This PDF file contains the front matter associated with SPIE Proceedings Volume 6884, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

In today's high-volume semiconductor world, one could easily take reliability for granted. As the MOEMS/MEMS industry continues to establish itself as a viable alternative to conventional manufacturing in the macro world, reliability can be of high concern. Currently, there are several emerging market opportunities in which MOEMS/MEMS is gaining a foothold. Markets such as mobile media, consumer electronics, biomedical devices, and homeland security are all showing great interest in microfabricated products. At the same time, these markets are among the most demanding when it comes to reliability assurance. To be successful, each company developing a MOEMS/MEMS device must consider reliability on an equal footing with cost, performance and manufacturability. What can this maturing industry learn from the successful development of DLP technology, air bag accelerometers and inkjet printheads? This paper discusses some basic reliability principles which any MOEMS/MEMS device development must use. Examples from the commercially successful and highly reliable Digital Micromirror Device complement the discussion.

This paper discusses issues relating to the reliability and methods for employing high-cycle life testing in capacitive RF MEMS switches. In order to investigate dielectric charging, transient current spectroscopy is used to characterize and model the ingress and egress of charges within the switch insulating layer providing an efficient, powerful tool to investigate various insulating materials without constructing actual MEMS switches. Additionally, an in-situ monitoring scheme has been developed to observe the dynamic evolution of switch characteristics during life testing. As an alternative to high-cycle life testing, which may require days or weeks of testing, a method for performing accelerated life tests is presented. Various methods for mitigating dielectric charging are presented including: reduced operating voltage, reduced dielectric area, and improved control waveforms. Charging models, accelerated life test results, and high-cycle life test results for state-of-the-art capacitive RF MEMS switches aid in the better understanding of MEMS switch reliability providing direction for improving materials and mechanical designs to increase the operation lifetime of MEMS capacitive switches.

We present an experimental study of the DC breakdown voltage of MEMS interdigitated aluminum electrodes with gaps ranging from 10 to 500 μm. Unlike most research on MEMS electrodes, that was done at atmospheric pressure, our work has focused on the effect of gas pressure and gas type on the breakdown voltage. A main goal was to identify geometries that favor the creation of low-voltage discharges. Helium, argon and nitrogen pressure was varied from 10² to 8.10⁴ Pa (1 to 800 mbar). The breakdown voltage was plotted as a function of the Paschen reduced variable P_red = p·g. For higher values of pressure, p or gap, d (high P_red), classical Paschen scaling was observed. For lower values of P_red however, significant deviations were seen, particularly at low pressures. We attribute these differences not to field emission, but to the scale of the mean free path (which explains the higher than predicted voltages), and to the many length scales effectively present in our planar geometry (on-chip and even off-chip, that lead to the superposition of several Paschen curves). Guidelines are proposed for low-pressure operation of MEMS to avoid or to encourage breakdown.

Metal based thermal microactuators normally have lower operation temperatures than those of Si-based ones; hence they have great potential for applications. However, metal-based thermal actuators easily suffer from degradation such as plastic deformation. In this study, planar thermal actuators were made by a single mask process using electroplated nickel as the active material, and their thermal degradation has been studied. Electrical tests show that the Ni-based thermal actuators deliver a maximum displacement of ~20 m at an average temperature of ~420 °C, much lower than that of Si-based microactuators. However, the displacement strongly depends on the frequency and peak voltage of the pulse applied. Back bending was clearly observed at a maximum temperature as low as 240 °C. Both forward and backward displacements increase with increasing the temperature up to ~450 °C, and then decreases with power. Scanning electron microscopy observation clearly showed that Ni structure deforms and reflows at power above 50mW. The compressive stress is believed to be responsible for Ni piling-up (creep), while the tensile stress upon removing the pulse current is responsible for necking at the hottest section of the device. Energy dispersive X-ray diffraction analysis revealed severe oxidation of the Ni-structure induced by Joule-heating of the current.

Development of MEMS constitutes one of the most challenging tasks in today's micromechanics. In addition to design, analysis, and fabrication capabilities, this task also requires advanced test methodologies for determination of functional characteristics of MEMS to enable refinement and optimization of their designs as well as for demonstration of their reliability. Until recently, this characterization was hindered by lack of a readily available methodology. However, using recent advances in photonics, electronics, and computer technology, it was possible to develop a NonDestructive Testing (NDT) methodology suitable for evaluation of MEMS. In this paper, an optoelectronic methodology for NDT of MEMS is described and its application is illustrated with representative examples; this description represents work in progress and the results are preliminary. This methodology provides quantitative full-field-of-view measurements in near real-time with high spatial resolution and nanometer accuracy. By quantitatively characterizing performance of MEMS, under different vibration, thermal, and other operating conditions, specific suggestions for their improvements can be made. Then, using the methodology, we can verify the effects of these improvements. In this way, we can develop better understanding of functional characteristics of MEMS, which will ensure that they are operated at optimum performance, are durable, and are reliable.

Interferometry is now an established technique for the measurement of surface topography. It has the capability of combining sub-nanometre resolution, high measurement speed with high repeatability. A very useful extension to its capability is the ability to measure thick and thin films on a local scale. For films with thicknesses in excess of 1-2 μm (depending on refractive index), the SWLI interaction with the film leads to the formation of localised fringes, each corresponding to a surface interface. It is relatively trivial to locate the positions of these envelope maxima and therefore determine the film thickness, assuming the refractive index is known. For thin films (with thicknesses ~20 nm to ~2 μm, again depending on the refractive index), the SWLI interaction leads to the formation of a single interference maxima. In this context, it is appropriate to describe the thin film structure in terms of optical admittances; it is this regime that is addressed through the introduction of a new function, the 'helical conjugate field' (HCF) function. This function may be considered as providing a 'signature' of the multilayer measured so that through optimization, the thin film multilayer may be determined on a local scale.

This contribution describes the investigation of the reasons for overload failure and overload reaction based on linear vibration theory by decomposition of the complex reaction into resonant mode reactions and on observation of the reaction. An impulse specific peak deflection (ISPD) is derived as a general characteristic property of a certain shock. It is applicable to predict the mechanical deflection of a certain resonant mode of an arbitrary resonant frequency due to a shock. This is further analyzed and proofed by scanning Laser Doppler interferometer (SLDI) measurement on the example of a Fabry Perot interferometer based tunable infrared filter. The results from ISPD prediction are compared to SLDI measurements and to finite element analysis results.

Recently it has been shown that structural vibrations are an efficient means to repair stiction failed microcantilever beams. Experiments and analysis have identified excitation parameters (amplitude and frequency) that successfully initiated the debonding process between the microcantilever and the substrate. That analysis could not describe what happened after the debonding process was initiated. For example it could not predict if the beam would transition from a s-shaped to an arc-shaped configuration or even be repaired to a free-standing beam. The current research examines the post-initiation behavior of stiction failed microcantilever beams. A new-coupled fracture/vibration model is formulated and used to track the evolution of the repair in order to determine the extent of repair under various conditions. This model successfully explains phenomenological observations made during the experiments regarding the repair process being dependent on direction of frequency sweeps, complete and partial repair, and monitors the degree of repair no repair, partial repair or complete repair along with releases time associated with such repairs.

Despite the initial skepticism of OEM companies regarding reliability, MEMS-based devices are increasingly common in optical networking. This presentation will discuss the use and reliability of MEMS in a variety of network applications, from tunable lasers and filters to variable optical attenuators and dynamic channel equalizers. The failure mechanisms of these devices will be addressed in terms of reliability physics, packaging methodologies, and process controls. Typical OEM requirements will also be presented, including testing beyond of the scope of Telcordia qualification standards. The key conclusion is that, with sufficiently robust design and manufacturing controls, MEMS-based devices can meet or exceed the demanding reliability requirements for telecommunications components.

To address the lack of micro-electro-mechanical systems (MEMS) reliability data as well as a standardized methodology for assessing reliability, the Metallic Materials Technology Branch at Picatinny Arsenal has initiated a MEMS Reliability Assessment Program. This lack of data has been identified as a barrier to the utilization the MEMS in DOD systems. Of particular concern are the impacts of long-term storage and environmental exposure on the reliability of devices. Specific objectives of the Metallic Materials Technology Branch (MMTB) program include: • Identify MEMS devices to be utilized in weapon systems. • Determine the relevant categories of MEMS materials, technologies and designs in these applications • Assess the operational environments in which the military MEMS device may be utilized. • Analyze the compatibility of MEMS devices with energetic and other hazardous materials. • Identify physics of failure, failure mechanisms and failure rates. • Develop accelerated test protocols for assessing the reliability of MEMS according to the categories. • Develop of reliability models for these devices. • Conduct testing and modeling on representative devices of interest to Army and DoD. • Develop of a methodology and capability for conducting independent assessments of reliability that cannot be obtained from private industry. In support of this effort, some testing has been performed on prototype mechanical Safety and Arming (S&A) devices for the 25-mm XM25 Air Burst Weapon. The objective is to test the S&A as a representative device for the identification of potential failure modes and effects for devices of the same class. Information derived from this testing will be used to develop standardized test protocols, formulate reliability models and establish design criteria and to identify critical parameters in support of the S&A development effort. To date, Environmental Stress Screening (ESS) tests have been performed on samples of the device. Along with the ESS testing, a failure modes and effects analysis has been developed and reliability modeling is under way.

Next generation of infra-red astronomical instrumentation for space telescopes as well as ground-based extremely large telescopes requires MOEMS devices with remote control capability and cryogenic operation, including programmable multi-slit masks for multi-object spectroscopy (MOS). For the complete testing of these devices, we have developed in parallel and coupled a high-resolution Twyman-Green interferometer and a cryogenic-chamber for full surface and operation characterization. The interferometer exhibits a nanometer accuracy by using phase-shifting technique and low-coherence source. The cryogenic-chamber has a pressure as low as 10e-6 mbar and is able to cool down to 60K. Specific interfaces minimizing stresses for vacuum and cryo have been set. Within the framework of the European program on Smart Focal Planes, micro-mirrors have been selected for generating MOEMS-based slit masks. A first 5×5 micro-mirror array (MMA) with 100×200μm² mirrors was successfully fabricated using a combination of bulk and surface silicon micromachining. They show a mechanical tilting angle of 20° at a driving voltage below 100V, with excellent surface quality and uniform tilt-angle. The mirrors could be successfully actuated before, during and after cryogenic cooling. The surface quality of the gold coated micro-mirrors at room temperature and below 100K, when they are actuated, shows a slight increase of the deformation from 35nm peak-to-valley to 50nm peak-to-valley, due to CTE mismatch between silicon and gold layer. This small deformation is still well within the requirement for MOS application.

Package Qualification and Verification (PQV) of advanced electronic packaging and interconnect technologies and various other types of qualification hardware for the Mars Exploration Rover/Mars Science Laboratory flight projects has been performed to enhance the mission assurance. The qualification of hardware (Engineering Camera and Platinum Resistance Thermometer, PRT) under extreme cold temperatures has been performed with reference to various project requirements. The flight- like packages, sensors, and subassemblies have been selected for the study to survive three times (3×) the total number of expected temperature cycles resulting from all environmental and operational exposures occurring over the life of the flight hardware including all relevant manufacturing, ground operations and mission phases. Qualification has been performed by subjecting above flight-like qual hardware to the environmental temperature extremes and assessing any structural failures or degradation in electrical performance due to either overstress or thermal cycle fatigue. Experiments of flight like hardware qualification test results have been described in this paper.

MEMS used in inertial sensors rely on the movement of mechanical elements, generally systems of masses and springs. Shielding these structures from particulate contamination requires encapsulating the MEMS structures. This encapsulation is typically accomplished by placing a silicon cap over the MEMS at the wafer level. In the event the device stops functioning as expected, it is necessary to visually inspect the MEMS structures. However, once the device is capped, the only way to visually inspect the sensor is to remove the cap using a destructive decapsulation process. Fortunately, product analysts can take advantage of the transmissive properties of infrared light through lightly doped silicon to examine MEMS structures through their silicon cap using IR microscopy. Although useful, the image quality of conventional IR microscopy has limitations resulting from the optics, geometry and detectors currently available. Recently, laser confocal microscopy techniques have been adapted to the infrared spectrum, offering improved image clarity and measurement capability. This paper reviews the use of conventional IR microscopy in imaging through silicon caps, the limitations of conventional IR microscopy in this application, and the new capabilities afforded by the use of laser confocal IR microscopy for through-cap imaging.

Optical MEMS devices rely on the micro assembly to achieve re-positioning, such as lifted up micro mirrors and lens and micro resistance welding benefits assembly of optical components. However, the characteristics of micro resistance welding are still unknown. The purpose of this study is to characterize micro resistance welding with electro-thermal actuator for micro assembly. In order to characterize influence of operation parameters on micro resistance welding, important parameters including contact pressure, contact resistance and electrical energy are calibrated. Further, welding strength provide robust join are also measured. The idea of resistance welding is based on generated heat by Ohm's law to melt material. From measured results, contact resistance decreases with increasing contact pressure due to increasing contact area. The stronger welding strength can be achieved at a smaller initial contact resistance which means that a larger clamping force could enhance the welding strength. The maximum welding strength is 74.4 μN at 2.7 ΩFurther, welding energy affects yield significantly. At high welding energy, between 1 to 10 J, the yield can reach 100%. The energy below 0.05 J would not generate adequate heat to weld structure.

Indium-silver as solder materials for low temperature bonding had been introduced earlier. In theory the final bonding interface composition is determined by the overall materials composition. Wafer bonding based multiple intermediate layers facilitates precise control of the formed alloy composition and the joint thickness. Thus the bonding temperature and post-bonding re-melting temperature could be easily designed by controlling the multilayer materials. In this paper, a more fundamental study of In-Ag solder materials is carried out in chip-to-chip level by using flip-chip based thermocompression bonding. Bonding at 180°C for various time duration under various bonding pressure is studied. Approaches of forming Ag₂In with re-melting temperature higher than 400°C at the bonding interface are proposed and discussed. Knowledge learned in this process technology can support us to develop sophisticated wafer level packaging process based wafer bonding for applications of MEMS and IC packages.

A RF wireless capacitive pressure sensor is developed. The sensor has integrated inductor with the pressure sensitive capacitor as LC circuit. The resonant frequency of the sensor changes as the capacitance changes with applied pressure. The sensor uses LPCVD silicon nitride as sensitive membrane and the residual stress of the membrane has been measure as 139MPa. The sensor has size of 10 mm × 4 mm × 0.5 um. The sensor presents a pressure sensitivity of 1.65 MHz/cmH₂O in pressure range of 0-20 cmH₂O. The deflection of different shape of membranes is discussed. The deflection of square membrane is 130% to circular membrane under same applied pressure.

A spin-on polymeric material has been developed to replace the silicon nitride mask used in the MEMS industry for silicon wet-etch processing. Built-in photosensitivity eliminates the need for additional photoresists in the system. The process consists of applying an organosilane-based primer layer onto a silicon wafer, followed by spin coating the photosensitive layer. After a soft bake, the coating is imaged by exposing it to ultraviolet light. After a post-exposure bake, the coating is developed by a solvent. After a final bake, the prepared wafer is then etched in a hot concentrated alkaline solution to complete the pattern transfer. The polymer-coated area remains protected with insignificant and controllable undercut after extended hours of wet etching. Etch protection performance was characterized as a ratio of undercut (u) to etch depth (h). The polymeric mask allows silicon substrates to be etched anisotropically in the same way as silicon nitride masks although more undercut occurs when KOH or NaOH are used as etchants. With use of tetramethylammonium hydroxide (TMAH) as an etchant, a consistent 1-2% undercut ratio (u/h×100%) was obtained. The effects of various parameters such as use of different etchants and the effects of etchant concentration and delayed processing on undercut ratio are investigated.

Micro-electromechanical (MEMS) oscillators are now in production and shipping in quantity. Early development of micro mechanical devices provided the understanding that metal beams could be fabricated and they would resonate as a time reference. The issues of performance and price have prevented silicon entry into the quartz dominated market until recent developments in semiconductor processing and assembly. Today MEMS oscillators are the world's smallest programmable precision oscillators and are displacing quartz technology in the +/- 50 ppm accuracy spec. New oscillators extend the technology with spread spectrum, voltage control, and improved jitter performance. New ultra-thin packaging, made possible by the small encapsulated MEMS resonators, provides the word's thinnest precision oscillators.

Many MEMs and MOEMs devices require controlled ambient environments for successful operation. Controlled ambients are usually obtained via hermetic packaging. These controlled environments must first be obtained and then maintained to prevent their degradation over the device lifetime. Controlled ambients decay in quality over time due to various mechanisms including leaks, permeation, poor processing and outgassing of species like hydrogen, water and organics external and internal to the package. The key to controlling the process of degradation is to understand in a quantitative manner which species are present and their mass flow rates into the controlled ambient. The current work describes a new technique for determining these species and mass flow rates. This new technology provides tremendous sensitivity to package volumes < 0.01cc compared to standard quadrupole techniques, which are applicable to samples larger than 0.01 cc. The technology is based on a high speed, high mass resolution, and highly sensitive Time-Of-Flight (TOF) spectrometer to test the tiniest of devices with significant advancement in signal-to-noise ratios. Key operational parameters demonstrated include: - Spectra Acquisition speed: 1 full spectra every 20 μs. - Mass Range: mass 2 to 150 standard (2-500 capable) - Mass resolution: 0.1 AMU - Calibration Fixtures: 0.0001, 0.0005, 0.001, 0.005 and 0.01 cc - Sample temperature: 100°C standard (room temperature to 150°C capable).

In many MEMS applications the level of vacuum is a key issue as it directly affects the quality of the device, in terms of response reliability. Due to the unavoidable desorption phenomena of gaseous species from the internal surfaces, the vacuum inside a MEMS, after bonding encapsulation, tends to be degraded, unless a proper getter solution is applied. The in situ getter film (PaGeWafer®) is recognised to be the most reliable way to get rid of degassed species, assuring uniform, high quality performances of the device throughout the lifetime. Moreover, post process vacuum quality control and reliability for hermetic bonding is extremely important for overall device reliability and process yield. In this paper we will discuss the main factors that are critical in the attainment of vacuum and will present a novel calculation model that enables the prediction of vacuum level after bonding, making also possible the estimate of the lifetime. Furthermore, a new analytical method based on the residual gas analyses (RGA) will be presented that gives the main characteristics of the materials. Modeling and simulation work support the process optimization and system design.

There is an increasing demand to build highly sensitive, low-G, microscale acceleration sensors with the ability to sense accelerations in the nano-G (10^-8 m/s²) regime. To achieve such sensitivities, these sensors require compliant mechanical springs attached to large masses. The high sensitivities and the difficulty in integrating robust mechanical stops into these designs make these parts inherently weak, lacking the robustness to survive even the low level accelerations encountered in standard handling, from release processing, where supporting interlayers present during fabrication are etched away, through packaging. Thus, the process of transforming a MEMS-based acceleration sensor from an unreleased state to a protected functional state poses significant challenges. We summarize prior experiences with packaging such devices and report on recent work in packaging and protecting a highly sensitive acceleration sensor that optically senses displacement through the use of sub-wavelength nanogratings. We find that successful implementation of such sensors requires starting with a clean and robust MEMS design, performing careful and controlled release processing, and designing and executing a robust handling and packaging solution that keeps a fragile MEMS device protected at all times.

Micro-Electro-Mechanical Systems (MEMS) packaging constitutes most of the cost of such devices. For the integration of MEMS with microelectronics systems to be widespread, a drastic reduction of the overall price is required. Wafer-level-packaging allows a fundamental reduction of the packaging cost by combining wafer-level microfabrication techniques with wafer-to-wafer bonding. To achieve the vacuum atmosphere required for the operation of many MEMS devices, bonding techniques such as anodic bonding, eutectic bonding, fusion bonding and gold to gold thermocompression bonding have been utilized, which require relatively high temperatures (>300°C) being in some cases incompatible with MEMS and microelectronics devices. Furthermore, to maintain vacuum integrity over long periods of time, getters requiring high activation temperatures are usually employed. INO has developed a hybrid wafer-level micropackaging technology based on low temperature fluxless solder joints in which the micropackaged MEMS device is not exposed to a temperature over 150°C. The micropackages have been designed for 160×120 microbolometer FPAs. Ceramic spacers are patterned by standard microfabrication techniques followed by laser micromachining. AR-coated floatzone silicon IR windows are patterned with a solderable layer. Both, microbolometer dies and windows are soldered to the ceramic tray by a combination of solder paste stencil printing, reflow and fluxless flip-chip bonding. A low temperature getter is also introduced to control outgassing of moisture and CO₂ during the lifetime of the package. Vacuum sealing is carried out by locally heating the vacuum port after bake out of the micropackages. In this paper, the vacuum integrity of micropackaged FPA dies will be reported. Base pressures as low as 5 mTorr and equivalent flow rates at room temperature of 4×10^-14 Torr.l/s without getter incorporation have been demonstrated using integrated micro-pressure gauges. A study of the influence of different packaging parameters on the lifetime of micropackages will be presented.

In a surface micromachined cantilever the beam thickness, width and the gap get modified during fabrication. Since performance of sensors and actuators strongly depend on the final geometry, it is essential to measure these parameters. Electrical measurements have several advantages over microscopy and we present here two different electrical techniques to measure undercut due to etching. In the resistance based approach, two polysilicon resistors of different length and width are used and the undercut is extracted from the ratio of the measured resistances. In the second technique, resonance frequency is measured for two sets of oxide anchored polysilicon cantilever beams with 20 and 30 µm widths. For a given length, the ratio between the measured frequencies for the two widths gives the value of undercut. Measurements are done on both wet and dry etched polysilicon.

Real world Microsystems devices are multi-disciplinary, adaptive, and non-linear. Along the critical development path of Microsystems is a conspicuous absence of materials data, including materials compatibility and life models. To advance the state-of-the art in simulation, ASM has completed the first of three phases of a materials database development effort. The "strides and stumbles" associated with the database are discussed and opportunities for collaboration identified, particularly in the area of material reliability and harsh environment life prediction efforts. A materials database can benefit systems design and simulation efforts, but a phased approach to this undertaking is essential. Case-studies originally intended to validate the database became a surprising component of development strategy. ASM is seeking and welcomes opportunities for collaboration with other research groups as this interdisciplinary project moves forward.

This research proposes a newly developed stray light filter, which might significantly eliminate the stray light and ghost image effect for the non-contact con-focal microscopy system handled by (Digital Micromirror Device, DMD) devise. DMD devise, which was introduced by Taxes instrument under advanced technology of Micro-Electro-Mechanical Systems, MEMS, could be the replacement of traditional scanning system. The employment of DMD system takes advantages of fast scanning rate, better resolution, simplifies optical system. However, traditional confocal microscopy system with pinhole will lead to light starving and potentially higher signal to noise ratio. Without pinhole, the stray light and ghost image effect might complicate the signal measurement. A newly developed stray light filter will be presented in this research in order to eliminate the potential stray light and ghost image without sacrifice of luminance. It indicated that not only optical system could be much simplified but also resolution could be one step higher because neither pinhole nor CCD camera lens will be employed in this system. Experimental results will be shown in this research demonstrating an increase in contrast up to 60%.

In this study, we analyze the uncertainty in an optical testing system using a Shack-Hartmann sensor for a wavefront measurement device. The main uncertainty sources of the optical testing system are the Shack-Hartmann sensor, the image relay optics, and the pinhole source. Using a homemade high-precision plane-wave source as a reference, we develop a simple method to calibrate the optics of the system and the Shack-Hartmann sensor itself. It is found that the wavefront error of a pinhole source is negligible, and that the error due to the image relay optics installed between the test lens and the Shack-Hartmann sensor is 0.030 λ (RMS). By warming up the Shack-Hartmann sensor for about 1 hour, the measurement values are stabilized to within 0.001 λ (RMS). After calibrating the optical testing system with the reference source, overall uncertainty in the optical testing system is reduced to 0.009 λ (RMS). Performance of the optical testing system is evaluated by measuring the wavefront errors of various optical components, such as a numerical aperture (NA) 0.25 aspheric lens and a digital video disc (DVD) pick up lens.