Investigation of design parameters and choice of substrate resistivity and crystal orientation for the CMS silicon microstrip detector

The electrical characteristics ( interstrip and backplane capacitance, leakage current, depletion and breakdown voltage) of silicon microstrip detectors were measured for strip pitches between 60 um and 240 um and various strip implant and metal widths on multi-geometry devices. Both AC and DC coupled devices wereinvestigated. Measurements on detectors were performed before and after irradiation with 24 GeV/c protons up to a fluence of 4.1x10E14 cm-2. We found that the total strip capacitance can be parametrized as a linear function of the ratio of the implant width over the read-out pitch only. We found a significant increase in the interstrip capacitance after radiation on detectors with standard <111> crystal orientation but not on sensors with <100> crystal orientation. We analyzed the measured depletion voltages as a function of the detector geometrical parameters ( read-out pitch, strip width and substrate thickness) found in the literature and we found a linear dependence in the case of non irradiated devices. After irradiation we found that the depletion voltages of high resistivity devices are always about 100 V higher than those of the low resistivity ones. From the measurement of the leakage current after exposure to radiation we determine the value of the damage constant after full beneficial annealing alpha_infinity ( 20 C)=( 3.2+/-0.4)x10E-17 A/cm. The high voltage stability of the detectors is significantly improved in the case where aluminum strips wider than the p+ implant are used.