L00 Prototype Detectors

L00 Prototype Detector

We received 2 detectors from Micron on March 29th.

Serial numbers:

  • MSL: 1721-24 T=299 microns
  • MSL: 1721-3 T=301 microns

    Our initial comments are detailed below:

  • Optical Examination:

    Both detectors were observed to have no continuity of the metal above the readout strips showing one of the main technological challenges of working with very narrow features. The attached pictures show the sensitivity of using narrow metal lines to over-etching and also the effects to be expected from misalignment, given the quoted tolerances of the manufacturer.

  • Leakage currents

    As we have reported to CDF and is availble on the web , our ATLAS detectors typically show 30-120 nA/cm^2 for Micron detectors from the <100> 6" processing at 1000V with the corresponding figure for Hamamatsu <111> 4" detectors being 3nA/cm^2 (11 out of 14 detectors) at 1000V.

    For the L00 CDF prototypes sent from Micron the quoted value at 1000V corresponds to 200nA/cm^2 (<111> 6" processing) and, in fact, our measured values are 50% higher than those quoted for these devices by the company. It would be interesting to know if the differences seen between the ATLAS results and the L00 devices are partly due to the very high fields associated with very narrow implants.

  • Capacitance Values

    Given the lack of metal over the strips, we could not carry out the conventional measurement of the interstrip capacitance and our results are based on the rather delicate technique of probing through the contact holes to the implant. We have, however, been able to determine what are probably lower limits on the nearest plus further neighbour interstrip capacitances of 0.8pF/cm, which added to the 0.18pF/cm backplane capacitance gives the ~1pF/cm expected from the usual parameterisation for a very low width/pitch. For double the width using that parameterisation one would expect an interstrip capacitance of 1.2 pF/cm, which only contributes at most an extra 3pF for 15 cm detectors (an extra 200 ENC).

    A further issue which may relate to narrow implants is the diffences seen between ATLAS and CMS detectors after irradiation. The very high interstrip capacitances seen below depletion are not reported by ATLAS and although these may be ameliorated by using <100>, the effect seen by ATLAS even for <111> 4" wafers from Hamamatsu is only 10% higher at well below depletion as long as high frequencies are considered (as is borne out by noise studies with voltage with LHC speed electronics).

  • Final comments on detectors

    Once we have agreed on the detector specification (50 microns with intermediary strips seems OK by us) i.e. length and width, we would like to start negotiations with Hamamatsu for delivery of final detectors for at least part of L00.

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