Improving the stability and reproducibility of the carbon nanotube gas ionization sensor by Co–Ti/Ti co-deposited catalyst layer

•We used co-depostied layer to grow CNTs as the cathode of the gas ionization sensor.•Such a GIS exhibited high stability and reproducibility for gas detection.•Such a GIS exhibited high sensitivity and selectivity for gas detection.•Such a GIS exhibited the good linearity for detecting the gas mixture. A novel gas ionization sensor (GIS) of the carbon nanotube (CNT) film using the Co–Ti/Ti co-deposited catalyst layer had been proposed for the first time to exhibit higher stability and better reproducibility with respect to the CNT film ones with the single catalyst layer. For the proposed CNT GIS, the variation of the breakdown voltage (Vbr) was less than 25% for the ten devices with the same structure measurement since the lengths of the CNT synthesized were uniform and aligned. Besides, the fluctuation of the Vbr was about 14% during 1000 operation times in nitrogen at the pressure of 0.035Torr. It was attributed to the adhesion between CNTs and the substrate could be improved since the co-deposited catalyst layer and Ti adhesion layer would be coalesced so that the Co nanoparticles would be partially immersed into Ti layer after hydrogen pretreatment. Such a CNT GIS with the co-deposited catalyst layer also exhibited high sensitivity and selectivity for different kinds of gases detection as well as the good linearity for detecting the gas mixture.