<p>The aim was to develop, manufacture and evaluate diffractive lenses, or diffractive optical elements (DOE), for use in correlation with a camera to add perspective in pictures. The application is a miniaturized submarine developed in order to perform distant exploration and analysis in harsh and narrow environments. The idea is to project a laser pattern upon the observed structure and thereby add geometrical information to pictures acquired with an onboard CMOS camera. The design of the DOE-structures was simulated using the optimal rotational angle method (ORA). A set of prototype DOEs were realized using a series of microelectromechanical system (MEMS) processes, including photolithography, deposition and deep reactive-ion etching (DRIE). The projected patterns produced by the manufactured DOEs were found to agree with the simulated patterns except for the case where the DOE feature size was too small for the available process technology to handle. A post-processing software solution was developed to extract information from the pictures, called Laser Camera Measurement (LCM). The software returns the x, y and z coordinate of each laser spot in a picture and provides the ability to measure a live video stream from the camera. The accuracy of the measurement is dependent of the distance to the object. Some of the patterns showed very promising results, giving a 3-D resolution of ~0.6 cm, in each dot, at a distance of 1 m from the camera. Lengths can be resolved up til 3 m distance from the submarine.</p> / <p>Tillämpningen finns i en miniatyriserad ubåt framtagen för utforskning och analys av svåråtkomliga och trånga håligheter. Målet var att designa, tillverka och utvärdera en diffraktiv lins (DOE) för användning tillsammans med en kamera för att skapa perspektiv i bilder. Idén var att projicera ett lasermönster på objektet och därmed lägga till geometrisk information till bilderna tagna med CMOS kameran. Utformningen av DOE-strukturerna simulerades med the optimal rotational angle method (ORA). En uppsättning av prototyp DOE-linser tillverkades med hjälp av en serie mikrostrukturteknikprocesser, bland annat fotolitografi, deponering och plasmaetsning. Mönster projicerade med de tillverkade DOE-linserna stämde väl överens med önskade mönster, med undantag för de DOEs där strukturstorleken underskred processens begränsningar. En programvara, kallad Laser Camera Measurement (LCM), utvecklades för att extrahera information från bilderna. Programvaran returnerar x, y, och z koordinaterna för varje laserpunkt i en bild och ger möjlighet att mäta i en kontinuerlig videoström från kameran.  Mätosäkerheten är beroende av avståndet till objektet. Vissa mönster gav mycket lovande resultat, med en 3-D upplösning på ~0.6 cm, i varje punkt, på ett avstånd av 1 m från kameran. Längder kan upplösas upp till 3 m från kameran där ett så kallat far-field uppstår.</p> / DADU

<p>Spacecraft on interplanetary missions or advanced satellites orbiting the Earth all require propulsion systems to complete their missions. Introducing microelectromechanical systems technology to the space industry will not only reduce size and weight of the propulsion system, but can also increase the performance of the mission.</p><p>Fluid handling systems are used in chemical and electric propulsion. Some components incorporated in a fluidic handling system are presented and evaluated in this work.</p><p>Microsystems are very sensitive to contamination. Reliable, robust, and easily integrated filters were modeled, manufactured, and experimentally verified.</p><p>A fluid connector, designed to withstand large temperature variations and aggressive propellants was manufactured and characterized. Similar designs was also be used as a thermally activated minute valve.</p><p>The feasibility of a cold gas system for precise attitude control has been demonstrated. Steps towards improving the performance (from specific im-pulse 45 s) have been taken, by the integration of suspended heater elements.</p><p>For electric propulsion, two thermally regulated flow restrictors have been characterized. These devices can fine-tune the propellant flow to e.g. an ion engine.</p><p>A single-use valve using a soldered seal has also been successfully dem-onstrated within a pressure range of 5 to 100 bar.</p><p>The microsystem-based propulsion systems of tomorrow’s spacecraft need to be demonstrated in space, in order to gain necessary credibility. </p>

Powder injection molding (PIM) is a net fabrication technique that combines the complex shape-forming ability of plastic injection molding, the precision of die-casting, and the material selection flexibility of powder metallurgy. For this study, the design issues related to PIM for fabrication of thin-walled high-aspect ratio geometries were investigated. These types of geometries are typical to the field of microtechnology-based energy and chemical systems (MECS). MECS are multi-scale (sizes in at least two or more different length scale regimes) fluidic devices working on the principle of heat and mass transfer through embedded micro and nanoscale features. Stainless steel was the material chosen for the investigations because of its high-thermal resistance and chemical inertness necessary for typical microfluidic applications. The investigations for the study were performed using the state-of-the-art computer aided engineering (CAE) design tool, PIMSolver��. The effect of reducing part thickness, on the process parameters including melt temperature, mold temperature, fill time and switch over position, during the mold-filling stage of the injection molding cycle were investigated. The design of experiments was conducted using the Taguchi method. It was seen that the process variability generally increased with reduction in thickness. Mold temperature played the most significant role in controlling the mold filling behavior as the part thickness reduced. The effects of reducing part thickness, process parameters, microscale surface geometry and delivery system design on the occurrence of defects like short shots were also studied. The operating range, in which the mold cavity was completely filled, was greatly reduced as the part thickness was reduced. The single edge gated delivery system designs, with single or branched runners, resulted in a completely formed part. The presence of microchannel features on the part surface increased the possibility of formation of defects like short shots and weld-lines when compared to a featureless part. The study explored some typical micro-fluidic geometries for fabrication using PIM. The final aspect of this study was the PIM experiments performed using a commercial stainless steel feedstock. Experiments were performed to study the mold-filling behavior of a thin, high aspect ratio part and also to study the effect of varying processing conditions on the mold-filling behavior. These experiments also provided correspondence to the mold filling behavior simulated using PIMSolver��. The PIMSolver�� closely predicted the mold-filling patterns as seen in the experiments performed under similar molding conditions. The study was successful in laying down a quantitative framework for using PIM to fabricate micro-fluidic devices. / Graduation date: 2005

Direct wafer bonding has been identified as an en-abling technology for microelectromechanical systems (MEMS). As the complexity of devices increase and the bonding of multiple patterned wafers is required, there is a need to understand the factors that lead to bonding failure. Bonding relies on short-ranged surface forces, thus flatness deviations of the wafers may prevent bonding. Bonding success is determined by whether or not the surface forces are sufficient to overcome the flatness deviations and deform the wafers to a common shape. A general bonding criterion based on this fact is developed by comparing the strain energy required to deform the wafers to the surface energy that is dissipated as the bond is formed. The bonding criterion is used to examine the case of bonding bowed wafers with etch patterns on the bonding surface. An analytical expression for the bonding criterion is developed using plate theory for the case of bowed wafers. Then, the criterion is implemented using finite element analysis, to demonstrate its use and to validate the analytical model. The results indicate that wafer thickness and curvature are important in determining bonding success and that the bonding criterion is independent of wafer diameter. Results also demonstrate that shallow etched patterns can make bonding more difficult while deep features, which penetrate through an appreciable thickness of the wafer, may facilitate bonding. Design implications of the model results are discussed in detail. Preliminary results from experiments designed to validate the model, agree with the trends seen in the model, but further work is required to achieve quantitative correlation. / Singapore-MIT Alliance (SMA)

AlₓGa₁₋ₓN (x>0.6) based Ultraviolet Light Emitting Diodes (UV LEDs) emit in the UV C range of 200 - 290 nm and suffer from low external quantum efficiencies (EQEs) of less than 3%. This low EQE is representative of a large number of non-radiative recombination events in the multiple quantum well (MQW) layers, which leads to high device temperatures due to self-heating at the device junction. Knowledge of the device temperature is essential to implement and evaluate appropriate thermal management techniques, in order to mitigate optical degradation and lifetime reduction due to thermal overstress. The micro-scale nature of these devices and the presence of large temperature gradients in the multilayered device structure merit the use of several indirect temperature measurement techniques to resolve device temperatures. This work will study UV LEDs with AlₓGa₁₋ₓN active layers, grown on sapphire or AlN growth substrates, and flip-chip mounted onto submounts and package configurations with different thermal properties. Thermal metrology results will be presented for devices with different electrode geometries (i.e., interdigitated and micropixel), for bulk and thinned growth substrates. The body of this work will present a comparative study of optical techniques such as Infrared (IR), micro-Raman and Electroluminescence (EL) spectroscopy for the thermal metrology of UV LEDs. The presence of horizontal and vertical temperature gradients within the device layers will be studied using micro-Raman spectroscopy, while the occurrence of thermal anomalies such as hotspots and shorting paths will be studied using IR spectroscopy. The Forward Voltage (Vf) method, an electrical junction temperature measurement technique, will also be investigated. The Vf method will be applied to the Thermal Resistance Analysis by Induced Transient (TRAIT) procedure, whereby electrical data at short time scales from an operational device will be used to discretize the junction-to- package thermal resistance pathway from the total junction- to-ambient heat path. The TRAIT procedure will be conducted on several LEDs, for comparison. The scope and applicability of each thermal metrology technique will be examined, and the merits and demerits of each technique will be exhibited.

The recent breakthroughs in genomics and molecular diagnostics will not be reflected in health-care systems unless the biogenetic or other nucleic acid-based tests are transferred from the laboratory to clinical market. Developments in microfabrication techniques brought lab-on-a-chip (LOC) into being the best candidate for conducting sample preparation for such clinical devices, or point-of-care testing set-ups. Sample preparation procedure consists of several stages including cell transportation, separation, cell lysis and nucleic acid purification and detection. LOC, as a subset of Microelectromechanical systems (MEMS), refers to a tiny, compact, portable, automated and easy-to-use microchip capable of performing the sample-preparation stages together. Complexity in micro-fabrications and inconsistency of the stages oppose integration of them into one chip. Among the variety of mechanisms utilized in LOC for cell lysis, electrical methods have the highest potential to be integrated with other microchip-based mechanisms. There are, however, major limitations in electrical cell lysis methods: the difficulty and high-cost fabrication of microfluidic chips and the high voltage requirements for cell lysis. Addressing these limitations, the focus of this thesis is on realization of cell lysis microchips suitable for LOC applications. We have developed a new methodology of fabricating microfluidic chips with electrical functionality. Traditional lithography of microchannel with electrode, needed for making electro-microfluidic chips, is considerably complicated. We have combined several easy-to-implement techniques to realize electro-microchannel with laser-ablated polyimide. The current techniques for etching polyimide are by excimer lasers in bulky set-ups and with involvement of toxic gas. We present a method of ablating microfluidic channels in polyimide using a 30W CO2 laser. Although this technique has poorer resolution, this approach is more cost effective, safer and easier to handle. We have verified the performance of the fabricated electro-microfluidic chips on electroporation of mammalian cells. Electrical cell lysis mechanisms need an operational voltage that is relatively high compared to other cell manipulation techniques, especially for lysing bacteria. Microelectro-devices have dealt with this limitation mostly by reducing the inter-distance of electrodes. The technique has been realized in tiny flow-through microchips with built-in electrodes in a distance of a few micrometers which is in the scale of cell size. In addition to the low throughput of such devices, high probability of blocking cells in such tiny channels is a serious challenge. We have developed a cell lysis device featured with aligned carbon nanotube (CNT) to reduce the high voltage requirement and to improve the throughput. The vertically aligned CNT on an electrode inside a MEMS device provides highly strengthened electric field near the tip. The concept of strengthened electric field by means of CNT has been applied in field electron emission but not in cell lysis. The results show that the incorporation of CNT in lysing bacteria reduces the required operational voltage and improves throughput. This achievement is a significant progress toward integration of cell lysis in a low-voltage, high-throughput LOC. We further developed the proposed fabrication methodology of micro-electro-fluidic chips, described earlier, to perform electroporation of single mammalian cell. We have advanced the method of embedding CNT in microchannel so that on-chip fluorescent microscopy is also feasible. The results verify the enhancement of electroporation by incorporating CNT into electrical cell lysis. In addition, a novel methodology of making CNT-embedded microfluidic devices has been presented. The embedding methodology is an opening toward fabrication of a CNT-featured LOC for other applications.

Current trends in technology are moving to increased use of wireless communication with rapidly increasing data transmission rates and higher frequencies. Miniaturization is essential to allow electronics of increasing complexity to fit into smaller devices. Adaptive technologies allow a single system to operate across multiple wireless protocols, adjusting to changing conditions to minimize interference and enhance performance. Flexibility is essential as the use of wireless technology increases and spreads to new industries. The objective of this research is twofold: to develop novel reconfigurable electromagnetic structures and a novel process to fabricate microelectromechanical systems (MEMS) devices on flexible substrates. The novel electromagnetic structures are passive frequency-switchable parasitic antennas, conformal MEMS-tunable frequency selective surfaces (FSS) and MEMS-tunable electromagnetic bandgap (EBG) structures. Fabricating the reconfigurable conformal FSS and EBG structures requires the development of a new fabrication process to produce MEMS devices monolithically integrated onto a flexible substrate. Novel frequency-switchable parasitic antenna arrays are developed, fabricated and measured. The structure radiates efficiently when placed over metal and absorbing material, improving the range of conventional RFID systems, as well as minimizing blind spots to provide continuous coverage in a hemisphere. A novel analysis method is developed to characterize frequency-switchable parasitic patch arrays. The purpose of the analysis is to provide an approximation of the input impedance and variation of the radiation pattern with frequency. The analysis combines models based on electromagnetic theory and circuit theory to provide a fast and yet reasonable approximation of the parasitic array characteristics. The analysis also provides a good deal of physical insight into the operation of multi-mode parasitic patch arrays. The end result is an initial array design which provides a good starting point for full EM simulation and optimization. The new analysis method is validated alongside measured and simulated results, with good correlation for both impedance characteristics and far-field radiation patterns. A MEMS-based switched parasitic antenna array is designed, fabricated and measured with good correlation between simulated and measured results. The structure is a direct-coupled parasitic patch array which is capable of frequency steering and has additional MEMS-enabled beam-steering capabilities at each frequency. An EBG-based multi-mode radiating structure design is presented, which is capable of frequency-switchable beam steering. The antenna area is significantly reduced compared to the parasitic patch array structure, but at a considerable cost in terms of gain and efficiency. A novel MEMS process is developed to fabricate large numbers of high-performance MEMS devices monolithically integrated onto a rigid-flex organic substrate using low-temperature processes. The rigid-flex substrate is all dielectric, which is amenable to low-loss electromagnetic structures. The substrate provides mechanical support to the MEMS devices while maintaining overall flexibility. The adaptation of each fabrication process step to handle flexible substrates is analyzed and documented in detail. The newly-developed MEMS process is used to fabricate a MEMS reconfigurable frequency-selective surface. A practical bias network is incorporated into the structure design to ensure that all devices are actuated simultaneously. FSS structures operating in the Ku and Ka bands are fabricated and tested, with good correlation between simulated and measured results for individual devices as well as the entire FSS structures. The newly-developed MEMS process is also used to fabricate a MEMS reconfigurable electromagnetic bandgap structure. An EBG structure operating in the Ka band is fabricated and tested to verify the validity of the proposed concept.

Spacecraft on interplanetary missions or advanced satellites orbiting the Earth all require propulsion systems to complete their missions. Introducing microelectromechanical systems technology to the space industry will not only reduce size and weight of the propulsion system, but can also increase the performance of the mission. Fluid handling systems are used in chemical and electric propulsion. Some components incorporated in a fluidic handling system are presented and evaluated in this work. Microsystems are very sensitive to contamination. Reliable, robust, and easily integrated filters were modeled, manufactured, and experimentally verified. A fluid connector, designed to withstand large temperature variations and aggressive propellants was manufactured and characterized. Similar designs was also be used as a thermally activated minute valve. The feasibility of a cold gas system for precise attitude control has been demonstrated. Steps towards improving the performance (from specific im-pulse 45 s) have been taken, by the integration of suspended heater elements. For electric propulsion, two thermally regulated flow restrictors have been characterized. These devices can fine-tune the propellant flow to e.g. an ion engine. A single-use valve using a soldered seal has also been successfully dem-onstrated within a pressure range of 5 to 100 bar. The microsystem-based propulsion systems of tomorrow’s spacecraft need to be demonstrated in space, in order to gain necessary credibility.

The aim was to develop, manufacture and evaluate diffractive lenses, or diffractive optical elements (DOE), for use in correlation with a camera to add perspective in pictures. The application is a miniaturized submarine developed in order to perform distant exploration and analysis in harsh and narrow environments. The idea is to project a laser pattern upon the observed structure and thereby add geometrical information to pictures acquired with an onboard CMOS camera. The design of the DOE-structures was simulated using the optimal rotational angle method (ORA). A set of prototype DOEs were realized using a series of microelectromechanical system (MEMS) processes, including photolithography, deposition and deep reactive-ion etching (DRIE). The projected patterns produced by the manufactured DOEs were found to agree with the simulated patterns except for the case where the DOE feature size was too small for the available process technology to handle. A post-processing software solution was developed to extract information from the pictures, called Laser Camera Measurement (LCM). The software returns the x, y and z coordinate of each laser spot in a picture and provides the ability to measure a live video stream from the camera. The accuracy of the measurement is dependent of the distance to the object. Some of the patterns showed very promising results, giving a 3-D resolution of ~0.6 cm, in each dot, at a distance of 1 m from the camera. Lengths can be resolved up til 3 m distance from the submarine. / Tillämpningen finns i en miniatyriserad ubåt framtagen för utforskning och analys av svåråtkomliga och trånga håligheter. Målet var att designa, tillverka och utvärdera en diffraktiv lins (DOE) för användning tillsammans med en kamera för att skapa perspektiv i bilder. Idén var att projicera ett lasermönster på objektet och därmed lägga till geometrisk information till bilderna tagna med CMOS kameran. Utformningen av DOE-strukturerna simulerades med the optimal rotational angle method (ORA). En uppsättning av prototyp DOE-linser tillverkades med hjälp av en serie mikrostrukturteknikprocesser, bland annat fotolitografi, deponering och plasmaetsning. Mönster projicerade med de tillverkade DOE-linserna stämde väl överens med önskade mönster, med undantag för de DOEs där strukturstorleken underskred processens begränsningar. En programvara, kallad Laser Camera Measurement (LCM), utvecklades för att extrahera information från bilderna. Programvaran returnerar x, y, och z koordinaterna för varje laserpunkt i en bild och ger möjlighet att mäta i en kontinuerlig videoström från kameran.  Mätosäkerheten är beroende av avståndet till objektet. Vissa mönster gav mycket lovande resultat, med en 3-D upplösning på ~0.6 cm, i varje punkt, på ett avstånd av 1 m från kameran. Längder kan upplösas upp till 3 m från kameran där ett så kallat far-field uppstår. / DADU

Current trends in technology are moving to increased use of wireless communication with rapidly increasing data transmission rates and higher frequencies. Miniaturization is essential to allow electronics of increasing complexity to fit into smaller devices. Adaptive technologies allow a single system to operate across multiple wireless protocols, adjusting to changing conditions to minimize interference and enhance performance. Flexibility is essential as the use of wireless technology increases and spreads to new industries. The objective of this research is twofold: to develop novel reconfigurable electromagnetic structures and a novel process to fabricate microelectromechanical systems (MEMS) devices on flexible substrates. The novel electromagnetic structures are passive frequency-switchable parasitic antennas, conformal MEMS-tunable frequency selective surfaces (FSS) and MEMS-tunable electromagnetic bandgap (EBG) structures. Fabricating the reconfigurable conformal FSS and EBG structures requires the development of a new fabrication process to produce MEMS devices monolithically integrated onto a flexible substrate. Novel frequency-switchable parasitic antenna arrays are developed, fabricated and measured. The structure radiates efficiently when placed over metal and absorbing material, improving the range of conventional RFID systems, as well as minimizing blind spots to provide continuous coverage in a hemisphere. A novel analysis method is developed to characterize frequency-switchable parasitic patch arrays. The purpose of the analysis is to provide an approximation of the input impedance and variation of the radiation pattern with frequency. The analysis combines models based on electromagnetic theory and circuit theory to provide a fast and yet reasonable approximation of the parasitic array characteristics. The analysis also provides a good deal of physical insight into the operation of multi-mode parasitic patch arrays. The end result is an initial array design which provides a good starting point for full EM simulation and optimization. The new analysis method is validated alongside measured and simulated results, with good correlation for both impedance characteristics and far-field radiation patterns. A MEMS-based switched parasitic antenna array is designed, fabricated and measured with good correlation between simulated and measured results. The structure is a direct-coupled parasitic patch array which is capable of frequency steering and has additional MEMS-enabled beam-steering capabilities at each frequency. An EBG-based multi-mode radiating structure design is presented, which is capable of frequency-switchable beam steering. The antenna area is significantly reduced compared to the parasitic patch array structure, but at a considerable cost in terms of gain and efficiency. A novel MEMS process is developed to fabricate large numbers of high-performance MEMS devices monolithically integrated onto a rigid-flex organic substrate using low-temperature processes. The rigid-flex substrate is all dielectric, which is amenable to low-loss electromagnetic structures. The substrate provides mechanical support to the MEMS devices while maintaining overall flexibility. The adaptation of each fabrication process step to handle flexible substrates is analyzed and documented in detail. The newly-developed MEMS process is used to fabricate a MEMS reconfigurable frequency-selective surface. A practical bias network is incorporated into the structure design to ensure that all devices are actuated simultaneously. FSS structures operating in the Ku and Ka bands are fabricated and tested, with good correlation between simulated and measured results for individual devices as well as the entire FSS structures. The newly-developed MEMS process is also used to fabricate a MEMS reconfigurable electromagnetic bandgap structure. An EBG structure operating in the Ka band is fabricated and tested to verify the validity of the proposed concept.