T-c tuning of tungsten transition edge sensors using iron implantation

We have developed a technique for precisely tuning the transition temperatu re of superconducting tungsten (W) films used in Quasiparticle trap-assiste d Electrothermal-feedback Transition edge sensors (QETs). We have demonstra ted our technique using several 350 Angstrom-thick PI films with "as-deposi ted" transition temperatures in the range of similar to 90-150 mK. The accu racy of our tuning process is excellent, and T-c suppressions of prescribed amounts ranging From a few mK to 100 mK have been demonstrated. Our implan tation method is highly reproducible and does not result in broadened trans itions of the superconducting films. Our results represent an important bre akthrough in the optimization of detectors used in the Cold Dark Matter Sea rch (CDMS) experiments, where we prefer W phonon sensors with T-0 similar t o 65 mK. In this paper, we describe in detail our T-c tuning technique and we present results from characterization experiments performed with the T-c - adjusted films. (C) 2000 Elsevier Science B.V. All rights reserved.