Enhancement of Tc in MgB2 thin films by laser local annealing

Films of magnesium diboride are promising for superconducting electronic and for detector applications. One of the main obstacles for device fabrication by traditional lithography is the sensitivity of this material to the chemical solutions normally employed in the standard structuring process. Moreover, underetching often limits the patterns resolution. By focused laser beam, high temperature can be reached suddenly in areas of few micrometer square, therefore in principle MgB₂ film patterning is feasible by local laser modification. In this work we investigate the effect of laser processing on MgB₂ thin films deposited by in-situ method. Before the exposure to the laser, the strip was wirebonded to enable the resistance to be monitored during the experiment. Increasing the power from 0.1 to 1 Watt, the room temperature resistance of the stripline increased until reaching the open circuit for higher laser power. By optical inspection, we observed that the color of irradiated area changed from yellow to black. The structure defined by laser presented a periodicity of about 1.7 μm, where the width of each tracks was 1.5 μm, thus comparable to the laser spot size. The T_c of the strip was increased by the laser process. This technique open the possibility to pattern superconducting film for device fabrication and circuits.