A QUASI-PARTICLE-TRAP-ASSISTED TRANSITION-EDGE SENSOR FOR PHONON-MEDIATED PARTICLE-DETECTION

We have demonstrated the operation of composite superconducting tungst en and aluminum transition-edge sensors which take advantage of quasip article trapping and electrothermal feedback. We call these devices W/ Al QETs (quasiparticle-trap-assisted electrothermal feedback transitio n-edge sensors). The quasiparticle trapping mechanism makes it possibl e to instrument large surface areas without increasing sensor heat cap acity, thus allowing larger absorbers and reducing phonon collection t imes. The sensor consists of a 30-nm-thick superconducting tungsten th in film with T-c similar to 80 mK deposited on a high-purity silicon s ubstrate. The W film is patterned into 200 parallel lines segments, ea ch 2 mu m wide and 800 mu m long. Eight superconducting aluminum thin him pads are electrically connected to each segment, and cover a much larger surface area than the W When phonons from particle interactions in the silicon crystal impinge on an aluminum pad, Cooper pairs are b roken, forming quasiparticles which diffuse to the tungsten lines wher e they are rapidly thermalized. The W film is voltage biased, and self -regulates in temperature-within its superconducting transition region by electrothermal feedback. Heat deposited in the film causes a curre nt pulse of similar to 100 mu s duration, which is measured with a ser ies array of de superconducting quantum interference devices. We have demonstrated an energy resolution of <350 eV full width at half-maximu m for 6 keV x rays incident on the backside of a 1 cmX1 cmX1 mm (0.25 g) silicon absorber, the highest resolution that has been reported for a fast (<1 ms pulse duration) calorimetric detector with an absorber mass>0.1 g. Applications of this technology include dark matter search es and neutrino detection. (C) 1995 American Institute of Physics.