[Show abstract][Hide abstract] ABSTRACT: In this study, the proposed sensor integrates a sensing layer, a heating device, and electrodes on the substrate. The micro heater is integrated in the sensor to provide instantaneous and precise temperature control capability. The electrodes are fabricated to connect resistance meter for measuring variation of electrical conductibility of the sensing layer. The grain size of the NiO thin film is almost to be nanometer level, and therefore both the sensitivity and the lowest sensing limit of the device are enhanced due to the enlarged area of the catalyst grains contacting with the surrounding gas. The experimental data show that decreasing thickness of sensing layer in the sputtering process significantly increases the sensitivities of the gas sensor and improves its lowest detection limit capability (0.7 ppm). Although we can further improve lowest detection limit by co-sputtering with NiO/Al2O3 (40 ppb), it needs to consider that selectivity will be reduced. The integrated micro heater simplifies the experimental set-up and can be realized using a simple fabrication process. The presented microfabricated formaldehyde gas sensor with a self-heating NiO/Al2O3 thin film is suitable not only for industrial process monitoring but for safeguarding the human health in buildings.
Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS, DTIP 2007, Stresa, lago Maggiore, Italy264-268. 01/2008;
[Show abstract][Hide abstract] ABSTRACT: The current study develops a new process for the fabrication of Pt resistor temperature detectors (RTD), cantilevers covered with a water-absorbent polyimide layer for humidity measurement and bending-up cantilevers to determining the wind velocity. Pt RTD's are fabricated on the silicon substrate. The temperature measurement is based on the linear resistance variations when temperature changes. The polyimide layer is spun on the cantilever to form a humidity sensing layer. A variation in humidity causes moisture-dependent bending of the microcantilever, which changes the measured resistance of the resistor on the microcantilever. The same type of microcantilever without spinning on polyimide is used to form an anemometer. It is found the cantilever slightly bends upward as a result of the released residual stress induced in the beam during the fabrication. When wind passes over the cantilever beam, a small deformation occurs. Variations in the wind velocity can therefore be determined by measuring the changes in resistance caused by the beam deflection using a LCR meter.
Symposium on Design, Test, Integration and Packaging of MEMS/MOEMS, DTIP 2007, Stresa, lago Maggiore, Italy69-73.
[Show abstract][Hide abstract] ABSTRACT: In realizing Lab-on-a-Chip systems, micro pumps play an essential role in manipulating small, precise volumes of solution
and driving them through the various components of the micro chip. The current study proposes a micro pump comprising four
major components, namely a lower glass substrate containing a copper micro coil, a microchannel, an upper glass cover plate,
and a PDMS-based magnetic diaphragm. A Co-Ni magnet is electroplated on the PDMS diaphragm with sufficient thickness to produce
a magnetic force of the intensity required to achieve the required diaphragm deflection. When a current is passed through
the micro coil, an electromagnetic force is established between the coil and the magnet on the diaphragm. The resulting deflection
of the PDMS diaphragm creates an acoustic impedance mismatch within the microchannel, which results in a net flow. The performance
of the micro pump is characterized experimentally. A deflection of 30 ìm is obtained by supplying the micro coil with an input
current of 0.6A, and results in a flow rate of 1.5 μl/sec when the PDMS membrane is driven by an actuating frequency of 240