Design and tests of the silicon sensors for the ZEUS micro vertex detector

Abstract

To fully exploit the HERA-II upgrade, the ZEUS experiment has installed a Micro Vertex Detector (MVD) using n-type, single-sided, silicon μ-strip sensors with capacitive charge division. The sensors have a readout pitch of 120 μm , with five intermediate strips ( 20 μm strip pitch). The designs of the silicon sensors and of the test structures used to verify the technological parameters, are presented. Results on the electrical measurements are discussed. A total of 1123 sensors with three different geometries have been produced by Hamamatsu Photonics K.K. Irradiation tests with reactor neutrons and 60 Co photons have been performed for a small sample of sensors. The results on neutron irradiation (with a fluence of 1×10 13 1 MeV equivalent neutrons/cm 2) are well described by empirical formulae for bulk damage. The 60 Co photons (with doses up to 2.9 kGy ) show the presence of generation currents in the SiO 2–Si interface, a large shift of the flatband voltage and a decrease of the hole mobility.