Lionel F. Houlet

Catalyst Combustors with B-Doped SiGe/Au Thermopile for Micro-Power-Generation

A micromachined thermoelectric (TE) power generator with a ceramic catalyst combustor operating at room temperature (RT) has been developed. A thermopile of 20 thin-film couples of B-doped Si0.8Ge0.2/Au and a Pt-loaded alumina ceramic thick-film catalyst combustor were integrated on a thin dielectric membrane, which was fabricated by bulk-Si wet etching. We have demonstrated a successful power generation of 0.26 µW using the micro-TE-generator with a fuel gas flow of 3 vol. % H2 in air, 1000 ccm, at RT.

Boron-Doped Si0.8Ge0.2 Thin Film Deposited by Helicon Sputtering for Microthermoelectric Hydrogen Sensor

A boron-doped Si 0.8 Ge 0.2 2 thin film of 300 nm thickness was deposited by helicon sputtering. Thermal annealing was carried out to crystallize as-deposited amorphous-like Si 0.8 Ge 0.2 thin films. The thermoelectric properties of the films, such as an electrical conductivity, a carrier concentration, a mobility, and a Seebeck coefficient, were investigated. As a result, the films by helicon sputtering exhibited finer grains and smoother surface than those of the film deposited by conventional radio frequency (rf) sputtering. The film deposited by helicon sputtering with an rf induction coil power of 50 W and annealed at 1100°C for 5 h showed a resistivity of 0.011 Ω cm, a Seebeck coefficient of 0.13 mV/K, a Hall mobility of 9.92 cm 2 /V s, and a carrier concentration of 5.7 X 10 19 cm -3 at 100°C. A microthermoelectric hydrogen sensor (micro-THS) with the boron-doped Si 0.8 Ge 0.2 thin film and annealed at 1100°C for 5 h showed high sensitivity for hydrogen gas in air. This sensor could have wide detection range of hydrogen concentration from 1 ppm to 3%. At an operating temperature of 100°C, for the low hydrogen concentration of 5 ppm, clear response was shown by the micro-THS with the Si 0.8 Ge 0.2 film deposited by helicon sputtering and annealed at 1100°C for 5 h.

InAs/AlGaSb Piezoresistive Cantilever for Sub-Angstrom Scale Displacement Detection

We report on the fabrication and characterization of 0.3-µm-thick piezoresistive cantilevers based on the InAs/AlGaSb heterostructure. The dependence of the displacement resolution on the cantilever size, which ranges from 20×10 to 2×1 µm2, has been studied by a novel characterization method using an atomic force microscope. The results show that downscaling the cantilevers improves their performances, and an optimum resolution of 0.26 A/Hz0.5 was obtained with a 3×1.5 µm2 cantilever at a modulation frequency of 714 Hz. A finite-element simulator allowed the calculation of the resonance frequencies and a maximum value of 20.5 MHz was obtained for the 3×1.5 µm2 cantilever.

Safe membrane-releasing process for thermoelectric hydrogen gas sensor

We present here a safe membrane-releasing process in KOH for the fabrication of a high performance freestanding device and the mass production of a single membrane device for the hydrogen gas sensing application. The fabricated devices are thermoelectric hydrogen gas sensors based on the thermoelectric detection of the catalytic hydrogen combustion. The free-standing device has a voltage response 2.7 times higher than the single membrane device. The proposed membrane-releasing process, which combines black wax and a KOH protective polymer coat, shows fabrication yields of 31%, 50% for the free-standing device and 47% for the single-membrane device produced in mass.

Micro-Thermoelectric Hydrogen Sensor of Three Different Membrane Structures

We prepared micro-thermoelectric hydrogen sensors (micro-THSs) operating with a combination of the thermoelectric effect of SiGe thin film and Pt-catalyzed exothermic hydrogen oxidation of the catalyst. The membrane area of each sensor was heated by a micro heater. The responses of the micro-THSs with three different types of membranes to hydrogen in air were investigated. The micro-THS with a single membrane, which had a better thermal isolation than those of other membranes, reduced the power consumption of 251 mW and the time required to heat the membrane by 5 s. This micro-THS with a single membrane showed the optimal gas sensing property of voltage signal of 1.13 mV for 1% hydrogen in air with the low detection limit of 50 ppm.