Microelectronic packaging technology has evolved over the years in response to the needs of IC technology. The fundamental purpose of the package is to provide protection for the silicon chip and to provide electrical connection to the circuit board. Major change has been witnessed in packaging and today wafer level packaging technology has further revolutionized the industry. MEMS (Micro Electro Mechanical Systems) technology has created new challenges for packaging that do not exist in standard ICs. However, the fundamental objective of MEMS packaging is the same as traditional ICs, the low cost and reliable presentation of the MEMS chip to the next level interconnect. Inertial MEMS is one of the best examples of the successful commercialization of MEMS technology. The adoption of MEMS accelerometers for automotive airbag applications has created a high volume market that demands the highest reliability at low cost. The suppliers to these markets have responded by exploiting standard semiconductor packaging infrastructures. However, there are special packaging needs for MEMS that cannot be ignored. New applications for inertial MEMS devices are emerging in the consumer space that adds the imperative of small size to the need for reliability and low cost. These trends are not unique to MEMS accelerometers. For any MEMS technology to be successful the packaging must provide the basic reliability and interconnection functions, adding the least possible cost to the product. This paper will discuss the evolution of MEMS packaging in the accelerometer industry and identify the main issues that needed to be addressed to enable the successful commercialization of the technology in the automotive and consumer markets.

Wafer level packaging, as well as, chip to wafer bonding has become reliable techniques for MOEMS and MEMS packaging. The main advantage of wafer level processing includes economy of scale and high throughputs. This requires high yielding wafers and a high degree of reproducibility. When these criteria cannot be met, chip to wafer packaging offers an intermediate solution to address the known-good-die concerns. A variety of packaging methods have come to fruition lately as the result of earnest research efforts. Many of these techniques focus on low temperature processing to meet the demands of nanotechnology and integrated materials and systems. Almost categorically, the miniaturization of devices has led to a need for reduced temperature processing to control thermal expansion, dimensional stability, material compatibility, and inclusion of processing circuits. Novel devices made from hot embossed plastics or heterostructures of compound semiconductors require new fabrication and packaging methods. Several wafer bonding options are available ranging from glass seals, low temperature metal based systems, plasma activated direct bonding techniques, and plastic to plastic bonding methods. Critical control of temperature profiles, applied force uniformity and surface preparation give the packaging engineer a wide range of choices for successful device packaging. Prior to 1st level packaging efforts engineered starting materials in the form of laminated substrates can greatly assist in process simplification. The following article describes methods and techniques to create starting materials and use these advanced substrates to the fullest extent for simplified device fabrication. The bonding and patterning techniques use in the front end are also the basis for packaging techniques needed to utilize new methods for wafer level packaging and chip to wafer bonding methods.

Assembly of single mode laser diodes requires a post bond alignment accuracy of less than 1 μm. The implementation of passive alignment in optoelectronics packaging is still a challenge. A low cost approach to achieve such high precision alignment is using the flip chip self alignment mechanism in combination with micro-mechanical stops. In order to prove that this approach is feasible test vehicles were designed and fabricated. This paper presents the concept of passive alignment pursued, the experimental setup and results thereof. The design of the test vehicles is described including the bump design as well as bumping and flip chip assembly process.

Zero-level packaging, i.e. the encapsulation of the MEMS device at wafer level, is an essential technique for MEMS miniaturization and cost reduction. A large number of different capping and sealing materials and techniques can be used. However, the testing and qualification of this type of packaging of MEMS devices requires special techniques. A number of conventional and new characterization techniques for mechanical and hermeticity testing are presented, as well as an overview about outgasing measurements and reliability testing.

Maintaining the integrity of the internal atmosphere of a hermetic device is essential for long-term component reliability because it is within this environment that all internal materials age. As MEMS package sizes decrease with miniaturization, characterization of the internal atmosphere becomes increasingly difficult. Typical transistor metal cans (e.g., TO-5 type) and large MEMS devices have internal volumes of tenths of a milliliter. Last year, gas-sampling methods for smaller-sized MEMS packages were developed and successfully demonstrated on volumes as low as 3 microliters (package outside dimensions: ~1 x 2 x 5 mm). This year, we present gas sampling methods and results for a much smaller MEMS package having an internal volume of 30 nanoliters, two orders of magnitude lower than the previous small package. After entirely redesigning the previous sampling manifold, several of the 30 nanoliter MEMS were gas sampled successfully and results showed the intended internal gas atmosphere of nitrogen was sealed inside the package. The technique is a radical jump from previous methods because not only were these MEMS packages sampled, but also the gas from each package was analyzed dozens of times over the course of about 20 minutes. Additionally, alternate methods for gas analyses not using helium or fluorinert will be presented.

Wafer-level, thermocompression bonding is a promising technique for MEMS packaging. The quality of the bond is critically dependent on the interaction between flatness deviations, the gold film properties and the process parameters and tooling used to achieve the bonds. The effect of flatness deviations on the resulting bond is investigated in the current work. The strain energy release rate associated with the elastic deformation required to overcome wafer bow is calculated. A contact yield criterion is used to examine the pressure and temperature conditions required to flatten surface roughness asperities in order to achieve bonding over the full apparent area. The results are compared to experimental data of bond yield and toughness obtained from four-point bend delamination testing and microscopic observations of the fractured surfaces. Conclusions from the modeling and experiments indicate that wafer bow has negligible effect on determining the variability of bond quality and that the well-bonded area is increased with increasing bonding pressure. The enhanced understanding of the underlying deformation mechanisms allows for a better controlled trade-off between the bonding pressure and temperature.

Texas Instruments’ Digital Micro-mirror Device, is used in a wide variety of optical display applications ranging from fixed and portable projectors to high-definition television (HDTV) to digital cinema projection systems. A new DMD pixel architecture, called "FTP", was designed and qualified by Texas Instruments DLPTM^TM Group in 2003 to meet increased performance objectives for brightness and contrast ratio. Coordination between design, test and fabrication groups was required to balance pixel performance requirements and manufacturing capability. "Corner Lot" designed experiments (DOE) were used to verify "fabrication space" available for the pixel design. The corner lot technique allows confirmation of manufacturability projections early in the design/qualification cycle. Through careful design and analysis of the corner-lot DOE, a balance of critical dimension (cd) "budgets" is possible so that specification and process control limits can be established that meet both customer and factory requirements. The application of corner-lot DOE is illustrated in a case history of the DMD "FTP" pixel. The process for balancing test parameter requirements with multiple critical dimension budgets is shown. MEMS/MOEMS device design and fabrication can use similar techniques to achieve agressive design-to-qualification goals.

The performance of MOEMS (Micro-Optical-Electronic-Micro-Systems) may be significantly improved and their service life-time extended by packaging under vacuum. For numerous applications the bonding process temperature has to be below 200°C and sealed joints must withstand a reflow temperature (about 250 - 280°C) without debonding and unsealing. The Ag-In system has been selected for developing such a bonding process. In this study, the kinetics and sequence of intermetallic phase growth in a Ti/Ag/In/Ag multilayer structure with various ratios of thicknesses, deposited on a silicon substrate, was investigated by DSC (Differential Scanning Callorimetry), SEM and XRD analysis. The joints were examined by DSC to determine the re-melting temperatures and the quality of a cavity sealing was evaluated using a helium leak detection system. It was established that annealing a Ag/In multilayer with a total AG to In layer thickness ratio equal to 3 and an overall thickness of about 10 μm under vacuum of 10^-7 torr at 190°C for 40 min allows achieving a void-free joint consisting of two intermetallic phases Ag₂In (γ) and AgIn₂ (φ). A further appropriate thermal treatment at a relatively low temperature in air leads to the formation of the joint with a re-melting temperature higher than 300°C. The helium leak rate of the integrated cavity was experimentally estimated in the 5 - 10 x 10^-9 mbar 1 s^-1 range.

Zyvex is developing a low-cost high-precision method for manufacturing MEMS-based three-dimensional structures/assemblies. The assembly process relies on compliant properties of the interconnecting components. The sockets and connectors are designed to benefit from their compliant nature by allowing the mechanical component to self-align, i.e. reposition themselves to their designed, stable position, independent of the initial placement of the part by the external robot. Thus, the self-aligning property guarantees the precision of the assembled structure to be very close to, or the same, as the precision of the lithography process itself. A three-dimensional (3D) structure is achieved by inserting the connectors into the sockets through the use of a passive end-effector. We have developed the automated, high-yield, assembly procedure which permits connectors to be picked up from any location within the same die, or a separate die. This general procedure allows for the possibility to assemble parts of dissimilar materials. We have built many 3D MEMS structures, including several 3D MEMS devices such as a scanning electron microscope (SEM) micro column, mass-spectrometer column, variable optical attenuator. For these 3D MEMS structures we characterize their mechanical strength through finite element simulation, dynamic properties by finite-element analysis and experimentally with UMECH’s MEMS motion analyzer (MMA), alignment accuracy by using an in-house developed dihedral angle measurement laser autocollimator, and impact properties by performing drop tests. The details of the experimental set-ups, the measurement procedures, and the experimental data are presented in this paper.

Optical actuation of microelectromechanical systems (MEMS) is advantageous for applications for which electrical isolation is desired. Thirty-two polycrystalline silicon opto-thermal actuators, optically-powered MEMS thermal actuators, were designed, fabricated, and tested. The design of the opto-thermal actuators consists of a target for laser illumination suspended between angled legs that expand when heated, providing the displacement and force output. While the amount of displacement observed for the opto-thermal actuators was fairly uniform for the actuators, the amount of damage resulting from the laser heating ranged from essentially no damage to significant amounts of damage on the target. The likelihood of damage depended on the target design with two of the four target designs being more susceptible to damage. Failure analysis of damaged targets revealed the extent and depth of the damage.

Sandia and Lawrence Livermore National Laboratories are developing a briefcase-sized, broad-spectrum bioagent detection system. This autonomous instrument, the BioBriefcase, will monitor the environment and warn against bacterium, virus, and toxin based biological attacks. At the heart of this device, inexpensive polymer microfluidic chips will carry out sample preparation and analysis. Fabrication of polymer microfluidic chips involves the creation of a master in etched glass; plating of the master to produce a nickel stamp; large lot chip replication by injection molding; and thermal chip sealing. Since the performance and reliability of microfluidic chips are very sensitive to fluidic impedance and to electromagnetic fluxes, the microchannel dimensions and shape have to be tightly controlled during chip fabrication. In this talk, we will present an overview of chip design and fabrication. Metrology data collected at different fabrication steps and the dimensional deviations of the polymer chip from the original design will be discussed.

As part of an effort to develop MEMS-based power generation system, an assembly solution for combustion test of a recent-developed micro combustion device micromachined from single crystal silicon were proposed. In order to supply hydrogen/air to inlets of micro combustor from room temperature to over 700°C at the pressure of 1~3bars, a stainless steel universal fixture was designed and fabricated for the combustion testing of prototype stacked by structured Si wafers of 21.5mmx21.5mm in square. By precisely welding and polishing process in fabrication of the fixture, a metal plate with 18nm roughness was prepared for tightly connecting micro combuster with fuel inlet of 2mm, air inlet 4mm in diameter on the top wafer, while the gap between tubings to be hermetically joined to top plate is about 0.3mm. Primary combustion experiments have been conducted after igniting the fuel/air mixture in the micro chamber. Stable hydrogen-air combustion has been observed to sustain inside the combustion chamber with exit temperature over 1200°C. During the combustion experiments, the silicon dies keep good mechanical integrity under assembly and no gas leakage is observed.

This paper will present the concluding results of a comprehensive study aimed at developing a model for predicting the overall reliability of an asymmetric thermal actuator. This actuator is designed for co-packaged use as a variable optical attenuator (VOA) within a 10 Gbps optical receiver. This paper will address the limitations of a previously reported vision recognition system. It is shown that the electrical resistance change correlates well with the displacement change over time, and as a result, simple in-situ resistance monitoring for degradation detection can easily be realized. The novel methodology employed to estimate the lifetime performance of the MEMS VOA is also presented; whereby, the accelerated ageing wearout model derived from 93,600 device hours is combined with the module characteristics, and all associated error coefficients in a Monte Carlo simulation. Simulation results will provide the end user with a 3 sigma confidence prediction of the receiver over-life attenuation curve and all end of life conditions associated with the MEMS component. It will be demonstrated that when designed properly, a thermal actuator will provide predictable accurate and reliable stability over life.

RF MEMS switches provide a low-cost, high performance solution to many RF/microwave applications and these switches will be important building blocks for designing phase shifters, switched filters and reflector array antennas for military and commercial markets. In this paper, progress in characterizing of THALES capacitive MEMS devices under high RF power is presented. The design, fabrication and testing of capacitive RF MEMS switches for microwave/mm- wave applications on high-resistivity silicon substrate is presented. The switches tested demonstrated power handling capabilities of 1W (30 dbm) for continuous RF power. The reliability of these switches was tested at various power levels indicating that under continuous RF power. In addition a description of the power failures and their associated operating conditions is presented. The PC-based test stations to cycle switches and measure lifetime under DC and RF loads have been developed. Best-case lifetimes of 10¹⁰ cycles have been achieved in several switches from different lots under 30 dbm RF power.

As the United States (U.S.) Army transforms into a lighter, more lethal, and more agile force, the technologies that support both legacy and emerging weapon systems must decrease in size while increasing in intelligence. Micro-electromechanical systems (MEMS) are one such technology that the Army as well as entire DOD will heavily rely on in achieving these objectives. Current and future military applications of MEMS devices include safety and arming devices, guidance systems, sensors/detectors, inertial measurement units, tracking devices, radio frequency devices, wireless radio frequency identification (RFID), etc. Even though the reliance on MEMS devices has been increasing, there have been no studies performed to determine their reliability and failure mechanisms. Furthermore, no standardized test protocols exist for assessing reliability. Accordingly, the U.S. Army Corrosion Office at Picatinny, NJ has initiated the MEMS Reliability Assessment Program to address this issue.

This paper focuses on recent developments in the localised characterisation of the mechanical properties of Microsystems and MEMS devices and structures. Conventional indentation techniques provide a highly powerful method for measuring the load and depth response of bulk and coated materials, but can also be used to measure the mechanical properties 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 covers 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. In addition, the localised testing of friction and wear in MEMS devices will be covered with some examples of the technology available and how it may be applied to such small contact areas in an accurate and reproducible way.

Single-crystal silicon thin films were forced to resonate at high frequency (~40 kHz) in different environments to study the long-term durability of this structural material used in microelectromechanical (MEMS) devices. The fatigue characterization structure consists of a notched cantilever beam attached to a plate shaped mass and is actuated at resonance, creating fully reversed, constant amplitude, sinusoidal stresses at the notch root. The dynamic behavior of the resonating structure has been meticulously quantified to allow accurate stress measurements from the knowledge of the driving voltage amplitude and the calculation of the quality factors in air and vacuum. In addition, the change in resonant frequency is periodically monitored for long-life specimens. Fatigue failure was observed for specimens tested in humid air and medium vacuum. In air, the stress-life (S-N) curve confirms the unique fatigue behavior already attributed to silicon thin films. In vacuum, the strength of the specimens appears to increase, and fatigue failure is delayed. Fracture surface examination reveals distinct features on the fracture surfaces of long-life fatigued specimens, not found in quasistatic failure, that are clear indications of initiation regions. The decrease rate in resonant frequency during cycling is demonstrated to be related to damage accumulation rate, and is strongly sensitive to both stress amplitude and humidity. The different currently proposed mechanisms are discussed in light of this new set of experimental evidence.

This paper reports on the results of an improved surface modification method called Molecular Vapor Deposition (MVD). MVD allows for the creation of molecular organic coatings which are denser and more durable than those obtained by current liquid or vapor-phase methods. This improvement has been achieved using a “sequential” or “layered” vapor deposition scheme of two different molecular films. The first molecular coating is a “seed” or adhesion promoter layer which is used to increase the binding sites for the subsequent functional molecular layer. The resulting surface coatings were observed to have improved stability to immersion applications, higher temperature stability and overall improved durability as a result of the increased surface coverage when compared to standard self-assembled monolayers (SAMs). These new film capabilities will have significant importance in improving the functionality and reliability of many micro- and nano-scale devices. The sequential approach with the seed layer has also been used to deposit molecular coatings on a variety of substrate materials (such as polymers, plastics and metals) which normally do not allow high quality surface coatings.

Commercial applications of micro-electromechanical systems (MEMS) continue to be plagued by reliability issues encountered during fabrication and operation. One of the most prevalent problems is the adhesion between adjacent components since adhesive forces are known to promote wear and defect-related failures. In extreme circumstances, the adhesion is large enough to prevent separation, a phenomenon commonly referred to as stiction-failure. The objective of current work is to determine analytically whether dynamic excitation may be used to repair stiction-failed cantilevers. This is accomplished by relating the structural dynamic response to the de-cohesion of stiction-failed micro-cantilever beams under various loading conditions.

Failure analysis tools and techniques that identify root cause failure mechanisms are key components to improving MEMS technology. Failure analysis and characterization are relatively simple at the wafer and die level where chip access is straightforward. However, analysis and characterization of packaged parts or components encapsulated with covers, caps, etc may be more cumbersome and lead to problems assessing the root cause of failure. This paper will discuss two methods used to prepare the backside of the package/device to allow for failure analysis and inspection of different MEMS components without removing the cap, cover, or lid on the device and/or the package. One method for backside preparation was grinding and polishing the package for IR inspection. This method involved backfilling the package cavity with epoxy to hold the die in place. The other method involved opening a window through the backside of the package, exposing the die for IR inspection. Failure analysis results showed both methods of backside preparation were successful in revealing the failure mechanisms on two different MEMS technologies.

The MEMS industry currently produces over $13 billion in annual revenue, with devices in such diverse applications as blood pressure sensors, projection displays, optical switches, printers, hard drives, and gyroscopes. As production techniques improve, ever more functions may be served by MEMS, and the industry is growing at an annual rate of more than 15%. The large diversity of MEMS leads to many challenges in metrology, as each design has different critical factors which will affect its performance. Unlike traditional semiconductor devices, MEMS require characterization both in their static state and under actuation. Parameters of interest include shape, dimensions, surface roughness, sidewall angles, film thickness, residual stress, feature volumes, response times, thermal properties, resonance frequencies, stiction, environmental immunity and more. This talk will discuss the strengths and weaknesses of a variety of techniques for MEMS surface metrology. Bright- and dark-field microscopy, scanning electron microscopy, contact and non-contact surface profilometry, atomic force microscopy, laser Doppler vibrometry and digital holography are some of the primary techniques used to evaluate MEMS surfaces and motion. While no single technique can fully characterize all MEMS devices, or even one device under all conditions, the utility of each of the different types of instruments is increasing as they are pushed by MEMS and other industries to provide more characterization capability. With a broad understanding of the various metrology techniques available, the one or few critical instruments to measure a given class of devices will hopefully be more easily understood.

The most commonly employed tools for wafer thickness and topography metrology are based on capacitance method, which due to physical size of probes, and may not be suitable for direct measurement of multi-layer non-conductive wafers or Micro Electromechanical Systems (MEMS) structures. Recently developed that low coherence interferometry provides solution, which overcomes limitations of these methods. Selected MEMS applications including characterization of deep (high aspect) trenches and membrane structures have been also developed. The above listed applications were limited to measurements of relative distance between two optical interfaces in material transparent at the wavelength of probing radiation. Absolute distance gauging by fiber optic low coherence interferometer is difficult due to large thermal drift (of the order of 0.04 mm/K). We demonstrate that this drift is a result of thermal changes of refractive index of fiber optic glass. We present solution eliminating this drift is based on introduction of the additional reference plane in the signal arm of the Michelson interferometer. Use of this reference plane eliminates influence of changes of refractive index of glass fibers on result of measurement and improves thermal stability of low coherence interferometer by three orders of magnitude.

An interferometric surface profiler for high-magnification fixed through glass measurement (patent pending), such as for a packaged MEMS or MOEMS measurement, is described in this paper. Three techniques are introduced into the profiler, including aberration correction and long working distance for the objective, substantially shaped illumination and dispersive compensation. Measurement results illuminate that the data of the through glass objective are very close to those of the standard objective.

A novel characterization method for MEMS devices based on the combination of measurement and simulation results is introduced on the example of an electrostatically actuated micro mirror array. The aim of this method is to determine geometrical parameters and built-in mechanical stress on the base of the measured eigenfrequencies. A Laser Doppler interferometer and a signal analyzer are used to determine the frequency response function (FRF) of the micro mechanical structure and the eigenfrequencies are calculated. For the numerical simulation of the micro mirrors behavior the finite element (FE) model is used and a series of nonlinear coupled-field analysis and pre-stressed nonlinear modal analysis have been performed. Hence the dependence of the eigenfrequencies on geometrical parameters and built-in mechanical stress is obtained. The comparison to the measured frequencies yields in values for the searched parameters that are mean values for the entire micro mechanical structure. The presented method is very efficient because it determines several characteristics of a MEMS device on the base of only one measured frequency response function. The article demonstrates that a sufficient accuracy is achieved and stress values are calculated that are hardly ascertainable using common measurement methods.

Since micro deformable mirrors based on Micro-Opto-Electronico-Mechanical Systems (MOEMS) technology would be essential in next generation adaptive optics system, we are designing, realizing, characterizing and modeling this key-component. Actuators and a continuous-membrane micro deformable mirror (3*3 actuators, 600*600 μm²) have been designed in-house and processed by surface micromachining in the Cronos foundry. A dedicated characterization bench has been developed for the complete analysis. This Twyman-Green interferometer allows high in-plane resolution (4 μm) or large field of view (40mm). Out-of-plane measurements are performed with phase-shifting interferometry showing highly repeatable results (standard deviation<5nm). Features such as optical quality or electro-mechanical behavior are extracted from these high precision three-dimensional component maps and FEM can be fitted. Dynamic analysis like vibration mode and cut-off frequency is realized with time-averaged interferometer. The deformable mirror exhibit a 350nm stroke for 35 volts on the central actuator. This limited stroke could be overcome by changing the components material and promising actuators are made with polymers.