Noise and spatial resolution in SQUID microscopy

We have used a scanning SQUID microscope to image magnetic field generated by currents in integrated circuits. To obtain current paths in these circuits, we apply a magnetic inversion technique to the magnetic field data. We find that the spatial resolution obtained from this technique is related to the signal-to-noise ratio, the SQUID-sample separation and the data sampling interval. We describe in detail a mathematical model of how these parameters relate to the spatial resolution. Finally, we discuss the limitations of our apparatus, and how to achieve higher spatial resolution.