Browsing by Subject "MEMS"

Now showing 1 - 9 of 9
  • Thumbnail Image
    Item
    Design and fabrication of state of the art uncooled thermopile infrared detectors with cavity coupled absorption
    (2013-06) Shea, Ryan Patrick
    We present the design, fabrication, and characterization of uncooled thermopile infrared detectors with cavity coupled absorption in the long wave infrared with performance exceeding all published works. These detectors consist of a two die optical cavity which enhances absorption in the desired spectral range while rejecting unwanted noise off resonance. The electrical transduction mechanism is a thermopile consisting of four thermoelectric junctions of co-sputtered Bi2Te3 and Sb2<\sub>Te3<\sub> having a room temperature unitless thermoelectric figure of merit of .43. Processing steps are described in detail for the fabrication of extremely thermally isolated structures necessary for highly sensitive detectors. Optical characterization of the devices reveals a responsivity of 4700 V/W, thermal time constant of 58 ms, and specific detectivity of at least 3.0x109<\super> cmHz1/2/W. Also presented are a theoretical proposal for a midwave infrared detector using semiconductor selective absorption to enhance detectivity beyond the blackbody radiation limit and a new method for the analysis of radiation thermal conduction in highly thermally isolated structures.
  • Thumbnail Image
    Item
    Development of a MEMS Proportional Pneumatic Valve
    (2018-12) Hargus, Alex
    The MEMS proportional pneumatic valve employs an array of micro-orifices paired with piezobender micro-actuators in parallel to achieve macro-flow rates. This design produces a miniature valve that is extremely fast, lightweight, compact, and efficient. This thesis describes the design, fabrication, and testing of a MEMS valve prototype. The prototype was able to achieve a maximum flow of 0.107 slpm at 0 V and a minimum flow of 0.038 slpm at 30 V, making the turndown ratio about 2.8 at a pressure of 0.69 bar. Operation requires very little power, and the entire valve is about the size of a dime. These findings signify a step forward on the path to employing these valves in fluid power systems, especially mobile applications, but also reveal the potential of this technology to improve upon these results.
  • Thumbnail Image
    Item
    Electromechanical Switches Fabricated by Electrophoretic Deposition of Single Wall Carbon Nanotube Films
    (2015-08) Lim, Jun Young
    Power dissipation is a critical problem of CMOS devices especially for mobile applications. Many efforts have been made to solve the problem, but there are still major issues associated with scaling the device size. Micro electromechanical (MEMS) and nano electromechanical (NEMS) devices are one candidate to solve the problems because of their excellent standby leakage. However, the switches have a tradeoff between low operating power and high device speed. Suspended beams with low mass density and good mechanical properties provide a way to optimize the device. Carbon nanotubes (CNTs) have the low mass density and excellent mechanical properties to enable high performance MEMS/NEMS devices. However, the high temperature required for the direct synthesis for CNTs makes it difficult for them to be compatible with a substrate containing transistors. Therefore, continuous film deposition techniques are investigated with low temperature (< 300 C). Electrophoretic deposition (EPD) is a simple and versatile processing method to deposit carbon nanotubes on the substrate at room temperature. The movement of the charged CNTs in suspension occurs by an applied electric field. The deposited CNT film thickness can be controlled through the applied voltage and process time. We demonstrate the use of an EPD process to deposit various thicknesses of CNT films. Film thicknesses are studied as a function of, deposition time, electric field strength, and suspension concentration. The deposition mechanism of the EPD process for carbon nanotube layers was explained with experimental data. We determined the film mass density and electrical/optical properties of SWCNT films. Rutherford backscattering spectroscopy was used to determine the film mass density. Films created in this manner had a mass density that varies with thickness from 0.12 to 0.54 g/cm3 and a resistivity of 2.1410-3 Ω∙cm. For the mechanical property measurements, we describe a technique to fabricate free-standing thin films using modified Langmuir-Blodgett method. Then we extracted the Young’s modulus of the film from the load-displacement data from nanoindentation using the appropriate modeling. The Young’s modulus had a range of 4.72 to 5.67 GPa, independent of deposited thickness. We fabricated two-terminal fixed beam switches with SWCNT thin films using the EPD process. Device pull-in voltages under 1V were achieved by decreasing the air-gap. The pull-in voltages were compared with the calculated results using the device geometry and extracted Young’s modulus from nanoindentation. Generally good agreement was observed. Also, we found a range of 2.4 to 3.5 MHz resonant frequency. However, we encountered several problems with the device including a gradual turn-on, hysteresis between pull-in and pull-out voltage, changes in the pull-in voltages with repeated on-off cycling, and early failure due to moisture absorption during testing in the air. Mechanisms for these observations are postulated. Further work is needed to improve device performance and reliability.
  • Thumbnail Image
    Item
    Long term mechanical performance of MEMS in liquid environments
    (2009-04) Ali, Shaikh Mubassar
    Micro-electro-mechanical-systems (MEMS) are exposed to a variety of liquid environments in applications such as chemical and biological sensors, and microfluidic devices. Environmental interactions between the liquids and micron sized structures can lead to unpredictable long-term performance of MEMS in liquid environments. The present understanding of long-term mechanical performance of MEMS is based on studies conducted in air or vacuum. The objective of this study was to extend the present understanding of long-term mechanical performance of MEMS to liquid environments. Two broad categories of long-term mechanical failures reported in the literature were experimentally investigated: operational failures and structural fatigue failures. Typically operational failures are observed to occur at low stress levels, while fatigue failures are reported at higher stress levels. In order to investigate these failure modes, two different designs of test specimens and experimental techniques were developed. Low stress level (0-5 MPa) tests to investigate operational failures of MEMS in liquids were performed on microcantilever test specimens. Higher stress level (~ 0.2 GPa) tests were conducted on MEMS tensile specimens for investigating fatigue failures in liquids. Microcantilever specimens were made of silicon and silicon nitride. In addition, performance of silicon microcantilevers coated with common MEMS coating materials such as Titanium and SU-8 was also investigated. Microcantilever specimens were tested in liquids such as de-ionized water, saline, and glucose solution and compared with results in air. The microcantilevers were subjected to long term cyclic actuation (10e8 to 10e9 cycles) in liquid filled enclosures. Mechanical performance of the microcantilevers was evaluated by periodically monitoring changes in resonant frequency. Any unpredictable change in resonant frequency was deemed to constitute an operational failure. Despite low stress levels, mechanical performance of microcantilever test specimens was affected to a varying degree depending on environmental interactions between the structural/ coating material and the liquid environment. The changes in resonant frequency, often to the extent of ~1%, were attributed to factors such as mineral deposition, corrosion fatigue, water absorption, and intrinsic stresses. Tensile-tensile fatigue tests (high stress level) were performed on aluminum MEMS tensile specimens, in air and saline solution. Fatigue life was observed to range between 1.2 x 10e6 to 2.2 x 10e6 cycles at mean and alternating stresses of 0.13 GPa. The effect of saline environment on fatigue failures of aluminum tensile specimens was inconclusive from the experiments performed in this study. In conclusion, experimental results indicate subtle operational failures to be a potential critical failure mode for MEMS operating in liquid environments. Long-term mechanical failures in MEMS are expected to depend on the particular combination of material, stress level, and environment.
  • Thumbnail Image
    Item
    The mechanical response of common nanoscale contact geometries
    (2008-03) Mook, William Moyer
    Characterizing the mechanical response of common nanoscale contact geometries is vitally important to fields such as microelectromechanical systems (MEMS) where the behavior of nanoscale contacts can in large part determine system reliability and lifetime. Therefore a research program was undertaken that focused on the development of innovative nanoindentation-based techniques capable of quantifying the mechanical response of freestanding nanostructures. Nanoindentation was used since it is a non-destructive, high resolution technique that has been proven to be very useful in characterizing materials at the nanoscale. Examples of tested structures include single crystalline nanoparticles and polycrystalline nanoposts. From these experiments methods to characterize the structures' effective elastic modulus, flow stress, fracture toughness and activation volume required for plasticity have been developed. It was noted that both modulus and toughness in nanoparticles scale with average contact stress. This result has lead to the development of an experimental analysis technique that accounts for the hydrostatic component of pressure which develops in a material under contact. The effect of hydrostatic pressure on indentation modulus is currently not accounted for in nanoindentation even though it is shown to be important at length scales below 100 nm.
  • Thumbnail Image
    Item
    MEMS Actuators for Tuning Nanometer-scale Airgaps in Heterostructures and Optical Instrumentation for Glacier Ice Studies
    (2016-01) Chan, Wing Shan
    MEMS Actuators for Tuning Nanometer-scale Airgaps in Heterostructures We developed a new actuator microstructure to control the spacing between closely spaced surfaces. Creating and controlling nanometer gaps is of interest in areas such as plasmonics and quantum electronics. For example, energy states in quantum well heterostructures can be tuned by adjusting the physical coupling distance between wells. Unfortunately, such an application calls for active control of a nano-scale air gap between surfaces which are orders of magnitude larger, which is difficult due to stiction forces. A vertical electrostatic wedge actuator was designed to control the air gap between two closely spaced quantum wells in a collapsed cantilever structure. A six-mask fab- rication process was developed and carried out on an InGaAs/InP quantum well het- erostructure on an InP substrate. Upon actuation, the gap spacing between the surfaces was tuned over a maximum range of 55 nm from contact with an applied voltage of 60 V. Challenges in designing and fabricating the device are discussed. Optical Instrumentation for Glacier Ice Studies We explored new optical instrumentation for glacier ice studies. Glacier ice, such as that of the Greenland and Antarctic ice sheets, is formed by the accumulation of snowfall over hundreds of thousands of years. Not all snowfalls are the same. Their isotopic compositions vary according to the planet’s climate at the time, and may contain part of the past atmosphere. The physical properties and chemical content of the ice are therefore proxies of Earth’s climate history. In this work, new optical methods and instrumentation based on light scattering and polarization were developed to more efficiently study glacier ice. Field deployments in Antarctica of said instrumentation and results acquired are presented.
  • Thumbnail Image
    Item
    Modeling, Fabrication and Testing of PZT Based MEMS and Meso-scale Pneumatic Proportional Valves
    (2019-12) Fikru, Nebiyu
    This thesis presents new modeling and process techniques used for the design and fabrication of Micro-Electro-Mechanical Systems (MEMS) based proportional valves for pneumatics applications. The modeling approach is further applied to a similar but larger envelope valve, hence called meso-scale valve, used to demonstrate the concept of the MEMS valve. Since the meso-scale valve is entirely fabricated in the machine shop using conventional machining technology and off-the-shelf components, the fabrication technique presented in the thesis applies to the MEMS valve only. The modeling work consists of two main sections: actuator modeling and flow modeling. In the actuator modeling section, a closed-form deflection equation of a piezoelectric bimorph is derived. The model takes into account the effect of the adhesive and electrode layers. The deflection model is used in a comprehensive steady state force model of a piezoelectric bimorph. In the flow modeling section, flow through the meso-scale and MEMS valves is modeled as an axisymmetric frictional flow between parallel plates. Friction factor is allowed to vary as a function of the Reynolds number in a new piecewise function for different regimes of the flow. The new flow modeling technique can be used estimate flow through the valve based on the position of the valve actuator. Without fabrication considerations, the actuator and flow modeling techniques are used to show that target specifications of 2cm3 MEMS valve with 700 kPa maximum pressure differential and 25 slpm flow capacity can be met. The success of such new MEMS valves has a revolutionary potential to miniature valve technology. The modeling techniques are used to design the final MEMS valve that was fabricated in the clean-room. The MEMS valve is created in a unique method that involves three separate processes: port plate fabrication, actuator fabrication, and bonding. In the port plate fabrication, the orifice array is created on standard silicon substrates using dry etching techniques. High aspect ratio (up to 20) through holes are created on standard silicon wafers using the technique. The actuator fabrication is performed on a separate substrate with bulk micromachining being the general fabrication methodology. Unique etch techniques have been used to release the actuator array. In the bonding process, adhesive bonding is used to permanently bond the port plate and the plate carrying the actuator array. The testing section presents testing of the port plates and actuators separately before testing the valves as complete sets. The port plate test results have demonstrated that target pressure and flow specifications of the MEMS valve are met. The actuator array tests have also shown that functional actuator arrays with deflection values that are nearly 90% of the predicted deflection have been successfully fabricated. The mesoscale valve test has produced results with proportional relationship between voltage and actuator deflection for a good range of the applied voltage. Several of the MEMS valves tested suffered from electrical shorting while in the test stand. However, one of the valves has shown promising results where flow rate increases with increases in applied voltage were recorded.
  • Thumbnail Image
    Item
    Protein crystallization using micro-fluidic devices
    (2009-08) Sugiyama, Masano
    X-ray diffraction is the most common way to determine protein structure at an atomic level. To determine the protein structure, a high-quality crystal of sufficient size is required. Obtaining such a crystal is difficult due to the multi-parametric phase space that needs to be screened to determine the best conditions for growth of a suitable crystal. In this work two microfluidic protein crystallization techniques have been developed and tested: the continuous-feed crystallization chamber and the phase diagram visualizer. The continuous-feed crystallization chamber (CCC) allows for kinetic path control through the crystallization phase diagram during crystallization. The CCC operates similarly to a continuously stirred tank reactor, where protein, salt, and buffer are fed at desired flow rates and concentrations to maintain desired conditions inside the chamber. A lumped kinetic model was developed, and parameters for heterogeneous nucleation kinetics were determined. Heterogeneous nucleation was found to have faster nucleation kinetics and slower growth kinetics than homogeneous nucleation, as expected. The lumped-model analysis gives a method to quantifying the effect of various crystallization variables by extraction of kinetic parameters. The phase diagram visualizer (PDV) determines the solution phase diagram for protein-precipitant systems in one experiment rather than many lengthy experiments as required for traditional methods. Laminar flow and diffusion in the PDV create significant gradients in concentration, so crystals form in only part of the chamber. By combining observation of the location of the crystal-rich regions with a computer simulation of flow and transport in the chamber, a solution phase diagram is generated. This PDV has been tested for the lysozyme-sodium chloride and lysozyme-soidum nitride system. Modeling results where used to design an improved PDV with grooves. This device has been fabricated and is to be tested in the next phase of experiments. These two microfluidic devices together can be used together to determine and execute an optimized growth strategy for a given protein or a condition change. The PDV will give a general road map of the phase space that will be traveled using the CCC.
  • Thumbnail Image
    Item
    Wireless resonant magnetic microactuators.
    (2008-12) Vollmers, Karl Eric
    Rapid advances in miniaturization and robotics are presenting new opportunities for collaboration between the elds of robotics and medicine. Since their development in the late 1990s, minimally invasive robotic systems have become an accepted partner in the surgical suite. This trend has continued with the development of noninvasive camera pills for GI tract inspection. Further miniaturization and development of noninvasive microrobotic platforms and procedures will occur in the near future. This thesis contributes to the development of viable medical microrobots with the presentation of new wireless micromotors capable of providing power and propulsion to sub-millimeter wireless robotic platforms. The wireless resonant actuator can be individually actuated by frequency-dependent power, which is delivered by oscillating external magnetic elds. By relying on magnetic forces between neighboring soft magnetic bodies, a high-power, individually addressable, scalable wireless microactuator was created. Utilizing the energy amplification of impact, impact forces as high as 300 microN have been demonstrated. The actuator is used to provide power, propulsion and control to a 300x300x70 micron3 microrobotic platform that can be driven with a full three degrees of freedom and can manipulate objects on a flat substrate in both air and liquid environments. An undergraduate student team using the microrobotic.