Distribution of Current in Closely Spaced Fine Metal Contacts Used in Graphene Hall Bar Devices

The future of resistance metrology will involve the development of quantum Hall array resistance standards (QHARS). At NIST, we have fabricated QHARS devices using monolayer graphene epitaxially grown on SiC. In order to develop next generation QHARS devices designed to specific resistance values, the arrays will need to be miniaturized to increase the density of devices on chip, and consequently will involve a high density of closely spaced split contacts. To better understand how current is distributed among closely spaced split contacts, we present our measurements of contacts spaced <10 um apart on graphene Hall bar devices, fabricated using a mixture of resist-residue-free photolithography and E-beam lithography, and measured using a Cryogenic Current Comparator with a DC SQUID as a current detector to enable ultra-high measurement sensitivity. We also present a comparison of our experimental data for closely packed contacts to published works on split contacts of larger scale Hall bar devices.