  The continuous scaling of semiconductor-based technologies to micron and
sub-micron regimes has resulted in higher device density and lower power
dissipation. Many physical phenomena such as self-heating or current leakage
become significant at such scales, and mapping current densities to reveal
these features is decisive for the development of modern electronics. However,
advanced non-invasive technologies either offer low sensitivity or poor spatial
resolution and are limited to two-dimensional spatial mapping. Here we use
near-surface nitrogen-vacancy centres in diamond to probe Oersted fields
created by current flowing within a multi-layered integrated circuit in
pre-development. We show the reconstruction of the three-dimensional components
of the current density with a magnitude down to about $\approx 10 \,\rm \mu A /
\mu m^2$ and sub-micron spatial resolution at room temperature. We also report
the localisation of currents in different layers and observe anomalous current
flow in an electronic chip. Our method provides, therefore a decisive step
toward three-dimensional current mapping in technologically relevant nanoscale
electronics chips.
