This PDF file contains the front matter associated with SPIE Proceedings Volume 8614, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The adhesion force between polycrystalline silicon surfaces in MEMS structures is studied using three different test structures. Electrostatic and thermal actuations are used to bring the two surfaces into contact and mechanical force stored in the structures is used to separate them. In particular, the devices consist of (i) double-clamped beam that is actuated electrostatically and measured optically, (ii) suspended plate that is actuated electrostatically and measured capacitively, and (iii) thermally actuated and optically measured beams. The devices are fabricated using PolyMUMPs® process. The results show that the adhesion force in tested structures has little or no dependence on the apparent contact surface and is highly affected by the test environment and the actuation methods. The test results at high temperatures (100-130 °C) show that in absence of capillary and electrostatic forces, the adhesion force drastically decreases and mainly depends on the number of contacting asperities.

This contribution reports on the analysis of metal-metal contacts of MEMS switches. A novel high aspect ratio MEMS fabrication sequence in combination with wafer level packaging is applied for fabrication of an RF MEMS switch with lateral motion. It allows for a relatively large actuation electrode area in a small package, and for high actuation force even with an actuation voltage of 5 V. The focus of this contribution is on the contact behavior. It is shown how operation conditions as like as actuation voltage, RF power, and DC bias influence the contact resistance. The power handling capability and its influence on the contacts, and the intermodulation were investigated also.

Micro-electro-mechanical (MEM) relays are an intriguing alternative to transistors for ultra-low-power digital logic applications [1]. This paper investigates various failure modes for logic relays. Experimental results are presented to show that structural fatigue, dielectric charging, and contact stiction are not reliability-limiting issues. Contact resistance instability caused by surface oxidation and contamination is the primary challenge, and can be influenced by device design and operating conditions.

With the rising need for microfabricated chip-scale atomic clocks to enable high precision timekeeping in portable applications, there has been active interest in developing miniature (<few cm³), chip-scale alkali vapor lamps, since vapor plasma discharge sources are currently the standard for optical pumping in double-resonance clocks. We reported in 2012 a first microfabricated chip-scale Rubidium dielectric barrier discharge lamp. The device’s preliminary results indicated its high potential for optical pumping applications and wafer-scale batch fabrication. The chip-scale plasma light sources were observed to be robust with no obvious performance change after thousands of plasma ignitions, and with no electrode erosion from plasma discharges since the electrodes are external. However, as atomic clocks have strict lamp performance requirements including less than 0.1% sub-second optical power fluctuations, power consumption less than 20 mW and a device lifetime of at least several years, it is important to understand the long-term reliability of these Rb planar mini-lamps, and identify the operating conditions where these devices can be most reliable and stable. In this paper, we report on the reliability of such microfabricated lamps including a continuous several month run of the lamp where the optical power, electrical power consumption and temperature stability were continuously monitored. We also report on the effects of temperature, rf-power and the lamp-drive parasitics on the optical power stability and discuss steps that could be taken to further improve the device’s performance and reliability.

Mobile devices have become an integral part of everyday life, and as the primary input/output interface, the display now represents a key factor of user experience. The display also consumes increasingly more of the power budget than ever before, resulting in a challenge for device makers to reduce display power consumption without negatively impacting perceived image quality. Pixtronix displays are digital, trans-flective and offer a low-power advantage, without sacrificing brightness or color gamut. Incumbent display technologies such as LCD, lose over 90% of backlight output due to polarizers and color filters. The core of the Pixtronix MEMS-based display technology is the Digital Micro Shutter (DMS). The micro-shutters are fabricated on active TFT backplanes in conventional LCD fabrication facilities. To complete the DMS display system, an aperture plate and backlight are added, and the display is filled with a fluid. This display technology promises a significant reduction in power consumption over conventional LCD displays, while maintaining the high-brightness, wide color gamut, 24-bit color video capabilities that users expect from today's mobile devices.

A review of three different systems based on the MEMS tunable blazed grating technology is presented. A MEMS tunable blazed grating is a versatile optical element providing a compact tunable mechanism for optical systems. The MEMS chip measures 5x5 mm², including a position encoder, and is shock resistant up to 3000 g. The grating can operate in different spectral regions (Visible to Mid-IR) and high optical throughput is guaranteed at all wavelengths by operating it in Littrow condition. The first system shown uses the MEMS grating in a compact wavemeter. It is tested as Fiber Bragg Grating interrogating system. At 1.5 μm wavelength, it detects lines as narrow as 0.2 nm, resolves lines 2 nm apart and retrieves the central wavelength with accuracy better than 20 pm. By using the position encoder the expected accuracy can be on the order of 1pm. The second system shown demonstrates a compact (<10 cm³) tunable external cavity Quantum Cascade Laser using the MEMS grating. The resulting laser operates at a center wavelength of 9.5 μm and is tunable over a range of 150 nm. Finally a double stage monochromator is presented. Two MEMS chips with different grating periods are cascaded, in order to cancel out undesired grating orders, and to improve the filter linewidth (~1nm) and the extinction ratio (26 dB). The cascaded filter can be combined with a broadband source to select an arbitrary wavelength in the 400-800 nm range or the 800-1600 nm range.

Tunable MOEMS Fabry-Perot interferometers (FPIs) are key elements in the miniaturization of spectroscopic instrumentation. Robustness and high reliability of the MOEMS structure are important factors especially for sensors utilized in challenging environments such as in space- and automotive applications. This paper presents reliability assessment of two types of MOEMS optical filters; a tunable ALD (atomic layer deposition) –based surface micromachined FPI for visible – near-infrared range, and a tunable FPI for mid- infrared applications based on LPCVD (low-pressure chemical vapor deposition) thin-film micromachining. High-G shock tests were performed on both MOEMS FPIs. The FPI structures can survive mechanical impact up to 18 000 G without any detectable changes in the capacitance, while detected failure mechanisms in this range arise from packaging and not from the MOEMS structures. The effect of DDMS SAM (dichlorodimethylsilane self-assembled monolayer) coating to prevent in-use stiction was evaluated in both humidity- and impact tests. In humidity tests, 20% stiction rate in non-coated devices vs. 0% stiction rate in DDMS-coated LPCVD FPIs under pull-in was observed. These results indicate good shock-impact robustness for both types of surface-micromachined structures, while DDMS SAM can be utilized to improve in-use reliability of MOEMS.

Digital Holographic Microscopes (DHMs) have unique features especially relevant for static and dynamical MEMS characterization. They provide both 3D topography with interferometric resolution and intensity image in a single acquisition at camera rate, without any lateral or vertical scanning. In this presentation, DHM is operated in conjunction with a laser pulsed stroboscopic module providing synchronization of camera, laser pulses, and MEMS excitation signal up to 25 MHz. Three methods for DHM analysis of resonant frequencies are presented with concrete examples. The first method, gives the more general, precise and complete information. Sine wave excitation with increasing (or decreasing) frequencies is used. For each frequency, laser pulses are used to “freeze” the movement of the MEMS. Using the stroboscopic synchronization, each period of the excitation signal is sampled at high resolution, and the topography of the MEMS can be measured at each of those samples points. As implemented, the change of frequency is a continuous sweep: quantitative values in term of displacement amplitude and Bode diagrams can be measured for nonlinear resonances as well. The second method uses sine wave excitation with increasing (or decreasing) frequencies. For each frequency, the optical signal is integrated over an entire number of periods of the MEMS. At resonance, constructive and destructive interference build up on the intensity images. It enables fast frequency scan over large ranges. But it provides neither quantitative values of displacement amplitude, nor Bode diagrams. The third method is to measure the system response to an impulse or chirp excitation signal for instance, and to make a Fourier analysis of this response to determine resonant frequencies. This method is less sensitive as it spreads the excitation energy in many frequencies.

In this paper, a new MEMS capacitive temperature sensor is presented which is based on a circular silicon plate with a gold annulus deposited on top forming a novel bimaterial structure. The bimaterial structure is anchored to a substrate on its edge and forms the top electrode of a capacitor. A stationary silicon electrode beneath the bimaterial structure forms the second electrode. The PolyMUMPs® foundry process has been used to fabricate the device. Experiments show that for an effective area of about 0.1 mm² this MEMS capacitive temperature sensor achieves a sensitivity of 0.75±0.25 fF/°C over the temperature range of 25 to 225 °C, which shows an improvement of more than 25% over equivalent microcantilever devices with the same effective area. Numerical modeling is used to show that the new design exhibits high flexibility in tailoring its thermomechanical response over the desired temperature range. The simplicity of its design and flexibility of the materials from which it can be constructed also makes this new MEMS sensor a good onchip temperature measurement device for MEMS characterization.

Nano- and hetero-structures of carbon nanotube (CNT), indium tin oxide (ITO), and Graphene nano Platelet (GnP) can control significantly piezoelectric and optoelectronic properties in Microelectromechanical Systems (MEMS) as acoustic actuators. Interfacial durability and electrical properties of CNT, ITO or GnP coated poly(vinylidene fluoride) (PVDF) nanocomposites were investigated for use in acoustic actuator applications. The GnP coated PVDF nanocomposite exhibited better electrical conductivity than either CNT or ITO, due to the unique electrical properties of GnP. GnP nanocomposite coatings also exhibited good acoustical properties. Contact angle, surface energy, work of adhesion, and spreading coefficient measurements were used to explore the interfacial adhesion durability between neat CNT (or plasma treated CNT) and plasma treated PVDF. The acoustic actuation performance of GnP coated PVDF nanocomposites were investigated for different radii of curvature and different coating conditions, using a sound level meter. GnP is considered to be a more appropriate acoustic actuator than either CNT or ITO because of its characteristic electrical properties. A radius of curvature of about 15 degrees was established as being most appropriate. Sound characteristics differed with varying coating thicknesses. The results of this study suggest that it should be possible to manufacture transparent actuators with good sound quality.

Recent progress in the packaging and integration of silicon photonics devices and systems is presented. An overview of various fiber packaging techniques is given, including a detailed description of a planar fiber packaging process for single fibers and arrays of fibers based on grating couplers. An overview of techniques for integrating lasers with silicon photonics circuits is also given, including details on a hybrid integration technology based on a ceramic micro-optical bench suitable for use with tunable and high-speed directly-modulated lasers. Both of the technologies discussed in detail are suitable for passive alignment and wafer-scale assembly.

This paper presents piezoelectric transduction and frequency trimming of silicon-based resonators with a center frequency in the low megahertz regime. The temperature coefficient of frequency (TCF) of the resonators is reduced using both passive and active compensation schemes. Specifically, a novel technique utilizing oxide-refilled trenches is implemented to achieve efficient temperature compensation while maintaining compatibility with wet release processes. Using this method, we demonstrate high-Q resonators having a first-order TCF as low as 3 ppm/°C and a turnover temperature of around 90 °C, ideally suited for use in ovenized platforms. Using active tuning, the temperature sensitivity of the resonator is further compensated around the turnover temperature, demonstrating frequency instability of less than 400 ppb. Such devices are ideally suited as timing units in space applications where size, power consumption, and temperature stability are of critical importance.

In this paper the authors report about the six inch wafer level vacuum packaging of electro-statically driven two dimensional micro-mirrors. The packaging was done by means of two types of wafer bonding methods: anodic and glass frit. The resulting chips after dicing are 4 mm wide, 6 mm long and 1.6 mm high and the residual pressure inside the package after dicing was estimated to be between 2 and 20 mbar. This allowed us to reduce the driving voltage of the micro-mirrors by more than 40% compared to the driving voltage without vacuum packaging. The vacuum stability after 5 months was verified by measurement using the so called “membrane method”. Persistence of the vacuum was proven. No getter materials were used for packaging.

INO has developed a hermetic vacuum packaging technology for uncooled bolometric detectors based on ceramic leadless chip carriers (LCC). Cavity pressures less than 3 mTorr are obtained. Processes are performed in a state-of-the art semi-automated vacuum furnace that allows for independent activation of non-evaporable thin film getters. The getter activation temperature is limited by both the anti-reflection coated silicon or germanium window and the MEMS device built on CMOS circuits. Temperature profiles used to achieve getter activation and vacuum sealing were optimized to meet lifetime and reliability requirements of packaged devices. Internal package components were carefully selected with respect to their outgassing behavior so that a good vacuum performance was obtained. In this paper, INO’s packaging process is described. The influence of various package internal components, in particular the CMOS circuits, on vacuum performance is presented. The package cavity pressure was monitored using INO’s pressure microsensors and the gas composition was determined by internal vapor analysis. Lifetime was derived from accelerated testing after storage of packaged detectors at various temperatures from room temperature to 120°C. A hermeticity yield over 80% was obtained for batches of twelve devices packaged simultaneously. Packaged FPAs submitted to standard MIL-STD-810 reliability testing (vibration, shock and temperature cycling) exhibited no change in IR response. Results show that vacuum performance strongly depends on CMOS circuit chips. Detectors packaged using a thin film getter show no change in cavity pressure after storage for more than 30 days at 120°C. Moreover, INO’s vacuum sealing process is such that even without a thin film getter, a base pressure of less than 10 mTorr is obtained and no pressure change is observed after 40 days at 85°C.

A System-in-Package (SiP) concept for the 3D-integration of a Single Wall Carbon Nanotube (SWCNT) resonator with its CMOS driving electronics is presented. The key element of this advanced SiP is the monolithic 3D-integration of the MEMS with the CMOS electronics using Through Silicon Vias (TSVs) on an SOI wafer. This SiP includes: A glass cap vacuum-sealed to the main wafer using an eutectic bonding process: a low leak rate of 2.7 10^-9 mbar•l/s was obtained; Platinum-TSVs, compatible with the SWCNT growth and release process; The TSVs were developed in a “via first” process and characterized at high-temperature — up to 850 °C. An ohmic contact between the Pt-metallization and the SOI silicon device layer was obtained; The driving CMOS electronic device is assembled to the MEMS using an Au stud bump technology. Keywords: System-in-Package (SiP), vacuum packaging, eutectic bonding, “via-first” TSVs, high-temperature platinum interconnects, ohmic contacts, Au-stud bumps assembly, CMOS electronics.

A technique of mounting a microlens array (MLA) on a solar cell as an encapsulation layer is presented. The uniform cylinder-shaped MLA was fabricated through simple and cost-effective micromachining processes. The efficiency of the triple-junction InGaP/GaAs/Ge solar cell was considerably enhanced by replacing a bare glass cover with the developed MLA as a surface protection layer. This is attributed to efficient conveyance of the refractive light into bare photoactive regions of the solar cell to avoid the gridlines. Under the optimal mounting condition with an optimal height of optical spacer, the MLA effect was maximized resulting in a 16.8% increase in power conversion efficiency (PCE) than that of the control device. The efficiency of the MLA-packaged solar cell remained for a long time without degradation. The MLA can therefore replace a conventional glass (or film) as a means of encapsulation layer to enhance photovoltaic performances of GaAs-based solar cells.

The impact of different types of radiation on the electromechanical properties of materials used in microfabrication and on the capacitive and piezoresistive transduction mechanisms of MEMS is investigated. MEMS technologies could revolutionize avionics, satellite and space applications provided that the stress conditions which can compromise the reliability of microsystems in these environments are well understood. Initial tests with MEMS revealed a vulnerability of some types of devices to radiation induced dielectric charging, a physical mechanism which also affects microelectronics, however integration of novel functional materials in microfabrication and the current trend to substitute SiO₂ with high-k dielectrics in ICs pose new questions regarding reliability in radiation environments. The performance of MEMS devices with moving parts could also degrade due to radiation induced changes in the mechanical properties of the materials. It is thus necessary to investigate the effects of radiation on the properties of thin films used in microfabrication and here we report on tests with γ, high energy protons and fast neutrons radiation. Prototype SOI based MEMS magnetometers which were developed in UCL are also used as test vehicles to investigate radiation effects on the reliability of magnetically actuated and capacitively coupled MEMS.

We have demonstrated two monolithically integrated Bragg grating based accelerometers, both with the optical path and mechanical structure being made from the same substrate. The unique fabrication techniques, Direct UV Writing and precision dicing, used to create the glass microcantilevers are discussed. We show experimental results from two different Bragg grating based interrogation systems, one utilizing a single Gaussian apodized Bragg grating and the other utilizes two spectrally matched Bragg gratings forming a Fabry-Pérot interferometer. Sinusoidal accelerations were applied to both devices and their sensitivities were found to be 0.67±0.035 mV/g and 14.0±0.44 mV/g for the single Bragg grating and Fabry-Pérot interferometer respectively.

Life testing/qualification of reflowed (1^st reflow) and reworked (1^st reflow, 1^st removal, and then 1^st rework) advanced ceramic column grid array (CCGA) surface mount interconnect electronic packaging technologies for future flight projects has been studied to enhance the mission assurance of JPL-NASA projects. The reliability of reworked/reflowed surface mount technology (SMT) packages is very important for short-duration and long-duration deep space harsh extreme thermal environmental missions. The life testing of CCGA electronic packages under extreme thermal environments (for example: -185°C to +125°C) has been performed with reference to various JPL/NASA project requirements which encompass the temperature range studied. The test boards of reflowed and reworked CCGA packages (717 Xilinx package, 624, 1152, and 1272 column Actel Packages) were selected for the study to survive three times the total number of expected temperature cycles resulting from all environmental and operational exposures occurring over the life of the flight hardware including all relevant manufacturing, ground operations, and mission phases or cycles to failure to assess the life of the hardware. Qualification/life testing was performed by subjecting test boards to the environmental harsh temperature extremes and assessing any structural failures, mechanical failures or degradation in electrical performance solder-joint failures due to either overstress or thermal cycle fatigue. The large, high density, high input/output (I/O) electronic interconnect SMT packages such as CCGA have increased usage in avionics hardware of NASA projects during the last two decades. The test boards built with CCGA packages are expensive and often require a rework to replace a reflowed, reprogrammed, failed, redesigned, etc., CCGA packages. Theoretically speaking, a good rework process should have similar temperature-time profile as that used for the original manufacturing process of solder reflow. A multiple rework processes may be implemented with CCGA packaging technology to understand the effect of number of reworks on the reliability of this technology for harsh thermal environments. In general, reliability of the assembled electronic packages reduces as a function of number of reworks and the extent is not known yet. A CCGA rework process has been tried and implemented to design a daisy-chain test board consists of 624 and 717 packages. Reworked CCGA interconnect electronic packages of printed wiring polyimide boards have been assembled and inspected using non-destructive x-ray imaging and optical microscope techniques. The assembled boards after 1^st rework and 1^st reflow were subjected to extreme temperature thermal atmospheric cycling to assess their reliability for future deep space JPL/NASA for moderate to harsh thermal mission environments. The resistance of daisy-chained interconnect sections were monitored continuously during thermal cycling to determine intermittent failures. This paper provides the experimental reliability test results to failure of assemblies for the first time of reflowed and reworked CCGA packages under extreme harsh thermal environments.

We report on the susceptibility of structural MEMS materials to proton radiation damage. Radiation tests at space relevant doses were conducted on MEMS resonators. The two materials examined were single crystal silicon and SU-8, which are both in widespread use in microsystems. The resonance frequency was monitored for measuring minute changes of the Young’s modulus. No radiation-induced changes of the elasticity were observed in the silicon devices up to fluences of 10¹³ cm^-2, corresponding to a total ionizing dose (TID) of over 5.5 MRad for 10 MeV protons. The SU-8 resonators showed a variation of less than ±5.5% at doses of up to 1.4 Mrad (TID). Chemical and structural analyses of the polymer were performed using infrared absorption spectroscopy and x-ray diffraction methods. We discuss possible mechanisms for the observed changes of the elasticity of SU-8.

Details on the first linear arrays of 512×3 VO_x microbolometers operating in space are reported. Arrays of this format are suited for remote sensing where relative motion between the spacecraft and target provides an inherent scanning mechanism. To take full advantage of the linear format, the array is built on a custom readout electronics that enables simultaneous integration of all pixels for scanning periods of up to 140 ms. The output signal from each pixel is digitized to 14 bits using a voltage-to-frequency conversion mechanism. Two arrays, integrated into two spectrally distinct radiometric packages, provide for coregistration of infrared images in three bands centered at 3.8, 10.85, and 11.85 μm for the retrieval of fire and sea surface temperatures. Analysis of the downlinked data confirms the reliable in-orbit operation and consistency with pre-launch characteristics for both arrays. Algorithms have been developed to perform post processing and absolute radiometric calibration of images in all bands. Image deconvolution using Wiener filtering was found effective in recovering the signal loss incurred in the active pixels when observing high temperature events. The in-flight gain and offset values were evaluated for all pixels by means of deep space measurements and cross calibration with reference spaceborne sensors. Preliminary assessment of the images calibrated using these values showed that they are in agreement with those retrieved from GOES sensor.