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Title: Characterisation of irradiated planar silicon strip sensors for HL-LHC applications
Author: Wonsak, Sven
ISNI:       0000 0004 6422 3609
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2016
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The upgrade of the Large Hadron Collider (LHC) to the High Luminosity LHC (HL-LHC) will increase the requirements on radiation hardness of silicon sensors of the two multi-purpose experiments, ATLAS and CMS, at CERN. For this purpose the CERN RD50 collaboration is investigating radiation hard semiconductor detectors for high luminosity applications. The work for this thesis was done within this framework. Charge multiplication can be beneficial in this context because the collected charge of irradiated devices decreases with increasing irradiation fluence. Thus the effect of different read-out strip pitch values and strip widths, as well as double implant energy or double diffusion time and intermediate strips, have been investigated for irradiated sensors. Intermediate strips have not shown any benefits, but sensors with a low width-over-pitch (W/P) ratio collect more charge then sensors with higher W/P values. This can be improved by doubling the implant energy. Annealing the sensors irradiated to 5 x 10¹⁵ neq/cm2 has shown that at bias voltages higher then 1000V the collected charge can increase with increasing annealing time. Measuring the collected charge of highly irradiated 50 μm thick sensors has been challenging because random noise peaks could be misidentified as signal due to the low signal value at fluences larger then 1 x 10¹⁶ neq/cm2. New analysis methods were tested and the use of a different fit function shows promising results. The measurement of the current of irradiated sensors with thicknesses from 50 μm to 298 μm has shown that the effective energy value has an upper limit, given by the literature value. For the current related damage rate of highly irradiated sensors the literature value describes an upper limit as well. The knowledge of these limits allows the design of large detector systems. A novel approach was tested to generate a multiplication layer close to the strip surface by irradiating sensors with low energy protons at the Birmingham irradiation facility. The target thickness of this multiplication layer is approximately 10 to 20 μm, but in the irradiations shown in this thesis this target has not been reached. However, the results have improved the knowledge of the irradiation facility and the simulation so that it should be possible to reach the expected thickness in a future irradiation.
Supervisor: Casse, G. ; Moll, M. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral