MEMS and Nanotechnology, Volume 2

For more than a decade, instruments based on local probes have allowed us to “touch” objects at the nanoscale, making it possible for scientists and engineers to probe the electrical, chemical, and physical behaviors of matter at the level of individual atoms and molecules. In principle, physical interactions on this scale are characterized by fixed, unique values that need only be reliably measured in terms of accurately realized units of force and length to serve as standards. For example, the silicon lattice spacing is often used as a convenient ruler for estimating length in atomic scale images, since this lattice spacing has been independently measured using x-ray interferometry. Recently, the force-induced failure of DNA, often referred to as the overstretch condition, has been proposed as both a standard of force and length in single-molecule bio-physics experiments. Still other nanomechanics researchers have suggested that the rupture force of a single-atom chain is unique to a given metal, and that this intrinsic force can be used to calibrate atomic break junction experiments. In both these examples, a fundamental assumption is that the irreducible nature of nanoscale experimentation, in this case tensile testing, yields consistency befitting a standard. This paper offers context and a condensed overview of recently published results from the NIST Small Force Metrology Laboratory regarding new instruments and capabilities we have developed to examine this fundamental assumption. The reviewed papers describe new test platforms, techniques, and calibration procedures that allow us to bring accurate picoscale measurements of both length and force to bear on the problems of single-molecule and single-atom tensile testing.

Ferromagnetic materials have shown to possess some unique and useful properties, one of which is that they are magnetomechanical transducers, that is, they exhibit a change in dimension when they are subjected to an external magnetic field and vice versa. This magneto-mechanical coupling enables magnetoelastic sensors to be driven to resonance via a modulated magnetic field to detect biological species via frequency shift by mass addition [1,2]. This work details the development of an algorithm to predict the number of captured

E. coli

cells based only upon the resonance frequency shift. This is an important issue as attaching cells influence resonance based upon their location on the sensor. It is therefore necessary to develop a statistical protocol to predict the concentration of the target agent present. A protocol was developed based upon data from microscale resonators using polystyrene beads as a simulant. The protocol was verified with numerical studies and experiments using

E. coli

cells.

With higher integration, smaller size, and automated processes, sensors and wireless devices have seen dramatic enhancements to their quality, robustness, and reliability. Recent efforts have been made toward developing autonomous, self-powered remote sensor systems that can offer enhanced applicability and performance with cost savings. With the decrease in power requirements for wireless sensors, the application of piezoelectricity to energy harvesting has become viable. The technological challenge of realizing such a system lies in the construction and fabrication of a miniaturized vibration energy harvester. The current design of MEMSscale devices comprises a seismic mass made of silicon connected to the substrate by a thin PZT cantilever beam. Factors relating to power improvement and reliability of the device are discussed by addressing the shape of the cantilever beam, piezoelectric mode, MEMS process, and environmental temperature.

Piezoelectric power generators can be effective power suppliers for small devices by collecting energy from ambient vibration and converting it into electrical energy. Since such small devices are usually mobile, their operation environments can vary widely. For example, the conditions such as vibration frequency and temperature energy highly affect harvesting efficiency of piezoelectric power generators. If the ambient vibration frequency is away from the resonance frequency, there will be a decrease of output power. The ambient temperature can be a possible factor to change the resonance frequency of the power generating device since temperature influences material constants of the constituent components in a power generator such as dielectric constant, piezoelectric strain coefficient, and the stiffness Therefore, the effect of temperature on output power is studied. Since the common piezoelectric material is PZT and it is known that hard- or soft-type PZT exhibits different dependence of materials properties as a function of ambient temperature, this paper investigates the output power of the soft and hard PZTbased power generator depending on ambient temperature.

The efficiency of micro-electro-mechanical systems (MEMS) energy harvesters using transverse and longitudinal piezoelectric modes was studied. Since the emergence of piezoelectric MEMS energy harvesters, studies have mainly focused on improving the conversion efficiency at a given strain on a transduction layer. The transverse piezoelectric mode has been applied to use a higher d33 piezoelectric coefficient of a lead zirconate titanate oxide (PZT) material, but few studies have verified its distinguished efficiency compared to that of transverse mode using d31. PZT thin films were deposited on Pt/Ti/SiO2 and ZrO2/SiO2 substrates as the mode by a chemical solution deposition method. The rectangular cantilever with a Si proof mass was fabricated on an SOI wafer, and it has 20 μm of Si device layer. The cantilevered energy harvesters in the same size were respectively fabricated for longitudinal {3-1} and transverse {3-3} mode using parallel electrode plates and interdigitated electrodes (IDE). The generated voltage and power were analyzed considering piezoelectric constants of the PZT films in transverse and longitudinal modes. Since the efficiency of the transverse energy harvester seems to be strongly affected by IDE configuration, a study of this is accompanied. This study might give the direction of choosing the piezoelectric mode for the higher efficiency of MEMS transducers based on the material study.

Microcompression is becoming an increasingly popular technique to investigate the orientation dependence and size effects associated with single crystals under uniaxial compression. Literature shows that for certain materials, as the diameter of these micro-scale pillars decreases, yield stresses and strain hardening rates may increase; however, this phenomenon has not yet fully been investigated for hexagonal close packed (hcp) materials. In this study, microcompression experiments are conducted on micropillars that are fabricated using focused ion beam (FIB) milling. These single crystal magnesium specimens are loaded in compression along the [0001] c-axis, and the stress-strain curves reveal that there are no significant size effects.

The reliability of metallic micro-electromechanical systems (MEMS) depends on time-dependent deformation such as creep. To this end, a purely mechanical experimental methodology for studying the time-dependent deformation of free-standing microbeams has been developed. It is found most suitable for the investigation of creep due to the simplicity of sample handling and preparation and setup design, whilst maximizing long term stability and displacement resolution. The methodology entails the application of a constant deflection to a µm-sized free-standing aluminum cantilever beam for a prolonged period of time. After this load is removed, the deformation evolution is immediately recorded by acquiring surface height profiles through confocal optical profilometry. Image correlation and an algorithm based on elastic beam theory are applied to the full-field beam profiles to yield the tip deflection as a function of time. The methodology yields the tip deflection as function of time with ~3 nm precision.

Cutting edge mass sensors are capable of discriminating mass changes as small as several dozens of atoms, however the smallest mass commercially available from NIST with a calibration traceable to the International System of Units (SI) is 0.5 mg. To bridge this gap, new metrological techniques are being developed. A mass change from the electrochemical dissolution of tungsten wire has been measured using a commercial microbalance, and applied to a dynamic calibration of the spring constant of a tuning fork oscillator designed for use in frequency modulated atomic force microscopy (FMAFM). The spring constant measured using the dynamic method agreed within experimental uncertainty with that determined using an instrumented indenter, however an improved model for the indenter’s contact mechanics will be necessary to validate the assumptions used in the dynamic method to less than 10 %.

Chemical and biological sensors based on resonant microcantilevers offer distinct utility due to their small size, low power consumption, high sensitivity, and, when bulk fabricated, comparatively-low cost. Modern resonant mass sensors typically utilize chemomechanically-induced frequency shifts in linear resonators for analyte detection. Recent results, however, have indicated that nonlinear sensors, which actively exploit dynamic transitions across sub-critical or saddlenode bifurcations in the device’s frequency response, have the potential to exhibit improved performance metrics and operate effectively at smaller scales. This relatively-novel sensing approach directly exploits chemomechanically-induced amplitude shifts, instead of frequency shifts, for detection. Accordingly, it has the potential to eliminate the need for numerous power-consuming signal processing components in final sensor implementations. The present work details the ongoing development of low-cost, linear and nonlinear, bifurcation-based mass sensors founded upon selectivelyfunctionalized, piezoelectrically-actuated microcantilevers. Specifically, the work describes the modeling, analysis, microinkjet functionalization, and experimental characterization of these devices.

We present a theoretical analysis of a packagable method for calibrating the force and displacement of a micro electro mechanical system (MEMS) that is subject to geometric and material property variations. Property variations are usually due to variations in the fabrication processes, packaging, and environmental exposure. Force and displacement are among the most important fundamental mechanical quantities for investigating, discovering, and exploiting micro and nanoscale phenomena. However, finding a practical and traceable method to accurately and precisely measure the minute forces and displacements in MEMS has been elusive. One reason is because the force generated by MEMS is quite often smaller than the force that can be measured by conventional force sensors. Similarly, displacements in MEMS can be as small as a fraction of the diameter of an atom, which is beyond the capabilities of standard displacement sensors. Our present analysis addresses the calibration of force and displacement for MEMS comprising comb drive sensors and actuators. Our approach for calibrating force and displacement is based on the strong and sensitive coupling between mechanical performance and electronic measurands at the microscale. That is, variations in geometry and material properties affect performance, which can be capacitively measured using on-chip or off-the-shelf capacitance meters. A novelty in our analysis is the elimination of unknown properties, which allows us to express mechanical quantities and their uncertainties solely in terms of electrical measurands. We derive analytical expressions for extracting measurements of force, displacement, stiffness, and their uncertainties by electrical probing. And we show how our method is expected to a few orders more precise than convention.

A novel experimental method for the interfacial mechanics of nanofibers and nanotubes was developed. The debond force was determined by MEMS devices whose motion was precisely measured from optical images by digital image correlation. Essential elements of this method are the submicron control of nanofiber/nanotube embedded length in a thermoplastic or thermosetting polymer and the application of well controlled pull-out force until terminal debonding. The cross-head displacement resolution is at least 20 nm and the force resolution of the order of nanonewtons. A traceable force calibration technique was integrated to calibrate the MEMS force sensors. The method allows for nanofiber pull-out experiments at time scales varying from microseconds to hours and at hot/cold temperatures. Experiments have been conducted for the first time with ø150-350 nm carbon nanofibers embedded in EPON epoxy to quantify the role of nanofiber surface functionalization in the interfacial shear strength. It was clearly shown than surface functionalization drastically increases interfacial adhesion by a factor of three. The present experiments are the first of their kind both in terms of experimental fidelity and data coherence compared to prior experimental attempts, pointing out the robustness of this new experimental method.

We present an investigation of electrostatically-actuated carbon nanotube-based nanoelectromechanical switches. The primary goal of this study is to create a metric for design of robust, high-cycle devices. Methods for fabricating arrays of freestanding carbon nanotubes are discussed. Parametric studies, both experimental and computational, are then conducted to elucidate the failure mechanisms common to this class of carbon nanotubebased nanoelectromechanical systems, and to identify their point of onset within the design space. Experiments are performed

in situ

the scanning electron microscope, enabling direct imaging of device operation and the mode of eventual failure. Complimentary dynamic multiphysics finite element simulations of device operation are also presented to investigate the underlying mechanisms of the experimentally-observed failure modes.

The effect of nano-deformation, damage and growth of carbon nanotubes (CNTs) reinforced polymer composites is investigated using electro-mechanical response at different loading conditions. Three different polymer systems namely polyurethane, polyurethane reinforced with gas bubbles (that induces porosity) and polyurethane reinforced with Aluminum Silicate hollow microspheres (Cenospheres) in this study. CNTs of different weight percentages are loaded into above three polymer systems and a combination of shear mixing and ultrasonication processes are used to fabricate composites. High-resolution scanning electron microscopy and transmission electron microscopy are used to verify homogenous dispersion of CNTs in the above systems. A four-point probe method is used to measure high resolution electrical response when the above polymer systems are subjected to mechanical loads. The effect of various types of mechanical loading on different stages of deformation of test samples, onset of damage and growth will be discussed using electro-mechanical response of polymer systems.

Tribology remains an active area of research for the Micro-electromechanical Systems (MEMS) community. At the micron scale, which is the scale relevant to commercial MEMS, a number of factors namely roughness, apparent contact area, surface topography, surface chemistry, etc. are known to have a significant impact on the tribological properties. Historically, researchers have found it difficult to study the effects of these factors individually. We report on a test platform designed and fabricated using a single mask scheme within a relatively smooth SOI wafer. The test platform includes several different micromechanisms on the same chip so that a systematic investigation of the factors that influence tribology in MEMS can be carried out. The test platform is therefore an ideal stage for testing and comparing the various strategies that can be used to address the tribological issues that are presently plaguing the MEMS community.

Artificial structures with sub-optical wavelength features are engineered to demonstrate material properties for optical and infrared permeability and permittivity not otherwise found in nature. Such artificial structures are referred to as optical and infrared metamaterials. The application space of electromagnetic metamaterials includes novel sub-wavelength waveguides and antennas, true time delay devices, optical filters, plasmonic electronic-optical interfaces, optical limiters and thermal management systems. In this paper, we present an optical diagnostic technique adapted for measuring and analyzing bidirectional polarimetric scatter from novel optical and infrared metamaterials of interest. This optical diagnostic technique is also broadly applicable to other optical/infrared metamaterial structures as well as other nanostructures such as plasmonic devices or photonic crystals that may be proposed or developed in the future. The specific project goals are a) Demonstrate a novel metamaterial characterization full-polarimetric diffuse ellipsometry technique suitable to measure desired material properties with stated uncertainty limits for novel optical and infrared metamaterials of interest. b) Demonstrate incorporation of predictive computational codes that estimate the electro-magnetic property values for metamaterial designs and concepts of interest.

Thermal metamaterials are materials composed of engineered, microscopic structures that exhibit unique thermal performance characteristics based primarily on their physical structures and patterning, rather than just their chemical composition or bulk material properties. In many cases, the heat transfer performance attributes of the thermal metamaterial are such that similar performance cannot be obtained using conventional materials or compounds. Thermal metamaterials are an emerging technology, and are just now beginning to be acknowledged and developed by the microelectronics and material sciences community. This paper presents a series of ten proof-of-concept thermal metamaterial devices. Modeling and testing of these microelectromechanical systems (MEMS) based thermal metamaterial prototypes showed that the electrical and thermal conductivity of the material can be switched or tuned within a certain operational range, and that this switching is a function of passive or active actuation of the metamaterial’s structural elements, not just its chemical composition.

Metamaterial structures for RF applications are becoming essential in the race to reduce the footprint of antenna and components necessary for RF systems. Metamaterials provide a viable option to engineer structures from commonly used materials and processes to reduce the weight and size requirements for systems that normally operate at ¼ wavelength or greater in size for optimal performance. The Split ring resonators (SRR) first developed by Pendry, et al., has proven to be a viable component necessary to create negative index material structures. A fabricated SRR has a specific

Metamaterials are materials with periodic, sub-wavelength inclusions believed by some to generate responses that behave electromagnetically like effective mediums. This behavior provides the capability to synthesize materials with special parameters that will allow for size reduction of existing devices as well as the creation of new devices with unique capabilities. A key limiting factor for metamaterials, however, is the restriction of the special parameters to a small frequency band. To overcome this limitation, a microelectromechanical systems (MEMS) cantilever-beam device is placed over the gaps of a pair of split ring resonator (SRR) particles designed to operate in the radio frequency (RF) regime. Along with a wire lattice, the SRR particles are believed by many to generate an effective medium with a negative index of refraction over a small frequency band. The variable capacitors change the capacitance of the SRRs and shift the resonant frequency of the device. Efforts to predict and measure the behavior of this device are critical to the design effort. This paper demonstrates the techniques employed to model and test the electromagnetic properties of this device.

Electrochemically-active conducting polymers (ECP) swell or shrink in response to ion and solvent incorporation or ejection as a result of electrochemical reaction of the polymer. As a consequence, they are, in principle, attractive materials to consider for inducing fluid motion of electrolytes in microfluidic systems. When anodic potential is applied to an electrode attached to one end of ECP strip, the oxidation process starts from the electrode and proceeds along the polymer, propagating as a wave. This wave is driven as a consequence of the electrochemical reactions and would be coupled to a propagating front of compositional change. This property of the ECP can be used to design pumps and mixers for microfluidic systems. We in this paper set up a 2-D transport model to explain this wave phenomenon that includes both diffusion and electro-migration, that is coupled to the reaction at the polymer-solution interface, and that also includes the effects of change of polymer conductivity on the charge transport in the polymer layer. We explore the design for a microfluidic pump that uses this process and its efficiency to pump electrolytes.

From the last decade MEMS has emerged as one of the major area of interest, not only in India but also in the globe. This is basically due to its wide application in various field including Bio-Engineering, Automotive system (transducers, accelerometers), manufacturing and fabrication etc. MEMS is an approach that conveys the advantages of miniaturization, multiple components and microelectronics, to design and to construct integrated electromechanical systems.

This paper is a high level discussion of surface micromachining and its applications amongst many such as sensors, actuators and micro motor etc. Micro fabrication can be done by the various techniques such as Lithography, Bulk micromachining, LIGA and surface micromachining. Surface micromachining enables the fabrication of complex multicomponent integrated micromechanical structures that would not be possible with other methods. This technique encases specific structural parts of a device in layers of a sacrificial material during fabrication process. In other methods even small misalignment between mask and structure can pose a problem. Further all other processes are subtractive micromachining processes but surface micromachining is an additive micro structuring technology.

In the present work, fabrication of micro motor by using surface micromachining technique is explained. One of the major advantage of surface micromachining is to fabricate quite small structural heights typically 2-5 µm and seldom exceeds 20 µm. The small structural height also allows for much lateral dimensions compared to other micromachining techniques. Though micromachining of micro motor is a complex process with different micro fabrication techniques, surface micromachining excels through this.

Past work associated with this project has focused on both symmetric and asymmetric base arrangement piezoresistive microcantilever beams used for gas detection. Symmetric piezoresistive microcantilever beams have been shown to detect the presence of surrounding gas through changes in the resonance behavior of the beam; however, the device sensitivity was relatively low, leading to challenges due to noise and clear identification of resonance changes. An asymmetric base arrangement has been shown to improve the sensitivity of the device dramatically by changing the nature of the stress state in the piezoresistive base. The current work is focused on both improved fabrication methods for the asymmetric piezoresistive microcantilever beams and their resonance behavior in vacuum. The new fabrication method employs new equipment and photoresistors to speed the process. Furthermore, the critical step in beam writing is upgraded to whole wafer writing rather than each individual diced component. This eliminates at least two time-consuming steps and has shown promising results. The new process is being applied to several different types of SOI wafers to assess the importance of resistivity and device/insulation layer thickness on device outcomes. Future studies using these new devices will focus on detection and sensing with gases with suitable modeling and validation to demonstrate their efficacy for general use.

Seeding a layer of cells at specific depths within scaffolds is an important optimization parameter for bi-layer skin models. Experimental investigation has been performed to investigate the effect of fiber diameter and its mechanical property on the depth of cell seeding of for electrospun fiber scaffold. Polycaprolactone (PCL) is used to generate scaffolds that are submicron (400nm) to micron (1100nm) using electro-spinning. 3T3 fibroblasts were seeded on the electro-spun fiber scaffold mat of 50-70 microns thickness in this study. In order to investigate the effect of fiber diameter on cell migration, first, the electrospun fiber scaffold was studied for variation of mechanical properties as a function of fiber diameters. Atomic force microscopy (AFM) was used to investigate the Young’s modulus (E) values as a function of fiber diameter. It was identified that as the fiber diameter increases, the Young’s modulus values decreases considerably from 1.9GPa to 600MPa. The variation in E is correlated with cell seeding depth as a function of vacuum pressure. A higher E value led to a lower depth of cell seeding (closer to the surface) indicating that nano-fibrous scaffolds offer larger resistance to cell movement compared to microfibrous scaffolds

An improved e-beam lithography technique has been developed to generate a high quality micro/nano-scale random speckle pattern on various specimens for metrology and characterization of specimens using Scanning Electron Microscope (SEM) images with Digital Image Correlation (DIC) for image analysis. In this application, a mathematical algorithm has been integrated into the e-beam control system to greatly reduce the time for etching a dual-layer photo-resist coating to obtain a random distribution with optimal size distribution in the resulting pattern. It was determined that the thickness of photo-resist must be carefully controlled to obtain the desired pattern spot size after completing the development process. The resulting beam lithography technique has been employed by the authors to obtain high quality Au random pattern ranging from 150nm to 500nm on Al and Si specimens.

In addition to the local application of high quality random pattern, the authors developed a marker-placement methodology so that the local pattern area could be readily located through specimen translations. Extension of the approach to the production of high quality 50nm pattern on silicon wafer using various metals (e.g., Al, Ti, Ni, Cu, Zn, W, Ag, Pt) is in progress.

An analytical model for residual-strain measurement based on the Scattering-type scanning near-field optical microscopy (s-SNOM) has been developed in this study. A-SNOM has a capability for inspection properties of materials in nanometer-scale and with resolution up to 10 nm. However, the scattering signals in s-SNOM are highly complex and contaminated by the background noise critically. To overcome the problem, we have proposed a mathematical model to improve the near-field signals by eliminating the background noise in heterodyne detection. According to the mathematical model, the study will discuss the signal in s-SNOM in detail, analyze the spectrum of measurements, and explore more methods to get better signal. Then, the mathematical model will be combined with other modified near-field ones to construct a novel near-field analytical model to fit the experimental data on phonon-polariton as possible. Based on the new analytical model, the dielectric constants of materials can be obtained more precisely, and the residual stress and strain relative to the variation of dielectric constants of SiC which most often utilized in micro- and nano-electromechanical system (MEMS and NEMS) can be determined more distinctly.

Two methods for microscale tension experiments with microscale freestanding thin films at elevated temperatures were evaluated by means of optical microscopy/Digital Image Correlation (DIC) and Infrared (IR) imaging. The two methods employed uniform and resistive specimen heating. Optical images processed by DIC were used to calculate the strain along the specimen gauge section of specimens subjected to both experimental methods, while IR imaging was used to measure the temperature distribution along the specimens’ gauge sections. The axial strain and temperature distributions were compared qualitatively to evaluate the efficacy of each method. Uniform specimen heating provided uniform temperature and axial strain distributions that were not affected in any measurable way by the use of the “cold” external probe employed to pull on the specimens. However, the resistively heated specimens had highly non-uniform temperature and axial strain distributions along their gauge sections. The associated high temperature gradients resulted in strain localization and significant reduction in yield and ultimate strength measured during resistive heating experiments compared to uniformly heated samples. The experiments revealed that the latter method provides high fidelity measurements at elevated temperatures.

Since the advent of Micro-electromechanical systems (MEMS) technology, researchers have used surface texturing as one of the approaches to alleviate unintentional adhesion in MEMS. However, the conventional methods used for surface texturing are reported to reduce apparent in-plane adhesion only by a factor of 20. Further, the test surfaces used to-date are inherently rough, as a result of which, the effects of surface texturing could not be studied independently. We report on a novel method of texturing inherently smooth Si(100) surfaces by depositing dodecanethiol capped gold nanoparticles using a gas-expanded liquid technique. The dodecanethiol capping ligands are removed by exposing the treated surfaces to UV-Ozone atmosphere for an hour and the textured surfaces thus obtained are characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The textured Si(100) surfaces exhibit a significant reduction in apparent in-plane work of adhesion, which is determined using the cantilever beam array (CBA) technique, compared to untextured smooth Si(100) surfaces having only native oxide on them.

Stiction which results from contact between surfaces is a major failure mode in micro electro-mechanical systems (MEMS). Increasing restoring forces using high spring constant allows avoiding stiction but leads to an increase of the actuation voltage so that the switch’s efficiency is threatened. A statistical rough surfaces interaction model, based on Maugis’ and Kim’s formulations is applied to estimate the adhesive forces in MEMS switches. Based on the knowledge of these forces, the proper design range of the equivalent spring constant, which is the main factor of restoring force in MEMS switches, can be determined. The upper limit of equivalent spring constant depends mainly on the expected actuator voltage and on the geometric parameters, such as initial gap size and thickness of dielectric layer. The lower limit is assessed on the value of adhesive forces between the two contacting rough surfaces. It mainly depends on the adhesive work of contact surfaces and on the surfaces’ roughness. In order to study more complicated structures, this framework will be used in a multiscale model: resulting unloading micro adhesive contact-distance curves of two rough surfaces will be used as contact forces in a finite-element model. In this paper the extraction of these curves for the particular case of gold to gold micro-switches is pursued.

Surface forces play a crucial role in the contact behavior of micro-components as well as the application of MEMS products. In this study, a microscopic measurement system based on multiple beam interferometry is developed to measure the adhesive force between two mica thin films. The contact area on the mica can be determined from the FECO fringes. A double cantilever spring is used to measure the adhesive (pull-off) forces between the two mica thin films. The usefulness of the adhesive force measurement system is validated by comparing with the result from JKR contact theory.

This paper presents the performance of a thermal actuator made from single crystal silicon. The thermal actuator, shaped like a chevron, has four beams on each side and a shuttle in the middle. The shuttle’s motion is caused by thermal expansion and bending of the beams. The power curve, temperature profiles, in-plane and out-ofplane displacements, frequency response, as well as load-displacement curves of this device were measured at various operating voltages at the ambient condition. Experimental setup and results are described.

A new class of thermal microactuators, Z-shaped thermal actuator, is introduced in comparison with the wellestablished V-shaped thermal actuator. Though they share many features in common, Z-shaped thermal actuator offers several advantages: compatibility with anisotropic etching, smaller feature size, larger displacement, and larger variety of stiffness and output force. While the Z-shaped thermal actuator was modeled analytically and verified by multiphysics finite element analysis (FEA), the beam width and length of the central beam were identified as the major design parameters in tuning the device displacement, stiffness, stability and output force. Experimental measurements were taken on three arrays of Z-shaped thermal actuator with variable parameters. Results agreed well with the finite element analysis. The development of Zshaped thermal actuator is applicable in simultaneous sensing and actuating applications. During the quasi-static test of individual Z-shaped thermal actuator, the average temperature in the device structure was estimated based on electric resistivity at each actuation voltage.

The use of electrothermal actuators to achi eve the necessary motion of a MEMS based safe and arming device was thoroughly explored. Multiple variants of thermal actuators were designed, modeled, fabricated, and tested in order to gain a better understanding of their specific characteristics. Design variations included both single and double hot arm actuators as well as bent beam thermal actuators. Studies were performed to analyze and compare the displacement and output force of these actuators both as standalone devices as well as multiple actuators joined together. Detailed analysis of the results of the modeling and testing demonstrated the advantages and disadvantages of each style of thermal actuator. Furthermore, the specific variant of electrothermal actuator that is best suited for implementation into MEMS based safe and arming devices can be effectively determined. Finally, detailed analysis of the performance of electrothermal actuators integrated into a functioning MEMS safe and arm device will be presented. Methods in which these actuators are incorporated to best take advantage of their particular characteristics is shown as well as methods that were incorporated in order to overcome some of the shortcomings inherent with these actuators in order to provide the overall safe and arming device with reliable and efficient performance.

We have performed surface plasmon resonance (SPR) experiments in the Kretchmann configuration on prisms coated with metal and alloy films. The experiment is performed at various wavelengths that include 1320 nm and 1550 nm wavelengths that are important for optoelectronic applications. The metal films of 20nm/50nm thickness are grown by magnetron sputtering and are binary alloy films of Nickel and Chromium (Nichrome). The aim of this study is two-fold. Our results would show SPR behavior as a sensitive function of film composition and film thickness. Our results also show two interesting thickness regimes where the reflectance is dominated by different processes that take place at the interface between the metal and the dielectric (fused silica prism in our study). Our measurements reveal a contrast reversal in plasmonic signal as we change the alloy thickness from 50 nm to 20 nm for the shorter wavelength.

Nano-characterization studies using atomic force microscopy (AFM) was conducted to study the effect of accelerated ultra violet (UV) and thermal degradation on mechanical properties of Nylon textile fibers. Nylon fibers were exposed to UV radiation for six different hours using Q-UV Panel Weatherometer. The exposed fibers were molded in an epoxy plug for nanaoindentation using AFM. Progressive nanoindentation from surface to the center of the fiber was used to investigate the effect of degradation on gradation of Young’s modulus across fiber cross-section. it was identified that UV degradation decreases the Young’s modulus from center to surface of the fibers up to 144 hours of exposure. Reduction of Young’s modules at surface was greater than the center implying more deterioration at the surface. To investigate thermal degradation effect on Nylon fibers, the fibers were exposed to 175

o

C for four weeks. initial experimentation indicates that the thermal exposure causes gradual reduction of Young’s modules. Wide angle x-ray spectroscopy (WAXS) and Fourier Transform infra Red Spectroscopy (FTIR) are used to correlate the fiber chemical and micro-structured changes to the variation of nano-mechanical properties.

An experimental investigation has been conducted to determine the effect of adding boron nitride (BN) nanoparticles on the thermal conductivity of polyurethane nanocomposites. BN nanoparticles (average size of 70 nm) were functionalized using three different materials: acetone, nitric acid, and an alkoxysilane. Various weight fractions of the alkoxysilane-coated particles were incorporated into a polyurethane via shear mixing and ultrasonication. The dispersion of nanoparticles within the fabricated nanocomposites was verified using fieldemission scanning electron microscopy (FE-SEM). Analysis of the FE-SEM images indicated that the particles were well dispersed in the polyurethane matrix, and functionalization with alkoxysilane improved BN adhesion to the polyurethane, as verified by water drop contact angle measurements. Thermal conductivity measurements, made using a thermal conductivity analyzer, indicated that non-functionalized BN particles (5% weight fraction) increased the thermal conductivity of the resulting nanocomposite by 50%, while the increase in thermal conductivity realized by the addition of the silane-treated BN particles was only about 20%. Additional testing is underway to determine why better thermal conductivity results were not obtained from the silane-treated BNpolyurethane nanocomposites.

When scaling the critical dimensions into nanotechnology, the impact of layout and line edge becomes important. Implementation of Cu and low dielectric constant (low-k) materials in the manufacturing process requires a complete understanding of these process characteristics and the challenges that appear during the hard mask based dual damascene approach. To create highly reliable electrical interconnects, the interfaces between the Cu metal and low-k must be optimized during the lithography, etching, ashing and copper processes. For higher aspect ratios interconnect profiles however this approach leads to increased sidewall roughness and undercut. To suppress problems in the photolithography and etching processes, the balance of the processes integration should be quantitatively and instantaneously controlled to the optimum manufacturing technologies. For copper filling engineering, this study also clearly demonstrated that the influence of liner barrier Ta and Cu seed performance of dual damascene manufacturing processes integration. Processes parameters that needed to be tuned are gas flow ratio, pressure and bias of the etch process. These process characteristics and manufacturing mechanism optimization will also be discussed.

A new model of thin film indentation that accounted for an apparent discontinuity in elastic strain transfer at the film/substrate interface was developed. Finite element analysis suggested that numerical values of strain were not directly continuous across the interface; the values in the film were higher when a soft film was deposited on a hard substrate. The new model was constructed based on this discontinuity; whereby, separate weighting factors were applied to account for the influence of the substrate in strain developed in the film and vice-versa. By comparing the model to experimental data from thirteen different amorphous thin film materials on a silicon substrate, constants in each weighting factor were found to have physical significance in being numerically similar to the bulk scale Poisson’s ratios of the materials involved. When employing these material properties in the new model it was found to provide an improved match to the experimental data over the existing Doerner and Nix and Gao models. Finally, the model was found to be capable of assessing the Young’s modulus of thin films that do not exhibit a flat region as long as the bulk Poisson’s ratio is known.

The elastic and failure mechanical properties, the d

31

piezoelectric coefficient and the effect of applied stress on the hysteresis curves of freestanding PZT composite films, comprised of SiO

2

, Pt, PZT and Pt, were measured from microscale tension specimens. The d

31

coefficient was measured from the out-of-plane deflection of biased PZT specimens with dimensions similar to those of MEMS components. An analytical solution for the bending of a multilayered piezoelectric beam was used to compute a first estimate of d

31

as 176±27 pm/V. The field induced inplane stress hysteresis loops were asymmetric at small in-plane stresses becoming of similar magnitude as the applied stress was increased beyond 300 MPa. Similarly, the intersection of the hysteresis loops shifted from negative to positive electric field at stresses larger than 150 MPa. The applied stress resulted in reduction of the hysteresis magnitude due to mechanical constraints imposed on 90° domain switching. The effect of high in-plane stress on domain switching was also the reason for the hysteretic non-linear stress-strain curves that were recorded for unbiased PZT films.

While it is intuitive that molecular interaction should correlate to the mechanical properties of a material, it has only recently become possible to make the measurements necessary to trace the effects of molecular interaction across length scales to properties at the level of the material. The utility of “classical” polymeric adhesives is underscored by their widespread use in primary structural applications ranging from aerospace, automotive, and civil structures to biomedical implants and microelectronic devices. To date, the vast majority of the efforts directed toward improving the strength and durability of adhesives have been largely empirical. At the same time, the drive towards miniaturization in MEMS and NEMS devices and nano patterning means that an understanding of adhesion and fracture at smaller and smaller scales needs to be developed. This actually provides an opportunity to decrease the amount of empiricism as the number of variables is essentially decreased.

Residual stresses in anodically bonded silicon devices can result in quality control and process control deficits if the stresses are not controlled. At the same time several geometries may benefit from a controlled introduction of residual stresses. For example, long, thin structures may utilize a residual tensile stress to minimize the likelihood of buckling, while etched cavities with sharp corners can benefit from a residual compressive stress to suppress crack initiation and growth.

In the present work, we quantify the residual stress fields present in silicon wafers that are anodically bonded to virgin Pyrex wafers. Anodic bonding is conducted using standard procedures as well as a proposed alternative method that utilizes differential thermal bonding to control the residual stress state. The experimental stress state is compared to theoretical finite element calculations to determine the capability of controlling stresses based on a simple thermal model.

Nanoindentation studies using atomic force microscopy (AFM) was conducted to investigate the effect of accelerated ultra violet (UV) and thermal degradation on mechanical properties of Polypropylene textile fibers. The Polypropylene fibers with initial stabilizers were exposed to UV degradation using Q-UV Panel Weatherometer. The effect of degradation on gradation of Young’s modulus values across fiber cross-section was investigated by doing progressive nanoindentation from the surface to the center of the fiber. It was identified that UV degradation initially increases the Young’s modulus values from center to surface of the fibers till 120 hours of exposure and the values show decreasing trend at 144 hours of exposure. The Youngs modulus values at 144 hours exposure are less than those of unexposed fibers. To investigate thermal degradation effect on Polypropylene fibers, the fibers were exposed to 125oC as a function of number of weeks in increments of one week for four weeks. Results indicate that the thermal exposure did not have much impact on variation of Young’s modulus values for the first three weeks and showed increase in Young’s modulus values at the surface when they are exposed to four weeks. The increase in Young’s modulus values of Polypropylene fibers exposed to UV will be correlated with oxidation chemistry and micro-structural changes using Wide Angle X-ray spectroscopy and infra red spectroscopy techniques.