|2.2 Qualification of vendors for delivery to ATLAS.
During the summer and fall of 1999 the ATLAS-SCT community was concluding its studies of prototype detectors for qualification of vendors for delivery to the project. Bergen and Oslo were involved in the studies of prototype detectors delivered by SINTEF. It was concluded that SINTEF is qualified as a vendor, and an open invitation to tender to supply the Nordic cluster with detectors for the construction of the innermost barrel was issued in October 1999. Results from prototype detectors on oxygenated material were not available at that time (and are still scarce), so the tender was for somewhat thinner detectors (260 mm instead of 285 mm) as thinner detectors operate at a slightly reduced depletion voltage at the expense of some loss of signal. Companies were also asked if they would deliver detectors on oxygenated material. Companies qualified for delivery were Eurosys/CiS (Germany), Hamamatsu (Japan), Micron (UK) and SINTEF (Norway).
2.3 The preseries detectors.
Based on price, SINTEF won the contract to deliver detectors for use in the innermost barrel of the SCT. The contract is organized in two steps: First a preseries of 5 % of the detectors should be delivered and accepted by us. If the detectors are found to satisfy specifications and the delivery is on time, order of series production of the remaining 95 % is done. The order is for a total of 1800 detectors, with a purchase option for 540 more detectors. Accounting for tests and breakage, the current best guess is that we will need a total of about 2000 detectors to deliver the required number of modules. The order is financed through a separate budget line, but all work and costs related to the tests and use of the detectors is the responsibility of this project. As oxygenation has been shown to be a very promising alternative, but was still not proven technology, the order was divided in two: half the detectors were produced on 285 µm oxygenated material, while the rest was produced on 260 µm standard material. This also provided the vendor with reasonable samples for yield studies.
By the end of July total of 80 detectors, out of 90 foreseen, were delivered by SINTEF. Of these, 16 have been irradiated to a fluence of 3x1014 protons. The remaining were evaluated in Bergen to check their quality. Nearly all have so far been found to comply with specification. Below we show a few examples of the tests performed: a) the quality of the 768 strips of a detectors, and b) distribution of currents measured at a bias of 150V. An extensive report on the results will appear soon.
Capacitance measurements of all 768 strips of a detector to determine strip quality. One can identify one broken strip, a hole in the coupling capacitance of a strip, and a quadruple short.
Distributions of leakage currents at 150V bias. Specification is that it should be below 6µA
The last figure above shows the I-V curves of detectors which have been irradiated to a fluence of 3x1014 protons/cm2 in the CERN PS. Data collected at a temperature of –18 degrees C. All detectors draw currents which are well below specification of a maximum of 0.25 mA, and there is no sign of breakdown at bias voltages well above 350V. Charge collection studies are by far the most difficult measurements to be done, but results from should appear within the next two months, to complete the study of the preseries detectors.
2.3 Sensor testing during production.
During production of the ATLAS silicon detectors the SCT University groups will have to continuously verify the quality of the delivered detectors (IV, CV, strip-quality, etc). A subsample of each batch of detectors will be irradiated and fully verified after irradiation. This program is crucial for maintaining good quality of the delivered components and to catch problems in the production lines not seen by the manufacturers. This quality assurance program is written into the contract with the manufacturers and allows us to terminate or pause the production if the detectors quality is not within pre and post-irradiation specifications. Inside the Scandinavian cluster UiB is responsible for this task.
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