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Grain size influences the mechanical strength of materials. In polycrystalline materials, strength increases with decreasing average grain size (for grains larger than 100 nm). This well-known Hall–Petch relationship typifies a strengthening mechanism, in which dislocation motion is impeded by grain boundaries. As grains become smaller, higher stresses are required to deform them. However, this formalism only considers the role of the “average” size of grains. Heterogeneous materials, however, have a broad “distribution” of grain sizes. Here we show that materials with narrowed grain size distributions have mechanical properties that differ from Hall–Petch predictions. Narrower distributions show increased strength, as their homogeneously sized grains yield at higher loads than the large grains in materials with broader grain size distributions. Plastic deformation depends on the coarsest grains, which yield first. These results suggest new routes for tailoring material properties.

The plastic deformation of several orientations of a monocrystalline NiTi shape memory alloy was investigated via nanoindentation. The onset of plasticity, indicated by a pop-in, was used to determine the activation volume for each orientation. Unlike other reports, we found the activation volume to be dependent on orientation; in particular, the (1 0 0) orientation had an activation volume double that of the (1 1 0) and (1 1 1) orientations. This is attributable to different recoverable transformation strain behaviors. These observations illuminate the deformation mechanisms that may exist in materials that undergo phase transformations.

The phase transformation and nanoindentation response as a function of crystallinity of NiTi thin films were assessed. A phase change was detectable in samples with 1% crystallization. Measured mechanical properties indicate that the films soften with crystallization. Films partway through crystallization presented a bimodal response: crystalline regions had moduli similar to fully crystallized films; and amorphous regions had larger moduli (larger than as-deposited amorphous films) attributable to structural relaxation. A modified Voigt model describes the evolution of the modulus in crystallizing films.

Fundamental to the development of three-dimensional microelectronic fabrication is a material that enables vertical geometries. Here we show low-melting-point metal alloys containing iron dispersions that can be remotely manipulated by magnetic fields to create vertical geometries and thus enable novel three-dimensional assemblies. These iron dispersions enhance the mechanical properties needed for strong, reliable interconnects without significantly altering the electrical properties of the alloys. Additionally, these iron dispersions act as susceptors for magnetic induction heating, allowing the rapid melting of these novel alloys at temperatures lower than those usually reported for conventional metal alloys. By localizing high temperatures and by reducing temperature excursions, the materials and methods described have potential in a variety of device fabrication applications.

The effect of copper additions (1.3 at%) on the crystallization of amorphous nickel-titanium thin films was explored. Using differential scanning calorimetry (DSC), the overall activation energy and crystallization temperatures were found to be similar to pure NiTi. However, in situ transmission electron microscopy (TEM) showed the nucleation and growth behaviors were markedly different. NiTiCu exhibited a lower nucleation rate, suggesting a higher activation energy in comparison to NiTi. The large grains in NiTiCu microstructures are consistent with a lower growth activation energy. These data suggest copper additions create higher interfacial energies. This paper presents experimental measurements that corroborate this mechanism.

We report the effects of crystallization temperature on the phase transformation behavior of NiTi thin films. With increasing crystallization temperature, the film stress during phase transformations drops sharply. Smaller grains were found as crystallization temperatures increased. These data suggest that, along with thermal stress, microstructure contributes to the phase transformation behavior, whereby smaller grains may suppress the conversion to martensite. This study illuminates the connection between processing, microstructure and phase transformation behavior for these technologically important materials.

Nickel–titanium thin films were deposited onto silicon substrates and subjected to incomplete martensitic transformations. With wafer curvature methods, we observed a stress discontinuity that seems analogous to the splitting of the endothermic peaks measured by differential scanning calorimetry due to the temperature memory effect. The martensite start temperature ( M s ) remains constant during incomplete forward transformations, resulting in a constant-stress range between the arrest temperature and M s . However, incomplete reverse transformations start immediately at the arrest temperature. X-ray diffraction measurements confirm these path-dependent behaviors, which are consistent with the thermodynamic model of martensitic transformations.

Ni–Ti thin films of various compositions were sputtered-deposited on silicon substrates. Their mechanical properties (hardness and Young's modulus) were then determined using a nanoindenter equipped with a Berkovich tip. This paper examines the effects of composition on the mechanical properties (hardness and Young's modulus) of the sputter deposited Ni–Ti thin films. This is of particular interest since the actuation properties of these shape memory alloy films are compositionally sensitive. The surface-induced deformation is revealed via Atomic Force Microscopy (AFM) images of the indented surfaces. Which show evidence of material pile-up that increases with increasing load. The measured Young's moduli are also shown to provide qualitative measures of the extent of stress-induced phase transformation in small volumes of Ni–Ti films.

Sputtered NiTi thin films are commonly deposited in an amorphous state and require a high-temperature annealing step to crystallize them. Their crystallization process is driven by the kinetic interplay of both nucleation and growth, and their resulting microstructure dictates the martensitic transformation behavior and actuation properties. In this paper, we present the full description of the individual contributions of nucleation and growth. Using in situ transmission electron microscopy heating methods with the Johnson–Mehl–Avrami–Kolmogorov, theory, we are able to determine these key parameters. During heating, we observed and analyzed the microstructural development and found a correlation between the average grain size and temperature. With cooling, we observed directly the conversion of the high temperature phase (austenite) to its low temperature phases (R-phase and martensite). We also examined the effect of composition on the martensitic transformation and found the crystallization behavior was markedly different for small variations. Such insights provide details that enable the continued development of thin film materials with optimal properties.

Sputtered-deposited nickel titanium thin films are commonly amorphous when synthesized and require annealing to crystallize them. The resulting microstructures, which are governed by nucleation and growth kinetics, dictate the actuation properties. The evolution of these microstructures was studied using in situ transmission electron microscopy (TEM) heating methods. The experimentally-determined kinetic values of nucleation and growth were inserted into a mathematical expression derived from the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory, which predicts the average grain size over a broad range of temperatures.

The crystallization and phase transformations of amorphous NiTi thin films were studied using in situ transmission electron microscopy (TEM). These films were sputter-deposited onto micromachined silicon-nitride membranes and subjected to heating and cooling conditions. The microstructural evolution was monitored and recorded. Kinetic parameters such as the nucleation rate, growth rate, and area-fraction transformed were independently determined by noting the number of grains per frame and their change in size. Using the Johnson–Mehl–Avrami–Kolmogorov analysis, fitted kinetic parameters were determined and found to be consistent with TEM observations. To explore the compositional sensitivity of crystallization, samples near-equiatomic and slightly Ti-rich were studied with these methods. TEM micrographs show that equiatomic films exhibit polymorphic crystallization while samples that are slightly off-stoichiometry showed more complicated behavior.

The ability to reliably and controllably micromachine membranes by wet anisotropic etching of silicon is essential in microelectromechanical system (MEMS) device fabrication. This paper proposes an effective way to dependably microfabricate SiO 2 and Si 3 N 4 membranes with little supervision. This two-step method takes full advantage of the different etching behaviors of both EDP (a solution of ethylene diamine, pyrocatechol, and water) and potassium hydroxide (KOH). First, EDP is used, which has almost no reaction with silicon nitride and a moderately fast silicon etching rate. Next, KOH is used, which has a negligible nitride etching rate and a significantly faster silicon etching rate. Using this method, fully etched membranes of large geometries can be consistently generated. The size of microfabricated membranes presented in this paper varies from 200 μm × 200 μm to 9000 μm × 9000 μm with a thickness variation from 100 nm to 1000 nm. High temperatures were used in both etchants to further increase the silicon etching rate.

Widely used electronic components and optical materials are made up of a variety of inorganic materials, such as nitrides, carbides, oxides, sulfides, fluorides, selenides, diamond, silicon, and GaAs. The surfaces of these materials are known to be very difficult to bond with low-melting-point solders. A direct and powerful bonding on these surfaces has been obtained in air, without using any flux, by using low-temperature solders containing rare earth (RE) alloying elements. The nature of the bonding is based on chemical reactions at the interface, and hence, strong bonds are obtained. The Sn-3.5%Ag-2.5%Lu (by weight) solder and the Au-19.5%Sn-2%Lu solder, for example, exhibit interfacial-bond strengths in excess of 6.9–13.8 MPa. They can be useful for providing direct, ohmic-electrical contacts and interconnects in a variety of electronic assemblies and for producing dimensionally stable and reliable bonding in optical fiber, laser devices, or thermal-management assemblies.

The influence of alumina and titanium carbide, components of magnetic recording sliders, on the carbon gasification reaction was investigated. Pure alumina and titanium carbide powders were each combined with graphite powder and subjected to thermogravimetric analysis (TGA). The molar ratio ranged from 0 to 20 mol percent; graphite powder was the balance. From the thermogravimetric analysis, the activation energy Ea of the reactions was determined. It was found that the activation energy for carbon gasification reduced slightly for increasing alumina mole percentage. Titanium carbide additions markedly increased the activation energy. This increase indicates a competitive oxidation reaction that forms titanium oxide, as confirmed by X-ray diffraction (XRD). As a result of these observations, titanium oxide was also mixed with graphite powders and analyzed by TGA. Titanium oxide has an activation energy behavior that becomes more complex with increasing mole percentage: the activation energy first increases and then decreases. These data are presented and the oxidation reaction is proposed.

Amorphous carbon thin films, which are often used as protective coatings for magnetic hard disks, were deposited in a carbon/cobalt alloy/carbon trilayers (20/10/20 nm) and subjected to thermal annealing and cooling. The associated microstructural changes were analyzed by in situ transmission electron microscopy (TEM). TEM micrographs show that the amorphous carbon in contact with the magnetic media increases in graphitic content at annealing temperatures near 400 °C. It fully crystallizes between 500 and 600 °C. The microstructural changes at these temperatures suggest that the metals of the magnetic layers mediate graphitization, similar to the behavior of other eutectic metal metalloid systems (e.g., Al–Si, Ag–Ge). Calorimetric and magnetic measurements are consistent with a graphitization mechanism that includes a diffusional process. This article presents the experiments and proposes a graphitization mechanism.

Alumina-titanium carbide composite sliders used in magnetic recording were coated with diamondlike carbon (DLC) to permit exploration of their effect on tribochemical wear. For comparison, testing was performed on both coated and uncoated sliders. Gases sampled directly from the sliding interface between a carbon-coated thin-film magnetic recording disk and the slider contained carbon dioxide in both dry nitrogen and dry oxygen environments. In the oxygen environment, uncoated sliders produce carbon dioxide at a rate 10 times greater than coated sliders. This suggests that catalysts in the slider composite material are necessary for carbon oxidation wear. Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in Kissimmee, Florida, October 8–11, 1995

A library of gold–cobalt alloys was synthesized by combinatorial methods to explore potential contact materials for microfabricated microrelays. After a compositionally graded film was deposited, it was subjected to heat treatments to create precipitates and to promote precipitation hardening. Using a high-throughput screening method, the film was then characterized for mechanical hardness, sheet resistance, composition, and microstructure by using nanoindentation, four-point probe, x-ray photoelectron spectroscopy, and transmission electron microscopy. The hardness exhibited a linear behavior from pure gold to pure cobalt from 2 to 9 GPa. The microstructure included a metastable gold–silicide with a grain size that seems dependent on the amount of cobalt. From this combinatorial method, we gain an understanding of the material’s structure–property relationship and can illuminate the link between mechanical and electrical properties to composition. This work presents the experiments and techniques for mapping material properties.

Amorphous sputtered nickel–titanium thin films were deposited onto micromachined silicon-nitride membranes and subjected to heating and cooling conditions. Their associated microstructure was monitored directly and simultaneously with in situ transmission electron microscopy. These electron-transparent membranes constrained the NiTi films and rendered it possible for observation of the complete transformation cycle, which includes: the crystallization of the amorphous phase to austenite phase (cubic B2 structure) with heating; and the conversion of austenite (B2) to martensite (monoclinic B19′ structure) with cooling. Electron micrographs show the nucleation and growth of grains occurs at a temperature of 470°C and at a rate that indicates a polymorphic transformation. The onset of martensitic transformation occurs between 25 and 35°C. Calorimetric measurements are consistent with the observed crystallization.

The ability of rare-earth-containing lead-free solders to wet and bond to silica was investigated. Small additions of Lu (0.5–2 wt. %) added to eutectic Sn–Ag or Au–Sn solder render it directly solderable to a silicon oxide surface. The bonding is attributed to the migration of the rare-earth element to the solder–silica interface for chemical reaction and the creation of an interfacial layer that contains a rare-earth oxide. It was found that additions of rare-earth materials did not significantly modify the solidification microstructure or the melting point. Such oxide-bondable solders can be useful for assembly of various optical communication devices.

The surfaces of electronic and optical materials such as nitrides, carbides, oxides, sulfides, fluorides, selenides, diamond, silicon, and GaAs are known to be very difficult to bond with low melting point solders (

Thin film shape memory alloys are a promising material for use in microscale devices for actuation and sensing due to their strong actuating force, substantial displacements, and large surface to volume ratios. NiTi, in particular, has been of great interest due to its biocompatibility and corrosion resistance. Effort has been directed toward adjusting the microstructure of as-deposited films in order to modify their shape memory properties for specific applications. The anisotropy of the shape memory and superelastic effects suggests that inducing preferred orientations could allow for optimization of shape memory properties. Limited work, however, has been performed on adjusting the crystallographic texture of these films. In this study, thin film NiTi samples are processed using excimer laser crystallization and the effect on the overall preferred orientation is analyzed through the use of electron backscatter diffraction and X-ray diffraction. A three-dimensional Monte Carlo grain growth model is developed to characterize textures formed though surface energy induced abnormal grain growth during solidification. Furthermore, a scaling factor between Monte Carlo steps and real time is determined to aid in the prediction of texture changes during laser crystallization in the partial melting regime.

The effects of wear and annealing on the microstructural features of amorphous carbon thin films were investigated. Amorphous-carbon thin films on hard disks were subjected to wear by full-sized alumina–titanium carbide sliders. The associated microstructural changes were analyzed by high-resolution transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). TEM micrographs and EELS spectra directly showed structural differences between worn and unworn regions, and indicated increased graphitic content. For comparison, unworn amorphous-carbon thin films were annealed and analyzed by near-edge x-ray absorption fine structure spectroscopy. The annealed unworn carbon films also showed structural changes. The microstructural changes at these low temperatures suggest that the metals of the magnetic layers mediate graphitization. This article presents the experiments and proposes a wear mechanism.

Amorphous sputter-deposited NiTi thin films were subjected to pulsed, melt-mediated laser crystallization techniques to engineer their microstructure. The effects of laser processing of pre-heated films are examined. Laser processing of films at an elevated temperature has a significant effect on the rate with which solidification occurs and therefore may be used as an added parameter to control the resulting microstructure. It is seen that the temperature at which processing is carried out has significant implications for the resulting phase and microstructure, and therefore mechanical properties. Furthermore, the microstructural effects of varying incident laser energy density are examined via atomic force microscopy (AFM), scanning electron microscopy (SEM) and x-ray diffraction (XRD), and mechanical/shape memory properties are characterized via nanoindentation.Amorphous sputter-deposited NiTi thin films were subjected to pulsed, melt-mediated laser crystallization techniques to engineer their microstructure. The effects of laser processing of pre-heated films are examined. Laser processing of films at an elevated temperature has a significant effect on the rate with which solidification occurs and therefore may be used as an added parameter to control the resulting microstructure. It is seen that the temperature at which processing is carried out has significant implications for the resulting phase and microstructure, and therefore mechanical properties. Furthermore, the microstructural effects of varying incident laser energy density are examined via atomic force microscopy (AFM), scanning electron microscopy (SEM) and x-ray diffraction (XRD), and mechanical/shape memory properties are characterized via nanoindentation.

This work utilizes pulsed, melt-mediated laser crystallization techniques to control the spatial distribution of crystalline zones within an as sputter-deposited amorphous matrix. Since shape memory responses stem from crystallographic shifts, only the selectively crystallized regions exhibit these properties. This process provides not only spatial control over the shape memory response, but potentially, through proper use of operational parameters, the shape memory response itself, i.e. phase transformation temperature, transformation strain, recovery stress etc. The solidification process is monitored in situ via transient reflectance. Furthermore, the effects of varying energy density within the irradiated region are examined with respect to the resulting micro-structure via atomic force microscopy (AFM), electron backscatter diffraction (EBSD) and x-ray diffraction (XRD).This work utilizes pulsed, melt-mediated laser crystallization techniques to control the spatial distribution of crystalline zones within an as sputter-deposited amorphous matrix. Since shape memory responses stem from crystallographic shifts, only the selectively crystallized regions exhibit these properties. This process provides not only spatial control over the shape memory response, but potentially, through proper use of operational parameters, the shape memory response itself, i.e. phase transformation temperature, transformation strain, recovery stress etc. The solidification process is monitored in situ via transient reflectance. Furthermore, the effects of varying energy density within the irradiated region are examined with respect to the resulting micro-structure via atomic force microscopy (AFM), electron backscatter diffraction (EBSD) and x-ray diffraction (XRD).

Combinatorial experiments provide a means of generating large amounts of experimental data; however that does not necessarily lead to high throughput interpretation of that data. In this paper we provide a brief summary of how one can use informatics techniques to accelerate data interpretation from high throughput experiments. We provide examples from high throughput nanoindentation and diffraction experiments.

As telecom networks increase in complexity there is a need for systems capable of manage numerous optical signals. Many of the channel-manipulation functions can be done more effectively in the optical domain. MEMS devices are especially well suited for this functions since they can offer large number of degrees of freedom in a limited space, thus providing high levels of optical integration. We have designed, fabricated and tested optical MEMS devices at the core of Optical Cross Connects, WDM spectrum equalizers and Optical Add-Drop multiplexors based on different fabrication technologies such as polySi surface micromachining, single crystal SOI and combination of both. We show specific examples of these devices, discussing design trade-offs, fabrication requirements and optical performance in each case.

A 1296-port MEMS transparent optical crossconnect with 5.1dB/spl plusmn/1.1dB insertion loss at 1550 nm is reported. Measured worst-case optical crosstalk in a fabric was n38 dB and nominal switching rise/fall times were 5 ms. A 2.07 petabit/s switch capacity was verified upon cross-connecting a forty-channel by 40 Gb/s DWDM data stream through a prototype fabric.

Micro machined relays provide switching solutions that are advantageous over existing technology in many aspects of device performance. In order to fully benefit from the MEMS solution n switching, however, a general integration strategy to various integrated circuit electronics needs to be developed. We describe the design and test of such an integration scheme utilizing flip-chip bonding of MEMS relays onto another substrate carrying the remainder of the circuitry. Individual devices consists of cantilever-like mechanical structure carrying a mobile electrode that is electrostatically actuated. The presence of a second substrate in the flip-chip bonded geometry provides the unique possibility of placing electrostatic actuators on both sides of the cantilever, thereby allowing active turn- on and turn-off of the relay device. The fabricated relays show switching time as short as 10 microsecond(s) , actuation voltages as low as 25V, on-state DC resistance as low as 2 (Omega) and open-state DC resistance as large as 1013 (Omega) . The device is assembled and packaged using a single-step flip- chip bonding process. Upon flip-chip bonding, the MEMS devices are completely enclosed in a small cavity between the two substrates that is sealed by a ring-type solder seal. Such techniques provide the opportunity for the integrated chip to be further packaged using conventional cost-effective packaging techniques.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A variety of carbon nanotube films have been fabricated and tested as cold cathodes. A spray deposition technique was developed for processing as-grown bulk nanotubes, both single-walled and multi-walled, into films of randomly oriented nanotubes. Films of randomly oriented multi-walled nanotubes were grown using thermal chemical vapor deposition, and arrays of well-aligned multi-walled nanotubes have been fabricated using a microwave plasma enhanced chemical vapor deposition technique. The emission current-voltage (I-V) characteristics of these nanotube cathodes have been measured. Both multi-walled (random and aligned) and single-walled carbon nanotubes exhibit low turn-on fields (∼ 2 V/μm to generate 1 nA) and threshold fields (< 5 V/μm to generate 10 mA/cm2). Significantly, these cathodes were capable of operation at very large current densities (> 1A/cm2), making them candidates for application in a variety of vacuum microelectronic devices.

We have investigated the optical properties of sputter-deposited silver-aluminum alloy thin films on silicon substrates at room temperature. In addition to the primary feature that corresponds to the bulk plasma resonance, a secondary dip appears in the optical reflectance spectra, which shifts and diminishes with thermal annealing. Careful structural characterization of both the as-deposited and annealed films suggests that the resonant feature originates from the surface plasmon resonances, which are localized in the dielectric gap between grains. This result indicates that the morphology of metal alloys could have a significant effect on their optical properties.

This letter demonstrates the effects of structural relaxation on the crystallization and phase transformation behavior of NiTi thin films. Heat treatments below the glass transformation temperature produce films with a greater hardness than as-deposited films. The reduction in free volume occurring during film relaxation plays a role. Using scanning electron microscopy, structural relaxation was found to decrease the overall crystallization time and increase the nucleation rate, thus modifying the resulting microstructures. Structural relaxation had little effect on the phase transformation temperatures of fully crystallized films, but slightly increased the resulting actuation force during transformation.

This letter demonstrates the role of film geometry on the phase transformation and shape memory behaviors of NiTi thin films. Lithographically patterned lines possess a strain profile that significantly alters their phase transformation behavior and surface morphology in comparison to continuous films, although the microstructures remain the same. The stress profile causes the film curvature to change with direction: concave parallel to the line and convex when perpendicular. Additionally, patterned lines require higher temperature excursions for complete phase transformations; their transformation temperature interval doubled that of the continuous film. Such observations illuminate how microelectromechanical system embodiments of these materials may behave.

This letter demonstrates the ability to induce laterally grown, large-aspect crystals via pulsed, melt-mediated laser crystallization in NiTi thin films. Sputter-deposited 200 nm NiTi films were pulse irradiated utilizing a homogenized 308 nm excimer beam over a series of varying incident laser energy densities. Solidification occurred via two distinct pathways: nucleation and growth occurred away from the boundary of irradiation, while lateral growth of unmelted seeds into the undercooled melt developed at the boundary of irradiation. The potential for exploiting this technique to produce rolling direction texture for anisotropic properties is also discussed.

Amorphous sputter-deposited NiTi thin films were subjected to pulsed, melt-mediated laser crystallization techniques to engineer their microstructure. The effects of laser processing of preheated films are examined. Laser processing of films at an elevated substrate temperature has a significant effect on the rate with which solidification occurs. It is observed that the preheating temperature at which processing is carried out has significant implications for the resulting phase and microstructure, and therefore mechanical properties. Furthermore, the microstructural effects of varying incident laser energy density are examined via atomic force microscopy, scanning electron microscopy, and x-ray diffraction, and mechanical/shape memory properties are characterized via nanoindentation.

Microstructures that emerge during the crystallization of amorphous materials depend on nucleation and growth kinetics. The ability to predict these final microstructures, particularly the average grain size, would allow better control of material properties. Well-established crystallization theories have proposed mathematical models to describe these microstructures. What remains missing, however, is an independent experimental verification of the microstructures these models predict. Here, we report in situ transmission-electron-microscopy experimental methods that assess independently the nucleation and growth rates of crystallizing grains. A consequence of having a separate, experimentally-determined description of nucleation and growth is the ability to predict the average grain size over a broad range of temperatures. The results from these experimental methods verify the theoretical models that were posed several decades ago.

In summary, a multi-service node based on an optical MEMS crossconnect switch with 1.33 dB mean loss has been demonstrated. While a simple 16-wavelength, channel-equalizing add/drop multiplexer was demonstrated as a possible node configuration, a broad range of new functions can be implemented by connecting conventional and different optical components to the low-loss crossconnect switch.

We have demonstrated a channelized micro-mechanical filter with 5 dB insertion loss and high extinction suitable for use as a channelized equalizing filter. The pass bands have been demonstrated to be sufficiently wide to permit its use with 40 Gb/s CSRZ signals.