Radiation hard diamond pixel detectors

Even though the LHC has not yet begun, already a high luminosity upgrade of the LHC is being planned. The sensors at radii of about 3 cm will have to withstand an expected fluence exceeding 1016 particles/cm2 in 5 years. At this fluence current silicon sensors cease to function. Due to its large bandgap and high displacement energy, diamond is an intrinsically very radiation hard material. Combined with its fast charge collection, its low dielectric constant and the absence of thermally generated leakage current, diamond is a very interesting detector material for the sensors close to the beam. A full size, 61×16.5 mm2, ATLAS pixel module using chemical-vapor deposition (CVD) diamond was built and characterized in a beam test. The measured position resolution is consistent with the expected binary resolution. The efficiency was larger than 97%. Nowadays also large size single-crystal CVD diamonds are available. A single-crystal diamond was used to produce a 2880 channel pixel detector. This detector showed an 99.992±0.002% efficiency at an electric field as low as 0.25 V/μm.