Title: Performance of irradiated thin n-in-p planar pixel sensors for the ATLAS Inner Tracker upgrade,
Abstract: The ATLAS collaboration will replace its tracking detector with new all
silicon pixel and strip systems. This will allow to cope with the higher
radiation and occupancy levels expected after the 5-fold increase in the
luminosity of the LHC accelerator complex (HL-LHC). In the new tracking
detector (ITk) pixel modules with increased granularity will implement to
maintain the occupancy with a higher track density. In addition, both sensors
and read-out chips composing the hybrid modules will be produced employing more
radiation hard technologies with respect to the present pixel detector. Due to
their outstanding performance in terms of radiation hardness, thin n-in-p
sensors are promising candidates to instrument a section of the new pixel
system. Recently produced and developed sensors of new designs will be
presented. To test the sensors before interconnection to chips, a punch-through
biasing structure has been implemented. Its design has been optimized to
decrease the possible tracking efficiency losses observed. After irradiation,
they were caused by the punch-through biasing structure. A sensor compatible
with the ATLAS FE-I4 chip with a pixel size of 50x250 $\mathrm{\mu}$m$^{2}$,
subdivided into smaller pixel implants of 30x30 $\mathrm{\mu}$m$^{2}$ size was
designed to investigate the performance of the 50x50 $\mathrm{\mu}$m$^{2}$
pixel cells foreseen for the HL-LHC. Results on sensor performance of 50x250
and 50x50 $\mathrm{\mu}$m$^{2}$ pixel cells in terms of efficiency, charge
collection and electric field properties are obtained with beam tests and the
Transient Current Technique.