We study performance of Hall sensors with the width range from 0.5 to 20.0 µm fabricated out of a monolayer graphene epitaxially grown on SiC.

Room temperature field dependence of the DC Hall voltage, VH, for a 1-μm cross.

The sensors have been studied at room temperature using transport and noise spectrum measurements. The minimum detectable field of a typical 10-µm graphene sensor is ≈ 2.5 µT/√Hz (Fig 1), making them comparable with state-of-the-art semiconductor devices of the same size and carrier concentration and superior to devices made of CVD graphene.

Fig 1: Size dependence of the minimum detectable field, determined from noise measurements at f = 3.3 kHz with devices biased at Ibias = 10 µA. Lines are guides for the eye only.

Relatively high resistance significantly restricts performance of the smallest 500-nm devices. We show that the carrier mobility is strongly size dependent (Fig 2), signifying importance of both intrinsic and extrinsic factors in the optimization of the device performance.

Fig 2: Dependence of the inverse carrier density, 1/n, on the carrier mobility. The group of data points in red (smaller) circle are measurement for 0.5-µm devices and the points in black (larger) circle are for 1 to 20 µm devices.

We also detected the stray field of a 1-µm Dynal bead with the magnetic moment of ~4×10⁸ μ_B by placing it on a 2-µm device using a nanomanipulator inside of a focused ion beam system (Fig 3).

Fig 3: Scanning electron micrograph showing 1-µm Dynal bead on cross 1 of the 2-µm graphene device. C1, C2 and C3 represent crosses 1, 2 and 3, respectively.

Using a phase sensitive AC-DC Hall magnetometry method, we reliably detected the bead with a relatively large response of the Hall voltage ~ 7 μV (Fig 4).

Fig 4: In-phase component of the AC Hall voltage in response to B_DC = 250 mT steps, 30 seconds in duration, at bias current = 50 μA.

References

1. Epitaxial Graphene Sensors for Detection of Small Magnetic Moments
   V. Panchal, D. Cox, R. Yakimova, and O. Kazakova
   IEEE Trans. Magn., Vol 49, No 1, pp 97–100 (2013).
2. Small Epitaxial Graphene Devices for Magnetosensing Applications
   V. Panchal, K. Cedergren, R. Yakimova, A. Tzalenchuk, S. Kubatkin, and O. Kazakova
   J. Appl. Phys., 111, 07E509 (2012).