The Digital Micromirror Device (DMD) developed by Texas Instruments (TI) has made tremendous progress in both performance and reliability since it was first invented in 1987. From the first working concept of a bistable mirror, the DMD is now providing high-brightness, high-contrast, and high-reliability in over 1,500,000 projectors using Digital Light Processing technology. In early 2000, TI introduced the first DMD chip with a smaller mirror (14-micron pitch versus 17-micron pitch). This allowed a greater number of high-resolution DMD chips per wafer, thus providing an increased output capacity as well as the flexibility to use existing package designs. By using existing package designs, subsequent DMDs cost less as well as met our customers' demand for faster time to market.
In recent years, the DMD achieved the status of being a commercially successful MEMS device. It reached this status by the efforts of hundreds of individuals working toward a common goal over many years. Neither textbooks nor design guidelines existed at the time. There was little infrastructure in place to support such a large endeavor. The knowledge we gained through our characterization and testing was all we had available to us through the first few years of development. Reliability was only a goal in 1992 when production development activity started; a goal that many throughout the industry and even within Texas Instruments doubted the DMD could achieve. The results presented in this paper demonstrate that we succeeded by exceeding the reliability goals.
This paper reports results on electrical characteristics, evaluation of design, and reliability of the first commercially available micromachined relays. The parts have been characterized in a wide range of temperatures (from 100 degrees C to +180 degrees C) and load conditions (voltages from 10 V to 70 V and currents from 5 mA to 200 mA). Mechanical integrity of the parts has been evaluated by subjecting them to multiple mechanical shocks in the range from 100 G to 1000 G up to 10,000 shocks. Life testing was performed at different contact voltages and current loads during 108 switching cycles. To simulate space operation conditions, characteristics of the parts were monitored during vacuum testing. Typical failure modes associated with different test conditions are discussed.
The main thrust in any reliability work is identifying failure modes and mechanisms. This is especially true for the new technology of MicroElectroMechanical Systems (MEMS). The methods are sometimes just as important as the results achieved. This paper will review some of the methods developed specifically for MEMS. Our methodology uses statistical characterization and testing of complex MEMS devices to help us identify dominant failure modes. We strive to determine the root cause of each failure mode and to gain a fundamental understanding of that mechanism. Test structures designed to be sensitive to a particular failure mechanism are typically used to gain understanding. The development of predictive models follows from this basic understanding.
This paper will focus on the failure mechanism of wear and how our methodology was exercised to provide a predictive model. The MEMS device stressed in these studies was a Sandia-developed microengine with orthogonal electrostatic linear actuators connected to a gear on a hub. The dominant failure mechanism was wear in the sliding/contacting regions. A sliding beam-on-post test structure was also used to measure friction coefficients and wear morphology for different surface coatings and environments. Results show that a predictive model of failure-time as a function of drive frequency based on wear fits the functional form of the reliability data quite well, and demonstrates the benefit of a fundamental understanding of wear. The results also show that while debris of similar chemistry and morphology was created in the two types of devices, the dependence of debris generation on the operating environment was entirely different. The differences are discussed in terms of wear maps for ceramics, and the mechanical and thermal contact conditions in each device.
The use of Laser Doppler Vibrometry (LDV) technology has been at the forefront of Micro-Electro-Mechanical Systems (MEMS) research since the early 1990’s. By its nature as a sensitive laser optical technique, it is well suited for non-contact dynamic response measurements of microscopic structures. The art of the technology has culminated into the latest micro-scanning vibrometer for automated scan measurement and display of deflection shapes with sub-nanometer resolution. To exemplify the use of this technology, Polytec PI presents characterization measurements in collaboration with Applied MEMS on two of their devices used in commercial applications. LDV characterization measurements are used for validating the design of the Applied MEMS two-axis micro mirror. Scan measurements reveal distinct, isolated rotation modes about x- and y- axes that can be used to promote the mirror motion in either direction. Settling time performance is evaluated from impulse response and optimized using Input Shaping techniques. Scan measurements of a low-noise accelerometer device from Applied MEMS reveals spurious high frequency modes of support spring causing unwanted response effects. Further use of a new time domain animation feature shows ringing response of the accelerometer to step motions.
For reliable MEMS device fabrication and operation, there is a continued demand for precise characterization of materials at the micron scale. This paper presents a novel material characterization device for fatigue lifetime testing. The fatigue specimen is subjected to multi-axial loading, which is typical of most MEMS devices. Polycrystalline silicon (polysilicon) fatigue devices were fabricated using the MUMPS process with a three layer mask process ground plane, anchor, and structural layer of polysilicon. A fatigue device consists of two or three beams, attached to a rotating ring and anchored to the substrate on each end. In order to generate a sufficiently large stress, the fatigue devices were tested in resonance to produce a von Mises equivalent stress as high as 1 GPa, which is in the fracture strength range reported for polysilicon. A further increase of the stress in the beam specimens was obtained by introducing a notch with a focused ion beam. The notch resulted into a stress concentration factor of about 3.8, thereby producing maximum von Mises equivalent stress in the range of 1 through 4 GPa. This study provides insight into multi-axial fatigue testing under typical MEMS conditions and additional information about micron-scale polysilicon mechanical behavior, which is the current basic building material for MEMS devices.
One of the primary challenges in MEMS metrology is the large variety of shapes, lateral feature sizes, and vertical steps on MEMS devices. This paper describes a software approach by which ideal surface templates are generated for each MEMS device from the design files or prior measurements. These templates may contain multiple sub-regions, or data islands, each of which is generally characterized in a different manner.
Surface measurements from a white-light interference microscope are matched with the ideal MEMS template using a variety of techniques and threshold criteria. The template-based technique is tolerant of errors both rotation and translation, allowing accurate characterization of each data island and their relative positions.
This paper will explore the concepts used to generate templates, align actual data with the original template, and sources of error and robustness of each technique on several datasets. The effect of measurement and positional errors on both the overall match and on the sub-region analyses will be explored for characterization of datasets.
Anodic oxidation can be a catastrophic failure mechanism for MEMS devices that operate in high humidity environments. Shea and coworkers have shown that positively charged polysilicon traces can fail through a progressive silicon oxidation reaction whose rate depends critically on the surface conductivity over the silicon nitride. We have found a related anodic oxidation-based failure mechanism: progressive delamination of Poly 0 electrodes from silicon nitride layers, which then mechanically interfere with device function well before the electrode is fully oxidized. To explain this effect, we propose that the silicon oxide which initially forms at the electrode edge has insufficient strength to hold the local Poly 0 / silicon nitride interface together. This low-density silicon oxide also creates a bilayer system, which curls the edge of the 300 nm thick Poly 0 electrode away from the nitride. As delamination progresses more nitride surface is exposed and more of the interface is then attacked. This process continues cyclically until the electrode edge pushes against other device components, catastrophically and irreversibly interfering with normal operation. Additionally, we observe that the delamination only starts at electrode edges directly under cantilevers, suggesting the oxidation rate also depends on the perpendicular electric field strength.
The current vs. voltage and electrical breakdown behavior for devices with micron and sub-micron gaps between conductors is studied. The limitations of the well-known but often-misinterpreted Paschen curve are discussed. The little-known modified Paschen curve, that includes field emission effects so important in understanding breakdown behavior for devices with sub-micron gaps, is described. Current vs. voltage measurements across metal-air-metal, metal-insulator-metal and metal-insulator-air-insulator-metal gaps with gaps ranging from 4 nm to 4 μm are reported. The breakdown voltage for an air gap of 0.9 μm was found to be 150 V, far below the Paschen curve minimum breakdown limit, and field emission behavior was confirmed via the Fowler-Nordheim plot. Metal-insulator-metal gaps with a diamond-like carbon thin-film with a thickness of 4 nm had a breakdown voltage of only 1V. SEM and AFM analysis show that the breakdown damage is crater-like and through the carbon layer. Other characterization of the damage caused by breakdown is presented. Tribocharging, electrostatic induction, and other ESD-related phenomena, are discussed for several devices with sub-micron gaps. It is concluded that devices with sub-micron gaps can face a serious challenge due to electrical breakdown during manufacturing, handling and operation. These devices include photolithographic reticles, magnetic recording heads, MEMS and field emission displays.
Spatial microstages are microfabricated controlled platforms that can be popped out of the fabrication plane and are free to move in three-dimensional (3D) space. Spatial microstages have shown promise for use in MOEMS for adaptive optics, automatic focusing systems, fiber optic alignment/precision positioning, real time optical alignment, interconnects, and a host of other applications. These devices were designed and fabricated to position a controllable stage in 3D space from microassembly and microfabrication. Microstages can be designed and fabricated to move in plane (x, y) and out of plane (z). Advanced microstages are designed to move in plane, out-of-plane, rotate, and tilt about x, y, and z.
Design and fabrication of the rotational and tilt components are critical in performing the three-dimensional pop up and tilting action needed for precise micropositioning. The device used for analysis contains linear racks driven by electrostatic actuators. The actuators are attached to a microstage through a hinge component with revolving, rotating, and tilting joints. The actuators allow x, y, and z positioning while the hinge allows rotational motion along the stage. Failure analysis of the Sandia fabricated microstage was performed on released and as fabricated microstages. Failure analysis of these devices revealed design and fabrication irregularities along the revolving components of the hinge. This paper will discuss the design and functionality of the microstage, failure analysis activities and failure mechanisms found in polysilicon fabricated microstages, corrective actions and design improvements.
High resolution investigation of the microstructure of materials and devices is very often restricted to the study of the very surface of the sample. This is because most high resolution analytical and imaging techniques like scanning electron microscopy (SEM), atomic force microscopy (AFM) or scanning tunnelling microscopy (STM) only provide information about the surface microstructure of the sample. To locally investigate the internal microstructure of the sample at high resolution, the sample has to be opened up. This can be done very precisely by the use of a focused ion beam (FIB) for cutting into the sample and the use of a field emission SEM for high resolution imaging of the internal structure. The combination of FESEM and FIB is a future key technology for semiconductor and material science related applications. A new CrossBeam tool is discussed in this presentation. Through the combination of the well known Gemini ultrahigh resolution field emission SEM column and the well known Canion31+ high performance FIB column a wide field of applications can now be accessed. This includes structural cross-sections for SEM and TEM applications, device modification, failure analysis, sublayer measurement and examination, as well as SEM and FIB related analytical techniques such as EDS, WDS, SIMS etc. Real time high resolution SEM imaging of the cutting and deposition process enables the researcher to perform very accurate three dimensional structural examinations and device modifications.
The field of MEMS/NEMS has expanded considerably over the last decade. The length scale and large surface-to-volume ratio of the devices result in very high retarding forces such as adhesion and friction that seriously undermine the performance and reliability of the devices. These tribological phenomena need to be studied and understood at the micro- to nanoscales. In addition, materials for MEMS/NEMS must exhibit good microscale tribological properties. There is a need to develop lubricants and identify lubrication methods that are suitable for MEMS/NEMS. Using atomic force microscopy-based techniques, researchers have conducted micro/nanotribological studies of materials and lubricants for use in MEMS/NEMS devices. In addition, component level testing have also been carried out to aid in better understanding of the observed tribological phenomena in MEMS/NEMS.
Due to the relatively high compliance, large surface-to-volume ratio, and small separation distances, micromachined polycrystalline silicon (polysilicon) structures are susceptible to high adhesion forces including van der Waals, electrostatic, and capillary forces. Since these forces depend on the surface separation distance, it is essential to understand the microtribological properties, especially the surface roughness. In this study, four types of polysilicon microhinged flaps were designed to characterize the surfaces. The flaps enable access to both the top and bottom surfaces of the structural polysilicon layers. Multiple locations are scanned for each surface type using a Digital Instruments 3100 atomic force microscope (AFM). The results indicate that the top surface is much rougher than the bottom surface for structural layers and the roughness is influenced by the adjacent layers. Since the base polysilicon layer (poly0) is six times rougher than a base silicon nitride layer, depositing the MEMS devices on the poly0 layer rather than directly on silicon nitride will reduce adhesion. An adhesion model was used to analyze the effect of roughness parameters on stiction force between structural layers and substrate. Since the tip condition impacts the accuracy of AFM measurement, a wear test of silicon tips was also performed.
Microelectromechanical systems (MEMS) with high out-of-plane stiffness are less susceptible to adhesion than more compliant structures, but reliable operation of sliding contacts still requires surfaces that exhibit adequate friction and wear performance after long periods of storage. Alkylsilane monolayers are popular surface treatments for silicon devices, and there has been some research to understand the performance of monolayers as a function of environment. However, there have been limited investigations of the tribological behavior of these surface treatments after exposure to harsh environments. There is a need to quantitatively determine the effects of storage environments on the performance of MEMS interfaces, rather than verifying device functionality alone. To this end, surface micromachined (SMM) structures that contain isolated tribological contacts have been used to investigate interface performance of alkylsilane monolayers after storage in inert environments, and after exposure to a variety of thermal and radiation environments. Results show that both octadecyltrichlorosilane (ODTS) and perfluorodecyltrichlorosilane (PFTS) exhibit little change in hydrophobicity or friction after Co-60 radiation exposures at a total dose of up to 500 krad. However, exposure to temperature cycles consistent with packaging technologies, in the presence of low levels of water vapor, produces degradation of hydrophobicity and increase in static friction for ODTS films while producing no significant degradation in PFTS films.
°Microelectromechanical systems (MEMS) have enormous potential to contribute in diverse fields such as automotive, health care, aerospace, consumer products, and biotechnology, but successful commercial applications of MEMS are still small in number. Reliability of MEMS is a major impediment to the commercialization of laboratory prototypes. Due to the multitude of MEMS applications and the numerous processing and packaging steps, MEMS are exposed to a variety of environmental conditions, making the prediction of operational reliability difficult. In this paper, we investigate the effects of operating temperature on the in-use adhesive failure of electrostatically actuated MEMS microcantilevers coated with octadecyltrichlorosilane (OTS) films. The cantilevers are subjected to repeated temperature cycles and electrostatically actuated at temperatures between 25°C and 300°C in ambient air. The experimental results indicate that temperature cycling of the OTS coated cantilevers in air reduces the sticking probability of the microcantilevers. The sticking probability of OTS coated cantilevers was highest during heating, which decreased during cooling, and was lowest during reheating. Modifications to the OTS release method to increase its yield are also discussed.
The microtribometer fabricated is designed to observe the wear of removable flat silicon test inserts, coated with thin film layers such as DLC and moving in an oscillating manner relatively to each other. For observing the low wear of DLC layers in a reasonable amount of time, high oscillating speed is essential and can be achieved by reducing the mass in motion. The silicon microtribometer reaches oscillating frequencies of 10 Hz while applying a normal force on the test inserts up to 9.6 N, the maximal displacement amplitude being 1.5 mm. The two silicon main parts of the microtribometer guide test inserts along one direction in a back and forth motion while avoiding any side friction, the actuation being done by an external linear motor. For such application crystalline silicon presents, compare to other materials, the advantage of the invariance of its behavior over time.
Several applications of metallic MEMS devices require that the component can endure cyclic stresses. Mechanisms for fatigue failure may be altered at length scales where the size of the component becomes comparable with the microstructure. For this reason, it is necessary to characterize the fatigue performance of MEMS-scale structures and understand the role of microstructure on potential failure modes. A new specimen configuration has been designed which allows for simple gripping and actuation using a fixed-free beam in bending. The cross-section of the beam is tapered to create a finite width gage section of constant maximum stress, as can be derived from elastic beam theory. This method has been applied to characterize the fatigue behavior of LIGA Nickel with a nominal cross-section of 26×260 microns, replicating the dimensions of a potential accelerometer device. The common stress-life approach was used to characterize the number of cycles to failure for a range of applied cyclic stresses. We found that the stress-life curve was similar to what has been observed for conventional Nickel. The endurance limit (defined in this study as the stress required to cause failure in ~10M cycles, below which the device has practically infinite life) was found to be 35-40% of the ultimate tensile strength. The surface condition of specimens at various stages in the fatigue life, characterized by scanning electron microscopy, revealed that failure initiated as microcracks within localized persistent slip bands (PSBs).
One of the major difficulties faced by MEMS researchers today is the lack of data regarding properties of electroplated metals or alloys at micro-levels as those produced by the LIGA and the LIGA related process. These mechanical properties are not well known and they cannot be extrapolated from macro-scale data without experimental verification. This lack of technical information about physical properties at microscale has affected the consistency and reliability of batch-fabricated components and leads to very low rates of successful fabrication. Therefore, this material issue is of vital importance to the development of LIGA technology and to its industrial applications. The research work reported in this paper focuses on the development of a new capability based on design, fabrication, and testing of groups of UV-LIGA fabricated nickel microspecimens for the evaluation of fracture strength. The devised testing mechanism demonstrated compatibility with the fabricated samples and capability of performing the desired experimentation by generating resistance-to-fracture values of the nickel specimens. The average fracture strength value obtained, expressed with a 95% confidence interval, was 315 ± 54 Mpa. Further data acquisition, especially involving tensile specimen testing, and material analysis is needed to fully understand the implications of the information obtained.
This paper presents recent results on the microstructural evolution and the resulting mechanical property changes as a function of elevated temperature exposure of two types of electroplated nanocrystalline LIGA Ni. Electroplated Ni structures are the main candidates for LIGA-based MicroElectroMechanical System (MEMS). Initial studies have been conducted to correlate microstructure of electroplated Ni and resulting mechanical properties. A major drawback is that upon exposure to elevated temperatures, electroplated Ni MEMS components suffer dramatic reductions in strength mainly due to grain coarsening. This kind of strength deterioration at elevated temperatures can be detrimental to many MEMS applications, especially to micro-engines and molding inserts. Thus, in order to improve the high temperature performance of LIGA Ni, knowledge of the underlying mechanism is needed. At present, there is very limited understanding of processing-microstructure-property relationship for LIGA Ni at both room and elevated temperatures. The current research is focused on temperature effects on the microstructure of LIGA Ni and the resulting mechanical properties. Two types of sulfuric acid-based solutions were used to produce electroplated Ni samples with different microstructural characteristics. The DSC technique was used to study the stability of plated Ni at elevated temperatures. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were used to examine the microstructural changes of plated Ni samples as a function of annealing temperature. Nanoindentation tests were performed to study the effects of the evolved microstructures on mechanical properties. The underlying mechanism correlating microstructure and mechanical properties of LIGA Ni at elevated temperatures is discussed.
This paper presents a new process flow for the fabrication of Air gap Insulated Microstructures (AIM) with strengthened interconnection beams based on standard single crystal silicon wafers. The main focus on the new development was set on the attributes of reliability and fatigue. As a result of our investigations, the interconnection beams were identified as weakest point in the system. To improve the quality of the beams, several material stacks with well defined properties were tested in order to find a suitable material stack for the interconnection beams instead of pure aluminum. The new process flow enables the use of layered structured beams without loosing any of the advantages of the AIM technology and also without increasing the number of masks.
SU-8 has been used directly as structural material for MEMS/BioMEMS components as well as optical MEMS components. Although the applications of SU-8 photoresist have widely been presented, the material properties and behavior at elevated temperature have rarely been reported. In this paper, the thermal stability of the SU-8 structures as the function of exposure doses and photo initiator concentration changes has been studied. Differential Scanning Calorimeter (DSC), Thermogravimetric Analyzer (TGA) and Dynamic mechanical analysis (DMA) are employed to study the thermal stabilities of exposed SU-8 microstructures. Mass loss as the function of exposure doses and post-baking time were studied by TGA. The results show that the relative mass loss is inversely proportional to the exposure dose as well as the post-baking time, which also directly affect the thermal stability of SU-8 components. The DSC results reveal that there is a phase change reaction occurs around the temperature of 150°C and is directly related to the photo initiator. The effects of this phase change on the tensile strength and creep behavior of SU-8 fabricated microstructures were also explored using DMA. These results will provide the MEMS researchers and engineers with the usable information in SU-8 applications. At the end, how to optimize SU-8 processing parameters to increase its thermal stability is discussed.
Microelectromechanical systems (MEMS) promise to revolutionize nearly every product category by bringing together silicon-based microelectronics with micromachining technology, thereby, making possible the realization of a complete system on a chip. As the MEMS application approaches the different market places cost, performance, hermeticity, and reliability become the key issues.
Flux free/void-free soldering is accomplished by controlling the atmosphere, time, and temperature. This is a simplified version of the Pressure Variation method. P1 V1 = P2 V2, V2 = V1 (P1/ P2).
The hermeticity level of the package can directly affect MEMS device performance. Hermeticity level of 10-8 and sometimes 109 are common measurements. Getter firing as part of the package seal process means higher yields, total control of the internal atmosphere of the package, improved quality and reliability. Getter pumps are based on those elements in the periodic table with features that make them suitable to act as a vacuum pump.
Quality control standards for MEMS technologies are needed. Part of the problem is that the technology is so new and ever changing that the fabricators do not yet know how to define quality, much less measure it.
MEMS surface-micromachining fabrication requires the use of many different tools to deposit thin-films, precisely define patterns using typical photolithography, and perform etching processes. As with any fabrication process there is inherent variation, which is acceptable when controlled within suitable limits. The ability to monitor and respond to this variation is paramount in maintaining a viable fabrication process. Electrostatic comb-drive resonators are candidate test structures used to validate uniformity in the MEMS fabrication process. Although directly dependent on mass and spring constant, a measure of their resonant frequencies generally provides a good indicator of both process repeatability and geometric variation.
In this study, sets of five graduated comb-drive resonator structures, located at each die on a ¼ wafer, were stimulated to resonant frequency using the “blur envelope” technique. This technique facilitates fast, straightforward, and repeatable resonant frequency measurements usually with a resolution of approximately 50-100 Hz. Wafer maps of resonant frequency versus die position for a ¼ wafer reveal a pattern with comb-drive resonator devices exhibiting highest resonant frequencies at the center and lowest at the perimeter of the wafer. Using a numerical model, coupled with discrete geometric measurements, a method was developed which links resonant frequency to fabrication parameters.
Supercritical CO2 drying has been shown to be an effective method for drying complex MEMS structures with little or no stiction. This process typically involves transferring released parts from ultrapure water into a solvent, such as methanol, that is miscible with liquid CO2, and subsequently displacing the methanol with liquid CO2. During this process sequence, transport of methanol into and out of the tortuous pathways of the MEMS device is dominated by diffusion. The non-steady state diffusion equation (Fick’s second law) with length scales relevant to MEMS structures can be applied to understand the speed at which diffusion occurs. This analysis indicates that diffusion of methanol into the pathways of a MEMS device occurs very rapidly, typically on the order of minutes. Experimental data are consistent with the rapid diffusion hypothesis.
In the fabrication of MEMS devices, what has come to be known as "release stiction" occurs when the device is removed from the liquid phase into the ambient air. One widely used method for dealing with stiction is to deposit a hydrophobic coating on the surface of the device before it is removed from the liquid phase. This method can produce coatings with inconsistent morphology and device yield. This is to be compared with a new coating deposition scheme developed at Sandia National Labs, termed VSAMS (vapor-deposited self-assembled monolayers) that employs supercritical CO2 drying and chemical vapor deposition to address many of the concerns associated with release stiction. VSAMS is attractive due to its process benefits, which include increased throughput, reduced waste, and most importantly, it can be easily scaled to full wafer production. It is also attractive because films produced by this method are uniform and very hydrophobic. The deposition step makes use of a class of compound that is particularly suited for vapor phase reactions, amino-functionalized silanes. The yield of microengine test devices coated with films made from amino-functionalized silanes was examined over an extended period. Their function was determined before and after the application of VSAMS. The advantage of using amino-functionalized silane precursors for VSAMS is related to the strength of the bond between the film and the polysilicon surface as evidenced by the fact that films made with these precursors are stable across the entire humidity scale.
Sandia National Laboratories has programs covering a broad range of MEMS technologies from LIGA to bulk to surface micromachining. These MEMS technologies are being considered for an equally broad range of applications, including sensors, actuators, optics, and microfluidics. As these technologies have moved from the research to the prototype product stage, packaging has been required to develop new capabilities to integrated MEMS and other technologies into functional microsystems. This paper discusses several of Sandia’s MEMS packaging efforts, focusing mainly on inserting Sandia’s SUMMiT V (5-level polysilicon) surface micromachining technology into fieldable microsystems.
The evolution from ceramic packages to wafer to wafer hermetic sealing poses tremendous technical challenges to integrate a proper getter inside the MEMs to assure a long term stability and reliability of the devices. The state of the art solution to integrate a getter inside the MEMs of the last generation consists in patterning the getter material with a specific geometry onto the Si cap wafer. The practical implementation of this solution consists in a 4” or 6” Si wafers with grooves or particular incisures, where the getter material is placed in form of a thick film. The typical thickness of these thick films is in the range of few microns, depending on the gas load to be handled during the lifetime of the device. The structure of the thick getter film is highly porous in order to improve sorption performances, but at the same time there are no loose particles thanks to a proprietary manufacturing method. The getter thick film is composed of a Zr special alloy with a proper composition to optimize the sorption performances. The getter thick film can be placed selectively into grooves without affecting the lateral regions, surrounding the grooves where the hermetic sealing is performed.
Soldering of components within a package plays an important role in providing electrical interconnection, mechanical integrity and thermal dissipation. MEMS packages present challenges that are more complex than microelectronic packages because they are far more sensitive to shock and vibration and also require precision alignment. Soldering is used at two major levels within a MEMS package: at the die attach level and at the component attach level. Emerging environmental regulations worldwide, notably in Europe and Japan, have targeted the elimination of Pb usage in electronic assemblies, due to the inherent toxicity of Pb. This has provided the driving force for development and deployment of Pb-free solder alloys. A relatively large number of Pb-free solder alloys have been proposed by various researchers and companies. Some of these alloys have also been patented. After several years of research, the solder alloy system that has emerged is based on Sn as a major component. The electronics industry has identified different compositions for different specific uses, such as wave soldering, surface mount reflow, etc. The factors that affect choice of an appropriate Pb-free solder can be divided into two major categories, those related to manufacturing, and those related to long term reliability and performance.
An approach to maintain vacuum in MEMS devices, by integrating MEMS fabrication process with getter material preparation, is presented in this paper. A coating process for thick film of getter material on silicon and glass wafers, which are common materials in fabrication of MEMS devices and package, has been investigated in detail. The getter material consists of a powder mixture of zirconium, vanadium and iron, which features high sorption capability to active gas such as H2, O2, N2, CO and H2O vapor. Several patterned NEG thick films to simulate different needs in MEMS application have been made. The sorption capacity of the coated getter material was examined. The coating of NEG thick film onto the inner surface of a MEMS pressure sensor and the activation of NEG during anodic bonding process were carried out.
MEMS fabrication and packaging requires a bonding technology that is universal for all substrates, has high resolution, requires relatively lower temperatures, is reliable and is low cost to implement. The bonding technology presented meets the above standards. The process is substrate independent and involves aligned bonding of two similarly patterned wafers using tin solder as the bonding material. The technique can be used for whole wafer or selected area bonding. The resolution of this technique is only limited by the resolution that can be achieved in the patterning and delineation of the seed metal.
Hermetic packaging of micro-optoelectromechanical systems (MOEMS) is an immature technology, lacking industry-consensus methods and standards. Off-the-shelf, catalog window assemblies are not yet available. Window assemblies are in general custom designed and manufactured for each new product, resulting in longer than acceptable cycle times, high procurement costs and questionable reliability.
There are currently two dominant window-manufacturing methods wherein a metal frame is attached to glass, as well as a third, less-used method. The first method creates a glass-to-metal seal by heating the glass above its Tg to fuse it to the frame. The second method involves first metallizing the glass where it is to be attached to the frame, and then soldering the glass to the frame. The third method employs solder-glass to bond the glass to the frame.
A novel alternative with superior features compared to the three previously described window-manufacturing methods is proposed. The new approach lends itself to a plurality of glass-to-metal attachment techniques. Benefits include lower temperature processing than two of the current methods and potentially more cost-effective manufacturing than all three of today’s attachment methods.
In this paper, the development of a dual-function leak detector is presented. The system consists of a laser interference instrument, a portable helium leakage detector, a specially designed test chamber with a quartz-glass observation window, a pressure gauge. The developed measuring system offers new features for experimental investigation on the integrity of hermetic sealed structure. Both helium bombing mode and diaphragm deflection mode were investigated using the developed detector. Basically, the system can be used for helium leak bombing detection. By employing this system for leakage detection in a micro optical switch, it was shown that a leakage of less than 10-7 std cc/sec can be measured. The system can also be used to measure the surface deflection of a diaphragm. The measurement was accomplished by using laser interference technique to monitor the pressure variation within the small cavity of MEMS devices after pressurized gas was introduced. A leakage as low as 10-14 std cc/sec could be detected for a sample with several cubic millimeter cavity of 10-4 mbar.
This paper describes a test system and presents preliminary results of a long-term reliability study of an electro-thermally actuated integrated MEMS optical attenuator. These tests are designed to address the specific failure modes and life prediction models required for "set and forget" components and to identify deficiencies that exist in the current telecom (Telcordia) testing standards as they apply to MEMS. The failure modes are activated by overstressing the devices to a much higher power than would be observed under normal operating conditions. The paper describes a multi-module experimental test station for exciting devices at up eight different power levels, both AC and DC. At set intervals devices are tested off-board to measure changes in actuator deflection and resistance over time. The preliminary results show that devices start to degrade at power levels 92% over operating power after 400 hours of stress.
Burn-in test has long been used in the semiconductor industry to screen out manufacturing defects. MEMS technologies, such as the DMD, can also use burn-in test to eliminate infant mortality failures. Burn-in test and test systems are among the most costly however, and it is always under review to shorten time or increase efficiency without reducing effectiveness. Detailed failure mode analysis from many thousands of device test logs resulted in the development of a novel application of an observed stress factor. Burn-in test time was reduced 55% on high volume DMD products with increased test efficiency and effectiveness.
Instrumentation of the Next Generation Space Telescope (NGST) will include a Multi-Object Spectrograph (MOS) in order to record simultaneously several hundred spectra in a single observation run. The selection of the objects in the field of view will be done by a MOEMS-based device: a micro-shutter array (MSA). In Laboratoire d’Astrophysique de Marseille, we have developed since several years different tools for the modeling and the characterization of these MOEMS-based slit masks. We are now developing a new bench for the measurement of the contrast value. The contrast is the amount of non-selected flux from sky background and bright sources passing through the multi-slit device. Contrast measurement have been carried out on the micro-mirror array fabricated by Texas Instrument. We can address several parameters in our experiment, as the size of the source, its location with respect to the micro-elements, the wavelength, and the input and output pupil size. In order to measure the contrast, the micro-mirrors are tilted between the ON position (towards the spectrograph) and the OFF position (towards a light trap). Contrast exceeding 400 has been measured for a 10° ON/OFF angle and values exceeding 6000 for a 20° ON/OFF angle.
Micro-electromechanical systems (MEMS) components find increasing use in devices which measure and control gas flow, for medical and industrial use. Little or no information on the reliability of these devices has been published. This work reports the results of long-term performance studies of pressure-based mass flow controllers (MFCs) comprised of MEMS microvalves, pressure sensors, and critical flow orifices. Specifically, the details of long-term drift in the silicon pressure sensors (which comprise the flow sensor) are presented. Generally, pressure-based MFCs using MEMS components retain a flow accuracy of better than 1% of full scale over a 20:1 dynamic range, with response time under 0.5 sec, after more than three million operation cycles. The primary cause of inaccuracy within this dynamic range, and of inaccuracy larger than 1% of full scale beyond this range, is attributable to uncompensated zero-offset drift in the silicon pressure sensors, whose behavior is intrinsic to the flow sensor. Data is presented which details this characteristic, across many MFCs. Mechanical, thermal, fluidic, pneumatic and electronic mechanisms possibly responsible for the drift are also presented. Means to overcome this long-term drift phenomenon in silicon pressure sensors will complete the discussion.