Feedback control of MEMS devices has the potential to significantly improve device performance and reliability. One of the main obstacles to its broader use is the small number of on-chip sensing options available to MEMS designers. A method of using integrated piezoresistive sensing is proposed and demonstrated as another option. Integrated piezoresistive sensing utilizes the inherent piezoresistive property of polycrystalline silicon from which many MEMS devices are fabricated. As compliant MEMS structures flex to perform their functions, their resistance changes. That resistance change can be used to transduce the structures' deflection into an electrical signal. This dissertation addresses three topics associated with integrated piezoresistive sensing: developing an empirical model describing the piezoresistive response of polycrystalline-silicon flexures, designing compliant MEMS with integrated piezoresistive sensing using the model, and implementing feedback control using integrated piezoresistive sensing. Integrated piezoresistive sensing is an effective way to produce small, reliable, accurate, and economical on-chip sensors to monitor compliant MEMS devices. A piezoresistive flexure model is presented that accurately models the piezoresistive response of long, thin flexures even under complex loading conditions. The model facilitates the design of compliant piezoresistive MEMS devices, which output an electrical signal that directly relates to the device's motion. The piezoresistive flexure model is used to design a self-sensing long displacement MEMS device. Motion is achieved through contact-aided compliant rolling elements that connect the output shaft to kinematic ground. Self-sensing is achieved though integrated piezoresistive sensing. An example device is tested that demonstrates 700 micrometers of displacement with a sensing resolution of 2 micrometers. The piezoresistive microdisplacement transducer (PMT) is a structure that uses integrated piezoresistive sensing to monitor the output displacement of a thermomechanical inplane microacutator (TIM). Using the PMT as a feedback sensor for closed-loop control of the TIM reduced the system's response time from 500~$mu$s to 190~$mu$s, while maintaining a positioning accuracy of $pm$29~nm. Feedback control of the TIM also increased its robustness and reliability by allowing the system to maintain its performance after it had been significantly damaged.

Compliant bistable micromechanisms have been proposed for use in applications such as switches, relays, shutters, and sensing arrays. Unpublished laboratory testing suggests that off-axis forces may affect the bistable nature of fully compliant bistable micromechanisms (FCBMs). The actuation forces required to snap the FCBM from one stable equilibrium position to another can be altered if the off-axis forces are applied to the mechanism during transition between stable positions. Understanding the three-dimensional characteristics of these mechanisms and the effect of eccentric loading conditions would be helpful in design and analysis of FCBMs. Two 3-D FEA models were developed for analysis and validation purposes. The 3-D solid element model includes great detail regarding the geometry and boundary conditions of the FCBMs. Including fillets, residual stress, and anchors proved to generate more accurate results. The 3-D beam element model is greatly simplified, and primarily used to validate the results produced by the 3-D solid element model. Both models were validated through comparison to experimental data. A test suite of FEA runs was constructed to better understand the 3-D behavior of FCBMs. A chief discovery provided by the test suite results was the existence of two phenomenon conditions, defined as Phenomenon 1 and Phenomenon 2. Phenomenon 1 tended to occur when smaller off-axis forces were included in the model. When comparing the two phenomenon, larger pitch rotation, smaller out-of-plane motion, larger reaction forces, and a more consistent bistable mechanism was associated with Phenomenon 1. Phenomenon 2 tended to occur when larger applied forces were included in the model. Once this phenomenon was generated, the FCBM tended to remain in this condition. Reduced reaction forces, larger out-of-plane motion, and a tendency of non-bistability were characteristics of this phenomenon. The FCBMs could experience much larger in-plane applied forces before transitioning to Phenomenon 2. In contrast, relatively small out-of-plane forces caused the same transition. The FCBMs proved to be well behaved when being pulled into their alternate stable position rather than being pushed. A pushing motion caused the shuttle to roll, pitch and yaw in an inconsistent manner.

As technology advances and engineering capabilities improve, more research has focused on microscopic possibilities. Microelectromechanical systems (MEMS) is one area that has received much attention recently. Within MEMS much research has focused on sensing and actuation. This thesis presents work on a particular actuator of interest, the thermomechanical in-plane microactuator (TIM). Recent work has shown the possibility of a novel approach of sensing mechanical outputs of the TIM without ancillary sensors. This sensing approach exploits the piezoresistive property of silicon. However, to implement this approach a full model of the TIM would need to be obtained to describe the physics of the TIM, as well as development of a calibration approach to account for variations between devices. This thesis develops a multi-physics model of the TIM to realize this sensing approach. This model determines the mechanical state of the TIM using the same electrical signal that actuates the TIM. In this way the TIM is able to operate as a self-sensing actuator. To allow this multi-physics model to be tractable, work was done to simplify the thermal modeling of the TIM. A preliminary calibration approach was developed to adequately compensate for variations between devices. Thermal modeling and calibration were coupled with mechanical modeling and a developed sensing approach to form the full multi-physics model of the TIM. Validation testing of the model was performed with a modified calibration approach which showed good correlation with experimental data.

A deeper understanding of human development and disease is made possible partly through the study of genetically modified model organisms, such as the common mouse (Mus musculus). By genetically modifying such model organisms, scientists can activate, deactivate, or highlight particular characteristics. A genetically modified animal is generated by adding exogenous (foreign) genetic material to one or more embryonic cells at their earliest stages of development. Frequently, this exogenous genetic material consists of specially engineered DNA, which is introduced into a fertilized egg cell (zygote). When successfully introduced into the zygote, the exogenous DNA will be incorporated into the cell's own genome, and the animal that develops from the zygote will exhibit the genetic modification in all of its cells. The current devices and methods for generating genetically modified animals are inefficient, and/or difficult to use. The most common and efficient method for inserting new DNA into zygotes is by directly injecting a DNA solution through a tiny glass tube into the cell in a process called microinjection. Unfortunately, microinjection is quite inefficient (success rates are commonly between 1 and 5%), but often it is the only method for inserting DNA into eggs, zygotes, or early stage embryos. This thesis presents the design and testing of a micrometer sale, pumpless microelectromechanical system (MEMS) nanoinjector. Rather than use pumps and capillaries, the nanoinjector employs electrostatic charges to attract and repel DNA onto and off of the surface of a solid lance. The nanoinjector also includes a mechanical system for constraining the target cells during injection. Initial testing indicates the nanoinjector does not decrease cell viability, and it has a very high initial success rate (up to 90%). With the addition of an on-chip actuator, the nanoinjector could be packaged as an inexpensive, fully automated system, enabling efficient, high volume genetic modification of developing animals. Such a device would greatly increase the ease and speed of generating the model organisms needed to study such critical diseases such as Alzheimer's disease, cancer, and diabetes.

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.

<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>

UV-LIGA is a microfabrication process realzed by material deposition through microfabricated molds. UV photolithography is conducted to pattern precise thick micro molds using UV light sensitive materials, mostly SU-8, and electroforming is performed to fabricate micro metallic structures defined by the micro molds. Therefore, UV-LIGA is a bottom-up in situ material-addition process. UV-LIGA has received broad attention recently than LIGA – a micro molding fabrication process using X-ray to pattern the micro molds. LIGA is an expansive and is limited in access. In comparing to LIGA, the UV-LIGA is a cost effective process, and is widely accessible and safe. Therefore, it has been extensively used for the fabrication of metallic micro-electro-mechanical-systems (MEMS). The motivation of this research was to study micro mechanical systems fabricated with nano-structured metallic materials via UV-LIGA process. Various micro mechanical systems with high-aspect-ratio and thick metallic structures have been developed and are presented in this desertation. A novel micro mechanical valve has been developed with nano-structured nickel realized with UV-LIGA fabrication technique. Robust compact valves are crucial for space applications where payload and rubstaness are critically concerned. Two types of large flow rate robust passive micro check valve arrays have been designed, fabricated and tested for robust hydraulic actuators. The first such micro valve developed employs nanostructured nickel as the valve flap and single-crystal silicon as the substrates to house inlet and outlet channels. The Nano-structured nickel valve flap was fabricated using the UV-LIGA process developed and the microchannels were fabricated by deep reactive etching (DRIE) method. The valves were designed to operate under a high pressure (>10MPa), able to operate at high frequencies (>10kHz) in cooperating with the PZT actuator to produce large flow rates (>10 cc/s). The fabricated microvalves weigh 0.2 gram, after packing with a novel designated valve stopper. The tested results showed that the micro valve was able to operate at up to 14kHz. This is a great difference in comparison to traditional mechanical valves whose operations are limited to 500 Hz or less. The advantages of micro machined valves attribute to the scaling laws. The second type of micro mechanical valves developed is a in situ assembled solid metallic (nickel) valves. Both the valve substrates for inlet and outlet channels and the valve flap, as well as the valve stopper were made by nickel through a UV-LIGA fabrication process developed. Continuous multiple micro molds fabrication and molding processes were performed. Final micro mechanical valves were received after removing the micro molds used to define the strutures. There is no any additional machining process, such as cutting or packaging. The alignment for laminated fabrication was realized under microscope, therefore it is a highly precise in situ fabrication process. Testing results show the valve has a forward flow rate of19 cc/s under a pressure difference of 90 psi. The backward flow rate of 0.023 cc/s, which is negligible (0.13%). Nano-structured nickel has also been used to develop laminated (sandwiched) micro cryogenic heater exchanger with the UV-LIGA process. Even though nickel is apparently not a good thermal conductor at room temperature, it is a good conductor at cryogentic temerpature since its thermal conductivity increases to 1250 W/k·m at 77K. Micro patterned SU-8 molds and electroformed nickel have been developed to realize the sandwiched heat exchanger. The SU-8 mold (200mm x 200mm x50mm) array was successfully removed after completing the nickel electroforming. The second layer of patterned SU-8 layer (200mm x 200mm x50mm, as a thermal insulating layer) was patterned and aligned on the top of the electroformed nickel structure to form the laminated (sandwiched) micro heat exchanger. The fabricated sandwiched structure can withstand cryogenic temperature (77K) without any damages (cracks or delaminations). A study on nanocomposite for micro mechanical systems using UV-LIGA compatible electroforming process has been performed. Single-walled carbon nanotubes (SWNTs) have been proven excellent mechanical properties and thermal conductive properties, such as high strength and elastic modulus, negative coefficient of thermal expansion (CTE) and a high thermal conductivity. These properties make SWNT an excellent reinforcement in nanocomposite for various applications. However, there has been a challenge of utilizing SWNTs for engineering applications due to difficulties in quality control and handling – too small (1-2nm in diameter). A novel copper/SWNT nanocomposite has been developed during this dissertational research. The goal of this research was to develop a heat spreader for high power electronics (HPE). Semiconductors for HPE, such as AlGaN/GaN high electron mobility transistors grown on SiC dies have a typical CTE about 4~6x10-6/k while most metallic heat spreaders such as copper have a CTE of more than 10x10-6/k. The SWNTs were successfully dispersed in the copper matrix to form the SWNT/Cu nano composite. The tested composite density is about 7.54 g/cm3, which indicating the SWNT volumetric fraction of 18%. SEM pictures show copper univformly coated on SWNT (worm-shaped structure). The measured CTE of the nanocomposite is 4.7 x 10-6/°C, perfectly matching that of SiC die (3.8 x 10-6/°C). The thermal conductivity derived by Wiedemann-Franz law after measuring composit's electrical conductivity, is 588 W/m-K, which is 40% better than that of pure copper. These properties are extremely important for the heat spreader/exchanger to remove the heat from HPE devices (SiC dies). Meanwhile, the matched CTE will reduce the resulted stress in the interface to prevent delaminations. Therefore, the naocomposite developed will be an excellent replacement material for the CuMo currently used in high power radar, and other HPE devices under developing. The mechanical performance and reliability of micro mechanical devices are critical for their application. In order to validate the design & simulation results, a direct (tensile) test method was developed to test the mechanical properties of the materials involved in this research, including nickel and SU-8. Micro machined specimens were fabricated and tested on a MTS Tytron Micro Force Tester with specially designed gripers. The tested fracture strength of nanostructured nickel is 900±70 MPa and of 50MPa for SU-8, resepctively which are much higher than published values.

A systematic investigation has been performed for "Electric Nose", a system that can identify gas samples and detect their concentrations by combining sensor array and data processing technologies. Non-silicon based microfabricatition has been developed for micro-electro-mechanical-system (MEMS) based gas sensors. Novel sensors have been designed, fabricated and tested. Nanocrystalline semiconductor metal oxide (SMO) materials include SnO2, WO3 and In2O3 have been studied for gas sensing applications. Different doping material such as copper, silver, platinum and indium are studied in order to achieve better selectivity for different targeting toxic gases including hydrogen, carbon monoxide, hydrogen sulfide etc. Fundamental issues like sensitivity, selectivity, stability, temperature influence, humidity influence, thermal characterization, drifting problem etc. of SMO gas sensors have been intensively investigated. A novel approach to improve temperature stability of SMO (including tin oxide) gas sensors by applying a temperature feedback control circuit has been developed. The feedback temperature controller that is compatible with MEMS sensor fabrication has been invented and applied to gas sensor array system. Significant improvement of stability has been achieved compared to SMO gas sensors without temperature compensation under the same ambient conditions. Single walled carbon nanotube (SWNT) has been studied to improve SnO2 gas sensing property in terms of sensitivity, response time and recovery time. Three times of better sensitivity has been achieved experimentally. The feasibility of using TSK Fuzzy neural network algorithm for Electric Nose has been exploited during the research. A training process of using TSK Fuzzy neural network with input/output pairs from individual gas sensor cell has been developed. This will make electric nose smart enough to measure gas concentrations in a gas mixture. The model has been proven valid by gas experimental results conducted.

Technical challenges for developing micro sensors for Ultra High Temperature and turbine applications lie in that the sensors have to survive extremely harsh working conditions that exist when converting fuel to energy. These conditions include high temperatures (500-1500°C), elevated pressures (200-400 psi), pressure oscillations, corrosive environments (oxidizing conditions, gaseous alkali, and water vapors), surface coating or fouling, and high particulate loading. Several technologies are currently underdeveloped for measuring these parameters in turbine engines. One of them is an optical-based non-contact technology. However, these nondirective measuring technologies lack the necessary accuracy, at least at present state. An alternative way to measure these parameters without disturbing the working environments is using MEMS type sensors. Currently, the techniques under development for such harsh environment applications are silicon carbide (SiC) and silicon nitrite (Si3N4) –based ceramic MEMS sensors. But those technologies present some limitation such as narrow processing method, high cost (materials and processing cost), and limited using temperatures (typically < 800 C). In this research we propose to develop two sensors based on recently developed polymer-derived ceramics (PDCs): Constant Temperature Hot wire Anemometer, temperature/heat-flux sensor for turbine applications. PDC is a new class of high temperature ceramics. As we shall describe below, many unique features of PDCs make them particularly suitable for the proposed sensors, including: excellent thermo-mechanical properties at high temperatures, enable high temperature operation of the devices; various well-developed processing technologies, such as injection molding,photolithography, embossing, DRIE etching and precise machining, can be used for the fabrication of the devices; and tunable electric conductivity, enable the proposed sensors fabricated from similar materials, thus reliability considerations associated with thermal mismatch, which is a big concern when using MEMS-based sensors at elevated temperatures, will be minimized.

In this work, we studied the electronic behavior of polymer-derived ceramics (PDCs) and applied them for the synthesis of carbon nanotube reinforced ceramic nanocomposites and ceramic MEMS (Micro-Electro-Mechanical Systems) structures. Polymer-derived SiCN ceramics were synthesized by pyrolysis of a liquid polyureasilazane with dicumyl peroxide as thermal initiator. The structural evolution during pyrolysis and post-annealing was studied using FTIR, solid state NMR and Raman. The results revealed that the resultant ceramics consisted of SiCxNx-4 as major building units. These units were connected with each other through C-C/C=C bonds or by shearing N/C. The amount of sp2 free carbon strongly depends on composition and processing condition. Electron paramagnetic resonance (EPR) was used to investigate electronic structure of PDCs; the results revealed that the materials contain unpaired electron centers associated with carbons. Electronic behavior of the SiCN ceramics was studied by measuring their I-V curves, temperature dependence of d.c.-conductivities and impendence. The results revealed that the SiCN ceramics exhibited typical amorphous semiconductor behavior, and their conductivity varied in a large range. The results also revealed that the materials contain more than one phase, which have the different electronic behavior. We explored possibility of using polymer-derived ceramics to make ceramic MEMS for harsh environmental applications with a lithography technique. The cure depth of the polymer precursor was measured as a function of UV intensity and exposure time. The experimental data was compared with the available theoretical model. A few typical SiCN parts were fabricated by lithography technique. We also prepared carbon nanotube reinforced ceramic nanocomposites by using PDC processing. The microstructures of the composites were characterized using SEM and TEM; the mechanical properties were studied characterized using nanoindentation. The significant improvement in mechanical properties was observed for the nanocomposites.