Speakers
Description
The CMS Inner Tracker for the High Luminosity upgrade of the Large Hadron Collider (HL-LHC) has to allow for tracking in a high track multiplicity environment caused by an instantaneous luminosity of up to $7.5 \times 10^{34}$ cm$^{-2}$ s$^{-1}$. In addition, the tracker has to tolerate 1 MeV neutron equivalent fluences $\phi_{eq}$ of up to $2 \times 10^{16}$ cm$^{-2}$ accumulating in the data taking period at 2.8 cm distance from the beam.
New n$^+$p-planar pixel sensors with pixel sizes of $50 \times 50$ $\mu$m$^{2}$ and $100 \times 25$ $\mu$m$^{2}$, 150 $\mu$m active thickness, with different implantation and metallization layout as well as different pixel isolation technologies have been produced by Hamamatsu Photonics (HPK). The sensors were bump bonded to a ROC4SENS or RD53A readout chip, where the former is dedicated to sensor studies and the latter is a common ATLAS and CMS prototype for the HL-LHC. Afterwards the sensor assemblies have been irradiated with protons at the PS-IRRAD Proton Facility at CERN and at the Irradiation Center Karlsruhe or neutrons in the TRIGA Mark II reactor in Ljubljana to fluences $\phi_{eq}$ above $5 \times 10^{15}$ cm$^{-2}$. Finally, the sensors were characterized in an electron beam at the DESY II test beam facility.
The presented results show that these planar sensors reach efficiencies above 99 % at bias voltages well below 800 V even after proton or neutron irradiation to the given fluences. Thereby, planar sensors fulfill a key requirement for the second layer of the CMS Inner Tracker for the HL-LHC. Furthermore the comparison of different sensor designs provides input for the final sensor.
Future measurements on sensors proton irradiated to $\phi_{eq}$ of $1 \times 10^{16}$ cm$^{-2}$ and beyond will show if planar sensors are an option for the innermost layer of the CMS Inner Tracker in case of a replacement after half the operation period.
