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(Color online) (a) Schematic of the device structure and experimental setup. (b) Optical micrograph showing two parallel devices. The doped contact regions (pink) and the metal electrodes can be clearly seen as well as the openings in the SU8 layer (passivation layer) atop the nanowires (NWs). An SEM image of a single nanowire is shown. (c) I-V curve for a NW device (after APTES functionalization) showing the drain current (Id) and solution gate leakage current (Isg).
(Color online) (a) Normalized current noise power density at f = 1 Hz is plotted against drain current. The noise profile does not change significantly with changes in PBS (phosphate buffered saline) concentration or by changing the electrolyte to KCl (potassium chloride). The proportionality to (gm/Id)2 confirms that our data are well fitted by the number fluctuation model. (b) Signal-to-noise ratio (as defined in text) is plotted against solution gate voltage to highlight the regime at which SNR is maximized. (c) Transconductance values extracted from I-V measurements are also plotted against solution gate voltage to point out that maximum SNR occurs close to the point of peak transconductance.
(Color online) The gate voltage noise fluctuations (√SV) are plotted against solution gate voltage (limited to the linear regime of operation). The absence of a linear dependence indicates that number fluctuations are the dominant cause of the noise of these bioFET devices. The dip in the data also highlights the region of maximum signal-to-noise ratio (1/√SV), which is again shown to occur around the region of peak transconductance.
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