Characterization of a Wake-Up Nano-Gap Gas Sensor for Ultra Low Power Operation

This paper reports the performance characterization of a wake-up nano-gap gas sensor with ultra-high-sensitivity due to its dependence on the electron tunneling distance that was experimentally modulated by a structural nano-gap, a chemistry linker length and a molecular size of target gases. The wake-up sensor became activated when the nano-gap was bridged for electron flow by the capture of specific target gas molecules. The fabricated nano-gap sensor demonstrated highly sensitive and selective responses to the dimensional variations in the gaps, the linkers and the target VOCs: (1) only 5-Å difference in either the nano-gap distance or the linker length produced the output signal ratios of two to five orders in magnitudes, indicating ultra-highly-sensitive characteristics; (2) only two carbon length difference of 2.3-Å between target gases with the identical functional group resulted in the output signal ratios of up to four orders in magnitudes, implying the unique distinguish capability of molecular-level length differences, and (3) the selectivity against 7 major interference gas groups in high concentrations (>1,000 ppm) was measured as at least by four orders in magnitude indicating the benefits of size-matching in gas detection on top of conventional chemistry-matching. The fabricated nano-gap gas sensor ultimately showed ultra-low power consumption of 20.08 pW during the sleep mode and repeatability of >10 cycles. These results indicated that the nano-gap sensor can be $a$ highly sensitive and selective alternative in gas sensing especially in resource-limited environments. [2022-0039]