Development of microstrip detectors for the CBM silicon tracking system

The CBM experiment will study the properties of nuclear matter at high net baryon densities and moderate temperatures - a weakly explored region of the QCD phase diagram. The Silicon Tracking System (STS) is its key component that will reconstruct hundreds of charged particle tracks per collision resulting from the interaction of an intense heavy-ion beam with a nuclear target. Together with high interaction rate of up to 10 MHz, this will impose a radiation load on the detector reaching up to 1015 1-MeV neq/cm2 in 6 years of operation. Sensors with different structure have been manufactured in order to test radiation tolerant design features and provide material for the construction of module prototypes. Small sensors with 2 x 256 orthogonal strips of 50 μm pitch are suitable to implement several designs (biasing structures, strip isolation technique etc) within one wafer keeping the same outer dimensions and bonding pad geometry. Large area sensors of 6.2 x 6.2 cm2 size and 2 x 1024 strips with ±7.5 stereo angle will be used for ladder type module construction with daisy chained sensors. We present the results of current-voltage and capacitance characterization for sensors irradiated up to 1013 1-MeV neq/cm2 and compare them to the preirradiated ones. Interstrip parameters have been measured to determine the proper biasing conditions and to control the crosstalk between the detector channels.