Tc tuning of tungsten transition edge sensors using iron implantation

We have developed a technique for precisely tuning the transition temperature of superconducting tungsten (W) films used in Quasiparticle trap-assisted Electrothermal-feedback Transition edge sensors (QETs). We have demonstrated our technique using several 350 Angstrom-thick PI films with "as-deposited" transition temperatures in the range of similar to 90-150 mK. The accuracy 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 implantation method is highly reproducible and does not result in broadened transitions of the superconducting films. Our results represent an important breakthrough in the optimization of detectors used in the Cold Dark Matter Search (CDMS) experiments, where we prefer W phonon sensors with T-0 similar to 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.