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Register a new userModeling of graphene Hall effect sensors for microbead detection
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This paper deals with the modeling of sensitivity of epitaxial graphene Hall bars, from sub-micrometer to micrometer size, to the stray field generated by a magnetic microbead. To demonstrate experiment feasibility, the model is first validated by comparison to measurement results, considering an ac-dc detection scheme. Then, an exhaustive numerical analysis is performed to investigate signal detriment caused by material defects, saturation of bead magnetization at high fields, increment of bead distance from sensor surface and device width increase.
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We demonstrate a novel concept for operating graphene-based Hall sensors using an alternating current (AC) modulated gate voltage, which provides three important advantages compared to Hall sensors under static operation: 1) The sensor sensitivity can be doubled by utilizing both n- and p-type conductance. 2) A static magnetic field can be read out at frequencies in the kHz range, where the 1/f noise is lower compared to the static case. 3) The off-set voltage in the Hall signal can be reduced. This significantly increases the signal-to-noise ratio compared to Hall sensors without a gate electrode. A minimal detectable magnetic field Bmin down to 290 nT/sqrt(Hz) and sensitivity up to 0.55 V/VT was found for Hall sensors fabricated on flexible foil. This clearly outperforms state-of-the-art flexible Hall sensors and is comparable to the values obtained by the best rigid III/V semiconductor Hall sensors.
We present the concept of magnetic gas detection by the Extraordinary Hall effect (EHE). The technique is compatible with the existing conductometric gas detection technologies and allows simultaneous measurement of two independent parameters: resistivity and magnetization affected by the target gas. Feasibility of the approach is demonstrated by detecting low concentration hydrogen using thin CoPd films as the sensor material. The Hall effect sensitivity of the optimized samples exceeds 240% per 104 ppm at hydrogen concentrations below 0.5% in the hydrogen/nitrogen atmosphere, which is more than two orders of magnitude higher than the sensitivity of the conductance detection.
Since the first graphene layer was fabricated in the early 2000s, graphene properties have been studied extensively both experimentally and theoretically. However, when comparing the many resistivity models reported in literature, several discrepancies can be found, as well as a number of inconsistencies between formulas. In this paper, we revise the main scattering mechanisms in graphene, based on theory and goodness of fit to in-house experimental data. In particular, a step-by-step evaluation of the interaction between electrons and optical phonons is carried out, where we demonstrate that the process of optical phonon emission scattering is completely suppressed for all low-field applications and all temperatures in the range of interest, as opposed to what is often reported in literature. Finally, we identify the best scattering models based on the goodness of fit to experimental data.
We report on room temperature THz detection by means of antenna-coupled field effect transistors fabricated by using epitaxial graphene grown on silicon carbide substrate. Two independent detection mechanisms are found: plasma wave assisted-detection and thermoelectric effect, which is ascribed to the presence of junctions along the FET channel. The superposition of the calculated functional dependence of both the plasmonic and thermoelectric photovoltages on the gate bias qualitatively well reproduces the measured photovoltages. Additionally, the sign reversal of the measured photovoltage demonstrates the stronger contribution of the plasmonic detection compared to the thermoelectric mechanism. Although responsivity improvement is necessary, these results demonstrate that plasmonic detectors fabricated by epitaxial graphene on silicon carbide are potential candidates for fast large area imaging of macroscopic samples.
The high flexibility, impermeability and strength of graphene membranes are key properties that can enable the next generation of nanomechanical sensors. However, for capacitive pressure sensors the sensitivity offered by a single suspended graphene membrane is too small to compete with commercial sensors. Here, we realize highly sensitive capacitive pressure sensors consisting of arrays of nearly ten thousand small, freestanding double-layer graphene membranes. We fabricate large arrays of small diameter membranes using a procedure that maintains the superior material and mechanical properties of graphene, even after high-temperature anneals. These sensors are readout using a low cost battery-powered circuit board, with a responsivity of up to 47.8 aF Pa$^{-1}$ mm$^{-2}$, thereby outperforming commercial sensors.
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