This PDF file contains the front matter associated with the Proceedings of SPIE Volume 6463, including the Title Page, Copyright information, Table of Contents, Conference Committee listing, and the Introduction.

Nanomechanical response of molecular adsorption has been demonstrated as the basis for a number of extremely sensitive sensors. Molecular adsorption on microcantilevers results in nanomechanical motion due to adsorption-induced surface stress variation. Chemical selectivity in nanomechanical sensors is achieved by immobilizing receptors on the cantilever surface. Although receptor-based detection has high selectivity for biomolecular detection, it fails when applied to small molecule detection. Nanomechanics, however, offer new possibilities for achieving chemical selectivity that do not use any receptors. For example, small thermal mass or high temperature sensitivity of a cantilever beam could be used for detecting molecular adsorption using photothermal effects and physical property variation due to temperature. Here we describe two such techniques for achieving chemical selectivity without using any receptor molecules.

Many metal containing devices and structures must function in corrosive atmospheres that can cause them to deteriorate over time. Corrosion may take the form of metal oxides or may be compounds formed by exposure to the effluent of industrial manufacturing processes. The electronic process measurement and control industry estimates that approximately one-third of all warranty repair work can be attributable to corrosion. Accordingly, the ability to accurately monitor corrosion and take appropriate measures to avoid, deter, or prevent it can be of utmost importance to the industry. One method and apparatus for monitoring corrosion utilizes a piezoelectric crystal as a corrosion monitor. The crystal is coated with one of several corrodible metals, and the coated crystal is attached to an oscillator before placement in a potentially corrosive atmosphere. As the metal corrodes, the frequency of vibration of the coated crystal decreases. The frequency reading is then converted to a corresponding corrosion film thickness. This monitoring method and apparatus are generally suitable for measuring and detecting certain degrees of corrosion, however, in some instances more precise measurements of corrosion are desired. This paper will describe a corrosion monitor based on a microcantilever device coated with a reactive metal. Information will be provided on the development of a working microcantilever-based corrosion sensor.

Recent advances in MEMS technology have led to development of a multitude of new devices. However applications of these devices are hampered by challenges posed by limited understanding of their reliability particularly the impacts of long-term storage. Current trend in micro/nanosystems is to produce ever smaller, lighter, and more capable devices in greater quantities and at a lower cost than ever before. In addition, the finished products have to operate at very low power and in very adverse conditions while assuring durable and reliable performance. Some of the new devices are being developed to function at high operational speeds, others to make accurate measurements of operating conditions in specific processes. Regardless of their application, the devices have to be reliable while in use. MEMS reliability, however, is application specific and, usually, has to be developed on a case by case basis. This paper presents a hybrid approach/methodology particularly suitable to quantitative studies of various aspects in MEMS reliability assessment. The presentation is illustrated with selected examples representing an initial study of reliability of specific MEMS. By quantitatively characterizing performance of MEMS, under different operating conditions, we can make specific suggestions for their improvements. Then, using the hybrid approach/methodology, we can verify the effect of these improvements. In this way, we can develop better understanding of functional characteristics of MEMS sensors, which will ensure that these sensors are operated at maximum performance, are durable, and are reliable.

It is well-recognized that MEMS switches, compared to their more traditional solid state counterparts, have several important advantages for wireless communications. These include superior linearity, low insertion loss and high isolation. Indeed, many potential applications have been investigated such as Tx/Rx antenna switching, frequency band selection, tunable matching networks for PA and antenna, tunable filters, and antenna reconfiguration. However, none of these applications have been materialized in high volume products to a large extent because of reliability concerns, particularly those related to the metal contacts. The subject of the metal contact in a switch was studied extensively in the history of developing miniaturized switches, such as the reed switches for telecommunication applications. While such studies are highly relevant, they do not address the issues encountered in the sub 100μN, low contact force regime in which most MEMS switches operate. At such low forces, the contact resistance is extremely sensitive to even a trace amount of contamination on the contact surfaces. Significant work was done to develop wafer cleaning processes and storage techniques for maintaining the cleanliness. To preserve contact cleanliness over the switch service lifetime, several hermetic packaging technologies were developed and their effectiveness in protecting the contacts from contamination was examined. The contact reliability is also very much influenced by the contact metal selection. When pure Au, a relatively soft metal, was used as the contact material, significant stiction problems occurred when clean switches were cycled in an N₂ environment. In addition, various mechanical damages occurred after extended switching cycling tests. Harder metals, while more resistant to deformation and stiction, are more sensitive to chemical reactions, particularly oxidation. They also lead to higher contact resistance because of their lower electrical conductivity and smaller real contact areas at a given contact force. Contact reliability issues could also be tackled by improving mechanical designs. A novel collapsing switch capable of generating large contact forces (>300μN) was shown to be less vulnerable to contamination and stiction.

Au, Au-V solid solution, and Au-V₂O₅ dispersion films were fabricated for comparison of electrical and mechanical characteristics. Resistivity and nanoindentation hardness increased with increasing V content in all films, but the ratio of resistivity increase to hardness increase was much lower for the Au-V₂O₅ films. Measurements of contact force and electrical contact resistance between pairs of Au or Au-V films show that increased hardness and resistivity in the alloy films results in higher contact resistance and less adhesion than in pure Au. These results imply that the Au-V₂O₅ films may exhibit attractive behavior when used in a contact configuration, but this has not yet been tested.

This paper is an extended work of our previous models [1-5] and an introduction of an experiment along this line. For the 1-D model, a pre-stressed rectangular stiff film clamped at both ends delaminates from a rigid punch. According to thermodynamic energy balance, the delamination mechanics in term of external tensile force applied to the punch, punch displacement, and contact area. Coupling effect of tensile residual stress, film-punch interfacial adhesion energy is discussed in this paper. "Pinch-off" (stable shrinking of the contact area to a line) is predicted at the moment when film is completely detached from substrate. The 1-D model can be further extended to a 2-D axisymmetric model. A thin circular film clamped at the periphery is adhered to the planar surface of a rigid cylindrical punch. An external tensile load is applied to the punch causing the film to delaminate from the substrate and the circular contact edge to contract. The film spontaneously separates from the punch, or, "pull-off", when the contact radius reduces to a range between 0.1758 and 0.3651 of the film radius, depending on the magnitude of the residual membrane stress. The constitutive relation of the delamination process is derived by a thermodynamic energy balance based on a coupled interfacial adhesion and residual membrane stress. The models are useful in understanding the behavior of various adhesion-delamination phenomena, such as capacitive MEMS-RF switches, micro pumps, micro-structure network, and nano-structures. Experiment is carried out simulating the axisymmetric model and will be presented in this conference.

The mechanical properties of the structural layer play important role in the design and optimization of MEMS structures. The pull-in measurement is a popular technique used to measure the mechanical properties of a material, but its success depends on the accurate measurement of the gap (g) between the beam and the ground plane and its uniformity. In this paper we propose a novel technique which does not require accurate knowledge of the value of 'g'. In our proposed method, a large number of beams with different lengths (L) are to be fabricated simultaneously and the off-Capacitance (C_off) in addition to pull-in voltage (V_pi) measured in the same set-up. This is followed by a plot of (C³_off V³_piL⁴/A³)vs (1/A) for beams under bending dominating condition and (C³_off V²_piL²/A³) 1/A for beams under stress dominating condition, where A is the area of a beam. The plots are extrapolated to intersect the y-axis. The value of the intercept can be used to extract the values of Young's modulus and residual stress, without any definite knowledge of the value of 'g'. In this paper, we have shown with the help of simulations that using our method the material properties can be extracted very accurately even when the gap (g) is very nonuniform.

The meantime between failures of the thin film strain sensor is a critical indicator for future U.S. Army field sensing application [1]. This accelerated lifetime aging test would characterize the existing flexible strain sensor for repeated load response/application. A typical industrial maximum number of testing cycles used are about 10x10⁶ cycles [2].

Self-sensing and actuation were investigated for CNF and Ni nanowire/epoxy and silicone composites. Electro-micromechanical techniques can be used for self sensing for loading, temperature. CNF/epoxy composites with smaller aspect ratio showed higher apparent modulus due to high volume content in case of shorter aspect ratio. Apparent modulus and electrical resistivity change were evaluated as functions of different carbon fiber types. Interfacial properties of CNF/epoxy with different aspect ratios were obtained indirectly. Using Ni nanowire/silicone composites with different content, load sensing response of electrical contact resistivity was investigated under tensile and compression condition. The mechanical properties of Ni nanowire with different type and content/epoxy composites were indirectly measured apparent modulus using uniformed cyclic loading and electro-pullout test. Ni nanowire /epoxy composites showed temperature sensing within limited ranges, 20 vol% reinforcement. CNF-PVDF and Ni-silicone actuator were made successfully. Electrochemical actuator of CNF-PVDF was responded in electrolyte solution. Magnetic actuator of Ni nanowire-silicone composites was monitored under electro-magnetic field. CNF-Ni nanowire-silicone actuator having meaningful merits can be expected to be new smart structural materials at a various applications. Nanocomposites using CNF and Ni nanowire can be applicable practically for multi-functional applications nondestructively.

MEMS Technology has become more ubiquitous in recent years but still metrology for MEMS materials has lagged in terms of standardization and common industry usage. MEMS metrology encompasses a very wide range of test methods for various kinds of functional and manufacturing characteristics of these devices but in this article we only refer to test techniques for extraction of mechanical properties essential to the product development process and process monitoring. These include methods such as test structures and other methods for measuring elastic modulus, Poisson's ratio, residual stress and stress gradients, and CTE, etc. as well as properties important to device reliability such as creep, fatigue and wear. Metrology for MEMS materials has always included attempts by researchers and engineers to miniaturize existing macro level test methods like the uniaxial tensile test, hardness test, bulge test etc. but historically another approach has always existed in parallel. Novel on-wafer or on-chip test structures are continuously being developed in an attempt to achieve stream-lined in-line tests that don't require the "destructive" nature of the former group of test methods. The vision is that in-line methods would eventually be standardized to the point where they, in the mask layout phase, could be "dropped onto" wafer as in-line process control monitors (PCMs). Today, we're still far away from realizing this ideal situation in the sense that the ASTM standards list does not include a single unique test structure for material property extraction. The focus of this current article is to critically compare the various techniques that have been developed so far and contrast their viability and potential as candidates for standardization either in-line or off-line.

As the Army transforms into a more lethal, lighter and agile force, the technologies that support these systems must decrease in size while increasing in intelligence. Micro-electromechanical systems (MEMS) are one such technology that the Army and Department of Defense will rely on heavily to achieve these objectives. Current and future military applications of MEMS devices include safety and arming devices, fuzing devices, various guidance systems, sensors/detectors, inertial measurement units, tracking devices, radio frequency devices, wireless RFIDs and network systems, GPSs, radar systems, mobile base systems, satellites, missiles and the like.

Adhesion between micro parts, also referred to as stiction, is a major failure mode in MEMS. Undesirable stiction, which results from contact between surfaces, can severely compromise the reliability of MEMS. In this paper, a model is developed to predict the dry stiction between uncharged micro parts in MEMS. In dry stiction, the interacting surfaces are assumed to be either hydrophobic or placed in dry environment. In this condition, the van der Waals (vdW) and asperity deformation forces are dominant. Here, a model is developed for the vdW force between rough micro surfaces and the new model is combined with a newly developed multiple asperity point model for the elastic/plastic deformation of rough surfaces in contact to solve for the equilibrium condition of the forces. This, in turn, will yield the equilibrium distance between micro surfaces, using which the apparent work of adhesion can be found. The result of the theory is compared with the available experimental data from literature. The developed model can be easily used for design purpose. If the topographic data and material constants are known, the adhesion parameters can be quickly calculated using the model.

The inter-disciplinary nature of MEMS makes its design a highly involved process. In Optical MEMS the addition of optical parameters only increases the complexity. It is almost impossible for a designer to know where to start given the number of variables involved. In order to design a device that will meet the required specifications over its entire lifetime, reliability issues must be included in the design process. This paper develops a method that can be used to create a step-by-step design process involving reliability issues at every stage. The process begins by listing out the constants and constraints of the design. The constraints could be due to physical parameters, MEMS fabrication processes, optical reasons, reliability issues, etc. They affect the design in different ways; for example, two fibres cannot be brought closer than 250μm. This constraint will affect the optical design and the overall dimensions of the device. Taking all such constraints into account, an optical design process is outlined. The effect of individual errors is studied on a key parameter like insertion loss. This gives the designer information about which parameters the design is more sensitive to and will help in deciding the manufacturing tolerances required in the different stages. Using all of this data, an "ideal design" is developed. A Monte Carlo analysis is carried out on that design to show the effect of errors occurring simultaneously. The paper concludes with a flow chart of a suggested design process to be used when designing optical MEMS devices.

Process engineering and failure analysis of MEMS and MOEMS require static and dynamical characterization of both their in-plane and out of plane response to an excitation. A remarkable characteristic of Digital Holography Microscopes (DHM) is the extremely short acquisition time required to grab the whole information necessary to provide 3D optical topography of the sample: a unique frame grab, without any vertical or lateral scan provides the information over the full field of view. First, it ensures DHM measurements to be insensitive to vibrations. Second, it opens the door to fast dynamical characterization of micro-systems. For periodic movement analysis, DHM can operate in stroboscopic mode with standard cameras. It enables precise characterization up to excitation frequencies of 100 kHz with recovery cycle of 10% simply by triggering properly the camera. Pulsed sources can be used for investigation of higher excitation frequencies. For non periodic movement analysis fast acquisition cameras and postponed treatment are used. DHM are therefore unique and very efficient tool for dynamical characterization of in-plane and out-of-plane response. In this paper we show the basics of the technology and illustrate process engineering and failure analysis using DHM with an example of in and out of plane characterization of movements of a variable capacitor using the stroboscopic mode of acquisition.

MEMS scanners are among the devices which have been investigated since the very beginning of MEMS development. The main concern of this paper is to report and discuss suitable measurement techniques and to compare and verify this methods on different scanners for examples. Analysis of scanner reaction based on image processing is covered in a first section. It is shown that an Electronic Speckle Interferometer (ESPI), a Scanning Laser Doppler Interferometer (SLDI) and a phase shift interferometer are suitable for measuring different motion characteristics. The SLDI is used for rapid measurement of FRF at a large number of locations at the scanner. A phase shift interferometer with stroboscopic illumination has been utilized for measuring the deformation of scanners operating them at resonant frequency. Measurement of static displacement and of thermal deformation is the main application of ESPI technique and shown on the example of a galvanometric scanner. A next section is dedicated to functional tests and to qualification of methods for wafer level test. The application of a tilt angle measuring set up containing a position sensitive semiconductor device and a laser diode and of a laser Doppler interferometer is analyzed. Measurement of resonant frequencies in an early production state is the topic of a third section. It provides information about geometry properties of the scanners suspension and about mechanical stress inside suspending torsion or bending beams. Moreover it enables selection of scanner chips with characteristics which do not meet the specification and the cost for packaging of this bad dies is saved.

It is well known that white light interferometry (WLI) is important to nano-scale 3-D profile measurement technology. To archive cost-effective and accurate measurements, the researches for WLI are widely spreading. Our objective is to build up a 3-D micro-structure profile measurement system based on WLI, for micro-mechatronic, micro-optical, and semi-conductor devices. This paper briefly reviews related WLI theory and then the principle of spectral coherence is employed to improve the system design. Specifically, proper spectral filters can be used to extend the coherence length of the light source to the order of several ten micrometers. That is, the coherence length of the filtered light source is longer than that of the original source. In this paper, Michelson interference experiments are conducted with filtered and unfiltered white light sources, to show the feasibility of the concept of spectral coherence. The Michelson interferometer is adopted due to its convenience of optical installation and its acceptable tolerance to noise. The experiment results indicate that our approach is feasible and thus it can improve the WLI measurement performance.

This paper describes charging effects on spatial light modulators (SLM). These light modulators consist of up to one million mirrors that can be addressed individually and are operated at a frame rate of up to 2 kHz. They are used for DUV mask writing where they have to meet very high requirements with respect to accuracy. In order to be usable in a mask-writing tool, the chips have to be able to work under DUV light and maintain their performance with high accuracy over a long time. Charging effects are a problem frequently encountered with MEMS, especially when they are operated in an analog mode. In this paper, the issue of charging effects in SLMs used for microlithography, their causes and methods of their reduction or elimination, by means of addressing methods as well as technological changes, will be discussed. The first method deals with the way charges can accumulate within the actuator, it is a simple method that requires no technological changes but cannot always be implemented. The second involves the removal of the materials within the actuator where charges can accumulate.

The application of thermopneumatic actuators to microvalves and microfluidic processing systems continues to attract research and development interest. Yet, as with most microvalve and microfluidic work, little information has been reported with respect to the reliability of microfluidic and microflow systems. In this work, therefore, we extend our earlier discussions of factors affecting silicon membrane reliability, to encompass particular effects of thermopneumatic actuators on such membranes. Specifically, we report experiments demonstrating the effect of cavitation in thermopneumatic actuators on silicon membranes. These experiments show that the nature of cavitation, in a hermetic, thermopneumatic actuator cavity which includes a silicon membrane, is to initiate fast transient pressure pulses in the cavity. The membrane moves mechanically in response to these pressure pulses. If the magnitude of these pressure pulses causes the membrane stress to exceed the silicon yield strength, then fracture of the membrane can occur. The work concludes with a conceptual approach to the design of thermopneumatic actuators, to ensure this failure mode does not occur.

MEMS are increasingly being considered for applications that involve immersion in liquids. However, there are very little reliability data for MEMS structures in liquids environments. In this study, an apparatus was developed which enables the investigation of fatigue failure of MEMS in liquids. MEMS cantilever beams were mounted on a PZT piezoelectric actuator and immersed in a liquid. A laser is reflected off the tip of the vibrating cantilever and onto a position-sensing photo-diode device (PSD) to obtain position data. From this data resonance frequency can be extracted for long-term monitoring. Cantilevers are resonated for at least 10⁸ cycles. This apparatus allows for the testing of many combinations of materials and environments. For this study, the fatigue performance in liquid of silicon nitride cantilever beams was evaluated and compared to single crystal silicon cantilever beams. Tests were conducted in deionized water and a saline solution. Silicon nitride exhibited no long-term degradation of resonance frequency within measurement limits in air, DI water, and saline environments. Silicon exhibited a steady decrease in resonance. Results showed that this method could be extended to conduct reliability studies on other MEMS materials.

Inertial MEMS (Micro Electro Mechanical System) sensors are normally sealed in hermetic enclosures. Some are assembled in hermetic packages but wafer level packaging has become much more important in recent years. Anodic bonding can be used to achieve wafer level seals between silicon and glass but most suppliers of inertial sensors screen print glass frit onto silicon cap wafers. After removing the organic vehicle, these patterned cap wafers are sealed to device wafer prior to wafer singulation and plastic packaging. Anodic and glass frit bonding are both cost-effective. However, they impose size, quality and performance limitations. Wafer level sealing with a metal removes some of these limitations but introduces other concerns. This paper will review the current wafer level hermetic processes followed by a description of a thermocompression metal seal technology that is compatible with IC fabrication.

This paper discusses a simple electrical measurement technique to determine resonance frequency of surface micromachined cantilever beams that is also suitable for packaged devices. Measurements are done on oxide anchored doped polysilicon beams. If the beam is driven by an AC signal riding on the DC bias, the beam starts vibrating. When the drive frequency matches the natural frequency of the beam, the oscillation amplitude is maximum. In this measurement, the DC bias is fixed at a value lower than the pull-in voltage. A small AC bias is then applied such that the sum of the DC and the maximum amplitude of the AC is less than the pull-in voltage. The frequency of the AC is then swept and at resonance, because of large displacement, the beam is pulled in and this is detected by a current flowing between the beam and the substrate. By iteratively adjusting the DC bias it is possible to make sure that pull-in occurs only due to resonance and the frequency setting at this point gives the natural frequency of the beam. Measured values for different beam lengths were compared with Doppler Vibrometry results and gave an excellent match.

Compliant micromechanisms are employed in the design of MEMS to amplify force or displacement. Models of compliant mechanism generally assume that its lever beam is rigid and does not experience deformation. In most cases, this assumption is acceptable since the lever beams are designed wide enough so that they undergo minimal deformity when transferring force or displacement from input to output; however, in some cases, the lever beam not only is the mechanical interface between its input and output, but it also couples them electrically and/or thermally. Therefore, it may be desirable to design the lever beam as thin as possible to reduce the coupling between the input and output systems. Consequently, the assumption of a rigid beam is no longer valid for calculating the amplification factor. In this paper, the assumption of the rigidity of the lever beam is relaxed to develop an analytical model for a compliant mechanism having a flexible lever beam. The results obtained using the flexible beam model, in contrast with the rigid beam model, shows very good agreement with the finite element model. For wide levers, the results of the flexible beam and the finite element models approach to those of rigid beam model. These results show that the amplification factor of a flexible lever beam is less than a rigid one. The reason is that the flexible lever beam absorbs a fraction of input energy in the form of elastic strain energy. Without significant loss of accuracy, this model can replace the finite element model to improve the computation time in the optimization procedure to achieve higher amplification factor and lower electrical/thermal coupling.

A fast model-order reduction algorithm is proposed for microelectromechanical devices. By breaking the system matrices obtained from FEM methods down into smaller ones, the proposed algorithm will reduce computational cost and memory requirements required by the inversion operation of the system matrix. As an example, experimental studies are presented for a linear-drive multiple-mode resonator demonstrating that predicted results are in very good agreement with results from previous publications.

This paper presents an integrated multifunctional microsensor based on 440MHz surface acoustic wave (SAW) reflective delay line on 41° YX LiNbO₃. A pressure sensor, a temperature sensor, and radio frequency identification (RFID) tag were integrated on two-bonded piezoelectric substrates. The pressure sensor was placed on the top plate, whereas the RFID tag and temperature sensor were located on the bottom substrate. Finite Element Methods (FEM) and Coupling of mode (COM) modeling were performed to extract the optimal design parameters before fabrication. The fabricated sensor was wirelessly characterized through the Network Analyzer. Sharp reflection peaks with high S/N ratio were observed. Obtained temperature and pressure sensitivity are ~10°/°C and ~2.9°/kPa, respectively.