Development of a Sub-10-ppm Limit of Detection Lateral Nanogap Gas Sensor

This letter reports a wake-up gas sensor based on a lateral nanogap structure that is capable of increasing nanogap surface area by 11.2 times and thus improving the limit-of-detection (LOD) by 10 times down to 5 parts per million (ppm) in comparison with the previous vertical nanogap structure. Unlike the vertical nanogap structure with a suspended membrane, this lateral nanogap structure avoided fragile components and thus was able to reliably release a relatively large surface area of a 5-nm gap structure. The microfabricated lateral nanogap structure spanned over an enlarged area of 700 µm
²
, in comparison with the maximum area of 62.5
µ
m
²
in the previous vertical gap structure, with the highest surface-area-to-nanogap-size aspect ratio of 130 µm
²
/nm. When coated with a customized linker, it demonstrated (1) a gas sensing capability down to 5 ppm under the exposure of hexanal at a flow rate of 50 sccm, (2) a high wake-up
on
current of 460 nA, and (3) an
on/off
ratio of 1.51, which are sufficient for detection.