Radiation damage effects and performance of silicon strip detectors using LHC readout electronics

Future high energy physics experiments as the ATLAS experiment at CERN, will use silicon strip detectors for fast and high precision tracking information. The high hadron fluencies in these experiments cause permanent damage in the silicon. Additional energy levels are introduced in the bandgap thus changing the electrical properties such as leakage current and full depletion voltage Vfd. Very high leakage currents are observed after irradiation and lead to higher electronic noise and thus decrease the spatial resolution. Vfd increases to a few hundred volts after irradiation and eventually beyond the point of stable operating voltages. Prototype detectors with either p-implanted strips (p-in-n) or n-implanted strips (n-in-n) were irradiated to the maximum expected fluency in ATLAS. The irradiation and the following study of the current and Vfd were carried out under ATLAS operational conditions. The evolution of Vfd after irradiation is compared to models based on diode irradiations. The qualitative behavior of Vfd as a function of time is well described by these models although quantitative differences are observed between the different detectors. For the first time an annealing study is carried out on full size detectors showing that compared to diodes additional effects have to be taken into account. These properties include surface effects, geometric effects and process parameters. Measurements of Vfd on irradiated detectors show a temperature and frequency dependence indicating an influence of deep radiation induced damage levels. The obtained value of Vfd after irradiation can no longer be regarded as an absolute value due to the temperature and frequency dependence. The leakage current after irradiation is dominated by bulk effects. Although currents from the edge regions are much smaller than from the active area, guard rings are necessary to allow stable operation at high voltages after irradiation. It is shown that full size detectors with optimized guard ring design allow stable operation up to more than 400 V after irradiation. Parameters influencing the guard ring performance before irradiation are illustrated on prototype detectors. In general no systematic difference between p-in-n and n-in-n detectors in leak age current, stability and the time dependence of Vfd is observed during this study. These results and the results from a test-beam with these detectors led to the change of the ATLAS detector baseline from n-in-n to p-in-n detectors. Non-irradiated and irradiated prototype detectors connected to fast analogue front-end electronics designed for LHC are tested with β-sources and in a pion-testbeam. They show full functionality even after irradiation to the maximum expected fluency in ATLAS. At Vfd the observed signal to noise ratio (S/N) has not saturated which is attributed to the ballistic deficit caused by change collection times in the order of the shaping time of the readout electronics. (author)