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This paper reports the design and implementation of a wake-up gas sensor node, including both a low-power sensor and a wake-up electrical circuit that was particularly capable of utilizing the “on/off” characteristic of a previously reported nano-gap sensor to produce the needed output electrical power for alerting operations (e.g. LED lighting) under power budgets. The designed circuit, as predicted by a SPICE model, consumed 3.7mW of power for its “on” operation at an applied voltage of 1V, while only consuming ∼970nW during its “off” operation. The measured power for both operations enabled an average power consumption of $155.1\mu\mathrm{W}$ and depicted the wake-up functionality of the integrated gas sensor node for longterm battery-supported deployment. The integrated sensor node successfully demonstrated the lighting of an LED as an alarm signal, when exposed to a threshold concentration of 550 ppm of 1,5-diaminopentane gas.

This paper reports the successful demonstration of modulating the threshold point in gas concentrations at which a gas sensor turns “on/of” for wake-up operation by adjusting the tunneling areas of a nano-gap in the previously reported ultra-low-power gas sensor. The nano-gap area of the sensor determines the total binding sites and thus the total amounts of “on” tunneling-current at a given concentration. Since the total current amounts trigger wake-up, their increase per given concentration could enable a lower minimum detectable wake-up concentration. Experimental results confirmed that the increase in the nano-gap area from 6.5 to $62.5\ \mu \mathrm{m}^{2}$ by 861.5% enabled the reduction in the required wake-up gas concentrations from 250.0 to 50.0 ppm by 80.0%, showing an exponential decay trend. Such a reduction in the wakeup threshold allows the previously-reported sensor to achieve the required wake-up range of 200.0 ppm for early detection of diamine gases for health safety, while indicating the design feasibility to enable various wake-up concentrations for adjustable operation.

This paper reports a new proof-of-concept gas sensor based on statistical behavior of multiple gas molecules. The reported gas sensor, consisting of a tiny gap, provides on/off switching behavior as it captures the target gas molecules. The key innovation lies in the fact that such an off/off switching becomes statistically-reliable when multiple gaps and molecules are utilized. Such a statistics-based gas sensor was demonstrated by fabricating multiple nano-gap arrays, coating the gaps with specific chemistry linkers, and monitoring the reliability of the performance as well as other variables. The fabricated sensors in $1\mathrm{x}1,\ 5\mathrm{x}5$ and $9\mathrm{x}9$ arrays showed statistics-based trends of (1) increasing decisiveness (sharper on/off slopes vs. concentrations), (2) decreasing failures (increasing repeatability) and (3) lower off-switching speed. The fabricated sensors also resulted in (4) ultra-low power of $ due to normally-off operation.

This paper reports the detection of gas molecules with an identical functional group, but in different lengths due to varying numbers of CH 2 backbone units, by utilizing a nano-gap gas sensor. Significance of such a gas sensor lies on its ability to distinguish molecular lengths by down to 0.15nm in this testing. The fabricated nano-gap sensor, after being functionalized by a specific linker on the surface, successfully captured all three target gas molecules of 2-CH 2 -diamine (0.3nm), 3-CH 2 -diamine (0.45nm) and 5-CH 2 -diamine (0.75nm). The capture of each target molecules demonstrated significant differences in both resistance and capacitances, resulting in successful identification of 2-CH 2 -diamine (0.3nm), 3-CH 2 -diamine (0.45nm) and 5-CH 2 -diamine (0.75nm) by producing different on/off resistance ratios of 105, 2905 and 3832 and capacitance changes of 4.45pF, 16.21pF and 26.64pF, indicating the capability of identifying multiple gas molecules in different lengths despite identical functional groups.

This paper reports the development of a nano-gap vapor sensor that is capable of detecting an airborne target in a repeatable manner in near-zero static power consumption. The nano-gap sensor employed a matching gap distance of 5.8 nm to the lengths of both linkers and targets for selectivity. The nano-gap sensor was fabricated based on deposition and removal of a thin sacrificial layer via atomic-layer-deposition (ALD), and then coated with newly-synthesized linkers. The fabricated vapor sensor demonstrated the detection of a target gas (1, 5-Diaminopentane) or Cadaverine in a concentration of

Functionalized engineered nanogap electrodes (pair of electrodes separated by a gap of a few nanometers) are utilized as tunneling chemoresistors for gas sensing and resistance switching at the molecular scale. The nanogap device consists of two gold electrodes vertically separated by a very thin spacer of 2 nm of α-Si and ∼4 nm of dielectric (SiO 2 or Al 2 O 3 ). A ∼10 nm wide sidewall air gap is formed by etching the spacer along the edge of the electrodes followed by linker functionalization. After exposure to a gaseous chemical target (1,5-Diaminopentane), the target gas molecules adsorb onto the linker-coated surface bridging the two electrodes and establish an electrically conductive path. Preliminary electrical measurements indicate a nearly reversible decrease of electrical resistance between five to seven orders of magnitude when exposed to the target. The large change in resistance and the high value of resistance in air makes this device suitable as a candidate for a gas-triggered on-off switch with pW standby power consumption.