Prototype MEMS Capacitive Pressure Sensor Design and Manufacturing.

This paper is intended to describe the design and manufacturing aspects of a simple micromachined capacitive pressure sensor working in the pressure range of 0-1000 mbar. 500 µm thick Borofloat® 33 glass and silicon wafers were used as substrates. The basic transducer structure consists of a rectangular silicon membrane as deformable electrode and a fix aluminum electrode formed on the glass surface. In order to determine the exact geometry of the silicon electrode structure numerical models and simulations were applied. The thin silicon membrane was fabricated by Si bulk micromachining, i.e. anisotropic alkaline etching with electrochemical etch-stop. The two wafers were bonded together at low temperature by anodic bonding. After bonding and dicing the wafers the pressure sensors were characterized mechanically and functionally also. Our results demonstrate the functional behavior of the manufactured sensor structures and provide excellent verification of the preliminary expectations based on theoretical calculations and electro-mechanical simulations

Micro-pellistor with integrated porous alumina catalyst support

Micro-pellistors capable to detect hydrocarbons below 50 mW power consumption at 550 degrees C operation temperature were developed by a novel processing technique. On the top of the full membrane type micro-heaters 1.4 mu m thick porous alumina was formed by laterally selective electrochemical etching of the deposited aluminum layer. The porous alumina of the active element is selectively covered by finely dispersed Pt catalyst using alternative methods; such as dropping of H-2[PtCl6] and sputtering technique, all aiming at deposition of controlled volume and structure of the catalyst. Constant current method in a Wheatstone-bridge configuration was applied in functional tests. (c) 2014 Published by Elsevier Ltd

Gas sensitivity enhancement of WO3 nano-rods by gold nanoparticles

AbstractTungsten oxide nano-rods were prepared by acidic precipitation from sodium tungstate solution and sensitized with gold nanoparticles prepared by Turkevich method from tetrachloroauric acid trihydrate. In order to prevent aggregation the gold nanoparticles of 18nm characteristic size were stabilized by methoxy-polyethylene glycol (mPEG-SH) and mixed with hexagonal WO3. Suspension drops of doped and non-doped WO3 were deposited on micro-hotplates with interdigitated gold electrodes to measure sensing layer conductivity. Sensor responses of pure and doped WO3 were measured for NH3 and H2S in synthetic air up to 100ppm at the operation temperature of 140-200°C. The presence of gold nanoparticles significantly increased the sensitivity for H2S, whereas for NH3 the response was not affected. Test results are compared in terms of sensitivity, response time and operating temperature

In-situ surface modification of microfluidic channels by integrated plasma source

In-situ modification of originally hydrophobic polymer surfaces by local plasma enhanced oxidation and its application in electrically controlled fluid capillary systems are demonstrated. A microfabricated coplanar dielectric barrier discharge (DBD) plasma source was developed [1, 2], integrated and applied to modify in-situ the surface properties of polydimethylsiloxane (PDMS) capillary channels. The local, immediate and successful setting of the wettability of the polymer microchannels is proved by development of effective water transport in the system subsequently the plasma treatment. The use of microfluidically integrated DBD microplasma system as switchable capillary pump is also presented. © 2014 Published by Elsevier Ltd

Effect of hexagonal WO3 morphology on NH3 sensing

Tungsten oxide nano - powders were prepared by acidic precipitation from so dium tungstate solution. The alternative processes of the applied hydrothermal method resulted in different structure and morphology of hexagonal WO 3 nano - crystals. Micro - hotplates wi th gold electrodes on top to measure sensing layer conductivity were fabricated. WO 3 layers of the two morphologies were depos ited using capillary dropping technique. Sensor responses were measured up to 22 0 °C operation temperature for NH 3 diluted in synthetic air in the 10 - 100 ppm range. Test results are compared in terms of conductivity, sensitivity and response time

Reliable aluminum contact formation by electrostatic bonding

The paper presents a detailed study of a reliable method developed for aluminum fusion wafer bonding assisted by the electrostatic force evolving during the anodic bonding process. The IC-compatible procedure described allows the parallel formation of electrical and mechanical contacts, facilitating a reliable packaging of electromechanical systems with backside electrical contacts. This fusion bonding method supports the fabrication of complex microelectromechanical systems (MEMS) and micro-opto-electromechanical systems (MOEMS) structures with enhanced temperature stability, which is crucial in mechanical sensor applications such as pressure or force sensors. Due to the applied electrical potential of  −1000 V the Al metal layers are compressed by electrostatic force, and at the bonding temperature of 450 °C intermetallic diffusion causes aluminum ions to migrate between metal layers

Fine-tuning of gas sensitivity by modification of nano-crystalline WO<inf>3</inf> layer morphology

Abstract The effect of WO3 nano-crystal characteristic size and layer morphology on gas sensitive properties was investigated in order to define the optimum preparation process. WO3 layers were synthesized by hydrothermal acidic precipitation method using different chemicals and reactive sputtering as reference. Micro-hotplate based conductivity type devices were fabricated and the sensitivity on NH3 up to 100 ppm was measured in the temperature range of 140-240°C. The measurements revealed that the characteristic size of the WO3 nano-crystal plays primary role, but layer morphology opens the way towards extended measuring range. The nano-rod structures operated at 220°C exhibit the best sensing characteristics in terms of sensitivity and stability over wide range of relative humidity. © 2015 Elsevier B.V

Bloch's conjecture and chow motives

Consiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7 Rome / CNR - Consiglio Nazionale delle RichercheSIGLEITItal