HTS scanning SQUID microscopy of active circuits

We have used a high-T(c) scanning SQUID microscope to image semiconductor circuits operating in air at room temperature. Our microscope uses a commercially available 77 K refrigerator to cool a YBa(2)Cu(3)O(7-delta) de SQUID. The system maintains vacuum isolation of the SQUID even when it is separated from a room-temperature sample by about 30 mu m. When operated in this manner, the SQUID has a magnetic field sensitivity of 20 pT/root Hz above 500 Hz. By inverting the magnetic field images to generate two-dimensional current density distributions, we localize current paths to within +/-36 mu m at SQUID-sample separations of 150 mu m, We present images and discuss the spatial resolution obtained with this technique.