Electrostatic discharge (ESD) and electrical overstress (EOS) damage of Micro-Electrical-Mechanical Systems (MEMS) has been identified as a new failure mode. This failure mode has not been previously recognized or addressed primarily due to the mechanical nature and functionality of these systems, as well as the physical failure signature that resembles stiction. Because many MEMS devices function by electrostatic actuation, the possibility of these devices not only being susceptible to ESD or EOS damage but also having a high probability of suffering catastrophic failure doe to ESD or EOS is very real. Results from previous experiments have shown stationary comb fingers adhered to the ground plane on MEMS devices tested in shock, vibration, and benign environments [1,2]. Using Sandia polysilicon microengines, we have conducted tests to establish and explain the EDS/EOS failure mechanism of MEMS devices. These devices were electronically and optically inspected prior to and after ESD and EOS testing. This paper will address the issues surrounding MEMS susceptibility to ESD and EOS damage as well as describe the experimental method and results found from EDS and EOS testing. The tests were conducting using conventional IC failure analysis and reliability assessment characterization tools. In this paper we will also present a thermal model to accurately depict the heat exchange between an electrostatic comb finger and the ground plane during an ESD event.

Many optical MEMS device designs involve large arrays of thin (0.5 to 1 (mu) m) components subjected to high stresses due to cyclic loading. These devices are fabricated from a variety of materials, and the properties strongly depend on size and processing. Our objective is to develop standard and convenient test methods that can be used to measure the properties of large numbers of witness samples, for every device we build. In this work we explore a variety of fracture tests configurations for 0.5 (mu) m thick silicon nitride membranes machined using the Reactive Ion Etching (RIE) process. Testing was completed using an FEI 620 dual focused ion beam milling machine. Static loads were applied using a probe, and dynamic loads were applied through a piezo-electric stack mounted at the base of the probe. Results from the tests are presented and compared, and application for predicting fracture probability of large arrays of devices are considered.

Failure analysis (FA) tools have been applied to analyze tungsten coated polysilicon microengines. These devices were stressed under accelerated conditions at ambient temperatures and pressure. Preliminary results illustrating the failure modes of microengines operated under variable humidity and ultra-high drive frequency will also be shown. Analysis os tungsten coated microengines revealed the absence of wear debris in microengines operated under ambient conditions. Plan view imagine of these microengines using scanning electron microscopy (SEM) revealed no accumulation of wear debris on the surface of the gears or ground plane on microengines operated under standard laboratory conditions. Friction bearing surfaces were exposed and analyzed using the focused ion beam (FIB). These cross sections revealed no accumulation of debris along friction bear surfaces. By using transmission electro microscopy (TEM) in conjunction with electron energy loss spectroscopy (EELS), we were able to identify the thickness, elemental analysis, and crystallographic properties of tungsten coated MEMS devices. Atomic force microscopy was also utilized to analyze the surface roughness of friction bearing surfaces.

The use of ultrasonic pulses incident on surface micromachines has been shown to reduce dormancy-related failure. We applied ultrasonic pulses from the backside of a silicon substrate carrying SUMMiT processed surface micromachined rotors, used earlier as ultrasonic motors. The amplitude of the pulses was less than what is required to actuate the rotor (sub-threshold actuation). By controlling the ultrasonic pulse exposure time it was found that pulsed samples had smaller actuation voltages as compared to non-pulsed samples after twelve-hour dormancy. This result indicates that the micromachine stiction to surfaces during dormant period can be effectively eliminated, resulting in long-term stability of surface micromachines in critical applications.

Techniques to predict the reliability of microdevices are necessary to facilitate the transfer of MEMS designs from the laboratory to the marketplace. An important reliability concern for microfabricated structures is in-use stiction, the operational failure of devices due to surface adhesion. The current study determines the temperature dependence of in-use stiction for polyscrystalline silicon microcantilevers subjected to three different release conditions: supercritical CO₂ drying; laser-irradiation repair; and self- assembled monolayer post processing. The microcantilever beam arrays were electrostatically actuated at temperatures between 22$DEGC and 300$DEGC. The supercritical CO₂ dried devices showed an overall decrease in sticking probability as the actuation temperature was raised to 300$DEGC. After a distinct improvement in the failure rate between the first and second actuation temperatures, arrays released using laser-irradiation did not exhibit a consistent trend. Samples coated with an OTS monolayer had large increases in their sticking probability as the temperature was raised. However, at temperatures above 200$DEGC, a decrease in in-use stiction was observed which continued through most of the cooling cycle.

The ability to anodically bond Kovar to Pyrex 7740 significantly expands the packaging approaches available for MEMS devices. This technique greatly simplifies and reliably interconnects micropropulsion MEMS components (thrusters, valves) with the attached propellant system. Experimental bonds of Kovar plates and fixtures have been made to numerous Pyrex samples in order to investigate the strength and failure modes of these bonds. An emphasis on experimentally bonding at low temperatures (~200 $DEGC) using large voltages (< 2000V) was also a important parameter of this research and a current microvalve project at JPL. Bond strength measurements have been made using calibrated pull and burst tests with their results being comparable to typical silicon to Pyrex anodic bonds. Detailed bonding conditions for the tested samples have been included in this manuscript to aid the MEMS designer in using this approach to satisfy their packaging needs.

The Polytec^TM laser Doppler vibrometer was used to characterize the dynamics mechanical reliability and lifetimes of surface-micromachined self-assembling MEMS tilting mirrors. The mechanical modes of micromirror can be identified and corresponding resonance frequencies measured. It was found, for certain experimental conditions, that micromirror operation simulating contact between poly-Si surfaces may result in device lifetime reduction due to stiction at the point of contact. The appropriate modifications in device design eliminate the effect of stiction on device lifetime. Moreover, for up to 10⁹ mechanical cycles completed no friction-related device degradation has been observed. In controlled dry ambient at room temperature, micromirrors have been able to complete about 2x10¹⁰ switching operations without signs of mechanical degradation. The results validate the robustness and long term mechanical ability of evaluated micromirror devices.

While considerable press has been given to characterization of mechanical properties of MicroElectroMechanical Systems (MEMS) as related to reliability, environmental robustness, and lifetimes studies, characterization of electrical properties of MEMS have not been widely published. In this paper we present an examination of electrical properties (surface and substrate leakage currents, sheet resistance, substrate contact resistance and interlayer contact resistances) of polysilicon thin films used in surface micromachined MEMS test structures. Environmental and electrical overstress conditions that affect leakage have been studied. Two test structures have been used to independently study surface and substrate leakage currents at different levels of humidity (0% to 80% RH) and applied voltage (100 to 150 volts). Both static and lifetime studies have been conducted. Significant differences in surface and substrate leakage lifetime characteristics are observed, suggesting different failure mechanisms for these two important electrical phenomena in MEMS reliability.

Micro-Nano Technology Visualization (MNTV) is critical to studies in MEMS reliability. The ability to see and characterize the microstructures and interfaces with high resolution at the microscale and nanoscale is invaluable. In this paper we present the motivation, paradigm and examples of visualization techniques applied to several aspects of surface micromachined polysilicon structures. High resolution cross-section imaging, using both a FIB/SEM and FIB/STEM, is used to acquire information on profile differences between fabrication facilities and grain size and orientation. The AFM is used to compare surface roughness on both sides (top and bottom surfaces) of thin film polysilicon after release etching. The data gathered will be extremely useful feedback for fabrication facilities in terms of process characterization and quality assurance. The data will also be useful for MEMS CAD tools where device and process models must be validated.

CMOS MEMS devices, fabricated from up to 13 layers of materials to create independent conducting paths, are subject to incremental fracture at high stress and to charging effects. This paper expands on preliminary reserach, which has revealed several stages of change in CMOS MEMS physical properties as they are exposed to resonant motion. Cracks are the first induced inside the stiffest lasyers, often silicon dioxide, in laterally resonant test structures with cyclic stress of 620 Mpa. Prior to cracking, the aluminum top layer of the structure can also deform, which affects the electrical integrity of the conductor. Measured frequency reponses of folded-flexure resonators demonstrate a nonlinear Duffling effect, producing mushroom-shaped resonant peak. Cyclic stress of 70 Mpa at the maximal stress points was insufficient to induce significant mechanical fracture in foled flexure resonators after 5 billion cycles, however an onset of change in stiffness was detected. Devices with a fixed dc actuation voltage experienced a change in electrostatic force attributed to charge accumulation in polymer and oxide layers. The force decayed with an approximate one-hour time constant while resonant frequency and quality factor remained constant.

We present a full factorial study of the effect of relative humidity and voltage on the oxidation of surface-micromachined poly-silicon wiring and electrodes. Our system consists of 500 nm thick poly-Si wires and electrodes insulated from the substrate wafer by 600 nm of Si-rch Si_xN_y, fabricated using a surface-micromachinging process. In dry ambients, oxidation or damage to the bottom poly-Si layer (the Poly0 layer) in MicroElectroMechanical Systems (MEMS) devices occurs so slowly that little can be learned in a timely manner, even when stressing the electrodes at electric fields close to dielectric breakdown. We observe however that in ambient with elevated relative humidity the Poly0 wires and electrodes anodically oxidize within a short period of time when operated at moderately large voltages. Only the most positively biased poly-Si structures oxidize, and we describe the anodic oxidation and association volume expansion as a function of a number of accelerating factors including relative humidity and voltage. A threshold is observed in relative humidity bot not in voltage.

In this study, the parameters affecting operational and nonoperational reliability of the Sandia Microengine were investigated. It was found that using a non-outgassing die attach material greatly improves storage life. The minimum force required to drive the microengines initially decreased from a much higher voltage to settle in at around 1250 V² for all devices tested. Drive signal parameters were optimzed for individual engines and the resulting device lifetimes were found to be marginally better that when average values were used (1.2x10⁶ cycles compared to 1.0x10⁶ cycles). There was no correlation between the value of the lumped parameter kr/a and lifetime found, however the longest living engines used a kr/a of around 1000 V². ues. Optimized drive signal lifetimes were found to be a factor of two higher than when sinewave drive signals were used (5x10⁵ compared to 1.2x10⁶),indicating the advantage of using optimizzed drive signals, but not the two order of magnitude in lifetime that was desired.

As the size of a mechanical structure used in microelectromechanical systems (MEMS) such as sensors and actuators becomes susceptible to defect, the effect of defects on mechanical reliability has a vital importance. So, new theoretical and experimental techniques need to be developed to estimate the micromechanical properties in MEMS. Experimental tools for macroscale testing are not necessarily applicable to MEMS structures. The electrostatically actuated test device is presented to evaluate force and frequency for microcrack initiation near sharp notch of micromachined silicon device. The designed test device consists of comb drives for loading and a suspending beam for testing. The sharp notch is introduced to the suspending beam in the test device. The notched microbeams are fully integrated with a simultaneously microfabricated electrostatic actuator, which allows microfracture and fatique test without the need of an external loading instruments and without any possible influences from external sources. On the basis of the proposed test structure and linear elastic fracture mechanics, a theoretical model to quantify the notch radius effect on fracture toughness can be obtained without pre-crack formation and critical notch radius is discussed. The test device is in its lateral resonance frequency by modifying the Rayleigh method. The microcrack initiation can be quantified from the shift in the resonance frequency that is related to the stiffness change. Diagnosis of microcrack developed in the suspending beams can be expected from the decrease in the resonance frequency. Furthermore, the microcrack growth rate may be analyzed from a decrease in resonance frequency withe time.

Silicon micromechanics in an emerging field which is beginning to impact almost every area of science and technology. In areas as diverse as the chemical, automotive, aeronautical, cellular and optical communication industries, Silicon micromachines are becoming the solution of choice for many problems. In this paper we will describe what they are, how they are built, and show how they have the potential to revolutionize lightwave systems. Devices such as optical switches, variable attenuators, active equalizers, add/drop multiplexers, optical crossconnects, gain tilt equalizers, data transmitters and many others are beginning to find ubiquitous application in advanced lightwave systems. We will show examples of these devices and describe some of the challenges in attacking the billions of dollars in addressable markets for this technology.

Silicon bulk micromachining which is based on a silicon etching and a glass-silicon anodic bonding plays important roles to make micro sensors and micro actuators. Three dimensional microfabrication of other functional materials as piezoelectric materials are also important to develop high performance microactuators, micro energy source and so on. Vacuum sealing is required to prevent a viscous dumping for packages micromechanical sensors. Extremely small structures as microprobe are required for high resolution, high sensitivity and quick response. As sophisticated microsystems which are made of many sensors, circuits and actuators are required for example for maintenance tools used in a narrow space. Developments for those required will be described.

The continuous progress in micro- and nano-system technologies has allowed the successful development of many innovative products in process control, environmental monitoring, healthcare, automotive and aerospace as well as information processing systems. In this paper on overview will be given of current progress in micro- and nanofabrication process technologies, such as deep reactive ion etching, micro-electro discharge machining, thick photoresistant processing and plating. The availibility of these micro- and nanofabrication processes will be illustrated with examples of new generations of silicon-based sensors, actuators and Microsystems with a particular emphasis on real applications of these components and systems.