Characterization of the activation of yttrium-based getter films by electrical measurements and ion-beam analyses

International audienceGettering properties of thin films of pure yttrium and yttrium-based alloys have been studied for application to MEMS vacuum packaging at the wafer level. Thin films of Y, Zr-Y, Ti-Y and V-Y were co-evaporated under ultra-high vacuum. It is demonstrated that the sheet resistance measured by 4-probes technique before and after activation at 250°C gives a good estimation of the oxygen sorption ability determined by NRA. Pure yttrium has been found to be highly reactive after deposition (sheet resistance increases by 40% after 1 month in air) but poorly efficient in oxygen trapping after activation. Conversely, the sorption ability of Y-V, Y-Zr and Y-Ti alloys is extremely high and increases with the yttrium content in the film. The bests results for sorption are obtained with Y-V (2.7 10 22 atom/cm 3 for Y44V56)

Plasma-activated fusion bonding for vacuum encapsulation of microdevices

A fabrication process for vacuum-encapsulating PZT microcantilevers was designed in this dissertation. Initially, a low temperature wafer-bonding recipe was optimized with the help of plasma-activation. Conventional direct fusion bonding temperature was reduced from 400°C to 85°C, and final thermal annealing temperature and time of 1000°C for 4 hours (hr) were significantly reduced to 300°C and 1 hr respectively. Tensile tests conducted on dies diced from the bonded wafer stack revealed bond strengths of 22.15 MPa, which was close to the bulk fracture strength of 24 MPa for silicon. Near infrared images of the wafer stack showed no debonded regions at the interface. Surface and interface chemistry of oxygen plasma-activated wafers before, during, and after bonding were investigated. Significance of wet chemical activation technique, like RCA (Radio Corporation of America) cleaning, was studied. The time interval between plasma-activation and fusion bonding was varied, and its effect on the bond quality and bond strength was investigated. Decrease in the bond-quality and strength was observed with an increase in storage time. However, an unexpected increase in the bond quality was observed after 48 hr, and was attributed to the increase in the interfacial oxide layer. Further investigations revealed that the interfacial oxide layer was capable of absorbing gas molecules released as a byproduct of ongoing reactions at the interface of the two wafers. Gettering capability of the interfacial oxide layer was confirmed through the bonding of plasma-activated and 48 hr stored silicon (Si) and silicon dioxide (SiO2) wafers. Infrared images showed a good bond for the wafer stack. Since designing a fabrication process flow for vacuum-encapsulation of microdevices was the primary objective, lead zirconate titanate microcantilevers were fabricated onto a silicon substrate. The microdevices were actuated in ambient air pressure as well as in a vacuum environment. Broadening of the resonance curve was observed with an increase in the magnitude of ambient pressure, and is a result of increased air-damping. Experimental results obtained were compared to theoretical results from finite element modeling analyses. Vacuum cavities were fabricated between two Si wafers. Optical lid-deflection method of measuring internal cavity pressure was explored and employed with the help of high aspect ratio pressure diaphragms on a capping wafer. An investigation of seal integrity of the vacuum package revealed real/virtual leaks. The gettering capability of the SiO2 layer was employed in order to preserve the vacuum-level in the cavities. Two types of gettering patterns were investigated. It was concluded that an SiO2 getter layer at the interface increased the seal-integrity of the vacuum packages, while getter rings still showed signs of real leaks. In addition, it was observed that the internal vacuum-level was higher for cavities with getter rings as compared to cavities without getters. It was concluded that getter rings were capable of preventing virtual leaks but not real leaks. A thick interfacial getter layer, however, prevented both the real and virtual leaks. Finally, a vacuum-packaging fabrication method to encapsulate lead zirconate titanate microcantilevers was proposed. In addition, more accurate methods of measuring package vacuum pressure magnitudes were proposed

Glassy Materials Based Microdevices

Microtechnology has changed our world since the last century, when silicon microelectronics revolutionized sensor, control and communication areas, with applications extending from domotics to automotive, and from security to biomedicine. The present century, however, is also seeing an accelerating pace of innovation in glassy materials; as an example, glass-ceramics, which successfully combine the properties of an amorphous matrix with those of micro- or nano-crystals, offer a very high flexibility of design to chemists, physicists and engineers, who can conceive and implement advanced microdevices. In a very similar way, the synthesis of glassy polymers in a very wide range of chemical structures offers unprecedented potential of applications. The contemporary availability of microfabrication technologies, such as direct laser writing or 3D printing, which add to the most common processes (deposition, lithography and etching), facilitates the development of novel or advanced microdevices based on glassy materials. Biochemical and biomedical sensors, especially with the lab-on-a-chip target, are one of the most evident proofs of the success of this material platform. Other applications have also emerged in environment, food, and chemical industries. The present Special Issue of Micromachines aims at reviewing the current state-of-the-art and presenting perspectives of further development. Contributions related to the technologies, glassy materials, design and fabrication processes, characterization, and, eventually, applications are welcome

Etudes des procédés d'encapsulation hermétique au niveau du substrat par la technologie de transfert de films

Les micro-dispositifs comportant des structures libérées et mobiles sont d une part très sensibles aux variations de leur environnement de travail, et d autre part très fragiles mécaniquement. L étape de découpe du substrat en plusieurs puces est extrêmement agressive et peut entrainer la destruction totale des micro-dispositifs. L encapsulation avant la découpe va alors prémunir les micro-composants lors de cette étape critique et continuer à garantir leur bon fonctionnement tout au long de leur utilisation en conservant la stabilité et la fiabilité de leur performance. Le conditionnement doit en outre interfacer les micro-dispositifs encapsulés avec le monde macroscopique en vue de leur utilisation. De nombreux procédés de fabrication ont déjà été développés pour l élaboration d un conditionnement. C est le cas de l encapsulation puce par puce, substrat - substrat, par couche sacrificielle par exemple. Ils sont toutefois très contraignants (encombrement, compatibilité, coût, ). Nous avons étudié, au cours de cette thèse, un procédé innovant de conditionnement hermétique par transfert de film utilisant une couche à adhésion contrôlée. Cette technologie consiste à élaborer des capots protecteurs sur le substrat moule puis à les reporter collectivement pour encapsuler les micro-dispositifs. Ce procédé est totalement compatible avec un interfaçage électrique de composant qui traverse les cordons de scellement ou le capot. Ce procédé nécessite la maîtrise de la croissance de divers films (C, CxFy, Ni, AlN, parylène, BCB, Au-In) et permet d obtenir des boitiers étanches, hermétiques et robustes qui devraient très rapidement pouvoir être utilisés pour le conditionnement de MEMS.Micro-devices which are composed of free standing or mobile structures are very sensitive to the working condition and mechanically very fragile. The saw dicing steps is very aggressive and it can destroy the micro-devices. Packaging will prevent the micro devices from any damage during this critical step and also take care of it all along its life by controlling its performance stability and reliability. Moreover, the suited devices use needs a connection to the macroscopic word through the packaging. Many packaging process flow has already developed such as pick and place, wafer to wafer, thin film packaging with a sacrificial layer. Nevertheless, they have got many drawbacks (footprint, process compatibility, cost ). We have developed an attractive wafer level hermetic packaging process by film transfer technology during this these. It relies on a transferred molded film cap from a carrier wafer to the donor wafer. Electrical path can be done through the cap or the bonding ring. Cap manufacturing need a high layer growth skill for example in C, CxFy, Ni, AlN, parylène, BCB, Au-In films to make robust, hermetic encapsulation which should be soon used for MEMS packaging.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

MEMS Accelerometers

Micro-electro-mechanical system (MEMS) devices are widely used for inertia, pressure, and ultrasound sensing applications. Research on integrated MEMS technology has undergone extensive development driven by the requirements of a compact footprint, low cost, and increased functionality. Accelerometers are among the most widely used sensors implemented in MEMS technology. MEMS accelerometers are showing a growing presence in almost all industries ranging from automotive to medical. A traditional MEMS accelerometer employs a proof mass suspended to springs, which displaces in response to an external acceleration. A single proof mass can be used for one- or multi-axis sensing. A variety of transduction mechanisms have been used to detect the displacement. They include capacitive, piezoelectric, thermal, tunneling, and optical mechanisms. Capacitive accelerometers are widely used due to their DC measurement interface, thermal stability, reliability, and low cost. However, they are sensitive to electromagnetic field interferences and have poor performance for high-end applications (e.g., precise attitude control for the satellite). Over the past three decades, steady progress has been made in the area of optical accelerometers for high-performance and high-sensitivity applications but several challenges are still to be tackled by researchers and engineers to fully realize opto-mechanical accelerometers, such as chip-scale integration, scaling, low bandwidth, etc

Development of microtubular solid oxide fuel cells design, fabrication and performance.

Solid oxide fuel cells (SOFCs) are the most efficient energy conversion devices known. Many designs exist, with most current ones based on planar, tubular or so-called hybrid geometries. Tubular designs have many advantages over planar ones, including robustness and simpler sealing. They suffer from somewhat lower area-specific power density and considerably lower volume-specific power density. The miniaturization of tubular cells offers great improvement to both, and more besides. Pushing the boundaries of state-of-the-art manufacture to ever thinner films increases performance further, greatly advancing the long road to large scale commercialisation of SOFCs. This is only possible via the rigorous selection of materials and careful design – both for optimal performance and for mass manufacture. Previous work by the author established the potential of a novel anode fabrication route as well as showing that even un-optimized electron beam physical vapour deposition (EB-PVD) was capable of creating demonstrator cells. In this work these manufacturing processes receive at least two passes of optimization towards both reproducible fabrication and maximising microtubular SOFC performance. The former was achieved by creating statistically significant quantities to assess reproducibility and studying the underlying science, and the latter was investigated in three aspects: gas transport, electrical and electrochemical. The unique oxidation-reduction route creates robust, highly reproducible anodes with excellent through porosity offering as much as 5 orders of magnitude superior gas permeance to published sources. Nickel tubes (Ni200 5.9 mm OD, 125 μm wall thickness, 100 mm long) were oxidised in air at 1,100 for 42 h and reduced in pure hydrogen at four different temperatures. The extremes (400 °C and 1,000 °C) proved sufficiently promising that both were considered in subsequent stages of experiments and analysis for the final anode design. The morphology of the electrolyte (in particular with respect to gas-tightness) is a critical aspect of SOFC miniaturisation, and a challenge to achieve via mass-manufacture-friendly EB-PVD. The yttria-stabilized zirconia (YSZ) electrolyte deposition was optimized as far as proved possible with the available equipment. While results are more than encouraging there are a number of important concerns to be addressed in future to assure successful commercialization of the design. Accurately measuring gas permeance through the anode-electrolyte tube (sometimes called a half-cell) provides quantified justification. Finally a porous platinum cathode film 300 nm thick was successfully magnetron-sputtered onto the YSZ electrolyte at p Aᵣ100 mTorr, demonstrating the fabrication process and creating complete cells for electrical and electrochemical characterisation.PhD in Manufacturin

High-Q Wafer Level Package Based on Modified Tri-Layer Anodic Bonding and High Performance Getter and Its Evaluation for Micro Resonant Pressure Sensor

In order to achieve and maintain a high quality factor (high-Q) for the micro resonant pressure sensor, this paper presents a new wafer level package by adopting cross-layer anodic bonding technique of the glass/silicon/silica (GSS) stackable structure and integrated Ti getter. A double-layer structure similar to a silicon-on-insulator (SOI) wafer is formed after the resonant layer and the pressure-sensitive layer are bonded by silicon direct bonding (SDB). In order to form good bonding quality between the pressure-sensitive layer and the glass cap layer, the cross-layer anodic bonding technique is proposed for vacuum package by sputtering Aluminum (Al) on the combination wafer of the pressure-sensitive layer and the resonant layer to achieve electrical interconnection. The model and the bonding effect of this technique are discussed. In addition, in order to enhance the performance of titanium (Ti) getter, the prepared and activation parameters of Ti getter under different sputtering conditions are optimized and discussed. Based on the optimized results, the Ti getter (thickness of 300 nm to 500 nm) is also deposited on the inside of the glass groove by magnetron sputtering to maintain stable quality factor (Q). The Q test of the built testing system shows that the number of resonators with a Q value of more than 10,000 accounts for more than 73% of the total. With an interval of 1.5 years, the Q value of the samples remains almost constant. It proves the proposed cross-layer anodic bonding and getter technique can realize high-Q resonant structure for long-term stable operation

Mission oriented R and D and the advancement of technology: The impact of NASA contributions, volume 2

NASA contributions to the advancement of major developments in twelve selected fields of technology are presented. The twelve fields of technology discussed are: (1) cryogenics, (2) electrochemical energy conversion and storage, (3) high-temperature ceramics, (4) high-temperature metals (5) integrated circuits, (6) internal gas dynamics (7) materials machining and forming, (8) materials joining, (9) microwave systems, (10) nondestructive testing, (11) simulation, and (12) telemetry. These field were selected on the basis of both NASA and nonaerospace interest and activity