A superconducting strip for fast pulse detection in high-energy physics

Results of preliminary tests on a prototype superconducting thin-film detector for tracking in high-radiation environments are reported. The detector consists of a 0.36-μm-thick niobium nitride (NbN) film, sputtered on a 1-mm sapphire substrate and etched out by photolithography for a 4-μm width by a 2-mm length. Its characteristics are: p≈100 μΩ-cm, J_c≈2×10⁶ A/cm², and T_c ≈14 K. The fact that the strip is sensitive to particles can be seen in the lowering, for the same temperature, of the DC current. Such a current as a function of temperature with and without the source has been measured. As soon as the switching to the normal state was detected by a DC voltage measurement, the current was set to 0 in about 100 ns and restored slowly after 300 μs. In this way, the effect of the source can clearly be observed. The curves with and without source are reported. Unsuitable contact conditions in the set up appear in the curve, but their effect is well below that expected from the source. The nature of the very fast signals detected during irradiation with a beta source are briefly discussed in terms of an energy balance model