<title>Prototype detector for 6-keV x-rays using nine series arrays of tunnel junctions</title>

Abstract

We have fabricated a device consisting of nine arrays of series- connected superconducting aluminum tunnel junctions on a thin sapphire substrate, as a detector of 6-keV X-rays. Tunnel junctions are of interest as particle detectors because their theoretical minimum excitation energy is on the order of one milli-electron volt, a factor of one thousand lower than conventional semiconductor detectors. We have experimented with a new SiN passivation layer, intended to prevent further oxidation of the tunnel barrier on exposure to air. Preliminary tests with 200 angstrom thick SiN layers indicate improved stability of junction resistance on exposure to air. We will present results from a device with a 400 angstrom thick passivation layer. We will also report on tests of a detector without a SiN layer, where we observed coincident pulses between two of the nine arrays. The energy resolution for 6-keV X-rays is about 1 keV, limited by noise. If the signal size can be increased, pulse height and timing information from the nine separate arrays of this detector should allow simultaneous determination of position and energy.