Irradiation effects on silicon microstrips detectors

For some CERN LHC experiments, silicon microstrip sensors will be positioned very close to the particle collision region to provide good resolution in the condition of high-density particle tracks. Therefore these sensors are required to operate in a high particles flux. The high rate of primary strong interactions will lead to important production of secondary particles which, interacting with the existing detector structures will produce a high isotropic neutron albedo, filling the entire tracking cavity. In such conditions, the radiation damage becomes important for all detection elements and represents a key issue for the design of such devices. In order to obtain radiation hard materials for detection systems, studies have been devoted to the changes induced by exposure to apropriate charged particles and neutrons beams. In our work, silicon test structures with different bulk resistivities have been irradiated in order to evaluate the radiation damage in the detector substrates. They were irradiated with neutrons from different facilities at several fluences, covering the maximum value expected after 10 years of LHC running (1.6x1014 n/cm2, expressed in 1 MeV neutron equivalent fluence). Measurements of the leakage current and capacitance have been performed. Comparison of the I-V and C-V characteristics before and after irradiation revealed negligible differences for the less irradiated structures. For the heavily irradiated structures, an increase in the leakage current per unit volume was detected, proportional to the fluence received. The changes that can influence some parameters such as the initial bulk resistivity, important for the good long-term functionality, were studied (and are shown in a diagram in the abstract) and the effective doping concentration changes were determined