237 research outputs found
Fluidic packaging of microengine and microrocket devices for high pressure and high temperature operation
No full textThe fluidic packaging of Power MEMS devices such as the MIT microengine and microrocket requires the fabrication of hermetic seals capable of withstanding temperature in the range 20-600/spl deg/C and pressures in the range 100-300 atm. We describe an approach to such packaging by attaching Kovar metal tubes to a silicon device using glass seal technology. Failure due to fracture of the seals is a significant reliability concern in the baseline process: microscopy revealed a large number of voids in the glass, pre-cracks in the glass and silicon, and poor wetting of the glass to silicon. The effects of various processing and materials parameters on these phenomena were examined. A robust procedure, based on the use of metal-coated silicon substrates, was developed to ensure good wetting. The bending strength of single-tube specimens was determined at several temperatures. The dominant failure mode changed from fracture at room temperature to yielding of the glass and Kovar at 600/spl deg/C. The strength in tension at room temperature was analyzed using Weibull statistics; these results indicate a probability of survival of 0.99 at an operational pressure of 125 atm at room temperature for single tubes and a corresponding probability of 0.9 for a packaged device with 11 joints. The residual stresses were analyzed using the method of finite elements and recommendations for the improvement of packaging reliability are suggested
Characterization of wafer-level thermocompression bonds
No full textThermocompression bonding joins substrates via a bonding layer. In this paper, silicon substrates were bonded using gold thin films. Experimental data on the effects of bonding pressure (30 to 120 MPa), temperature (260 and 300/spl deg/C), and time (2 to 90 min) on the bond toughness, measured using the four-point bend technique, are presented. In general, higher temperature and pressure lead to higher toughness bonds. Considerable variation in toughness was observed across specimens. Possible causes of the nonuniform bond quality were explored using finite element analysis. Simulation results showed that the mask layout contributed to the pressure nonuniformity applied across the wafer. Finally, some process guidelines for successful wafer-level bonding using gold thin films are presented
Improving the contact resistance at low force using gold coated carbon nanotube surfaces
No full textInvestigations to determine the electrical contact performance
under repeated load cycles at low force conditions for carbonnanotube
(CNT) coated surfaces were performed. The surfaces
under investigation consisted of multi-walled CNT synthesized
on a silicon substrate and coated with a gold film. These planar
surfaces were mounted on the tip of a PZT cantilever and
contacted with a hemispherical Au plated probe. The dynamic
applied force used was 1mN. The contact resistance (Rc) of
these surfaces was investigated with the applied force and with
repeated loading cycles performed for stability testing. The
surfaces were compared with a reference Au-Au contact under
the same experimental conditions. This initial study shows the
potential for the application of gold coated CNT surfaces as an
interface in low force electrical contact applications
A piezoelectric microvalve for compact high frequency high differential pressure micropumping systems
No full textA piezoelectrically driven hydraulic amplification microvalve for use in compact high-performance hydraulic pumping systems was designed, fabricated, and experimentally characterized. High-frequency, high-force actuation capabilities were enabled through the incorporation of bulk piezoelectric material elements beneath a micromachined annular tethered-piston structure. Large valve stroke at the microscale was achieved with an hydraulic amplification mechanism that amplified (40/spl times/-50/spl times/) the limited stroke of the piezoelectric material into a significantly larger motion of a micromachined valve membrane with attached valve cap. These design features enabled the valve to meet simultaneously a set of high frequency (/spl ges/1 kHz), high pressure(/spl ges/300 kPa), and large stroke (20-30 /spl mu/m) requirements not previously satisfied by other hydraulic flow regulation microvalves. This paper details the design, modeling, fabrication, assembly, and experimental characterization of this valve device. Fabrication challenges are detailed
The influence of toughening-particles in CFRPs on low velocity impact damage resistance performance
No full textThe role of particle-toughening for increasing impact damage resistance in carbon fibre reinforced polymer (CFRP) composites was investigated. Five carbon fibre reinforced systems consisting of four particle-toughened matrices and one system containing no toughening particles were subjected to low velocity impacts ranging from 25 J to 50 J to establish the impact damage resistance of each material system. Synchrotron radiation computed tomography (SRCT) enabled a novel approach for damage assessment and quantification. Toughening mechanisms were detected in the particle-toughened systems consisting of particle–resin debonding, crack-deflection and crack-bridging. Quantification of the bridging behaviour, increase in crack path length and roughness was undertaken. Out of the three toughening mechanisms measured, particle systems exhibited a larger extent of bridging suggesting a significant contribution of this toughening mechanism compared to the system with no particle
Materials selection in micromechanical design: an application of the Ashby approach
No full textThe set of materials available to microsystems designers is rapidly expanding. Techniques now exist to introduce and integrate a large number of metals, alloys, ceramics, glasses, polymers, and elastomers into microsystems, motivating the need for a rational approach for materials selection in microsystems design. As a step toward such an approach, we focus on the initial stages of materials selection for micromechanical structures with minimum feature sizes greater than 1 /spl mu/m. The variation of mechanical properties with length scale and processing parameters is discussed. Bounds for initial design values of several properties are suggested and the necessity for the measurement of other properties (especially residual stresses and intrinsic loss coefficients) is discussed. Adapting the methods pioneered by Ashby et al., materials indices are formulated for a number of properties and materials selection charts are presented. These concepts are applied to illustrate initial materials selection for shock-resistant microbeams, force sensors, micromechanical filters, and micromachined flexures. Issues associated with the integration of materials into microsystems are briefly discussed
Gold coated carbon nanotube surfaces as low force electrical contacts for MEMS devices: part 1
No full textAn experimental investigation of a gold coated vertically aligned carbon nanotube surfaces is undertaken to determine the limits of the electrical contact performance over a large number of switching cycles under low force conditions and with current loading (1mA-50mA at 4V). The multi-walled CNT’s (MWCNT’s) are synthesized on a silicon planar and sputter coated with a gold film. The planar surfaces are mounted on the tip of a PZT actuator and mated with a coated Au hemispherical probe. The electrical load is selected to reflect typical MEMs relay loads with a 4V supply, 1 and 10mA current load with an applied force of 1mN. The surfaces tested maintain a stable contact resistance over 106 switching cycles. To determine the limits, the contact force is increased to 3mN under dry circuit conditions and the current increased at the 1mN load to 20mA-50mA. The surfaces are compared with a reference Au-Au contact under the same experimental conditions. For the surfaces investigated the current loading limit was determined to be 20mA where the contacts failed after 50x106 cycles
Low force electrical switching using gold coated vertically aligned multi-walled carbon nanotubes surfaces
No full textGold coated vertically aligned multi-walled carbon-nanotubes (Au/MWCNT) surfaces are investigated to determine the electrical contact performance under low force conditions with repeated load cycling. The multi-walled CNT's are synthesized on silicon planar and sputter coated with a gold film. These planar surfaces are mounted on the tip of a PZT actuator and mated with a coated Au hemispherical probe. The load is typical of MEMs devices, with a 4V supply, 1 and 10mA current, and applied force of 1mN. The contact resistance (Rc) is monitored with the repeated loading cycles (over 1000 and a million cycle) to determine reliability and durability testing. The surfaces are compared with a reference Au-Au contact under the same experimental conditions. This study shows the potential for the application of CNT surfaces as an interface in low force electrical contact applications
Materials Issues in MEMS
No full textMicroelectromechanical systems (MEMS) have recently become an important area of technology, building on the success of the microelectronics industry over the past 50 years. MEMS combine mechanical and electrical function in devices at very small scales. Examples include pressure sensors, accelerometers, gyroscopes and optical devices, as well as chemical, biomedical and fluidic applications. The status of MEMS technology is reviewed with particular emphasis on materials issues therein. The materials issues in MEMS are divided into three categories, the MEMS material set, microfabrication processes, and material characterization and design. Each of these areas is addressed, with particular emphasis on the potential impact of materials solutions. A discussion of the future of MEMS and the role of materials in that future is given
Fabrication of wafer-level thermocompression bonding
No full textThermocompression bonding of gold is a promising technique for achieving low temperature, wafer-level bonding. The fabrication process for wafer bonding at 300ºC via compressing gold under 7 MPa of pressure is described in detail. One of the issues encountered in the process development was e-beam source spitting, which resulted in micrometer diameter sized Au on the surfaces, and made bonding difficult. The problem was solved by inserting a tungsten liner to the graphite crucible. Surface segregation of Si on the Au surface at the bonding temperature was observed. Using Auger spectroscopy, a 1500 Å SiO2 barrier layer was shown to be sufficient in preventing Si from reaching the surface. Lastly, a four-point bend delamination technique was used to quantify the bond toughness. The associated process steps that were required to prepare the test specimens are described. The critical strain energy release rate for the bonds ranged between 22 to 67 J/m2 and was not shown to be strongly associated with the gold bond layer thickness in the thickness range studied (0.23 to 1.4 µm)
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