  To extend the physics reach of the LHC, accelerator upgrades are planned
which will increase the integrated luminosity to beyond 3000 fb^-1 and the
pile-up per bunch-crossing by a factor 5 to 10. To cope with the increased
occupancy and radiation damage, the ATLAS experiment plans to introduce an
all-silicon inner tracker with the HL-LHC upgrade. To investigate the
suitability of pixel sensors using the proven planar technology for the
upgraded tracker, the ATLAS Upgrade Planar Pixel Sensor R&D Project (PPS) was
established comprising 19 institutes and more than 80 scientists. Main areas of
research are the performance assessment of planar pixel sensors with different
designs and substrate thicknesses up to the HL-LHC fluence, the achievement of
slim or active edges to provide low geometric inefficiencies without the need
for shingling of modules and the exploration of possibilities for cost
reduction to enable the instrumentation of large areas. This paper gives an
overview of recent accomplishments and ongoing work of the R&D project.
