Dynamic Range Enhancement Using the Electrostatically Formed Nanowire Sensor

Abstract

The evolution of nanotechnology based sensors has enabled detection of ultra-low-level concentrations of target species owing to their high aspect ratio. However, these sensors have a limited dynamic range at room temperature characterized by saturation in the sensor response following certain concentration exposure. In this work, we show that the dynamic range towards a target gas can be significantly enhanced using the electrostatically formed nanowire sensor. The size and shape of the nanowire conducting channel are defined and tuned by controlling the bias applied to the surrounding gates. The nanowires thus formed vary in their response, detection limit, and dynamic range for a given target gas exposure depending on its size and shape. By electrostatically tuning to the appropriate nanowire, we can not only enhance the sensor response in the low concentration regime, but also broaden the overall dynamic range capacity using a single sensor. It is demonstrated that the sensor is capable of detecting ∼26–2030 ppm ethanol and ∼40–2800 ppm of acetone efficiently with reasonably high response (≥20%) throughout the whole range. The broad dynamic range concept is also demonstrated using scanning gate microscopy measurements of the device. This represents the first nanotechnology-inspired work towards tunable dynamic range of a sensor using a single electronic device.

The Electrostatically Formed Nanowire: A Novel Platform for Gas-Sensing Applications

“…The transistor characteristics (I DS vs drain-source voltage, V DS ) of an n-type EFN device are shown in Figure 3a for a range of junction gate voltages [35]. It is easy to see that I DS decreases as V JG becomes more negative.…”

“…We define the sensor response as the change in I DS upon the introduction of the target molecule in the following manner: ΔI/I 0 = (I 0 − I f )/I 0 , where I 0 = I DS in a nitrogen environment prior to exposure, and I f = I DS after exposing the EFN to the target molecule. The below reviews the basic sensing performance of the EFN gas sensor by using the target molecule ethanol [35] (a performance similar to that of ethanol was also demonstrated for acetone [35]). Ethanol adsorbs on the silanol (Si–OH) groups of SiO 2 by hydrogen bonding [37,38,39], and it is also likely to adsorb by weakly bonding to the siloxane (Si–O–Si) sites under exposure to a high ethanol concentration [37].…”

“…Typically, the high end of the dynamic range is limited by the saturation effects of the sensor response. The ability to electrostatically manipulate the EFN response toward a given concentration of the target molecule directly leads to the large dynamic range of the sensor [35]. This is evident in Figure 4d; the EFN is most sensitive to low concentrations, with V JG = −0.8 V (diameter of 29 nm), but the EFN response saturates above ~1000 ppm.…”

“…Note that the critical dimension (650 nm) is the distance between the two metallurgical PN junctions on both sides of the conducting channel. ( b ) is reprinted with permission from [35]. Copyright 2016 American Chemical Society.…”

“…V BG was maintained at 0 V; ( e ) the EFN diameter in the axial direction along the nanowire was extracted from the measured CPD profile at V JG12 = 0 V. In both ( d ) and ( e ), V JG12 = V JG . ( a , b ) are reprinted with permission from [35]. Copyright 2016 American Chemical Society.…”