Radiation damage effects on CMS sensors quality assurance and irradiation tests

The large hadron collider (LHC) at the Centre Europeenne pour la Recherche Nucleaire (CERN), Geneva, Switzerland, is a proton-proton collider with a luminosity of 10³⁴/cm²s and will be working for ten years (starting in 2007). Compact muon solenoid (CMS) will be one of the four general-purpose detectors. The CMS tracker consists of ten barrel layers, plus 2 × 9 end cap discs, which amounts to a total of 24 328 silicon sensors with a total area of 206 m² silicon, covering a pseudorapidity of |η|≤2.5. For the sensors close to the beam pipe, fluences of 1.6·10¹⁴n_{1 MeV}/cm² are expected over the ten-year lifetime. To guarantee the functionality of the single-side silicon sensors during the runtime of the LHC, quality assurance was developed. In the two Irradiation Qualification Centers (IQCs) in Karlsruhe, Germany, and Louvain-la-Neuve, Belgium, a fraction of 1% of the sensors are electrically qualified. In Karlsruhe, the sensors are irradiated with 26-MeV protons and in Louvain-la-Neuve with neutrons at an average energy of 20 MeV. For reasons of flux uncertainties in the CMS tracker, sensors are irradiated with a fluence 50% higher than predicted. For standard float zone silicon, large material dependencies have been observed under irradiation resulting in changes to various electrical parameters. To guarantee the functionality of the sensors in the tracker, it is very important to know these parameters. These electrical parameters have been determined before and after irradiation and are discussed in the following sections.