Design optimisation of silicon microstrip detector modules for operation in high radiation levels at the LHC

The Large Hadron Collider (LHC) operation conditions amount to considerable challenges in track and vertex detector design, which is driven by many conflicting requirements. The high luminosity, 1034 cm−2 s−1, planned for the 10 years of LHC operation are at the expenses of a particle interaction rate of ∼109 Hz and, hence, high total hadron radiation fluences, about 2×1014 neq/cm2. Such a luminosity is achieved using a bunch–bunch crossing frequency of 40 MHz that will require very fast and low noise signal processing, in order to separate signals from different bunch crossings, very long on-detector buffers to keep the data during the trigger latency together with fast and reliable data links for the off-detector data transmission. Since radiation effects are strongly temperature dependent, the thermal properties of the devices will drive severely the design options. This, together with the stringent requirements set by the expected performance of the LHC trackers translates into constraints on the mechanical precision and stability. Last but not least, access for maintenance and repair will be very restricted and, since radiation damage is severe, redundancy is another key point in the design. This paper describes the design options chosen for the ATLAS Semiconductor Tracker (SCT) modules and will show results on their performance.