Optical links are used for the readout of the 4088 silicon microstrip modules that make up the SemiConductor Tracker of the ATLAS experiment at the CERN Large Hadron Collider (LHC). The optical link requirements are reviewed, with particular emphasis on the very demanding environment at the LHC. The on-detector components have to operate in high radiation levels for 10 years, with no maintenance, and there are very strict requirements on power consumption, material and space. A novel concept for the packaging of the on-detector optoelectronics has been developed to meet these requirements. The system architecture, including its redundancy features, is explained and the critical on-detector components are described. The results of the extensive Quality Assurance performed during all steps of the assembly are discussed.

In previous research, epitaxial Si PIN photodiodes produced by Centronic which will be used in the ATLAS semiconductor tracker have been irradiated with 1MeV neutrons and 24GeV protons with fluences up to an equivalent of 10151MeV neutrons [1,2]. In this work 30MeV proton beams were used to irradiate Centronic and Truelight epitaxial Si PIN diodes with accumulated fluences of up to 2.1×1014–30MeVpcm−2, an equivalent of 5.7×1014cm−2 1MeV neutrons, to reach the pixel radiation environment. The responsivity was measured with different levels of fluence in order to study the responsivity behaviour of two different types of photodiodes. The responsivity behaviour of these two photodiodes was similar: a linear degradation at large fluences, >1014 30MeVpcm−2, but with different slopes. The response of the Centronic PIN diode showed a degradation to 73% after a proton fluence of 1013pcm−2 of 30MeV and a linear degradation at a rate of −0.32% per 1013pcm−2 for fluences larger than 1013 30MeVpcm−2. The Truelight PIN degraded to 84% after a fluence of 1013 p cm−2, with a linear degradation rate of –1.8% per 1013pcm−2. Annealing of both photodiodes with a bias voltage of –10V for 180h showed a 7% recovery for the Truelight PIN diode and a 2% recovery for the Centronic PIN diode after irradiation fluences of 2.1×1014pcm−2. A gamma source was also used to irradiate 6 Truelight PIN diodes with a total dose larger than 600kGy; no obvious responsivity change was observed in this case.

The design and technology of the silicon strip detector modules for the Semiconductor Tracker (SCT) of the ATLAS experiment have been finalised in the last several years. Integral to this process has been the measurement and verification of the tracking performance of the different module types in test beams at the CERN SPS and the KEK PS. Tests have been performed to explore the module performance under various operating conditions including detector bias voltage, magnetic field, incidence angle, and state of irradiation up to 3×1014 protons per square centimetre. A particular emphasis has been the understanding of the operational consequences of the binary readout scheme.

Studies have been performed on the radiation hardness of the type of VCSELs(2) that will be used in the ATLAS SemicConductor Tracker. The measurements were made using 30 MeV proton beams, 24 GeV/c proton beams and a gamma source. The lifetime of the devices after irradiation was studied. (C) 2002 Elsevier Science B.V. All rights reserved.