This PDF file contains the front matter associated with SPIE Proceedings Volume 7592, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

Microfluidic systems offer compact and efficient thermal management strategies. In this work, we investigate novel nanostructured surfaces to control fluidic behavior and enhance heat dissipation in microfluidic systems. We fabricated silicon nanopillars ranging from 200 nm to 800 nm in diameter and heights of approximately 5 μm. In the presence of notches on the pillars, the liquid separates into multiple layers of liquid films. The thicknesses of the liquid layers subsequently increase as the film propagates, which is determined by the specific position and geometry of the notches. In the presence of asymmetric nanopillars, where the pillars have deflection angles ranging from 0-50 degrees, directional spreading of water droplets can be achieved. The liquid spreads only in the direction of the pillar deflection and becomes pinned on the opposite interface. We performed detailed measurements and developed models to predict the behavior based on pillar geometries. These studies provide insight into the complex liquid-nanostructure interactions, which show great potential to design nanostructures to achieve high flux thermal management solutions.

Until now, the determination of the hermeticity of microelectronic packages is related to the MIL-STD-883 method 1014 which is based on the He leak detection method. But this method is no more suited for small packages due to the resolution limit of the apparatus used conventionally. Indeed the minimum detectable leak rate is of the order of 5.10^-11 atm.cm³.s^-1. Leaks induced by non hermetic MEMS packages are often one order of magnitude smaller. So, the sensitivity of the He leak detector method is too low and this method can not be applied anymore. The MEMS packages produced with wafer level encapsulation techniques, require new methodologies to measure hermeticity appropriately and accurately. The purpose of this paper is to present the development of alternative methods for testing the hermeticity of MEMS micro-cavities. Two methods will be investigated in the context of this study: The membrane deflection measurement exposed to different pressures, using optical profilometry, and the measurement of the variation of gas concentration in a sealed silicon cavity by Fourier-transform infrared spectroscopy (FT-IR). The calculated leak rates are compared for samples where standard fine leak test gave no results. The values obtained for the leak rates within optical test and FT-IR test for the same sample are identical, showing the relevance of these two methods.

Packaging constitutes one of the most costly steps of MEMS/MOEMS manufacturing. Uncooled IR bolometers require a vacuum atmosphere below 10 mTorr to operate at their highest sensitivity. The bolometer response is also dependent on the package temperature. In order to minimize cost, real estate and power consumption, temperature stabilization is typically not provided to the package. Hence, long term high sensitivity operation of IR bolometric radiometers requires a calibration as function of in package pressure and temperature. A low-cost and accurate means of measuring the pressure in the package without being affected by the operating temperature is therefore needed. INO has developed a low-cost, low-temperature hybrid vacuum micropackaging technology ^1-3. An equivalent flow rate of 4×10^-14 Torr·L/sec for storage at 80°C has been obtained without getter. Even with such low flow, the long term stabilization of residual pressure variations affects the sensitivity and calibration of the IR bolometers. INO has developed MEMS pressure sensors that allow for real-time measurement of package pressure above 1 mTorr, and can be integrated with the IR bolometers in a die-level packaging process or microfabricated simultaneously on the same die. In this paper, the typical performance and measurement uncertainty of these pressure sensors will be presented along with a reading method that provides a pressure measurement with a dependence on the package temperature as low as 0.7 %/°C. Complex reading circuit or temperature control of the packages are not required, making the pressure sensor well adapted for low-cost high-volume production and integration with IR bolometer arrays.

An overview of wafer-level packaging technologies developed at the University of Michigan is presented. Two sets of packaging technologies are discussed: (i) a low temperature wafer-level packaging processes for vacuum/hermeticity sealing, and (ii) an environmentally resistant packaging (ERP) technology for thermal and mechanical control as well as vacuum packaging. The low temperature wafer-level encapsulation processes are implemented using solder bond rings which are first patterned on a cap wafer and then mated with a device wafer in order to encircle and encapsulate the device at temperatures ranging from 200 to 390 °C. Vacuum levels below 10 mTorr were achieved with yields in an optimized process of better than 90%. Pressures were monitored for more than 4 years yielding important information on reliability and process control. The ERP adopts an environment isolation platform in the packaging substrate. The isolation platform is designed to provide low power oven-control, vibration isolation and shock protection. It involves batch flip-chip assembly of a MEMS device onto the isolation platform wafer. The MEMS device and isolation structure are encapsulated at the wafer-level by another substrate with vertical feedthroughs for vacuum/hermetic sealing and electrical signal connections. This technology was developed for high performance gyroscopes, but can be applied to any type of MEMS device.

Various getter materials have been developed over the years to deal with hydrogen and moisture caused problems in MEMS/MOEMS packages. These materials consist of two major families, metal alloy systems and polymeric systems. Both systems have pluses and minuses for the MEMS/MOEMS packaging engineer. In order to determine applicability, careful characterization of these systems is critical. The advent of a new class of polymeric getter materials originally developed for other industries has brought a need to readdress the issue of how to characterize such materials for MEMS/MOEMS service. While MIL-STD-883 gives a degree of guidance, it is not the complete answer. Characterization of these materials has consequently been clean sheeted to address the key areas of hydrogen and water capacity determination, and determination of ionics concentrations. Methods used and the results of this work will be discussed.

Traditionally, the use of organics within a vacuum-sealed hermetic electronics package has been avoided. Organics, including adhesives, may outgas and degrade over time, resulting in a rapid reduction in vacuum quality within a sealed device package. However, MEMS device fabrication is now blurring the lines between strictly electronic devices, which contain very few organic components, and electro-mechanical devices, whose secondary assembly steps require the integration of stable organics. The Chip Scale Atomic Clock (CSAC) device developed and implemented with funding from DARPA by a team from the Symmetricom Technology Realization Center, Sandia National Laboratory, and Charles Stark Draper Laboratory, is a prime example of a device that integrates organics and chip scale die into an assembly that requires operation within a good vacuum environment over the lifetime of the device. Through the use of analytical chemistry techniques such as TGA, DSC, and IVA, we measured outgassing of assembly materials to be sealed in the package. We have been able to determine the magnitude of initial outgassing and to measure the stable vacuum pressure of complete sealed devices to within a few milliTorr. Comparison of these results with predictions based on IVA data of specific gas species and getter capacity has allowed us to optimize processing conditions (such as cure schedule for adhesives and vacuum bake-out profile before sealing) for minimal outgassing. This information has allowed us to design and build MEMS devices which require an internal vacuum level of < 20 milliTorr and seal them in hermetic packages without substantial degradation.

We have developed a method for predicting the reliability of a brittle microstructure. This method enables a MEMS designer to simulate the reliability of a MEMS device and to make design corrections before investing the time and expense of fabrication and development. Our method combines empirical data gathered from fracture of test specimens, analyzed by Weibull methods, and finite element analysis results, in an algorithm that estimates failure probability for a specified load. MEMS devices typically have multiple and varying surface qualities resulting from fabrication processes. In this work, we demonstrate that the accuracy of the prediction method depends on the inclusion of the Weibull parameters for all surface types.

We report on long-term stability experiments on a novel MEMS radio frequency (RF) resonator fabricated in Aluminum Nitride technology. The AlN fabrication process allows for the realization of resonators, filters, and resonant sensors operating over the frequency range from 500 kHz to in excess of 10 GHz using CMOS compatible materials. The 100 MHz resonators used in these experiments were a ring design with 140-micron outer diameter and 100-micron inner diameter. Electrodes on the top and bottom of this AlN ring enable measurement of resonance. Wafer sections were stored in air and vacuum and tested daily. We observed a steady degradation in the resonant frequency (600 ppm over the 800 hours) for the devices stored in a vacuum. Small degradation was observed in the air experiment (50 ppm over 1200 hours). Failure analysis using secondary emission microscopy (SEM) revealed no differences between control devices and devices on test. However, subsequent investigation of blank wafer sections by Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) found small levels of silicone surface contamination from vacuum chamber exposure. This contamination added enough mass to shift the resonant frequency. These experiments demonstrate the need for clean environments for future wafer-level testing and also packaging for these small-mass resonators.

Comparisons between several pairs of contact materials have been done with a new methodology using a commercial nanoindenter coupled with electrical measurements on test vehicles specially designed to investigate the micro-scale contact physics. Experimental measurements are obtained to characterize the response of a 5 μm² square contact bump under electromechanical stress with increased applied current. The data provide a better understanding of micro-contact behaviour related to the impact of current at low- to medium-power levels. Contact temperature rise is observed, leading to shifts of the mechanical properties of contact materials and modifications of the contact surface. The stability of the contact resistance, when the contact force increases, is studied for contact pairs of soft (Au/Au contact), harder (Ru/Ru contact) and mixed material configuration (Au/Ru contact). An enhanced stability of the bimetallic contact Au/Ru is demonstrated considering sensitivity to power increase, related to creep effects and topological modifications of the contact surfaces. These results are compared to previous ones and discussed in a theoretical way by considering the temperature distribution around the hottest area at the contact interface.

Microelectromechanical systems (MEMS) are an important enabling technology for reducing electronic component geometries and device power consumption. An example of MEMS technology, used in radio frequency (RF) circuits and systems, is the microswitch. Although the operation of microswitches is relatively simple, they are plagued by poor reliability - they must operate over 100 billion cycles. Improvements in the mechanical design of the microswitch have helped to increase their reliability but further improvements are necessary. To accomplish this, research needs to be conducted on the actual contact surfaces for investigation of the mechanical, thermal and electrical phenomena that affect reliability. The focus of this paper is the development of a unique high lifecycle test fixture capable of the simultaneous measurement of contact resistance and contact force. By incorporating a high resonance force sensor, cycle rates reaching 3kHz will be achieved enabling researchers to conduct a wide range of reliability studies. The fixture will be isolated from vibrations and will be housed in a dry-box enclosure to minimize contamination. The test fixture will be automated with control and data acquisition instrumentation to optimize data collection and test repeatability. It is predicted that this new test fixture will provide the potential for significant work to be done to improve the reliability of MEMS microswitches. Several tests were conducted using components of the new test fixture. Preliminary results indicate the feasibility and support the need for the continuing development of this new test fixture.

In this work, we quantify and analyze the rate of accrual of stiction and mechanical fatigue in a MEMS micro-mirror device to understand its reliability under a set of controlled temperature and humidity splits. An accelerated aging system was employed by using a non-standard actuation procedure to more rapidly induce failure of the micro-mirrors. The array is hermetically packaged with a low surface energy self-assembled-monolayer (SAM) based anti-stiction coating, along with an encapsulated source of this anti-stiction coating that serves as a reservoir. Exposure of the micro-mirror array to the environmental conditions was made possible by drilling two 1 mm holes in the hermetic package. This enabled the retention of the encapsulated SAM source in the package which was vital to understanding the effects of SAM re-deposition on the surface in the operating environment. The fastest accrual of stiction was seen in the 90°C, 80% RH split with approximately 80% of the micro-mirrors failing within 4.4 × 10⁹ cycles (10 hours) with 2.7×10^-14 Joules of Stiction Equivalent Energy while the 60°C, 20% RH showed the least stiction accrual rate with less than 2% failure for 2.26×10¹² cycles (1500 hours). The failure data obtained from the experiments were used to do a reliability analysis by utilizing the Weibull distribution.

This research investigates the effect of storage time on the bond strength of plasma activated Si wafers by studying the surface characteristics and chemistry of the wafers at each of the various processing levels. Initially pairs of silicon (100) wafers were plasma activated using O2 in a reactive ion etch chamber. The wafers were stored for various time intervals before bonding in a substrate bonder. Different surface characteristics like the growth of the oxide layer, surface roughness, etc. were compared and profiled with respect to storage time, before bonding the wafers. An optimized plasma activation and bonding recipe was proposed. After a final thermal anneal, near infrared imagery was employed in order to optically assess the bond quality of the wafer stack. Conducting tensile tests on dies diced from the wafer stack quantized the bond strength between the wafers. The chemistry involved during the plasma activation, bonding, and thermal annealing were investigated thoroughly. Interesting phenomenon such as the increase in the bond strength of wafers stored for more than a specific amount of time was analyzed. Finally a closer look was taken at the interface layer of the wafer stack through scanning electron microscopy, and the formation of a silicon dioxide layer at the interface was confirmed.

This work will present a detailed discussion on development of an automated test platform for reliability and lifetime expectancy studies of electrothermal micro-actuators. The actuators are designed using the top-most polysilicon layer of Sandia National Laboratories' SUMMiT V process. The image acquisition of the device is done using a Basler A 601f digital CCD c-mount camera, connected to a microscope with a 100 × magnification. To calculate the in-plane displacements of the device, a National Instruments' Vision image analysis software routine was utilized. An initial study is done to determine the actuator displacement characteristics with respect to the applied power. Based on the results from this study, the region of plastic deformation of the devices is determined. Arrhenius relationship theory is presented to model the plastic deformation based failure mechanism and allow the activation energy to be calculated.

Ceramic Column Grid Array packages have been increasing in use based on their advantages such as high interconnect density, very good thermal and electrical performance, compatibility with standard surface-mount packaging assembly processes, etc. CCGA packages are used in space applications such as in logics and microprocessor functions, telecommunications, flight avionics, payload electronics, etc. As these packages tend to have less solder joint strain relief than leaded packages, the reliability of CCGA packages is very important for short and long-term space missions. CCGA interconnect electronic package printed wiring boards (PWBs) of polyimide have been assembled, inspected non-destructively and subsequently subjected to extreme temperature thermal cycling to assess the reliability for future deep space, short and long-term, extreme temperature missions. In this investigation, the employed temperature range covers from -185°C to +125°C extreme thermal environments. The test hardware consists of two CCGA717 packages with each package divided into four daisy-chained sections, for a total of eight daisy chains to be monitored. The CCGA717 package is 33 mm × 33 mm with a 27×27 array of 80%/20% Pb/Sn columns on a 1.27 mm pitch. The resistance of daisy-chained, CCGA interconnects were continuously monitored as a function of thermal cycling. Electrical resistance measurements as a function of thermal cycling are reported and the tests to date have shown significant change in daisy chain resistance as a function of thermal cycling. The change in interconnect resistance becomes more noticeable with increasing number of thermal cycles. This paper will describe the experimental test results of CCGA testing under wide extreme temperatures. Standard Weibull analysis tools were used to extract the Weibull parameters to understand the CCGA failures. Optical inspection results clearly indicate that the solder joints of columns with the board and the ceramic package have failed as a function of thermal cycling. The first failure was observed at 137th thermal cycle and 63.2% failures of daisy chains have occurred at about 664 thermal cycles. The shape parameter extracted from Weibull plot was about 1.47 which indicates the failures were related to failures occurred during the flat region or useful life region of standard bath tub curve. Based on this experimental test data one can use the CCGAs for the temperature range studied for ~100 thermal cycles (ΔT = 310°C, 5oC/minute, and 15 minutes dwell) with high degree of confidence for high reliability space and other applications.

Estimation of triglyceride concentration is important for the health and food industries. Use of solid state biosensors like Electrolyte Insulator Semiconductor Capacitors (EISCAP) ensures ease in operation with good accuracy and sensitivity when compared to conventional sensors. In this paper we report on packaging of miniaturized EISCAP sensors on silicon. The packaging involves glass to silicon bonding using adhesive. Since this kind of packaging is done at room temperature, it cannot damage the thin dielectric layers on the silicon wafer unlike the high temperature anodic bonding technique and can be used for sensors with immobilized enzyme without denaturing the enzyme. The packaging also involves a teflon capping arrangement which helps in easy handling of the bio-analyte solutions. The capping solves two problems. Firstly, it helps in the immobilization process where it ensures the enzyme immobilization happens only on one pit and secondly it helps with easy transport of the bio-analyte into the sensor pit for measurements.

The sequentially plasma activated bonding (SPAB) of silicon/silicon interface has been characterized after annealing up to 900°C for packaging of micro- electro mechanical systems (MEMS) and microfluidic devices at low temperature. The bonding strength of the interface in the SPAB was as high as that of the conventional hydrophilic bonding method, which requires annealing as high as 1000°C to achieve covalent bonding. The interfacial voids evolution with annealing temperatures has been correlated with the bonding strength. Although the rearrangement of water such as absorption and desorption across the bonded interface was found below 225°C, the voids were not significant up to 400°C. Annealing above 600°C resulted in a considerable amount of thermal voids due to viscous flow of oxides. The thermal voids were grown preferentially at the plasma induced defect sites. The contact angle and roughness of the sequentially plasma (reactive ion etching plasma followed by microwave radicals) treated surfaces have been observed to explain the void formation and reduction of the bonding strength of the interface. The plasma induced defect sites such as nanopores and craters have been indentified using an atomic force microscope. The electron energy loss spectroscopy showed oxygen deficiency in the nanometer thick interfacial amorphous silicon oxide.

A novel conductive adhesive has been used to interconnect MEMS test structures with different pad sizes directly to a PCB in a medium caliber ammunition fuze. The fuze environment is very demanding with a setback acceleration exceeding 60 000 g and a centripetal acceleration increasing radially with 9000 g/mm. The adhesive shows excellent mechanical and thermal properties. The mounted MEMS test structures have been subjected to rapid temperature cycling according to MIL-STD 883G method 1010.8 test condition B and performed well. The test structures with the largest pad sizes passed 100 temperature cycles and firing test where the test structures have been exposed to an acceleration of more than 60 000 g.

Time-dependent-dielectric-breakdown is quickly becoming a very important topic as low-k materials are integrated into back-end-of-the-line processes and as interconnect dielectric thicknesses approach the sub 100 nm range. There still exists a considerable amount of debate on the dominant failure mechanism with or without the presence of a diffusion barrier. We have developed a series of models for copper-accelerated time-to-failure that we are using to guide an experimental program to understand failure mechanisms. The models are based on the injection and drift of copper ions and focus on an increase in the local electric field that allows electrons to enter the dielectric's conduction band. The models are successful at correlating the time-to-failure for SiO₂ dielectrics with and without barriers. The most important aspects of the model that we are trying to verify experimentally include the role of moisture in the dielectric oxidizing Cu to form injectable ions, the initiation of failure at the pore-matrix interface in porous dielectrics, a decrease in the time-to-failure in porous dielectrics due to an increase in Cu solubility, and the need for near perfect barriers to realize the advantage of using a barrier. The key unknown parameters in all these models are the diffusivities and solubilities of copper ions in the materials. Models of this type are not restricted to just interlayer dielectrics. Several failure mechanisms associated with semi-conducting and organic light emitting diodes may also be described by models of this type.

We report on the construction of a remotely accessible and interactive laboratory for testing microdevices (aka: MicroElectroMechancial Systems - MEMS). Enabling expanded utilization of microdevices for research, commercial, and educational purposes is very important for driving the creation of future MEMS devices and applications. Unfortunately, the relatively high costs associated with MEMS devices and testing infrastructure makes widespread access to the world of MEMS difficult. The creation of a virtual lab to control and actuate MEMS devices over the internet helps spread knowledge to a larger audience. A host laboratory has been established that contains a digital microscope, microdevices, controllers, and computers that can be logged into through the internet. The overall layout of the tele-operated MEMS laboratory system can be divided into two major parts: the server side and the client side. The server-side is present at Texas Tech University, and hosts a server machine that runs the Linux operating system and is used for interfacing the MEMS lab with the outside world via internet. The controls from the clients are transferred to the lab side through the server interface. The server interacts with the electronics required to drive the MEMS devices using a range of National Instruments hardware and LabView Virtual Instruments. An optical microscope (100 ×) with a CCD video camera is used to capture images of the operating MEMS. The server broadcasts the live video stream over the internet to the clients through the website. When the button is pressed on the website, the MEMS device responds and the video stream shows the movement in close to real time.

This contribution describes a fully automated optical inspection system suited for end test of MOEMS which are fabricated in large volume. The system consists on one hand of necessary handling tools for MOEMS which are not necessarily part of a rigid wafer. On the other hand, a crucial part is an image processing system that can be adapted to changing requirements on accuracy for different parts of one MOEMS device as well as allows easy reconfiguration of the complete image analysis for diverse MOEMS types. First proof of usability has been obtained for micro scanning mirrors developed at Fraunhofer IPMS.

General access to MEMS is hampered by the expense of probe stations. We report on the construction of a lowcost system for operating MEMS devices for research and education. The system includes a driver-board, packaged MEMS chip (48 pin DIP - optical), and LabView VI. Typically, 20-40 separate devices (electrothermal and electrostatic actuators, micromirrors, and micro-positioners) are fabricated within the standard SUMMiT chip footprint (6.3x2.8mm). Educators can use the system to carry out labs for a variety of education levels. Researchers can use the system for prototyping new devices, developing better models for computer simulations, and utilizing devices for new applications.

We are exploring nanoelectronic engineering areas based on low dimensional materials, including carbon nanotubes and graphene. Our primary research focus is investigating carbon nanotube and graphene architectures for field emission applications, energy harvesting and sensing. In a second effort, we are developing a high-throughput desktop nanolithography process. Lastly, we are studying nanomechanical actuators and associated nanoscale measurement techniques for re-configurable arrayed nanostructures with applications in antennas, remote detectors and biomedical nanorobots. The devices we fabricate, assemble, manipulate and characterize potentially have a wide range of applications including sensors, detectors, system-on-a-chip, system-in-a-package, programmable logic controls, energy storage systems and allelectronic systems.

A surface acoustic wave (SAW)-based gyroscope was developed on a piezoelectric substrate. The developed gyroscope consists of two SAW oscillators, metallic dots, and absorber. Coupling of mode (COM) modeling was conducted to determine the optimal device parameters prior to fabrication. Depending on the angular velocity, the difference of the oscillation frequency was modulated. The obtained sensitivity was approximately 52.35 Hz/deg·s at an angular rate range of 0~1000 deg/s.

The Fraunhofer Institute for Photonic Microsystems (IPMS) develops and fabricates MOEMS micro-mirror arrays for a variety of applications in image generation, wave-front correction and pulse shaping. In an effort to extent the application range, mirrors are being developed that withstand higher light intensities. The absorbed light generates heat. Being suspended on thin hinges, and isolated from the bulk by an air gap, the mirrors heat up. Their temperature can be significantly higher than that of their substrate. In this paper we describe an experiment carried out to verify simulations on the temperature within the mirror plates during irradiation. We created a structure out of electrically connected mirror plates forming a four-point electrical resistor, and calibrated the thermal coefficient of the resistor in a temperature chamber. We irradiated the resistor and calculated the mirror temperature. In the experiment, the temperature in the mirror plates increased by up to 180 °C. The mirrors did not show significant damage despite the high temperatures. Also, the experiment confirms the choice of heat transport mechanisms used in the simulations. The experiment was done on 48 μm x 48 μm mirrors suspended over a 5 μm air gap, using a 355 nm solid-state laser (4 W, up to 500 W/cm²).

We present the design, fabrication, and testing of a micro-scale positioning system. The SUMMiT V™ processed design allows an in-plane, bi-directional, micron-scale linear motion of a shuttle using a ratcheting mechanism and multilayered chevron actuators. A single latching system with oppositely faced ratchet teeth on either side of the shuttle is used for achieving the actuation. The design is intended to reduce the footprint and number of electrical connections needed, compared to similar devices. A LabVIEW based optical characterization setup was developed for automated testing of the device. The device produced a maximum displacement of ~180μm.

A microlens array (MLA) was developed based on isotropic wet etching of quartz and coating of polymer on the etched substrate for maskless lithography application. Through the optimized manufacturing procedures, uniform elements, excellent light focusing ability, and dense fill factor were obtained. The fabricated MLA has the focal length ranging from 32.2 to 45.4 μm depending on the etching time and the thickness of the coated polymer. The collimated light was uniformly focused on the whole focal plane after passing through the fabricated array of microlenses and the size of the each focused beam was ~1.5 μm. By using the compact imaging ability of the miniaturized lenses, the MLA was applied to UV photolithography process. The illuminated UV passing the MLA focused on the photoresist, producing micron scale pattern array. Various sizes and shapes of micropattern arrays were realized onto the PR via controlling the experimental variables. Even at high temperature, the MLA performances were not changed indicating thermal stability of the developed MLA.

We report on the design, fabrication, and testing of a 2 degree of freedom MEMS positioning system. Sandia National Laboratories' MEMS foundry process was utilized for the fabrication of the device; this process incorporates five layers of polysilicon and four sacrificial layers of silicon dioxide. The actuation was achieved by identical comb-drives on both axes. The comb drives produce a displacement of ~ 4 μm which was amplified to ~ 30 μm by the use of a distance multiplier. A pin and track arrangement in the X and Y arms, extending from the actuator assembly, allows bi-axis motion. The stage is connected to the central pin. For testing the performance of the fabricated design a custom made optical characterization setup was assembled. To provide the actuation signals to the stage, a Keithley 2400 source meter was programmed using LabView to provide actuation voltages from 0-100 V with a 2 volt step. An optical microscope, interfaced with a Canon S5 IS digital camera, was used to record the actuation events for the measurement of in-plane displacement. Displacement at the various actuation voltages was obtained using a National Instruments' Vision image analysis software routine. The device has been tested and demonstrates a useful design for realizing a bi-directional 2-D positioning system. The positioning system is capable of 0 - 30 μm of motion in both the X and Y axes, with displacement showing a quadratic relationship with the applied voltage.

The electric field is affected by the arrangement of the vertically aligned carbon nanotube (VACNT) columns in field emission devices. We fabricated VACNT column array for use in micro time-of- flight mass spectrometer (TOF MS) and investigated the influence of the VACNT column array on the characteristics of field emission. According to the electric field distribution simulation based on FEMLAB, the field screening effect depends on the CNT arrangement and the pitch-to-height ratio. The different types of VACNT column array cathodes were fabricated and tested for field emission. All these VACNT column array cathodes showed excellent field emission properties and a trend consistent with electric field distribution simulation.

We present a low cost, self-aligned, process to etch cavities under movable structures in commercially available SOI wafers. The cavity is formed by electrochemically etching the substrate through the openings in the SOI structural layer. A tuning fork structure fabricated with the cavity SOI process has resonant frequency of 247 kHz and the measured intrinsic is Q = 82,000 at 35 mTorr. Comparing the measured quality factor as function of pressure for devices with and without the cavity, the devices with cavity showed a consistent improvement in the quality factor by a factor of 2-3 except for very low pressures where the intrinsic mechanical quality factor dominates. As the distance between the device and substrate is increased from 2 μm (buried oxide thickness) to 10 μm (electrochemically etched cavity), the parasitic capacitance to the substrate is also reduced by 5x. In addition, the stiction between the device and substrate is effectively eliminated.

We report on the effects of mechanical stress on thermal microactuator performance. Packaging processes such as die attach and lid sealing usually result in stresses on the die containing microsystems devices. While this phenomenon is known, quantifying the effects systematically is difficult due to challenges in controlling the resultant stress resulting from packaging. In this study, we use a four-point bending stage to apply loads of 12 lbf (53.4 N) in tension and compression to 11.5 mm by 2.9 mm samples. Thermal microactuators and stress gauges were fabricated using the Sandia 5-layer SUMMiT surface micromaching process and diced to fit in the bending stage. At each stress level, the vernier scales on the thermal microactuator were imaged in order to determine the displacements. Thermal microactuator displacements are reported as a function of applied current up to 35 mA at varying stress levels. Increasing tensile stress decreases the initial displacement and flattens the thermal microactuator displacement versus applied current curve. Raman spectroscopy and stress gauge measurements indicate that the stress range for the fourpoint bending stage experiments extends from 200 MPa tensile to -250 MPa compressive. Numerical model predictions of thermal microactuator displacement versus current are in qualitative agreement with the experimental results. Quantitative information on the reduction in thermal microactuator performance as a function of stress provides validation data for MEMS models and can guide future designs so that they will be more robust to stresses resulting from packaging processes.

Due to the low Young's Modulus of porous silicon (PS), Si/PS composite membranes - where the silicon membrane is converted into PS to a certain depth - deform more than silicon membranes and hence MEMS pressure sensors with composite membranes have higher sensitivity. But the Si/PS composite membranes exhibit a smaller range of linear response with applied pressure than silicon membranes with the linear range being less for Si/microPS as compared to Si/macroPS composite membranes. In addition, while the composite membrane deformation saturates at high pressures like silicon membranes, the deformation is irreversible unlike that seen with silicon membranes within reasonable limits. With the possibility that the irreversible deformation could be due to stiction force between the collapsed pore walls at high pressure, we investigate the effect of formation of self-assembled monolayer (SAM) antistiction coating on the performance of Si/PS composite membranes.

Our investigation addresses the modeling, design and fabrication of artificial structures, commonly called metamaterials. Metamaterials enable electromagnetic properties which do not naturally exist from basic structural symmetry. This investigation focuses on the modeling, fabrication and testing of metamaterials at terahertz wavelengths. This research utilizes a foundry fabrication process called PolyMUMPs to construct the metamaterial array. The PolyMUMPS process is commonly used for MEMS devices and consists of three polysilicon and two silicon dioxide layers. An array of split ring resonators consisting of the polysilicon and silicon dioxide layers was constructed. The split ring resonators are an important aspect to the metamaterial because they allow us to take advantage of structural properties such as scaling, resonant frequency response, and magnetic flux. The metamaterial structure obtains its symmetry from the etching process used to isolate the individual patterns. The "as-built" figure of merit (FOM) is defined as the ratio of the real component to the imaginary component of the refractive index. By comparing the analytical and FEM models to identify key limitations of the FOM structures, this investigation will point out manufacturing limitations that can be adjusted to improve the FOM. By gaining a higher ratio to the FOM, this improves the overall performance of the metamaterial structure at the selected wavelength. Through the understanding obtained from the modeling data and actual manufacturing comparison, changes to key parameters which limit the FOM can lead to metamaterial array improvements and ultimately to better components suitable for terahertz applications.

Optical MEMS switching technology has attracted attention in managing data flow due to its compactness and robustness. It allows hundreds of optical channels to be switched by micro-mirrors with very low power consumption. Furthermore, the ability to switch signals independent of data rates, formats, wavelengths and protocols is advantageous in many real world environments such as internet peering exchanges, undersea cable landing locations and data centers. All of these applications require a highly reliable and stable switching system. Dielectric isolation has a huge impact on major failure modes of capacitive MEMS devices such as breakdown and charging. This issue becomes more challenging in electrostatic MEMS optical switches since they usually operate at relatively high voltages. The charges trapped in this dielectric layer could cause interference in the electric field, resulting in erratic responses of the steering mirrors and instability of pointing accuracy over temperature and time, which greatly degrades the system performance. Aiming at reducing charging and preventing high voltage breakdown, a dielectric charging guard has been developed by using an oxide "fence" with extended breakdown path length that is shielded by conductive sidewalls of the silicon interposer. In this paper, the reliability tests as well as the performance impact to the optical switch will be presented, including characterizations of breakdown voltage, leakage current, and charging verses temperature. The test results demonstrate highly repeatable switching accuracy of micro-mirrors with very low drift at varied temperature. Failures induced by fabrication will also be discussed.