Heat dissipation from suspended self-heated nanowires: gas sensor prospective

The strong temperature dependence of the electrical conductivity in semiconductors was employed for gas and pressure sensing with a self-heated Si nanowire resistor. The electrical conductivity in such a device depends on heat dissipation and partitioning inside the device and was studied comparatively for suspended and supported device architectures. The appearance of the exhaustion region in the temperature-dependent resistivity of a Joule-heated nanowire was used as a temperature marker for implementation of the quasi-constant temperature operation mode. At low pressures, the sensor is idle due to dominant heat dissipation from the nanowire to the substrate and/or electrodes. Above ca. 10 Torr the sensitivity to gases has a strong dependence on pressure as well as on the type of gas and is determined by conductive heat transfer between the nanowire surface and ambient. This implies that, in contrast to macroscopic devices, the heat dissipation via the convection mechanism does not contribute significantly to the heat transfer from the self-heated nanowire. The thermal sensitivity of the sensor to reactive gases depends on the effectiveness of the particular endothermic/exothermic reaction at the surface of the nanowire and was explored for the case of acetone-air mixture. The strong coupling of the electrical and thermal properties in the individual Joule-heated semiconducting nanowire allows fabrication of power-efficient multi-parametric nanoscopic gas/pressure sensors that are analogs of Pirani and pellistor type detectors.