Three technologies for a smart miniaturized gas-sensor: SOI CMOS, micromachining, and CNTs - challenges and performance

In this paper we propose a new type of solid-state gas sensor by combining three recent advances, namely silicon-on-insulator CMOS technology, through wafer etching and growth of gas-sensitive carbon nanotubes. We have developed novel tungsten-based CMOS micro-hotplates that offer ultra low power consumption (less than 10 mW at 250degC), on-chip CNT deposition at temperatures up to 700degC, and full integration of CMOS circuitry. Moreover, the tungsten micro-hotplates possess better stability than other CMOS materials such as polysilicon. The multi-walled CNT resistive gas sensors showed a good response to PPB levels of NO₂ in air but required additional heating to provide reasonable baseline recovery times. We believe that our approach is attractive for the mass production of low-cost, low-power gas sensors in silicon foundries.