Successful production of MEMS devices in a volume-manufacturing environment requires high reliability, efficient process and product characterization, and cost-effective testing capabilities. Integration of process engineering, design, yield engineering, reliability, characterization and test from the early development phases through to product release and into manufacturing is an effective model for success in the MEMS industry. An integrated process/product approach utilizing quality systems and high volume manufacturing is critical to producing a reliable part; proper data collection, careful interpretation and fast feedback are the backbone of a stable fabrication and product line. Elimination of process and design-related failure mechanisms through statistical analysis and understanding of physics of failure, and a well-executed defect reduction program will result in a high yielding, profitable and reliable production line. Accurate characterization and testing of MEMS mechanical structures and electrical circuitry on one chip requires understanding the complex interactions of electro-mechanical behavior. This model of efficient production and test for a reliable cost-effective product is not new, however, successful application of this model to high volume MEMS manufacturing is not common. The continuous dedication of a talented, versatile, and experienced workforce is required to make this a reality.

Optical Micro-Electro-Mechanical Systems (Optical MEMS, or MOEMS) comprise a disruptive technology whose application to telecommunications networks is transforming the horizon for lightwave systems. The influences of materials systems, processing subtleties, and reliability requirements on design flexibility, functionality and commercialization of MOEMS are complex. A tight inter-dependent feedback loop between Component/ Subsystem/ System Design, Fabrication, Packaging, Manufacturing and Reliability is described as a strategy for building reliability into emerging MOEMS products while accelerating their development into commercial offerings.

This paper presents the work we have done on micro-relays with gold micro-contacts in MUMPs. Firstly, the theoretical physical principles of MEMS micro-relay are described. This study is divided in two parts: the micro-contact and the micro-actuator. The micro-contact part deals with resistance of constriction, contact area, adhesion, arcing and wear. Whereas the micro-actuator part describes general principles, contact force, restoring force and actuator reliability. Then, in a second part, an innovative electrostatic relay design in MUMPs is presented. The concept, the implementation and the final realization are discussed. Then, in the third part, characterization results are reported. This part particularly focuses on the micro-contact study. Conduction mode, contact area, mechanical and thermal deformation, and adhesion energies are presented.

High volume ICs production companies (telecom, etc) show a growing interest in MEMS components, especially RF and optical ones. Prototypes of integrated inductances and optical switches demonstrate very promising performances. The transition to the high volume production implies the development of Design For Manufacturability (DFM) tools featured to handle MEMS specific processes and related problems such as yield loss due to process dispersion. These tools must be part of a MEMS dedicated CAD environment. This paper presents results of what could be yield enhancement using usual statistical optimization tools and methods, and a new approach currently developed by MEMSCAP and LIRMM, based on response variability minimization.

Exposure to elevated temperatures can cause permanent alteration of the shape of a multimorph MEMS device. In particular, the cantilever beam structure has been characterized extensively for the bimorph polysilicon and gold materials combination. Environments even briefly elevated above 110 C can induce change in structural displacement. That is, when observed at some reference temperature, the displacement is different from the original shape prior to baking, when monitored at the same reference temperature. Thermal exposure can cause the magnitude of displacement to increase in excess of two or threefold. Structural bifurcation can magnify the displacement of a plate-like structure. The process used to increase deformation of a multimorph MEMS structure will be described, and characterized according to the part's geometry. Such change in shape is not entirely permanent and is subject to relaxation. Change in deformation has been characterized throughout the time-span of approximately one-year. Lastly the implications of the so-called heat-treatment (or energy storage) mechanism are discussed in terms of MEMS device reliability, manufacture and packaging, as well as design.

Review of current and emerging methods of holography and speckle metrology is given. Onboard research by means of holography and speckle metrology is analyzed. Advanced holographic rapid access system (RAS) is presented. It is very simple, compact, portable, user-friendly and requires minimal hardware. Holographic RAS has several modifications and spin-offs. Ultra high resolution silver halide media are used in this RAS.

The development and fabrication of microfabricated propulsion components at the Jet Propulsion Laboratory is reviewed. These include a vaporizing liquid micro-thruster, which vaporizes propellant to produce thrust. Thrust performances of 32 (mu) N for an input power of 0.8 W were measured. Miniature solenoid and latch valves are being developed by Moog, Inc. in collaboration with JPL.

The high piezoelectric effect of lead zirconate titanate (PZT) films enables improved performance in microelectromechanical systems (MEMS). The material's reliable integration into current and mainstream MEMS microfabrication processes is then of great interest. In this paper we report on high reliability fabrication processes that can be used for producing PZT based MEMS devices. Pattern definition and release of PZT, low stress silicon nitride, platinum, and/or zirconia structures via wet and dry chemical etching and ion beam etching, including their affects on the piezoelectric properties of PZT are reported. Ion beam etching results in appreciable imprint in the polarization - electric field hysteresis loop of the PZT, which can be ameliorated by annealing in ambient air at 450 degree(s)C. PZT on silicon nitride cantilever structures were defined and released by dry xenon difluoride silicon sacrificial etching. The advantages and difficulties of wet release etching versus xenon difluoride are also presented.

The measurement of electrostatic discharge (ESD) tolerance for a capacitive fingerprint sensor LSI in which the sensor is stacked on a 0.5-micrometers CMOS LSI is described. To compare the contact discharge method and air discharge method, we investigated the dependence of the ESD failure voltage on the distance between the sensor surface and ESD electrode for a conventional planar-type fingerprint sensor LSI. The ESD failure voltage decreased as the electrode approached to sensor surface and reached its lowest value when the electrode touched the surface. Therefore, we conclude that the contact discharge method is more suitable for evaluating ESD tolerance for fingerprint sensor LSI because the measurement condition is clearly defined and ESD failure value is the most critical. Moreover, we revealed that our proposed sensor LSI with the grounded wall (GND wall) has high ESD tolerance of over +/- 8.0 kV by the contact discharge method.

This paper describes the reliability approach performs at CNES to evaluate MEMS for space application. After an introduction and a detailed state of the art on the space requirements and on the use of MEMS for space, different approaches for taking into account MEMS in the qualification phases are presented. CNES proposes improvement to theses approaches in term of failure mechanisms identification. Our approach is based on a design and test phase deeply linked with a technology study. This workflow is illustrated with an example: the case of a variable capacitance processed with MUMPS process is presented.

The reliability study of advanced 3D self-assembled micro- machined polysilicon structures is investigated here with the aim of preventing the dynamic snap-through from occurring; snap-through is a vibratory phenomenon, which can lead to the destruction of a whole structure. 3D polysilicon micro-parts are self-assembled by beam buckling induced by the compressive force produced by Scratch Drive Actuator; this work considers the reliability of these micro-parts, and particularly the response of homogeneous, clamped- clamped polysilicon microfabricated buckled beams.

We describe an improved stroboscopic interferometer system making possible static-deformation measurements of MEMS structures as well as motion measurements at frequencies up to 1MHz. The time resolution of the system is determined by the width of the strobed laser pulse. To demonstrate high-frequency measurement capabilities, we investigate acoustic waves on a flexural plate-wave micropump developed at the Berkeley Sensor & Actuator Center. We also characterize the micropump with a commercial micro scanning vibrometer (Polytec). The results are compared and different features of the two systems are discussed.

Microactuators are one of the key components in MEMS and Microsystems technology, and various designs have been realized through different fabrication processes. One type of microactuator commonly used is the scratch drive actuator (SDA) that is frequently fabricated by surface micromachining processes. An experimental investigation has been conducted on the characteristics of SDAs fabricated using the Cronos Microsystems MUMPs process. The motivation is to compare the response of SDAs located on the same die, and SDAs located on the different dies from the same fabrication batch. A high-speed imaging camera has been used to precisely determine important SDA characteristics such as step size, velocity, maximum velocity, and acceleration over long travel distance. These measurements are important from a repeatability point of view, and in order to fully exploit the potential of the SDA as a precise positioning mechanism. 2- and 3-stage SDAs have been designed and fabricated for these experiments. Typical step sizes varying from 7 nm at a driving voltage of 60 V to 23 nm at 290 V have been obtained.

In this paper, the testing principles and different application examples of the Micro-Chevron-Test (MC) are discussed. The chevron pattern required for testing can be fabricated either by wet or reactive ion etching. It is shown that the test has a higher accuracy than common tensile or bend strength tests, allowing also the determination of fracture mechanic parameters, such as fracture toughness. In addition one can characterize the spatial strength distributions for the bonded wafer in order to determine the sources of production yield problems. Furthermore, the sample size can be reduced to the typical size of micro electro mechanical systems (MEMS) devices allowing the MC sample fabrication to be integrated into the MEMS fabrication process. Therefore, the test can be applied as an effective, reliable and precise tool for wafer bond process development and for quality control during the fabrication of micromechanical devices.

We present measurements of the nanoscale elastic properties of hinge structures supporting micro-mirror arrays using a new characterization technique called Ultrasonic Force Microscopy (UFM). This technique is based on Atomic Force Microscopy with ultrasonic excitation which provides a means of testing the elastic response at MHz frequencies. The simultaneous recording of topography with elastic imaging allows the elimination of any artifacts. In this report, we demonstrate that UFM can achieve nano-scale elastic resolution to reveal mechanical stress induced changes as well as process induced material fatigue in the micro-mirror devices. The main aim of this study is polysilicon-based hinge structures that support the micro-mirror because they show the highest stress during mirror switching. Our results indicate that no significant structural and mechanical change of the polysilicon-based hinge support structure occurs even after more than 1,000,000,000 switching cycles. This method offers a non-destructive way to perform reliability characterization on MEMS devices. This technique developed will offer new opportunities for the evaluation of structural and mechanical integrity of MEMS devices.

Electroplated gold surfaces of the type used for MEMS switches were surveyed by atomic force microscopy (AFM) to define the surface topographical features, and by x-ray photoelectron spectroscopy (XPS) to determine the chemical composition of the contact surface. The gold surfaces were contacted with electrochemically sharpened gold and tungsten probes using an interface force microscope (IFM), capable of simultaneously measuring contact currents from 10 fA to 10 mA and forces ranging from 0.01 to 100 uN. Both attractive and repulsive forces were observed, and attractive forces on the probe tip were found to exist at significant distances (greater than 5 nm) from the gold surface. The radius of the probe tip is on the order of a micron, making it a useful model system for a single-asperity contact on an actual MEMS switch-contact surface. The results of these single-contact measurement events are compared with contact measurements made with MEMS switches of various sizes and actuation schemes to understand the origins of contact resistance and switch failure.

The fracture toughness of micromachined polycrystalline silicon samples, pre-cracked with an indenter or notched using a focused ion beam (FIB) machine, were tested using either bending or tensile loading. Fracture mechanics approaches were applied to determine the fracture toughness from these results. For the pre-cracked specimens tested by tensile loading, a fracture toughness value of K_I,crit equals 0.86 MP(root)a derived. The FIB notched specimens had higher fracture toughness values, probably due to the influence of the notch tip radius and the FIB process. In addition, fatigue investigations of un-notched tensile specimens were performed using tensile cyclic loading with frequencies of 50, 200 and 1000 Hz. A reduction in the tensile strength from 1.10 GPa to 0.75 GPa after 10⁸ cycles was detected while no influence of the test frequency on the fatigue behavior was observed.

MEMS are rapidly emerging as critical components in the telecommunications industry. This enabling technology is currently being implemented in a variety of product and engineering applications. MEMS are currently being used as optical switches to reroute light, tunable filters, and mechanical resonators. Radio frequency (RF) MEMS must be compatible with current Gallium Arsenide (GaAs) microwave integrated circuit (MMIC) processing technologies for maximum integration levels. The RF MEMS switch discussed in this paper was fabricated using various layers of polyimide, silicon oxynitride (SiON), gold, and aluminum monolithically fabricated on a GaAs substrate. Fig. 1 shows a metal contacting series switch. This switch consists of gold signal lines (transmission lines), and contact metallization. SiON was deposited to form the fixed-fixed beam, and aluminum was deposited to form the top actuation electrode. To ensure product performance and reliability, RF MEMS switches are tested at both the wafer and package levels. Various processing irregularities may pass the visual inspection but fail electrical testing. This paper will focus on the failure mechanisms found in the first generation of RF MEMS developed at Sandia National Laboratories. Various tools and techniques such as scanning electron microscopy (SEM), resistive contrast imaging (RCI), focused ion beam (FIB), and thermally-induced voltage alteration (TIVA) have been employed to diagnose the failure mechanisms. The analysis performed using these tools and techniques led to corrective actions implemented in the next generation of RF MEMS metal contacting series switches.

The main type of Acoustic Micro Imaging (AMI) system utilized in this study was the C-Mode Scanning Acoustic Microscope, which is a reflection mode instrument. In this paper we describe the method and application of AMI at frequencies beyond 200 MHz, which reveals defects in the 5 micron size range at depths of 500 microns within silicon.

We report on the high-speed 3D imaging capabilities of a newly developed inspection tool for MEMS. The instrument is capable of performing an imaging operation for a complete image at once, which is a large advantage over scanning laser Doppler vibrometers and related equipment. This new instrument is able to `slow down' fringe movements when illuminating a MEMS device with a dedicated interferometer, by using a slow beat frequency between object excitation and reference beam excitation and averaging over a lot of phase images. It is used in such a way that an ordinary CCD camera can be used to obtain 3D images and movies of the periodic mechanical motion of MEMS devices, either in mechanical resonance when excited using a piezo actuator, or using electronic excitation with probe needles at any frequency required (up to the limitations of the waveform generators). Two modes of operation are possible: a mode in which slow deformations (seconds or more) can be monitored, and a mode in which fast periodic movements (100 Hz - 1 MHz) can be investigated. We show that this imaging technique is especially useful for the investigation of the mechanical behavior of MEMS, both to monitor the intended movement of a structure, and to have a close look at the erratic mechanical behavior of defective parts.

Reliability is a key parameter for the eventual prevalence of microelectromechanical systems (MEMS) as either sub-components or as standalone products. Traditionally, micromachined components have been made by separating the micromachined chip design and fabrication processes from the packaging and reliability issues.

Ink-jet printing technology is, in many ways, ideally suited for addressing a number of these MEMS device packaging challenges. The general advantages of this form of microdispensing derive from the incorporation of data-driven, non-contact processes which enable precise, picoliter-level volumes of material to be deposited with high accuracy and speed at target sites, even on non-planar surfaces. Being data-driven, microjet printing is a highly flexible and automated process which may readily be incorporated into manufacturing lines. It does not require application-specific tooling such as photomasks or screens, and, as an additive process with no chemical waste, it is environmentally friendly. In short, the advantages obtainable with incorporation of micro-jet printing technology in many fabrication applications range from increased process capability, integration and automation to reduced manufacturing costs.

The development of sensitive MEMS now requires either high purity inert atmosphere or a vacuum environment. Therefore, encapsulation is mandatory to ensure performances over the projected lifetime of the devices. The knowledge of the behavior of the MEMS components and assembly with respect to vacuum compatibility is therefore of outmost importance, both to understand and reduce the impurities' release mechanisms and to design a suitable solution to the lifetime issue. This solution is based on the use of specific getter materials and configurations to be incorporated into the MEMS cavity. Outgassing and residual gas composition data are necessary to address the choice of the proper getter material and provide information on the design of the getter. Different solutions can be envisaged depending on the type of gas to be sorbed, the process constraints and the operating conditions of each specific device. If moisture is the main gas to be removed from the cavity, the choice is between physical and chemical dryers. In case other species have also to be sorbed, then the choice of a non-evaporable getter (NEG) has to be preferred. The various getter materials and solutions to the vacuum problems in MEMS will be discussed in detail.

A Si based capacitive microrelay has been packaged in a premolded package and the packaging issues has been studied and verified by FEA and experimental methods. A quasi-3D finite element modeling has been used to understand the thin cap warpage on the microrelay under different process conditions. Experimental verification on the cap warpage showed that thermal loading is not the only contributing parameter for the cap warpage. A modified model with air loading effect and thermal loading effect validated the experimental result. Solution to overcome this problem has been studied with a hole in the package and reinforcement of cap with epoxy.

This work describes full wafer encapsulation of released, self-assembled monolayer (SAM) coated, multi-level polysilicon surface micromachines using the anodic bonding technique. This process has been utilized to protect fragile surface micromachines from damage due to particles, moisture contamination, and post-release die handling. The anodic bonding process was optimized to ensure strong glass-to-wafer bonds, while maintaining the effectiveness of liquid-phase and vapor-phase deposited SAM coatings. The temperature, time, and voltage effects on each SAM coating was analyzed. Glass-to-silicon and glass-to-SAM coated silicon had shear strengths of approximately 18 MPa. Glass-to-polysilicon bonds had lower shear strengths of approximately 10 MPa. Bonds were hermetic to 5 X 10^-8 atm-cm³/s.

This paper reports on a set of parametric monitors for Sandia National Laboratories SUMMiT V (TM) (Sandia Ultra-planar Multi-level MEMS `i' Technology) five-level polysilicon surface micromachining process. Parametric monitors are typically used to monitor changes in the process due to either process drifts or intentional process changes. These parametric monitors are one of three types: electrical, electromechanical, or stress. In this paper we report on the design and characterization of these devices as well as how these devices are used to quantify the characteristics of the SUMMiT VTM process. We will demonstrate the use of these parametric devices in defining a baseline process.

We describe the design, fabrication, test and preliminary analysis of a polycrystalline silicon MEMS inchworm actuator fabricated in a five level surface micromachining process. Large force generation (500 micronewtons), large range of motion (+/- 100 microns), small area requirements (600 X 200 um), small step size (10, 40 or 120 nanometers), and a large velocity range (0 to 90 microns per second) are demonstrated. We characterize force with a load cell whose range is calibrated on a logarithmic scale from micronewtons to millinewtons. We characterize out-of-plane displacement with interferometry, and in-plane displacement with Moire metrology sensitive to approximately 60 nm. The actuator serves well for testing friction under conditions of well- known applied pressure. We found that our surfaces exhibited a static coefficient of friction (cof) of approximately 0.3, and a dynamic cof of approximately 0.2. We also present initial wear studies for this device.

Selectively deposited tungsten films on MEMS surfaces that are subject to friction and wear can substantially reduce wear-related failures. Because deposition of the tungsten film is highly selective to silicon, a pristine surface is required to obtain high quality, contiguous films. Vapor phase HF was used to remove the thin chemical oxide that resides on the surface following traditional liquid phase dissolution of sacrificial oxide films and supercritical CO₂ drying of MEMS devices. The use of vapor phase HF after mechanical parts have been released, rather than liquid processes, mitigates potential device damage and surface tension-induced stiction that may occur during liquid phase processing. Tungsten film thickness and morphology were identical to films that were obtained through the use of liquid phase pre-cleaning processes.

Stiction induced by capillary forces during the post-release drying step of MEMS fabrication can substantially limit the functional yield of complex devices. Supercritical CO₂ drying provides a method to remove liquid from the device surface without creating a liquid/vapor interface, thereby mitigating stiction. We show that a continuous stirred-tank reactor (CSTR) model can be applied as a method to estimate the volume of liquid CO₂ required to effectively displace the post release solvent. The CSTR model predicts that about 8 volume exchanges is sufficient to effectively displace the methanol to a concentration below the saturation point. Experimental data indicate that about 10 exchanges are adequate for repeatable drying of complex devices, which is in reasonable agreement to the model prediction. In addition to drying devices without inducing stiction, the process must be inherently non-contaminating. Data indicate that the majority of contaminants deposited during the drying process can be attributed to contaminants originating in the post-release solvent, rather than the supercritical CO₂ process.

A system-level model of an electrostatically actuated accelerometer is presented. The accelerometer comprises a proof mass levitated between an arrangement of upper and lower pie-shaped electrodes. The proof mass is an electroplated nickel disk, 1 mm in diameter and 200 micrometers thick. The position and orientation of the disk is detected by measuring the differential capacitance between the disk and each of the four upper and corresponding lower electrodes.

Flows in microscale domains are found in many places such as biomedical microdevices (Bio-MEMS), inkjet printer heads, micropropulsion systems, and microchannel networks, among many others. In fact, microfluidic devices represent the fastest growing and what is projected to be the dominant segment of the MEMS market. Because microscopic flows frequently display counter-intuitive behavior due to the different dominating forces at microscopic length scales, experimental diagnostic techniques are essential for characterizing microfluidic MEMS beharior. In recent work, we have developed several micron-scale fluidic diagnostic techniques. Micro-Particle Image Velocimetry (mPIV) measures the velocity of a flow by tracking the motion of small tracer particles seeded into the flow. To measure high velocity, small length scale flows, such as those found inside an inkjet, high-speed lasers and cameras are used in conjunction with a microscope to image the tracer particles with sub microsecond temporal resolution. Two extensions of the mPIV technique allow for flow boundary topology to be measured to with tens of nanometers and for the temperature of the flow to be measured. Combined, these three technique provide experimenters a very complete look at microfluidic device behavior at length scales on the order of 1 micron.

This paper focuses on recent developments in the localised characterisation of the mechanical properties of Microsystems and MEMS devices and structures. Indentation techniques provide a highly powerful method for measuring the load and depth response of very small micro-machined silicon structures. Beam structures, such as are used for accelerometers, need to be characterised in terms of the number of cycles to failure, the spring constant or the energy required to bend the beam by a required amount. Such localised testing needs to be adapted to work at various distances from the origin of the beam with a positioning accuracy of less than a micron. Initial studies have proved to be highly repeatable. A range of examples is presented which cover a range of application areas, including accelerometer beam structures, microswitches and printer head structures. The basic instrumental concepts are explained together with the modifications required for testing small structures in a localised way.