Enhanced Ionic Sensitivity in Solution‐Gated Graphene‐Hexagonal Boron Nitride Heterostructure Field‐Effect Transistors

Abstract

surface optical phonons. [14] As a dielectric interface, SiO 2 limits carrier mobility, and increases current-voltage hysteresis. [13,15] With a wide band gap (5.97 eV) and layered hexagonal Bernal structure (1.7% lattice mismatch to graphene) with dangling bond-free chemically inert surface, hexagonal boron nitride (hBN) is a near-ideal dielectric interface to graphene. The goal of this study is to investigate the graphene ISFET characteristics changed by introducing hBN under graphene. Incorporation of hBN as a dielectric in metal-gated graphene transistors has been shown to enhance performance by an order magnitude in terms of device mobility, reduced carrier inhomogeneity, lower extrinsic doping concentration, reduced chemical reactivity, and improved high-bias performance compared to devices fabricated with SiO 2 under graphene. [13,16] This has been attributed to increased flatness of graphene and opening of a band gap. Graphene has been shown to conform more to hBN than thermally grown amorphous SiO 2.[16e,17] This increased flatness aids charge homogeneity compared to the charge puddles on the order of 10 nm with 10 11 cm −2 charge variation that have been reported with SiO 2 device. [13,18] Unlike graphene on SiO 2 , using hBN, a new set of Dirac points is opened in the valence and conduction bands at the energy where the periodic potential connects the k and -k bands. [16e] The use of lowest-energy lattice configuration model shows a band gap of 50 meV is opened in graphene when on hBN. [19] Further, it has been shown that the presence of hBN can aid in heat spreading in field-effect transistors (FET) device geometries, thus reducing operating temperature. [20] In this paper, we report the differences in performance of solution-gated graphene ISFETs using thermal SiO 2 and polycrystalline chemical vapor deposition (CVD) hBN as the substrate for graphene, which here onwards are referred to as SiO 2 and hBN devices, respectively. Using solutions of varying concentrations of KCl and CaCl 2 , we characterize the changes in transfer curves for each of the devices in terms of Dirac voltage, transconductance, charge carrier concentration, and mobility. Results and DiscussionFigure 1a-c shows details of the device layout and setup for characterization. Further details have been included in the Experimental Section. Graphene and hBN were characterizedThe charge transport in solution-gated graphene devices is affected by the impurities and disorder of the underlying dielectric interface and its interaction with the solution. Advancement in field-effect ion sensing by fabricating a dielectric isomorph, hexagonal boron nitride between graphene and silicon dioxide of a solution-gated graphene field-effect transistor is being reported. Ionic sensitivity of Dirac voltage as high as −198 mV per decade for K + and −110 mV per decade for Ca 2+ is recorded. Increased transconductance due to increased charge carrier mobility is accompanied with larger ionic sensitivity of the transconductance due to larger ionic sensi...

Graphene‐Based Electronic Immunosensor with Femtomolar Detection Limit in Whole Serum

“…These discrepancies among reported works are likely attributable to differences in the device's design, composition, and manufacturing-highlighting the importance of the standardization of these processes for graphene-based sensors. [61,62] For the present device, however, the characteristic V g,min shifts and the asymmetric mobility changes suggest that modulation of scattering by charged impurities significantly contribute to the charge transport, similar to what was previously reported. [26,63] Although contributions from other effects cannot be fully discounted and further work is still needed to fully elucidate the detection mechanism/s, [64] it is clear that the electronic signal generated from the device can be used for quantitative protein measurements, making this graphene-based immunosensor suitable for future diagnostic applications.…”

“…Table 1 lists some representative works showing that the same type of analyte could induce different electronic responses from graphene. These discrepancies among reported works are likely attributable to differences in the device's design, composition, and manufacturing—highlighting the importance of the standardization of these processes for graphene‐based sensors . For the present device, however, the characteristic V g,min shifts and the asymmetric mobility changes suggest that modulation of scattering by charged impurities significantly contribute to the charge transport, similar to what was previously reported .…”

Two-Dimensional Materials in Biosensing and Healthcare: FromIn VitroDiagnostics to Optogenetics and Beyond

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Extended Gate Ion-Sensitive Field-Effect Transistors Using Al2O3/Hexagonal Boron Nitride Nanolayers for pH Sensing

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