation system described in part (iii), the system is capable of performing advanced assembly applications, including accurate assembly and 3D mounting of microparts. </p> <p><br></p> <p>With the introduction of TPP technologies to these works, the next generation of adaptable microrobotics and micromanipulation systems for advanced biomedical applications is starting to take shape, ever more versatile, smaller, more accurate, and with more advanced capabilities. This work shows the progression of these overall systems and gives a glimpse of what is possible with TPP and the technologies to come.</p>

The resonance frequency of a silicon nitride (SiN) nano-electromechanical systems (MEMS/NEMS) can be measured precisely due to their large quality factor that is associated to low thermomechanical fluctuations. While these properties enable the fabrication of high performance sensors, their use will eventually raise questions regarding their long-term stability, notably for calibration purposes. The long-term frequency stability and aging of SiN are less studied than the short-term fluctuations such as thermomechanical noise. Long-term aging studies exist for quartz clocks as well as MEMS silicon clocks and accelerometers, but not for SiN resonators with high quality factors. Thus, in this work we conduct the aging study of SiN membranes fabricated by our lab, by constantly tracking changes of the resonance frequency of the device over a long period. The evolution of the frequency drift is tracked, by optical interrogation, continuously for 135 days with a digital phase locked loop (PLL). Our device is placed in a cell under high vacuum to suppress air damping on our resonating membrane. Furthermore, due to its high sensitivity to temperature changes, our silicon nitride resonator and vacuum chamber are placed in an air bath providing a stable temperature (within 0.5 K over 135 days in the present case). To compensate further the frequency drifts induced by temperature changes, a multimeter measures the resistance of a calibrated thermistor placed inside the vacuum environment. The measured frequency drift for the aging periods of 135 days was of 300 parts per million (ppm) and was consistent with previously reported double logarithmic models for quartz oscillators. The initial stage of negative frequency drift, in our aging data, is consistent with the behaviour expected from the desorption of water due to the transition from ambient air environment to high vacuum. We review models explaining how water adsorption/desorption impacts our membrane's frequency by (1) inducing chemical reaction stresses (most important effect), (2) through the contribution of the water surface tension stress (non-negligible effect), and (3) through mass loading from water molecules (weakest effect). After this initial negative trend, the membrane frequency drift inverts and increases almost linearly, in a fashion consistent with loss of mass from desorption of other chemical species. To identify these chemical species, X-ray photoelectron spectroscopy measurements were conducted on a reference membrane stored in an ambient setting and on our membrane placed under vacuum during our aging studies. The aged membrane, compared to its reference counterpart, contained substantially less alkaline ion contaminants (i.e., sodium, calcium and potassium), most likely due to desorption of these species during the aging measurement, and to the increase in adsorption occurring on the reference membrane concurrently. We therefore hypothesize that trapped negative charges, which is a typical phenomenon within dielectric materials such as SiN, might progressively attract positive ion contaminants over time when the device is exposed to ambient air.