OPTIMIZATION OF SUPERCONDUCTING TUNNEL JUNCTION BASED X-RAY-DETECTORS

Current research into x-ray detection using superconducting tunnel jun ctions indicates that the poor spectral resolution obtained so far, in comparison with theoretical expectations, is partly due to the excell ent acoustic coupling of the junction and substrate. The substrate act s both as a source of noise and as a heat sink for the nonequilibrium junction, thus masking the intrinsic response of the superconducting e lectrodes to photoexcitation. A new design for a superconducting tunne l junction based on an x-ray detector is presented. The design effecti vely decouples the substrate and junction and should therefore elimina te many causes of spectral degradation, bringing resolution closer to that predicted theoretically, and thus allowing experimental investiga tion of the intrinsic superconducting film response to x-ray photoexci tation. An outline of the way in which the design can be optimized geo metrically to achieve the decoupling is given. Further optimization of the intrinsic film response to x-ray photons is achieved through the introduction of specific absorbing and trapping regions to improve bot h the quantum efficiency and charge output of the new design. The use of ''pairing potential barriers'' within the electrode leads will also improve the intrinsic resolution of this device.