  We report the fabrication and measurement of top gated epitaxial graphene p-n
junctions where exfoliated hexagonal boron nitride (h-BN) is used as the gate
dielectric. The four-terminal longitudinal resistance across a single junction
is well quantized at the von Klitzing constant R_K with a relative uncertainty
of 10-7. After the exploration of numerous parameter spaces, we summarize the
conditions upon which these devices could function as potential resistance
standards. Furthermore, we offer designs of programmable electrical resistance
standards over six orders of magnitude by using external gating.
