Programmable quantum Hall array resistance standards in epitaxial graphene devices*

The quantum Hall effect (QHE) provides an invariant reference for resistance related to the elementary charge e and Planck constant h, and the International System of Units (SI) unit of resistance has been redefined, thereby fixing the von Klitzing constant , to a constant value[1-3]. Graphene, due to its inherently two-dimensional structure and superior electrical properties, has a robust quantum Hall plateau at , where  is the filling factor, and has become an ideal material for developing quantum Hall resistance standards.

Based on a single Hall bar device with quantized resistance value (R_K/2~12.9 kΩ), many possible resistance values (m*R_K/2) can be obtained by connecting quantum Hall devices in parallel or in series connection [4]. So far, the nearly 1 kΩ and 1.29 MΩ quantum Hall resistance array standards have been tested [5,6] using Multi-terminal superconducting contacts are used for interceonnection and magnetotransport measurements [7].

In this work, epitaxial graphene is grown on a SiC substrate [8], and is functionalized with Cr(CO)₃ [9].  The quality of graphene is assessed by confocal laser scanning microscopy. To obtain various quantized resistances, we fabricated graphene Hall bar network devices using graphene as interconnections. We use top gate to manipulate graphene interconnections, and program the graphene array. Precision measurements are obtained with a DC current comparator and cryogenic current comparator.