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In this paper, a thermal flow sensor consisting of two or three heated wires, the Microflown, is treated for application to acoustic measurements. It is sensitive to flow ('particle velocity'), contrary to conventional microphones that measure acoustic pressures. A numerical analysis, allowing for detailed parametric studies, is presented. The results are experimentally verified. Consequently, improved devices were fabricated, and also sensors with a new geometry consisting of three wires, instead of the usual two, of which the central wire is relatively most heated. These devices are the best performing Microflowns to date with a frequency range extending from 0 to over 5 kHz and a minimum detectable particle velocity level of about 70 nm/s at 2 to 5 kHz (i.e., 3 dB PVL or SPL, corresponding to a pressure of 3.1 * [10.sup.-5] Pa at a free field specific acoustic impedance). [1383]

A submicron thick and detect-free palladium-silver (Pd-Ag) alloy membrane is fabricated on a supporting microsieve by using microfabrication techniques. The microfabrication process also creates a robust wafer-scale membrane module, which can easily be inserted into a membrane holder to have gas-tight connections to the outer world. The microfabricated membrane demonstrated high separation fluxes of up to 4 mol [H.sub.2]/[m.sup.2] x s with a minimal selectivity of 1500 for hydrogen over helium ([H.sub.2]/He) at 450 [degrees]C and 83 kPa [H.sub.2] retentate pressure. The present membrane has great potential for hydrogen purification and in applications like dehydrogenation chemistry. In addition, the presented technology can be used to fabricate other kinds of ultrathin but strong and defect-free membranes to set up new applications. [1235] Index Terms--Hydrogen separation, membrane module, membrane reactor, microfabrication technology, Pd-Ag membrane, SiN microsieves, {110} wafers.

In this paper, a process for the microfabrication of a wafer-scale palladium-silver alloy membrane (Pd-Ag) is presented. Pd-Ag alloy films containing 23 wt% Ag were prepared by co-sputtering from pure Pd and Ag targets. The films were deposited on the unetched side of a -oriented silicon wafer in which deep grooves were etched in a concentrated KOH solution, leaving silicon membranes with a thickness of ca. 50 [micro]m. After alloy deposition, the silicon membranes were removed by etching, leaving Pd-Ag membranes. Anodic bonding of thick glass plates (containing powder blasted flow channels) to both sides of the silicon substrate was used to package the membranes and create a robust module. The hydrogen permeability of the Pd-Ag membranes was determined to be typically 0.5 mol [H.sub.2]/[m.sup.2] * s with a minimal selectivity of 550 for [H.sub.2] with respect to He. The mechanical strength of the membrane was found to be adequate, pressures of up to 4 bars at room temperature did not break the membrane. The results indicate that the membranes are suitable for application in hydrogen purification or in dehydrogenation reactors. The presented fabrication method allows the development of a module for industrial applications that consists of a stack of a large number of glass/membrane plates. [901] Index Terms-- wafers, co-sputtering membrane module, hydrogen separation, microfabrication technology, palladium-silver (Pd-Ag) membrane.

New methodologies in anisotropic wet-chemical etching of -oriented silicon, allowing useful process designs combined with smart mask-to-crystal-orientation-alignment are presented in this paper. The described methods yield smooth surfaces as well as high-quality plan-parallel beams and membranes. With a combination of pre-etching and wall passivation, structures can be etched at different depths in a wafer. Designs, using the -crystal orientation, supplemented with pictures of fabricated devices, demonstrate the potential of using -oriented wafers in microsystem design. [523] Index Terms--Bulk micromachining, etch technology, wafers, reactive ion etching, wet chemical etching.

Ever since its prediction, experimental investigation of the Casimir force has been of great scientific interest. Many research groups have successfully attempted quantifying the force with different device geometries; however, measurement of the Casimir force between parallel plates with sub-micron separation distance is still a challenging task, since it becomes extremely difficult to maintain sufficient parallelism between the plates. The Casimir force can significantly influence the operation of micro devices and to realize reliable and reproducible devices it is necessary to understand and experimentally verify the influence of the Casimir force at sub-micron scale. In this paper, we present the design principle, fabrication and characterization of micromachined parallel plate structures that could allow the measurement of the Casimir force with tunable separation distance in the range of 100 to 1000 nm. Initially, a gold coated parallel plate structure is explored to measure the Casimir force, but also other material combinations could be investigated. Using gold-silicon eutectic bonding, a reliable approach to bond chips with integrated suspended plates together with a well-defined separation distance in the order of 1--2 μm is developed. [ABSTRACT FROM AUTHOR]

Borofloat® (borosilicate 8330) glass is an important type of inorganic glass, both scientifically and commercially. During prolonged heat treatment of this glass above its glass transition temperature of 525°C, heterogeneous nucleation, and growth of cristobalite crystals occur. The kinetics and morphology of this crystal growth have been studied for heat treatment temperatures at and above 660°C. The activation energy for crystal growth is estimated to be 185±10 kJ/mol. This is attributed to the diffusion of boron, rather than sodium, being the rate-limiting step within the borosilicate framework. Contact with the atmosphere is shown to initiate the nucleation of cristobalite crystals, while deposition of a thin silicon nitride surface coating on the glass helps to prevent this nucleation. [ABSTRACT FROM AUTHOR]

A submicron thick and defect-free palladium-silver (Pd-Ag) alloy membrane is fabricated on a supporting microsieve by using microfabrication techniques. The microfabrication process also creates a robust wafer-scale membrane module, which can easily be inserted into a membrane holder to have gas-tight connections to the outer world. The microfabricated membrane demonstrated high separation fluxes of up to 4 mol 112/rn2 . s with a minimal selectivity of 1500 for hydrogen over helium (H2 /He) at 450 °C and 83 kPa 112 retentate pressure. The present membrane has great potential for hydrogen purification and in applications like dehydrogenation chemistry. In addition, the presented technology can be used to fabricate other kinds of ultrathin but strong and defect-free membranes to set up new applications. [1235] [ABSTRACT FROM AUTHOR]

In this paper, a process for the microfabrication of a wafer-scale palladium—silver alloy membrane (Pd-Ag) is presented. Pd-Ag alloy films containing 23 wt% Ag were prepared by co-sputtering from pure Pd and Ag targets. The films were deposited on the unetched side of a 〈110〉-oriented silicon wafer in which deep grooves were etched in a concentrated KOH solution, leaving silicon membranes with a thickness of ca. 50 µm. After alloy deposition, the silicon membranes were removed by etching, leaving Pd-Ag membranes. Anodic bonding of thick glass plates (containing powder blasted flow channels) to both sides of the silicon substrate was used to package the membranes and create a robust module. The hydrogen permeability of the Pd-Ag membranes was determined to be typically 0.5 mol H[sub 2]/m² · s with a minimal selectivity of 550 for H[sub 2] with respect to He. The mechanical strength of the membrane was found to be adequate, pressures of up to 4 bars at room temperature did not break the membrane. The results indicate that the membranes are suitable for application in hydrogen purification or in dehydrogenation reactors. The presented fabrication method allows the development of a module for industrial applications that consists of a stack of a large number of glass/membrane plates. [ABSTRACT FROM AUTHOR]